TEXT BOOK OF CYANIDE PRACTICE BY H. W. MAcFARREN f r AUTHOR OF "Practical Stamp Mitting and Amalgamation." "Mining Law for the Prospector, Miner and Engineer." McGKAW-HILL BOOK COMPANY 239 WEST 39TH STREET, NEW YORK 6 BOUVERIE STREET, LONDON, B.C. 1912 COPYRIGHT, 1912 BY THE McGRAW-HILL BOOK COMPANY Stanhope F. H.GILSON COMPANY BOSTON, U.S.A. PREFACE THE cyanide process is a subject comprehending many divi- sions, and one that can best be treated along some phase or with a special point in view. The point in view or purpose of this work is to furnish students, cyanide workers, and those generally and technically interested in the subject, with a practical and technical exposition of the principles and basic practice appli- cable to cyanidation in general, and not of the particular practice at any plant or locality. An exposition not too technical and complicated or comprehensive for those who are acquiring or about to acquire their technical equipment, nor too superficial for the experienced operator. Intended primarily to guide the first footsteps and early progress of those who hope to eventually operate plants, the author has used simple explanations and many repetitions and references to other parts of the text in the effort to clarify a subject that is confusing, to say the least, to the beginner. Desiring to produce a work that will be of use in actual practice, rather than something to simply add to one's technical library, the author has not kept within academic limitations, but has resorted to homely methods of explanation where deemed advisable. Though going into considerable de- tail, no branch of the subject has been carried to that point where it should be taken up as a special subject. It aims to lift the careful reader and student to that point where he may in- telligently seek further information in the literature on investi- gations into special and abstruse details of the subject, for which purpose and as an aid to the advanced worker an extended Classified Bibliography of the more accessible literature on the cyanide process is included. Where it has been impossible to give definite figures without going into explanatory details, obviously beyond the scope of this work, figures representing the average or rational extremes in practice have been given. The reader may consider these as carefully selected to represent accurately approved modern practice. H. W. MAcFARREN. 241260 CONTENTS PAGES PREFACE vii CHAPTER I HISTORY AND DEVELOPMENT 1-6 Discovery and Early Use of Cyanide MacArthur-Forrest Proc- ess Development of the Cyanide Process. CHAPTER II NATURE AND PROPERTIES OF CYANIDE 7-10 Definition of Cyanide and Cyanogen Properties and Reac- tions of Cyanide and Cyanogen Cyanogen Used in the Cyanide Process Difference between Sodium and Potassium Cyanide. CHAPTER III DISSOLUTION OF GOLD AND SILVER 11-20 Reactions Necessity and Source of Oxygen Bromocyanide and Mercury Salts as Supersolvents Strength of Solution Required Cyanicides Heating the Solution Effect of Size of Metal Particles Effect of Crushing and Form in which Metal is Held Volume of Solution Required and Method of Applica- tion Time Required for Dissolution Silver Ores. CHAPTER IV SUITABILITY OF AN ORE FOR CYANIDATION 21-27 Classification of Ores Iron Sulphur Copper Lead Ar- senic Antimony Tellurium Mercury and Cinnabar Zinc Nickel and Cobalt Manganese Carbon and Carbonaceous Matter Aluminum and Magnesium Silver. CHAPTER V CHEMISTRY OF CYANIDE SOLUTIONS 28-53 Classification of Cyanide Tests A. Free Cyanide Standard Silver Nitrate Test Reactions in Standard Silver Nitrate Test Reactions of the Potassium Iodide Testing Strength of Solid Cyanide B. Hydrocyanic Acid and Acidity Test for Hy- drocyanic Acid Acidity Test for Hydrocyanic Acid Nature of Acid Cyanide Solutions C. Total Cyanide Definition vii viii CONTENTS PAGES Test with Standard Silver Nitrate and Alkali Action of Double Cyanides D. Protective Alkalinity Definition Test for Protective Alkalinity Preparation of Indicators Theory of Standard Acid and Alkali Solutions Preparation of Standard Decinormal Acid and Alkali Solutions E. Total Alkalinity F. Ferrocyanides and Ferricyanides Definition and Occurrence Determination G. Alkaline Sulphides and Sulphocyanides Definition and Occurrence of Alkaline Sulphides Alkaline Sul- phides and Sulphocyanides or Thiocyanates Action and Re- moval of Alkaline Sulphides Application of Lead Acetate Test for Alkaline Sulphides H. Available Cyanide Definition - Test for Available Cyanide I. Cyanates and Total Cyano- gen J. Reducing Power K. Assay of Metals in Cyanide Solu- tion Classification of Methods for Gold and Silver Lead Tray Evaporation Evaporation with Litharge, etc. Pre- cipitation, Incinerating, Fusing, etc. Precipitation with Direct Cupellation The Chiddy Method Assay of Base Metals in Solution. CHAPTER VI ALKALINITY AND LIME 54-64 Definition and Properties of Lime Uses of Lime and Alka- linity in the Cyanide Process Neutralization of Metallic Salts Lime and Alkalinity in Zinc Precipitation Lime as a Neutral- izer of Carbonic Acid Dissolving Effect of Al.kalis upon Metals Amount of Lime or Protective Alkalinity Required Methods of Adding Lime Lime v. Caustic Soda Determination of Causticity of Lime, etc. CHAPTER VII ORE TESTING AND PHYSICAL DETERMINATIONS 65-86 Facts to be Determined Methods of Testing Securing Samples Physical Examination of Ores Free Acidity La- tent Acidity Total Acidity Extraction Tests with Bottles Percolation Tests Fineness of Ore Required Sizing Tests Amalgamation Tests Tests on Concentrate Summary of Small Ore Tests Tests on Large Scale Leaching Rate Slime Settling Rate Determination of the Cause of Low Extraction Determination of the Cause of Cyanide Consumption Pre- cipitation Tests Specific Gravity Determination. CHAPTER VIII PERCOLATION 87-107 Definition Treatment of Tailing Deposits Treatment of Dry Crushed Ore Direct Filling of Vats with Wet Pulp Depth of Sand Charge Arrangement of Leaching Plant Weak and Strong Solution and Their Separation Application of Solution to Treatment Vats. CONTENTS ix CHAPTER IX PAGE8 SLIME TREATMENT AND AGITATION 108-124 Definition of Slime Slime Settlement Classification or Sepa- ration of Sand and Slime Pulp Thickening Charging for Agitation Amount of Solution in Agitation Strength of Solu- tion and Time Required in Agitation Intermittent and Con- tinuous Agitation Types of Agitators. CHAPTER X DECANTATION 125-130 Theory of the Decantation Process Decantation Process in Practice Mechanical Decantation Processes. CHAPTER XI FILTRATION 131-158 Plate and Frame Filter Press Filter Press Practice in Australia The Merrill Press Vacuum or Pressure Leaf Filters Classi- fication of Leaf Filters. CHAPTER XII PRECIPITATION 159-175 Reactions in Zinc Precipitation and Formation of White Precipi- tate Clarifying the Solution Zinc Boxes Size of Shavings Weight of Shaving and Amount Required Packing and Dressing the Boxes General Care of Precipitation White Precipitate Zinc-Lead Couple Copper in Solution Mer- cury in Solution Cutting of Zinc Shavings Mechanical and Chemical Consumption of Zinc Regeneration of Cyanide and Alkalinity Zinc Dust Precipitation. CHAPTER XIII CLEANING -UP 176-178 CHAPTER XIV ROASTING AND ACID TREATMENT , 179-183 Roasting Acid Treatment Sulphuric Acid Treatment Sul- phurous Acid Treatment Bisulphate of Sodium Treatment. CHAPTER XV FLUXING AND MELTING 184-196 Constituents of Zinc Slime to be Melted Purpose of Fluxing and Smelting Sodium and Potassium Carbonates as Fluxes Borax and Borax Glass as Fluxes Silica as a Flux Fluor Spar as a Flux Niter as a Flux Manganese Dioxide as a Flux Determining the Flux to be L T sed Variation Due to Zinc and the Use of Oxidizers General Variations and Fluxing Proced- ure Matte Formation Annealing of Graphite Crucibles x CONTENTS PAGES Melting Furnaces Preparation of Precipitate and Flux Melt- ing Procedure Treatment of Slag and Crucibles Treatment of Matte Smelting with Litharge and Cupellation Assay of Zinc Precipitate. CHAPTER XVI CYANIDATION OF CONCENTRATE 197-204 Treatment by Percolation Treatment by Agitation and Fine- Grinding General Considerations. CHAPTER XVII ROASTING ORE FOR CYANIDATION 205-206 CHAPTER XVIII CYANIDE POISONING 207-212 Internal Poisoning Treatment by Hydrogen Peroxide Treat- ment by Cobalt Solution Treatment by Ferrous Salts Poison- ing in Precipitate Refining Prevention of Poisoning. CHAPTER XIX CLASSIFIED BIBLIOGRAPHY 213-269 Books History and Progress Chemistry and Physio-chem- istry of Cyanidation Aeration and Oxidation Commercial Cyanide and Its Analysis Analytical Chemistry of Cyanide Solution Assaying, Samplers, and Sampling Ore Testing and Physical Tests Alkalinity and Lime Classification, Dewater- ing, and Settlement Sand Treatment and Percolation Slime Treatment, Agitation, and Decantation Filtration Precipi- tation Cleaning-up, Refining, and Melting Telluride Ore, Roasting, Bromocyanide, and Chlorination Cupriferous Ore and Solution Concentrate Cyanidation Other Refractory Ores Cyanide Poisoning Construction, Pulp and Residue Conveying and Disposal Tube-Milling and Fine-Grinding Cyanidation of Silver Ores, and in Mexico Cyanidation in United States and Canada Cyanidation in South Africa Cyanidation in Aus- tralia Miscellaneous. CHAPTER XX TABLES 269-281 Metric System with Conversions United States Weights and Measures English, Mexican, and United States Money Value of Gold Conversion of Thermometer Readings Weight and Measure of Water Weight of Rock and Sand International Atomic Weights (1911) Maximum Solubilities Formula? for Circles and Circular Tanks Capacity of Circular Tanks Slime Pulp Table. INDEX.. 283 TEXT BOOK OF CYANIDE PRACTICE CHAPTER I HISTORY AND DEVELOPMENT THE cyanide process for the extraction of gold and silver from their ores is based on the facts that a very dilute cyanide solu- tion will dissolve the precious metals from the ore, and that when this enriched solution is brought into contact with finely divided zinc, the gold and silver will be precipitated so that it may be collected and melted into a bar of bullion. Discovery and Early Use of Cyanide. Prussian blue, the first cyanide compound known, was discovered in 1704. In 1782 it was first dimly noted that a cyanide solution would dis- solve gold and silver. During the succeeding years many dif- ferent compounds of cyanide were determined and something of their properties learned. The first patent on the solubility of gold in cyanide solution was taken out in Great Britain in 1840, and led to the use of cyanide solution for dissolving gold and silver for electroplating purposes. In 1844 Eisner published valuable investigations regarding the solubility of gold and silver in cyanide solution. The first patent purporting to use a cyanide solution for dis- solving gold and silver from their ores was taken out in the United States by J. H. Rae in 1867. Later on several somewhat similar patents were issued, the most important one being to J. W. Simpson in 1885. In this last patent, cyanide of potassium was to be used in connection with other chemicals for extract- ing gold, silver, and copper from their ores; while the metals were to be precipitated from the solution on zinc plates, and obtained therefrom by scraping the plates or dissolving them in sulphuric or hydrochloric acid. Electroplaters were at this 1 2 TEXT BOOK OF CYANIDE PRACTICE time making use of zinc to recover gold and silver from cyanide solution. . Cyanide of potassium was also being used to a very limited extent at this time in the amalgamation of gold ores, being intro- duced into the stamp-mill mortar, grinding pan, or other crush- ing device with a rather vague idea that it would increase the amount of gold amalgamated. This it undoubtedly did by removing any film of grease or oxide surrounding the grains of gold and brightening them for easier amalgamation, but as it also may have caused a little gold to be dissolved and carried away in solution, it was poor practice. However, since it some- times caused a lower tailing and any shortage of gold was not noticed, the use of cyanide of potassium in this way had some favor. MacArthur-Forrest Process. Though the attention of scien- tists and metallurgists had been drawn to the solvent action of cyanide compounds on gold and silver, resulting in considerable experimentation, the various experiments, studies, and patents can hardly be considered as a prologue to the discovery of the present cyanide process, or as having a direct bearing upon it. In 1886 extended experiments were being carried out in Glasgow, Scotland, by J. S. MacArthur, R. W. Forrest, and W. Forrest, for the purpose of developing an incipient gold-extract- ing process. In the course of their experiments, tests were made with all the known solvents of gold, and it was found that a solution of cyanide of potassium gave a high extraction with a small consumption of the chemical. Their first application for patent covering the dissolving power of cyanide was made in Great Britain in 1887. The principal detail and then novel feature was the low strength of solution to be used. The dis- coverers next turned their attention to winning the^old from the solution, resulting in a patent being taken out on the use of zinc in a state of fine division, such as in the form of shavings or threads, for the precipitation of the gold from the solution. Their patents also included the use of caustic alkalis to neutralize the cyanide-destroying acidity of the ore, which involved no new idea or detail. Following these experiments of MacArthur-Forrest, practical and successful applications of the process were made with sur- prising rapidity in all parts of the world. This was mainly due HISTORY AND DEVELOPMENT 3 to the inherent virtue and applicability of the process and to the fact that the syndicate under whose direction Mac Arthur-Forrest developed the process, trained a force of chemists and sent them into the principal gold-bearing regions of the world. The first plant on a commercial scale was established at Karangahake, New Zealand, in 1889. In South Africa the first plant was in- stalled near Johannesburg, Transvaal, in 1890. Both of these plants were established under the direction of the owners of the patents. The first application of the process in America was made at Mercur, Utah, as a result of experiments instigated by the reports of the success being attained in Africa and Australia. Development of the Cyanide Process. The first material treated by the cyanide process was mill tailing taken from the ponds or banks in which they had accumulated, and treated by the leaching process. Then quickly followed the direct-filling method of conducting the tailing flow from the mill to revolving distributors operating similar to a revolving garden sprinkler, and known from its inventors as the Butters and Mein distrib- utor. This distributor was placed over a leaching vat and oper- ated to fill the vat with sand containing some slime, the major portion of the slime overflowing the rim of the vat. It was found that the sand charge was not easily leached owing to the amount of slime, and this led to the double-treatment system in which the sand is transferred in a drained condition from the collecting vat to a leaching and final-treatment vat. This method was perfected on the South African Rand, and was followed by the development there between 1894 and 1896 of the decantation process of slime treatment by J. R. Williams. In this process the settled and dewatered slime is diluted and agitated with several times its weight of cyanide solution until the gold and silver are dissolved, when the slime is allowed to settle and the supernatant clear, rich solution siphoned off; after which the slime is washed free of the dissolved metals by being again diluted, agitated, settled, and the clear solution drawn off, these washings being continued as long as profitable. About 1898 the filter-press method of slime treatment was introduced in Australia by Sutherland, where it has been exten- sively and very successfully used. In America the filter press was used to only a limited extent up to the introduction of the leaf or vacuum filter, previous to which slime treatment was 4 TEXT BOOK OF CYANIDE PRACTICE mainly by the decantation process. Filter presses, with the exception of the Merrill type, have fallen into disuse in America since the introduction of the vacuum filter. In the standard filter-press method the slime, after being agitated in cyanide solution until the precious metals are dissolved, is forced into a plate-and-frame filter press. After the press is full of slime, the dissolved metals are washed out of the slime by water or solution under pressure, when the press is opened and the cakes or plates of slime are dropped into a car or sluice for the waste dump. The first practical vacuum or suction filter, often called the leaf filter, was devised in the United States by Moore in 1903. In this method a leaf consisting of a flat canvas slip or pocket stretched over a suitable frame is immersed in the slime pulp and a suction applied to the interior of the leaf, causing the slime to be drawn against it, and the solution within. This action in- duces a leathery coating or cake, one-half to three inches thick, to form, when the leaf with its cake is separated from the excess pulp and brought into contact with a wash solution or water, which washes the dissolved "metal out of the cake by being drawn by the suction or vacuum through the slime cake into the interior of the leaf, to run into a suitable tank to which the leaf is connected; after which the wash solution is removed and the cake is discharged. ' In some of these filters the cake is formed and washed by direct mechanical pressure on the pulp and wash solution, and not through atmospheric pressure by the produc- tion of a suction or vacuum in the interior of the leaf. The best- ; known vacuum and pressure leaf filters are the Butters, Moore, Kelly, Burt, Ridgeway, and Oliver. --The development and use of leaf filters has marked a period in which fine-grinding and all-sliming of ore, crushing in cyanide solution, and the treatment of silver and other ores heretofore giving a low extraction has been rapidly developed, especially in America. Fine-grinding had to some extent been practiced in connection with the use of the plate-and-frame filter press, the tube mill having been introduced by Diehl and by Sutherland in Australia in 1896 and 1898. Crushing in solution had been carried on with questionable success at a few plants since early in the history of the cyanide process, the first attempt being by Paul in northern California in 1891, and later by others in the Black Hills. But it is only since the introduction of leaf filters HISTORY AND DEVELOPMENT 5 that fine-grinding and crushing in solution has become generally practicable and desirable. Dry-crushing for cyanidation was rapidly developed during the early days of the process, but, since the introduction of leaf niters and fine-grinding, has fallen into disuse, except where coarse crushing is permissible. Roasting as a preliminary to cyaniding has practically disappeared, except for sulphotelluride ores, to which it was first applied in 1895. The discovery that bromine together with cyanide as a bromocyanide was a more active solvent or a supersolvent of the precious metals, and its application, date from 1892. It has been extensively and successfully used in the treatment of sulphotelluride ores in Australia, but its use elsewhere has been almost unknown. The electrical precipitation of the dissolved metals from cyanide solution was introduced in South Africa in 1893, and great importance was attached to it. However, it has been al- most entirely abandoned, though used in a few isolated instal- lations to-day. Electrical precipitation without removing the solution from the pulp has never been a commercial success. The use of zinc dust as a precipitant in place of shavings dates from 1894. It has been in favor in many large plants, but only during the last few years has there been a tendency to consider it preferable to the standard zinc shavings, and then mainly in America. Some of the early experiments made by MacArthur-Forrest, and of the first work in actual practice, were done upon sulphide or mill concentrate, but the cyanidation of this material may be said to be only partly developed, except as the general improve- ments of the cyanide process have been applied. It is a fertile field for improvement. The fundamental chemistry of cyanidation was fairly well worked out, considering the numerous and complex reactions that take place, during the early years of the process. The investigation of the chemical side of cyanidation has been com- paratively slow during the latter years, due to the high techni- cal and scientific ability requisite in doing such work, and to the fact that investigations into the physical and mechanical side have been much more profitable individually, and have so com- tletely occupied the time and attention of investigators and perators that time for scientific research has not been available. 6 TEXT BOOK OF CYANIDE PRACTICE , The physical and mechanical side of cyanidation has been in a state of continuous development since the first introduction of the process, and the field is now wider and better than ever. The proof of this is to be seen in the widely varying methods of leaching, agitating, filtering, and other details in the same locality, and the still wider variations in . the different gold- silver regions of the world, also in the constant introduction of new devices. The field of cyanidation has been and is constantly widening through its encroachment upon amalgamation, concen- tration, and smelting. CHAPTER II NATURE AND PROPERTIES OF CYANIDE Definition of Cyanide and Cyanogen. Cyanogen is the com- pound radical CN, the carbon (C) and nitrogen (N) constituents of hydrocyanic acid (HCN), which is composed of hydrogen (H), carbon, and nitrogen, and is often called prussic acid. Cyanide is a compound of the cyanogen radical CN with usually a metallic substance, as potassium (K) or sodium (Na), forming potassium cyanide (KCN) or sodium cyanide (NaCN). A radical in chemistry may refer to a single element, in which case it is a simple radical, but more often refers to a group of two or more elements, which, once united, thereafter combine in chemical union or break the chemical bonds with other elements or com- pounds as if they were a single element incapable of being dis- associated into two or more elements. The radical cyanogen (CN), or cyanide radical, is composed of one atom of carbon (C) and one of nitrogen (N), and in all the phases of the cyanide process and its chemistry this chemical union is never broken. To do so would be to lose the solvent action on the metals, for neither carbon nor nitrogen has any such dissolving effect. Nei- ther is there much tendency for the two elements to disassociate. While the chemical symbol for cyanogen, or the cyanide radical, is CN, it has become a custom to write it Cy, a contraction of cyanide. Properties and Reactions of Cyanide and Cyanogen. Cyano- gen is a colorless gas and does not exjst free to any extent, con- sequently it must be fixed by being combined with a metal or other substance to hold it. It is a most active radical, especially in combining with the metals, with which it forms several hundred compounds, thus increasing the difficulty in isolating and deter- mining the properties of each, more especially under working conditions, a fact that has hindered the investigations of the chemistry of the cyanide process. Cyanogen, or the cyanide radical, is related to the cyanides as chlorine is related to the 7 8 TEXT BOOK OF CYANIDE PRACTICE chlorides, and iodine to the iodides. As the acid radical 864 of sulphuric acid (H 2 S0 4 ) unites with iron (Fe) to form an iron sulphate (FeS0 4 ), and the acid radical Cl of hydrochloric acid (HC1) unites with iron to form an iron chloride (FeCl 2 ), so does the cyanide radical CN unite with iron to form primarily an iron cyanide (Fe(CN) 2 ), and similarly with other metals. The result of the chemical combination of the radical CN with a base or metal is to form a salt, such as potassium cyanide (KCN or KCy) or sodium cyanide (NaCN or NaCy). The chemical principles involved in the formation of common table salt, sodium chloride (NaCl), are the same as those involved in the formation of sodium cyanide (NaCN). Cyanogen combines to form simple or single cyanides, which may be regarded as metals replacing the H of HCN, as: and to form double cyanides which may be considered as a com- bination of two single cyanides, as: Zn(CN) 2 + 2 KCN = K 2 Zn(CN) 4 , in which the zinc cyanide (Zn(CN) 2 ) first formed between zinc and cyanide and the potassium cyanide are the single cyanides, and the potassium zinc cyanide (K 2 Zn(CN) 4 ) finally formed is the double cyanide. Other and more complex cyanogen com- pounds form and are found under working conditions. The metal or base with which cyanogen is combined to form a cyanide is easily replaced by one for which cyanogen has a greater affinity. Thus in a KCN solution the K is replaced by gold (Au), forming the simple cyanide AuCN, and finally the double cyanide KAu(CN) 2 , because cyanogen has a greater affinity for gold than for potassium (K). When the solution containing a gold cyanide is brought into contact with zinc (Zn), the gold is replaced by the zinc owing to the greater affinity of cyanogen for zinc than for gold, the reaction being: 2 KAu(CN) 2 + Zn = K 2 Zn(CN) 4 + 2 Au. It is the action of this principle that makes the cyanide process for gold and silver extraction possible. Cyanogen Used in the Cyanide Process. The sources of cyanogen in the cyanide process are potassium cyanide and sodium cyanide, the simple cyanides of the alkaline metals potas- NATURE AND PROPERTIES OF CYANIDE 9 slum and sodium. There are other simple cyanides of the alka- line earths and metals, such as ammonium cyanide (NH 2 CN), barium cyanide (Ba(CN) 2 ), calcium cyanide (Ca(CN) 2 ), mag- nesium cyanide (Mg(CN) 2 ), and strontium cyanide (Sr(CN) 2 ). These have solvent powers similar to those of potassium and sodium cyanide, but are not used in the ordinary cyanide process, mainly for economic reasons. The double cyanides have con- siderable solvent power in some cases, but are too stable and hold their cyanogen too firmly to be a source of it, except so far as it is possible to utilize that formed in working solutions. The other and complex cyanogen compounds have little or no dis- solving effect. Potassium cyanide is a white salt with the usual salty taste. It gives an alkaline reaction and is easily dissolved and very soluble in water. One part of boiling water will dissolve 1.2 parts of the salt. Exposed to the atmosphere, especially in the presence of moisture, there is a slight decomposition into hydro- cyanic acid sufficient to give the characteristic odor similar to that of an almond or peach kernel and irritating to the mucous membrane. It is an irritant to the skin externally and a deadly poison internally. Sodium cyanide has almost identical prop- erties. The salts are made by fusing nitrogenous substances, as horns, hoofs, dried blood, old leather, etc., with alkali and iron, followed by a refining or eliminating process, leaving the desired salt; or by synthetic processes fixing nitrogen from the atmosphere or ammonia by passing them over heated alkaline salt and carbon to form a union of the carbon, nitrogen, and sodium or potassium as sodium or potassium cyanide. Difference between Sodium and Potassium Cyanide. - Practically the only difference between sodium and potassium cyanide, and in the main with the other simple alkaline cyanides, is the dissolving strength, which depends upon the amount of the CN radical. The atomic weight of potassium is 39.1, of sodium is 23, of carbon is 12, and of nitrogen is 14. Consequently the weight of a molecule of potassium cyanide is: K c N 39.1 +12 + 14 =65.1, of which the cyanogen (CN) represents 26 of the total 65.1 parts by weight, which is 40 per cent or 40 parts CN in 100 of the salt. The weight of a molecule of sodium cyanide is in a similar way: 10 TEXT BOOK OF CYANIDE PRACTICE Na C N 23 + 12 + 14 = 49, of which the cyanogen represents 26 parts of the total 49 parts by weight, which is 53.06 per cent or 53.06 parts CN in 100 of the salt. If, in equal weights of the salt, potassium cyanide con- tains 40 parts CN and sodium cyanide contains 53.06, then the dissolving strength of sodium cyanide is 1.3265 times that of potassium, or it is 132.65 per cent strong when the pure potassium salt is considered as 100 per cent strength. This method of considering pure potassium cyanide as 100 per cent strong and marking all cyanide, whether potassium or sodium and pure or impure, according to its strength or amount of CN radical as compared with pure potassium cyanide at 100 per cent, is now in practice everywhere. It is impossible to say which of the two salts is the better for use in cyanide work. Potassium cyanide was at first used en- tirely, apparently because it was the only salt available. In recent years sodium cyanide has been extensively used and has met with considerable favor at some plants, while others have found it unsatisfactory and have preferred to return to the use of potassium cyanide. Sodium cyanide, whether in the solid form or in solution, appears to be less stable and consequently to decompose faster than potassium cyanide. In wet climates it absorbs moisture faster and gives some trouble in this way through deliquescing. Its base, sodium, forms more soluble compounds than the potassium of potassium cyanide, and may give trouble by precipitating them in the zinc boxes. Com- mercial cyanide is generally far from being pure, owing to alka- line constituents that are introduced in the process of manu- facture. Potassium cyanide may often contain considerable of the stronger sodium cyanide, introduced for the purpose of bring- ing it up to the branded strength. The effect of these impur- ities, like any difference between pure potassium and sodium cyanide, is not well understood, but is being studied, and prob- ably will result in requiring cyanide of a certain purity and com- position. This will be an improvement of the method in the past of purchasing the most economical salt as determined by calcula- tions based on the branded strength and the cost of the cyanogen (CN) delivered at the plant; the higher strength salt often being more economical owing to the indirect saving in transportation. CHAPTER III DISSOLUTION OF GOLD AND SILVER Reactions. It is generally accepted that gold is dissolved by a cyanide solution in accordance with the equation first brought to public attention by Eisner and known as Eisner's equation: 2Au + 4 KCN + + H 2 = 2KAu(CN) 2 +2KOH; the gold (Au) combining with potassium cyanide (KCN), oxygen (O), and water (H 2 O) to form a gold potassium cyanide (KAu(CN) 2 ) and caustic potash (KOH). The simple gold cyanide (Au(CN)) is probably first formed to be changed into the double gold cyanide (KAu(CN) 2 ), as: 2 Au + 2 KCN + O + H 2 O = 2 Au(CN) + 2 KOH. Au(CN) + KGN = KAu(CN) 2 . Silver is dissolved in a way similar to gold, as : 2 Ag + 4 KCN + O + H 2 O = 2 KAg(CN) 2 + 2 KOH. One part of potassium cyanide should dissolve 1.51 parts of gold or .83 part of silver according to the above formula?. Necessity and Source of Oxygen. It is seen from the above equations that oxygen is necessary in dissolving gold and silver. This has been confirmed in experiments and practice. The necessary oxygen is supplied by the air or oxygen which the solu- tion has absorbed through being exposed to the atmosphere, and by that absorbed or held by the ore itself. Oxygen may also be supplied by pumping air through the charge or solution, or by chemical oxidizers. However, it has been abundantly proven in practice that the attempt to supply oxygen artificially soon reaches a point where it is uneconomical. Consequently the necessary supply of oxygen is relied upon to be had by the use of a sufficiently large volume of freshly precipitated and aerated solution, by aerating the ore through draining and drawing the 11 12 TEXT BOOK OF CYANIDE PRACTICE atmosphere into the interstices between the grains of pulp, by bringing the pulp into contact with the atmosphere when agitat- ing, by agitating with compressed air, and in exceptional cases by pumping or drawing air through the charge. The necessit.y of providing much oxygen by stress on these means is small with a clean, gold ore, but increases with the quantity of sulphide or baseness of the ore, and with most silver ores, since the metallic compounds of these ores decompose or oxidize to form new compounds, thereby utilizing or abstracting the oxygen neces- sary in the dissolution process. The best-known chemical oxi- dizers that may be used are sodium peroxide (Na 2 O 2 ), potassium permanganate (KMnO 4 ), and manganese dioxide (Mn0 2 ). While these hasten the dissolution, they have never been found to be of economic value, as they invariably do not give any increased extraction over that which can be obtained by using a little more time or more aeration of the charge and solution. Bromocyanide and Mercury Salts as Super solvents. The dissolving power of cyanide solution has been increased by the addition of chemicals which have something of an oxidizing effect, but act mainly through the liberation of cyanogen in a nascent state ready and strongly desirous of uniting with a substance replacing the H of HCN. Bromine in connection with cyanide as bromocyanide is the only chpmical that has been used to any extent for this purpose, and then only on telluride and sulphide ores that will not give a good extraction otherwise. Its use requires such care and expense that it is undesirable for treating ores from which a good extraction can be secured other- wise by the usual processes. The reactions that occur in the use of bromocyanide have never been solved, but the super- solvent qualities are presumed to be due to the liberation of nascent cyanogen and to some oxidizing effect, since the bromine does not enter into combination with the gold. Mercurous (Hg 2 Cl 2 ) or mercuric chloride (HgCl 2 ) has been added as a chemical in addition to the cyanide used. Its effect appears to be due to the affinity of mercury for cyanogen, form- ing a mercuric cyanide (Hg(CN) 2 ) or a double mercuric cyanide of potassium (K 2 Hg(CN) 4 ), by decomposing such stable com- pounds as the ferrocyanides and ferricyanides (K 4 Fe(CN) 6 and K 3 Fe(CN) 6 ) in addition to the simple cyanides and easily- decomposed double cyanides, thus removing the interference of DISSOLUTION OF GOLD AND SILVER 13 the ferrocyanides. The double mercuric cyanide dissolves gold and silver without requiring oxygen, as : K 2 Hg(CN) 4 + 2 Au = 2 KAu(CN) 2 + Hg. From the silver sulphide the dissolution may proceed as: K 2 Hg(CN) 4 + AgaS = 2 KAg(CN) 2 + HgS. The mercuric sulphide (HgS) formed being stable and insoluble, and therefore not a detriment as the alkaline sulphide (K 2 S) formed when the silver sulphide is acted upon by KCN, as : 4 KCN + AggS = 2 KAg(CN) 2 + K 2 S. The alkaline sulphide being an abstractor of oxygen unless altered into an insoluble and stable sulphide, as the mercuric sulphide (see Alkaline Sulphides and Sulphocyanides). The mercury salts have been used to a slight extent in this way in the working of sulphide silver ores. Strength of Solution Required. The strength of solution required varies. Experimental work in the laboratory will indi- cate the most advisable strength for starting a new ore or plant. But this strength is invariably reduced in the course of time, due to the desirableness of starting new operations with a sufficiently strong solution, and that a cyanide solution after being in use for some time is found to contain cyanogen compounds that are not apparent in the usual test for cyanide strength, but which have a direct or indirect solvent effect. Experiments have shown that both pure gold and silver dis- solve most rapidly in a solution of .25 per cent (5 pounds per ton of solution) KCN, that between .1 per cent (2 pounds) and .25 per cent (5 pounds) the dissolving rate is nearly constant, but grows less with solutions above or below these strengths. The lessened efficiency of cyanide solutions stronger than .25 per cent (5 pounds) KCN in the above experiments is ascribed to the fact that the amount of oxygen soluble in a solution grows less as its cyanide content becomes greater. When oxygen is supplied as needed, a stronger solution will dissolve the metals faster than a weak one, but the weaker the solution the more highly efficient equal amounts of cyanide will be, and the less will be the cyanide consumption per ton of ore treated or unit of precious metals dissolved. The present practice in leaching an ore containing gold that 14 TEXT BOOK OF CYANIDE PRACTICE is easily dissolved is to use about a .1 per cent (2 pounds) KCN solution, and seldom higher than .2 per cent (4 pounds); while in the agitation treatment of such ores, solutions from .05 per cent (1 pound) to .1 per cent (2 pounds) are generally used. On silver ores a .1 per cent (2 pounds) to .3 per cent (6 pounds) solution is usual in agitation, and from a .25 per cent (5 pounds) to .5 per cent (10 pounds) in leaching practice. For treating concentrate by agitation, solutions ranging from .15 per cent (3 pounds) to .4 per cent (8 pounds) are in use, and from .2 per cent (4 pounds) to .75 per cent (15 pounds) for leaching. To enable the stronger solutions to act most efficiently and get the increased advantage of their higher strength, it is necessary to supply plenty of oxygen, which the method of operating does by aerating the solution and ore frequently. The use of a stronger solution causes a higher consumption of cyanide mainly by the increased effect of the stronger solution upon the base metals and cyanicides. This action upon the base metals is slow, and while they dissolve according to their slower rate of solubility at the time the gold and silver is being dissolved, their dissolution continues as vigorously after the comparatively quick dissolution of gold and silver is made; con- sequently the strong or dissolving solution should be withdrawn as soon as the precious metals are dissolved, and the weak solu- tions used thereafter for washing. The so-called " selective action " of cyanide in dissolving the precious metals is not a true selection of these in preference to the base metals, but is due to the somewhat quicker dissolution of the precious metals under equal conditions, and to the fine state of division and small amount of them in comparison with the base metals conditions which allow comparatively quick and easy dissolution of the precious metals. t/Cyanicides. The solubility of gold and silver in cyanide solu- tions is reduced by the presence of " cyanicides " in the ore. A " cyanicide " is any substance outside of the precious metals and those involved in the working of the process as the zinc that will unite chemically with the cyanide or tend to decompose it, thereby destroying the cyanide or rendering it inert for dis- solving purposes. Such substances may be a mejbal, as copper (Cu) or iron (Fe) when in a condition to be acted upon by a cyanide solution, such as in the form of a salt, producing in the DISSOLUTION OF GOLD AND SILVER 15 case of copper a potassium cuprous cyanide (K2Cu 2 (CN) 4 ) or in the case of iron a potassium ferrocyanide (K 4 Fe(CN) 6 ). Acids are active cyanicides, forming hydrocyanic acid (HCN) with the cyanogen. Cyanicides hinder the solubility of gold and silver in two ways: first, by destroying or neutralizing the cyanide so that it is not available for dissolving the gold and silver; and second, by going into solution to such an extent that the solution becomes inactive towards the dissolution or precipitation of gold and silver, in which condition it is said to be " foul." The action of cyanicides is met by removing them from the ore by concentration, water- washing, etc.; by neutraliz- ing them into inert salts by the use of the proper quantity of lime, etc., including aeration introduced into the ore or solution; by the passage of the solution through the zinc boxes, which often appears to cleanse it of the influences which retard its dissolving effect; and by keeping the solution so low in cyanide strength that it will, by its greater affinity or dissolving influence on gold and silver, its selective action towards them dissolve these metals and leave the base metals and cyanicides unacted upon as much as possible. Heating the Solution. Laboratory experiments often indi- cate that a higher extraction can be obtained by a heated solu- tion than a cold one. In practice it has generally been impossible to notice any difference between the normal extraction and that made by heating the ore and solution, or that obtained during the heat of summer or the frigid weather of winter. A few cases have been reported in which some virtue has been found in heat- ing the solution. However, it is the more general experience that no additional extraction is obtained, or at least nothing sufficient to warrant the cost of heating the solution and the additional consumption of cyanide due to its decomposition, and the increased decomposition and resulting activity of the base metals and cyanicides; though the decomposition of the base metals, compounds, and alloys is beneficial in liberating the precious metals, that they may be more easily dissolved. One reason that militates against the use of a heated solution is that as the solution is heated it is unable to retain the oxygen dissolved in it. Effect of Size of Metal Particles. The size and shape of the particles of gold and silver have an important influence on their 16 TEXT BOOK OF CYANIDE PRACTICE rate of solubility. Where the metal is in very fine particles, it will be quickly dissolved and require only a weak solution to get the maximum dissolution within a reasonable length of time. When the particles are large, a larger surface is exposed to the action of the solution, causing a large amount of metal to go into solution in a given time. Presuming that the metal is in spheres, the solution is constantly removing a film of metal and reducing the spheres to smaller diameters, consequently larger spheres or metal in thick particles will require considerable time for dissolution over that necessary when the same amount of metal exists in thin plates or in a larger number of smaller particles. In practice, ore containing the metal in a comparatively coarse state, not removed by amalgamation or concentration, needs to be treated with a strong dissolving solution to reduce the time of dissolution to that of an ore containing finely-divided metal treated with a weak and more slowly solvent solution. Effect of Crushing and Form in which Metal is Held. The crushing must either liberate the gold and silver from its matrix or expose a face of it, that the cyanide solution may act upon it. Though with porous ore, that the solution can penetrate and be withdrawn from, it is not so essential that the precious metal be liberated. Following the above principle, various factors affect the degree of fineness to which the ore must be crushed. Where the gold is finely divided it naturally follows that fine crushing will be required to liberate it, more especially with hard dense ores, which the solution cannot penetrate. When the gold is comparatively coarse, a face may be exposed by coarse crush- ing which will allow dissolution to continue slowly inward, until the entire amount of metal is eaten out. Sulphides especially require fine grinding to liberate the gold they mechanically hold. Many ores contain the gold on the breaking or parting planes, from which it is liberated in the crushing process which naturally splits the grains along these planes, or the solution easily pene- trates the fractures. Fine-grinding, especially of a sliming nature, besides liberating the particles of precious metal, also breaks them up or hammers them into thin particles so that they are quickly dissolved by cyanide. Whereas, by a system of crushing that only liberates the metal, considerable time for dissolution would be required by the larger particles. Sliming in solution is especially efficacious, for the metals are ground fine DISSOLUTION OF GOLD AND SILVER 17 in a large volume of well-aerated solution under an agitation that is very favorable for causing the metals to go into solution. When the metals exist as compounds, as gold combined with tellurium, and silver with sulphur, chlorine, etc., fine-grinding is necessary to get the highest efficiency of the cyanide solution in attacking the compounds and removing the precious metals, it being very much on the same principle as gold and silver mechanically held or more or less alloyed with base metals. Some ores may only require crushing to J- to J-inch cubes, such as low-grade, porous, friable ores. Others may give good ex- tractions only when crushed to a 200-mesh or even finer. The rule may be given that the harder, denser, higher-grade, more sulphuretted, and baser the ore is, the finer-grained and more tightly held mechanically, combined, or alloyed the gold and silver is, the finer will be the crushing required. That the softer, more leachable, oxidized, friable, porous, less base, and lower grade the ore is, the coarser and freer that the gold and silver is mechanically and otherwise held, the coarser will be the crushing permissible to obtain an economic extraction. This rule is subject to the effect the solution will have upon the cyanicides, the cost of crushing and grinding, and the trouble or expense and the efficiency in handling the slime, all of which increase with finer crushing. Volume of Solution Required and Method of Application. The volume of solution and method of application should be such that the solution at all times contains sufficient oxygen and cyanide strength for efficient dissolution. An ore containing cyanicides that destroy the cyanide or coarse metal that con- sumes it in the dissolving process will require leaching or agita- tion with a large volume of solution or, less preferably, the addition of more cyanide during the agitation; that a solution of reasonable dissolving strength may be always available about each particle of metal, and yet that there be not the loss due to the use of an inordinately high cyanide strength. An ore con- taining reducing or deoxidizing agents rapidly fouls the solution towards dissolving the metals by abstracting the necessary oxygen, to remedy which the charge must be aerated or, as is sometimes more convenient and desirable, the fouled solution is replaced by a freshly-aerated one. Where the cyanicides and reducing agents exert themselves in this way, a large volume of 18 TEXT BOOK OF CYANIDE PRACTICE solution is required and is applied by being continuously leached through the percolation charge, or by a large amount of solution in comparison to the dry pulp in an agitation charge, or by re- placing with fresh solution through settling the pulp and decant- ing off the old solution. The distinction between that solution required to dissolve the metals and that required to wash these dissolved metals out of the ore must be clearly borne in mind, though in practice the functions of both may be considered as more or less united. With an ore containing easily dissolved gold treated by percolation, J of a ton of solution may dissolve the metals and f of a ton may wash them from a ton of the ore. Other ores in which the metal is slowly dissolved, as those of silver, may require many tons applied continuously, so that dissolution and washing continue together until no longer profitable. Time Required for Dissolution. The time required for dis- solving the gold and silver depends upon the nature of the ore and its treatment; the size and thickness of the metal particles; the mechanically-held, chemically-combined, and metallically- alloyed condition of the metals; the action of cyanicides and reducers; the cyanide strength of solution; and the volume of solution as referring to keeping a solution that is an active dis- solver always in contact with the ore. With some ores contain- ing extremely fine gold practically all the dissolvable gold will be in solution by the time the pulp leaves the tube mill, when crushing and sliming in cyanide solution. Where the metal is in coarse, thick particles, chemically combined or mechanically covered or alloyed, or only a small part of its area or cross- section is exposed to the cyanide activity, the dissolution must be comparatively slow. The presence of cyanicides consuming the cyanide and oxygen render the dissolution slow, owing to the inability to get these to the dissolving metal as fast as needed, or to their more or less complete destruction. Weak solutions are more slowly solvent than strong ones in the presence of sufficient oxygen, consequently: Maximum dissolution = Strength of solution X Dissolution period. k In which either or both of the factors, " strength of solution" or " dissolution period," may be varied within certain limits to DISSOLUTION OF GOLD AND SILVER 19 produce a corresponding result in their products the " maxi- mum dissolution "or " rate of dissolution." That is, a strong solution will dissolve the same amount of metal as a weak one in a less length of time, but a weaker solution given a longer contact will generally dissolve the same amount at a slower rate than a strong one. However, this rule is subject to the chemical law of mass action. Gold ores will usually require a contact of 12 hours to 3 days for dissolution of the gold by leaching, or 3 to 18 hours by agita- tion. Silver ores may require a contact of 4 to 12 days by leaching, or 18 hours to 3 days by agitation. Concentrate may require a contact of 10 to 30 days by leaching, or 12 hours to 10 days by agitation. The fineness to which the ore is ground, out- side of leaching vs. agitation, is usually the most important factor in the rate of dissolution in practice for reasons that have been referred to. Silver Ores. Silver ores require to be treated with' stronger solutions and for a greater length of time than gold ores, for the metal in a gold ore is usually as native gold or a gold-silver alloy in small particles, while the silver in a silver ore is more often as a compound with sulphur, bromine, chlorine, antimony, arsenic, etc., usually the first. When it occurs as native silver the mass is relatively large as compared with the mass of the gold of a gold ore, and in all cases the mass or amount of the silver is com- paratively large. It has also been shown that the rate of solu- bility of silver is about two-thirds that of gold, while almost double the amount of cyanide is required in the formation of the silver potassium cyanide as the gold potassium cyanide. The solution of silver from the silver sulphide (Ag 2 S) the principal silver mineral worked by cyanidation proceeds through the decomposition of the sulphide by cyanide, as : Ag 2 S + 4 KCN = 2 KAg(CN) 2 + K 2 S. In which 1 part of cyanide dissolves .414 parts of silver, or one- half as much as of native silver and about one-quarter as much as of native gold. Unfortunately the soluble or alkaline sulphide (K 2 S) formed is not stable, and in a weak solution the silver sul- phide may not be decomposed, or if it is the alkaline sulphide may tend, especially if the solution becomes weakened, to reverse the reaction by which it was formed and reprecipitate the silver as a 20 TEXT BOOK OF CYANIDE PRACTICE sulphide. Consequently the solution must be strong to decom- pose the sulphide and hold the silver in a dissolved condition. The alkaline sulphide if not precipitated as an insoluble sulphide by some metal in solution, as lead, zinc, or mercury, will unite with the cyanide and with oxygen to form a sulphocyanide or thiocyanate, or will be oxidized into a sulphate, which is one of the reasons for using a large volume of freshly-aerated solution in the treatment of silver ores. The subject of alkaline sulphides is more fully treated under Alkaline Sulphides and Sulphocyanides. The dissolution of silver from the other ores must necessarily be slow and consume much cyanide and oxygen, owing to the necessity of breaking down the silver compounds in removing the silver from them. CHAPTER IV SUITABILITY OF AN ORE FOR CYANIDATION IT may be stated tentatively that all ores of gold and most silver ores can be cyanided. Modifications and special treatment may be required with refractory ores, but those ores for which some successful treatment system cannot be devised are few. The refractory qualities of an ore toward cyanide are of two kinds, physical and chemical. What may be termed refractory physical qualities refer to the necessity of crushing the ore ex- tremely fine to liberate the metal to the solvent action of cyanide solution, and to the trouble encountered in treating a very slimy material ; these will be considered elsewhere. To speak of an ore as being refractory to treatment generally refers to its chemical or physical-chemical nature whereby the precious metals cannot be economically dissolved owing to their being chemically com- bined or mechanically alloyed with some substance that prevents the metals from being dissolved by cyanide, also to some con- stituent of the ore that combines with the cyanide in large quan- tities or may retard the dissolution of the precious metals from the ore, or their precipitation from the solution. These unde- sirable constituents are spoken of as " interfering substances." The results of an analysis of an ore containing interfering sub- stances or refractory compounds will not indicate whether it can be cyanided or not, for a quantity of mineral or element which may not interfere in one ore, may, in a somewhat different form in another, partly or completely prevent successful treatment. With what success an ore can be cyanided can only be judged and determined by laboratory tests, preferably followed by small working tests, which will be discussed in a later chapter. Classification of Ores. Ores may be divided into three classes. Clean ores having no sulphides or base metals and their compounds; base ores containing unaltered sulphides or base- metal compounds; and oxidized ores as a result of the decom- position of original base or sulphide ores. Clean ores are easily 21 22 TEXT BOOK OF CYANIDE PRACTICE treated, as they consume but little cyanide, do not introduce fouling substances into the solution, and the precious metals readily dissolve. Ores containing fresh, unaltered sulphides or base metal compounds cyanide less easily, depending partly upon the tendency of the sulphides and compounds to alter and decompose, thus consuming cyanide and oxygen, and introducing substances that may foul the solution toward further dissolution of the gold and silver and its precipitation; also upon the ability of the cyanide to unlock the mechanical or chemical combination in which the gold and silver is held by the base metals. Oxidized ores act similarly to decomposing base ores, with the exception that their more complete decomposition has allowed a large part of the troublesome constituents to be removed, though that which remains is in a better condition to be acted upon by cyanide and has better liberated the precious metals for easy dissolution. Chlorides, carbonates, and partially oxidized ores, as representing an intermediate or final stage in the transition of unaltered sul- phides to fully oxidized or weathered ores, are the hardest to treat, owing to the activity with which cyanide attacks these soft and easily acted upon base metal compounds. Iron. Metallic iron is so much less soluble than gold and silver in cyanide solution and dissolves so slowly that the fine iron and steel introduced into the pulp in the process of crush- ing and grinding has no noticeable deleterious effects, but many of the iron compounds are readily acted upon. Limonite (2 Fe 2 3 .3H 2 0), the soft, yellow iron oxide, which is found in oxidized ores as one of the final stages in the oxidation of iron, is practically unacted upon by cyanide solution, though it causes trouble mechanically through its tendency to slime. Pyrite, the brass-colored, cubical iron sulphide and the one most generally found, is slowly acted upon by cyanide, but does not easily de- compose. Marcasite, the white iron pyrite, which is also quite common, is much less soluble in cyanide solution than pyrite, but readily decomposes. Metallic iron never enters the solution sufficiently to be harmful, neither does metallic iron oxidize to an extent that is injurious in ordinary cases. It is the products of the decomposition of the sulphides, of which iron is one of the principal constituents, that are harmful; these are ferrous sulphate and oxide, and sulphuric acid, consuming the cyanide through the iron entering the solution as a potassium ferrocyanide SUITABILITY OF AN ORE FOR CYANIDATION 23 (KiFe(CN) 6 ) and the cyanide being neutralized by the acid. The interference is met by the use of water washes removing the soluble compounds, and the neutralizing properties of lime and alkalinity as more fully given under Alkalinity and Lime. Sulphur. Sulphur does not react directly with cyanide, but, as the principal constituent of the sulphides, it forms alkaline sulphides when the metallic sulphides are decomposed by cyanide or alkali. The alkaline sulphides react with cyanide and oxygen to form sulphocyanides or thiocyanates, or with oxygen to form sulphates, the abstracting of the oxygen being especially harm- ful. They also precipitate silver under certain conditions and possibly gold. The interference is met by precipitating the soluble alkaline sulphides by means of zinc, lead, or mercury into inert sulphides. The subject is fully treated under Alkaline Sulphides and Sulphocyanides. Copper. Cyanide has a great affinity for copper and will strongly act upon metallic copper, especially when finely divided. Copper compounds in a physically hard state, such as unoxidized pyrite or sulphide, are more slowly acted upon. When the com- pounds are soft, porous, and spongy, the dissolution is fast, resulting in an excessive consumption of cyanide, a precipitation of copper in the zinc boxes, and, with much copper in solution, trouble in dissolving and precipitating the gold and silver. Chalcopyrite, the principal copper sulphide found in gold ores, gives but little trouble when unoxidized. Malachite and azurite, the carbonates of copper, are easily dissolved and a very small amount will give trouble. An assay of the copper content of the ore will not indicate if it can be profitably worked, for the extent of the action of cyanide depends mainly upon the form or state the copper is in. In some cases, as with oxides and car- bonates, a few pounds of copper per ton of ore may prohibit cyaniding by ordinary methods, whereas an ore containing several per cent of unaltered chalcopyrite may perhaps be amenable to treatment. Modifications for treating copper ores involve the use of low strengths of solution and special methods or treatment of precipitation, the use of ammonia as a prelimi- nary dissolver of the copper or to give a greater selective action to the cyanide solution on the gold, and the preliminary removal of the copper by concentration or a dilute acid wash. 24 TEXT BOOK OF CYANIDE PRACTICE Lead. Lead is strongly acted upon by cyanide, but galena (PbS), the sulphide of lead, is only slightly attacked and very slowly dissolved. The cyanidation of ores containing galena is generally attended with no excessive consumption of cyanide or any trouble except that which but seldom occurs in the zinc boxes from the precipitation of a large amount of lead. Finely- ground concentrate containing 36 per cent of galena has been successfully cyanided. Arsenic. Arsenic is very slightly acted upon by cyanide, but may sometimes be found in small quantities in the zinc precipitate resulting from the treatment of arsenical ores. Mis- pickel or arsenopyrite (FeS 2 .FeAs 2 ), containing 46 per cent of arsenic, a silver-white to steel-gray pyrite, is abundant in gold ores. Concentrate containing 65 to 72 per cent of mispickel has been successfully cyanided. Realgar (AsS), the sulphide of arsenic, containing 70 per cent of arsenic, as a prominent con- stituent of ore has been successfully cyanided, as at Mercur, Utah. Arsenical ores in most cases give a good extraction by ordinary methods, in others they require fine-grinding, the de- composing effect of strongly alkaline solutions, roasting, or the increased dissolving effect of bromocyanide. In some cases the decomposition of the arsenical pyrite or sulphide causes a high consumption of cyanide. In all cases there is a strong reducing action through the formation of alkaline sulphides which must be met by aerating the solution and charge, and in most cases by treatment for the removal of the alkaline sulphides by other means. Arsenical ores have a reputation of being refrac- tory, but in most cases are amenable to successful treatment. Antimony. Ores containing antimony are generally hard and in some cases impossible to treat. Antimony does not appear to react with cyanide, but the decomposition of stibnite (Sb 2 S 3 ), the sulphide of antimony, decomposes cyanide, probably by forming alkaline sulphides and the resulting sulphocyanides, and hydrocyanic acid. There is a reducing action similar to that with arsenical ores, but so pronounced as to make it impossible to treat the ores in some cases. With stibnite the precious metals appear to be firmly held by the antimony so that they cannot be dissolved out. Strongly alkaline solutions will de- compose the antimony to allow the precious metals to be better liberated, but may increase the reducing or deoxidizing power SUITABILITY OF AN ORE FOR CYANIDATION 25 and cyanide-consuming tendencies of the ore to such an extent as to prohibit cyanide treatment. Preliminary treatment with hot alkaline solutions has been suggested. Roasting has been very successful. Fine-grinding will better liberate the value, but cannot remove the evil effecfs on the solution. Tellurium. Tellurium does not react with cyanide or only slightly in alkaline solutions, but holds the gold in a chemical combination that is unaffected by cyanide under ordinary con- ditions, so that the usual processes give little extraction. Fine- grinding with the increased solvent action of bromocyanide is used in Australia to extract the precious metals. The method in America has been to break the combination between the precious metals and the tellurium by roasting, which volatilizes or oxidizes the tellurium, allowing the gold and silver to be readily dissolved, but new chemical methods analogous to the use of bromocyanide have been introduced. Mercury and Cinnabar. Metallic mercury is so slowly dis- solved by cyanide that it introduces no difficulties into amal- gamating in cyanide solution, or treating tailing containing metallic mercury. The mercury in old tailing is generally altered to an oxide or chloride which is easily dissolved to be precipitated in the zinc boxes like that dissolved when amalga- mating in solution. The dissolution of a small amount of mercury is beneficial in precipitating the obnoxious soluble or alkaline sulphides as an insoluble and inert sulphide of mercury (HgS), and in forming a galvanic couple with the zinc in the zinc boxes which assists the precipitation. Cinnabar (HgS), the sulphide of mercury, is practically the only mineral of mercury found in ores of the precious metals, and may be said to be unaffected by cyanide. In fact, mercury by special treatment and gold by the usual cyanide treatment have been produced from the same ore, the production of mercury ceasing as its percentage fell, but the cyaniding for gold con- tinuing. Zinc. Metallic zinc is more easily dissolved than gold, but sphalerite or zinc blende (ZnS), the sulphide of zinc containing 67 per cent of zinc, is probably less acted upon by cyanide than iron pyrite. The products and compounds formed by the oxidation or decomposition of zinc blende, as the carbonate and oxide, act similarly to other decomposing sulphides and their 26 TEXT BOOK OF CYANIDE PRACTICE products for whose metallic base cyanogen has a strong affinity, consuming much cyanide and alkali. Nickel and Cobalt. Nickel and cobalt have an effect in cyanide treatment similar to that of copper. Manganese. Cyanide reacts with manganese and while it may increase the cyanide consumption, it does not appear to harm the solution, being removed as an insoluble compound by oxidation or the use of lime. Manganese in silver ores usually prevents a good extraction by locking up the silver in a manganese compound so as to prevent the solution from dissolving it. With the silver in a soluble form and the manganese separate from and uncombined with the silver, there is no difficulty in getting a good extraction and no fouling of the solution. No practical method of unlocking the silver from the manganese compound has yet been devised, but it would appear that fine- grinding, roasting, the use of a supersolvent as bromocyanide, or a treatment by acid or alkali to decompose and break up the compound are the points from which experiments should be started. Treatment with a weak acid solution preliminary to cyaniding has given excellent results in laboratory experi- ments. Carbon and Carbonaceous Matter. Vegetable matter, char- coal, and other organic material in an ore or tailing give trouble both in the dissolution and in the precipitation, owing to their deoxidizing or reducing power, their cyanide-consuming proper- ties, their tendency to reprecipitate the metals in the ore, and to a too vigorous evolution of hydrogen in the zinc boxes. Con- siderable alkalinity and aeration should be used when they cannot be removed. Lime itself may be the source of the trouble when carrying carbon introduced in the lime-burning process. Graphite gives trouble mechanically by causing a scum or froth and chemically by reprecipitating the metals. The remedy appears to be roasting, which may not always be successful, drying and agitating in that condition with air, or by sun drying and weathering. Aluminum and Magnesium. These metals as sulphates resulting from the oxidation and decomposition of sulphides may interfere by uniting with the cyanide to form hydrocyanic acid, as: MgS0 4 + 2 KCN + 2 H 2 = Mg(OH) 2 + K 2 S0 4 + 2 HCN. SUITABILITY OF AN ORE FOR CYANIDATION 27 These metals may also be dissolved and precipitated in the zinc boxes. The presence of sufficient lime or alkalinity will remedy this, as: MgSO 4 + Ca(OH) 2 = Mg(OH) 2 + CaSO 4 . The calcium sulphate (CaSO 4 ) and magnesium hydrate (Mg(OH) 2 ) are harmless and insoluble. Silver. The amenability of silver ores to cyanide treatment varies with the nature of the mineral or the silver compound. Argentite (As^S), the silver sulphide; cerargyrite (AgCl), the silver chloride; bromyrite (AgBr), the bromide; embolite (Ag(BrCl)), the chlorobromide; and native silver when in a fine state of division, are readily acted upon and dissolved by cyanide and give a good extraction. Proustite (Ag 3 AsS 3 ), the light-red ruby silver; pyrargyrite (Ag 3 SbS 3 ), the dark-red ruby silver; and stephanite (Ag 5 SbS 4 ), the brittle silver, do not so readily respond to cyanide treatment; these are the arsenical and antimonial ores of silver. Coarse native silver and that in galena (PbS), the sulphide of lead; in tetrahedrite (Cu 8 Sb 2 S7), the gray copper sulphide; and in sphalerite or zinc blende (ZnS), the sulphide of zinc, cannot be successfully treated by the cyanide process. Ores containing manganese, in which the silver is locked with the manganese in an embrace that cannot be broken by cyanide, are not amenable to treatment. The treatment of re- fractory silver ores includes fine-grinding to liberate the precious metals and allow the mineral to be attacked and decomposed in general; in the use of a strong alkalinity in the. cyanide solutions to assist in decomposing the sulphides and metallic compounds; and in the use of lead and mercury salts to precipitate the alka- line sulphides. CHAPTER V CHEMISTRY OF CYANIDE SOLUTIONS Classification of Cyanide Tests. The tests and experiments made in connection with a cyanide plant may be divided into three classes: (1) Those made daily by the man on shift, which consist of titrating the solution for its strength in " free cyanide " and possibly in " total cyanide/' and its alkaline strength in " pro- tective alkalinity," as a guide to the amount of cyanide to be added for dissolving purposes, and the amount of lime for neutralizing. (2) Those made daily by the assayer, which consist of assays of the ore before and after treatment, and of the solutions used in treatment, also of the slag, matte, and bullion produced. These are made for the purpose of determining if the routine of treatment is being carried out with maximum efficiency, and for checking the bullion returns. (3) Those made by or under the direction of the chemist or superintendent of the plant, which consist of laboratory ex- traction and sizing tests on the ore, and a determination and investigation of certain or most of the constituents of the ore, solution, etc. These are- made for the purpose of studying the ore and its treatment with a view to increasing the extraction, decreasing the costs, and meeting some unsolved problem or any difficulties that may arise unusual to the daily routine. The nature and extent of these experiments will vary with each plant and operator. The education, training, and activity of the operator is the* principal 'determining factor, the necessity of investigation usually coming second. Because a plant operates smoothly and an ore treats easily is no reason for not making a thorough chemical and physical investigation, for it is the facts brought out by such an investigation, and corroborated from time to time by renewed and further investigation, that enable one to operate a plant successfully and quickly locate and remedy trouble when it arises. 28 CHEMISTRY OF CYANIDE SOLUTIONS 29 The analytical chemistry of cyanide solutions is an exhaustive subject, due to the numerous and complex reactions that occur and their influence when working on mill solutions, which always contain a multitude of complex substances. The methods to be given are the standard and more simple methods in general use and adapted to ordinary mill practice, for further methods in- volving a thorough familiarity with analytical chemistry, the student is referred to " Clennell's Chemistry of Cyanide Solu- tions," second edition, and the articles listed in the Classified Bibliography. Helpful information of a less direct nature will be found in the works on analysis by Sutton, Fresenius, and others, also in the chemical journals. A. FREE CYANIDE The commonest and most important test is for the strength of the solution in cyanide as a guide to the quantity of solid potassium or sodium cyanide that must be added to the solution, by the man on shift, to bring it up to the working strength used in the plant. This has been called the test for " free cyanide." The result is taken to indicate in terms of potassium cyanide, all the cyanogen (CN) or cyanide radical which is present in the solution as potassium cyanide (KCN), sodium cyanide (NaCN), and all the other simple cyanides of the alkalis and alkaline earth metals. The test for free cyanide in both theory and practice does not give all the cyanide strength that has a solvent action on gold and silver not that of the double cyanides but gives that strength obtained when making up new solution, or that additional strength obtained by adding the solid cyanide tq_a solution already in use and in good condition. , Standard Silver Nitrate Test. A standard silver nitrate (AgN0 3 ) solution is made by dissolving 6.5232 grams pure crystallized silver nitrate in water and making up with pure water to one liter (1000 c.c.). To test the cyanide solution, 10 c.c. is measured by a pipette into a small beaker of three or four times that capacity. If the cyanide solution is turbid or muddy, it should be filtered before being measured out. To the 10 c.c. in the beaker is added as an indicator a few drops of a 3 to 5 per cent solution 3 to 5 grams of the salt or substance dissolved in water and made up to 100 c.c. of potassium iodide (KI), though the use of an indicator is not highly important and .-CO- / (As 30 TEXT BOOK OF CYANIDE PRACTICE it is therefore often omitted. The standard silver nitrate solution is then run from a burette into the cyanide solution in the beaker; at first very fast, and finally drop by drop, shaking the beaker that the white cloud, formed as each drop of the standard silver nitrate is run in, may be dissolved until a faint, indistinct white cloudiness appears; then cautiously adding the drops until there is a permanent opalescence, slightly yellowish. Each c.c. of the silver nitrate solution used on 10 c.c. of the cyanide solu- tion indicates one pound of potassium cyanide or its equivalent in a ton of solution. Thus, if 2.3 c.c. of silver nitrate were required, the solution contains the equivalent of 2.3 pounds potassium cyanide per ton. In titrating weak solutions where close results are required in connection with experimental work, as much as 50 c.c. of the | solution may be used for a tes_tj Excessively strong solutions may be diluted with a little water after the portion for titration has been measured out, to prevent the formation of a granular precipitate of single cyanide, which does not so readily dissolve as the fine, white cloud of it first formed and quickly dissolved in weak solutions. It is customary to titrate against a black back- ground, holding the beaker on a level with the eye and looking through a thick body of the liquid, that the end reaction may be better observed. Though the exactness of the end reaction may be observed with pleasing satisfaction in the case of solutions newly made up for test purposes, the exact end point cannot be so easily distinguished with complex mill solutions. The errors that may occur in this way in the daily routine of plant work or through the limitations of the method are generally unimpor- tant, for mill solutions should be of such a strength that an accidental reduction of 10 to 20 per cent in their working strength for a short period should not be harmful. As the strength of solution used in a plant is eventually determined by the results obtained in practice and various experiments relating to the daily practice, the careful operator instructs his shift men to carry the end reaction to the same point that he does, thereby keeping the error usually a case of carrying the reaction too far and overestimating the strength constant and minimizing the danger in this direction. p Reactions in Standard Silver Nitrate Test. The test depends/ / upon the following reactions: CHEMISTRY OF CYANIDE SOLUTIONS 31 A. AgNO 3 + KCN = AgCN + KNO 3 , B. AgCN + KCN = KAg(CN),, C. AgNO 3 + KAg(CN) 2 = 2 AgCN + KN0 3 , in which the single silver cyanide (AgCN) formed in A } as indi- cated by the temporary white precipitate or cloud, redissolves in an excess of cyanide to form the soluble double silver cyanide (KAg(CN) 2 ) in B. After all the cyanide has been converted into the double silver cyanide, an additional drop of the silver nitrate will cause a precipitate of the single silver cyanide as in C, which is insoluble and does not dissolve in the absence of free cyanide, but forms a permanent-Dpalescence--- The amount of silver nitrate to be used in standardizing may be computed by combining A and B into one equation, since the silver nitrate converts the cyanide into the double silver cyanide, as: Ag N 3 + 2 K C N = KAg(CN) 2 + KN0 3 . 5 8 E? oo H- j (.3 S) 169.89 130.22 If 169.89 parts AgNO 3 combine with 130.22 parts KCN, then 1 on oo 1 part AgNO 3 = y \ or .766496 parts KCN. If 1000 c.c. solution contains 6.5232 grams AgNO 3 , 1 c.c. will contain .0065232 grams, which is equal to .766496 X .0065232 or .005 grams KCN. Consequently if 1 c.c. of AgNO 3 solution is re- quired on 10 c.c. of the cyanide solution, the 10 c.c. contains .005 grams KCN, equal to .05 per cent or 1 pound KCN per ton solution. Reactions of the Potassium Iodide. The use of a few drops of a neutral 3 to 5 per cent solution of potassium iodide (KI) is said to correct or reduce the liability of errors in titrating com- plex mill solutions, but is added mainly as an "indicator" to make the end reaction more distinct. The reactions occurring are somewhat similar to those in the case of cyanide: A. AgNO 3 + KI = Agl + KN0 3 , B. Agl + 2 KCN = KI + KAg(CN) 2 , C. AgNO, + KI = Agl + KN0 3 , in which any single silver iodide (Agl) as first formed in A is 32 TEXT BOOK OF CYANIDE PRACTICE dissolved by an excess of cyanide to form the double silver cyanide, while the iodide again becomes potassium iodide, as in B. When no more free cyanide is present, the single silver iodide forms and remains as a permanent precipitate as in C, giving a yellowish color to the solution. The tendency is for the iodide in a cyanide solution to be precipitated in preference to the cyanide, consequently the final permanent precipitate where the potassium iodide indicator is used becomes more the final potassium iodide reaction of: C. AgN0 3 + KI = Agl + KN0 3 , than the final cyanide reaction of: C. AgNO 3 + KAg(CN) 2 = 2 AgCN + KN0 3 . Testing Strength of Solid Cyanide. The strength of solid cyanide may be tested or determined by this method through weighing out a sample of the salt from the interior of the cakes where the surface has absorbed moisture through exposure to the atmosphere and making it into a solution of a certain theoretical strength, and then titrating a sample of the solution. Thus 5 grams of cyanide may be dissolved in water and made up to 500 c.c., making a 1 per cent (20 pounds) solution. Should the solution titrate .97 per cent (19.4 pounds per ton of solution) strong, then it is " 97 per cent pure " or " strong " potassium cyanide. Should sodium cyanide be taken, it may be found to indicate 1.2 per cent (24 pounds per ton of solution), showing that the cyanide is 120 per cent strong when computed in terms of potassium cyanide. B. HYDROCYANIC ACID AND ACIDITY Occurrence. The hydrocyanic acid existing in cyanide solu- tion is formed mainly by the decomposition of cyanide by acids in the ore, as: H 2 S0 4 + 2 KCN = 2 HCN + K 2 SO 4 . Test for Hydrocyanic Acid. The hydrocyanic acid may be determined in cyanide solutions by first estimating the free cyanide in the usual way. Another sample of the solution is then taken, to which is added an excess of a solution of potassium or sodium bicarbonate (KHC0 3 or NaHC0 3 ). The solution is then titrated with the standard silver nitrate solution without CHEMISTRY OF CYANIDE SOLUTIONS 33 the indicator, and the difference between this titration and that for free cyanide is taken as the hydrocyanic acid. The addition of the solution of potassium or sodium bicar- bonate causes the following reaction: HCN + KHCO 3 = KCN + C0 2 + H 2 0. Since the HCN is titrated as KCN and the atomic weight of hydrogen (H) is 1, of potassium (K) is 39.1, of carbon (C) is 12, and of nitrogen (N) is 14: 1 12 14 H C N 27 KCN 65.1 39.1 12 14 = .415. The above titration less that for free cyanide indicates directly the pounds of potassium cyanide to which the cyanogen of the hydrocyanic acid is equivalent, or when multiplied by .415 the result indicates the amount of hydrocyanic acid. Acidity Test for Hydrocyanic Acid. Another method of de- termining the hydrocyanic acid, one which may more properly be denned as giving the " acidity " of the cyanide solution in the absence of any protective alkalinity, consists in neutralizing the cyanide, rendering the zinc innocuous, and determining the acidity with standard alkali. For this test one-half more to double the amount of standard silver nitrate required in the total cyanide test is added to 10 c.c. of the cyanide solution, to convert all the free cyanide and any other easily-decomposed cyanides into the double silver cyanide salt neutral to acidity or alkalinity. To this is added about 5 c.c. of a 5 per cent solution of potassium ferrocyanide (K 4 Fe(CN) 6 ) or an excess over that required to precipitate the zinc in the solution as a potassium zinc ferrocyanide (K 2 Zn(Fe(CN) 6 )) inert in the test. Phenol- thalein is now added as an indicator of alkalinity and if the solu- tion turns red, indicating that there is a protective alkalinity, it should be titrated with the standard decinormal acid solution for the amount of protective alkalinity. But if the solution does not turn red, it is either neutral or acid and should be titrated with standard decinormal alkali until the solution becomes alkaline by turning red, for the amount of acidity. (See Pro- tective Alkalinity for the preparation and use of standard acid and alkali solutions and indicators.) The acidity may be re- 34 TEXT BOOK OF CYANIDE PRACTICE ported in the number of pounds of caustic soda (NaOH). or lime (CaO) that would be required per ton of solution to neutralize the acidity, the number of pounds of hydrocyanic acid it repre- sents, or the cyanide that has been decomposed. Using 10 c.c. of cyanide solution, each c.c. of the standard decinormal alkali equals .04 per cent (.8 pound per ton of solution) caustic soda (NaOH) or .028 per cent (.56 pound) lime (CaO). Or each cubic centimeter of the decinormal alkali used equals .027 per cent (.54 pound) hydrocyanic acid (HCN), as indicated by the equation: (1 + 12 + 14) + (23 + 16 + 1) = (23 + 12 + 14) +((2 X 1) + 16) H C N + Na H = Na C N + H 2 O. 27 40 49 18 A decinormal caustic soda solution contains 4 grams NaOH in 1000 c.c., or .004 grams NaOH in each c.c. In the equation 40 parts NaOH neutralizes 27 parts HCN, or 1 part NaOH equals .675 parts HCN, therefore 1 c.c. decinormal alkali equals .675 X .004 grams or .0027 grams HCN. If 1 c.c. decinormal alkali is equal to .0027 grams HCN in 10 c.c. of cyanide solution, it is equivalent to .027 per cent HCN or .54 pound per ton. Since, as shown before, the cyanogen in .415 pound HCN is equiva- lent to that in 1 pound KCN, .027 per cent or .54 pound HCN equals .065 per cent or 1.3 pounds KCN per ton solution. To tabulate: One c.c. decinormal alkali taken in 10 c.c. solution = .04 per cent NaOH or .8 pound per ton solution. = .028 per cent CaO or .56 pound per ton solution. = .027 per cent HCN or .54 pound per ton solution. = .065 per cent KCN or 1.3 pounds per ton solution. Nature of Acid Cyanide Solutions. Cyanide solutions do not often become acid with careful manipulation, operators universally aiming to have at least a slight protective alkalinity. Though in working gold ores a few cases have been reported where a slight acidity of the solutions seemed beneficial, appar- ently owing to the retarding influence of excessive alkalinity on the dissolution of gold and the deleterious effects of the substances resulting from the decomposition of sulphides and base com- pounds by alkali, mainly the alkaline sulphides produced, generally a solution that is acid causes a waste of cyanide by CHEMISTRY OF CYANIDE SOLUTIONS 35 the new acid that appears, a poor extraction through the fouling of the solution by base metals which alkali would render inert, and a poor precipitation in the zinc boxes, especially with a weak solution, when the tendency for a white precipitate of zinc cyanide to be formed in the boxes is great, owing to the inability of the weak solution to hold the zinc cyanide in a dissolved or soluble state. ' C. TOTAL CYANIDE Definition. The test for total cyanide is considered to give, in terms of potassium cyanide, all of the cyanogen or CN radical present in the form of simple cyanides as determined by the test for free cyanide, which is the potassium and sodium cyanide and the other single cyanides of the alkalis and alkaline earths metals, and additionally that contained in the hydrocyanic acid (HCN) and the double cyanide of zinc (K 2 Zn(CN) 4 ) and possibly some other easily-decomposed double cyanides. Test with Standard Silver Nitrate and Alkali. For deter- mining the total cyanide, from 10 to 50 c.c. of the cyanide solu- tion to be tested are taken, a few drops of the potassium iodide indicator are added, and then a few cubic centimeters of a nor- mal caustic ' soda (XaOH) or caustic potash (KOH) solution sufficient to make the solution excessively alkaline. It is then titrated with the standard silver nitrate solution as in the case of free cyanide, carrying the titration past a white turbidity until a permanent yellow color is obtained. The number of cubic centimeters of silver nitrate solution used in 10 c.c. of cyanide solution indicates in terms of potassium cyanide the number of pounds of total cj-anide in a ton of solution. It should be observed if increasing the amount of alkali added will increase the total cyanide obtained, the highest ' result being taken. The normal caustic alkali solution is made by dissolving 4 grams caustic soda or 5.6 grams caustic potash in water and making up to 100 c.c. Any strength of caustic alkali solution may be used in a sufficient quantity. Reactions in Total Cyanide Test. The above test depends in the case of hydrocyanic acid upon the production of a cyanide on the addition of an alkali to hydrocj'anic acid, as: HCN + KOH = KCN + H,O. 36 TEXT BOOK OF CYANIDE PRACTICE In the case of the zinc potassium cyanide (K 2 Zn(CN) 4 ) and other easily-decomposed double cyanides, the addition of an alkali causes, or apparently causes, a formation or regeneration into the simple cyanide, as: K 2 Zn(CN) 4 + 4 KOH = 4 KCN + Zn(KO) 2 + 2 H 2 O. Action of Double Cyanides. This is an important test, but in most cases is only made occasionally by the chemist in charge. The importance of the test arises from the fact that it has been found both in laboratory experiments and plant practice, that zinc potassium cyanide is an active solvent of gold and silver, and more active when apparently regenerated into KCN or a simple cyanide by the addition of alkaH, as shown in the last equation. The following from tests by W. H. Virgoe* is typical: Test No. Solvent. Strength. KCN Consumption. Extraction. Per cent Lbs. Per cent 1 KCN .22 1.0 87 2 K,Zn(CN) 4 .22 0.4 45 3 K 2 Zn(CN) 4 +CaO .22 0.2 75 The practice that the above test would indicate has been adopted in many silver plants by adding the lime used for neutralizing and for giving a protective alkalinity in such a quantity that the tests for free and total cyanide closely approach each other or are practically the same, thus performing in the plant practice what is experimentally performed in the total cyanide test. The following adapted data by L. N. B. Bullock regarding his cyanide practice at Copala, Sonora, Mexico,! is an excellent illustration of this principle put into practice. The ore is valuable for its silver, which occurs as a sulphide and carries from 12 to 20 ounces of the metal per ton. When treat- ment was first commenced the protective alkalinity in the work- ing solution was carried at .04 per cent NaOH (.56 pound lime (CaO) per ton solution), the use of 5.2 pounds lime per ton of ore being sufficient. The cyanide consumption varied from 4.3 to 4.5 pounds per ton of ore. With the object of ascertaining what results could be secured by decomposing the zinc cyanide * Journal Chemical, Mining, and Metallurgical Soc. of S. A., Vol. 4, Aug., 1903. t Mining and Scientific Press, June 8, 1907. Recent Cyanide Practice, pp. 264.- CHEMISTRY OF CYANIDE SOLUTIONS 37 or double cyanides and regenerating cyanide through increasing the alkalinity, the amount of lime used was increased and kept gradually increasing until the solutions tested .2 per cent NaOH (2.8 pounds lime per ton) in protective alkalinity. The working solution for slime treatment, which was carried at .125 per cent (2.5 pounds) KCN, at once began to gain in strength, and kept gradually growing stronger until it showed .3 per cent (6 pounds) KCN; the alkalinity then being allowed to fall to .09 per cent NaOH (1.26 pounds lime per ton), the cyanide strength also fell. After many experiments with various strengths, it was found that .135 per cent NaOH (1.9 pounds lime per ton) was the least protective alkalinity that would give the desired regenera- tion of cyanide, and consequently the protective alkalinity has been kept at that figure since. As a result of this regeneration the cyanide consumption has not exceeded 1.5 pounds per ton treated for more than five months with no indication of any increase; as a matter of fact, no cyanide was added to the slime treatment solutions for nearly 13 weeks, and the amount used to bring the leaching plant solutions up to strength was small; this, of course, was due to the large excess of zinc cyanide existing in the system. The use of an excessive protective alkalinity, while in many cases effecting a considerable saving in cyanide and by decom- posing the base metal compounds to some extent better liberates the precious metals, decreases the solubility of native gold and silver, lessening the extraction or increasing the time required for dissolution. Consequently an excessive alkalinity is not used in treating gold ores and only on silver ores when found beneficial. The amount of double cyanides in a plant solution should be watched and an attempt made to gauge their dissolving influence. Where there is a considerable amount, it is well to report the strength of the solution in both free and total cyanide. A sudden material reduction in the amount of double cyanide may indicate the need of a solution stronger in free cyanide, and that some important change is taking place in the solution that should be investigated. The zinc potassium cyanide is formed by the passage of the solution through the zinc boxes and in connection with the precipitation. It is customary to consider the double cyanide or the difference between the free and total cyanide as zinc potassium cyanide only. 38 TEXT BOOK OF CYANIDE PRACTICE D. PROTECTIVE ALKALINITY Definition. The " protective alkali " of a cyanide solution is taken to mean those substances, excepting the simple cyanides and the easily-decomposed double cyanides determined by the total cyanide test, that are alkaline to an indicator, the theory being that this protective alkalinity will be neutralized or de- stroyed by any acidity which the solution may encounter, before the cyanide is consumed or destroyed; that hydrocyanic acid will be prevented from forming or that which is already formed will be regenerated into free cyanide; and that many cyanicides will be rendered inert and harmless by direct or indirect reaction with the alkali. Test for Protective Alkalinity. The protective alkalinity is determined by taking 10 c.c. of the solution to be tested. To this is added about 5 c.c. or sufficient of a 5 per cent solution of potassium ferrocyanide (K 4 Fe(CN) 6 ) that any zinc in. solution as the double cyanide or otherwise may be rendered neutral by conversion into zinc potassium ferrocyanide, as: K 4 Fe(CN) 6 + K 2 Zn(CN) 4 = K 2 ZnFe(CN) 6 + 4 KCN. The cyanide liberated in this equation is converted by an excess of silver nitrate into a double silver cyanide, which, like the zinc potassium ferrocyanide, is neutral and inert to indicators in the test. Standard silver nitrate is added for this purpose to the extent of perhaps one-half more or. double that required in the determination of total cyanide, to insure all the cyanide being converted into the neutral double silver cyanide. A few drops of phenolthalein solution are then added, which will turn the solution a bright red if any protective alkalinity is present. The solution will be unchanged if it is neutral or acid, in which case it should be titrated for its " acidity " with decinormal alkali as described in the test for hydrocyanic acid. If the solution is alkaline, it is titrated with decinormal acid until the red or pink shade of phenolthalein just disappears. Each cubic centimeter of the decinormal acid used on 10 c.c. of solution indicates the following equivalents: .04 per cent caustic soda (NaOH), or .8 pound per ton solution. .056 per cent caustic potash (KOH), or 1.12 pounds per ton solution. CHEMISTRY OF CYANIDE SOLUTIONS 39 .028 per cent unslacked lime (CaO), or .56 pound per ton solution. .037 per cent slacked lime (Ca(OH) 2 ), or .74 pound per ton so- lution. In mill work the results should be reported in pounds of the neutralizer used invariably unslacked lime (CaO) per ton of solution. Percentage may be used for technical purposes, and the kind of alkali in terms of which the results are stated, preferably as NaOH or CaO, should always be given. The test may be conveniently, though somewhat less accurately, made in mill work by adding the silver nitrate in excess after the usual free cyanide test, then with or without potassium ferrocyanide, adding the indicator and titrating. Preparation of Indicators. The phenolthalein solution is prepared by dissolving 5 grams of phenolthalein in 1 liter (1000 c.c.) of a solution one-half pure water and one-half alcohol. Methyl orange may also be used as an indicator, except with oxalic acid. It is prepared by dissolving 1 gram of the powder in 1 liter of water. Litmus is seldom used. Theory of Standard Acid and Alkali Solutions. A normal (N) solution of a substance contains in 1 liter of the solution, the molecular weight in grams of the substance divided by the number of atoms of the active element (hydrogen or hydrogen equivalent) in the molecule of the substance. One c.c. of such a solution prepared from any acid will be exactly neutralized by 1 c.c. of such a solution of any alkali, by the active base of the alkali replacing the hydrogen equivalent of the acid, as: JHC1 + NaOH = NaCl + H 2 O. lH 2 S0 4 + 2 NaOH = Na 2 S0 4 + 2 H 2 0. CN\ /N\ /N\ 2-J, fifth-normal ( 1, or decinormal ( J solution is one-half, one-fifth, or one-tenth as strong as a normal (N) solution. Preparation of Standard Decinormal Acid and Alkali Solu- tions. The standard acid solution may be prepared from nitric acid (HNO 3 ), hydrochloric acid (HC1), sulphuric acid (H 2 SO 4 ), or oxalic acid (C 2 H 2 O 4 .2 H 2 0), usually from the latter two. A decinormal 1^1 acid solution made up to 1000 c.c. with pure water contains 4.9 grams H 2 S0 4 , 3.646 grams HC1, 6.3 grams 40 TEXT BOOK OF CYANIDE PRACTICE HNO 3 , or 6.3 grams C 2 H 2 O 4 .2H 2 O. The quantities being arrived at by dividing the molecular weight of the acid by the number of hydrogen atoms in the chemical proper (not including the water of crystallization), and again by 10 to give the amount for a decinormal solution, as: H 2 S O 4 2 + 32 + 64 = 98 -=- 2 -^ 10 = 4.9. H Cl 1 + 35.46 = 36.46 -^ 1 -H 10 = 3.646. H N 3 1 + 14 + 48 _ = 63 ^ 1 -^ 10 = 6.3. C 2 H 2 O 4 . 2H 2 24 + 2 + 64 + 4 + 32 = 126 -s- 2 ^ 10 = 6.3. For mill work the solution may be prepared by weighing out, or by measuring from a burette, the required amount of the highest-grade, chemically-pure acid of a reputable maker, and diluting with pure water up to the necessary amount. When the acid is measured from a burette the amount must be calcu- lated from its specific gravity, for as water has been given a specific gravity of one as a standard and 1 c.c. has been taken as weighing 1 standard gram, so does a cubic centimeter of sul- phuric acid of 1.845 specific gravity weigh 1.845 grams, and similarly with the other acids. For more exact work the acid solution must be standardized against a standard alkali solution of high accuracy, though solutions prepared from oxalic acid are very accurate without standardizing. Pure sodium carbonate (Na 2 C0 3 ) is heated without fusing, to drive off the absorbed moisture, in a porcelain or platinum dish until the dish assumes a dull-red color, being kept at that heat for about 15 minutes. It is cooled under a dessicator and 5.3 grams (Na 2 C0 3 = 2(23) + 12 + 3(16) = 106 + 2 -T- 10 = 5.3) weighed out quickly, - to prevent absorption of moisture, dissolved in water, and made up to 1000 c.c. This is an exact decinormal alkali solution of which 25 or 50 c.c. are taken, the indicator added, and titra- tion made with the decinormal acid solution, which must \^ diluted with water Q^ strengthened with acid until a cubic centi- meter of the standard acid will exactly neutralize a cubic centi- meter of the standard alkali. . CHEMISTRY OF CYANIDE SOLUTIONS 41 Decinormal alkali for rough mill work is prepared by dis- solving 4^rams of caustic soda (NaOH =23 + 16 + 1 =40 -T- 1 -r- 10 = 4), or 5.61 grams caustic potash (KOH = 39.1 + 16 + 1 = 58.1 -f- 1 -f- 10 = 5.61) and making up to 1000 c.c. with water. The pure chemical should be used from a well- stoppered bottle in which the tendency to deliquesce or absorb moisture, which is especially great with caustic potash, is at a minimum. The solution in any case will not be very accurate and should be adjusted to a standard acid solution. When using 10 c.c. of the cyanide solution, each cubic centi- meter of the decinormal acid used indicates a protective alka- linity, or each cubic centimeter of the decinormal alkali used equals an acidity equal to the following: .04 per cent caustic soda (NaOH) , or .8 pound per ton solution. .056 per cent caustic potash (KOH), or 1.12 pounds per ton solu- tion. .028 per cent unslacked lime (CaO), or .56 pound per ton solu- tion. .037 per cent slacked lime (Ca(OH) 2 ), or .74 pound per ton solu- tion. The above values may be computed from the quantities in any of the standard acids or alkalis, since they exactly equal or neutralize each other. Taking caustic soda as the illustration, the decinormal solution contains 4 grams in 1000 c.c., or .004 gram in each cubic centimeter. The .004 gram NaOH or its equivalent in acid used in titrating 10 c.c. of solution is equal to .04 per cent of the 10 c.c., showing the solution to contain the equivalent of .04 per cent NaOH. The value of the caustic potash can be figured out in a similar way, using 5.61 grams as required in the decinormal solution. In the case of unslacked lime (CaO), one atom of calcium (Ca) replaces two of hydrogen as indicated in the formation of calcium sulphate by sulphuric acid and lime : H 2 SO 4 + Ca = CaSO 4 + 2 H. Consequently CaO = 40 + 16 = 56 -T- 2 + 10 = 2.8 grams in 1000 c.c. of decinormal solution or .0028 gram in each cubic centimeter. The .0028 gram or its equivalent in acid used in titrating 10 c.c. of solution is equal to .028 per cent of the 10 c.c., showing the solution to contain the equivalent of .028 per cent 42 TEXT BOOK OF CYANIDE PRACTICE . CaO. The value of slacked lime (Ca(OH) 2 ) may be figured in a similar way: Ca(OH) 2 = 40+2 (16+ 1) = 74 * 2 -MO = 3.7 grams N required in 1000 c.c. ^ solution, and so on. The amounts of the chemicals required in 1000 c.c. of solution N to make up a ^ solution may be tabulated: 4.9 grams sulphuric acid, 2.66 c.c. (specific gravity of 1.845). 3.646 grams hydrochloric acid, 3.04 c.c. (specific gravity of 1.20). 6.3 grams nitric acid, 4.44 c.c. (specific gravity of 1 .42) . 6.3 grams oxalic acid. (Exists in solid form.) 4 grams caustic soda. (Exists in solid form.) 5.61 grams caustic potash. (Exists in solid form.) 5.3 grams sodium carbonate. (Exists in solid form.) (For standardizing.) It is convenient in plant practice to make the solutions so that 1 c.c. of the standard solution when used on 10 c.c. of cyanide solution will indicate a protective alkalinity or an acidity equal to 1 pound CaO (unslacked lime) per ton of solution. For this purpose 1000 c.c. of the standard solution must contain its chemical in the following quantity: 8.75 grams sulphuric acid, 4.74 c.c. (specific gravity of 1.845). 6.51 grams hydrochloric acid, 5.42 c.c. (specific gravity of 1.20). 11.25 grams nitric acid, 7.92 c.c. (specific gravity of 1.42). 11.25 grams oxalic acid. (Exists in solid form.) 7.143 grams caustic soda. (Exists in solid form.) 10.02 grams caustic potash. (Exists in solid form.) 9.464 grams sodium carbonate. (Exists in solid form.) (For standardizing.) The action and use of alkalinity have been indirectly referred to before and will be more fully treated under Alkalinity and Lime. CHEMISTRY OF CYANIDE SOLUTIONS 43 E. TOTAL ALKALINITY The " total alkalinity " of a cyanide solution is that alkalinity which is visible in the presence of an alkaline indicator. It may be said to be that of the protective alkalinity and additionally of the cyanides simple, double, and otherwise. The test is conducted and computed exactly the same as in the determination for protective alkalinity, except that the cyanide and zinc are not rendered neutral and inert by the addition of silver nitrate and potassium ferrocyahide. F. FERROCYANIDES AND FERRICYANIDES Definition and Occurrence. Iron in a metallic form is attacked by cyanide with extreme slowness, but most of the iron compounds are more readily affected and dissolved. Iron may be introduced into the solution in this way by contact with corroded pipes and iron tanks, or iron originating in the milling process and subsequently altered to a compound susceptible of being readily dissolved by cyanide solution. Also through iron that is a constituent of the ore as an oxide, sulphate, etc. 2 from the previous decomposition of the iron or other pyrite, or in the case of a fresh unweathered pyrite by the slow alteration when it is attacked by the cyanide or alkali of a solution, especially in the presence of oxidation. The combination of iron (Fe) and cyanide forms an infinite variety of compounds under the head of ferrocyanides and ferri- cyanides, in the simplest form, as: FeS0 4 + 6 KCN = K4Fe(CN) 6 + K 2 S0 4 . In which the ferrous salt, iron sulphate (FeS0 4 ), when brought into contact with cyanide forms potassium ferrocyanide (K 4 Fe(CN) 6 ) and potassium sulphate (K 2 SO 4 ), while the ferro- cyanide may eventually be changed by oxidation to ferricyanide (K 3 Fe(CN) 6 ). Iron in these combinations is one of the principal foreign constituents of a cyanide solution. The ferrocyanides have been considered as reducers through utilizing the oxygen to form ferricyanides, while the ferricyanides have been con- sidered as oxidizers by the reversal of the method of their forma- tion. The more practical, view is that they are reducers and thereby harmful. They occur in the solution in proportion as the iron found in the ore in a state subject to being acted upon 44 TEXT BOOK OF CYANIDE PRACTICE by cyanide has not been removed or oxidized into the innocuous ferric oxide or hydrates by water-washing, alkaline treatment, and aeration. When occurring in small quantities their in- fluence is unnoticeable, but when present in large amounts their effect is very harmful, reducing the percentage of extraction or retarding the dissolution of the precious metals, and hindering the precipitation chemically and also mechanically through the precipitation of ferrocyanide compounds in the zinc box, such as zinc potassium ferrocyanide and similar. When solutions become highly charged with ferrocyanides and ferricyanides so that they cannot be made to effect the extraction made in labo- ratory tests with clean solutions, they should be discarded, which may be after only a few months of use. However, this periodi- cal discarding of the solutions used in working a decomposed highly pyritic ore can usually be avoided by a proper removal, neutralization, or alteration of the iron by water-washing, alkali, or aeration. Or the solution may often be brought to a healthy state again by aeration and possibly by the addition of alkali. Mercurous or mercuric chloride has been added to such solutions with the effect, through the activity of mercury in combining with the cyanogen of the simple and double cyanides and including the ferrocyanides and ferricyanides, to form a potas- sium mercuric cyanide which is an active solvent even without oxygen, and probably regenerates the cyanogen of ferrocyanides and ferricyanides into the active mercuric cyanide. The presence of ferrocyanides is second only to the formation of alkaline sulphides in fouling working solutions, and the part that each plays in such a fouling effect is an interesting and difficult study. Determination. The simplest method of determining the ferrocyanides and ferricyanides is to consider all the iron in solution as a ferrocyanide. The cyanogen is decomposed by evaporating a measured quantity of solution with HNO 3 , taking up with H 2 S0 4 , evaporating almost to dryness, and taking up with water, when the iron may be determined by any of the usual methods for determining iron. The amount of iron found is multiplied by 6.6 to give the potassium ferrocyanide as K4Fe(CN) 6 , as: 4 (39.1) + 55.85 + 6 (12 + 14) K 4 Fe (CN) 6 368.25 Fe 55.85 55.85 = 6.6. CHEMISTRY OF CYANIDE SOLUTIONS 45 G. ALKALINE SULPHIDES AND SULPHOCYANIDES Definition and Occurrence of Alkaline Sulphides. Alkaline or soluble sulphides, as potassium sulphide (K 2 S), sodium sul- phide (Na^S), etc., are often formed in a cyanide solution, or may be contained in small quantities in the cyanide used. They are considered to occur principally through the decomposition of a metallic sulphide by cyanide or alkali. In the case of treating the silver sulphide (Ag2S) or the iron pyrite (FeS 2 ) by cyanide, as: ( Ag2S + 4 KCN = K 2 S + 2 KAg.(CN) 2 . I FeS 2 + 6 KCN = 2K 2 S + K 2 Fe(CN) 6 . The decomposing effect of alkali with the formation of an alka- line sulphide is shown by the equation: FeS 2 + 2 KOH = K 2 S + Fe(OH) 2 + S. The general effect of an alkali in attacking a metallfc sulphide is to form an alkaline sulphide with the sulphur and a hydrate (as Fe(OH) 2 ) of the base remaining. While the alkalis do not easily act upon all the metallic sulphides, they undoubtedly have some solvent or decomposing effect in all cases. Alkaline Sulphides and Sulphocyanides or Thiocyanates. - The alkaline sulphides reduce the dissolving power of the solu- tion by abstracting the oxygen present, probably in two ways. First, by the oxidation of the alkaline sulphide into an alkaline sulphate, as: K 2 S+4O = K 2 SO 4 ; and second, by forming a sulphocyanide or thiocyanate (KCNS), as: K 2 S + KCN + H 2 O + O = KCNS + 2 KOH. In which both oxygen and cyanide are utilized and rendered useless for dissolving purposes. The double reaction, first into the sulphide and then into the thiocyanate, may be stated as: 5 KCN + H 2 O + O =2 KAg(CN) 2 +KCNS+2 KOH. = K 2 Fe(CN) 6 +2KCNS+4KOH. Action and Removal of Alkaline Sulphides. The alkaline sulphides are unstable and tend to reverse the equation made by their formation, precipitating the silver as a sulphide, and possibly doing the same to a slight extent with the gold, or at 46 TEXT BOOK OF CYANIDE PRACTICE least retarding its dissolution. The tendency of the silver to be reprecipitated in this way increases as the solution becomes weaker in cyanide in obedience to the law of mass action; which is, that in the case of one substance acting chemically on another, the action will proceed until the mass of the acting substance is overcome by the mass of the active substance formed, at which point equilibrium is established, and if the mass of the active substance formed is then increased or that of the acting substance decreased, there will be a reversal of the chemical reaction until chemical equilibrium is again established. Consequently, the mass or strength of the cyanide must be high in the case of con- siderable alkaline sulphides, to keep them from reversing the reaction and reprecipitating the silver. This is one of the reasons for the stronger solutions used in silver plants. The principle can be shown by dissolving silver sulphide (Ag 2 S) in strong cyanide solution, and then diluting the solution until a precipi- tate of the Ag 2 S forms. In plant practice too weak a solution either does not dissolve the silver or may allow it to be repre- cipitated; while an accidental wash of very weak solution or water before dissolution is completed, appears to stop further extraction with strong solution, possibly by coating the metal or mineral with a hard, insoluble film of silver sulphide which is extremely difficult to dissolve. The quantity of alkaline sulphides formed in treating a gold ore is small, probably increasing as the amount or percentage of pyrite or metallic sulphide (concentrate) increases and as stronger cyanide or alkaline solutions are used. The alkaline sulphides are probably removed as fast as formed in ordinary gold ores by being precipitated and discharged in the pulp residue as an insoluble zinc sulphide (ZnS), through reacting with the zinc potassium cyanide (K 2 Zn(CN) 4 ) formed in the passage of the cyanide solution through the zinc boxes, as: K 2 Zn(CN) 4 + K 2 S = 4 KCN + ZnS. Though the zinc in solution, reacting in a way similar to that of silver when reprecipitated, is a valuable ally in this way, it may not as completely remove the sulphides as desirable, or be able to cope with the large quantities produced in treating sulphide ores, especially the sulphide ores of silver. A lead compound is more active for this purpose, precipitating the sulphur as CHEMISTRY OF CYANIDE SOLUTIONS 47 an insoluble and inert lead sulphide (PbS). Lead acetate (Pb(C 2 H 3 O 2 )2) has principally t>een used for this purpose. Lith- arge (PbO), the oxide of lead, has also been employed, but being insoluble cannot be conveniently used. The reaction in the case of using lead acetate is: Pb(C 2 H 3 O 2 ) 2 + 4 KOH = K 2 PbO 2 + 2 K(C 2 H 3 O 2 ) + 2 H 2 O. K 2 PbO 2 + K 2 S + 2 H 2 O = PbS + 4 KOH. Mercury dissolved in amalgamating in cyanide solution or added as a soluble salt is even more active in precipitating the alkaline sulphides than lead compounds, and mercurous (HgjjC^) or mercuric chloride (HgCl 2 ) has been used for this purpose. Oxidation of the alkaline sulphides into sulphates or thiocyanates, by aeration of the solution and charge, will cause a solution con- taining alkaline sulphides to regain its solvent ability. It is this tendency of the alkaline sulphides to oxidize, this strong reducing action in utilizing the oxygen that is necessary in dis- solving the gold and silver, that causes the poor or retarded extraction from ores giving rise to the alkaline sulphides. The sulphides are often precipitated in the zinc boxes as a zinc or silver sulphide, the sulphur of which may give trouble in the clean-up. There is a possibility that some of the influence that running a solution through the zinc boxes has on cleansing it and making it a more active solvent is due to the precipitation of the soluble sulphides by the zinc dissolved and other influences in the passage through the boxes. Application of Lead Acetate. Lead acetate for the purpose of precipitating the alkaline sulphides is not often used in gold plants, for small amounts of the sulphides are not harmful and are removed by the zinc. It is used in most silver plants, though it does not appear necessary unless working on sulphide ores. Since the alkaline sulphides are generally oxidized or changed to the thiocyanates in a short time, solutions in which they have formed do not often show them, but rather the resulting thio- cyanates, the determination of which since only a part of the alkaline sulphides are changed to the thiocyanates does not appear to be of practical value in the matter of removing the soluble sulphides. Consequently, the amount of lead acetate or other precipitant to be used can only be determined in an empirical way, by attempting to learn its influence on the ex- 48 TEXT BOOK OF CYANIDE PRACTICE traction and by examining the solution for the alkaline sulphides before time has been allowed them to oxidize. The tendency of the solution to foul against further dissolution of the precious metals until aerated, its reducing power, and its efficiency in competition with newly-made solutions are studied in this con- nection. Most plants treating sulphide silver ores use a half- pound or less of lead acetate per ton of ore treated; some use as high as a few pounds. It is prepared as a solution to be added to the agitation charge or sprinkled throughout the sand to be leached, or less often -added to the solution in some convenient manner. Test for Alkaline Sulphides. The presence of alkaline sulphides may be determined by agitating 200 c.c. of the solu- tion with a small quantity of lead carbonate (PbCO 3 ). A black precipitate of lead sulphide will indicate the presence of alkaline sulphides. Another method of testing consists of preparing a solution of nitroprusside by adding a little nitric acid to a solu- tion of ferro or ferricyanide of potassium. Add a few drops of the nitroprusside solution to the cyanide solution. If alkaline sulphides are present, even in minute quantities, the solution will assume a brilliant purple color. H. AVAILABLE CYANIDE Definition. " Available cyanide " has been given as an in- definite term referring to the " solvent ability " of a cyanide solution to dissolve the precious metals. This ability is due and proportional to the amount of the free or simple cyanide mainly, to some extent to the easily-decomposed double cyanides and perhaps the hydrocyanic acid, and to little if any extent to the other cyanogen compounds. It is indirectly affected by many other things, as the protective alkalinity, the amount of oxygen available, the quantity and nature of the foreign constituents, and the substances in combination with the cyanogen. This will indicate that an estimation of the constituents and char- acteristics usually determined will not clearly indicate the solvent ability or efficiency of a solution. Consequently the available cyanide or the solvent ability cannot be reduced to any terms. It can only be compared with a so-called standard, for which a new or freshly-made-up solution may be taken. CHEMISTRY OF CYANIDE SOLUTIONS 49 Test for Available Cyanide. The usual method of estimating the available cyanide or dissolving efficiency is to run compara- tive laboratory tests on two portions of the same sample of ore, treating one with the mill solution to be tested and the other with a new solution. Care should be taken that the amount of sample taken, the volume of solution used, and the strength of solution, etc., is exactly similar in the duplicate tests. Where these are made frequently a large sample of 50 to 100 pounds may be prepared and check tests made on it with fresh solution, after which tests may be made on portions of the sample with mill solutions whenever desired. This will give the results with only one test, but most operators will prefer the first method, taking for their sample the discard from the sample for assay taken of a working charge, and thereby checking the working extraction by laboratory tests. L CYANATES AND TOTAL CYANOGEN Cyanic acid has the composition HCNO. In cyanates the H is replaced by a metal or base as KCNO. The decomposition of cyanide through oxidation in a solution may be considered as into a cyanate, which is without effect in the practical working of the process. " Total cyanogen " is a term that has been used to indicate or refer to all the cyanogen or CN radical present in a solution, in any form whatever, such as in the simple and double cyanides, the hydrocyanic acid, and the ferrocyanides, ferricyanides, thio- cyanates, cyanates, etc. J. REDUCING POWER Cyanide solutions vary in their reducing power, in the tendency for substances in the solution to oxidize and thus abstract the dissolved oxygen that should be available for the dissolution of gold and silver. The reducing power can be determined in a (N\ -jrl solution of potassium permanganate (KMn0 4 ), containing 3.16 grams of the chemical in one liter of water. Any convenient but standard amount of the cyanide solution may be taken and acidulated by a standard amount of sulphuric acid, to which the standard 50 TEXT BOOK OF CYANIDE PRACTICE potassium permanganate solution should be added, until the color no longer disappears. The results, as stated in the amount of decinormal potassium permanganate solution used on a con- stant amount of cyanide solution, are recorded and studied in a comparative way, to learn the advisability or necessity of aerating the solution and ore, and any changes that may take place in the reducing power of the solution or ore. K. ASSAY OF METALS IN CYANIDE SOLUTION Classification of Methods for Gold and Silver. The usual methods of assaying cyanide solution for gold and silver fall naturally into four classes: A. Evaporation of the solution in a tray or boat of lead foil, followed by the cupellation of the residue and lead tray. B. Evaporation of the solution with litharge, addition of suitable fluxes, fusion in the assay furnace, and cupellation. C. Precipitation of the precious metals, nitration, incinerating the filter and its precipitate, fluxing the residue, melting, and cupeling. D. Precipitation of the precious metals with a large amount of lead, removing precipitate from the solution, and cupeling without fusion the Chiddy method. A . Lead Tray Evaporation. A block of wood about f inch thick, If inches wide, and 2J inches long is prepared. The lead foil is cut into strips to be folded about this block into a tray f inch deep. A test tube is graduated by a file mark or a sticker to hold 1 assay ton of solution as indicated by 29.166 c.c. of solu- tion run in from a burette. By means of this measuring tube, 1 assay ton of the solution is placed in the tray, which is set on a piece of asbestos board on a hot plate to be evaporated to dry- ness. After evaporation the tray is folded into a compact mass and placed in a cupel to be cupeled. This method does not give extremely accurate results, through the spitting of the solu- tion while evaporating and through the impurities in the solution affecting the subsequent cupellation. It has the further disad- vantage of requiring considerable time and enabling only a small amount of solution to be taken for assay though larger trays taking 3 assay tons may be conveniently used. However, being a simple method it is often employed. CHEMISTRY OF CYANIDE SOLUTIONS 51 B. Evaporation with Litharge, etc. Any measured quantity of the solution may be taken, usually 5 to 10 assay tons. This is placed in a porcelain evaporating dish, covered with from 20 to 40 grams of litharge, to lessen the tendency to spit, and evapo- rated without boiling for the same purpose. The residue after evaporation is transferred to an assay crucible, to which is added the fluxes necessary to produce the usual assay fusion, which may consist of 15 grams bicarbonate of soda, 5 grams borax glass, 4 grams silica or more of powdered glass, and 1 gram flour as a reducer. The flux may be varied in any way that will give a satisfactory fusion. The amount of silica or powdered glass used should be just sufficient to prevent the charge from attack- ing the crucible. The amount of flour or reducer should be varied to give a button of the desired size. The lead button obtained from the fusion is cupeled, etc., in the usual way. Evaporation with litharge is supposed to give the most exact results of the different methods in use. It has been, and will continue to be, the method by which all other methods will be checked, but owing to the time and labor involved is not used in ordinary work. C. Precipitation, Incinerating, Fusing, etc. This method involves the precipitation of the precious metals from the solu- tion by the addition of a metal, metallic salt, or other substance; the filtering off of the precipitate followed by incinerating it and the filter; and the fluxing and fusing of the residue as in the usual fire assay. Numerous reliable methods have been used, each of which has its advocates. They are the methods that were formerly used in plant practice, but which have largely been superseded by the Chiddy method. The following is one of the simplest and most practical of these methods. Take 10 assay tons of the cyanide solution in a beaker. Add 4 grams of zinc dust on point of spatula. Stir vigorously. Allow to stand for a few minutes and again stir. Finally add about 10 c.c. of commercial H 2 SO 4 and stir. After action has ceased, add more H 2 SO 4 if needed, until sulphuric acid is in excess and zinc is all dissolved, which will be indicated by no more action when a small quantity of the acid is added. Filter and incinerate filter and precipitate by placing in an assay crucible and setting in muffle or furnace. Add suitable flux after incinerating and cool- ing, which may consist of 10 grams litharge, 10 grams bicar- 52 TEXT BOOK OF CYANIDE PRACTICE bonate of soda, 3 grams silica or more of powdered glass, and 1 gram flour. Fuse, cupel lead button, etc. D. Precipitation with Direct Cupellation the Chiddy Method. The Chiddy method with various modifications is now generally used, as it is an easily-handled, quick, and reliable method for gold and silver. Place 5 to 10 assay tons of the solution in a beaker. Heat nearly to boiling. Add before or during the heating, 10 c.c. of a clear saturated solution of lead acetate (Pb(C 2 H 3 2 )2.3 H 2 0) and .5 gram zinc dust. One part of lead acetate will dissolve in 2 parts of water, while any excess will remain undissolved in the bottom of the bottle or vessel holding the solution. Stir well and bring nearly to boiling. Allow to heat for several minutes. Stir again and add 15 c.c. of commercial HC1, and continue heating. After effervescence has ceased, add more HC1 until the absence of action shows that the zinc is dissolved and the acid is in excess. The lead has now settled into a sponge which should be tapped together and pressed into a mass with a glass rod, the solution poured off, and the lead washed once or more by decantation. The lead is pressed into a compact mass with a glass rod or the fingers to remove the water. It is placed on a piece of lead foil 1J inches square, which is folded to allow the steam to escape at the top, and is placed in a hot cupel for cupellation. The principal trouble encountered in using this method is the tendency of the lead to break up instead of agglomerating, and thus become lost in the decanting. This may be prevented to some extent by not allowing the solution to come to a boil. Another method is to introduce into the solution a piece of aluminum from 1 to 1J inches square and T V to | inch thick, which will more readily collect the lead, and can easily be re- moved before cupellation. Where the lead breaks up, it may be finally transferred to the point of a small filter paper, which should be dried before cupeling. A simple expedient is to transfer or wash the lead into a small lead foil tray an inch or more square, drain the moisture through a folded corner, and dry tray before cupeling. Where zinc dust is not available a somewhat larger amount of the shavings may be used. This method gives good results with very, weak solutions, but it is advisable to have some strong solution on hand and bring very weak solutions up to not to exceed .5 per cent (10 pounds) KCN. CHEMISTRY OF CYANIDE SOLUTIONS 53 L. ASSAY OF BASE METALS IN SOLUTION The base metals in a cyanide solution, such as iron, copper, lead, zinc, etc., may be determined in any of the usual ways by first decomposing the cyanogen. This may be performed by adding to a measured quantity, of solution, as 100 to 300 c.c., from 5 to 10 c.c. HNO 3 and the same amount of H 2 SO 4 , evapo- rating to dryness, and taking up with a few cubic centimeters of H 2 SO 4 diluted with water. This gives the metals as sul- phates for determination in the usual manner. CHAPTER VI ALKALINITY AND LIME Definition and Properties of Lime. Lime (CaO) is an alka- line earth, an oxide of the metal calcium (Ca). Neither calcium nor its oxide (lime) occurs free in nature. Lime is prepared by burning or calcining limestone, which when pure is calcium car- bonate (CaCO 3 ) or carbonate of lime, thereby driving off the carbonic acid (CO 2 ) and leaving lime (CaO) in unfused lumps in the form of the original stone. In this state it is called burnt lime, unslacked lime, quicklime, caustic lime, calcium oxide, or dehydrated or anhydrous calcium oxide or lime. When this lime is exposed to the atmosphere, it attracts moisture and falls into a powder with a rapidity dependent upon the amount of moisture in the air and the quality of the lime, more rapidly as the quality of the lime or absence of impurities becomes higher and the calcining process has been carried to the proper point. This process is called air-slacking. When lime (CaO) is brought into contact with water (H 2 0), it decomposes the water with the evolution of much heat a process called slacking to form Ca(OH) 2 , known as slacked lime, or calcium or lime hydroxide or hydrate; it is the same prod- uct as is formed by air-slacking. The term " lime " in connec- tion with the cyanide process always refers unless otherwise noted to the equivalent of unslacked lime (CaO), whether the lime is slacked before use or not. Lime after being slacked readily mixes with water to form a smooth and liquid paste called " milk of lime." A filtered or clear saturated solution of lime is called " lime water." This, as representing the maximum solubility of lime in water, contains about 1 part unslacked lime (CaO) in 800 parts of water, equal to .125 per cent or 2J pounds per ton of water. This is equal to 1 part of slacked lime (Ca(OH) 2 ) in 600 parts of water, but the results are invariably stated as unslacked lime. By the use of an excess of lime, cyanide solutions can be made to show a pro- 54 ALKALINITY AND LIME 55 tective alkalinity of higher than .125 per cent (2J pounds) CaO, but probably not more than .15 per cent (3 pounds); this is due to the alkalinity of other substances, more especially those result- ing from chemical reactions. Uses of Lime and Alkalinity in the Cyanide Process. Lime and alkalinity have no solvent action upon the precious metals, but enter into numerous reactions occurring in the cyanide proc- ess. Through these they protect the cyanide from being de- stroyed or decomposed, mainly by entering into the combinations that cyanide would otherwise enter; by liberating or regenera- ting cyanide through replacing it in compounds; and by pre- cipitating or rendering inactive substances that may interfere, thus keeping the solution clean and in excellent condition for dissolving the precious metals out of the ore and precipitating them in the zinc boxes. A further use of lime and alkalinity is as a solvent upon base metals and compounds, thereby better liberating the precious metals from the chemical combination or mechanical alloy or covering for easy dissolution. In doing this lime acts as an alkali, and any alkali could be used with more or less advantage for this purpose, but lime is almost exclusively used owing to its cheapness and that its properties and reactions are preferable to those of the other alkalis which have been used, principally caustic soda and to a slight extent caustic potash. In illustrating the chemical reactions of the cyanide process it is customary to use caustic potash (KOH) as the alkali formed or decomposed, probably because the K of the alkali is convenient to add to the CN as KCN. The student should bear in mind that the use of caustic potash in this way is as a generic or class term referring to alkalis in general and not to caustic potash in particular, consequently K, Na, and Ca may be considered to have similar properties when united to CN as a cyanide or to OH as an alkali, and likewise to a more or less extent with the other alkaline earths and metals. Lime also acts physically in addition to chemically. It is used in connection with slime treatment for the purpose of causing the light, feathery, suspended slime to agglomerate and settle rapidly for decantation or pulp-thickening purposes. This subject is treated under Slime Treatment and Agitation. Neutralization of Metallic Salts. The main use of lime is as a neutralizer of the acid and metallic salts formed in the ore 56 TEXT BOOK Of CYANIDE PRACTICE through the oxidation and decomposition of the metallic sulphides. The principal stages in the decomposition of iron pyrite may be adapted from those given by W. A. Caldecott,* as: (1). FeS 2 . Iron pyrite. (2). FeS + S. Ferrous sulphide and sulphur. (3). FeS0 4 + H 2 SC>4. Ferrous sulphate and sulphuric acid. (4). Fe 2 (S0 4 ) 3 . Normal ferric sulphate. (5). 2Fe 2 3 .S0 3 . Basic ferric sulphate. (6). Fe 2 O 3 .zH 2 O. Ferric hydrate. (7). Fe 2 3 . Ferric oxide. A fresh unoxidized metallic sulphide, as an iron pyrite, is but little acted upon by cyanide solution. But in a weathering and partially decomposing iron pyrite this reaction probably occurs: FeS 2 + H 2 + 7 = FeSO 4 + H 2 S0 4 . The sulphuric acid (H 2 SO 4 ) formed, if brought into contact with the cyanide, will destroy it through forming hydrocyanic acid (HCN), as: H 2 SO 4 + 2 KCN - 2 HCN + K 2 SO 4 . The decomposition into hydrocyanic acid may be prevented by washing the soluble sulphuric acid out of the ore before the application of cyanide, by a neutralizing alkali wash, or less perfectly by a protective alkalinity in the cyanide solution, as: H 2 SO 4 + Ca(OH) 2 = CaSO 4 + 2 H 2 O. The calcium sulphate (CaS0 4 ) formed being an insoluble salt harmless to the cyanide. If caustic soda (NaOH) is used, the resulting sodium sulphate (Na 2 SO 4 ) is very soluble. The potas- sium sulphate (K 2 SO 4 ) resulting from the use of caustic potash (KOH) is also very soluble. Any hydrocyanic acid will be re- generated in the presence of lime or protective alkalinity into a cyanide, as: HCN + KOH = KCN + H 2 O. The ferrous sulphate (FeS0 4 ) formed in the first equation of the previous paragraph will destroy cyanide, as : FeS0 4 + 2 KCN = Fe(CN) 2 + K 2 SO 4 . Fe(CN) 2 + 4 KCN = K 4 Fe(CN) 6 . In which the simple iron cyanide (Fe(CN) 2 ), if it is formed at all, * Proc. Chemical and Metallurgical Soc. of S. A., Vol. 2. ALKALINITY AND LIME 57 is immediately changed into the species of double cyanide, the ferrocyanide (K 4 Fe(CN) 6 ). Further complex reactions between the ferrocyanide and the ferrous sulphate may result in the for- mation of Prussian blue (Fe 4 (Fe(CN) 6 ) 3 ), which will give a blue color to the solution and deposit small quantities of the dark- blue compound in the ore, tanks, and piping, acting as a sign that the neutralization has been poorly carried out. The ferrous sulphate is very soluble and may be washed out or may be neutralized into the harmless insoluble calcium sulphate by means of lime, or into other harmless salts by other alkalis, as : FeSO 4 + Ca(OH) 2 = CaSO 4 + (FeO + H 2 O or Fe(OH) 2 ). The ferrous oxide (FeO), if it does form, is hydrolized into the ferrous hydroxide or hydrate (Fe(OH) 2 ), a white precipitate which turns a dirty green, is insoluble, and is easily oxidized into the insoluble ferric oxide (Fe 2 O 3 ), thus acting as a strong reducer or deoxidizer in the solution and ore. The ferrous hydroxide or hydrate is acted upon by cyanide, as: Fe(OH) 2 + 6 KCN = K4Fe(CN) 6 + 2 KOH. It is probably the principal source of loss through the reaction between iron and cyanide, and the hardest iron interference to remove. The loss of cyanide is reduced by affording every means for the ferrous hydrate (Fe(OH) 2 ) to be oxidized into the ferric oxide (Fe 2 O 3 ), which is unacted upon by cyanide. The use of aeration or oxygen besides reducing the cyanide consump- tion, increases the extraction of the precious metals by supplying the oxygen that would otherwise be abstracted by the iron from the solution or ore. To meet such conditions it may be necessary to pump air through the charge before or during treatment. If the ferrous sulphate (FeSO 4 ) is not removed when formed, it will oxidize into the poorly soluble normal ferric sulphate (Fe 2 (SO 4 ) 3 ), and from that into the insoluble basic ferric sulphate (2Fe 2 O 3 .SO 3 ), both of which will react with cyanide and thereby cause a high consumption in the same manner as ferrous sulphate, but in the presence of alkali these are probably converted or oxidized into the hydrous ferric oxides, as: ( Fe 2 (SO 4 ) 3 + 6 KOH == Fe 2 O 3 .3 H 2 O + 3 K 2 S0 4 . I 2 Fe 2 O 3 .SO 3 +2 KOH = 2 Fe 2 O 3 .H 2 O + K 2 SO 4 . 58 TEXT BOOK OF CYANIDE PRACTICE The hydrous ferric oxides or ferric hydrates have the formula Fe 2 O 3 .xH 2 O in which x, representing the number of molecules of H 2 0, is variable and indeterminate. The ferric hydrates are formed from the ferrous and ferric salts as the sulphates by the action of alkali. Some of them are to some extent soluble and act upon cyanide, others do not. Taken as a whole, they may be considered to be insoluble and harmless to cyanide, more especially in the presence of alkalinity and aeration which in- creases these properties or carries the compound nearer to the inert ferric oxide (Fe 2 3 ) ferric hydrate less its water of com- bination. The red or blood color sometimes noted in solutions is usually due to a soluble iron or manganese compound which the addition of alkali or a continued aeration will precipitate as an inert ferric or other hydrate. The decomposition of sulphide ores may result in the formation of sulphates of other metals, such as magnesium and aluminium, which would interfere in a way similar to the iron salts, but the use of lime or alkalinity converts them into hydroxides that are harmless. Lime and Alkalinity in Zinc Precipitation. Lime and alka- linity play an important part in the zinc precipitation of the precious metals. In weak cyanide solution the zinc in solution may be considered to take the form of a hydroxide (Zn(OH) 2 ), or the single zinc cyanide (Zn(CN) 2 ), both of which are insoluble in water and only slightly soluble in weak cyanide solution. In strong cyanide solution the zinc may be considered to exist as the double zinc potassium cyanide (K 2 Zn(CN) 4 ) which is highly soluble, and in alkaline solutions of the alkalis as a zincate (Zn(KO) 2 ) which is also very soluble. With weak solution the zinc shavings will be more or less coated with zinc hydroxide and zinc cyanide, so that little dissolution of the zinc takes place under conditions to replace the gold in the double gold potassium cyanide (KAu(CN) 2 ),or to chemically set up the electric currents that assist in depositing the gold. This results in poor precipi- tation and the formation of the white precipitate of the zinc boxes, consisting mainly of zinc hydroxide and zinc cyanide. The use of a strong cyanide solution dissolving the white pre- cipitate of hydroxide and simple cyanide to form the soluble double cyanide and actively dissolving the zinc, keeps it clean and promotes good precipitation. Lime or alkalinity may be used in the same way as cyanide for this purpose, with the ex- ALKALINITY AND LIME 59 ception that the soluble zincate is formed instead of the double cyanide. The subject is further discussed and the reactions given under Precipitation. While a protective alkalinity is usually necessary for good precipitation, at least with weak solution, too high an alkalinity must be avoided as it causes an excessive action on the zinc, as: Zn + 2 KOH = Zn(KO) 2 + 2 H, resulting in an increased consumption of zinc and the production of much hydrogen, which may cause an undesirable disturbance in the zinc boxes and poor precipitation, by the entangled hydro- gen bubbles preventing good contact between the solution and the zinc. Too high a protective alkalinity may cause a deposi- tion of lime salts in the zinc boxes, covering the zinc with a flocculent or hard precipitate which interferes with precipitation, and increases the bulk of the clean-up and melt, even with sul- phuric acid treatment, for the calcium sulphate formed is very insoluble. Lime as a Neutralize? of Carbonic Acid. Carbonic acid (C0 2 ) decomposes cyanide into hydrocyanic acid, as: KCN + C0 2 + H 2 = HCN + KHCO 3 . The hydrocyanic acid liberated is regenerated into cyanide by any alkali present, or the carbonic acid is itself neutralized, as: ( HCN + KOH = KCN + H 2 0. I CO 2 + KOH = KHCO 3 . The source of carbonic acid or carbon dioxide may be the atmos- phere, the air used in agitation and aeration, organic matter, carbonate ores, etc. The air used in agitation, besides perhaps increasing the cyanide consumption to a small extent through its carbonic acid, increases the consumption of alkali very materially, forming insoluble calcium carbonate (CaC0 3 ) in the case of lime. This coats or clots the filtering canvases of the leaf filters so that they must be treated with dilute hydrochloric acid to dissolve out the calcium carbonate as a soluble calcium chloride. A high protective alkalinity is not used in many plants for this reason alone. The use of a high protective alkalinity may also give trouble in this way, by coating and gradually closing the solution pipes with a deposit of calcium carbonates and other alkaline earths. 60 TEXT BOOK OF CYANIDE PRACTICE Dissolving Effect of Alkalis upon Metals. Alkalis have an important influence in cyaniding, through their tendency to act upon the base metals to convert them into oxides and hydrates. This action is noticeable in connection with nearly all the base metals. By altering the metals into the softer oxides and hy- droxides, and by decomposing and breaking down and altering the compounds, it causes a greater action in many cases in those in which it does not act to produce, or to the extent of pro- ducing inert salts and oxides between the substance and the cyanide. By breaking down the compounds it better liberates for easy dissolution the precious metals that they have chemically and mechanically imprisoned. These effects are to a large ex- tent undesirable in treating gold ores, since gold is invariably in a native or metallic form and any increased liberation of gold which would be from the sulphides in most cases would be overcome by the deleterious effects of the greater reactions between the base metals or compounds and the cyanide, the mechanical liberation by fine-grinding being preferable. With silver ores this effect is in many cases highly desirable, for silver is generally both chemically combined and mechanically alloyed or held with other substances. The effect of high protective alkalinity in treating gold ores is to lessen the extraction and increase the time of dissolution. High alkalinity or lime de- creases the solubility of both native gold and silver in cyanide solutions, and where sulphides and base metal compounds are found, will cause more alkaline sulphides to form in the solution (see Alkaline Sulphides and Sulphocyanides) and the base metals to be more acted upon. For this reason a high protective alkalinity when treating sulphide gold ores is especially unde- sirable, but of value in the working of sulphide silver ores in which the silver and sulphur are chemically combined. Cases have been noted in working sulphide gold ores where solutions slightly " acid," showing no protective alkalinity, have given a higher extraction than those having a protective alkalinity, though at the expense of an increased cyanide consumption. Amount of Lime or Protective Alkalinity Required. The amount of lime or protective alkalinity used will vary with the material treated, the method of cyanidation used, and the ideas of the metallurgist in charge. Even the metallurgist may vary the amount greatly, as the result of careful study of the plant ALKALINITY AND LIME 61 practice and laboratory experiments. Where it is necessary to assist the settling of the slime by using lime, the results when using varying quantities are noted, and that amount used which will give good settling results with a reasonable quantity. The amount used for neutralizing purposes depends upon the nature of the ore, and indirectly upon how the lime is applied. In the treatment of gold ores it is aimed to have only a slight protective alkalinity. It will be attempted in the average gold plant to keep the protective alkalinity of the solutions at some standard be- tween .005 per cent (.1 pound) and .025 per cent (.5 pound) lime (CaO). Except where necessary for settling purposes, solu- tions containing an average protective alkalinity of more than .04 per cent (.8 pound) CaO will seldom be found in gold plants. On the other hand, in the treatment of silver ores a high pro- tective alkalinity is generally used, ranging from .025 per cent (.5 pound) to a maximum or saturated solution of lime, .125 per cent (2.5 pounds), and even a little higher where the pulp or solution contains other alkaline constituents. Some plants treating silver ores use that protective alkalinity in the solution or that quantity of lime which will cause the mill solution titra- tions for free cyanide and total cyanide to approximately coincide, usually a case of a protective alkalinity of about .1 per cent (2 pounds) CaO the principle and some discussion of which has been given under Total Cyanide. Plants treating gold ores will usually use from 1 to 5 pounds CaO per ton of ore treated, and silver plants from 3 to 10 pounds, though as high as 20 pounds are being used. Methods of Adding Lime. The lime is added in cyanide practice in various ways. It may be added dry to the ore in the bins, or fed dry or wet as a milk of lime into the crushing and grinding machines. Feeding the lime into the fine-crushing machinery is an excellent method when crushing in solution or when the mill water is circulated for reuse, as it allows early action upon the cyanicides of the ore, and yet there is no mechani- cal loss. When used in this way, the pipes returning the water or solution for reuse in crushing should be large and easily taken down, for they may be gradually lined with a deposit of lime and alumina salts that must be periodically removed. These pipes have sometimes been replaced with open wood troughs. Lime often causes trouble by coating the mill screens and blinding 62 TEXT BOOK OF CYANIDE PRACTICE their openings, especially with woven-wire screens. A change to the punched or slotted-plate type may remedy the difficulty. Lime has in some cases given trouble on the amalgamating plates, but this can usually be overcome, especially if a thick bed of amalgam, free from substances that the alkali may alter, is kept on the plates. A favorite method of adding the lime is after the crushing, but just before the pulp reaches the cyanide tanks, supplying the lime freshly wet-crushed from a single-stamp battery or grinding pan fed by an automatic feeder; or from a small tank fitted with agitator blade, ascending current of water, or other method of agitation, into which lime is dumped at intervals. Lime is sometimes added in unslacked form directly to an agitation charge, but should first be slacked and then added as a milk of lime. When leaching vats are filled with dry ore, the lime is distributed, invariably slacked in a dry, powdery form, in small lots to be well mixed with the charge; this is the most effective way of adding lime. Where the sand vats are filled with wet, flowing pulp, the necessary lime is usually added crushed wet into the pulp stream as stated before. Much of the finer and the quickly-dissolved portion of the lime overflows the vat and is lost, unless the mill water is reused or crushing in solution is practiced. Small quantities may be added by the inconvenient method of sprinkling it over the top of the charge and raking it in. A method which can be resorted to is to add the lime to the stock solution tanks, thus making the cyanide solution a strongly saturated solution of lime water. This method is open to criticism as temporarily giving an inordinately high protective alkalinity where a constant low one is desired. Yet on ore con- taining many cyanicides, a solution low in cyanide and strong in alkalinity is often used first on a leaching charge, that the cyanicides may be cheaply neutralized before adding the stronger cyanide solution. The method of adding the lime deserves careful consideration. If milk of lime is added to the pulp flowing to leaching vats, the overflow of which runs to waste, much of the lime will be lost. If added in granules, they will sink with the grains of pulp, become imbedded in the charge, and gradually dissolve and give off their alkali, thus doing effective work. The size of the granules of lime required will vary with the nature of the ore and ALKALINITY AND LIME 63 its treatment. They should be of such size that the lime will dissolve and give off its neutralizing power as fast as needed. This will be indicated by the solution issuing from the vat. It should at all times have a small protective alkalinity, but at no time an inordinately high amount, yet on the principle of economy the lime should be all dissolved and used by the time the treat- ment is finished. The cyanicides of some ores show themselves very fully at the start, others, especially heavily sulphuretted ores, gradually undergo oxidation and develop cyanicides and alkali and cyanide-consuming compounds during the whole time of their treatment. Consequently, each case is a separate problem of both how to add the lime to the best advantage in view of its influence on the dissolution and precipitation of the precious metals and the consumption of cyanide, and how to get the maximum efficiency of the lime. Between adding lime in un- slacked coarse granules and as a milk of lime is a wide variation. Lime v. Caustic Soda. Caustic soda (NaOH) was at one time used extensively for neutralizing purposes, but lime was generally found to be superior as the salts or compounds of lime mainly calcium sulphate are very insoluble, while those of caustic soda are extremely soluble. In this way the lime salts are precipitated in the ore where formed instead of entering the solution, where they may exert some influence and perhaps be precipitated in the zinc boxes as sometimes occurs in using caustic soda. The exces- sive use of caustic soda as a neutralizer will cause trouble with the zinc precipitation much quicker than the use of lime. One ad- vantage of caustic soda when such an advantage is desired is its extreme solubility; it will dissolve in an equal weight of water, while 1 part of CaO requires 800 parts of water. Pure lime has 1.43 times the neutralizing strength of caustic soda and is much cheaper. Determination of Causticity of Lime, etc. Commercial lime is always more or less impure, containing varying amounts of sand, clay, iron, carbon, etc. These were contained in the origi- nal limestone or are due to the fuel. The available or useful alkali may be roughly estimated by taking a weighed and pow- dered sample of the unslacked lime, mixing it with water to form a very dilute and liquid emulsion containing a definite per cent of the commercial' CaO, and titrating it, as in the test for pro- tective alkalinity. The comparative efficiency of the lime when 64 TEXT BOOK OF CYANIDE PRACTICE dissolved or slacked in cold water and in hot water should be tested by titrating a similar lime-test solution that has been boiled, for grinding or thoroughly disintegrating the lime in hot water will usually give a higher alkalinity. For more accurately obtaining the causticity or available CaO or alkali, weigh out 2 grams of the powdered unslacked lime, make up to 1000 c.c. with water and 20 grams of pure cane sugar, shake at intervals over a period of 12 hours, and finally remove an aliquot part and titrate with the decinormal acid and phenolthalein. If it is feared that the lime contains reducing agents that will destroy the cyanide, a clean, hew, cyanide solution should be made up for test purposes, titrated for its strength, and lime added in varying quantities with titrations to determine if the cyanide strength is reduced. Lime sometimes gives trouble by the car- bon and carbonaceous matter in it or introduced in the burning- process, precipitating the gold and silver. Agitating lime with metal-bearing solution, either in the laboratory or in the gold stock tanks, with assays of the solution before and after, will indicate regarding this. CHAPTER VII ORE TESTING AND PHYSICAL DETERMINATIONS IN making laboratory tests on ore for the extraction of its gold and silver by cyanide, the principles governing and the points arising in the actual working of the ore must be borne in mind, rather than an attempt to imitate the -exact details of plant practice. The experienced cyanide operator in making tests on ore, while employing careful laboratory methods, observation, and study, visualizes the sample of a few pounds into a full-sized working charge, correlating each detail occurring in the sample to that which would take place in a working charge. Facts to be Determined. The principal things to be ascer- tained or to be examined into are: nature and composition of the ore; nature of the metal and the condition in which it is held in the ore; special treatment which may be necessary, as roasting, water-washing, aeration, removal of cyanicides, amal- gamation, concentration, etc.; amount of lime or other neutral- izer required; strength of cyanide to be used, with probable quantity required, and consumption that will take place; time required for dissolving the gold and silver; fineness of crushing required for an economically high extraction, and the variation due to crushing to varying degrees of fineness, including the results of sizing tests showing the amount of different mesh material produced, and the value of each before and after treat- ment; tendency of ore to slime, and quick or slow settling effect; also how it will percolate. Methods of Testing. To work these tests out fully requires a great amount of labor and time. It is customary to start with small bottle tests of perhaps a few ounces or pounds, and after the characteristics of the ore have been learned to increase to 25 to 100-pound lots; and finally, especially if the ore is a silver one or shows any refractory tendencies, to test at a custom test- ing plant or in a small experimental plant at the rate of 500 pounds 65 66 TEXT BOOK OF CYANIDE PRACTICE or a few tons per charge. Tests in bottles are easily made and will quickly exhibit to the experienced operator the lines along which the metallurgical system is to be developed. They are insufficient to build a plant on, even presuming that the same dissolution would be effected in the plant as in the preliminary tests, for cyanide and crushing plants and processes are not fully standard to all classes of material, and consequently should be designed to meet the necessities of the ore, which must be learned by extended experimental work. Securing Samples. The first, and probably the hardest thing, unless under the direction of an experienced man alive to the dangers, is to get proper samples of the ore. The tendency is to take samples that are too well oxidized, for the ore promi- nently exposed during the early days of a mine is the oxidized ore near the surface. Often the samples are taken from dumps that have long weathered. Tests on this nature of ore will invariably indicate a high extraction with coarse crushing and either without or with but little concentration. Whereas, when the harder, unoxidized, baser ores are worked, there is a lower extraction obtained, a finer crushing required, and after a lapse of considerable time the operators awake to the fact that con- centration or closer concentration by a more elaborate concen- trating plant, or changes to give greater attention to the sulphide content of the ore, will increase the profits to a large extent. In some cases the samples represent too fine a material, in others too coarse. This may result in increasing or decreasing the appar- ent value of the material to be treated or the amount of some constituent in it, or, by giving undue proportions between the slime and sand, may cause the installation of an unsuitable system. When the mine contains different classes of ore, as oxidized and unoxidized, clean " free milling " and base, high and low grade, those that slime and those that are hard and dense, and separate shoots or ledges containing copper, zinc, lead, etc., each class should be tested separately and not averaged together. This distinction should be borne in mind after the plant is in operation, for a plant using cyanidation may, like a smelter, find it desirable to mix certain ores in some cases and keep them separate in others, to get a certain proportion of sand and slime, or to treat an easily worked ore differently from a refractory one. ORE TESTING AND PHYSICAL DETERMINATIONS 67 Physical Examination of Ores. The ore to be tested should first be closely examined and studied, for its characteristics, conditions under which it is found, the methods employed upon similar ore in the same or other districts, and the results from assays, pannings, microscopical examination, etc., will indicate the nature of treatment that will probably be required. If it is a soft, porous ore which a solution can easily penetrate, coarse crushing such as is done in a dry-crushing mill may be sufficient. If it is a hard, dense ore which the solution cannot penetrate, fine crushing will be required to liberate the metal to the solvent action of the cyanide. The metal may lie on the breaking or parting planes of the ore or on the faces of the crystals, in which case extremely fine crushing will not be required to expose it; whereas when it is embedded in the crystals or sulphide, very fine crushing is required. Where the metal is in coarse grains, it must be removed by amalgamation or careful concentration, or a long contact with a strong solution will be required to dis- solve it, unless it is ground into small particles or thin scales by a tube mill or other slimer. Where the metal^ is in an extremely fine state of division or in very thin scales, a low strength of solution will dissolve it quickly. If the ore contains limonite, kaolin, alunite, talc, etc., that becomes a colloidal, slow-settling, and unmanageable slime, only the leaf filter can handle it to an advantage. Where the ore contains sulphides, it becomes a question whether to remove them or not before cyanidation. It is customary to remove them by concentration when they represent a considerable proportion of the value, or introduce interfering substances into the ore. A sulphide or base ore will generally necessitate finer grinding to liberate the metal. Tel- luride ore is invariably treated by roasting or bromocyanide. Ore containing copper may require the removal of the copper by concentration or by leaching with very dilute sulphuric acid be- fore applying the cyanide, while other copper ores may be suc- cessfully worked by using low-strength solutions that will act less strongly upon the copper. Ores containing antimony, and to a less extent manganese or arsenic, may give low extractions and require aeration, etc. Sulphide ore may require considerable aeration. Clean and unoxidized ore will require little lime or other neutralizer of the acidity, while oxidized and base ore will require a large amount. 68 TEXT BOOK OF CYANIDE PRACTICE Free Acidity. The first test that may be made is for free acidity or that which is soluble and can be washed out of the ore. Take 20 grams or more of ore ground to the mesh expected to be used. Add the same number of cubic centimeters of water and agitate for ten minutes or longer. Filter dnd titrate 10 c.c. of the filtrate with decinormal caustic soda solution until the solu- tion becomes alkaline as described under the test for hydro- cyanic acid and protective alkalinity. This will give the number of pounds of caustic soda or lime required to neutralize the soluble acidity in one ton of water, and if the same weight of water as of ore was taken, the results indicate the caustic soda or lime required per ton of ore to neutralize the free or soluble acidity. Latent Acidity. Latent acidity, or that which is insoluble, is determined by washing a weighed sample or that used in de- termining the free acidity until the washings show no acidity, then adding some water to the ore and the alkaline indicator, and titrating with the decinormal alkali solution until the ore solution becomes alkaline. The results are figured in the same way as for free acidity, except that the titration is computed for the number of grams of ore used. A method giving higher and more correct results consists of diluting with the necessary amount of water and adding standard caustic soda solution in some excess of that required to make alkaline, agitating for half an hour or longer, filtering and washing ore until no more alkalinity, then titrating to neutrality by standard acid. As a standard acid and alkali exactly equal each other, the difference between the alkali added and the acid required to neutralize the excess, will give the latent acidity. Total Acidity. The total acidity, that due to both the free and latent, which is what is usually required, is found as for latent acidity without first water-washing. Where the ore to be tested is wet, it should not be dried, for more acidity will be gen- erated from the iron, pyrites, etc.; but the tests should be made first, after which the ore is dried and weighed for calculating the results. These tests for acidity will indicate with little accuracy con- cerning the amount of lime required, for more will be used in practice, owing to the large proportion of impurities in the lime, which should always be borne in mind, to the lime not dissolved or uneconomically used, and to further acidity which may be ORE TESTING AND PHYSICAL DETERMINATIONS 69 generated. A closer approximation of the amount can be ob- tained through tests made by the use of bottles, introducing 20 grams or more of ore into each, together with the same num- ber of cubic centimeters of a fresh cyanide solution of .working strength and varying weighed quantities of lime, as .05 (1 pound per ton of ore), .15 (3 pounds), or .25 per cent (5 pounds) or more of the weight of ore, agitating for 3p minutes or lonjger, filtering and testing 10 c.c. of each for cyanide consumption and pro- tective alkalinity. That solution which indicates a protective alkalinity below .3 per cent (.6 pound) CaO will probably show a low consumption of cyanide, and indicates the amount of lime to be used on clean ores, though as the ore becomes baser the lime and cyanide consumption cannot be estimated from such short contacts or so generally - the actual practice must be imitated. Extraction Tests with Bottles. The most important thing in all cyanide tests is to learn the highest dissolution of gold and silver that can be effected. Bottle tests on gold ores will usually give this as closely as a working charge of several hundred tons, if the sample is representative, in the same way as a small por- tion taken for assay represents a carload or a day's run of ore. As the ore becomes baser and with silver ores, bottle tests cannot be relied upon so strongly, for on account of the comparatively slow dissolution of the precious metals in such ores the maximum dissolution may not be effected. Bottle tests, besides giving the maximum extraction, indicate less accurately the strength of cyanide to be used, the consumption that will take place, the time required for dissolution, and the amount of lime to be used; also, by testing the solution, the nature of the cyanicides. For making simple bottle tests on gold ores, take wide-mouthed bottles and introduce into each 2 assay tons of ore ground to the mesh expected to be necessary, together with the amount of lime or neutralizer that the bottle test before described shows to be necessary to give a small protective alkalinity. In the absence of having made this test, use an amount in excess of that indicated by the test for total acidity. Add 120 c.c. of a new cyanide solution to each bottle, making the first . 1 per cent (2 pounds) KCN, the second .175 per cent (3.5 pounds) KCN, and the third .25 per cent (5 pounds) KCN. If it is a clean ore con- taining the gold in a finely-divided state, a charge should be tried 70 TEXT BOOK OF CYANIDE PRACTICE using a strength of .05 per cent (1 pound) KCN. With a base gold or an easily-worked silver ore a charge of .375 per cent (7.5 pounds) KCN should be tried, while with a base silver ore or a very base gold ore, the test should be made with solutions from .1 per cent (2 pounds) to .6 per cent (12 pounds). These bottles should be agitated for 24 hours, or left stand with occa- sional shakings for 48 to 72 hours. If the ore contains the gold in a finely-divided state and little sulphide, the value will be dissolved within 12 hours. If the ore is very base, it may require more than 72 hours' contact, unless continuous agitation is given. Some silver ores may require a few days' continuous agitation or contact for a week with strong solution. The bottles should be uncorked at times to aerate. At the end of the period, filter each charge and test for cyanide consumption and protective alkalinity, which can be reduced to tons of ore, since each assay ton of ore was treated with approximately 2 assay tons of solution. Wash the ore by decantation or on a filter for some time after all alkalinity is removed, a thorough washing is most essential. Finally dry and assay. At the same time as making these tests it would be well to grind a sample of the pulp to 200-mesh and treat it with a strong solution (.375 to .5 per cent 7.5 to 10 pounds KCN) with a few decantations and additions of new solutions, that the results of the residue assay may be taken as the maximum extraction under ideal conditions for comparison with the regular bottle tests. With silver ores and sulphides, lead acetate at the rate of 1 pound per ton of ore should be added to the charge or solution to remove any alkaline sulphides formed. If the ore reaches the cyanide plant wet and without drying, it should be treated that way in the test, for a pre- liminary drying would oxidize the ore and probably give a higher extraction than the plant could in actual practice. The differ- ence between the assays of the sample before and after treatment gives the extraction; this may be checked by drawing off 30 c.c. or any aliquot part of the solution and assaying. Or the effect of further contact with the solution may be tested by drawing off or removing the aliquot portion of the solution and assaying the same, followed by retreating the ore with fresh solution before washing and drying it for assay. The bottles may be continuously agitated by being attached to some suitable moving device, as a wheel, in which case the extraction will take place ORE TESTING AND PHYSICAL DETERMINATIONS 71 quickly, just as agitation in actual practice causes the value to go into solution in a comparatively short period. Agitation tests with lots of 2 or 3 pounds of ore may be con- veniently made in large acid bottles. The amount of solution used should be from two to four times that of the dry ore by weight, or even more. An air-agitating tank may be constructed in various ways, such as by cutting off the bottom of a large wine or other bottle having a long, sloping neck. This is placed in an upright position with neck down. A f-inch glass tube is suitably supported from near the bottom of the neck to within 2 inches of the top. Through the cork in the neck of the bottle passes a J or J-inch glass tube delivering air into the bottom of the f-inch glass tube. A charge sufficient to nearly submerge the central tube is placed in the agitator and a slight amount of air turned on, resulting in circulating the pulp up the central tube and down the outside of it. Any modification of this the Pachuca air-lift tank principle may be used. In agitation tests, samples should be taken hourly or every few hours by means of a tube, preferably of glass, inserted to the bottom of the charge, the upper end closed with the finger and quickly withdrawn, or some of the pulp may be syphoned off. Care must be exercised to get a true sample of the pulp and not one containing too little of the coarser material, nor should the amount removed be sufficient to vitiate the final sample. The sample should be tested for cyanide strength, protective alkalinity, and gold and silver. If the consumption of cyanide or alkalinity is large, it may be necessary to add more during the agitation. Percolation Tests. Percolation tests more closely imitate leaching practice and consequently are often used. These are made in glass percolators or by using large acid or smaller bottles as such by cutting their bottoms off, the discharge of the per- colator being fitted with a rubber tube and a pinchcock. A filter bottom of muslin or light canvas is arranged on a platform in the bottom of the percolator, after which the charge of Ore containing the proper amount of neutralizer is added; this may be as small as 2 pounds if crushed medium fine. There is set above the percolator a vessel containing the cyanide solution to be used, which may be drawn off by a small cock or syphoned out by a rubber tube, the stream of which is regulated by a pinch- cock. If it is desired to measure the solution, an amount by 72 TEXT BOOK OF CYANIDE PRACTICE weight equal to twice the amount of ore is convenient. Thus if 600 grams of ore have been taken, 1200 c.c. of solution may be used. The ore in the percolator is covered with this solution, after which the discharge cock is opened to allow a drip sufficient to drain the entire amount of solution through the charge in the allotted time, which is usually three days with simple gold ores, and longer with very base and silver ores. The solution in the reservoir being allowed to drip into the percolator at a rate sufficient to keep the charge covered. Occasionally the entering drip should be shut off to allow the charge to drain and to aerate for a short time, after which the charge should be covered with solution and percolation started. After final percolation and drainage, the charge should be thoroughly washed past the point where the washings show not even a trace of alkalinity, when it is dried and assayed. The solutions and washings are saved, measured, titrated for cyanide strength and protective alkalinity, assayed for gold and silver, and the results figured out. By using a good sized charge and sampling at regular periods when drained by a sampler resembling a cheese drier, by plunging a tube into the charge, or by removing the charge, the progress of the dissolution of gold and silver can be noted. These samples must be well washed without any delay. By running several percolation tests together on parts of the same sample, using different strengths of solution and sampling at regular intervals, the necessary data regarding strength of solution to be used, consumption of cyanide, and time required for dissolution can be learned, but not the degree of fineness to which the ore should be crushed. Fineness of Ore Required. To learn the degree of fineness to which the ore should be crushed, the simplest forms of bottle tests that use a solution sufficiently strong and a long enough application to get the maximum extraction is all that is required. The ore should be crushed and ground to those of the following sizes which may be deemed necessary, 4, 10, 20, 30, 60, 100, 150, and over 200-mesh. The 'results of cyaniding those sizes that give a good extraction should be shown in a comparative way by plotting, etc., and studied, for that degree of fineness which gives the highest extraction may yield less profit than when crushing to a coarser size, on account of the increased cost of crushing finer and cyaniding the finer material. ORE TESTING AND PHYSICAL DETERMINATIONS 73 Sizing Tests. The last x tests to be made are sizing tests. These occupy some time and are usually not made until the pre- liminary tests are well worked out, though it is an advantage to make them at all times. A sample of the crushed ore to be tested by cyanide amounting to about 2 pounds is taken and weighed. It is first concentrated and reconcentrated until all sulphide is removed. It is then stirred up with the water used in concentrating and the muddy water poured off, care being exercised that no fine sand passes off with the water, when it is again stirred up with water and the muddy water poured off. This is repeated and repeated until the sand is washed entirely free from slime that is of a light, flocculent, feathery nature, that agglomerates together, makes water muddy, and does not readily settle; while the slime product contains no sand or granular matter, however fine. The slime is allowed to settle, the water poured off, and the sludge either dried in a pan or run onto a filter paper and dried after draining, when it is weighed. The sand and concentrate are also dried, after which they are sized through screens. To divide the concentrate into two sizes and possibly three is good. The sands should be sieved into at least four sizes, the coarsest size containing not more than 5 or 10 per cent of material that may be considered as a coarse oversize, as that which failed to be crushed to the desired mesh, while screens should be used that will divide the remainder about evenly. Taking the case of material crushed in a mill through a 40-mesh screen, the sizing test should produce the following sizes: a con- centrate or a coarse and fine concentrate, a slime, an oversize of 5 or 10 per cent held on a 40-mesh laboratory screen, a held on 60, 100, and 150-mesh, and a passed 150-mesh sand; these sizes should be weighed, assayed, and the results tabulated. If the ore contains free gold liberated by the crushing, this sizing test is of little or no value unless the gold is removed by amalgamation or panned out with the concentrate, preferably removed by amalgamation. The remainder of the sample from which the sizing test and the head assay sample were taken is now cyanided in the labora- tory until the maximum extraction is obtained, which is best performed by introducing the ore and solution into a large acid bottle and agitating it intermittently or continuously as usual. After the charge is washed free of dissolved gold and silver, it is 74 TEXT BOOK OF CYANIDE PRACTICE sized as before, the results being compared with those of the ore before cyaniding, and both with other tests in which the ore was crushed finer or coarser. The sizes obtained* of the sample be- fore cyaniding may be assayed, then cyanided separately, and the residues assayed, or the coarser sizes after cyaniding may be recrushed and recyanided and the results observed. The whole purpose of sizing tests is to show in what part of the ore the value lies before and after cyanidation, and the effect of coarser or finer crushing on the extraction. While the straight cyanide tests made on the ore as crushed to different degrees of fineness will show the increase or decrease in extraction, so that the most economical size can be selected, the sizing tests are necessary to a true diagnosis of conditions. To act without them is too much like a physician prescribing for a sick man without learn- ing the nature of the complaint. It may be that by crushing only the oversize an increased economical extraction can be had, or all sizes of the sand may respond to finer crushing, or the sul- phide or coarser sulphide only may require finer crushing. Knowing exactly where the trouble is, the metallurgist can pro- vide to meet that point. When studying sizing tests or the effect of crushing to different degrees of fineness, the metallurgist must consider more than the conditions directly affecting cyani- dation. He must also consider the crushing devices at his dis- posal or which can be reasonably installed. To make a practical success he must bring such knowledge and study to bear that he can adjust the conditions necessary to secure a high extraction by cyanidation to those necessary to obtain a high tonnage at a reasonably low cost from the crushing machinery, and find the economic mean of the two. While many in making sizing tests include the flocculent slime in the finest sand, the remaining sands should always be washed free of the adhering slime, this slime to be added to the finest size. The following will indicate the method of tabulating the results. TESTING AND PHYSICAL DETERMINATIONS 75 OQ * - in ilt 10 (N O xo 3 1 1 ^ ^ OS lO JB 1 I (M^OOGOOO^O rHrHOOCDOtl. 00 g fS o (M T-< OI-H oT 1 - I bo o "? c3 ^.S-5| Nsl S^H 00 ^ >0 10 0 CO 00 (M Q Ot (Oi lOOT IT I Q i 'N o J-T 3 H^ . o> CQ ^ g j> & I'? 2 "o O s h33 3.2 ^ J ^ooS^S^^ ^ i-i i-i ' rH c3 ' ~ 6 ss 1 O 10 G- O 1 2 2 js b) 1 rHiQOOO >O O ^O 1C t^ t^ iO t^ (M 8 111 2 o OOCOrt.COOaiCD (MOO(Mt^T t r-l i l O5 H cS eing discharged in the residue may ^alsoTbe obtained by taking 300 grams of the residue, adding ^water" sufficient to make a one to one solution, estimating the moisture or determining it in another part of the sample, agi- tating for several minutes and drawing off and testing any aliquot part. Thus if 300 grams of residue containing 20 per cent of moisture are taken, it is equivalent to 240 grams of dry sand and 60 c.c. of water, to which 180 c.c. of water should be added to give a one. to one solution. If 120 c.c. of the solution is used for assay, it will represent that metal held in 120 grams dry pulp (practically 4 assay tons), while the titration of 10 c.c. will give the pounds of KCN mechanically lost per ton of dry pulp. Samples should be taken on test charges representing different depths of the sand charge, for it is sometimes found that the metal is not as thoroughly dissolved in the lower part of the charge, due to the lack of aeration and possibly the weakened condition of the strong solution reaching that part of the charge. The bottom of the charge contains more moisture due to its packed condition preventing free draining, and to the tendency of the moisture just above the filter bottom to be retained in the sand by a species of surface tension, while this lower moisture must be much richer than that above. CHAPTER IX SLIME TREATMENT AND AGITATION Definition of Slime. Solids may be said to exist in two forms, crystalline and amorphous. Substances in a crystalline form have a definite and regular shape; they are compact and substantially solid. Grains, crystals, and solid bodies represent the crystalline structure. The amorphous is the opposite of the crystalline structure; it is irregular and indeterminate in shape, and less compact and substantial than the crystalline. In the cyanide process the crystalline is represented by " sand " and the amorphous by " slime." Sand may be said to be that part of the ore, however fine it may be, which is crystalline, granular, sharp, clean, compact, and under the microscope presents reg- ular structure, sharp edges, and solid faces; which readily settles in still water and does not muddy water, and which can be leached. While slime may be said to be noncrystalline, light, feathery, flaky, non compact, impalpable material, showing irreg- ular shape and structure; which muddies water and does not readily settle in still water, but remains in suspension dissemi- nated throughout the water, to gradually agglomerate and settle as a flocculent slime to form a plastic clay or mud, very unleach- able and impermeable by water. Slime is sometimes spoken of as a " colloid," a term applied to substances suspended in solu- tion in a semisolid state. While sand partakes of the nature of quartz, slime partakes of the nature of clay. Slime is usually a silicate of aluminum, iron, or alkaline earths. The hydrated aluminum silicate, kaolin (A1 2 3 .2 SiO 2 .2 H 2 O), is a most prominent slime or con- stituent of the slimes, and shows that the term " colloid hydrate " is not a misnomer as a technical term for slime. Slime is found least in hard, crystalline quartz, and most in talcose, clayey, feldspathic, and oxidized ores, or those containing kaolin, alunite, and limonite. The percentage increases with finer crushing as the amount of impalpable powder produced must necessarily 108 SLIME TREATMENT AND AGITATION 109 increase. The slime produced in crushing a hard quartz probably has certain crystalline qualities to account for its quicker settling and more permeable nature than that arising from a clayey ore, for a slime resulting from a quartzose ore can be settled or fil- tered much easier than that from a clayey ore. Flocculent slime undoubtedly carries considerable fine sand covered and held in suspension by a coating of slime or colloidal material. Slime is sometimes defined without reference to the crystalline or amorphous qualities, as that part of the ore which will pass a 200-mesh screen. This interpretation has been given the term because it is generally considered by many that material finer than 200-mesh had best be treated in the slime plant, even though it contains grains that are leachable, also because material ground to 200-mesh is excellent to treat in a slime plant. The use of the term slime in this manner has rendered it necessary in refer- ring to an amorphous slime as discussed in the preceding para- graphs to use the terms " flocculent slime," " clay slime," '' col- loid slime," or " true slime." It would be well to distinguish a granular slime passing a 200-mesh by some modifying term, as a " sandy slime/' reserving the word " slime " for the amorphous and real slime, but using the term " true slime " or other until the present confusion in the use of the word " slime " has passed away. It is highly necessary to distinguish between a sandy slime and a true slime as some processes, agitating machinery, and filters may be wholly or better adapted for treating the one class of material than the other. This is owing to the plasticity and the impermeability by water of a true slime, which as granu- lar material is added and it becomes sandier, becomes less plastic and more permeable and leachable, and in part settles faster. Also because a sandy slime settles to a denser, more compact sludge that is harder to move and disintegrate. Dehydrating or removing the moisture from a slime by heat- ing or roasting renders it more susceptible to leaching and less adsorptive of moisture which cannot be displaced, a fact that has weight when the roasting of dry-crushed ore is being con- sidered. Slime Settlement. The addition of any one of various acids, alkalis, or neutral salts to water containing slime in suspension causes the suspended matter to coagulate and settle much faster and to a smaller bulk than naturally. Lime is the only substance 110 TEXT BOOK OF CYANIDE PRACTICE added for settling purposes in the cyanide process. Some idea of the amount of lime required can be obtained by laboratory tests on average samples of the slime pulp placed in graduates, to which known quantities of lime are added, and the subsidence compared at different periods of time. However, the amount used in actual practice is determined by that which gives the quickest settling into the least bulk with an economical amount of lime. Too much lime may retard the settling. The amount of lime used is variable, in some plants a few pounds per ton of dry slime will suffice; in others as much as 10 or 20 pounds of lime has been used per ton of ore. The settlement of slime by lime or other alkali, an acid, or a neutral salt is on the theory that particles of any kind when suspended in a liquid are electrostatically charged. That these charges while they may be positive or negative for different kinds of suspended matter, are still of the same sign for all parti- cles of the same substance, and consequently repel each other, for two different substances in contact have equal and opposite electrostatic charges at their contact surfaces. The tiny slime particles by the repulsion of their like electrostatic charges together with their relatively large surface in proportion to their weight and their solubility or saturation similar to that of a sponge suspended in water, counterbalance the action of gravity and remain suspended in the water. In short, their density differs so little from that of the surrounding liquid that they remain in suspension or settle at an infinitesimally slow rate. Heating the water lightens its density and lessens its viscosity and confers greater mobility so that the particles may better settle through their higher specific gravity, but on a working scale the cost of heating overbalances the advantage of the quicker settling. The introduction of an acid, alkali, or salt capable of disassociating produces both positively and negatively- charged ions which attract the slime particles having different charges, causing a coagulation of the slime to expose less surface for a given mass and consequently to better settle. Substances used for connecting other substances in this way by their electro- static charges are termed electrolytes; thus lime is an electrolyte in the settling of slime by its aid. The settling rate decreases with the density or viscosity of the pulp. With a very dilute pulp the slime at first settles rapidly SLIME TREATMENT AND AGITATION 111 to leave a clear solution, but the settling rate, the downward movement of the line of demarcation between the slime pulp and the clear. solution, gradually grows less as the underlying slime pulp becomes thicker and denser until the settling rate practi- cally becomes nil. In this movement the true slime appears to move downward by layers, that slime at the top of the charge when settling was started becoming the top of the settled slime. While the settling rate is thus decreased through the settling of the slime being retarded by the density or increasing density of the medium through which it is settling, in a practical way the depth of the settling column has a most important influence. It is apparent that the slime particles in a charge 4 feet deep in a small-diameter tank will have to settle through practically four times the distance as in the same charge when 1 foot deep in a large-diameter tank of four times the area, and that there is a greater retardation in the 4-foot charge owing to the greater weight of solution or solution and pulp overlying any section of the depth and thus making the density greater. This will ex- plain why shallow tanks of large diameter are necessary in de- canting, instead of deep tanks of small diameter. Classification or Separation of Sand and Slime. Slime treat- ment may refer to the treatment of a true slime, of a sandy slime containing the finer sand made in crushing together with the true slime, or of all the ore ground fine a case of " all-sliming." The methods used in treating these three classes of material do not vary in the main, though the presence or absence of sand is an important detail. Where the decantation system of treatment is used, it is aimed to treat only the true slime, on account of the greater ease with which the sand can be treated in a leaching plant and the higher efficiency of the leaching plant in washing out the dissolved value. With a modern filter plant it is, with most filters, desirable to treat all or a part of the sand with the slime, since they can handle a sandy slime better than a true slime. For producing a true slime and furnishing a clean sand at the same time, the Dorr classifier is the only machine approach- ing perfection. Where it is necessary to throw the finer sand into the slime, cone classifiers may be used, or the Dorr clas- sifier modified so as to produce a sandy slime. Cone classifiers never give an absolutely slime-free sand for the leaching plant, 112 TEXT BOOK OF CYANIDE PRACTICE consequently their underflow of coarse sand should be reclassi- fied in a Dorr machine. Pulp Thickening. The slime pulp runs from the classifiers to pulp thickeners. These are of two kinds: those operating on the settling principle with cone bottoms discharging a thickened pulp, and those using the same settling principle, but discharging the settled slime by some mechanical means. Lime is usually added to the slime flow before entering the thickeners for neu- tralizing the acidity and to effect quicker settling. The pulp EED LAUNDER 1 , CLEAR SOLUTION DISCHARGE Fig. 7. The Dorr Slime Thickener. flow is conducted to the center of the tank or cone and introduced into it through a central pipe emptying a few feet below the sur- face of the water. In this way the slime flow does not disturb the water and settling slime, but emits from the bottom of the pipe and rises and moves at a very slow rate of speed, under con- ditions favorable for the deposition of the slime material, to overflow the side or rim of the cone or tank as a clear or partly clarified solution or water ready to be reused or run to waste. From the bottom of the tank, the thickened sludge may be drawn off continuously, or intermittently with more or less trouble, with a dilution that is variable but seldom less than one part of solution or water to one part of dry slime. SLIME TREATMENT AND AGITATION 113 Charging for Agitation. The pulp is drawn continuously or intermittently into the agitation tank, or the slime flow may be settled in an agitation or collecting tank in a way similar to that in the pulp thickeners. After the agitator has received its charge, lime may be added as a milk-of-lime, also sufficient cyanide, by being dissolved in a small stream of solution, to bring the lime and cyanide strength up to the desired amount. Lead acetate Fig. 8. The Hendryx Slime Thickener or Tailing Dewaterer. dissolved in water may also be added for the purpose of precipi- tating any alkaline sulphides which may form. Any extra solu- tion to bring the charge to the desired proportion of solution and dry pulp is added. If the crushing has been done in solution, the pulp thickeners may only be required to reduce the pulp to the consistence desired for agitation, so that no additional solu- tion need be added. But if crushing is done in water, the pulp thickeners are worked to their highest efficiency or the pulp in the collecting or combined collecting and agitating tank is allowed to settle, and as much water decanted off as is possible before adding cyanide solution and beginning agitation. With a plant crush- 114 TEXT BOOK OF CYANIDE PRACTICE ing in water, it is necessary to dewater the pulp to the lowest possible percentage of moisture, or the amount of solution in the plant will soon increase to such a quantity that some of it must be run to waste. Amount of Solution in Agitation. Slime is agitated with varying amounts of solution. Where decantation is practiced, 1 part of dry slime will be agitated with from 3J to 6 parts of solution, that a large volume of solution may be decanted off to enable a low tailing to be obtained. Where the slime is filtered without decantation it will be kept much thicker, perhaps as much as 1 part of dry pulp to 1.2 parts of solution (by weight). The density of the pulp or the proportion of solution to dry pulp has an important influence on the dissolution of gold and silver, even though the strength of the solution be the same. The dis- solution of the gold and silver will be slower with a thicker pulp. A pulp of 3 parts of solution to 1 of ore against one containing only 1J parts of solution brings double the amount of cyanide and dissolved oxygen into play, consequently with a thin pulp the strength of solution can be kept lower, while with the same strength the dissolving rate will be faster. In both agitation and percolation, so far as concerns the dissolving of the metal, the effect of a strong solution small in quantity and applied for a short time can be equaled by a weaker solution larger in quantity and applied for a greater length of time. A thin pulp is often agitated and then settled and decanted from to a thicker con- sistence before being filtered, in the effort to meet the above conditions and to reduce the value per ton of the solution re- maining in the pulp to be filtered. With air agitation there is no question but that a good aeration is obtained, but with me- chanical agitators the necessity of aeration and the action of reducers in the pulp should be examined. It has been noted in many cases that after a certain length of agitation, no more value would go into solution, but by removing the old solution and applying new, either by decantation or the short contact with wash solution during the filtering process, the remaining dissolvable value goes into solution quickly. The same results on the aeration of a charge and adding newly aerated and pre- cipitated solution has been noticed in the leaching process. Strength of Solution and Time Required in Agitation. The strength of solution that it is advisable to use will vary with the SLIME TREATMENT AND AGITATION 115 (nature of the ore and the volume of solution used. On gold ore a strength of .05 per cent (Impound) to .1 per cent (2 pounds) is generally sufficient, on silver ores up to .4 per cent (8 pounds), and on gold concentrate up to .5 (10 pounds). In some few cases a .025 per cent (i pound) solution is sufficient on gold o^es when using a large volume of solution and a long contact. Some gold ores contain the metal in such a fine state that when crushing in solution and all sliming crushing all the ore to a sandy slime nearly all the gold will be in solution by the time the tube mill is passed. But in most cases an agitation of 3 to 18 hours is required with gold ores, up to a few days with silver ores, and up to 10 days with concentrate. The progress of the dissolution of the metals and the consumption of cyanide and lime should be frequently tested by taking samples of the charge, testing and assaying the filtered solution, and assaying the washed pulp. The results may be tabulated and plotted and filed for compari- son with others. The solution during agitation may be tested for its reducing power and the alkaline sulphides formed. Intermittent and Continuous Agitation. It is not necessary to completely dissolve the gold and silver at the first agitation where decantation is practiced, especially if the dissolving rate becomes slow during the latter part of the period of agitation. The agitations following, for the purpose of mixing the solution with the pulp, can be relied upon to effect final dissolution, together with the long-continued contact between the .ore and the solution that takes place in the decantation process. "Where the pulp is to be filtered, the value should be dissolved in one agitation unless, on account of the action of reducers and the fouling of the solution toward further dissolving of the precious metals, it is necessary to use fresh solution; though this can probably be met by aeration, at least the cause should be investi- gated and studied. Two methods of agitation are in use. The charge, intermit- tent, or single-agitation system, treating each charge separately and individually, which was formerly used entirely; and the con- tinuous system more recently developed. In the continuous sys- tem the charge is delivered continuously to the first of a series or battery of agitation tanks, through which the pulp passes to be delivered from the last agitator in the series to a filter or a stock tank supplying a filter. The method is illustrated in Fig. 9. 116 TEXT BOOK OF CYANIDE PRACTICE The pulp flows from pulp thickeners which settle the slime to the proper dilution or consistence, through the launder A to the first of the tanks which are the Pachuca or Brown air-agitator type. Here it is drawn to the bottom of the tank to rise to the top through the central column and again descend to the bottom, in the process of being circulated up through the central column and down outside of it. The iron pipe B, whose inlet end is at least a few feet below the discharge of the central column of the agitator and about midway between the column and the outside of the tank, and which is set on an angle of 60 degrees, discharges Fig. 9. Continuous Agitation System. into the next tank at a point midway between the column and the outside of the tank. In this way the pulp introduced at A is agitated in each tank and flows through the series to be dis- charged at C. The advantage of this system is that the large amount of labor, worry, wear and tear, and loss of time involved in charging and discharging a tank is entirely avoided. With well regulated tanks and equipment, attention need only be given to keeping the machinery in order and a watch over opera- tions. The gain in mill height or the elimination of the costly item of lifting the pulp to a higher level is an important item in this system. In the charge system with the regulation Pachuca tank, the pulp will be discharged at D which is 45 feet below the top of the tank. With the continuous system the discharge is at SLIME TREATMENT AND AGITATION 117 Cj which is only a few feet below the top of the tank. A longer agitation is given the pulp, for with the charge system from J to J of the time is occupied in filling and discharging the tank, whereas in the continuous system the tank is agitating all the time except when it is desired to work on or repair a tank, which can be done by cutting it out of the series through pipes and valves connecting the tank to tank discharges, the pulp in the tank to be worked upon being drawn off from the bottom of the tank. If the filter or filter-stock tank is placed just underneath the discharge from the last tank, an emergency pump should be provided to lift the pulp from the bottom discharges of the tanks. The success of the continuous system primarily depends on the pulp being homogeneous in all the tanks ; which has been proven to be the case with Pachuca tanks through sizing tests made of samples taken from the different tanks ; though in some cases with a pulp containing coarse sand it may require consid- erable experimenting in the arrangement of the connecting pipes to get the pulp homogeneous in all the tanks. And secondly, that no particle of pulp shall move faster than others through the series and be discharged with less than the proper amount of agitation. That there must be a tendency to do this can easily be seen, but a particle of pulp that is undertreated in one tank, by passing out before receiving its share of agitation, -on entering the next tank is placed on an equal footing with all particles entering the tank at that time. Consequently the probability of evil results due to a particle of pulp being shunted across the series of tanks and discharged without the proper amount of agitation becomes less as the number of tanks is increased. By using the same number of agitating tanks in the continuous system as would be required in the charge system, the use of a number of tanks together with the extra agitation due to no loss of time through filling and discharging which acts as a factor of safety the same extraction ought to be secured as with the charge system, while actual working results have shown a higher dissolution due to the more prolonged agitation. Even if a lower dissolution was obtained, the saving in labor and other costs by the continuous system would in most cases overbalance the lower extraction. It has been proposed to employ a single, continuous-treatment tank by using the Just silica-sponge brick bottom. These pre- 118 TEXT BOOK OF CYANIDE PRACTICE pared bricks are used just as a filter cloth in a leaching vat, by being laid and held in a steel frame to act as a false or filtering bottom. The bricks are so porous that by introducing air at a low pressure underneath the false bottom, it will pass through the bricks to emerge in tiny streams that will keep the slime in agitation. Its adaptation to the continuous-agitation system consists in using a rectangular tank somewhat similar to a zinc box with a series of compartments having an upward and down- ward flow, all compartments being of the same length. The pulp as it flows through this large box would be agitated by the air passing through the brick bottom, while the number of com- partments may be many to lessen the tendency for any of the particles of pulp to get less than their proper share of agitation. The successful use of the silica-sponge brick in this manner would allow an agitator to be built and worked at a reasonable cost, to be economical of space, and which could be used as a filter-stock tank or with a variable amount of pulp, for which the Pachuca air-agitating tank is not adapted, since it must have a certain amount of pulp or the air-lift principle will not cause the pulp to circulate and agitate. The perfection of the continuous system has advanced the cyanide process to a point where the ore may flow in a continu- ous stream from the ore bin to the tailing dump without any intermittent operations. With the perfection of a continuous filter that with all classes of pulp will cheaply and thoroughly wash out the dissolved metal, even with rich pulp, and that will reduce the cyanide mechanically lost to a relatively small amount, together with a determination of the simplest and most eco- nomically efficient agitator for continuous agitation, the day of percolation will be passed and cyanide plants and processes will tend to become as standard in design as the stamp-mill process. Types of Agitators. The first style of agitator that was employed, and which has been generally used with the decanta- tion process, is the mechanical or stir agitator. These consist of large, round, flat-bottomed tanks as much as 40 feet in diameter and 20 feet deep. They are equipped with stirring blades attached to a shaft actuated by a gear mounted over the tank or underneath, and passing up through the bottom. Agitation of charges containing only true slime by these agitators is not SLIME TREATMENT AND AGITATION 119 difficult, especially if the pulp is dilute, but as the amount of sand in the charge increases, ttie difficulty in agitating becomes greater. This is owing to the tendency of the sand to pack and to resist the movement of the blades, which results in increased power being required, great trouble in starting a settled charge, and severe wear and tear on the machinery. The stirring gear in some types may be started with the arms raised and in the upper and more dilute portion of the charge, to be gradually lowered as the charge responds to the agitation and loosens up. Tanks without facilities for raising or lowering the blades should have them set 2 feet above the bottom of the tank to enable them to be easily started, as the sand then settles below them and yet can be brought into agitation when using a speed of 500 to 800 feet per minute. Short chains and iron cables have sometimes been hung from the arms to assist in stirring the slime below. Baffle plates may be attached to the sides of the tanks to insure better mixing. Two sets of arms, one near the bottom of the tank and the other near the center are excellent. Air may be pumped through perforated pipes in the bottom of the tank or through pipes attached to the arms, to assist in the agitation and to aerate as well. Agitation is often further assisted by centrif- ugal pumps taking the pulp from the bottom of the tank and returning it to the top of the charge. The mechanical or stir agitators have been comparatively costly in the horse power and repairs required, and the agitation has been far from perfect. Yet the facts that the tanks, being large in diameter and rather shallow, were well adapted for slime settling and for decantation, and that the arm stirs were excellent for repulping the settled slime with the fresh solution added, is the reason for their extensive use in the past. The thinness of the slime agitated in working with the decantation process 3J to 6 parts of solution to 1 of dry slime has assisted them to do good work. Likewise the treating of all the sand in the leaching plant and all the true slime in the slime plant, so far as the classifying apparatus enabled this, as is always the case with plants treating the slime by decantation. The new plants being built are all equipped with some form of slime filter, consequently mechanical or stir agitating tanks are seldom installed now, except as stock tanks to hold and keep in agitation the pulp to be supplied to the filters. They are well adapted for this, since they do not 120 TEXT BOOK OF CYANIDE PRACTICE have to be kept full or nearly full, as is the case with air and some of the other agitators. Agitation by a centrifugal pump drawing from the bottom of the tank, usually a conical-bottom tank, and pumping to the top of the tank, has been generally discarded owing to the great wear on the pump and pipe by the attrition of the sand. With a true slime the wear is much less than if the charge contains Fig. 10. The Trent Agitator. sand. Centrifugal pumps for this purpose are equipped with liners that may be removed when worn, but no liner or stuffing- box arrangement has yet been made that will last for any con- tinued length of time. Aeration with this form of agitation is provided by flowing the pulp over an apron on introducing it to the top of the tank and by means of an air valve between the tank and the pump allowing a small quantity of air to be drawn in and pumped with the pulp. A patented method of using the SLIME TREATMENT AND AGITATION 121 centrifugal pumps for agitating consists in using a deep cone- bottomed tank which has a hollow, central column. The centrif- ugal pump discharges slimy solution upward into the foot of the column, lifting the pulp up through the column by its force, as the hydraulic elevator does, and in that way starting and keeping up a circulation similar to that with the Pachuca tank. A shield or cap is suspended from the top of the tank around the air lift to form a calm zone of about 6 inches between the shield and the outside of the tank. The slimy solution passing through the centrifugal pump is drawn from the top of this calm zone, and is very dilute and free from sand, consequently it does not cause excessive wear on the pump and piping. An agitator combining the principle of the mechanical stirrer and the use of centrifugal pumps is the Trent agitator, as shown in Fig. 10. With this agitator the thinner slime taken from the top of the charge is pumped by a centrifugal pump through the bottom of the tank into a revolving four-armed stirrer, from which the slime is emitted by a number of discharges set along the length of each arm, the discharges being at right angles to the arms. The force of the discharge causes the arms to revolve in the same manner as a Butters and Mein sand-pulp distributor. The same principle can be employed by using air under pressure instead of solution to cause the arms to revolve. The Hendryx agitator, as shown in Fig. 11, is one of the most successful in use. It consists of a cone-bottom tank of ordinary height in which is mounted a central column or tube. In the tube is a shaft driven by a gear overhead the tank. Three pro- peller blades are distributed along the shaft. The rapid revolution of the shaft causes the blades to lift or force the pulp up the tube to flow over an apron, similar to an umbrella, to the edge of the tank, from which it sinks to the bottom of the cone to be drawn into the central tube again. The tank cannot agitate unless fairly well filled with pulp. The agitation is excellent, the wear little, and the trouble small or practically none. The Brown or Pachuca tank, Fig. 12, invented by F. C. Brown and first used in Mexico at Pachuca, the air-lift agitator, is con- sidered to be the most successful agitating tank. It consists of a cylindrical tank 45 feet high and 15 feet in diameter, though tanks of greater height and relatively less diameter are in use. For the treatment of slime comparatively shallow tanks will suffice, 122 TEXT BOOK OF CYANIDE PRACTICE but for sand a greater height with a smaller diameter will cause less tendency to clog. These tanks end in a cone with 60-degree sides; the steeper the cone the less is the tendency to settle and clog or pack. Within the tank is a hollow column 15 inches in diameter, extending from within 18 inches of the bottom to Fig. 11. The Hendryx Agitator. within 18 inches of the top of the tank. A IJ-inch air pipe dis- charges upward at and into the bottom of the tube. To operate the tank it is filled with pulp, and air under pressure is turned into the bottom of the column. The air passing upward lightens and lifts the column of pulp within the tube, causing it to over- flow and that outside the tube to enter the bottom by its greater hydrostatic head. This results in circulating the pulp up through SLIME TREATMENT AND AGITATION 123 Corapreswd Air Mite* the central tube and down the tank outside of the tube. The action is that of the air lift and not similar to the hydraulic elevator. That is, it is not de- pendent upon the air entering the tube with sufficient force to carry the pulp up, but on the lessening of the specific gravity or density of the pulp through the air mixed and entangled, that the pulp out- side may rush into the tube to equalize the hydrostatic head. The Pachuca tank gives a thor- ough agitation with undoubtedly a less consumption of power than any other agitator. It can be easily started after once settled, possibly excepting when run on pure sand, in which case the charge should not be allowed to settle. It gives a good aeration, for only a gentle current of air is used, which, according to the theory of the air lift, must be- come more or less entangled with the pulp. It will do excellent work with a thick pulp, even as dense as 1.2 parts of solution to 1 of dry pulp. It is not adapted for de- cantation, for as with all tanks of relatively great height and small diameter, the settling rate per ton of clear solution obtained is too low. The Just process has already been described as a false bottom of porous, silica-sponge bricks which Fig. 12. The Pachuca Agitator. may be placed in any flat-bottom tank. Air under pressure, which may be as low as 5 pounds and thereby within the field of a rotary blower, is introduced underneath the false bottom to pass through the bricks in fine jets and keep the pulp in agita- 124 TEXT BOOK OF CYANIDE PRACTICE tion and suspension. A similar method of agitation by intro- ducing the air through perforated pipes was early tried, but found impracticable on account of the rapid clogging of the pipes and the poor distribution of the air. Agitation by air is supposed to cause a greater consumption of cyanide through the formation of hydrocyanic acid, though it has not been demonstrated to be a fact. Air agitation causes an increased consumption of lime by the CO 2 of the air uniting with the lime to form a carbonate. The calcium carbonate formed in this way and otherwise gives trouble by coating or clotting the pores of the leaf niters so that they become impermeable and require to be frequently treated with dilute hydrochloric acid to dissolve out the lime. CHAPTER X DECANTATION THE decantation system was the first method devised for treating slime, and was the principal one used until the invention and perfection of the leaf or vacuum filter. A large number of slime plants were working until recently by the decantation proc- ess and it now plays a part in many equipped with modern filter- ing devices. It is used in them to remove part of the dissolved metal that the amount lost by being discharged in the residue from the filter, through the low efficiency of the filter in washing or its use as a dewaterer only and without washing, may be as low as possible. Decantation cannot be entirely eliminated until filtering devices do more efficient work then they are doing under average conditions to-day, for it seems to be a well-accepted rule that pulp containing rich solution should be sent to the fil- ters only after the value of the solution has been reduced. Theory of the Decantation Process. The decantation proc- ess depends upon the principle that if 1 ton of dry slime having a value of $5.00 per ton in dissolvable gold and silver is agitated with 4 tons of solution until the maximum dissolution has been effected, allowed to settle, and the clear solution syphoned off until the slime contains one part of dry pulp and one part of so- lution or 50 per cent moisture, 3 tons of solution or three-fourths of the dissolved metal will have been removed, an extraction (referring to the dissolved gold and silver) of 75 per cent. If 3 tons of barren solution are now added for each ton of the dry pulp, the slime agitated for a thorough mixing, left settle, and again decanted down to 50 per cent moisture, there will be an extraction of three-fourths of the remaining value or a total extraction of 93f per cent, with 31 cents of dissolved metal per ton of dry pulp yet remaining. A repetition of the cycle of operations will bring the total extraction of the dissolved metal to 98.4 per cent, which would leave 8 cents per ton in the residue. While another cycle would bring the extraction or efficiency of 125 126 TEXT BOOK OF CYANIDE PRACTICE the washing up to 99.6 per cent and give a residue containing 2 cents in dissolved metal. The use of a larger volume of solution for each wash will reduce the number of washes required or increase the efficiency of the washing, likewise when the slime is settled to a smaller percent- age of moisture. This principle is illustrated in the case of a dilution of four parts solution to one part of pulp drawn down to one and one, giving a wash extraction of 75 per cent. Had the dilution been eight to one, the wash extraction would be 87.5 per cent. While had the pulp been drawn down to two of solu- tion to one of dry pulp (66f per cent moisture), the wash extrac- tion would only be 50 per cent. Decantation Process in Practice. In plant practice it is impossible to obtain such satisfactory results in an economic way or to carry the washings to the extent that may be theorized. The defects of the process are the inordinate amount of the fol- lowing: the solution to be handled and precipitated, the con- sumption of lime for settling purposes, the labor in giving the washes, the time consumed in mixing solution and pulp and resettling, the pulp and solution tankage space, and the water, chemicals, and dissolved metal discharged with the residue. Also the inability in many cases to get a thorough intermixing of the settled slime and the wash solution. When treating 100 tons of dry pulp per 24 hours with a dilu- tion of four of solution to one of dry pulp, it may require four days to give the necessary treatment of dissolving and taking off three solutions. This may be presumed to be equal to 400 tons of dry slime in the plant in the process of being treated, requiring 2000 tons of diluted-pulp tankage space, and the handling of 900 tons of decanted solution per day. If the mill crushes in water it will be almost impossible to wash the slime with any water, or the bulk of the solution in the plant will increase to a point where it must be run to waste. Consequently, a pulp discharged con- taining 50 per cent of moisture will cause a loss of 1 ton of the final wash solution for each ton of the dry slime discharged. The cyanide in this last wash, often a half pound or more per ton of solution, which is discharged will be lost. If the crushing is done in solution the theoretical amount of water that may be used in washing is equal to that discharged with the residue. Consequently 100 tons of water may be mixed with the 100 tons DECANTATION 127 of dry pulp and the same amount of solution (to which proportion the pulp has settled), and allowed to settle, after which it should be possible to syphon off 100 tons of clear solution. In this way the cyanide mechanically lost per ton of dry slime is equal to one-half the number of pounds in a ton of the last cyanide solu- tion added. Decantation practice does not proceed along strictly theo- retical lines, but according to methods which may be deemed most expedient, one of the principal features of which is that not all of the solution is precipitated. That which comes off in a final or the final decantations, with only a small amount of value, is used as a first or the first washes to dilute and remove the rich solution from a new charge, then precipitated to be again used as a final wash, it being considered more profitable to proceed this way than to precipitate all the solution. The time required for agitating and settling depends upon the nature of the ore and must necessarily vary in each case. The following is an example of decantation practice with an ore crushed in water, settling one to one, treated with a dilution of 4 tons of solution to 1 of dry pulp, and given three washes. The pulp is drawn from the set- tling or stock tanks to the agitator; to each ton of the dry pulp is added 3 tons of the unprecipitated intermediate or second wash from a previous charge. Cyanide is added to bring the strength up to .05 per cent (1 pound) KCN, no lime being nec- essary on account of the high protective alkalinity of the solu- tion. Agitation is carried on for 12 hours, by which time the maximum dissolution has been effected. A short time before stopping the agitation 2 pounds of lime per ton of ore are added to be thoroughly mixed for settling the charge. After the agita- tion has been stopped, the solution is drawn off as fast as it be- comes clarified by the settling of the slime, through a hinged pipe left down on the inside of the tank. The solution often contains some suspended matter or, from carelessness in decanta- tion, contains considerable slime, and is run through a sand filter to be clarified before being precipitated. Eighteen hours are required for settling and decanting the first wash. Gold and silver to the amount of $5.00 per ton have been dissolved from the ore; this has been diluted by the four parts of solution to enrich each ton of solution $1.25, to which is added $0.45, for the un- precipitated intermediate wash carried $0.60 per ton and 3 tons 128 TEXT BOOK OF CYANIDE PRACTICE of this solution were used to 1 of water in the settled slime. This gives a solution of $1.70 to be decanted and sent to the zinc boxes as the first wash. After the decantation there still remains 1 ton of solution worth $1.70 with each ton of dry slime. To each ton of this solution is added 3 tons of the unprecipitated final or third wash of a previous charge, containing $0.16 per ton. This gives a value to the resulting mixture of (1.70 -f- 4) + (f of 0.16) = $0.55 per ton of solution. An agitation of 3 hours is given to thoroughly mix the charge, followed by settling and decanting for 18 hours to remove the second or intermediate wash. After which 3 tons of a precipitated first wash solution practically barren are added and agitated for 1J hours and the charge pumped into another tank to insure thorough mixing, requiring 2 hours. Another settling and decanting period of 18 hours is given to draw the solution down to a one and one consistence. TJie_value _of..iMs last wash is a little higher than the theoretical amount which should be ($0.55 -f- 4) = $0.14 per ton, consequently the residue which is now discharged con- tains a little over $0.14 in dissolved metal per ton of dry pulp, and an amount in cyanide equal to that of the last wash given, which was about 0.4 pound KCN. Had all the wash solution been precipitated, the final tailing would have a theoretical value of 8 cents in dissolved metals. If the intermediate wash had been precipitated, but not the final, the theoretical value remain- ing would be 9 cents. In the first case 6 tons more of solution would have to be precipitated for each ton of dry pulp at a cost of 3 cents per ton of solution or 18 cents per ton of ore. In the second case, 3 tons more of solution would have to be precipi- tated at a cost of 9 cents per ton of ore to obtain the theoretical difference of 5 cents (.14 .09). If the dissolution of the last of the gold and silver is slow, the agitation may be stopped and the first wash removed with a reliance on the solvent activity of fresh solution or of the long, general contact to effect the dissolution still to be made in time to allow it to be removed by the washes. Owing to the inability to get a thorough intermixing with mechanical agitators and flat-bottomed tanks, it is the custom in many plants to transfer the pulp from one tank to another when applying a wash. In this way any sand that has hugged the bottom and corners of the tank together with its adsorbed rich moisture responds to DECANTATION 129 the washing process. If only one transfer can be made, it should be effected after the bulk of the value has been removed by one or two first decantations. The pulp may be transferred after the last agitation to a deeper settling tank than usual and with- out an agitating device, wherein only the thicker, denser pulp is drawn off intermittently from the bottom of the tank as a residue to go to the slum pond. The drawing off of part of the settled pulp together with a decantation of the clear solution from the top makes room for each charge as added; the entire amount of pulp not being withdrawn at any time. The use of compara- tively deep tanks, preferably with cone bottoms, in this way, as a more or less continuous or intermittent method of decanting and discharging, gives a sludge to be discharged having a higher percentage of dry slime, owing to the greater length of time allowed for settling and the pressure weight of the deep column of pulp. Many attempts have been made to make use of these principles in connection with that of cone or other overflow settling devices, especially for a continuous washing and treat- ment system, but without much practical success except in the case of the last wash. Mechanical Decantation Processes. The Adair-Usher proc- ess developed in South Africa is dependent somewhat on the above principles. After the metal has been dissolved, and with- out allowing more than a slight settling of the slime, barren solution is introduced through pipes evenly over the bottom of the slime tank, which should be comparatively deep. This solu- tion enters in sufficient quantity to rise at a rate slightly slower or equal to the settling rate of the slime and to always give a clear overflow of solution from the tank. In theory the barren solution lifts or displaces the rich solution and washes the slime in suspension. When the washing has been carried as far as practicable, the inflow of solution is stopped, the slime left settle, and the clear solution decanted off as usual. This process does not do away with decantation in its entirety, but is only an adjunct or expedient to reduce the number of decantations. While continuous decantation without mechanical means has not been a practical success, continuous decantation with mechani- cal appliances has been rendered possible by the introduction of the Dorr pulp thickener. This appliance is now in use dewatering the pulp to a low percentage of moisture, followed by diluting the 130 TEXT BOOK OF CYANIDE PRACTICE pulp with wash solution to be again dewatered, using a sufficient number of such machines to thoroughly wash out the dissolved metal. This method seems to be well adapted for some conditions or in a modified form to precede filtration for the purpose of re- ducing the value of the pulp and solution supplied to the filter, thereby lessening the mechanical loss through the low efficiency of the filter wash. CHAPTER XI FILTRATION Plate and Frame Filter Press. Owing to the trouble and low efficiency encountered in treating slime by the decantation process, the plate arid frame filter press was early made use of for dewatering and washing the dissolved gold and silver out of slime pulp. The filter press shown in Fig. 13 was already in wide use in clay- working plants for dewatering a thin, clay pulp, and in the sugar- making industry for filtering the juices and washing the residuum in the process of making sugar. The plate and frame filter press as used in the cyanide process consists of a number of solid metal plates with a hollow plate or frame alternated between each. These plates are square or rectangular in shape and up to 3 or 4 feet in dimensions, the frames being from 2 to 4 inches thick. The alternate plates and hollow frames are set in an upright position face to face by means of projecting arms or shoulders on each plate and frame resting on two strong bars on each side of the assembled press. This makes a box-like structure with a height and width equal to the dimensions of the plates and frames, and with a length dependent upon their thickness and their number, which may be as high as fifty. Each end of the press is closed with a solid plate, while between each plate and frame is placed a sheet of canvas as a filter cloth. At the ends of the press are screw devices for forcing the plates together and thereby making the press water-tight, or hydraulic or air pressure instead of hand screws is used to open and close the presses. Each plate and frame contains lugs or shoulders bored with holes. When the press is in position these holes form a passageway for the slime pulp and solution. The passageway for the slime pulp is provided with a small opening into each frame or hollow plate only. This allows the pulp under pressure to enter and fill each hollow frame. The solution in the pulp under pressure is forced through the canvas on one of the sides and runs down between the canvas and the solid plate, which is corrugated to 131 132 TEXT BOOK OF CYANIDE PRACTICE better allow the passage of the solution between the canvas and the plate, to a small open- ing in the corner of the plate where it runs to an- other passageway or chan- nel of bored holes leading to the solution tank. In some types each plate is provided with small indi- vidual cocks emptying into a launder leading to the solution tank. The flow of pulp is stopped as soon as the press is filled with a solid cake of pulp, and wash solution or air followed by wash solution is pumped through a third passage- way to enter between the other canvas and the other corrugated side of each plate. Whence it is forced through the canvas into the cake of pulp, washing it or displacing the moisture in it, passing through the op- posite filter cloth, and run- ning down between the corrugations to pass out through the hole in the corner of the . plate into the passageway leading to the solution tank, just as the solution does which is expressed from the pulp in , filling the press. After suf- ficient washing with barren solution, a water wash, per- haps preceded by an air wash or displacement, is introduced through the same passageway. Finally air under pressure is ad- FILTRATION 133 mitted, which displaces a large part of the moisturise that a cake containing as low as 15 to 25 per cent of moisture may be obtained. After which the closing screws of the press are opened, allowing the plates and frames to be separated and the washed cake of slime to be dropped into a car or sluice for discharge to the resi- due dump. The plates, frames, and filter cloths are next brought Fig. 14. Plate and Frame of Filter Press. A, Passageway for pulp. B. Passageway for entering solution. C. Passageway for departing solution. together, the closing screws are tightened, and a new cycle of operations is started. The pulp may be forced into the press by pumps capable of giving a high pressure, by gravity under a high head, or by com- pressed air and a monteju, though the last method is practically obsolete. The monteju is a large, closed, metal tank or receiver into which the pulp is run as required. To fill the press, the monteju is closed and air under pressure admitted at the top to force or displace the pulp into the press. The principal advan- tage of the monteju is the lack of 'wear through the attrition of the pulp. Filter Press Practice in Australia. The following details* of treatment with the Dehne press, the bes^ known of the standard filter presses and which has been successfully used in Australia, represents the highest type of work. The slime from the agita- tors having a consistence of about 1 and 1, is pumped to the presses by a Pern pump having three plungers, 12 by 10 inches, running at 20 revolutions per minute. This is a powerful pump * M. W. von Bernewitz in " Slime Treatment at Kalgoorlie," Min. and Sci. Press, Dec. 14, 1907. More Recent Cyanide Practice, pp. 82. 134 TEXT BOOK OF CYANIDE PRACTICE and will fill a press in 10 minutes, lifting in that time about 10 tons of pulp, and charging against a final pressure of 60 pounds per square inch. The time taken in filling may be divided as follows : Up to 25-lb. pressure 4 min. Up to 50-lb. pressure 3 min. Up to 60-lb. pressure 1 min. Finishing with safety valve blowing off at 60-lb 2 min. Total 10 min. Average screen tests of the ore are: Held on 40-mesh Nil per cent Held on 60-mesh 0.5 per cent Held on 80-mesh 2.5 per cent Held on 100-mesh 4.3 per cent Held on 150-mesh 4.9 per cent Passed 150-mesh 87.5 per cent The three Dehne presses each have 50 3-inch frames for the slime. Each press will hold about 4.5 tons dry slime. After a press is filled, the slime is washed for 25 minutes with weak cyanide solution, and a water wash of 5 minutes at 100-pound pressure, during which time each ton of slime is washed with 2 tons of solution. The washing is done by a similar pump to that used in filling, only that it runs at 13 revolutions per minute. The final water wash is dispensed with when there is an excess of mill solution, the press getting 30 minutes with wash solution. The decrease in the assay value of the solution during the wash- ing is: At start of wash $12.50 After 5 min 6.60 After 10 min 1.50 After 15 min 1.50 After 20 min 1.00 After 25 min 1.00 After 30 min . 0.80 After washing, the content of the press is dried with air for 10 minutes at 80-pound pressure. The press is then opened ready for discharging. Two men empty 11 presses per shift of 8 hours, say 50 tons, onto a traveling horizontal belt-conveyor 18 inches wide. Most of the solution used in washing the presses passes FILTRATION 135 into the mill solution to be again used in the grinding pans, etc. The cyanide solution is made up to .07 per cent (1.4 pounds) and the consumption averages 1 pound per ton treated. An average of three months' costs of slime treatment is: Agitation and cyaniding $0.34 per ton Filter-pressing 0.41 per ton Precipitation, etc 0.12 per ton Disposal of residue 0.04 per ton Total 0.91 per ton The time taken in the different press operations is : Filling press 10 min. Washing 30 min. Drying 10 min. Discharging 30 min. Screwing-up, etc ' 10 min. Total li hours The daily capacity is 123 tons of roasted telluride ore and 43 tons of retreated old residue, having an average recovered value of $14.10. The Merrill Press. The Merrill press, as developed by C. W. Merrill and shown in Fig. 15, does not differ in principle from the standard filter press. Its dimensions are: Number of frames 64 to 92. Size of frames 4 by 6 ft. Length Up to 45 ft. Capacity per charge Up to 25 tons. Thickness of cake 3 to 4 ins. With ores in which the metal goes into solution quickly and that are not too slimy, the dissolution as well as the washing may take place in the press. The pulp is dewatered down to 3 parts of water to 1 of dry slime, or thicker if there is a tendency for the sand to classify in the filling process. It is run into the press by gravity under a pressure of 20 to 30 pounds per square inch (equal to 40 to 70 feet fall). After the press is filled, the water is displaced and the pulp partly dried by air under pressure, when cyanide solution is slowly pumped through the charge fol- lowed by air under pressure. The application of the dissolving 136 TEXT BOOK OF CYANIDE PRACTICE solution and the aeration is alternated until the precious metals are dissolved, when the usual washing with weak solution and water with final air displacement follows. On the completion of the treatment, which may require 6 hours, the charge is washed from the press by water introduced through a " sluicing bar," which is a pipe extending lengthwise throughout the press. This pipe is provided with nozzles in each chamber and an outside mechanism which causes it to revolve back and forth sufficiently to direct the water discharged from the nozzles into every part of each frame or chamber. In this way the charge is washed out Fig. 15. The Merrill Filter Press. of the press through the balance of the passageway in which the " sluicing bar " lies. From 4 to 8 tons of water per ton of dry slime are required to wash the press out. A large part of the water may be saved by the use of pulp-thickening tanks. Where the metal has been dissolved before entering the press, the operations are similar to those of an ordinary filter press, except in regard to sluicing out the press. It is reported that 50,000 tons of dry slime have been treated per month at the Homestake slime plant at a total cost of 25 cents per ton, of which the filtering cost amounted to If cents per ton. The value of the untreated slime is said to be about 85 cents per ton and the extraction to be 90 per cent. This is a record that has never been approached by any other slime treatment or filtration system, but much of which must be credited to the costly plant and large tonnage available. FILTRATION 137 The plate and frame filter press is best adapted for the granu- lar slime of quartzose ore, and then requires the addition of con- siderable fine sand to render the slime more permeable by the solution. The filter press as ordinarily used will not do good washing on an abnormally talcose, clayey slime. Such material is washed in the Merrill press (dissolution of the value having taken place before filling the press) by what is termed " center- washing." In this method the solution expressed from the pulp is allowed to flow through both canvases and tEe frames are not filled with solid cakes of pulp. An opening of a quarter of an inch or more is allowed in the center of each cake, through which the barren solution immediately following the pulp, without any interlude of aeration, and finally the water wash and air displace- ment pass to wash the metal-bearing solution out of the slime. The following is the data on a cycle of operations working in this way: Filling with a pulp of Ij parts of solution to 1 of slime, 30 minutes; washing with 2J tons wash solution and water per ton dry slime, 35 minutes; discharging, 45 minutes; total, 1 hour and 50 minutes. , Vacuum or Pressure Leaf Filters. The vacuum or pressure- leaf filter differs entirely from the plate and frame filter press. The principle of these filters is the use of a flat slip or bag of can- vas over a suitable thin frame of wood or metal. The inside of the filtering leaf in the suction type is connected to a suction or vacuum pump. On completely immersing the leaf into a homoge- neous slime pulp and starting the suction removing the air and solution from the interior of the leaf, the atmospheric pressure causes the slime to collect on the leaf and the solution to pass within and be drawn through the pump or into the vacuum tank through which the pump works. This results in collecting a layer of thickened pulp on the filter leaf, which increases in thickness until the atmospheric pressure is no longer able to force the solution through the cake formed and consequently there is a vacuum within the leaf. The success of the leaf filter has hinged upon the equal permeability of the cake formed, for should any part at the time of forming the cake be more per- meable than the rest, more pulp will be drawn to that part and more solution will pass through it, until the resistance to filtra- tion at this point and all others is equal. With a pulp that is homogeneous and a filter cloth of equal permeability, a cake of 138 TEXT BOOK OF CYANIDE PRACTICE FILTRATION 139 even thickness will be formed. But should the pulp tend to classify and the sand or pulp in general sink to the bottom, the lower part of the cake will be thick and sandy, while the upper will be thin and slimy. Similarly, a spot on the canvas leaf that is less porous, through a coating of carbonate of lime or other, will have a thinner coating of material, but one of the same com- position as that of the surrounding cake. Having formed a cake upon the leaf as thick as the atmospheric pressure will allow, it may be removed from the pulp without Fig. 17. The Butters Filter. breaking or cracking and immersed in a wash solution, provided the vacuum is continued to an extent just sufficient to hold the cake on the leaf intact. The continuation of the vacuum will cause the atmospheric pressure to force the solution through the cake into the interior of the leaf to be withdrawn by the vacuum pump. This passage of the solution through the charge or cake is the washing process, just as takes place in a leaching vat or in the plate and frame filter press. An equal amount of solution will be drawn through all parts of the leaf, even if the texture and thickness of the cake vary as noted before, for unless the cake cracked or sloughed during the removing process, its resistance will be the same all over its area. 140 TEXT BOOK OF CYANIDE PRACTICE After passing barren solution or wash water through the cake until the dissolved metal is displaced and removed from the interior of the leaf, the leaf and its cake are removed and exposed in the air. The vacuum is continued to remove as much of the wash water as practicable, especially should the cake be washed in barren solution and it be desired to keep the mechanical loss of cyanide as low as possible. The next step is to introduce air and water into the interior of the leaf to remove or slough off the treated slime, when a new cycle of operations may be taken up. Classification of Leaf Filters. The different leaf niters divide themselves into two classes, the suction or vacuum and the pressure niters. These are further divided into the station- ary and movable niters, into the continuous and intermittent, and then into lesser gradations. The Butters is the best known of the stationary, intermittent, vacuum niters. A large number of leaves up to two hundred are arranged in a box with cone bottoms. The pulp is run by gravity or pumped into the bottom of this box to rise and keep the leaves submerged. A vacuum is applied to the interior of the leaves to form a cake an inch or more in thickness. After the cake is formed, the surplus pulp is removed by gravity or pumping to the stock tank supplying the filter, and wash solution or water introduced into the box and drawn through the cakes. Having removed the wash solu- tion, the box may be filled with water to assist in carrying out and removing the slime, or the slime may be dropped into the bottom of the box to receive a little sluicing or water to make it slide out and run to the slum pond. In either case the cake is dropped by reversing the force that has formed and held it in place, by turning air or water or both into the interior of the leaf. The Moore is the best known of the movable, intermittent vacuum filters. The series or " basket " of leaves is fastened together in such a way that it may be easily and quickly lifted and transferred from one tank to another by means of a traveling crane or a lifting and revolving device. The basket of leaves is lowered into and kept submerged in the stock-pulp tank until the cake is formed. It is then raised and transferred by means of the crane to an adjoining wash-solution tank where it is washed. After which it is lifted and transferred to a tank or hopper into which the cake or charge is dropped in a way similar to with the Butters filter. s 141 FILTRATION 143 The Oliver shown in Fig. 20 is a vertically-revolving, continu- ous vacuum filter. It consists of a revolving drum which may be as large as 12 feet in diameter and 18 feet broad. The surface or face of the drum or wheel is prepared as a leaf-filtering surface Fig. 20. The Oliver Continuous Filter. and divided into a number of compartments, connected on the inside with a vacuum or suction pipe and a pipe for admitting compressed air. The drum is partly immersed in a tank or box of thick pulp and revolves at a slow rate of speed. The mech- 144 TEXT BOOK OF CYANIDE PRACTICE Fig. 21. The Oliver Continuous Filter (End View). List of Parts. Filter Drum. Steel Filter Tank. Cast Iron Pedestals. Steel I Beam Frame. Manhole. 6. Cast Iron Spider Rim. 7. Channel Steel Arms. Hollow Trunnion. Steel Shaft. Main Bearings. 8. 9. 10. 11. Stuffing Boxes. 12. Worm Drive Gear. 13. Worm Shaft. 14. Oil Well for Worm. 15. Filter Drive Pulleys. 16. Pulleys for Agitator and Wiring. 17. Chain Drive for Agitator. 18. Bevel Gears on Agitator Shafts. 19. Agitator Shafts. FILTRATION 145 Fig. 22. The Oliver Continuous Filter (Side View). List of Parts. 20. Agitator Shaft Bearings. 21. Wood Staves for Drum. 22. Section Division Strips. 23. Filter Medium. Wire Winding. Steel Scraper. Scraper Adjustment. Tailing Apron. Vacuum Pipes. Compressed Air Pipes. 24. 25. 26. 27. 28. 29. 30. Regrinding Valve Seat. 31. Automatic Valve. 32. Adjusting Lever for Valve. 33. Vacuum Hose Connection. 34. Compressed Air Connection. 35. Discharge Spray Pipe. 36. Emergency Agitator Pipe. 37. Drain Flange. 38. Wash W T ater Pipes. 146 TEXT BOOK OF CYANIDE PRACTICE anism acts automatically to cause a vacuum which makes a cake of | to J-inch thickness as the drum passes through the pulp. As the cake emerges from the pulp the atmospheric pressure displaces a large part of the solution adsorbed by the slime, after which a line of wash water or solution across the width of the drum applies the wash. Air is finally drawn through to displace Fig. 23. A 50-ton Oliver Continuous Filter, at North Star Mines Co., Grass Valley, California. as much of this wash as possible. Just before each section of the drum with its washed and air-dried part of the cake reenters the pulp, the vacuum is automatically shut off and air under a light pressure introduced to cause the cake to drop off, assisted by a scraper. The Hunt is a horizontally-revolving, continuous vacuum filter as shown in Fig. 24. It consists of a horizontal, annular filter bed underneath which a vacuum only is applied. A carriage mounted inside of the filter ring and supported on a track outside of it re- FILTRATION 147 volves continuously. The pulp is roughly classified into sand and slime and each is delivered to a hopper at the middle of the filter. Fig. 24. The Hunt Continuous Filter. Fig. 25. Carriage of the Hunt Continuous Filter. From the hoppers the pulp runs out through arms to be delivered evenly across the width of ,the filter ring. The sand is first 148 TEXT BOOK OF CYANIDE PRACTICE deposited to form a good filtering medium, and is immediately followed by a layer of slime delivered over it. The vacuum operates to withdraw part of the moisture from the bed of deposited pulp, while a pipe delivering a spray of wash solu- tion or wash water follows at a suitable interval; the vacuum finally drying the pulp which is scraped off to fall over the outer edge of the filter ring by a scraper placed in front of the arm delivering the sand. A novel feature is the use of a filter bed consisting of triangular, wooden slats filled with coarse sand and dispensing with filter cloths. A similar device is being used in South Africa to dewater the sand before adding cyanide solution and transferring to the leaching tanks. The Ridgeway Filter, as shown in Fig. 26, is a horizontally-re- volving, continuous vacuum filter with an intermittent action. It consists of an annular ring made up of a pulp, a wash-water, and a discharge tank. A revolving carriage with suitable mechanism carries 14 trays of over 3 square feet area each. The under sides of these trays or plates are prepared as leaf filters with vacuum and compressed-air attachments. As the carriage revolves the trays or leaves are first immersed in the pulp, through which they pass and from which they are mechanically lifted to emerge with a cake of pulp and then to be lowered into the wash solution through which they pass. Each tray is finally lifted out and brought over the discharge hopper, where the vacuum is auto- matically cut off and compressed air admitted to detach the cake, when the tray again passes into the slime pulp. The Kelly, as shown in Fig. 27, is a movable, intermittent pres- sure filter. It consists of a long boiler-like tank set on a small incline. The lower head of this pressure tank is fitted with a quick-acting closing device. Upon opening the clamp, the frame carrying the head together with the set of vertical filter leaves running the length of the tank may be run out of the tank cham- ber, running on suitable tracks within and without the tank. After dropping in the usual way the cake adhering to the leaves, the carriage now lightened by the removal of the load of slime can easily be drawn into the pressure tank and the head locked. Pulp is then pumped into the tank under suitable pressure which may be as high as 80 pounds per square inch. As soon as the air has been displaced and the tank is consequently full of the pulp, the cake commences to form. The pressure of the pump acts FILTRATION 149 just as atmospheric pressure would, except that on account of the increased pressure the cake is made and washed in a com- paratively short time. The pressure of the pump in forming the cake causes the solution expressed and filtered out of the Wash Solution l -H UJ Stroug Solution To Vacuum Pump Fig. 26. Section and Plan of Ridgeway Filter. pulp to pass into the interior of the leaves, there to run through suitable pipes out of the press into the solution tank. The cake having formed, which is indicated by the decrease in the solution flowing from the press, pumping pulp into the tank under pressure is stopped. The surplus pulp is then allowed 150 TEXT BOOK OF CYANIDE PRACTICE FILTRATION 151 to run from the filter back into the stock tank, being displaced by air under a low pressure to hold the cakes in place. After the surplus pulp has been removed, wash water or solution is pumped into the tank and continued under high pressure for as many minutes as experiments have indicated are required to give a good wash or to pass a certain volume of solution through, Fig. 28. Kelley Filter Presses, and Continuous Agitation. when the surplus solution is removed in the same manner as the surplus pulp was. The remaining moisture in the cake is displaced by the air under pressure until no more solution runs from the press. The final step is to cut off the air pressure, and unclamp the head to run out the carriage and remove the load of slime. The details of the press have been perfected to such an extent that a battery of four presses has been handled by one set of levers and valves, and two batteries of four presses each have been tended by one operator and a helper. 152 TEXT BOOK OF CYANIDE PRACTICE The Burt rapid filter is a stationary, intermittent pressure filter. It is somewhat similar to the Kelly, except that the filter leaves are suspended vertically at right angles to the length of the tank, which, being set at a considerable incline that the surplus pulp may easily run to the outlet, makes the leaves in the shape of an elongated circle. These leaves are only removed Fig. 29. The Burt Rapid Filter. for repairs, consequently the slime cake is discharged by intro- ducing air and water into the interior of the leaf and letting the pulp slide out through a discharge opening. The Burt revolving filter is a revolving, intermittent pres- sure filter. It consists of a long revolving shell very similar to a tube mill or revolving drier. It has a length of about 40 feet and a diameter of about 42 inches, and revolves at a speed of 15 revolutions per minute. The interior shell of the cylinder FILTRATION 153 154 TEXT BOOK OF CYANIDE PRACTICE is prepared as a leaf-filtering surface. The required amount of slime pulp for a charge is delivered to the interior of the filter through a valve at the point where the feed is delivered to a tube mill. After the charge of slime has been admitted, air under a pressure of 25 to 45 pounds is turned in. The liquid slime pulp remains constantly in the bottom of the filter through- out its length as it revolves. The air pressure causes the solu- tion to pass through the filter cloth and out through holes in the shell to a sump over which the filter revolves. The pulp gradually collects as a shell on the filter surface. When the cake has been made, as is indicated by air coming out of the solution discharges, the wash solution is admitted and kept under air pressure. As the tube is constantly revolving this results in a very good washing or displacement of the original gold solution in the pulp. After final air displacement the en- tire end of the filter is opened by a quick-acting device. The removal of the air pressure causes the cake to fall to the bottom of the cylinder, and the addition of a little water together with the revolving of the filter causes the washed pulp to slide out the discharge end; when the end gate is closed and a new charge started. The advantages claimed are that it will handle very sandy pulp, requires no excess pulp or solution to be re- turned, gives a very efficient wash through its method of making and washing a cake, and requires but little repairs on the filtering medium. To tabulate these illustrations of the different types of filters: Stationary charge, intermittent, vacuum. Butters. Movable charge, intermittent, vacuum. Moore. Movable charge, vertically revolving, continuous, vacuum. Oliver. Stationary charge, horizontally revolving, continuous, vac- uum. Hunt. Movable charge, horizontally revolving, continuous-inter- mittent, vacuum. Ridgeway. Movable charge, intermittent, pressure. Kelly. Stationary charge, intermittent, pressure. Burt rapid filter. Movable charge, vertically revolving, intermittent, pressure. Burt revolving filter. The leaf filter in many cases is more efficient than the plate and frame filter press, and is much cheaper to operate, excepting FILTRATION 155 the Merrill press, which when used with the " center-washing " system may be considered as another type of the leaf filter. Leaf filters are especially efficacious in handling a clayey slime that the plate and frame press cannot wash or only with diffi- culty, and by the " center- washing " process. This is due mainly to the inability to wash such a slime cake 2 or 3 inches thick, whether made in the plate and frame press or in the leaf filter. However, the leaf filters are far from being per- fect and able to handle all classes of material, consequently while they are in most cases the best device available, the par- ticular one to be used should be selected with great care, bear- ing in mind its limitations and the conditions with which it must cope. One of the first troubles encountered is the necessity of having a slime that contains a considerable amount of granular mate- rial to give porosity to the cake and enable a thick and easily- washed charge or cake to be made. This is a condition which is not hard to meet, but the necessity of this granular material being extremely fine may work a hardship where all of the ore is being treated as a slime, in requiring the ore to be crushed far beyond the economic point that will allow a high dissolution of the precious metals. As the amount of sand or granular material increases, the slime becomes less plastic and more permeable by the wash solution, consequently with a true slime a cake of only j to ^ inch may be possible, but as the amount of sand increases, a cake up to 2 inches and even more may be made. Besides the increase in capacity that the sandier charge gives, there is invariably a quicker and better washing. But an increase in the amount of sand or its coarseness increases the inability to make a good cake and give all the pulp a good washing, for as the pulp supplied to the filters becomes more dilute and the sand becomes larger in quantity and coarser, the pulp classifies more in the making of a cake through the settling of the sand. This introduces difficulties into the making and washing of a cake and removing the pulp, even though the principle of the cakes being built up with an even permeability works admirably. That coarse sand which settles in the corners and bottoms of the filter tanks especially gives trouble. It has been attempted, without entire success, to stop this classifying in the stationary vacuum type by pumping the thicker sand set- 156 TEXT BOOK OF CYANIDE PRACTICE tling to the bottom of the filter to the top as the cake forms. With the movable vacuum type the pulp is kept in agitation usually by air, causing the formation of considerable carbonate of lime which closes the pores of the filter cloths. In both cases there is trouble with pulp containing a large amount of coarse sand. The pressure filter is able to handle this material much better than the vacuum or atmospheric-pressure filter, for by reason of the higher pressure used (up to 80 pounds) as against the atmospheric pressure (up to 15 pounds) a cake can be made in the pressure filter in 10 minutes, including filling and emptying, that will require from 40 minutes to 1J hours to make with the vacuum filter. The higher the specific gravity of the pulp, the more viscous and dense it is, and the larger the amount of dry pulp in it, the better it can be worked, for the larger the amount of dry pulp and true slime the better it will hold the slime and sand in suspension and prevent classifying. When containing but little sand and that very fine, a dilute pulp may be used, but as the sand becomes greater in quantity and coarser the pulp must be thickened. The advantage of the pressure filter over the vacuum type in making quick charges on this class of material pulp containing much sand is pro- nounced. The pressure filters have the disadvantage of small capacity per charge which they overcome to some extent by the rapidity with which the charges are made, but this requires that much additional attention. The intermittent-vacuum filters can be built with enormous capacities, which reduce the amount of labor required per ton treated considerably over the pressure type. The movable-pressure filter has the advantage over the stationary type, of each charge being exposed to view after the washing, so that it is possible to know just how the operations are proceeding and take steps to overcome any acute difficulties, as well as allow repairs to be easily made. It probably gives the most efficient washing of all the types of filters, but requires more manipulation than the others. Intermittent-pressure fil- ters can be installed in small plants cheaper than the intermit- tent-vacuum filters, but are not so suitable in first cost and operating expenses for large plants. The Ridgeway, in which the charge revolving horizontally is immersed in the wash solution, appears to give the most efficient FILTRATION 157 wash of the continuous filters, but has the disadvantage of low capacity and extreme delicatehess. Those filters, whether con- tinuous or otherwise, that wash by means of a spray cannot be considered as such efficient washers as those in which the cake is washed by submersion, but have the advantage of simplicity, requiring little attention, and simplifying the operations gener- ally. The Oliver, the revolving-drum filter, appears to be well adapted and working largely at present on filtering a true slime, a material that other filters have not yet satisfactorily handled. The Hunt and similar filters, as horizontally-revolving mechan- isms treating sand or slime, would appear to be well adapted to treating a pulp containing a large amount of coarse granular material. Apparently coarse sand is best treated by a mechan- ism in which gravity assists in holding the sand at the point where it is attached to the filter, as on the bed of a horizontal filter. Continuous filters have the advantage of requiring little attention, whereas all intermittent ones require continuous at- tendance. Like pressure filters their small capacity well adapts them for small plants, but not so well for large plants. Another advantage of the continuous filters is that the costly item of returning the surplus pulp from the stationary-vacuum filters, moving the filter basket in the movable-vacuum type with its complicated machinery and wear and chance for breakage, or the pumping against pressure in the pressure type, is avoided in the continuous filter which takes by gravity the feed of pulp at a constant rate. A great advantage of the continuous over the intermittent system, in which the surplus wash solution is returned to its stock tank, is that there is no " building up " in the value of the solution. When the surplus wash solution is returned from a filter tank, it is richer than when it entered, through its contact with the rich solution of the unwashed pulp as found in the pipes, the bottom and sides of the filter tank, and in the cakes themselves. Likewise in wash-solution tanks after the movable leaves have been introduced and removed, though undoubtedly not to the extent where the unwashed pulp and the wash solution enter and are withdrawn from the same box or tank. The value in the wash solution builds up rapidly in this way and would soon approach that of the solution in the slime cakes as first formed, were it not that this solution is sent to the zinc boxes as soon as its value mounts to a certain 158 TEXT BOOK OF CYANIDE PRACTICE figure. This is one of the principal weaknesses of the leaf- filter process and is a source of great mechanical loss of the dis- solved precious metals. Some plants keep down this loss by constantly washing with barren solution, returning the surplus to the crushing department or elsewhere, but this involves the precipitation of a large amount of solution and generally results in a high mechanical and .other loss of cyanide, through the im- possibility of segregating a low-strength solution for filter wash- ing and for crushing. The filter cloths of all filters using the leaf filter or " center- washing " system are subjected to being encrusted, coated, or clotted by a carbonate of lime, much of which results from the action of air used in agitation upon the lime in solution, and in some silver plants has caused the protective alkalinity to be kept lower than otherwise desired. This coating, in spots and generally, reduces the permeability of the cloth or increases its resistance to the flow of solution through it, so that a thinner cake is formed than usual and the capacity is reduced. The deposit of lime is removed by immersing the leaves in a \ to 2 per cent solution of hydrochloric acid, which removes the lime as a chloride. The item for the removal of the lime by treating the leaves is quite large with some types of filters. With the pressure and plate and frame types the acid wash may be pumped through the press, but with the other types the leaves must be removed or other means employed, involving considerable labor. The type of filter to be installed is a matter of personal opinion. All have their good and bad features, each is well adapted for certain conditions and poorly for others. That none of them is perfect or is the acme of what is to be desired, is a matter of universal knowledge, and is indicated by the number of promi- nent plants that use their modern filters as dewaterers, without attempting to give the pulp any wash. CHAPTER XII PRECIPITATION THE cyanide solution carrying gold and silver, in which con- dition it is often called " pregnant " or " gold " solution, having been removed from the ore by draining the percolation charge if a sand or leaching plant, by decanting the clear supernatant solution from the settled slime if a decantation plant, or by forcing the solution from the pulp through a filter cloth or other medium if the slime pulp is finally filtered, is conveyed to the gold tanks to be supplied to the precipitating department as needed. This solution after precipitation is called " barren " solution. Outside of a few plants where electrical precipitation is used on silver ores, and which appears to be assisted by zinc boxes where a close precipitation of the gold is required, zinc is universally used as a precipitant, either in the form of threads or shavings or as a fume or dust. Reactions in Zinc Precipitation and Formation of White Pre- cipitate. - The precipitation of the precious metals may be said to be due to the replacement of the gold and silver in the double cyanide by the zinc and to electric currents set up by the chemical reactions which electrochemically deposit the precious metals from the solution. Other theories have been advanced and undoubtedly have some weight, but the above is both more acceptable and more illustrative of the principles and practice of precipitation. The precipitation of gold and similarly of silver in the presence of free cyanide may be expressed in the equation: KAu(CN) 2 + 2KCN+Zn+H 2 O=K 2 Zn(CN) 4 + Au+H-hKOH. In the absence of free cyanide as : KAu(CN) 2 + Zn + H 2 O = Zn(CN) 2 + Au + H + KOH. The following reaction may take place in the absence of any metal to be precipitated: Zn + 4 KCN + 2 H 2 O = K 2 Zn(CN) 4 + 2 H + 2 KOH. 159 160 TEXT BOOK OF CYANIDE PRACTICE Alkalis act upon zinc to form an alkaline zincate, as: Zn + 2 KOH = Zn(OK) 2 + 2 H. While the alkaline zincate may be dissolved in free cyanide, as: Zn(OK) 2 + 4 KCN + 2 H 2 O = K 2 Zn(CN) 4 + 4 KOH. Zinc oxide (ZnO) formed through exposure of the zinc to the atmosphere, especially when the zinc is moist, may be changed to zinc hydroxide (Zn(OH) 2 ), or the zinc hydroxide may be formed directly, as: f ZnO + H 2 O = Zn(OH) 2 . ( Zn + 2 H 2 O = Zn(OH) 2 + H 2 . Zinc oxide or hydroxide may be formed in a similar way by the oxidizing effect of a solution without free cyanide or alkali to combine with the zinc. The oxide or hydroxide may be changed to the zincate by an alkali, as: f ZnO + 2 KOH = Zn(OK) 2 + H 2 O. (Zn(OH) 2 + 2 KOH = Zn(OK) 2 + 2 H 2 O. In the presence of free cyanide the oxide or hydroxide may be changed to the potassium zinc cyanide, as: (ZnO + H 2 0) + 4 KCN = K 2 Zn(CN) 4 + 2 KOH. The law of mass action undoubtedly prevails to make some of the above reactions reversible. The tendency is strong for the double cyanide of zinc, the zinc potassium cyanide (K 2 Zn(CN) 4 ), to disassociate in a weak cyanide solution into the simple cyanides, as:. K 2 Zn(CN) 4 = 2 KCN + Zn(CN) 2 . Zinc cyanide (Zn(CN) 2 ) is insoluble in water, hence in very dilute cyanide solutions it precipitates to form the white precipitate of the zinc boxes. Zinc cyanide is dissolved and reacted upon by alkali, as: |Zn(CN) 2 + 4 KOH = 2 KCN + Zn(OK) 2 + 2 H 2 O. [2 Zn(CN) 2 + 4 KOH = K 2 Zn(CN) 4 + Zn(OK) 2 + 2 H 2 0. As both the zinc potassium cyanide and the potassium zincate (Zn(OK) 2 ) are soluble in water and still more so in alkaline solutions, the white precipitate appears to a slight extent only in strongly alkaline solutions, even though weak in cyanide. PRECIPITATION 161 The dissolved zinc or the zinc oxide eventually forming zinc hydroxide (Zn(OH) 2 ) is acted Upon by free cyanide, as: Zn(OH) 2 + 4 KCN = K 2 Zn(CN) 4 + 2 KOH. Thus the zinc oxide or hydroxide which is insoluble in water and, in consequence, in a very weak cyanide solution will precipi- tate to form the white precipitate of the zinc boxes; in a solution strong in cyanide will form the soluble double potassium or other alkaline zinc cyanide; or in a solution strong in alkali will form the soluble potassium or other alkaline zincate. Clarifying the Solution. If there is a tendency for the solu- tion to leave the sand vats or agitation tanks carrying consid- erable suspended matter or slime which would interfere with precipitation, the solution may be filtered before or after the gold tanks by means of sand filters. These consist of boxes or small tanks with filter bottoms similar to those of leaching vats, except that the filter cloth is very porous, usually coarse burlap. This is covered with about twelve inches of coarse sand. The solution filtering through leaves its slime covering the sand, where it may be periodically scraped off. Or the solution may be introduced into the bottom of the gold tank by means of a pipe or baffle board, and syphoned off the top for precipitation in a much clearer and more settled state. Plate and frame filter presses have also been used for clarifying purposes. Zinc Boxes. Zinc boxes for holding the zinc shavings are arranged that the solution may in all cases flow upward through the shavings. This gives better results than a downward flow for several reasons. It permits an easier, gentler, and better- distributed movement of the solution as it rises upward through the zinc. It allows the partly consumed and better precipitat- ing zinc in the bottom of each compartment to come in contact with the solution before the newer zinc, giving more effective precipitation, greater economy in zinc, and less trouble. It causes less disturbance in dressing the boxes of the fine gold and silver slime adherent or fallen from the zinc. The upward move- ment assists the hydrogen bubbles formed to naturally rise and become liberated instead of adhering to the zinc, coating and fouling it against precipitation. In the bottom of each compartment is placed a screen or false bottom from three to six inches above the floor or bottom 162 TEXT BOOK OF CYANIDE PRACTICE of the zinc box. This screen may vary from 4 to 12-mesh. It serves to hold the zinc some distance from the bottom of the box that the solution may easily reach the entire lower area of the zinc shavings to rise evenly throughout the mass, and that the space below the screen may act as a retainer for the fine gold and silver slime falling off the zinc and passing through the screen. The first compartment of the box is often used as a Fig. 31. Zinc Box. settler to assist in clarifying the solution by having no zinc placed in it; while the last compartment may be used in a similar way to prevent fine gold-silver slime from being carried away when the box is disturbed or the flow is too great. Often a filter of coarse sand, sawdust, oakum, fiber packing, or coarse filter cloth is used in these end compartments. The filtering medium in the last compartment is eventually added to the zinc slime melted to get any gold-silver slime which it may have caught. Zinc boxes vary considerably in size. The larger sizes should PRECIPITATION 163 always be used to secure economy of space and care. A good size for a large box would be to consist of eight compartments for upward flow, each 21 inches long (in direction of flow), 27 inches wide (across box), and 33 inches deep above the screens. Each compartment of this box will hold approximately 10 cubic feet of zinc shaving. The six compartments, allowing the end ones for settling purposes, will contain a total of 60 cubic feet. The majority of zinc boxes are built with their compartments in the form of a perfect cube or nearly so. Size of Shavings. The important point in zinc precipita- tion is the necessity of exposing a large area of zinc to the solu- tion. Consequently to get the highest efficiency from the zinc, it is prepared as a fine dust or in shaving or threads ^ to I inch wide and from 4^ to ysW inch in thickness. A pound of shavings cut with a thickness of yyVer inch will expose about 80 square feet of zinc surface, and when cut with a thickness of T$-Q inch will give about 40 square feet of zinc surface. This will indicate why equal weights of the finer-cut shaving will precipitate better than those cut coarser. Some idea of how zinc becomes effective through fine division can be seen when it is said that a pound of zinc equals 3.854 cubic inches, and when cut into shaving and placed in the boxes at the rate of 6 to 8| pounds per cubic foot, the solid metal amounts to only 1.3 to 1.9 per cent of the space actually occupied by the zinc shavings. How fine a shaving should be used must be deter- mined by actual practice. The coarsest shaving that will give a satisfactory precipitation should be employed, as the coarser the shaving the slower it will be to break up into short zinc which entails a higher mechanical loss when gathered into the clean-up and greater trouble in operating and dressing the boxes. A thickness of TFG mcn is generally used in gold plants, and from T ^j to T /(ytf inch in silver plants. Weight of Shaving and Amount Required. The weight of a cubic foot of finely-cut zinc shaving when packed in the boxes, in the customary manner in gold plants, will vary from 6 to 8J pounds, depending upon their thickness and how snugly and tightly they are packed in. With the coarser-cut shaving a greater weight of zinc may be packed in a cubic foot, both because the greater thickness of the threads gives a greater weight of zinc in comparison to the voids, and because the 164 TEXT BOOK OF CYANIDE PRACTICE thicker and stronger threads or shaving may be more tightly packed in the boxes without being easily broken and channeled by the solution. Silver plants using coarser shaving pack 12 to 13 pounds of zinc per cubic foot. It is reported that as high as 18 to 23 pounds of zinc per cubic foot have been packed in the boxes in an experimental way. In gold plants it is customary to allow 1 cubic foot of zinc- box space for each ton of solution to be precipitated in 24 hours. The rate of flow in the average gold plant is probably a little higher than this; in some it reaches over 2 tons per 24 hours for each cubic foot of zinc shaving. In silver plants the rate of flow will vary from 1 to 6 tons of solution per 24 hours for each cubic foot of zinc shaving; probably 1J to 3 tons would repre- sent the average practice. The higher rate of flow in silver plants is due to the stronger solution used causing more effective precipitation, and to the fact that the efficiency of the precipi- tation, as referring to the weight of precious metal still remaining unprecipitated in the solution, need not be as great as in gold precipitation. A flow of 1 ton per cubic foot of zinc per 24 hours gives a contact between the solution and the shaving of about 45 minutes. The number of compartments to be filled with zinc will de- pend upon the tonnage put through the boxes and the effective- ness of the precipitation. No more zinc should be kept in the boxes than is necessary to secure good precipitation, or zinc will be consumed unnecessarily. It hardly appears necessary to have more than one or possibly two lower compartments, in which the new zinc is added, containing bright zinc. If the zinc in too many of the lower compartments remains bright and assays of solution taken from the different compartments show that the precious metals are all precipitated in the upper com- partments, either some of the lower compartments should be left empty or the flow should be increased to the point where the filled compartments are working at a proper efficiency. In short, under normal conditions it is the rate of flow per cubic foot of zinc that must be kept constant. If the flow through the boxes is increased, the number of cubic feet of zinc must be increased. If the flow is decreased, the number of cubic feet of zinc may be lessened. It is also necessary in studying con- ditions or making comparisons to remember that under equal PRECIPITATION 165 conditions the effectiveness of the precipitation depends upon the area of zinc exposed person or unit of solution, and that the thickness of the shaving and the quantity or weight per cubic foot as packed are just as important factors in giving the zinc area as the number of cubic feet of packed shaving used. Packing and Dressing the Boxes. It is necessary in packing the boxes with zinc shaving to take the greatest care to prevent channeling and an uneven flow through the zinc. The use of a number of compartments, through each of which the solution must flow, reduces the danger of poor precipitation from this cause. Taking the case of a clean-up of the gold-silver slime being made to illustrate the method of caring for the boxes, after the compartment has been washed clean of all slime through a hole in the bottom emptying into a launder, the dis- charge is closed and the screen put in place. New zinc is now taken, preferably that cut a little coarser than as ordinarily used. This is fluffed by gently pulling apart and untangling the bunches, especially the more compact ones, and is placed evenly over the screen to the depth of a few inches. On top of this is spread an even layer of the short zinc being returned to the boxes, then a layer of the long zinc being returned, to be fol- lowed by a layer of the short zinc, and so on until the compart- ment is filled. The purpose of the coarse new zinc is to act as a screen as long as it is able to withstand the dissolving action, to diffuse the solution passing up through it, and to utilize the short zinc even after it is well eaten up by catching and holding it, instead of allowing it to drop and pass through or clog the screen. The compartments being used are packed in this man- ner; the short zinc and that already much acted upon are con- centrated in the first two or three compartments. After the short zinc is utilized, the already-acted-upon long zinc is used, and finally whatever new zinc is needed is placed in the lower compartments. The fluffing of the zinc and its arrangement together with the placing of the layers of short zinc must be studied with a view to preventing channeling and an uneven flow. The boxes should be dressed as frequently as needed, which is usually every second or third day. The necessity of dressing and how often it should be done can be studied from three points: the increase in the assays of the solution leaving the box, the amount of zinc consumed and extent of channeling, 166 TEXT BOOK OF CYANIDE PRACTICE and the gradual creeping down of the blackening and discol- oration of the bright new zinc in the lower compartment or compartments by the gold and silver precipitated. Small lots of new shaving may be placed in the lower compartments to experimentally observe the progress of discoloration. In dressing the boxes between clean-ups, the flow is first turned off and the operator begins work, using a pair of rubber gloves or with hands and arms greased with vaseline or other harmless grease compound to keep the skin from becoming rough, irritated, and sore by contact with the solution. He either moves the zinc from the lower compartments to the upper ones, where practically all of the consumption has taken place, adding the new zinc to the lower compartments, or adds new zinc to whatever compartments are in need without mov- ing any of the old zinc. It is preferable to move the zinc toward the head compartments and add the new zinc at the foot of the box, as zinc that has already been acted upon is a more active precipitant than new zinc, and by moving it toward the head of the boxes it causes a greater precipitation in these head com- partments and collects that occurring in the balance of the box into them. Moving the zinc up gives a better precipitation, a higher-grade slime, and a concentration of the gold and silver into a smaller area of the box, making the clean-up less bulky and leaving less gold and silver in the box. In moving the zinc up, the well-acted-upon and rotten zinc should be disturbed as little as possible. Most of the precipitation can be effected and collected in the first two or three compartments. These should be disturbed as little as possible, the operator confining himself to closing up any channels or open edges or corners, and placing the necessary zinc taken from the third or fourth and lower compartments. No zinc should be removed from any compartment in which such an amount of precipitation takes place that the shaving becomes rotten and tends to break up in handling, as it causes a greater mechanical loss and disturbs the gold-silver slime, rendering it more liable to be carried out of the box. The zinc should be spread out and laid down in layers, which, being at right angles to the movement of the solution, conduce to allow an even flow and contact. The zinc should be well packed into the edges and corners of the compart- ments, as the greatest channeling occurs at these places. A PRECIPITATION 167 little experience and study will soon indicate the best procedure. The practice of beating the zmc tightly into the compartments with a stick is inadvisable, since it may pack the zinc too tightly for a uniform flow. Yet the zinc should be firmly and carefully and not loosely packed in place. In some cases the zinc when being cut has been folded into skeins or hanks the length of the compartments. The skeins are packed into the compartments in layers at right angles to each other, new zinc being added as needed without disturbing the old zinc. This method tends to give a more uniform flow with less channeling. General Care of Precipitation. The boxes may be allowed to stand for 15 minutes after dressing before starting the flow through, for the purpose of settling any disturbed zinc slime. The highest rate of flow can only be determined by assaying the solution as it leaves the box and observing the progress of discoloration of the bright zinc in the lower compartments, but must not be so rapid as to carry the fine zinc slime out. It must be remembered in determining this that the best precipi- tation takes place after the boxes have been newly dressed and more especially after a clean-up, when the zinc is clean, active, and well-arranged; while it reaches its poorest just before dress- ing and cleaning-up. The maximum efficiency of precipitation takes place when an equal volume of solution passes by each part of the zinc, which is when the zinc is newly arranged. This efficiency rapidly lessens, for channeling quickly forms whereby the solution is not brought evenly in contact with all the zinc, which must be met by rearranging the zinc through a new dressing of the box. Solution strong in cyanide keeps the zinc clean and active and gives a good precipitation, consequently it can be run through the boxes much faster than weak solution. One of the evidences of good precipitation is the rising to the surface of the bubbles of hydrogen which are generated during the precipitation, as is shown in the equation representing the process of precipitation. Too many bubbles given off are un- desirable, for it indicates a large consumption of zinc. Strong cyanide solutions cause a large evolution of hydrogen through the excessive dissolution of the zinc. Too high a protective alkalinity will act similarly, and besides consuming an unnec- essary amount of zinc may give rise to excessive hydrogen which may cling to and lift the zinc out of the boxes or which 168 TEXT BOOK OF CYANIDE PRACTICE may polarize it against effective precipitation. Where the zinc has been fouled in this way, a low strength of solution may be run through rather fast, followed by shaking and rearranging the zinc. An excess of lime or alkali may cause a deposit of lime salts or other compounds as a species of white precipitate. Where slime from the ore has been carried into the boxes, or lime salts and other compounds have formed loose deposits or incrustations, such deposits as cannot be dissolved and washed out by solutions strong in cyanide and alkalinity, and good precipitation cannot be secured, the boxes should be cleaned up. In some cases the incrustations have been removed by dipping the shavings in dilute acid to dissolve the deposit, followed by rinsing the shavings in water. Trouble is often experienced in precipitating from weak solu- tions. It is impossible to predict how weak a cyanide solution can be successfully precipitated, for mill solutions showing no free cyanide have been precipitated to a trace of gold and silver. Solutions weak in cyanide precipitate better when carrying con- siderable protective alkalinity and the cyanogen compounds that accumulate in a solution when working a clean ore. But such solutions precipitate poorly when without or low in pro- tective alkali or when fouled through the large accumulation of the compounds that enter a solution when treating an acid or base ore. The cause and remedying of poor precipitation from weak solutions, and without increasing the strength of solution, is in some cases a difficult problem to solve. The effectiveness of the precipitation is mainly a matter of keeping the zinc clean and free from everything except metallic zinc and the metals precipitated. More especially in keeping the zinc free from the zinc oxide, hydroxide, and cyanide insoluble in water and poorly soluble in weak solution, and which tend to form by contact of zinc and water or weak solution. An alkali will be efficient in doing this, just as cyanide, by promoting a vigorous chemical action which dissolves and removes the fouling compounds, which dissolves the zinc for replacing the precious metals, arid which sets up the electric currents to deposit or further assist in the deposition of the gold and silver. White Precipitate. One cause of poor precipitation has been the formation of a white precipitate in the zinc boxes. In a few cases this precipitate has been lime salts, due to the excessive PRECIPITATION 169 use of lime or other alkaline neutralizer, but it is generally zinc as a hydrate (Zn(OH) 2 ), a cyanide (Zn(CN) 2 ), or a zinc potas- sium ferrocyanide (K 2 Zn 3 (Fe(CN) 6 )2), with some salts of the bases. This precipitate is an inert, grayish-white, and some- what granular substance which usually forms in the weak-solu- tion zinc boxes or when very dilute solution is being run through a box. It also forms more rapidly when treating pyritic ores or those containing considerable acidity, especially when there is no protective alkalinity in the solution. It forms in the upper compartments of the boxes and greatly hinders precipitation by coating the zinc and matting and caking it together. A consideration of the equations shown before in this chapter and what has been said under Alkalinity and Lime regarding the reactions in the zinc boxes show that the white precipitate is due to too low a strength in cyanide and alkalinity of the solution passing through the box. When solutions are low in cyanide and alkalinity the zinc potassium cyanide, which may be considered to normally exist, tends to disassociate with the formation of zinc cyanide, while considerable zinc hydroxide forms from the action of the weak solution on the zinc. Zinc cyanide and zinc hydroxide are insoluble in water and naturally precipitate in weak solutions, but are soluble in solutions of some strength in cyanide and alkali. Consequently the solu- tion should be kept up to a sufficient strength in cyanide and alkali to prevent the white precipitate from forming, or if formed a strong cyanide solution which may have considerable alka- linity should be run through the boxes to dissolve and carry out the precipitate, which will take some time. In some cases the zinc has been taken out of the boxes and washed in strong caustic soda solution, but this course is inadvisable, as increasing the cyanide strength and alkalinity will generally remedy the trouble, except where the zinc and zinc slime are caked with a large amount of the white precipitate, which may necessitate disintegrating the cakes and lumps by a species of clean-up. The zinc potassium ferrocyanide, which probably forms to a greater extent in the working of decomposed pyritic ores, is less soluble in alkaline solutions than the zinc hydrate and zinc cyanide, and when once formed may require a clean-up to remove. For the purpose of keeping the boxes clean and active and the quantity of white precipitate small, the solution flows 170 TEXT BOOK OF CYANIDE PRACTICE entering the strong and weak-solution boxes may be made in- terchangeable, the flows to be alternated as may be necessary; or no division is made in the solution to create one of high and another of low strength, but all is kept at a strength that will give good precipitation. The strength of weak solution is some- times increased by a drip of strong solution into the head of the box, or occasionally adding a chunk of solid cyanide there, or by standardizing or adding cyanide or lime or caustic soda to the contents of the gold tank. Zinc-Lead Couple. -- The zinc-lead couple has been used to a large extent to secure satisfactory precipitation from weak solutions. It is prepared by dipping the new shavings into a 5 to 10 per cent solution of lead acetate (Pb(C 2 H 3 O 2 )2.3 H 2 O) for a few minutes until they turn black from the lead deposited, when they are placed in the compartments as usual. In some cases a 1 per cent solution of lead acetate has been allowed to drip into the head of the boxes, though dipping appears to be the better. The zinc and lead together form a galvanic couple which greatly assists precipitation. Copper in Solution. Copper in solution tends to precipitate when the solution is low in cyanide, and to remain in solution when the cyanide strength is high and interfere with the disso- lution and precipitation of the precious metals. Small quanti- ties of copper in weak solutions are precipitated upon the bright new zinc in the lower compartments. When the amount of copper is small, this does not interfere with the precipitation, in fact it usually assists through the formation of a galvanic couple, but large quantities may interfere by giving the zinc too thorough a coating of copper or, when remaining in solution, may prevent precipitation of the gold and silver. The principal means of removing the copper have been the use of lead shav- ings in the head compartments or the zinc shavings dipped in lead acetate and placed in the lower compartments, lead or the zinc-lead couple being a good precipitant of copper. Attempts have been made to keep the amount of copper dissolved from the ore low by the use of weak dissolving solutions, and then to keep the copper in solution by raising the strength of the solu- tion before entering the zinc boxes, but the best method appears to be to precipitate the copper from the solution in some con- venient way and get it out of the system. PRECIPITATION 171 Mercury in Solution. Mercury found in old tailing from amalgamation mills is usually changed to an oxide, salt, or other compound which is readily attacked by cyanide solution. Mercury in its metallic state is slowly dissolved by cyanide solution, the dissolved metal in any case being precipitated in the zinc boxes if not before. A small amount of mercury dis- solved in this manner is not harmful but very beneficial, for it is the best substance for removing alkaline sulphides by form- ing an insoluble mercuric sulphide (HgS) with the sulphur. Compounds of mercury, principally mercuric chloride, have sometimes been used for this purpose with excellent results. Small quantities of mercury on the shavings may increase pre- cipitation through the formation of a mercury-zinc galvanic couple, but large quantities are detrimental through causing the shavings to break up and slime. Where the zinc slime contains a large amount of mercury, it may be retorted to secure the mercury before being treated for its gold and silver. Cutting of Zinc Shavings. Care must be exercised in cut- ting zinc shavings or in purchasing shavings already cut, as zinc oxidizes easily when heated. With careless cutting the zinc heats rapidly and is often further assisted to oxidize through being cooled by cold water poured over it. Such partly-oxi- dized zinc is not highly efficient in precipitating and unduly breaks into short zinc. Zinc exposed to the atmosphere slowly oxidizes, consequently fresh-cut zinc is the best. Zinc contain- ing a small amount of lead is an excellent precipitant as it is a zinc-lead galvanic couple without further treatment; in fact, most zinc shavings contain a small amount of impurities which are beneficial, and zinc dust containing a small percentage of lead is sometimes ordered. Mechanical and Chemical Consumption of Zinc. Zinc is consumed in the precipitating process in two ways chemically and mechanically. The zinc chemically consumed by the reac- tions in the zinc boxes goes out of the plant in the solution dis- charged with the tailing residue and lost by leakage, by being precipitated in the zinc boxes as spoken of in connection with the white precipitate, and mainly by being precipitated in the ore. The nature of the precipitation occurring in the ore is not well known, but is supposed to be with alkaline sulphides to form the insoluble zinc sulphide, to be precipitated as a zinc 172 TEXT BOOK OF CYANIDE PRACTICE carbonate, or the precipitation may take place in the ore under conditions similar to those by which the white precipitate is formed in the zinc boxes. It is an interesting fact that the amount of zinc in a plant solution remains fairly constant though the solution be used for years. The zinc in solution is generally considered to exist as a zinc potassium cyanide (K 2 Zn(CN) 4 ), more especially when the difference between the free and total cyanide indicates enough cyanogen to be com- bined with the zinc, which by the formula would be 1 pound cyanogen in terms of potassium cyanide combined with .251 pound of zinc. It has been observed that as the zinc potassium cyanide is apparently regenerated into free cyanide, by increasing the protective alkalinity or as the free and total cyanide ap- proach each other, the amount of zinc in solution falls, but exactly how it is removed under these conditions is unknown. The zinc consumed mechanically in the precipitating process is that removed from the boxes with the gold-silver slime to be treated and melted into bullion. The amount of zinc con- sumed in this way is high in a gold plant, since much short zinc is removed from the boxes to be acid treated, etc., in the effort to get all the bullion possible. In a silver plant the amount is much less since a close clean-up, as referring to the comparative weight of precious metal left in the boxes, is not made. The stronger the solution used, the greater will be the chemical consumption. The weaker the solution, the greater will be the mechanical loss, for the use of weak solutions is attended with the production of much short zinc and other zinc-box troubles, especially when the solution is also low in gold and silver. The precipitation of rich solutions is attended with a much less con- sumption of zinc mechanically and often chemically than that of low-grade solutions. The consumption of zinc is usually reported on the basis of the tons of ore treated. For technical purposes it is also de- sirable to report it on the basis of tons of solution precipitated and ounces of bullion produced, for ores require widely varying amounts of solution for their treatment; likewise the value of ores and the richness of their solutions vary. The amount of zinc shavings used will vary from J to J pound per ton of ore treated in a gold plant, and in a silver plant from f to 1| pounds and upward. The consumption will vary from J to J pound per PRECIPITATION 173 ton of solution precipitated. On a gold plant the consumption will be from 4 to 20 parts of -zinc to 1 part of bullion produced, while in a silver plant 1J parts and upward will produce 1 part of bullion. Theoretically, in the replacement by zinc of the gold and silver in the potassium gold or silver cyanide (KAu(CN) 2 or KAg(CN)o) formed in the dissolving process, 1 part of zinc should precipitate 3 parts of gold or 1.65 parts of silver. Regeneration of Cyanide and Alkalinity. There is often an apparent regeneration of free cyanide taking place in the zinc box as shown by titrating the solution entering and leaving the box. This may amount to as much as J or \ pound per ton of solution. The exact cause of the regeneration is inde- terminate, but is due to the complex reactions occurring in the zinc box. There is also a slight increase in the alkalinity; this can be more clearly understood than the regeneration of cyanide, by considering the equation representing the pre- cipitating reaction which indicates the formation of caustic potash or a similar alkali. Zinc-Dust Precipitation. Zinc dust is a highly satisfactory precipitant of gold and silver, due to its fine state of division, its agitation with the solution, and the forcing of the solution through that already in use. As at first developed the solu- tion to be precipitated was run into tanks holding from 15 tons upward of solution. After a tank was filled with solution it was agitated, usually by air pipes in the bottom of the tank. Fresh zinc dust amounting to about J to J pound per ton of solution was sprinkled over the charge. This zinc dust together with that already in the tank from previous charges and stirred up by the agitation was sufficient to precipitate the metal with 15 minutes or more agitation, after which the solution was drained through plate and frame filter presses to the barren sump tanks. In the filter press the solution passed through the already-acted-upon zinc which gradually accumulated by being carried in from the agitation tanks. As at present used the zinc dust is fed continuously to the solution by being spread upon a long, slow-moving belt or by other feeding device due to the small quantity of dust con- stantly required and its tendency to agglomerate, it has been hard to secure a satisfactory automatic feeding mechanism. The dust is usually fed together with the solution into a mixing 174 TEXT BOOK OF CYANIDE PRACTICE and agitating device wherein the precious metal is largely pre- cipitated. The solution then runs to or is pumped through the precipitation plate and frame filter press. Or the zinc dust is fed to the solution at the intake of the pipe leading to the press. The press is located as far from the intake or mixing device as possible, to secure the better precipitating effect of moving solution and zinc dust. No air is allowed to reach the press as would be the case were it or the intake drained, or the Fig. 32. Merrill Precipitation Press. zinc will become much oxidized. The precipitated metal or zinc- gold slime is removed by opening the press and separating the frames, allowing the slime to fall into pans underneath. The filter cloths are scraped clean and returned, or are occasionally burned and added to the meltings. An increased quantity of zinc dust is used when starting anew after a clean-up at which time any zinc slime in the agitation tanks or mixing device is removed until a quantity has accumulated in the press. The amount of dust used is increased or decreased as the tailing solution increases or decreases in the amount of gold and silver still unprecipitated. Zinc dust is especially efficacious in pre- cipitating from weak and low-grade solutions. In these cases it is often assisted by the zinc-lead couple formed through PRECIPITATION 175 allowing a solution of lead acetate to drip into the mixing device or using dust containing a little lead. The amount of zinc dust used is about equal to the shavings that would be required; in some cases more is necessary, but with careful manipulation less can be employed. The cost of dust is about one-third less than of shavings. The fineness of the precipitate in gold and silver, or the proportion of the precious metals to the base metals or zinc, is about that of slime from zinc shavings washed through a 30-mesh screen, and is subject to being increased by careful manipulation, principally through the cyanide dissolving more of the zinc collecting in the press and thus reducing the zinc content of the precipitate. One of the advantages of using zinc dust is that the entire metal precipitated is obtained each clean-up, and none is left remaining as in the case of using zinc shavings. This indicates that the zinc-dust process is more applicable for gold than for silver plants, since in a gold plant much of the short zinc is collected into the clean-up and con- siderable value left in the box, whereas in a silver plant only the fine, slimy precipitate is taken, making the cost of refining and the mechanical consumption of zinc less, while less value is left in the box. The zinc-dust process is more adapted to large than to small plants, since the installation cost is high and it requires more continuous attention than the zinc-shaving method. The installation and labor costs are not in proportion to the tonnage, but fall rapidly per ton treated as the plant is increased in size. The installation and working out of a success- ful zinc-dust precipitation method requires higher ability and closer study than with shaving precipitation, but is capable of being developed to a higher degree of efficiency and economy. CHAPTER XIII CLEANING-UP THE precipitated gold and silver are removed from the zinc boxes or presses usually weekly or semi-monthly in a silver plant, and semi-monthly or monthly in a gold plant It is customary to run a strong cyanide solution .75 per cent (15 pounds) to 1 per cent (20 pounds) through the boxes for a few hours before the clean-up is started, to loosen the gold- silver slime deposited on the zinc; it also cleans some of the dissolvable white precipitate out of the boxes. The cyanide solution is displaced by running water through the boxes for an hour or longer, that the cyanide may not injure the hands, tend to redissolve the gold, or appear in the cleaned-up pre- cipitate. The operator lifts the zinc from the first compart- ment into a tub, preferably filled with water to prevent the zinc from oxidizing through exposure to the air. All the zinc is removed from the compartment, also the screen in the bottom. A screen is now suspended in the compartment and the removed zinc washed on it as free from slime as possible, by being dis- entangled, gently teased, rinsed, and finally being rinsed in a clearer water. Care is taken to break the zinc up as little as possible into short zinc. Three products are made in the proc- ess of washing : the slime passing through the screen, the washed " shorts " or " met allies " not passing through the screen and up to two or three inches in length, and the washed long zinc. After all the zinc taken from the first compartment is washed, the drain plug at the bottom of the compartment is opened to allow the water and the gold-silver slime, including that just washed free from the zinc and that which had previously fallen through the screen, to run through a launder or hose into a sludge or precipitate tank. The compartment is washed out with a little clean water, and the plug and screen replaced. If there is no bottom discharge and drain launder or hose, the contents of the compartment may be allowed to settle, the 176 CLEANING-UP 177 water syphoned off, and the slime dipped out and carried in pails to the sludge or clean-up tank. Having replaced the screen, a two or three-inch layer of new zinc, preferably cut coarser than regularly, is placed evenly over the screen; on this is spread a two-inch layer of the washed short zinc, then a layer of the washed long zinc, followed by short zinc, and so on until full, as described in connection with the care of zinc boxes. The zinc is kept under water as much as possible at all times to prevent oxidation. The second and succeeding compartments are treated similarly, though in most cases where the zinc has been moved toward the head of the box, not more than the first three compartments need be cleaned out, for in the others an appreciable amount of slime cannot be secured. In some cases the zinc is transferred to a clean-up tank, there to be washed and returned to the compartments. The slime flowing from the compartments is washed through a screen into the sludge or clean-up tank. The mesh of this screen and that used in washing the zinc in the boxes will vary with how close a clean-up is desired, or how much short zinc is to be included in the clean-up. In a gold plant all zinc not washed through a 10 or 20-mesh screen is usually returned to the boxes, in some cases still coarser zinc is put into the clean- up, though the amount of precious metal in the short zinc is comparatively very small. In a silver plant, owing to the lesser value of the same weight of silver bullion as of gold bullion, only the slime passing through a 30 to 60-mesh screen is generally taken, all the short zinc being returned to the box. This results in a precipitate high in bullion, usually 60 to 75 per cent, and low in zinc. When the quantity of short zinc is too large to be advantageously placed with the long zinc, it may be put in trays suspended in the head compartment, or provisions made for agitating it with rich solution to precipitate the gold and silver in a way similar to zinc dust, being used in this manner until cut or dissolved to a slime. It may be advisable to screen the precipitate to be refined into two classes, that held on a 30 to 60-mesh screen, high in zinc and low in bullion, and that passing the screen, which would be high in bullion and low in zinc, so that separate treatment may be given each. If the precipitate is not to be acid treated it is pumped into a small plate and frame filter press, where it may be dried by 178 TEXT BOOK OF CYANIDE PRACTICE blowing air through before the frame is opened for the removal of the precipitate. Or the precipitate may be run into a small tank with a false bottom similar to that of a leaching vat, the moisture being drawn off and the precipitate partially dried by producing a vacuum underneath the filter cloth. In either case the water drawn from the precipitate is pumped to the head of the zinc boxes to catch any fine precipitate, or run into a tank where it is settled and later used as plant solution, the settlings going into a clean-up. CHAPTER XIV ROASTING AND ACID TREATMENT THE precipitate may be refined into bullion in four ways: Melting. Roasting and melting. Acid treatment and melting, with or without roasting. Smelting with litharge and cupellation. In melting the precipitate without further treatment, it may be completely dried in a pan set in an oven or over a fire or in a steam-jacketed pan. Or it may be dried as well as possible while in the plate and frame precipitation or clean-up press or in the clean-up vacuum tank, by blowing or drawing air through, followed by mixing with flux and melting without further drying. Melting without further treatment is advisable with a precipitate high in gold and silver and low in zinc, such precipitate as would pass a 40 to 60-mesh screen. As the quantity of metallic zinc in the precipitate increases, the fine- ness of the bullion will decrease and more zinc will go into the bar. Also more gold and silver will be carried off mechanically in a finely-divided state by the dense fumes arising from the volatilization of the zinc. Roasting. Roasting the precipitate before melting con- verts the zinc into an oxide, so that it can much more easily enter into the slag as a silicate of zinc or dissolved metallic oxide, instead of into the bullion as much of it does when it has not been converted into the oxide. Other base metals and substances are more or less oxidized, decomposed, or volatilized to render the subsequent melting and the slagging off of the foreign substances easier and the grade of the bullion higher. Roasting is especially advisable with the coarser precipitate which must contain much zinc, as a high-grade bullion with but little zinc and bases can be secured in this way from such material. The precipitate to be roasted is placed in heavy 179 180 TEXT BOOK OF CYANIDE PRACTICE cast-iron pans which are put into ovens or roasting furnaces; they are even put over fireplaces and a fire built directly under them. It is hard to say to what extent the roasting should be carried. The better the roasting, the better the zinc and bases will be oxidized to pass into the slag. The roasting is often carried to the point where the zinc takes a dull fire. This is not harmful if the roasting has been carried on slowly so .that the fumes and ebullition do not carry off gold and silver, so that the zinc oxidizes instead of volatilizes. Niter, potassium nitrate (KNO 3 ), to the amount of 3 to 10 per cent is sometimes well mixed with the precipitate before roasting, either as a powder or as a solution saturating the precipitate. This causes a rapid and complete oxidation by converting the zinc into zinc oxide, which being nonvolatile, does not carry finely- divided gold and silver away in the fumes. The farther the roasting is carried, the higher the loss will be, though the use of condensing chambers has shown that the loss is small. During the roasting process the slime should be stirred as little as pos- sible or not at all to avoid loss by dusting. Acid Treatment. In the acid treatment the precipitate is settled and dewatered by decantation in the sludge tank into which it runs from the zinc boxes, and acid added to dissolve the zinc. The acids used are sulphuric (H 2 SO 4 ), sulphurous (H 2 SO 3 ), hydrochloric (HC1), and bisulphate of sodium (NaHSO 4 ). Nitric acid (HNO 3 ) has also been used, but its use is inadvisable as it dissolves more of the precious metals than the other acids. Hydrochloric acid has been used to a slight extent. It has a greater cost and a higher dissolving effect on the precious metals, but has the advantage of forming soluble chlorides with the lime and lead that may be removed by washing. Acid treat- ment is generally not attempted with silver precipitate, since the short zinc is usually returned to the boxes leaving a slime high in bullion, while the acid tends to dissolve silver and thereby cause a loss. Gold precipitate is usually acid treated, especially if it contains much short zinc, either treating all the precipitate or only that going into the clean-up which does not pass a 40 to 60-mesh. It is seldom profitable to treat the gold slime passing a 40-mesh by acid, except when it is desired to treat coarser material and the facilities do not allow of a segregation of the two classes of material. ROASTING AND ACID TREATMENT 181 Sulphuric Acid Treatment. Sulphuric acid (H 2 SO 4 ) is gen- erally used for dissolving out the zinc and to some extent the other bases before melting, forming zinc sulphate (ZnSO 4 ) and other sulphates. After the water has been decanted off the settled slime in the sludge or clean-up tank, which, if acid treat- ment is to be carried out, should be of wood or lead lined, the sulphuric acid is slowly and carefully added to avoid the charge boiling over, in an amount making from a 10 to 20 per cent solution of sulphuric acid. Theoretically one part of zinc requires 1J parts of sulphuric acid to be converted into zinc sulphate, while a 16 per cent solution of sulphuric acid appears to act to the best advantage on zinc. In actual practice from f to 1J pounds of cheap commercial sulphuric acid is used for each pound of dry precipitate, the amount of dry precipitate and its moisture being estimated and the sulphuric acid and any additional water being first added by this estimation, sulphuric acid being finally added according to the continuance of the reaction. On the addition of the acid, there is an active libera- tion and forcible ebullition of hydrogen as vile- smelling fumes, also some hydrocyanic acid from the decomposition of cyanogen compounds in the precipitate, for which reason the refining tank is covered with a hood and uptake to carry off the fumes. As soon as it is seen that the boiling has subsided to a point where the sludge may be stirred without danger of boiling over, stirring is carried on mechanically or by hand. A sudden tendency to boil over is stopped by the addition of cold water. The heat developed by mixing the acid and water and the chem- ical reactions is sufficient to cause the active formation of zinc and other sulphates. Sulphuric acid is added from time to time with thorough stirrings until there is no more reaction, showing that the zinc has been dissolved and that the acid is in excess of that required. Stirring should be continued for half an hour after all action has ceased. The " cutting down " of the precipitate by acid may be accomplished within a few hours, but usually an entire shift is allotted to it. The operator must use care not to be overcome by the fumes. Breathing the fumes of ammonia affords relief. Where the ore contains arsenic, fumes of arseniureted hydrogen may be given off which are highly poisonous; several deaths have occurred from this. Pre- liminary treatment with nitric acid or a general treatment with 182 TEXT BOOK OF CYANIDE PRACTICE one part nitric and two parts sulphuric acid to change the arsenic into a nonvolatile arsenic acid has been recommended or treat- ment made with bisulphate of sodium, though it would appear better to dispense with acid treatment on such precipitate. - The tank is filled with water and thoroughly stirred after the zinc has been cut down by the acid, after which the precipitate is allowed to settle and the acid and sulphate solution decanted off. Three or four or more washes by decantation may be given in this way with water, when the sludge is allowed to run or is pumped into a small plate and frame filter press or a vacuum filter tank as used in the clean-up process, where it is washed free from all sulphates and soluble matter by pumping or draw- ing water through. The washing by decantation and in the press or tank is usually with cold water, though there is some advantage in using hot water as is often the practice, since one part of water at 1 C. will dissolve .42 part zinc sulphate, at 20 degrees will dissolve .53 part, at 50 degrees will dissolve .67 part, and at 75 degrees will dissolve .80 part. Lead sulphate (PbS0 4 ) is practically insoluble, while one part of calcium sul- phate (CaSO 4 ) is soluble- in 500 parts of water. Whereas the solubility of calcium chloride is one part in 1J of water, and of lead chloride (PbCl) is one part in 93 parts of water. Which indicates the advantage of using hydrochloric acid when the precipitate contains large quantities of lime or lead. The lead and calcium sulphates besides entering the acid-treated slime, may coat the zinc so that it is not acted upon. A thick, solid deposit of gold and silver, such as sometimes takes place from an extremely rich solution, may prevent the zinc from being acted upon. The acid washes should be collected in a tank and allowed to settle until the next clean-up, when they are syphoned to waste. Or they may be agitated with scrap zinc before settling, or run to waste through such zinc. The partly-dried slime is removed from the clean-up press or vacuum tank and may, if containing a small amount of moisture, be fluxed and melted without further drying; it may be dried before fluxing and melting, or it may be roasted before fluxing and melting, the roasting being very similar to that given precipitate that has not been acid treated and may include adding a small amount of niter. Acid treatment by sulphuric ROASTING AND ACID TREATMENT 183 acid followed by a thorough roasting is the method usually employed in America on gold> slime, while silver slime with or without roasting is melted without acid treatment. Sulphurous Acid Treatment. Refining by sulphurous acid (H 2 S0 3 ) does not differ materially from that by sulphuric acid. Metallic or solid sulphur is burned in a simple generator or air- tight stove supplied with air under a pressure of a few pounds, sufficient to give the necessary oxygen to form sulphur dioxide (S0 2 ), and force it into a clean-up tank to be absorbed by the water therein with the formation of sulphurous acid, as : SO 2 + H 2 O = H 2 SO 3 . The precipitate may be added before or after the water has absorbed sufficient acid. The zinc is dissolved as: Zn + H 2 SO 3 = ZnSO 3 + 2 H. The sulphites of lead and lime formed appear to be more soluble in an excess of the acid than the sulphates formed similarly in the sulphuric-acid treatment, but are not soluble in water. The method seems to be as efficient as the sulphuric-acid treatment with a remarkably low cost, while the solid sulphur is much easier transported than the liquid and dangerous sulphuric acid. The method has been successfully used in America. Bisulphate of Sodium Treatment. In refining or cutting down the zinc by a solution of bisulphate of sodium (NaHSO 4 ), which occurs as a solid substance, the chemical is dissolved in a stock tank to dilute the acid solution used in treating the zinc to equal about 10 per cent H 2 SO 4 . The dissolving takes place as in the ordinary sulphuric-acid method, but it is claimed with less danger from gassing or from poisoning by arseniureted hydro- gen. The reaction being: 2 NaHSO 4 -f Zn = NasSO, + ZnSO 4 + 2 H. The principal advantage of using bisulphate of sodium is that, occurring as a solid chemical, it may be easier transported than sulphuric acid, and may be a cheaper method of refining. It will be noticed that not all of the sulphur is made available to unite with the zinc. The method is being used to a limited extent in South Africa. CHAPTER XV FLUXING AND MELTING Constituents of Zinc Slime to be Melted. The nature of the precipitate to be smelted varies widely, due to the different conditions under which the precipitation takes place, and more so as to the methods of cleaning-up and preliminary refining. This relates to the amount in the precipitate of gold and silver, of zinc, of other base metals and substances, what these bases are, and in what form they exist, whether metallic or as oxides, sulphates, etc. The constituents of a precipitate may be divided into four classes: Gold and silver. Metals and bases as oxides and sulphates. Metals in their metallic form and other reducers. Silica or lime. The larger the amount of gold and silver, the less will be the amount of flux required, for the bases to be slagged off will be less. The percentage of precious metals in the precipitate is controlled by the manner in which the precipitation is conducted and the fineness of the screen through which the clean-up is made. The percentage in the precipitate is further increased by the roasting or acid treatment which removes part of the bases. The bases changed to sulphates by the acid treatment are removed by washing, except those sulphates which are insoluble in water and sulphuric acid, mainly, calcium sulphate and lead sulphate. Imperfect washing may cause some of the soluble sulphates to remain in the precipitate. The oxides are formed in the roasting process, whether without or following acid treatment. The base metals in their metallic form are those that have not been acted upon by the roasting or acid treatment, or are to be found wnen no such treatment has been given the precipitate. They are principally zinc and also lead where the zinc-lead couple has been used. Other reducers are insoluble cyanogen compounds that have been precipitated in 184 FLUXING AND MELTING 185 the zinc boxes. Silica is due to turbid and slimy solutions passing through the boxes, or to a deposition of dissolved silica or alumina on the zinc. Lime and other alkaline substances may be deposited in the boxes when the protective alkalinity is high, and not be removed by roasting or acid treatment. Purpose of Fluxing and Smelting. The purpose of fluxing and smelting is to form a slag containing the base metals and substances, mainly as silicates, borates, and dissolved oxides, and to form a bar of fine bullion containing the gold and silver. To form these two, the slag and the bullion, it is necessary to add flux to the precipitate that will unite with the bases in the proper proportion to give a slag that is fluid, so that the small shots and particles of gold and silver may easily settle down into the bar of bullion, instead of remaining suspended to form a rich slag: one that will form and be liquid at a low heat; that will be neutral and not so basic as to destroy the crucible through abstracting the clay in its demands for acid or siliceous flux to slag with the bases of the precipitate; that will not be so acid as to utilize more flux than can be economically gotten along with and require a high heat to make fluid a neutral slag is usually more liquid; and that will be of small bulk to fuse the largest amount of precipitate and take up the least melting space. Sodium and Potassium Carbonates as Fluxes. As fluxes used in melting zinc slime are sodium carbonate (NaaCOs), sodium bicarbonate (NaHCO 3 ), potassium carbonate (K 2 CO 3 ), or potassium bicarbonate (KHCO 3 ), preferably the carbonates of sodium, and of these the sodium carbonate which is 1| times stronger than the sodium bicarbonate. The sodium and po- tassium carbonates and bicarbonates are a basic flux and unite with acid fluxes or substances, especially with silica, to produce a sodium silicate, as: SiO 2 = Na 2 SiO 3 + CQ 2 . The carbonates fuse between 800 and 900 C. Borax and Borax Glass as Fluxes. Borax (Na 2 B 4 O 7 . 10 H 2 0) and borax glass (Na 2 B 4 O 7 ), the 'anhydrous borax from which the water of crystallization has been driven off, are acid fluxes and unite with basic fluxes and substances to form a borate or to dissolve the metallic oxides and hold them in the slag solution. 186 TEXT BOOK OF CYANIDE PRACTICE The formula of a borate may be written Na 2 O . 2 B 2 O 3 , in which the boracic acid (B 2 3 ) acts similarly to silica (SiO 2 ), or in this way: ZnO -f Na 2 O . 2 B 2 O 3 = Na 2 O . ZnO . 2 B 2 O 3 . Silicates and borates dissolve together to form what may be termed silicate-borates, which will lower the fusing or slag-forming points and promote fusion in general. Borax melts at 560 C. It helps to give a quick fusion and a liquid slag. Too much or too little borax in the fusion will cause a thick slag. Borax glass has nearly twice the strength or available Na 2 B 4 O 7 of the hydrous borax. Silica as a Flux. Silica (SiO 2 ) is an acid flux which combines with metallic oxides and bases to form silicates containing vary- ing quantities or proportions of silica. Generally the higher the proportion of silica in the silicate, the less fusible or fluid it is. Silica itself can only be melted. at a tremendous heat, but melts easily with a basic flux. Fluor Spar as a Flux. Fluor spar (CaF 2 ) is a neutral flux that fuses at a high temperature. It is but little used. Its chief value is to give fluidity to the slag. Niter as a Flux. Niter, potassium nitrate (KNO 3 ), is a basic flux fusing at 339 C. It is used to oxidize the base metals that they may more readily pass into the slag as a silicate, borate, or dissolved metallic oxide, instead of into the bullion in a metallic state. It is especially valuable for oxidizing zinc when the same has not been effected by roasting, or the zinc removed by acid treatment. It does not so readily oxidize lead and the other metals, as it gives off its oxygen at too low a heat. Niter in the process of oxidizing gives off its acid portion leaving the base, potassium, which actively combines with silica to form a potassium silicate and will abstract the siliceous matter of the crucible if silica is not otherwise available, and is assisted in this by the oxidizing influence of the acid portion on the carbon of the crucible. Manganese Dioxide as a Flux. Manganese dioxide (Mn0 2 ) is a basic flux and oxidizing substance, as niter, but is not as destructive to the crucible. It is a better oxidizer of lead than niter, though with silver bullion it causes more silver to enter the slag. Determining the Flux to be Used. The flux for a precipitate cannot be calculated in a practical way. A method that has FLUXING AND MELTING 187 been used is to prepare test charges of precipitate and flux, smelt them in assay crucibles in the assay furnace, and observe the resulting slag and button, probably assaying or panning the slag to find how low in value it is. This method is rather un- satisfactory, for the fusion in an assay furnace is a quick one at a high heat, as against the slow and lower heat when melting on a working scale. Also the extent to which the charge will abstract silica from the graphite crucible cannot be well deter- mined; in fact, a higher silicate containing a larger proportion of silica will generally be made in the assay furnace fusion. In preparing the flux for a precipitate at a new plant, past experience is relied upon in connection with a careful observation of the conditions under which the precipitate has been prepared, to indicate the quantity and proportions of the flux to be used. The melting is watched and studied, the effect of the flux on the crucible is noted, the slag is examined for its character and later assayed, and any necessary flux added. In this way a formula for the flux is worked out. The flux must be varied according to what is to be slagged off, and it would appear that the proper way to discuss the proportions would be to take a type of flux and vary it to meet the different requirements, for an examination of the formulae given by various authorities gives little information, except as the proportions are varied to meet variations in the precipitate. The following is given as the normal extremes of a well propor- tioned flux that has been found very satisfactory: Low High Precipitate 100 parts. 100 parts. Borax glass 12 parts. 30 parts. Sodium carbonate 6 parts. 15 parts. Silica 3 parts. 8 parts. The borax glass (or equivalent of borax) as an acid flux unites with the bases and oxides of the base metals to form borates, it also dissolves the metallic oxides that they may remain sus- pended in the slag. The sodium carbonate (or sodium bicar- bonate or the potassium carbonates) as a basic flux unites with the acid constituents which are mainly if not entirely silica, forming a sodium (or potassium) silicate which acts as a flux on bases and metallic oxides for which sodium or potassium alone is not a flux. The silicates acting with the borates as silicate- 188 TEXT BOOK OF CYANIDE PRACTICE borates lower the melting point of the charge and assist in the fusion; their increased complexity more readily dissolving and holding suspended the slag constituents of the charge. The silica unites with the soda and the base oxides to form various silicates, so that the slag is partly a complex solution of vari- ous silicates, a thing which assists the fusion. It would appear at first that sodium carbonate being a base should not be added to the precipitate which is basic itself, that only borax and silica should be added, but it is found that the formation of a certain amount of sodium silicates by the addition of soda is desirable to get a rapid and satisfactory fusion at low heat. For, as men- tioned before, sodium silicates are a flux for the bases and metallic oxides, as in the formula Na 2 O . ZnO . SiO 2 of a sodium zinc silicate. Soda is a desulphurizer and, consequently, may be useful for that purpose with a precipitate containing sulphur as a sulphide. Fine quartz tailing or other sand high in silica is generally used to supply the silica. Ground glass, assay slag, and less preferably the slag from previous meltings is sometimes used. These are already complex silicates and easily fused, but had best be dispensed with in favor of silica and sodium carbonate, as giving more desirable silicates and a greater effect. A fluxed charge may be considered to be divided into two components, acid oxides and basic metallic oxides, which are to be fused to a liquid neutral slag. The acid oxides consist of the silica (SiO 2 ) and the boracic acid or boron oxide (B 2 3 ) of borax, which are supplied as a flux. The basic metallic oxides are the constituents of the precipitate outside of the gold and silver, to which is added sodium carbonate (Na 2 C0 3 ) that its sodium oxide (Na 2 0) may form the desirable sodium silicates with the silica to act as an acid flux and carrier for the bases. Variations Due to Zinc and the Use of Oxidizers. The low amount of flux in the formula given before will give a high-grade bullion on a precipitate containing 60 to 80 per cent of bullion and not roasted or acid treated, such as that screened through a 40 or 60-mesh screen. As the amount of zinc increases, the amount of the flux must be increased or more zinc will enter the bullion. The low amount of flux will give a slag containing considerable of the precious metals and quite often some matte. So that it is more suitable and economical for a silver than for FLUXING AND MELTING 189 a gold plant, which would use more flux, perhaps to the extent of the high amount and more when the percentage of bullion obtained is low and the base metals are in a metallic form. Where the amount of zinc is high and it has not been oxidized through roasting but tends to enter the bullion, from 3 to 10 per cent of niter may be added to the precipitate, even 20 per cent has been used when the slime contained lead, for the pur- pose of oxidizing the base metals. Manganese dioxide has been used in quantity up to 40 per cent and is especially recommended for oxidizing lead which usually enters the precipitate through the zinc-lead couple, and if not oxidized and slagged off or com- bined with sulphur as a matte a sulphide of a base metal will enter the bullion. The manganese base of the manganese dioxide does not appear to so actively combine with silica as the potassium base of niter does, and consequently does not attack the crucible to such an extent. Graphite crucibles are usually made of one part of fire clay and two of graphite, the clay acting as a binder to give form and plasticity. Clay is practically a silicate of alumina and the potassium base set free by the niter in its oxidizing action will act upon the clay, unless plenty of silica be otherwise present, thereby corroding and destroying the crucible, which is assisted by the oxidizing of the carbon by the niter or manganese dioxide. The use of niter or manganese dioxide in the flux is generally avoided by thoroughly roasting or acid treating the precipitate. Their use involves considerable care so that the experienced melter prefers to dispense with them or use clay liners in the graphite crucible when using a large amount of the oxidizers. When used, an amount of sodium equal to the potassium or manganese should be omitted. A large amount of zinc is also taken care of through the use of plenty of silica and soda to form a zinc silicate or sodium zinc silicate; the amount or proportion of the silica should be kept high or it will be abstracted from the crucible, for zinc silicate has a corrosive action upon crucibles. The soda is also valuable in this way by having an oxidizing influence on the zinc and giving a liquid slag. But as borax also fluxes the zinc by the formation of a borate, it should be used together with the soda and silica and to jointly assist by the formation of silicate- berates, more especially when the zinc is in the form of an oxide as borax has a high dissolving effect on the oxides. When 190 TEXT BOOK OF CYANIDE PRACTICE metallic zinc is present, it bubbles and boils off at a high tempera- ture with dense fumes of zinc oxide, which may cause a loss by carrying off the precious metals. General Variations and Fluxing Procedure. The presence in metallic form of other metals than zinc, and other reducers, call for similar treatment as zinc. If the precipitate contains much sand, the silica in the flux is lessened or dispensed with. The presence of a large amount of lime would call for an increase in the silica or borax, or the use of less soda. The addition of soda will increase the fluidity of the charge, but an excess of soda or its addition without sufficient silica in the charge must be guarded against on account of its corrosive action on the crucible. It should always be borne in mind that soda is hard on a crucible. Borax increases the fluidity under normal con- ditions, but too large an excess makes the slag thick Borax should be used to thin the charge and give fluidity when the silica is not in excess when the slag is not stringy its use for that purpose is preferable to soda as it is not destructive to the crucible. Silica in the quantity giving a neutral slag gives a fluid charge, which increases in pastiness as the amount of silica is increased. The higher the silica, the less corrosion of the crucible. Where the charge is too thick from excess of silica, it should be thinned down by the addition of soda. An acid or siliceous slag is stringy, can be pulled into long strings when cooling, and is glassy and brittle when cold. A basic slag is " short," cannot be pulled into strings when melted or cooling, and is stony and dull looking when cold. Raising the temperature liquefies the pastiness due to a high percentage of silica, and makes the slag more fluid in general. A noncorrosive slag at a red heat may attack the crucible at a white heat, because the higher the heat the higher will be the silicate formed, but this corrosion increases with the time, for the higher silicates are slowly formed in this way. The appearance of graphite in the slag indicates that the crucible is being attacked and that more silica should be added to the charge. The addition of glass, assay slag, or fluor spar should thin down the charge with- out materially varying the acid or basic qualities of the slag, at least not to the unsafe side, and may be preferable to the practice of adding lime with a corresponding amount of borax and silica to confer fluidity and complexity. FLUXING AND MELTING 191 The fusion must be carried on for some time after the charge has subsided and settled in a^ quiet fusion, to insure all the con- stituents being decomposed or in a homogeneous slag, and the precious metals fused and settled into the bullion in the bottom of the crucible. Shots of precious metal throughout the slag or settled on top of the bar indicate too thick a slag, owing to an insufficiency or wrong proportion of flux or to too low a heat. Bullion of a high degree of fineness, a rich slag, and a high cost of treatment, fluxing, and melting go together. Dehydrated or anhydrous fluxes, those free from moisture and water of crystallization, have been generally recommended that loss by ebullition and boiling may be minimized, but the success being attained in melting partly-dried precipitate will cause less atten- tion to be paid to this. Oxidizers especially cause boiling and ebullition. Clay liners set inside of graphite crucibles have been used to lessen the corrosive effect of the slag. Their use causes a long and slow fusion with /a large quantity of flux, so that they are but little used. They are valuable when using an oxidizing agent, as niter or manganese dioxide. Matte Formation. A matte is a combination of sulphur with a base metal as a sulphide. It may be formed artificially by adding sulphur if the base metals are present, as they usually are, or by adding iron if the sulphur is present. With both sulphur and base metals in the precipitate, it forms naturally. The sulphur in the precipitate may be principally as zinc sul- phate due to poor washing of the precipitate after acid treat- ment, to lead and calcium sulphates formed by acid treatment and insoluble, and to insoluble sulphur compounds deposited in the zinc boxes. The removal of the bases by acid treatment, the oxidation of the bases and sulphates by roasting, or the use of an oxidizer, as niter or manganese dioxide, reduces the amount of matte or eliminates its formation. The use of an excess of soda will reduce the amount of matte formed, for soda is a de- sulphurizer, while the basic slag formed will dissolve the matte and hold it in suspension. A matte increases the fineness of the bullion by taking into itself base metals that would other- wise enter the bullion. It lowers the value of the slag by col- lecting gold and silver into the matte that would otherwise be found in the slag, but it also prevents some gold and silver from entering the bullion. 192 TEXT BOOK OF CYANIDE PRACTICE Annealing of Graphite Crucibles. The graphite crucibles must be thoroughly annealed, by being placed in a warm or hot place for perhaps a week, and finally by being slowly brought to a high heat, to drive off all the absorbed moisture. This is done by placing the crucible on a boiler, stove, or furnace, and finally in the fire box, before using it for the first time. If this is not done, the sudden heating of the crucible will in all cases crack off part of it by an explosion resulting from the steam formed by the absorbed moisture. There is less tendency for the crucibles to break after they have once been annealed, but between melts they should be kept in a warm, dry place. Melting Furnaces. Two types of melting furnaces are used: the stationary, in which the crucible must be removed by a pair of|tongs in pouring the bullion, and the tilting furnace, in which the entire furnace with the contained pot is tilted for pouring off the slag and bullion. The application of the tilting furnace to the melting of cyanide precipitate is of comparatively recent origin and has been very successful, though trouble has been encountered in some cases in learning the best method of hand- ling it. Both hard fuel, such as coal, coke, and charcoal, and soft fuel, as oil, distillate, and gasoline, are used. Gasoline or distillate is the most advisable fuel where only a small amount of gold bullion is to be melted at a time, as the furnace and accessories are obtained and installed at small cost. For plants of some size, oil or cheap distillate is the most satisfactory and economical, except where the local conditions make the cost of oil or distillate inordinately high above hard fuel. Liquid fuel gives a higher and quicker heat with less labor and dirt than hard fuel, but is more severe on the crucibles. Preparation of Precipitate and Flux. The precipitate may be only partly dried before putting into the crucible. This will save the labor and loss involved in drying and in the dusting when mixing with flux, but care must be used in the melting to add the precipitate before the last has fused down, or loss by spitting may result. Or the precipitate may be thoroughly dried before placing in the crucible, the flux being added before or after the drying. In some cases the precipitate is partly, but not thoroughly dried, then mixed with the flux and made into briquettes by a briquetting machine, that the briquettes may be handled without loss by dusting. When the precipitate is FLUXING AND MELTING 193 not thoroughly dried but is melted moist, the necessity of bri- quetting is small. The amount of the precipitate is weighed or estimated for adding the necessary amount of flux. The flux may be added by charging it and the well-dried precipitate into a closed revolv- ing barrel, by spreading it over the precipitate and shoveling to mix, or by spreading the precipitate and flux in alternate layers which receive some further mixing when being trans- ferred to the crucibles. A thorough mixing of the flux and pre- cipitate is good, but is not absolutely essential. If it tends to cause a loss by dusting, it need not be so thoroughly done. Melting Procedure. The annealed crucible is generally loaded with the fluxed precipitate nearly to the top before start- ing the fire. After the crucible . becomes heated the charge subsides through the melting of the precipitate in the bottom, and more precipitate is added as space is made. Care is taken to add the precipitate before that in the pot has fused down, that there may be little dusting of the newly-added fluxed pre- cipitate. Often a little borax glass is spread over the charge to melt quickly and prevent loss by dusting and fumes. When no more precipitate can be added to the pot, the top of the charge is allowed to fuse, and after having subsided for some time into a quiet fusion is stirred with an iron rod previously made red hot to prevent the slag and metal from adhering to it. The slag and fusion are critically inspected to note if addi- tional flux or longer heat is required. The fusion being brought to the proper condition for pouring, by the application of sufficient heat for a period long enough to bring the mass into quiet fusion, and by the addition of any required flux to vary or thin the slag, it is well stirred with the heated-iron rod to settle any shots of metal before pouring. The fusion may be poured into a conical mold or into a regular bullion mold, allowing the slag to overflow or run through a slot into the slag mold, while the precious metals sink through the slag, to be held in the bottom of the bullion mold. The slag only may be poured into the conical or slag mold; or the slag may be dipped off by a heated assay crucible held in a pair of assay tongs. The slag may be granulated for easy sampling and shipping by being slowly poured into water. The buttons of bullion from the bottom of the conical molds 194 TEXT BOOK OF CYANIDE PRACTICE or the slabs from the bullion molds are collected and melted together to form the bar of bullion for shipment, or if the bullion is retained in the pot it is poured after the final fusion. After the slag or slag and bullion have been poured, fresh precipitate is charged into the crucible and the melting continued. In some cases before pouring the bar for shipment, the slag is dipped off and some attempt made to refine the bullion, it being finally cast without any slag, though casting a bar without a covering of slag appears to be of no advantage, in fact may cause trouble by the metal sloughing off the top of the bar. The mold should be painted with a lime emulsion or a carbon, as a mixture of lampblack and oil, soot from burning waste, etc., before the pouring to prevent the bullion and slag from sticking to the mold. The mold must also be well warmed that the cold mold may not be cracked by the sudden introduc- tion of the hot metal, and that the slag and metal first introduced will not be chilled, so that a good bar or button of bullion cannot be secured. Treatment of Slag and Crucibles. The slag obtained and the old crucibles all contain considerable metal. The method of securing this varies. It is invariably in a metallic condition, as shots. The material may be run through the crushing mill and perhaps most of the metal caught by amalgamation. It has been run through a separate stamp battery, when the quan- tity was large, to be concentrated, the concentrate being melted in the melting furnace and the residue cyanided or shipped to the smelters. It has been charged into an amalgamating barrel and amalgamated, the residue being cyanided. Cyaniding the residue is not usually very efficient. It has been sacked up and shipped to the smelters. A lesson has been taken from smelter practice by pouring the slag into a conical mold with a clay- stoppered hole a few inches above the bottom or apex of the mold. The slag is tapped by removing the clay plug after a shell J inch thick has formed, allowing the core to be granulated for milling or shipment to the smelters by running into water, while the richer shells, into which much of the shot and prills of metal have settled, are treated separately or used as flux in melting precipitate. Treatment of Matte. Matte forms on top of the bar of bullion as a tough, brittle film of base metal and sulphur. It is FLUXING AND MELTING 195 usually undesirable, though it has been artificially produced for the purpose of increasing the grade of the bullion. As it con- tains considerable gold and silver, it should be saved to be melted into a large bar and shipped, or to be refined at the plant. It has been fused with borax and soda, and the addition of niter to oxidize the metals, to give a button of gold and silver and a matte and slag of very low value. A. E. Drucker * gives the following method of obtaining an extraction of 85 to 94 per cent of the value in the matte. Alternate layers of borax, matte, and cyanide, all finely crushed, are put into a graphite crucible. The crucible is heated at a white heat for two or three hours until the charge subsides and action ceases, when the thick slag is skimmed off and the contents of the crucible poured. Smelting with Litharge and Cupellation. In the lead smelting of zinc slime, the precipitate with or without acid treatment is dried to a small per cent of moisture and mixed with litharge, borax, silica, and powdered coke. The fluxed material is bri- quetted to enable easier handling and less dusting. The bri- quettes are melted in a cupel furnace, the resulting slag being drawn off. The lead that has been reduced with the gold and silver is cupeled off as litharge by means of a current of air blown across the molten metal, oxidizing the lead to litharge, which is drawn off to be ground and reused in the next melting. After the lead has been removed in this way, the fine gold and silver is allowed to cool, when it is removed, cut up, and melted in the usual graphite crucible into a bar of high fineness for shipment. The slag, cupel bottoms, sweepings, and by-products are smelted in a small lead blast furnace, the lead produced being cupeled later. The method, like the zinc-dust process of precipitation, is well adapted for large plants producing a con- siderable quantity of precipitate. It is apparently a cheaper and more efficient method of turning the precipitate into fine bullion than the usual practice. Assay of Zinc Precipitate. f Zinc precipitate maybe assayed by three methods: by scorification, crucible fusion, or a com- bination method involving preliminary refining by acid. In * Mining and Scientific Press, May 18, 1907. Recent Cyanide Practice, p. 260. fSee C. H. Fulton and C. H. Crawford in Bull. No. 5, South Dakota School of Mines. 196 TEXT BOOK OF CYANIDE PRACTICE the assay by scorification, ^ to T V assay ton of precipitate is taken to 70 grams or more of test lead and a cover of a small amount of borax glass. The crucible fusion may be made with the following charge: T V assay ton precipitate. 70 grams litharge. 5 grams sodium carbonate. 1 gram flour (or other reducer). 5 grams silica. 2 grams borax glass. By the combination method, T V assay ton or more of precipitate is boiled for a continued length of time with 20 c.c. sulphuric acid and 60 c.c. water, finally filtered, washed, dried, incinerated at low heat, and residue fluxed and fused in the usual crucible fusion. In all cases the slag and cupel of the first fusion should be ground up, fluxed, and fused in the same crucible dr scorifier, and the results added to the first fusion. CHAPTER XVI CYANIDATION OF CONCENTRATE THE cyanidation of concentrate or the separated sulphide constituent of an ore involves no departure in principle from standard cyanide practice, but simply stress upon certain parts of the manipulation to meet the abnormal conditions connected with the sulphide and its treatment. A clean gold ore with the precious metal finely divided and upon the breaking planes or faces of the crystals of the ore, and a sulphide with the metal in a coarse state and interbedded with and in the pyritic crystals are the two extremes, of which the base or pyritic ores being cyanided to-day are an intermediate. The methods of cyanid- ing concentrate include roasting, leaching, agitation, nitration, decantation, oxidation, and fine-grinding as with ordinary ores. The prominent characteristics to be considered, are: Precious metal, especially with gold ores, is usually in a comparatively coarse metallic state, susceptible of being amalgamated to a certain extent, and requiring considerable time for dissolution. The holding of the precious metals to a large extent within the pyritic crystals, requiring fine-grinding, oxidation, drying, or roasting to liberate the value. The presence of iron, copper, lead, arsenic, antimony, etc., either metallic or as compounds, and the resultant high consumption of cyanide and the tendency of the solution to foul. The necessity of meeting the high acidity generated. The action of cyanide and alkalinity upon the sulphide to form soluble or alkaline sulphides and the con- sequential necessity of supplying oxygen. The quick settling of the concentrate and its tendency to pack and become imper- meable. Its comparatively high value and that of the solutions resulting from its treatment. Treatment by Percolation. The treatment of concentrate by percolation usually requires from 10 to 30 days to obtain a good extraction. In some cases the concentrate as obtained is stored under water to prevent the formation of ferrous sul- phate and sulphuric acid through the decomposition of the 197 198 TEXT BOOK OF CYANIDE PRACTICE pyrite. Though where the concentrate is not to be finely ground it is better to spread it out to dry, as this causes the grains of pyrite to fall apart, decompose, and allow solution to enter them, that the metal may be better dissolved. If the concentrate, as charged into the leaching vat, contains much soluble acidity, lime may not be added to it, but the charge water-washed until drainings indicate no acidity, to be followed, to remove the latent acidity, by a wash of water saturated with lime a saturated solution of lime water will contain about 2J pounds CaO per ton until the drainings show some alkalinity. The latter method is not advisable unless the cyanide solution can be used with a protective alkalinity high enough to meet the acidity as it may be generated in the charge, which would be indicated by the outflowing solution always showing a protective alkalinity. When lime is added to the concentrate it is impossible to say, without studying each case in detail, what quantity should be used and how fine it should be crushed. It should be added in quantity and crushed to such a mesh that its alkalinity will be dissolved and given off at the same rate that the acidity is generated. This, of course, cannot be satisfactorily accom- plished. The results of laboratory tests and experience with previous charges must be relied upon. With a gold sulphide, from 3 to 10 pounds of lime will usually be sufficient; this had best be added unslacked and crushed to a 10-mesh, the larger part being coarse granules. After the concentrate and lime have been charged into the leaching vat, they should be water- washed until the drainings show alkalinity. Any lack of alka- linity through the slow dissolution or insufficiency of the lime should be met by alkalinity in the water wash or solution. It is inadvisable to dispense with water-washing and at once run on weak cyanide solution, as a better neutralization of the acidity is made and all the soluble compounds are removed instead of entering the cyanide solution, which they may foul and make more viscous, and finally be precipitated in the zinc boxes. The charge is drained after the drainings show alkalinity, when the first cyanide solution is run on, preferably one low in cyanide and strong in alkalinity. The weak solution is run on once, or for a short time, until it is apparent that the active cyanicides have been met and the strong cyanide solution will not be too quickly destroyed, after which strong standardized CYANIDATION OF CONCENTRATE 199 solution is used until the dissolution is accomplished, with final washes of weak solution and water. The strength of the strong solution will vary from .2 per cent (4 pounds) to .75 per cent (15 pounds), seldom higher; a strength above .5 per cent (10 pounds) is generally undesirable. Strong solutions in the presence of sufficient oxygen are more active than weaker ones in dissolving the precious metals, but they also act more upon the base metals and compounds, causing them to enter the solution more and a greater consumption of cyanide. Fresh strong solution should be constantly supplied, perhaps by con- tinuous leaching, to replace about each particle of gold that which has been utilized and weakened by dissolving coarse gold or neutralized by the strong cyanicides. Each strong solution should be well drawn off that air may be drawn into the charge, both to assist in the dissolution of the precious metals and, by oxidation, to decompose and break open the pyrite for better contact between the gold and silver and the solution, though this is bound to develop considerable acidity. The iron and other metallic salts from the decomposition of the sulphide abstract oxygen from the charge in effecting their formation, and by supplying plenty of oxygen the salts are finally oxidized into harmless oxides or less active cyanicides, as the oxidation of ferrous salts into the ferric oxide or hydrate. The first solu- tion should be allowed but short contact with the charge if rich solutions are undesirable, as where there is considerable leakage or they go directly and undiluted to a zinc box, the shavings of which they would coat with solid metallic gold to cause considerable metallic zinc to enter the melting. Fresh solutions are necessary to supply oxygen to get quicker dis- solution, consequently continuous leaching with periodical complete drainings to aerate the charge is best. It is not only desirable but usually essential to oxidize artificially, not by chemical oxidizers, but by pumping air through the charge at a pressure of 3 to 5 pounds below the filter bottom when the charge is drained. It is not advisable to draw air through by means of a vacuum pump applied beneath the filter bottom, on account of packing the charge. Leaching charges of concen- trate should be shallow, say 4 or 5 feet, to allow of easy aeration. The solutions should be well aerated, which may be, when exces- sive aeration is desired, by means of an air cock between the 200 TEXT BOOK OF CYANIDE PRACTICE pump and the solution tank whereby a small quantity of air is drawn in and pumped with the solution, or by allowing a little air under pressure to escape into the solution tank. The solution should be tested for its reducing power and for alkaline sulphides. It may be advisable when about half the treatment period has passed, to shovel the charge over, placing the bottom on the top. This is an excellent method of aerating, especially when it places the bottom where the least dissolution has taken place owing to the absence of oxidation which is often noticed in treating sulphide on top where the greatest dissolution is effected. However, when air is occasionally pumped through the charge, shoveling over may be more beneficial on account of the packing and peculiar cementing or caking of the sulphide. To lessen the tendency to pack and cake, coarse tailing or ore sand may be mixed with the concentrate. The protective alkalinity of the inflowing solution should be sufficient to give a slight protective alkalinity in the outflowing solution. Though a high protective alkalinity is necessary to protect the cyanide from decomposition, it will form some soluble or alkaline sulphides, for many sulphides are acted upon in this way by alkaline solutions, while cyanide decomposes these and other sulphides to form the alkaline sulphides. The alkaline sulphides abstract the oxygen necessary for dissolving purposes and in weak solutions reprecipitate silver, and perhaps gold or at least retard its dissolution, so that they should be prevented from forming or should be gotten out of the solution when once formed. These are removed as insoluble sulphides by the zinc in solution or by the addition of lead acetate. The effect of adding lead acetate occasionally to the solution to the extent of a total of one-half to one pound per ton of concentrate should be studied, even if no alkaline sulphides are ever found in the solution. Another way of accounting for the reduced extraction, that has often been noted when using a high pro- tective alkalinity on sulphide gold ore, is that the alkali acts upon the pyrite and partly-decomposed pyrite, causing a gradual oxidation into ferric oxide (Fe 2 3 ), in which process is consumed a large amount of oxygen, this being taken from the solution causes it to lose its dissolving power. Whether the cause is the reducing action of alkaline sulphides or of ferrous salts or some unknown process, it is apparent that aeration is a most CYANIDATION OF CONCENTRATE 201 important thing. The effect of a high and a low protective alkalinity on both the rate and extent of extraction and the consumption of cyanide should be studied. Treatment by Agitation and Fine- Grinding. Treatment by agitation will usually give a little higher extraction than leaching in about one-sixth to one-third the time, and with a less con- sumption of cyanide, but is generally carried out hi connection with fine-grinding. The fine-grinding is best accomplished in a tube mill or grinding pan. The pulp may be caused to flow over amalgamating plates, for in some cases over 50 per cent of the gold may be secured as amalgam, reducing the cost and losses in the subsequent cyaniding, and probably reducing the time of dissolution by removing the coarse gold. Unless the concentrate contains cyanicides that it is desirable to remove before applying the cyanide, it may be advantageously ground in a medium cyanide solution about .1 per cent (2 pounds). Mechanical agitators, unless of a special type that can be started while raised free from the charge, are not suitable owing to the high specific gravity of the concentrate and its tendency to pack. Some form of air agitator is preferable, and in all cases air should be supplied during the agitation. It should be learned how the dissolution progresses, for with base ores it has been noted that after the passage of some time, the rate of dissolution rapidly falls until the old solution is removed and aeration effected, when new solution again causes a rapid dissolution. If supply- ing air to the charge does not cause the gold to go into solution with the maximum rapidity, the charge should be allowed to settle, the clear solution syphoned off, and new solution added for further agitation. Treatment of slimed sulphide by decan- tation is easy as it rapidly settles to a small bulk, and while it gives satisfactory results, the up-to-date plants shorten the time of treatment by filtering the pulp after the bulk of the value has been washed out by decantation. Most of the leaf filters are unsuitable for handling this class of material, since on account 'of Hie high specific gravity of the sulphide, the cake must be formed within a few minutes, or the sulphide will settle out of the solution, and owing to the richness of the solution a thorough and highly-efficient wash must be given. The Kelly filter press making a cake under pressure in 2J to 5 minutes is now in satis- factory use in such plants. 202 TEXT BOOK OF CYANIDE PRACTICE General Considerations. Sliming the sulphide should be carried as far as possible, as giving a higher and quicker extrac- tion. It is often the case that the finer concentrate is higher in value before regrinding and treatment, and lower in value after treatment than the coarser concentrate. In some cases the finely-ground sulphide may be mixed with coarse sand and successfully leached, though agitation is better, for it gives a higher extraction than leaching, a thing that is not noticeable with gold ores but holds to some extent with silver ores. Treat- ment costs by agitation are generally slightly less than by per- colation, for the less consumption of chemicals, due to lessened oxidation and formation of cyanicides, overbalances the cost of agitation. A plant for leaching concentrate is comparatively inexpensive, consequently that process is the one often em- ployed by small operators, whereas with a large amount of con- centrate to be treated the high installation cost of a sliming and agitation plant is soon met by the increased extraction. The concentrate after treatment often contains sufficient value to warrant its shipment to the smelter, if the original heads were extremely high, or to be exposed on a dump for retreat- ment later, after it has oxidized, or by some new process yet to be devised to treat this class of material. In case of placing on a dump, a thorough washing should be given, that no soluble cyanogen may be left remaining to effect a dissolution that will later be washed out by rains and lost. Many plants that are now shipping their sulphides would find it more profitable to first treat them in a simple leaching plant, or more expensive fine-grinding and agitating plant, before shipping the residue; the cost of treatment being offset by a return of nearly 100 per cent of the amount extracted by cyanide, instead of on a basis of 95 per cent as paid by the smelters, and the lower freight rate and smelter charge on the lower grade of material shipped. To which may be added the shrinkage of the actual value and quantity, which is made by the smelters, as a factor of safety for their own protection and profit, and the quicker realization of the value in the concentrate when produced at an isolated mine. In some cases where a large amount of concentrate is produced, it might be advantageous to run it continuously to a grinding mill and amalgamating plates and ship the residue. Treatment of sulphide involves a problem as to whether it should be cyan- CYANIDATION OF CONCENTRATE 203 ided with the ore or removed by concentration and treated sepa- rately. When treated with the ore, much of the dissolvable value in the sulphide is not obtained, on account of the short treatment given the ore, but this may be more than offset by the cost of a concentrating plant and its operation. As the sulphide is small in quantity even if high grade, and large in quantity but low in grade, treatment of it in the ore without concentration becomes more advisable. Fine grinding and agi- tation of the ore and a quick dissolution of the larger part of the value in the sulphide make for treating the sulphide in the ore, especially where means are provided for grinding the sul- phide finer than the ore in general. This may be performed by a slow-speed Chilian mill discharging the lighter particles by overflow, or by returning to the tube mill the coarse sand and sulphide separated out by a cone classifier, or a " roughing " or concentrating table following the tube mill and making a closed circuit of the heavier material. A determination of the extrac- tion from the sulphide with varying periods of treatment, both when contained in the ore and as concentrated out, will give enlightenment on this subject. Gold concentrate is nearly always amenable to cyanide treatment. Silver concentrate is less amenable, but important advancement in the treatment of this class of material may be expected. Iron pyrite, zinc blende, and galena present little interference or it is easily met. Arsenopyrite or mispickel, the sulphide of arsenic, may usually be treated satisfactorily in large quantities, though it has a high reducing action. Stibnite, the sulphide of antimony, often causes trouble or may prevent successful treatment. It is an active reducer, in which it is similar to mispickel but much more pronounced in its action, and by removing the oxygen, through the formation of alkaline sulphides, hinders or prevents the dissolution of the precious metals. It also holds to some extent the precious metals in a mechanical combination which the cyanide cannot break. Copper in unoxidized pyrite or in a hard state is but little acted upon by cyanide, and a considerable quantity is not a barrier to successful cyanidation, but when in a soft oxidized state readily dissolved by cyanide, a small quantity of copper may render the consumption of cyanide too high and require special methods of treatment and precipitation. 204 TEXT BOOK OF CYANIDE PRACTICE Where the sulphide contains a large amount of cyanicides which are not removable otherwise, especially iron and copper, a preliminary treatment may be given with a very dilute sul- phuric or hydrochloric acid solution to remove the cyanicides. After the acid has performed its work, the soluble salts and any excess of acid remaining are removed by washing, the excess of acid to be used on the next charge. The acid treatment appears to effect a decomposition of the sulphide to give a higher extrac- tion, in addition to greatly reducing the consumption of cyanide. It would appear that the acid solution for dissolving or altering the cyanicides could be prepared very cheaply, by passing the sulphur dioxide (S0 2 ) given off by burning sulphur into water to form sulphurous acid, as is done in making sulphurous acid for the acid treatment of zinc slime. The copper in the acid solution washed out of the ore can be recovered by running the solution over scrap iron. Roasting of the sulphide will usually allow a high extraction to be obtained in a short length of time with a low consumption of cyanide. It has been generally abandoned in favor of fine- grinding and agitation, except with telluride ores where the roasting is used to separate the tellurium from the gold, since gold in combination with tellurium is not amenable to cyanide treatment outside of the bromocyanide process or analogous chemical processes. In the bromocyanide process, the addition of bromine to cyanide enables the cyanide to dissolve gold from telluride and arsenical ores, which it could not otherwise do, and increases the dissolving efficiency generally. It has been success- ful in treating sulphide, though but little interest has been taken in its use as the advantages of its employment are usually not warranted by its increased cost. CHAPTER XVII \ ROASTING ORE FOR CYANIDATION ORES are roasted preliminary to cyanidation in two distinct ways: a dehydrating roast to remove the moisture and an oxidiz- ing roast to remove the sulphur or tellurium and render the cyanicides innocuous. The dehydrating roast is a misnomer, for the process is simply a drying one. When ore to be dry- crushed is of a wet, clayey, talcose nature it is necessary to remove the moisture by passing the ore through driers, or it will clog the rolls and screens and be poorly sized. This drying process dehydrates or drives the moisture out of the ore, destroy- ing to a large extent the adsorptive and flocculent qualities of the clayey matter, making it less plastic and more granular and leachable. It also opens the capillaries and parting planes of the more crystalline ore so that it is more easily fractured and crushed, and that the cyanide solution may better penetrate it. The influence of drying, and more especially of roasting, is very marked on some ores, which, due to the large amount of clayey matter and its adsorbent and plastic qualities, will adsorb the cyanide solution and refuse to allow it to be displaced even when mixed with much coarse material. In drying, if the ore con- tains much sulphide, a high heat or a real roasting tendency cannot be allowed unless carried to a " dead " or complete roast owing to the formation of ferrous salts and other cyani- cides. In such a case the soluble salts or free acidity should be water-washed out of the ore, and the insoluble acidity neutral- ized by an alkaline wash. The dry big of ore followed by dry- crushing was formerly much in vogue, but the perfection of fine-grinding, agitating, and filtering machinery has caused a decline in the practice, especially where drying and fine-crushing are necessary. The leaf filter is well adapted for handling the clayey slime, which formerly gave unsatisfactory results until de- hydrated and rendered more granular and leachable by roasting. The oxidizing roast, while rendering the ore more leachable 205 206 TEXT BOOK OF CYANIDE PRACTICE and easily crushed, is for the purpose of driving off the sulphur as sulphur dioxide (SO 2 ), thereby converting the base metals into inert oxides, that are not reducers or cyanicides, and liberat- ing the gold and silver mechanically held, or for driving off the tellurium chemically combined with the precious metals in a telluride ore. Due to the high insolubility in a cyanide solution of gold in combination with tellurium, such ore must be roasted before being cyanided, though bromine is used in connection with cyanide as the bromocyanide process in Australia, the bromine giving a higher solvent effect to the cyanide solution. The changes occurring in the roasting of an iron pyrite (FeS 2 ) may be given as : FeS 2 = FeS + S. 3 FeS + 11 O = Fe 2 O 3 + FeSO 4 + 2 SO 2 . 2 FeS0 4 = Fe 2 O 3 .+ SO 3 + SO 2 . It is necessary that a complete oxidizing roast, often spoken of as a "dead" or " sweet " roast, be given the ore and that all the sulphur is driven off, for the insoluble ferric oxide (Fe 2 3 ) finally formed is not affected by cyanide, whereas those com- pounds formed between the unoxidized iron pyrite and the final ferric oxide may be considered as cyanicides. In this way the consumption of cyanide is reduced and the amount of soluble salts entering the solution kept at a minimum. Telluride ores are roasted until the' sulphide content is fully, oxidized. The efficiency of the roast may be tested by taking 100 grams or more of the ore and shaking for a few minutes with the same number of cubic centimeters of water, filtering off the water and slowly adding to it a small quantity of new cyanide solution of the working strength. If no cloudiness appears, the ore is dead roasted and the consumption of cyanide due to cyanicides will not be high, but if a discoloration appears, the ore still con- tains soluble salts that will destroy cyanide and foul the solution. Or the test may be made by adding a few drops of a solution of barium chloride (BaCl 2 ), which will indicate soluble sulphates by forming a white cloud of barium sulphate (BaSO 4 ). ^CHAPTER XVIII CYANIDE POISONING THE poisonous effects of cyanide are due to hydrocyanic acid (HCN), either that generated in the working of the process or that formed by the acid of the stomach, when cyanide is taken internally. Hydrocyanic acid, or prussic acid as it is sometimes called, is one of the most deadly poisons, investigators having been killed by it as a result of a few drops of the liquid acid falling on the skin. The gas or the vapor of the acid is likewise poisonous, producing headaches, dizziness, and nausea, which slowly pass away when the sufferer is removed to a pure atmos- phere, while breathing the fumes of ammonia will afford relief. Exposure to small amounts of hydrocyanic acid gas seldom causes harm beyond possible headaches, depending somewhat upon the susceptibility of the person exposed to it. The contact of cyanide solution with the skin tends to irritate the skin, cause it to become hard and crack, and may cause sores and eruptions a species of eczema though with the weak solu- tions now in use there are seldom harmful results unless the skin contains open wounds or cuts. To prevent this and the ends of the finger nails from being eaten down, rubber gloves are worn when working in solution, as when cleaning the zinc boxes. Or the hands and arms are given a coating of vaseline, or even the stiff lubricating grease used in mills, to render the contact between the skin and solution less. The solution should always be displaced from the boxes by water preliminary to cleaning- p, to lessen the danger from contact with it and the hydro- yanic acid fumes arising. Internal Poisoning. When cyanide as in a solution is taken nternally, the acid of the stomach forms hydrocyanic acid with t, which enters the blood as a blood poisoning, paralyzing the lervous system and muscular sensibility and suspending the iction of the heart. The hydrocyanic acid acting in the blood 207 208 TEXT BOOK OF CYANIDE PRACTICE deprives it and the tissues of the ability to absorb oxygen, resulting in severe cases of cyanide poisoning, of the sensation of strangling, and inability to get air or to swallow. With strong solution, or when having taken a large quantity of medium strength, insensibility results almost immediately, and death within a few minutes. Where the amount taken has been small, death may result after considerable delay and suffering, if an antidote is not at once administered. Small quantities of weak solution are not necessarily fatal, but unless an antidote is used the risk is great. Treatment by Hydrogen Peroxide. In a case of poisoning, whether by the vaporous hydrocyanic gas causing incipient insensibility or by swallowing cyanide solution, it is necessary to act with all speed possible. If a case of poisoning by being overcome by gas, the sufferer should be removed to a pure atmos- phere, caused to breathe the fumes of ammonia, and given a number of hypodermic injections of a 3 per cent solution of hydrogen peroxide (H 2 2 ) underneath the skin. In the absence of facilities to give injections a 10 per cent solution should be taken in internally that it may enter the blood and system. If the cyanide has been taken internally, as by drinking a solu- tion, a wineglass or more of a 30 per cent solution of hydrogen peroxide should be taken at once, and subcutaneous injections may be made of a 3 per cent solution. The patient's throat should be tickled with the finger, or more preferably by a soft rubber hose, to cause vomiting, after which a fresh and more dilute solution of hydrogen peroxide should be given and the process repeated. Finally water, preferably warm, should be taken and vomited to wash out the stomach. The hypodermic injections may be given at several places over the body, and thereafter at intervals one minute apart and gradually lengthen- ing until the patient is relieved. If a stomach pump is available, the stomach should be pumped out after each dose of the antidote or wash. In case the patient is unconscious and only able to breathe with difficulty or not at all, artificial respiration should be induced, as in a case of drowning, by kneading and compress- ing the body and pulling the arms, chest, and abdomen. Steps to promote the circulation may be taken by rubbing and knead- ing the body. Tickling the throat is perhaps the best method to produce vomiting, though emetics may be used, such as a CYANIDE POISONING 209 spoonful of mustard in a pint of warm water, if they can be given at once and act promptly. The action of hydrogen peroxide (H 2 O 2 ) as a powerful oxidizer is to form an oxamide ((H 2 CNO) 2 ) with the hydrocyanic acid and a cyanate (KCNO) with the cyanide, which are harmless, by decomposing the fiydrocyanic acid and cyanide, as: ( 2 HCN + H 2 2 = (H 2 CNO) 2 . I KCN + H 2 O 2 = KCNO + H 2 O. To do this advantageously it must be introduced before the hydrocyanic acid or cyanide enters or is absorbed into the system. The objection to the use of hydrogen peroxide as an antidote when cyanide is taken internally is its slow action, which may allow considerable of the poison to enter the system before the decomposing action is completed, so that the removal of the cyanide and the washing out of the stomach by vomiting may be of more value than the oxidizing action of the hydrogen peroxide. Treatment by Cobalt Solution. A solution of nitrate of cobalt, or other salt of cobalt, has been used with success as an antidote. It acts almost instantaneously to convert the cyanide into an insoluble and innocuous cyanide of cobalt. But an excess of the cobalt salt must be used to insure the imme- diate neutralization of the cyanide, which requires the excess to be removed by vomiting or the stomach pump, since the nitrate of cobalt itself has a somewhat poisonous effect. Treatment by Ferrous Salts. The quickest and best method of neutralizing the poison when it has been taken internally is by means of ferrous hydrate or carbonate. Due to the fact that these decompose quickly, they must be prepared at the time when used, which is accomplished by making up the follow- ing: A. A bottle containing 1\ grams ferrous sulphate (FeSO 4 ) dissolved in 30 c.c. of water. B. A wide-mouthed bottle with a capacity of about 400 c.c. containing 1J grams caustic soda (NaOH) dissolved in 300 c.c. of water. C. A tube or phial containing 2 grams powdered magnesia. These three bottles, together with directions for their use, are kept in a convenient place in the plant, the bottles being tightly 210 TEXT BOOK OF CYANIDE PRACTICE corked with stoppers that can be instantly removed. In a case of cyanide poisoning the three are emptied together into the larger bottle, well shaken, and drunk by the sufferer from the wide mouth of the bottle. The contents of the stomach should be removed and washed out by vomiting or the stomach pump. At the same time hypodermic injections of hydrogen peroxide may be given under the skin, if the case is serious, to reduce the evil effect of any cyanide that has entered the system. The magnesia is used to increase the alkalinity to the amount re- quired to overcome the acidity of the stomach, and for quick conversion of the cyanide into a ferrocyanide, as the use of caustic alkali to that extent would be too severely caustic on the mucous membrane. The caustic soda and magnesia may be replaced by sodium carbonate (Na 2 CO 3 ) equal in weight to the ferrous sulphate. In either case the cyanide is converted into a ferrocyanide (K4Fe(CN) 6 ) which is nonpoisonous, as: FeSO 4 + 2 NaOH = Fe(OH) 2 + Na 2 SO 4 . Fe(OH) 2 + 6 KCN = K4Fe(CN) 6 + 2 KOH. FeSO 4 + Na 2 CO 3 = FeCO 3 + Na 2 SO 4 . FeCO 3 + 6 KCN = K4Fe(CN) 6 + K 2 CO 3 . In all cases of internal cyanide poisoning the poison must be removed or neutralized and removed as soon as possible. Con- sequently, one person should assist the sufferer to vomit, using water to wash out the stomach, while another hurriedly secures and prepares the antidote. Hydrogen peroxide is one of the stock articles about a laboratory and should always be found in a cyanide plant, to fall back upon in emergency if no other antidote has been prepared. It should be kept well corked, covered, and in a dark place to prevent decomposition. If no antidote is at hand, washing out the stomach through drinking watet and vomiting by tickling the throat which the sufferer can perform alone are always available. Poisoning in Precipitate Refining. Another form of cyanide poisoning is that due to the gas or fumes arising in the acid treatment of zinc-box slime. The fumes are principally hydro- gen and act to suffocate the person exposed to them. In some cases the fumes contain hydrocyanic acid from insoluble cyanogen compounds in the precipitate, which are decomposed by the CYANIDE POISONING 211 sulphuric acid; this will result in greater danger. Where arsenic has been deposited in the boxes, fumes of arseniureted hydrogen will be given off when treating the precipitate with sulphuric acid. This is deadly poisonous and has resulted in a number of deaths, in one instance that of every person in the treatment house. The methbd of preventing the formation of this arsen- iureted gas has been given under Roasting and Acid Treatment. The treatment of acute poisoning or the distress caused by gas consists in breathing pure air and the fumes of ammonia. For the more severe cases the hypodermic injections of hydrogen peroxide and the promotion of artificial respiration will un- doubtedly be efficacious. Prevention of Poisoning. Means to prevent accidental cyanide poisoning should be taken by posting a sign at the works calling the attention to the use of cyanide and its poisonous effects, and more especially that pure drinking water may be obtained at a certain point, which should be labeled and removed from the vicinity of all other taps. Promiscuous drinking from taps and hose should be discouraged. Care should be taken in planning the piping that cyanide solution may never pass into the water pipes, and dependence should not be put entirely upon check valves for this purpose. Care should also be used in the laboratory and elsewhere that cyanide solution contained in pails, vessels, or otherwise may never be mistaken for drinking water. While fatalities from drinking cyanide solution are rare, cyanide solution is often swallowed by mistake. The quantity so taken is usually small, for unless the drinker is in a hurry and gulps down the liquid, he at once detects the insipid and slightly salty taste of weak cyanide solution. No harmful results follow when an antidote is immediately taken, except that due to the agitated state of mind and the vomiting. Workmen who are troubled with or subject to cyanide eczema or disorders due to cyanogen should be transferred to other work. Ventilating an enclosed cyanide plant is often desirable to re- move the hydrocyanic acid fumes arising. Trouble is sometimes encountered in working in deep tanks in which hydrocyanic acid has accumulated, especially with pyritic ores generating acidity. A closed or partly-closed tank that has held cyanide solution should never be entered or death will usually result from the hydrocyanic acid it contains. Working in the presence 212 TEXT BOOK OF CYANIDE PRACTICE of obnoxious or dangerous gases may be rendered less harmful by displacing the air and working in the presence of air sup- plied under pressure through a hose. Hoods and good ven- tilation should be provided in the precipitate refining house to carry away the fumes, for a man who has once been " gassed," as most cyanide workers have been, is very susceptible to it thereafter, and a slight touch may physically incapacitate him for a day or more. Cows are easily poisoned by drinking the diluted solution or moisture from the discharged residue or by licking the salts resulting from the evaporation of such moisture; horses are not so often poisoned and pigs very seldom. The addition of copperas, the commercial term for ferrous sulphate (FeS0 4 ), or other cyanicide to the moist tailing has lessened the trouble in this direction. CLASSIFIED BIBLIOGRAPHY A. Books. PAGE 1. Treatises on cyanidation 215 2. Treatises in part on cyanidation 215 3. Treatises in part on special topics of cyanidation 216 B. History and progress 217 C. Chemistry and physio-chemistry of cyanidation 218 D. Aeration and oxidation 221 E. Commercial cyanide and its analysis 222 F. Analytical chemistry of cyanide solution 223 G. Assaying, samplers, and sampling 225 H. Ore testing and physical tests 226 7. Alkalinity and lime 228 J. Classification, de watering, and slime settlement 228 K. Sand treatment and percolation 230 L. Slime treatment, agitation, and decantation 231 M. Filtration 235 N. Precipitation 238 0. Cleaning-up, refining, and melting 242 P. Telluride ore, roasting, bromocyanide, and chlorination 244 Q. Cupriferous ore and solution 246 R. Concentrate cyanidation 247 S. Other refractory ores 248 T. Cyanide poisoning 249 U. Construction, and pulp and residue conveying and disposal 250 V. Tube-milling and fine-grinding 252 W. Cyanidation of silver ores, and in Mexico 256 X. Cyanidation in United States and Canada. 1. Nevada 260 2. Black Hills 261 3. Outside of Nevada and Black Hills 262 F. Cyanidation in South Africa 264 Z. Cyanidation in Australia 265 Miscellaneous. . . 266 213 CHAPTER XIX CLASSIFIED BIBLIOGRAPHY A. Books 1. TREATISES ON CYANIDATION BOSQUI, F. L. Practical notes on the cyanide process. 1900, 201 pp. CLENNELL, J. E. The chemistry of cyanide solutions resulting from the treatment of ores. Second edition, 1910, 202 pp. The cyanide handbook. 1910, 520 pp. EISSLER, M. The cyanide process for the extraction of gold. Third edition, 184 pp. GAZE, WM. H. Practical Handbook of Cyanide Operations. JAMES, ALFRED. Cyanide practice. 1901, 174 pp. JULIAN (H. F.) and SMART (E.). Cyaniding gold and silver ores. Second edition, 1907. McCANN, FERDINAND. Beneficio de metales de plata y oro por cianuracion. (Reduction of gold and silver ores by cyanidation.) 1910, 381 pp. Printed in Spanish. MEGRAW, HERBERT A. Practical data for the cyanide plant. 1910, 93 pp. MILLER, ALFRED S. The cyanide process. Second edition, 1906, 95 pp. PARKS, JAMES. The cyanide process of gold extraction. Fourth edition, 1906, 239 pp. ROBINE (R.) and LENGLEN (M.). Translated by J. Arthur Le Clerc. The cyanide industry theoretically and practically considered. (Dealing with the properties and manufacture of cyanide.) 1906, 408 pp. SCHEIDEL, A. The cyanide process. 1901, 140 pp. WILSON, E. B. Cyanide processes. Fourth edition, 1908, 249 pp. Recent cyanide practice. (Compiled by T. A. Rickard from articles on cyanidation in Mining and Scientific Press between Jan., 1906, and Oct., 1907.) 334 pp. More recent cyanide practice. (Compiled by H. Foster Bain from articles on cyanidation in Mining and Scientific Press between Oct., 1907, and July, 1910.) 418 pp. 2. TREATISES IN PART ON CYANIDATION AUSTIN, L. S. The metallurgy of the common metals. Third edition, 1911, 528 pp. (71 pages on cyanidation.) CHARLETON, A. G. Gold mining and milling in Western Australia, with notes upon telluride treatment, costs, and mining practice in other fields. 1903, 648 pp. (192 pages on cyanide practice in Australia.) 215 216 TEXT BOOK OF CYANIDE PRACTICE CLARK, DONALD. Australian mining and metallurgy. 1904, 531 pp. (Consisting mainly of valuable technical descriptions of cyanide practice in Australia.) Gold refining. 123 pp. (Largely on the refining of cyanide precipitate. From series of articles ending Jan., 1908, in Australian Mining Standard.) EISSLER, M. The metallurgy of gold. Fifth edition, 1900, 638 pp. (90 pages /on cyanidation.) HOFFMAN, O. Hydrometallurgy of silver. 1907, 345 pp. (42 pages on cyanidation of silver ores, principally an abstract of practice at Palmarejo, Chihuahua, Mexico, from T. H. Oxnam in T. A. I. M. E., vol. 36, 1905.) Louis, HENRY. Handbook of gold milling. (Chapter on the cyanide process.) ROSE, T. KIRKE. The metallurgy of gold. Fifth edition, 1907, 534 pp. (90 pages on cyanidation.) International Library of Technology of the International Correspondence School. Vol. 21, 1902. Metallurgy of gold, silver, copper, and lead. 531 pp. (94 pages on cyanidation.) The Mineral Industry. Vols. 1 (1892) to 19 (1910). (Containing an extremely valuable technical review of cyanidation by years.) Proceedings of Chemical and Metallurgical Society of South Africa. Vols. 1 (1894-1897) to 4 (1903-1904). (Mainly containing valuable technical articles on principles of cyanidation.) (Later proceedings appear unbound as monthly Jour. Ch., Met., & Min. Soc., S. A.) 3. TREATISES IN PART ON SPECIAL TOPICS OF CYANIDATION ARGALL, PHILIP H. Western mill and smelter methods of analysis. 1905, 124 pp. (Contains analytical methods used in cyanide plants.) BARR, JAMES A. Testing for metallurgical processes. 1910, 216 pp. (Contains 43 pages on testing of ores for cyanidation.) BROWN, WALTER LEE. Manual of assaying. (Contains methods of cyanide testing.) FURMAN, H. VAN F. A manual of practical assaying. (Revised by Pardoe.) Eighth 1 edition, 1911, 530 pp. (15 pages on testing in the cyanide process, also other allied matter.) HUTCHINSON, J. W. Operations of Goldfield Consolidated Mill. (Re- printed in pamphlet form from M. & S. P., May 6 to June 10, 1911.) LODGE, R. W. Notes on assaying. Second edition, 1906, 312 pp. (20 pages on cyanide testing.). MACFARREN, H. W. Practical stamp milling and amalgamation. 1910, 166 pp. (Contains information on amalgamating in cyanide solution, mill tests, and relation between stamp-milling, amalgamation, fine-grinding, and cyanidation.) RICHARDS, R. H. Ore Dressing. Vols. 1 and 2, pp. 1-1200, 1903; vols. 3 and 4, pp. 1200-2052, 1909; index to four volumes, 112 pp., 1909. (Contains no direct matter on cyanidation, but much allied matter on crushing, arrange- ment of mills, and general metallurgy.) SHARWOOD, W. J. Measurement of pulp and tailing. 1910, 22 pp. (Re- print from Min. Mag., Nov., 1909, to Jan., 1910.) CLASSIFIED BIBLIOGRAPHY 217 Notes on metallurgical mill construction. (Compiled by W. R. Ingalls from articles in Eng. & Min. Jour. Contains information on tube-milling, fine-grinding, construction, conveying, water-saving, etc.) 1906, 256 pp. B. History and Progress ARGALL, P. Historical summary of steps in cyanidation. Mines & Mins., vol. 28, p. 368, 1 p. Limitations of cyanide process. Eng. & Min. Jour., vol. 64, p. 278. Metallurgical progress in Colorado. M. & S. P., Jan. 1, 1910, 6 pp. Review of cyanidation in 1910. Eng. & Min. Jour., Jan. 7, 1911, 4 pp. Steps in eyanidation. Proc. Colo. Sci. Soc., Nov., 1907, 25 pp. BARBOUR, P. E. Developments in cyanide practice. Mines & Mins., May, 1911, 4 pp. BROWNE, R. S. Progress in cyano-metallurgy during 1909. Pac. Miner, Jan., 1910, 4 pp. Review of cyano-metallurgy in 1910. Pac. Miner, Jan., 1911, 3 pp. DURRANT, H. T. Limitations of cyanide process. M. & S. P., Mar. 5, 1904, 1 p.; abstract from Jour. Ch., Met., & Min. Soc., S. A. FULTON, C. H. Review of the cyanide process in United States during 1902. Eng. & Min. Jour., Jan. 3, 1903, 4 pp. Cyanidation in United States. Eng. & Min. Jour., Jan. 7, 1904, 2 pp. Cyanidation in United States. Eng. & Min. Jour., Jan. 5, 1905, 3 pp. Cyanidation during 1905. Eng. & Min. Jour., Jan. 13, 1906, 3 pp. (See annual reviews in The Mineral Industry.) GORDON, R. W. Progress in cyaniding during 1910. Met. & Chem. Eng., Jan., 1911, 1 p. GUESS, H. A. Progress in ore dressing in United States and Mexico during 1910. Met. & Chem. Eng., Jan., 1911, 2 pp. JAMES, A. Improvements in cyanidation. Eng. & Min. Jour., Jan. 28, 1904, 1 p. Progress in cyanidation in 1906. M. & S. P., Jan. 5, 1907, 5 pp. "Recent Cyanide Progress, " p. 197. Progress in ore treatment during 1906. Eng. & Min. Jour., Jan. 5, 1907, 3pp. Progress in the treatment of gold ore. M. & S. P., Jan. 4, 1908, 2 pp. "More Recent Cyanide Practice," p. 114. Progress in cyanidation. M. & S. P., Jan. 2, 1909, 7 pp. "More Recent Cyanide Practice, " p. 233. Progress in cyanidation. Eng. & Min. Jour., June 12, 1909, 1 p.; Min. World, June 12, 1909, 1 p. Annual cyanide letter. M. & S/P., Jan. 1, 1910, 6 pp.; discussion, Feb. 26, Apr. 2, and May 28, 1910. "More Recent Cyanide Practice," p. 362. Progress in treatment of gold and silver ores during 1910. M. & S. P., Jan. 7, 1911, 5 pp. LAMB, M. R. Progress and developments in cyanide practice. Eng. & Min. Jour., Jan. 15, 1910, 2 pp. MERRILL, C. W. Present limitations of cyanide process. T. A. I. M. E., vol. 25, 1895, 4 pp. 218 TEXT BOOK OF CYANIDE PRACTICE NICOL, J. M. Discussion of Leopoldo Salazar's paper on MacArthur- Forrest cyanide patents in Mexico, and lessons to be learned from history of subject. Trans. Mex. Inst., Feb., 1910, 8 pp. MACARTHUR, J. S. Gold extraction by cyanide. (A retrospect.) Eng. & Min. Jour., Aug. 12, 1905, 1 p. McCoMBiE, J. History of cyanide process. (First plants.) M. & S. P., June 24, 1911, 1 p. PAUL, A. B. MacArthur-Forrest process. M. & S. P., Jan. 21, 1893, 1 p. SALAZAR, L. MacArthur-Forrest cyanide patents in Mexico. Trans. Mex. Inst., Oct., 1909, 6 pp. TRAPHAGEN, DR. F. W. Cyanide process a review. West. Ch. & Met., Nov., 1907, 6 pp. Mining and Scientific Press. American progress in cyanidation during 1910. Jan. 7, 1911,4pp. Bibliography of early articles and books on cyanide process. Nov. 28, 1896, 1 p. Cyanide process. July 2, 1892, 10 pp. MacArthur-Forrest cyanide process. Vol. 65, p. 3, 2 pp. MacArthur-Forrest cyanide process. Vol. 66, p. 36, 1 p. C. Chemistry and Physio-Chemistry of Cyanidation ALDERSON, M. W. Loss of gold in cyanidation by volatilization. M. & S. P., Oct. 29, 1898, 1 p. ANDERSON, I. Regenerating copper cyanide solution. M. & S. P., Feb. 5 and May 28, 1910, 1 p. "More Recent Cyanide Practice, " pp. 352, 355. BECKMAN, J. W. What is a cyanamide ? M. & S. P., Jan. 28, 1911, 1 p. BETTEL, WM. Osmotic pressure, disassociation, and electrolysis. Proc. Ch. & Met. Soc., S. A., vol. 2, 1899, 8 pp. BURGGRAF, J. Efficiency of a lead salt in cyaniding. Mex. Min. Jour., Oct., 1911; abstract in Min. & Eng. World, Nov. 18, 1911. CALDECOTT, W. A. Cyanidation of silver ores. (Chemistry.) M. & S. P., Dec. 12, 1908, 1 p. "More Recent Cyanide Practice," p. 184. Precipitation of gold and silver by soluble sulphides. Eng. & Min. Jour., Apr. 24, 1909, 1 p. Relative efficiency of strong and weak cyanide solutions for dissolving gold. Proc. Ch. & Met. Soc., S. A., vol. 1, 1896, 3 pp. Some features of silver ore treatment in Mexico. Jour. Ch., Met., & Min., Soc., S. A., Jan., 1908, 3 pp., Mar., 3 pp., May, 1 p., June, 1 p., July, 3 pp., Sept., 1908, 1 p.; abstract in Eng. & Min. Jour., June 27, 1908; ab- stract in M. & S. P., Mar. 28, 1908, 2 pp., May 2, 1908, 3 pp., Aug. 29, 1908, 2 pp. CAREY, E. E. Clancy process. Pac. Miner, Nov., 1910. Electrochemical lixiviation. Pac. Miner, Oct., 1909, 2 pp. Electrochemical system of amalgamation and cyanidation. Eng. Mag., Dec., 1909, 7 pp. CARTER, T. L. Notes on cyanide solutions. Eng. & Min. Jour., vol. 73, P. 237, 1 p. CLASSIFIED BIBLIOGRAPHY 219 CHRISTY, S. B. Electromotive force of metals in cyanide solutions. T. A. I. M. E., vol. 30, 1900, 83 pp. Solution and precipitation of gold. T. A. I. M. E., vol. 26, 1896, 37 pp.; vol. 28, 1898, 25 pp.; discussion in Proc. Ch. & Met. Soc., S. A., vol. 2, 1897. CLANCEY, J. C. Clancey process. Min. World, Feb. 11, 1911. Cyanamide process in the metallurgy of gold. Met. & Chem. Eng., Jan., 1911, 6 pp. CLENNELL, J. E. Electrolytic cyanide regeneration. Eng. & Min. Jour., May 27, 1911, 3pp. COEHN (A.) and JACOBSON (C. L.). Passivity of gold. M. & S. P., Mar. 28, 1908. CROSSE, A. F. Regeneration of working cyanide solutions where zinc precipitation is used. Proc. Ch. & Met. Soc., S. A., vol. 3, 1903, 28 pp.; vol. 4, July and Sept., 1903, 8 pp.; abstract in Eng. & Min. Jour., May 30, 1903, 1 p.; discussion, June 20, Sept. 19, and Oct. 31, 1903; abstract in M. & S. P., May 30, 1903, 1 p. Solvent power of various cyanide solutions. Proc. Ch. & Met. Soc., S. A., vol. 1, 1897, 8 pp. DAVIS, W. H. Care of cyanide solutions. Eng. & Min. Jour., July 21, 1904, 1 p. DIXON, W. A. Note on so-called "selective action" of cyanide for gold. Inst. Min. & Met., vol. 6, 1897, 6 pp. EKELEY (J. B.) and TATUM (A. L.). Electrochemistry of solution of gold in cyanide. Elec. & Met. Ind., Apr., 1909, 1 p. ; abstract from West. Ch. & Met. EYE, C. M. Lead acetate in cyanidation. M. & S. P., Jan. 9, 1909. "More Recent Cyanide Practice," p. 246. HAMILTON, E. M. Lead acetate in the cyanidation of silver ores. Mex. Min. Jour., Aug., 1910, 1 p. HOBSON, F. J. Cyanidation in Mexico. (Chemistry with some history.) M. & S. P., Aug. 1 and 8, 1908, 4 pp. "More Recent Cyanide Practice," p. 167. HOLT, T. P. Chemical advances in silver cyaniding. Salt Lake Min. Rev., Jan. 15, 1910, 1 p. Cyanidation of silver ores. (Chemistry.) M. & S. P., Apr. 17, 2 pp., and July 31, 1909, 3 pp. "More Recent Cyanide Practice, " pp. 186 and 282. HUNT, B. Cyanidation in Mexico. (Chemistry.) M. & S. P., Aug. 29, 1908, 1 p. " More Recent Cyanide Practice, " p. 176. Recovery of cyanide. (By precipitating zinc as a sulphate.) M. & S. P., May 4, 1901. JULIAN, H. F. Losses in Cyanidation. Min. Mag., Oct., 1911. LOEVY, J. Notes on action of alkaline sulphides in solutions. Proc. Ch. & Met. Soc., S. A., vol. 1, 1895, 5 pp. LOWDEN, H. B. Phase rule in cyanidation. Met. & Chem. Eng., July, 1911, 1 p. LUNGWITZ, E. E. Lixiviation of gold deposits by vegetation. Eng. & Min. Jour., vol. 69, p. 500, 1 p. 220 TEXT BOOK OF CYANIDE PRACTICE McCAUGHEY, W. J. Solvent effect of ferric and cupric salt solutions upon gold. Jour. Am. Ch. Soc., Dec., 1909, 10 pp. MACTEAR, J. On "selective action" of very dilute solutions of cyanide. Inst. Min. & Met., vol. 4, 1895, 12 pp. Mora (J.) and GRAY (J.). Destruction of cyanide. Jour. Ch., Met., & Min. Soc., S. A., Oct., 1910, 8 pp. MOSHER, D. Chlorine in cyanidation of silver ores. Pac. Miner, May, 1910, 1 p. Clancey process. Pac. Miner, Mar., 1911; Eng. & Min. Jour., Apr. 1, 1911; Min. World, Feb. 11 and Mar. 25, 1911; M. & S. P., Mar. 25, 1911. Cyanidation of silver ores. M. & S. P., May 15, 1909, 3 pp. ORR, W. Regeneration of cyanide solutions. M. & S. P., June 20, 1903. PARKS, J. Notes on action of cyanogen on gold. Inst. Min. & Met., vol. 6, 1897, 1 N pp. PLUNKETT, T. H. Rate of solution of gold in cyanide. Jour. Can. Min. Inst., vol. 7, p. 192, 6 pp. SCHNEIDER, E. A. Contributions to chemistry of cyanide process. Eng. & Min. Jour., vol. 60, pp. 489 and 514, 2 pp. SEAMON, W. H. Chemistry of cyanide process. Mex. Min. Jour., Aug., 1910, 1 p. SHARWOOD, W. J. Analysis of (four) cyanide mill solutions. Eng. & Min. Jour., Aug. 20, 1898, 1 p. Cyanidation of silver ores. (Chemistry.) M. & S. P., Sept. 26, 1908, 3 pp. "More Recent Cyanide Practice, " p. 178. Double cyanides of zinc with potassium and with sodium. Eng. & Min. Jour., May 26, 1904. Notes on action of potassium zinc cyanide solutions on gold. Eng. & Min. Jour., Oct. 2, 1897, 1 p.; Oct. 9, 1897, 1 p.; Oct. 16, 1897, 2 pp. SIMPSON, D. Two deterrents (lime and oil) to the dissolution of free gold in cyanide process. Inst. Min. & Met., vol. 17, 1908, 1 p.; abstract in Eng. & Min. Jour., Oct. 10, 1908. STUART, J. B. Theory of dissolution of metals by cyanide. M. & S. P., Aug. 6, 1910, 2 pp. SULMAN, H. L. Notes on behavior of haloid elements in conjunction with cyanide process. Proc. Ch. & Met. Soc., S. A., vol. 1, 1895, 14 pp. TIPPETT, J. M. Effect on solubility of gold when ore is crushed between iron surfaces. Met. & Ch. Eng., Sept., 1910, 1 p. VON OETTINGEN, A. Theory of solutions. Proc. Ch. & Met. Soc., S. A., vol. 2, 1899, 10 pp. WARWICK, A. W. Notes on the Clancy process and its operation. Min. World, Feb. 4, 1911, 1 p. Rate of solution of gold in cyanide solutions. Eng. & Min. Jour., June 29, 1895, 2 pp. Regeneration of cyanide solutions. Min. Sci., Feb. 9, 1911, 1 p. WELLS, J. S. C. Is zinc potassium cyanide a solvent for gold? Eng. & Min. Jour., Dec. 21, 1895, 1 p. WHEELOCK, R. P. Tests on acid regeneration of copper cyanide solutions. CLASSIFIED BIBLIOGRAPHY 221 M. & S. P., Dec. 18, 1909, 5 pp.; Mar. 12, 1910, 1 p. "More Recent Cyanide Practice, " pp. 341 and 352. WHITE, H. A. Solubility of gold in thiosulphates and thiocyanates. Jour. Ch., Met., & Min. Soc., S. A., Oct., 1905, 3 pp.; Dec., 1905, 1 p.; Jan., 1906, 1 p.; Mar., 1906, 1 p. ZACHERT, V. Electrolytic difficulties in Clancy process. Min. & Met. Jour., Sept., 1911, 2 pp; Min.. & Eng. World, Nov. 4, 1911, 2 pp. Engineering and Mining Journal. Care of cyanide solutions. Vol. 78, p. 103. Clancy process of ore treatment. Dec. 24, 1910, 1 p. New Clancy cyanide patents. Oct. 8, 1910, 3 pp. Cyanogen. Mar. 16, 1905. Mexican Mining Journal. Clancy process. Sept., 1910, 1 p. Mining World. New Clancy method of ore treatment. Oct. 15, 1910, 3pp. Pacific Miner. Clancy process. Nov., 1909, 1 p.; May, 1910; Oct., 1910, 4pp. D. Aeration and Oxidation ALDRICH, T. H. Electrolytic oxygen in cyanide solutions. Min. & Eng. World, Oct. 21, 1911, 2 pp. BANKS, J. H. G. Upward leaching of sand. Eng. & Min. Jour., July 22, 1911, 1 p. CROSSE, A. F. Assisting the solution of gold in cyanide process by com- pressed air. Jour. Ch., Met., & Min. Soc., S. A., Aug., 1907, 1 p. DEANE, A. J. Aeration of sand charges. Eng. & Min. Jour., July 29, 1911. DURANT, H. T. Application of oxygen in cyanide process. Proc. Ch. & Met. Soc., S. A., vol. 2, 1897, 5 pp. GROPELLO, E. F. Dorcas pneumatic cyanide mill. M. & S. P., May 11, 1901, 1 p. GROTHE, A. Use of . compressed air in cyanidation. Min. World, Jan. 11, 1908, 1 p. HUBBARD, J. D. Cyaniding concentrate at Taracol, Korea. (Includes aeration.) M. & S. P., Oct. 2, 1909, 2 pp. " More Recent Cyanide Practice, " p. 318. JAMES, G. A. Preliminary treatment of water and air in cyanide process. M. & S. P., Sept. 30, 1911. JULIAN, H. F. Action of oxygen in cyanide solutions. M. & S. P., Oct. 27, 1906, 1 p. "Recent Cyanide Practice," p. 155. Abstract from Jour. Ch., Met., & Min. Soc., S. A. How oxygen assists and retards the dissolution of gold in cyanide. M. & S. P., Dec. 30, 1905, 1 p. MEGRAW, H. A. Oxidation and cyanidation. Eng. & Min. Jour., Oct. 2, 1909, 2 pp. MOSHER, D. Ozone in treatment of silver ores in cyaniding. Pac. Miner, Sept., 1909, 4 pp. OHLY, J. Pneumatic process for leaching and cyaniding. M. & S. P., Apr. 27, 1901, 1 p. 222 TEXT BOOK OF CYANIDE PRACTICE TAYS, E. A. H. Cyanide notes on leaching and aeration. M. & S. P., Sept. 1, 1906, 2 pp. TERRY, J. T. Oxidizing agents in cyanide mill solutions. M. & S. P., Aug. 30, 1902. Mining and Scientific Press. Barium dioxide. (Results of use in cyanid- ing.) M. & S. P., Nov. 15, 1902. Begeer cyanide process. (Aeration of solution.) May 31, 1902. E. Commercial Cyanide and its Analysis ALLEN, A. H. Manufacture and impurities of commercial cyanide. Eng. & Min. Jour., vol. 76, p. 239, 1 p., p. 241. BELL, RALSTON. Commercial cyanide. (Concerning estimation.) Eng. & Min. Jour., July 30, 1910, 1 p. Rapid analysis of commercial cyanide. Eng. & Min. Jour., May 28, 1910, 2pp. Spurious potassium cyanide. Eng. & Min. Jour., May 21, 1910, 1 p. BETTEL, WM. Fixture of atmospheric nitrogen in cyanide manufacture. S. A. Min. Jour., Aug. 7, 1909, 1 p. CLENNELL, J. E. Commercial potassium cyanide. Eng. & Min. Jour., June 25, 1910, 1 p. Methods of determining potassium in sodium cyanide. Eng. & Min. Jour., June 25, 1910, 1 p. Spurious potassium cyanide. Eng. & Min. Jour., Jan. 15, 1910, 1 p. DOVETON (G.) et al. Impurities in commercial cyanide. Eng. & Min. Jour., Mar. 28, Apr. 4, Apr. 11, May 2, and Aug. 15, 1903. DURANT, H. T. Notes on commercial cyanide. Eng. & Min. Jour., Aug. 18, 1906, 1 p. EWAN, T. Estimation of sulphide in alkali cyanide. Jour. Soc. Ch. Ind., Jan. 15, 1909, 3 pp. FELDTMAN (W. R.) and BETTEL (WM.). Notes on estimation of sulphides and cyanates in commercial cyanide. Proc. Ch. & Met. Soc., S. A., vol. 1, 1896, 9 pp. HAMILTON, E. M. Spurious potassium cyanide. Eng. & Min. Jour., Feb. 12, 1910, 1 p. HOLBROOK, E. A. Sodium cyanide. (Undesirable.) M. & S. P., May 16, 1908. "More Recent Cyanide Practice," p. 142. LAWRIE, R. B! Use of cyanide of sodium. M. & S. P., May 7, 1904, lp. LOEVY, J. Estimation of sulphides in cyanides. Proc. Ch. & Met. Soc., S. A., vol. 2, 1899, 3 pp. MAGENAU, W. Negative experience with sodium cyanide. Eng. & Min. Jour., Aug. 25, 1906. MOORE, T. W. Composition of commercial cyanide of potassium. Jour. Soc. Ch. Ind., Mar. 31, 1902. OLDFIELD, F. W. Commercial cyanide. Eng. & Min. Jour., May 2, 1903. Ross, F. A. Spurious potassium cyanide. Eng. & Min. Jour., Oct. 23, 1909, and Apr. 2, 1910. CLASSIFIED BIBLIOGRAPHY 223 SEAMON, W. H. Analysis of commercial cyanide. In "A Manual for Assayers and Chemists," 1910. SHARWOOD, W. J. Commercial sodium and potassium cyanide. (Includ- ing bibliography.) Eng. & Min. Jour., Mar. 19, 1910, 3 pp. SNODGRASS, J. Manufacture of cyanide. S. A. Mines, Aug. 31, 1907, 1 p. STAYER, W. H. Strength of cyanide. Eng. & Min. Jour., Sept. 16, 1905. WHITBY, W. A. Noles on commercial cyanide of potassium. (With determinations.) Proc. Ch. & Met. Soc., S. A., vol. 3, 1902-1903, 7 pp.; abstract in Eng. & Min. Jour., Feb. 28, 1903, 1 p. Engineering and Mining Journal. Sodium cyanide. July 14, 1904. The two cyanides. June 29, 1905. Mining and Scientific Press. Sodium cyanide in practice. Aug. 5 and Sept. 16, 1905. F. Analytical Chemistry of Cyanide Solution AD AIR, A. Estimation of cyanide. Eng. & Min. Jour., Apr. 11, 1903; abstract from Jour. Ch., Met., & Min. Soc., S. A. ALLEN, A. W. Titrating cyanide- solution in presence of silver. M. & S. P., JulyS, 1911. BAILAR, J. C. Potassium cyanide and silver nitrate. (Titration.) Min. World, Aug. 13, 1910. BELL, R. Protective alkalinity in cyanide solutions. Eng. & Min. Jour., July 2, 1910, 1 p. BETTEL, WM. Estimation of oxygen in working cyanide solution. Proc. Ch. & Met. Soc., S. A., 1896, vol. 1, 5 pp. Technical analysis of working cyanide solutions. Proc. Ch. & Met. Soc., S. A., vol. 1, 1895, 8 pp. BROWNE, R. S. Estimation of efficiency of solutions. Pac. Miner, May, 1910. BROWNING (P. E.) and PALMER (H. E.). Method for qualitative separation and detection of ferrocyanides, ferricyanides, and sulphocyanides. Am. Jour. Sci., June, 1907, 3 pp. BULLOCK, L. N. B. Cyanide practice at Copala. (Estimation of pro- tective alkalinity.) M. & S. P., June 8 and Nov. 23, 1907, Jan. 11, 1908. BURGGRAF, J. Notes on normal acid and alkali solutions. Mex. Min. Jour., Aug., 1910. CLENNELL, J. E. Analytical work in connection with cyanide process. Trans. Inst, Min. & Met., vol. 12, 1903, 24 pp.; abstract in Eng. & Min. Jour., June 27, 1903, 1 p. Cyanide solution test at Creston-Colorado plant. Mex. Min. Jour., Aug., 1910, 2 pp. Estimation of available cyanide. Eng. & Min. Jour., Mar. 31, 1904, 1 p. Estimation of chief constituents in cyanide solutions. Eng. & Min. Jour., June 29, 1905, 2 pp. Estimation of cyanide in cyanide solutions. Eng. & Min. Jour., July 4, 1903, 1 p.; abstract from Inst. Min. & Met., vol. 12, 1903. 224 TEXT BOOK OF CYANIDE PRACTICE Estimation of cyanogen in impure solutions. Eng. & Min. Jour., June 22, 1895, 2 pp. Examination of various methods for estimation of ferrocyanides. Eng. & Min. Jour., Nov. 7, 1903, 3 pp. Manganese in cyanide solutions. (Detection, estimation, etc.) Eng. & Min. Jour., Nov. 24, 1904. Notes on analysis of cyanide solutions. Proc. Ch. & Met. Soc., S. A., vol. 1, 1895, 7 pp. COLLINGRIDGE, B. Errors due to presence of potassium iodide in testing cyanide solutions for protective alkalinity. Inst. Min. & Met., Jan. 20, 1910, 3pp. CRANE, W. R. Bibliography of chemical analysis in cyaniding. In "Index of Mining Engineering Literature," 1 p. CROSSE, A. F. Analysis of cyanide solutions. Proc. Ch. & Met. Soc., S. A., vol. 3, 1902, 12 pp. Estimation of oxygen in working cyanide solutions. Proc. Ch. & Met. Soc., S. A., vol. 2, 1898, 14 pp. Estimation of protective alkali in cyanide solutions. Proc. Ch. & Met. Soc., S. A., vol. 2, 1899, 7 pp. DEL MAR (A.) et al. Estimation of cyanide in mill solutions. M. & S. P., Jan. 15, Mar. 26, and Apr. 16, 1910. . GREEN, L. M. Estimation of sulpho- and ferricyanides, etc., in cyanide solutions containing copper. Inst. Min. & Met., vol. 18, 1908, 7 pp. Method of testing cyanide solutions containing zinc. Inst. Min. & Met., vol. 10, 1901, 12 pp. Use of mercuric chloride in testing cyanide solutions. M. & S. P., Jan. 28, 1905. HAMILTON, E. M. Silver in sulphocyanide determinations. M. & S. P., Mar. 11, 1911, 1 p. JAY, C. H. Duties of cyanide chemist. Eng. & Min. Jour., Oct. 17, 1908, 1 p.; abstract from West. Ch. & Met. Laboratory methods used in modern cyanide mills. West. Ch. & Met., May, 1908, 8 pp. Some laboratory methods in use at cyanide plant of Golden Sunlight and Ohio mining properties. West. Ch. & Met., Sept., 1906, 3 pp. PRISTER, A. Industrial method for determination of oxygen in working cyanide solutions. Jour. Ch., Met., & Min. Soc., S. A., Apr., 1904, 5 pp.; May, 1904. SHARWOOD, W. J. Analysis of (four) cyanide mill solutions. Eng. & Min. Jour., Aug. 20, 1898, 1 p. Estimation of cyanide effluents. (Protective alkalinity.) Eng. & Min. Jour., Aug. 8, 1908; abstract from Jour. Ch., Met., & Min. Soc., S. A. Estimation of cyanogen. Jour. Am. Ch. Soc., May, 1897. TREADWELL, W. D. Titration of potassium cyanide in presence of potas- sium ferrocyanide. M. & S. P., Nov. 11, 1911. VAN OSDEL, E. R. Alkaline zinc titration. Eng. & Min. Jour., vol. 82, p. 1110. WILLIAMS, G. W, Determination of (chemical) constants in" working CLASSIFIED BIBLIOGRAPHY 225 cyanide solutions. Jour. Ch., Met., & Min. Soc., S. A., Feb., 1904, 12 pp.; May, 1904, 7 pp. Mining and Scientific Press. Crosse's method of determining oxygen in cyanide solutions. May 3, 1902. G. Assaying, Samplers, and Sampling ARENTS, A. Test for precious metals in cyanide solutions. T. A. I. M. E., vol. 34, 1903, 1 p.; abstract in Eng. & Min. Jour., Mar. 21, 1903; abstract in M. & S. P., Apr. 18, 1903. BARTON, W. H. Assay scheme for cyanide solutions. (Chiddy method.) West. Ch. & Met., Feb., 1908, 1 p.; abstract in Eng. & Min. Jour., Aug. 8, 1908. BETTEL, WM. Estimating gold in cyanide solutions. Min. World, July 16, 1910, 1 p.; abstract from S. A. Min. Jour. Colorimetric estimation of gold in cyanide solutions. Min. & Eng. World, Nov. 11, 1911; abstract from S. A. Min. Jour. BIRD, F. A. Assay of cyanide precipitate. M. & S. 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Assay of cyanide solutions. Eng. & Min. Jour., Dec. 5, 1903. LINDEMAN, M. Assay of cyanide solutions. Eng. & Min. Jour., July 7, 1904. LODGE, R. W. Assay of zinc-box precipitate. T. A. I. M. E., vol. 34, 1903, 19 pp. See "Notes on Assajdng" by Lodge. MACFARREN, H. W. Sand-tank sampler. M. & S. P., Nov. 30, 1907, and Nov. 7, 1908. McMiLLEN, D. A. An auto-hydraulic sampling device. Eng. & Min. Jour., Nov. 19, 1910, 1 p. MAGENAU, W. Assay of cyanide solutions. (Various typical methods.) M. & S. P., Apr. 14, 1906, 3 pp. "Recent Cyanide Practice," p. 42. 226 TEXT BOOK OF CYANIDE PRACTICE MARTEL, J. L. Assay of cyanide solutions. West. Ch. & Met., Apr., 1907, 1 p. MILLER, G. D. Assay of cyanide solutions. Eng. & Min. Jour., June 23, 1904. MOIR, J. New and rapid method of detecting and estimating gold in working cyanide solutions. Jour. Ch., Met., & Min. Soc., S. A., Sept., 1903, 2 pp.; Mar., 1904, 3 pp.; abstract in M. & S. P., Nov. 28, 1903, 1 p. MONAHAN, F. W. Device for sampling zinc-box solutions. Eng. & Min. Jour., Mar. 12, 1910. PEAD, C. H. Automatic sampler for tailings, sands, and slimes. Proc. Ch. & Met. Soc., S. A., vol. 3, 1903, 2 pp.; abstract in M. & S. P., June 17, 1903, 1 p. PICKETT, T. L. Lead tray method of assaying cyanide solutions. Pac. Miner, May, 1910, 1 p. PRISTER, A. Colorimetric method for determination of gold in cyanide solutions. Jour. Ch., Met., & Min. Soc., S. A., Dec., 1903, 2 pp.; abstract in Eng. & Min. Jour., Feb. 25, 1904, 1 p. Purple of Cassius test for use in cyanide works. Jour. Ch., Met., & Min. Soc., S. A., June, 1904. SEAMON, W. H. Methods for assaying in cyanide plants. West. Ch. & Met., Aug., 1909, 4 pp.; abstract in Eng. & Min. Jour., Sept. 25, 1909. See "A Manual for Assayers and Chemists" by Seamon. SIMPSON, D. Sand sampling in cyanide works. Inst. Min. & Met., vol. 16, 1906, 12 pp. Engineering & Mining Journal. Filter for slime samples. Nov. 11, 1911. Mining World. Automatic tailing samplers. 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P., Feb. 18 and 25, 1899, 2 pp. CLEVENGER, G. H. Agitator for cyanide tests. M. & S. P., May 29, 1909, 1 p, "More Recent Cyanide Practice," p. 278. CLASSIFIED BIBLIOGRAPHY 227 DENNY, H. S. Grading analyses. Eng. & Min. Jour., Mar. 9, 1905, 1 p.; M. & S. P., Mar. 25, and Apr. 1, 1905, 2 pp.; abstract from S. A. Ass. of Engrs. FURMAN, H. VAN F. Laboratory tests in connection with extraction of gold from ores by cyanide process. T. A. I. M. E., vol. 26, 1896, 13 pp.; abstract in M. & S. P., Nov. 7 to Dec. 5, 1896. See "A Manual of Practical Assaying" by Furman. ^ GAYFORD, E. Mill tests. M. & S. P., May 16, 1908. Ore testing at Salt Lake City. M. & S. P., Jan. 25, 1908, 3 pp. GLOVER, A. L. Simple laboratory agitator. Eng. & Min. Jour., Aug. 5, 1911. HALLETT, S. I. Treatment of oxidized silver-lead ores of Aspen, Colo., in laboratory by cyanide. M. & S. P., May 2, 1903, 1 p. HYDER, F. B. Estimation of pulp from its specific gravity. Proc. Colo. Sci. Soc., Nov., 1910, 7 pp.; abstract in Mines & Mins., July, 1911, 2 pp. LAMB, M. R. Rapid estimation of pulp in cyanide tanks. Eng. & Min. Jour., Jan. 15, 1910, 1 p. LAWLOR, T. S. Brown type of laboratory agitator. M. & S. P., Aug. 7, 1909, 1 p. "More Recent Cyanide Practice, " p. 290. MERRILL, C. W. MacArthur-Forrest process. Experiments in the met- allurgical laboratory. M. & S. P., Apr. 23, 1892, 1 p. NUTTER, E. H. Simple solution meter. M. & S. P., Dec. 1, 1906, 1 p. "Recent Cyanide Practice," p. 170. RIEBLING, H. F. A. Notes on preliminary cyanide work. (Laboratory testing.) West. Ch. & Met., Oct., 1907, 5 pp. Recommending the cyanide process. (Concerning laboratory tests.) Min. Reptr., Feb. 28, 1907, 1 p. ROBERTSON, J. J. Cyanide tests on Temiskaming ores. Jour. Can. Min. Inst., vol. 9, p. 396, 6 pp. SHARWOOD, W. J. Measurement of pulp and tailing. Min. Mag., Nov., 1909, to Jan., 1910, 23 pp. Reprinted in pamphlet form. SIMMONDS, E. H. Laboratory investigation of ore. Pac. Miner, Oct., 1909, 2 pp. Place and value of small scale ore tests. M. & S. P., Apr. 22 and 29, 1905, 2 pp.; abstract from Trans. Cal. Miners' Assn. SIMPSON, D. I. R. New method of obtaining density of settled sand. Jour. Ch., Met., & Min. Soc., S. A., Dec., 1906, 1 p. SPAULDING, C. F. Measuring spacific gravity in agitators. M. & S. P., Sept. 16, 1911. STABLER, H. Grading analyse -.d their application. Bull. Inst. Min. & Met., May 19, 1910, 14 pp. Grading analyses and their application. Jour. Ch., Met., & Min. Soc., S. A., May, 1910, 7 pp.; Dec., 1910, 7 pp. STEINEN, C. Solution meter. Eng. & Min. Jour., Oct. 7, 1911. TOOMBS, C. Screen assay on Meyer and Charlton under "the new metal- lurgy." Jour. Ch., Met., & Min. Soc., S. A., Mar., 1907, 2 pp.; May, 1907, 2 pp.; June, 1907, 3 pp.; Aug., 1907, 2 pp. YATES, A. Grading assays and grinding efficiencies. Jour. Ch., Met., & 228 TEXT BOOK OF CYANIDE PRACTICE Min. Soc., S. A., Dec., 1908, 3 pp.; Jan., 1909, 1 p.; Apr., 1909, 2 pp.; May, 1909, 1 p.; abstract in M. & S. P., May 1, 1909, 1 p". YOUNG, G. J. Method of slime testing. Min. Mag., Aug., 1910, 1 p. Mining and Scientific Press. Bibliography of testing ores preliminary to cyaniding. M. & S. P., Nov. 11, 1905. 7. Alkalinity and Lime BARNEY, L. W. Rapid estimation of available calcium oxide in lime used in cyanide process. Trans. A. I. M. E., Oct., 1911. Abstract in Eng. & Min. Jour., Nov. 18, 1911; in Min. & Eng. World, Nov. 4, 1911; in M. & S. P., Oct. 14, 1911. BEALL, R. S. Determination of causticity of lime. West. Ch. & Met., Oct., 1905, 2 pp. BISHOP, L. D. Notes on cyanidation. (Lime and increased temperature.) Electrochem. & Met. Ind., Feb., 1909, 2 pp.; Eng. & Min. Jour., Apr. 24, 1909, 2 pp.; Min. World, Mar. 13, 1909, 2 pp.; abstract from Proc. Colo. Sci. Soc. BULLOCK, L. N. B. Cyanide practice at Copala, Mexico. (Increasing protective alkalinity.) M. & S. P., June 8, 1907, 1 p. "Recent Cyanide Practice," p. 231. CROGHAN, E. H. Notes on estimation of caustic lime. Jour. Ch., Met., & Min. Soc., S. A., Aug., 1907, to Jan., 1908, 20 pp. DEL MAR, A. Precipitation of gold by lime. Eng. & Min. Jour., Jan. 15, 1910. GARDNER, B. L. Action of alkaline solutions in cyaniding weathered py- ritic tailing. Jour. W. A. Cham, of Mines, Oct. 31, 1907, 4 pp. GAYFORD, E. Use of lime as an alkaline reagent in cyaniding. M. & S. P., Jan. 3, 1903, 1 p. GRAY, J. Influence of moist air on quicklime. Jour. Ch., Met., & Min. Soc., S. A., May, 1909, 1 p. HOLT, T. P. Lime reactions in Cyaniding. Mines & Mins., Mar., 1911, 1 p. SHARWOOD, W. J. Laboratory tests on use of coarse and fine lime for cyaniding. Jour. Ch., Met., & Min. Soc., S. A., Apr., 1908, 5 pp.; abstract in Eng. & Min. Jour., Aug. 8, 1908. SWEETLAND, E. G. Use of alkalis in cyanide process. M. & S. P., July 25, 1903. WILLIAMS, G. W. Notes on lime, clean-up, etc. Jour. Ch., Met., & Min. Soc., S. A., July to Sept., 1905, 7 pp. Engineering and Mining Journal. Lime and caustic soda in cyaniding. Vol. 82, p. 771. J. Classification, Dewatering, and Settlement ALMETTE, S. Notes on classifiers. (For tube mills.) Min. Sci., Dec. 30, 1909, 1 p. ASHLEY, H. E. Chemical control of slime. T. A. I. M. E., vol. 41, 1910, 16pp. Colloid matter of clay and its measurement. U. S. Geol. Survey, Bull. No. 388, 1909, 65 pp. CLASSIFIED BIBLIOGRAPHY 229 Theory of settlement of slime. M. & S. P., June 12 and Aug. 28, 1909, 2 pp. AYTON, E. F. Sand and slime separation at Arianena mill. Pac. Miner, Nov., 1910, 2 pp. BAILDON, S. R. Free settlement method of separating slime. M. & S. P., Oct. 23, 1909, 1 p. BIGELOW, D. E. Water consumption in ore treatment, Kalgoorlie, W. A. M. & S. P., Apr. 23, 1904. Boss, M. P. Segregation of solids in liquids. M. & S. P., Sept. 9, 1911. BROOKS, H. J. Sand collecting. M. & S. P., Dec. 4, 1909. "More Recent Cyanide Practice, " p. 302. BROWN, S. E. . 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Jour. Frank- lin Institute, June and July, 1910, 29 pp. FULTON, C. H. Separation of sand from slime in cyanide process. (Home- stake and Hidden Fortune mills.) Mines & Mins., Dec., 1904. GARDNER, B. L. Slime settlement. Min. & Eng. World, Nov. 11, 1911; Eng. & Min. Jour., Sept. 2, 1911; Min. Mag. ; Aug., 1911; abstract from Jour. W. A. Cham. Mines, May, 1911. HAMILTON, E. M. All-sliming. (Sand collection.) M. & S. P., Aug. 21, 1909, 1 p. "More Recent Cyanide Practice," p. 293. HUNTLEY, R. E. Slime settler or dewaterer at Kalgoorlie. Jour. W. A. Cham, of Mines, July 30, 1910. JOHNSON, E. H. Classification of tailing pulp prior to cyaniding. Jour. Ch., Met., & Mm. Soc., S. A., Oct., 1910, 8 pp.; Jan. and Feb., 1911, 7 pp. Classification of tailing pulp. Min. & Eng. World, July 15, 1911, 1 p. JOHNSON, J. E. Removal of sand from waste water in ore dressing oper- ations. Eng. & Min. Jour., Dec. 31, 1903, 1 p. " Notes on Metallurgical Mill Construction. " NEAL, W. 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(Dewatering tank and device.) Eng. & Min. Jour., Dec. 10, 1903, 2 pp. "Notes on Metallurgical Mill Con- struction. " SPERRY, E. A. Handling slime, with special reference to sizing and classi- fication. West. Ch. & Met., Mar., 1908, 12 pp. STRICKLAND, H. Decantation tank for utilizing waste water. Min. Sci., Oct. 7, 1909, 2 pp. SULMAN, H. L. Slime settlement. Eng. & Min. Jour., Oct. 31, 1908; abstract from Inst. Min. & Met. TAYS, E. A. H. Experience in water recovery.. (Slime settling.) M. & S. P., Aug. 19 and Oct. 28, 1905, 1 p. WIARD, E. S. Syphon device for removing floating material. M. & S. P. Feb. 2, 1907, 1 p. "Recent Cyanide Practice," p. 215. WILLIS, H. T. Separation and settlement of slime. M. & S. P., July 25, 1908, 1 p. Engineering and Mining Journal. Method of handling slime and tailing. (Conveying and dewatering.) Eng. & Min. Jour., Apr. 9, 1910, 1 p. South African Mining Journal. Sand classification on Rand. (Diaphragm classifiers.) July 1,1911. K. Sand Treatment and Percolation ALDERSON, M. W. Cyaniding slimy ores and tailing. M. & S. P., June 3 to July 1, 1899, 5 pp. BOTSFORD, R. S. Method of leaching gold ore tailing. Inst. Min. & Met., vol. 16, 1907, 1 p. CALDECOTT, W. A. Use of vacuum pump in cyaniding of sand. Jour. Ch., Met., & Min. Soc., S. A., Jan., 1909, 1 p.; abstract in M. & S. P., Feb. 27, 1909, 1 p. CALDECOTT (W. A.) and JOHNSTON (A. M.). Elimination of gold-bearing solution from sand. Jour. Ch., Met., & Min. Soc., S. A., Nov., 1907, 1 p. CROSSE, A. F. Treatment of slimy material with cyanide. Min. World, Feb. 12, 1910, 2 pp.; abstract from Jour. Ch., Met., & Min. Soc., S. A. DENNY, H. S. Cyanide treatment of sand on the Rand. M. & S. P., Sept. 19, 1903, 2 pp.; abstract from Jour. Ch., Met., & Min. Soc., S. A. CLASSIFIED BIBLIOGRAPHY 231 DURANT, H. T. Upward leaching of sand. Eng. & Min. Jour., Feb. 25, 1911, 1 p. FELL, E. N. Treatment of tailing by the cyanide process at Athabasca mine, Nelson, B. C. T. A. I. M. 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Ch., Met., & Min. Soc., S. A., July, 1911, 4 pp.; S. A. Min. Jour., July 29, 1911, 2 pp. ALLEN, R. Air-lift agitation of slime pulp. Jour. Ch., Met., & Min. Soc., S. A., Mar., 1911, 3 pp.; April, 1911, 4 pp.; June, 1911, 2 pp. APLIN, D. G. Slime treatment. M. & S. P., Jan. 23, 1904, 1 p. BETTEL, W. Slime treatment by Adair-Usher process. S. A. Min. Jour., Nov. 6, 1909, 1 p. 232 TEXT BOOK OF CYANIDE PRACTICE BRODIE, W. Cyanide lixiviation by agitation. Eng. & Min. Jour., Apr. 3, 1909, 1 p. BROWN, F. C. Agitation by compressed air with Brown tanks. M. & S. P., Sept. 26, 1908, 3 pp. "More Recent Cyanide Practice," p. 210. B. and M. circulating tank. N. Z. Mines Record, Oct. 16, 1907, 5 pp. BUEL, J. F. Modified form of Pachuca tank. Min. & Eng. World, Nov. 11, 1911. CALDECOTT, W. A. Discrepancies in slime treatment. (Including sub- ject of specific gravity with complete specific gravity table of slime pulp.) Proc. Ch. & Met. Soc., S. A., vol. 2, 1898, 17 pp. Solution of gold in accumulated and other slime. Proc. Ch. & Met. Soc., S. A., vol. 2, 1897, 6 pp. CARTER, T. L. Slime problem. Eng. & Min. Jour., Mar. 27, 1904, 3 pp. CLARK, W. C. Saving slime. Mines & Mins., vol. 21, p. 343, 1 p. CROSSE, A. F. Treatment of ore slime. Jour. Ch., Met., & Min. Soc., S. A., Nov., 1909, 2 pp.; abstract in Eng. & Min. Jour., Feb. 26, 1910. DE KALB, C. Trapezoidal slime agitator. Eng. & Min. Jour., vol. 77, p. 241, 1 p. DENNY, H. S. Slime treatment on the Rand. Eng. & Min. Jour., Oct. 24, 1903, 3 pp. DORR, J. V. N. Continuous cyanidation. Met. & Chem. Eng., Sept., 1911, 1 p. EGGERS, J. H. Continuous agitation and decantation in Pachucas. Pac. Miner, Feb., 1911, 1 p. EHRMANN, L. Sampling, analyzing, and treating slime. Proc. Ch. & Met 1 . Soc., S. A., vol. 2, 1899, 8 pp. FLEMING, J. Extraction of gold from cyanide house slime by a wet method. Proc. Ch. & Met. Soc., S. A., vol. 3, 1903, 12 pp.; abstract in Eng. & Min. Jour., Sept. 5, 1903, 1 p. FRASER, L. New cyanide device for agitating. M. & S. P., Oct. 15, 1910, Ip. Notes on slime treatment process. Min. World, July 17, 1909, 1 p. FULTON, C. H. Treatment of slime by cyanidation in Black Hills. Eng. & Min. Jour., Nov. 3, 1904, 1 p. GLAZE, H. L. Principles of air-lift pumps (and agitators). Min. & Eng. World, Sept. 23, 1911. GROTHE, A. Notes on cyaniding in Pachuca tanks and continuous system. Mex. Min. Jour., Aug., 1910, 3 pp. Principles governing agitation in Pachuca tanks. Min. World, May 27, 1911, 1 p. Principles of agitation in Pachuca tanks. M. & S. P., July 15, 1911; Mex. Min. Jour., July, 1911. HALEY, C. S. Recent progress in slime-filtration development. M. & S. P., July 1, 1911, 1 p. HURTER, C. L. Agitation process for cyaniding slime. Eng. & Min. Jour., Jan. 19, 1901, 1 p. IRWIN, D. F. Continuous decantation. M. & S. P., July 22, 1911. JAMES, A. Lixiviation of slime. Eng. & Min. Jour., vol. 67, p. 378. CLASSIFIED BIBLIOGRAPHY 233 Notes on process for treating slime without filtration or decantation. Inst. Min. & Met., vol. 7, 1898, 11 pp. " JAY, C. H. Continuous dewatering, agitating, and filtering cyanide process. Min. Sci., June 3, 1909, 2 pp. KLUG, G. C. Slime treatment for extraction of gold. Jour. W. A. Cham, of Mines, June 30, 1910, 4 pp. KNIFFEN, L. M. Metnods of pulp agitation. M. & S. P., June 4, 1910, 1 p. "More Recent Cyanide Practice, " p. 401. KURYLA, M. H. Continuous Pachuca tank agitation at Esperanza mill. Trans. Mex. Inst., Apr., 1910, 7 pp.; abstract in Eng. & Min. Jour., July 30, 1910, 1 p.; abstract in Min. World, July 9, 1910, 1 p. Continuous agitation process with bottom drive storage tank at Esperanza mill. Mex. Min. Jour., Aug., 1910, 2 pp. LAMB, M. R. Charge and series systems of cyaniding slime. Min. World, Feb. 19, 1910, 2 pp.; abstract from T. A. I. M. E. Cyaniding slime. T. A. I. M. E., vol. 40, 1909, 5 pp.; vol. 41, 1910, 6 pp. New cyanide plant. 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A., vol. 2, 1898, 2 pp. LYLE, G. G. Solis compressed-air slime agitator. West. Ch. & Met., Dec., 1907, 4 pp. McCANN, F. Proposed new system for cyanide treatment of slime. Can. Min. Jour., Sept. 15, 1909, 3 pp.; Min. World, Nov. 6, 1909, 2 pp.; abstract from Trans. Mex. Inst. MACDONALD, B. Improvements in cyanide process. (Agitation tank.) M. & S. P., May 28, 1910, 2 pp. " More Recent Cyanide Practice, " p. 396. MACDOXALD, B. Parral tank system of slime agitation. Min. & Eng. World, Oct. 28, 1911, 3 pp.; abstract from Trans. A.I.M.E. MclxTYRE, A. C. A. Z. agitator. Pac. Miner, Jan., 1910, 2 pp. MEGRAW, H. A. All-slime treatment of ore in cyanide plant. Eng. & Min. Jour., Feb. 5, 1910, 2 pp. 234 TEXT BOOK OF CYANIDE PRACTICE Discussion of some continuous processes for cyanide treatment of silver- gold ores. Mex. Min. Jour., Aug., 1910, 4 pp. What is a slime? Eng. & Min. Jour., Nov. 3, 1904. MENNELL, J. L. Continuous cyanide treatment. Mex. Min. Jour., Feb., 1909, 3 pp. NAHL, A. C. Nahl intermittent slime decanter. Eng. & Min. Jour., Feb. 11, 1911, 1 p. NARVAEZ, F. Cyanidation with Brown vat. M. & S. P., Nov. 30, 1907, 1 p. "More Recent Cyanide Practice," p. 60. O'HARA, J. D. Treatment of accumulated slime. Mex. Min. Jour., Sept., 1910, 2 pp. PEAD, C. H. Notes on improvements in cyanide treatment of sands and slimes. Jour. Ch., Met., & Min. Soc., S. A., Sept., 1905, 2 pp.; Dec., 1905, 1 p.; Jan., 1906, 2 pp.; Feb., 1906, 2 pp. PEARCE, S. H. Assay of slime residue. (Discrepancies.) Jour. Ch., Met., & Min. Soc., S. A., May, 1909, 1 p. Cyaniding low grade slime. M. & S. P., Nov. 28, 1903, 1 p.; abstract from Jour. Ch., Met., & Min. Soc., S. A. RAND, E. T. Continuous process of slime treatment. Proc. Ch. & Met. Soc., S. A., vol. 2, 1899, 9 pp. ROTHWELL, J. E. Continuous cyanide treatment. Met. & Chem. Eng., July, 1911, 1 p. Counter-current of continuous agitation, decantation, and dilution applied to cyanide process. Met. & Chem. Eng., Sept., 1911, 2 pp. SHARWOOD, W. J. What constitutes a slime. Eng. & Min. Jour., Oct. 10 and 31, 1903, 1 p. SPILSBURY, E. G. Improvement in cyanide practice. (Just silica brick agitation process.) T. A. I. M. E., vol. 41, 1910, 14 pp.; abstracts in Eng. & Min. Jour., Mar. 26, 1910, 1 p.; in Min. Sci., June 9, 1910, 5 pp.; in Min. World, June 4, 1910. STACKPOLE, M. D. New treatment of slime problem in cyaniding talcose ores. Eng. & Min. Jour., July 12, 1902, 1 p. STARBIRD, H. B. New system for cyanide treatment of slime. Mex. Min. Jour., Dec., 1909. SWAREN, J. W. Historical notes on air-lift agitators. M. & S. P., Sept. 30, 1911. SYMONDS, L. Notes on treatment of gold slime in Venezuela. Inst. Min. & Met., vol. 12, 1903, 7 pp. TAYS (E. A. H.) and SCHIERTZ (F. A.). Treatment of clay slime by cyanide process and agitation. T. A. I. M. E., vol. 32, 1901, 36 pp.; abstract in M. & S. P., Feb. 15 to Mar. 15, 1902, 6 pp. TORRENTE, M. Improvements in slime treatment. Jour. Ch., Met., & Min. Soc., S. A., vol. 5, p. 46, 1904, 6 pp. VON BERNEWITZ, M. W. Slime agitation at Kalgoorlie. M. & S. P., June 3, 1911, 2 pp. WARWICK, A. W. Mechanical air agitation for slime treatment. Min. World, Jan. 28, 1911, 2 pp.; Apr. 22, 1911, 1 p. WILLIAMS, J. R. Indirect advantages of a slime plant. Proc. Ch. & Met. Soc., S. A., vol. 2, 1899, 16 pp. CLASSIFIED BIBLIOGRAPHY 235 Treatment of battery slime. Proc. Ch. & Met. Soc., S. A., vol. 2, 1897, 6 pp. WILSON, E. B. Cyaniding slime. Mines & Mins., Sept., 1908, 3 pp.; Oct., 1908, 5 pp.; Nov., 1908; Dec., 1908. YAGER, A. J. Modification of Pachuca-tank practice. (Also concerning zinc-dust precipitation.) M. & S. P., Oct. 22 and Dec. 24, 1910; abstract in Pac. Miner, Nov., 1910> 1 p. Australian Mining Standard. Gold saving appliances. (Agitator and aerator.) Oct. 20, 1909, 1 p. Usher sand process for extraction of gold. Aug. 4, 1909, 2 pp. Engineering and Mining Journal. Cyanide tank record. Jan. 29, 1910. Treatment of slime in tanks with conical bottoms. Mar. 28, 1903. Mexican Mining Journal. Clear-solution hydraulic agitator. Oct., 1911, Ip. Mining and Engineering World. New Patterson agitator. Oct. 21, 1911. Abstract from S. A. Min. Jour. Mining and Scientific Press. Air-lift agitation of slime pulp. May 6, 1911. Hydraulic cyanide tank. Jan. 16, 1904. Modern slime plant. Apr. 4, 1903, 1 p. Pacific Miner. Dilution system of slime treatment. Dec., 1909, 1 p. South African Mines. Adair-Usher process. Apr. 20, 1907, 2 pp. M. Filtration ALLEN, A. W. Improvement in treatment of slime by vacuum filter proc- ess. Eng. & Min. Jour., May 15, 1909, 1 p. BENNETT, S. E. Treatment of slime in the Black Hills. (Merrill process.) Min. World, Feb. 22, 1908, 1 p.; Min. Sci., Feb. 27, 1908, 1 p. BOERICKE, W. F. Sand filters. Eng. & Min. Jour., Oct. 9, 1909. BOSQUI, F. L. Moore and Butters filters. M. & S. P., Feb. 2^1907, 1 p. Proposed filter press slime plant. T. A. I. M. 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G. Note on treatment of zinc-box precipitate from cyanide process. Inst. Min. & Met., vol. 4, 1896, 11 pp. BULLOCK, L. N. B. Cyanidation at Copala, Mex. (Clean-up, melting, etc.) M. & S. P., Mar. 14, 1907, 1 p. "Recent Cyanide Practice," p. 231. BURNETT, D. V. Some future appliances for cyanide clean-up. (Washing trommel.) Jour. Ch., Met., & Min. Soc., S. A., vol. 5, p. 145, 1 p.; abstract in Eng. & Min. Jour., May 18, 1905, 1 p. CALDECOTT (W. A.) and JOHNSON (E. H.). Smelting and refining of gold zinc slime. Proc. Ch. & Met. Soc., S. A., vol. 3, 1902, 18 pp. CAMPBELL (B. P.). Refining zinc-box precipitate with sulphurous acid. Pac. Miner, June, 1910. CLARKE, D. Gold refining. Aust. Min. Stand., series of articles ending Jan. 22, 1908. See "Gold Refining," by Clarke. CLEVENGER, G. H. Refining of precipitate obtained by means of zinc in cyanide process. T. A. I. M. E., vol. 34, 1903, 26 pp. COLLIE, J. E. Matte refining. Pac. Miner, Mar., 1910, 1 p. COOLIDGE, R. F. 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Jour., Jan. 22, 1910, 3 pp. VON BERNEWITZ, W. M. Treatment of concentrate at Kalgoorlie. Min. Jour., May 21, 1910, 2 pp. WRIGHT, C. M. P. Cyaniding concentrate by percolation at Choukpazat. Inst. Min. & Met., vol. 12, 1902, 4 pp. Australian Mining Standard. Treatment of concentrate. Jan. 1, 1908. Mining and Scientific Press. Cyaniding raw sulphide. Sept. 9, 1905; abstract from Jour. Ch., Met., & Min. Soc., S. A. Cyaniding sulphide gold ores. June 7, 1902, 1 p. Kalgoorlie, Western Australia. (Concentrate cyanidation.) Mar. 6, 1909, p. 342, 1 p. S. Other Refractory Ores ALDERSON, M. W. Cyaniding base ore. M. & S. P., Feb. 4, 1899, 1 p. BETTEL, W. Nature and treatment of refractory ores. (Cyanidation.) S. A. Min. Jour., Dec. 11, 1909, 3 pp.; abstract in Min. World, Feb. 26, 1910, 2pp. BRETT, H. T. Metallurgy at Globe and Phoenix, Rhodesia. (Cyaniding antimonial ores.) Min. Mag., July, 1911; abstract in Min. & Met. Jour., Sept., 1911. . CLASSIFIED BIBLIOGRAPHY 249 BROWN, E. P. Treatment of gold-bearing antimony ore. M. & S. P., June 9, 1906. BURNETT, D. V. A quick treatment by cyanide of black sands. Jour. Ch., Met., & Min. Soc., S. A., Feb. to May, 1906, 3 pp. CIRKEL, F. Treatment problem of the Republic, Washington ores. Eng. & Min. Jour., Feb. 1,4908, 1 p. DAY (D. T.) and RICHARDS (R. H.). Investigation of black sands from placer mines. Bull. 285, U. S. Geol. Survey, p. 150, 15 pp. Useful minerals in black sands of Pacific Slope, with bibliography of papers bearing on black sands. U. S. Geol. Survey Min. Res. of U. S., 1905, p. 1175, 84 pp. Nothing on cyanidation in above. FRASER, LEE. A cyanide problem. (Suggested treatment for antimonial ores.) M. & S. P., Dec. 3, 1910. HAMILTON, E. M. Cyanidation of manganese silver ores in Mexico. M. & S. P., Dec. 4, 1909, and Feb. 5, 1910; abstract from Jour. Ch., Met., & Min. Soc., S. A. LAMB, M. R. Treating low grade refractory ores of Mexico. Min. World, July 3, 1909, 3 pp. MASON, F. H. Separation of gold in antimony ores. (Experiments.) M. & S. P., Apr. 28, 1906, 2 pp. PROBERT, F. H. Cyaniding complex gold ores. M. & S. P., June 15, 1901, Ip. STEVENS, F. B. Treatment of highly acidic tailing by cyanide. M. & S. P., June 14, 1902, 1 p. VON BERNE WITZ, M. W. Graphite an obstacle to good cyaniding, M. & S. P., Dec. 4, 1909, Feb. 5 and June 11, 1910, 2 pp. "More Recent Cyanide Practice," p. 336. WILSON, J. K. Notes on occurrence and treatment of an auriferous ore containing insoluble arsenides. Jour. Ch., Met., & Min. Soc., S. A., Feb., 1907, 4 pp. Mining and Scientific Press. A cyanide problem. (Antimonial ore.) Aug. 13, 1910. Mining Science. Cyanjflation of manganese-silver ores. Jan. 20, 1910. ,/ T. Cyanide Poisoning V/BOYD, F. K. Poisoning of animals by cyanide solutions. Mex. Min. Jour., Jan., 1911. ^/BROWN, H. L. Cyanide poisoning. (Of cattle by cyanide discharged.) Eng. & Min. Jour., Nov. 3, 1906, 1 p. JENKINS, H. C. First aid treatment of acute cyanide poisoning. Inst. Min. & Met., vol. 13, 1904, 5 pp. I/JOHNSTON, A. M. Experiment in cyanide poisoning. Proc. Ch. & Met. Soc., S. A., vol. 2, 1899, 9 pp. JONA, J. L. Antidote for cyanide poisoning. Eng. & Min. Jour., Sept. 30, 1911. KENNEDY, A. P. Cyanide poisoning. (Eczema.) M. & S. P., Mar. 9, 1907. 250 TEXT BOOK OF CYANIDE PRACTICE MARTIN (C. J.) and O'BRIEN (R. A.). Antidote for cyanide poisoning. Eng. & Min. Jour., Aug. 8, 1903, 1 p. ^ROGERS, A. H. Poisoning by cyanide. Eng. & Min. Jour., Dec. 3, 1910. WOODRUFF, C. H. Cyanide poisoning and antidotes. Mex. Min. Jour., Aug., 1910, 1 p. ^x&ustralian Mining Standard. Cyanide poisoning. Jan. 6, 1909, 1 p. ^Engineering and Mining Journal. Poisoning by cyanide. Nov. 26, 1910. ^^Fburnal Chemical, Metallurgical, and Mining Society, S. A. Report of committee upon cyanide poisoning. May, 1904, 3 pp. See vol. 2 (Proc. Ch. & Met. Soc., S. A.), 1897-1899, generally. Mining and Scientific Press. Cyanide poisoning. Sept. 29, 1906, 1 p. "Recent Cyanide Practice," p. 123. Pacific Miner. Cyanide poisoning. Aug., 1909, 2 pp.; abstract in Mex. Min. Jour., Jan., 1910, 1 p. U. Construction, and Pulp and Residue Conveying and Disposal ADAMS, H. Disposal of residue at Kalgoorlie. Proc. Aust. Inst. Min. Engrs., July, 1909, 13 pp. BALDWIN, C. K. Tailing disposal plant at Wolverine mill. Eng. & Min. Jour., July 10, 1909, 3 pp. BLUE, T. K. Flow of water carrying sand in suspension. Eng. & Min. Jour., Sept. 21, 1907, 4 pp. BOERICKE, W. F. Tailing elevators for dumps. Eng. & Min. Jour., Sept. 23, 1911. BOERICKE (W. F.) and EASTMAN (B. L.). Home-made cyanide plant. M. & S. P., Nov. 21, 1908, 1 p. ''More Recent Cyanide Practice," p. 231. BOSQUI, F. L. Iron v. wood for cyanide leaching tanks. M. & S. P., Apr. 14, 1906, 1 p. "Recent Cyanide Practice," p. 39. BROWN, A. S. Modern cyaniding practice and machinery. Eng. Mag., Sept., 1909, 18 pp. BROWN, R. G. Tailing elevators. Eng. & Min. Jour., Apr. 14, 1904, 1 p. "Notes on Metallurgical Mill Construction." BROWNE, R. S. Designing of a sand leaching plant. Pac. Miner, Aug. and Sept., 1910, 7 pp. Mechanical equipment of cyanide plants. Pac. Miner, Sept., 1909, 4 pp. How to set up wood stave tanks. M. & S. P., Aug. 22, 1905, 1 p. COLEMAN, W. N. Cost of small cyanide plant. Pac. Miner, Aug., 1909, 2pp. COLLINS, E. A. Tailing wheels v. pumps. M. & S. P., Oct. 31, 1908, 2pp. CRANK, A. F. Cyanide sand handling at Robinson mine. Min. Jour., July 25, 1908, 1 p. CRANK (A. F.) and BUTTERS (C.). System of handling sand mechanically for cyanide vats. Inst. Min. & Met., vol. 13, 1903, 26 pp.; abstract in Eng. & Min. Jour., Dec. 5, 1903, 2 pp. EGGERS, J. H. Cyanide plant constructed of masonry. Pac. Miner, Jan., 1911, 4 pp. CLASSIFIED BIBLIOGRAPHY 251 HERRICK, R. L. Handling (and impounding) tailing at Colorado City. Mines & Mins., May, 1910, 4 pp. HUNTER, CHAS. Cheap form of cyanide plant. Inst. Min. & Met., vol. 17, 1907, 7 pp. LOBO, G. Electricity in cyanide plants. Mex. Min. Jour., Aug., 1910, 3 pp. JARMAN, A. Silting (of rivers by tailing) at Waihi. Min. Mag., Sept., 1910, 4 pp. JONES, A. H. Tailing wheels v. pumps. M. & S. P., Oct. 3, 1908. LAMB, M. R. Variables influencing cyanide plant design. Eng. & Min. Jour., July 2, 1910, 1 p. LASCHINGER (E. L.) and WOOD (W. H.). Tailing elevators. Eng. & Min. Jour., Mar. 24 and Apr. 14, 1904, 3 pp. "Notes on Metallurgical Mill Con- struction." MACFARREN, H. W. Impounding mill tailing. M. & S. P., Sept. 4, 1909, Ip. Tailing disposal at Mercur, Utah. M. & S. P., July 25, 1908, 1 p. MESS, L. Reinforced concrete tanks. M. & S. P., July 25, 1908, 1 p. MILL, A. R. Air-lift for transporting sand. Pac. Miner, Mar., 1911, 1 p.; Eng. & Min. Jour., Apr. 8, 1911, 1 p. NEAL, W. Conical bottom tanks. M. & S. P., July 25, 1908. NICOL, J. M. Dynamics of cyanide process. Mex. Min. Jour., Aug., 1910, 6 pp. OVERSTROM, G. A. Conveying tailing in launders. M. & S. P., Sept. 14, 1907, 1 p. " Recent Cyanide Practice," p. 331. READ, T. T. Sand launders. Eng. & Min. Jour., Dec. 16, 1905, 1 p. REID, W. L. Tailing wheels compared with centrifugal pumps. M. & S. P., Sept. 19, 1908, 1 p. "Recent Cyanide Practice." RICE, C. T. Sluicing out sand tanks at Grass Valley, Calif. Eng. & Min. Jour., Jan. 28, 1911. RICKETTS, L. D. Tailing dam of Cananea Copper Co. Eng. & Min. Jour., Mar. 5, 1909, 1 p. Rix, R. A. Air-lift pumping. M. & S. P., Oct. 15, 1910, 2 pp. SCHMITT, C. O. Table of grades for launders and pipes in reduction plants. Jour. Ch., Met., & Min. Soc., S. A., Jan., 1909. SHAPLEY, E. Air-lifts at Santa Natalia mill. Pac. Miner, Sept., 1909 IP- SMART, E. Plant for extraction of gold by cyanide process. Eng. & Min. Jour., vol. 60, p. 417, 2 pp. STORMS, W. H. Tailing dams and conservation of mill water. Eng. & Min. Jour., Aug. 6, 1910, 2 pp. VAN LAW, C. W. Conveying tailing in launders and pipes. M. & S. P., July 20 and Oct. 12, 1907, 2 pp. "Recent Cyanide Practice, " pp. 320 and 331. VON BERNE WITZ, M. W. Dumping residues at Kalgoorlie. M. & S. P. Sept. 21, 1907, 2 pp. WEPPER, G. W. Tailing wheels or pumps. M. & S. P., Oct. 31, 1908, 1 p. WESTON, E. M. Tailing elevators on the Rand. Eng. & Min. Jour. Sept. 12, 1908, 1 p. 252 TEXT BOOK OF CYANIDE PRACTICE Description of cheap cyanide plant erected in Western Australia. Jour. Ch., Met., & Min. Soc., S. A., vol. 5, p. 23, 1 p. Australian Mining and Engineering Review. Sludge problem in New Zealand. (Tailing in rivers.) Aug. 5, 1910, 3 pp. Engineering and Mining Journal. Blaisdell apparatus at El Oro. Eng. & Min. Jour., vol. 83, p. 230, 1 p. Conveying at El Oro mill. (Launder grade.) Eng. & Min. Jour., Apr. 4, 1908. Disposal of slime and tailing at Stella mine, N. Y. Eng. & Min. Jour., Sept. 18, 1909, 1 p. Efficiency of air-lift as a solution pump. Eng. & Min. Jour., Aug. 7, 1909. Jackson method of tailing disposal. (Michigan copper mines.) Eng. & Min. Jour., Mar. 28, 1908, 1 p. Engineering News. Handling stamp-mill tailing by belt conveyors. Oct. 28, 1909, 2 pp. Metallurgical and Chemical Engineer. Cyanide tailing disposal in Mexico. Nov., 1911, 2 pp. Mining and Scientific Press. Building a concrete tank. Mar. 3, 1906. Handling residue in New South Wales. Oct. 12, 1907, 1 p. Elevating sand. July 8, 1911, 1 p. Mining World. Sand filling (of worked-out stopes) on the Rand. Aug. 6, 1910, 1 p. Pacific Miner, Method of erecting wood tanks. Feb., 1910, 1 p. South African Mining Journal. New Rand tailing elevator. Sept. 26, 1908, 1 p. Sand filling (of worked-out stopes) at the Simmer and Jack. Sept. 17, 1910. V. Tube-Milling and Fine-Grinding ABBE, R. F. First tube mill in metallurgy. Eng. & Min. Jour., May 26 and June 16, 1906, 1 p. ARGALL, P. Modern crushing and grinding machinery. Eng. & Min. Jour., May 11, 1904, 2 pp. "Notes on Metallurgical Mill Construction." BALL, H. S. Economics of tube milling. Bull. No. 83, Inst. Min. & Met., Aug., 1911; abstract in M. & S. P., Sept. 23, 1911, 3 pp. BANKS, E. G. Grinding in tube mills at Waihi, New Zealand. T. A. I. M. E., vol. 38, 1907, 4 pp.; Mines & Mins., vol. 27, p. 492, 1 p.; Min. World, Apr. 6, 1907, 2 pp. BARRY, H. P. Tube-mill lining. Aust. Min. Stand., Dec. 2, 1908, 1 p. Tube-mill lining. M. & S. P., Mar. 30, 1907, 1 p. "Recent Cyanide Practice, " p. 239. BELL, J. W. Critical moisture in tube mill feed. Min. Mag., Apr., 1911, Ip. BELL (J. W.) and QUARTANO (A.). Critical moisture in tube-mill feed. Min. Mag., Sept., 1911, 2 pp. BOSQUI, F. L. Fine-grinding. M. & S. P., Feb. 3 and 10, 1906, 2 pp. "Recent Cyanide Practice," p. 25, CLASSIFIED BIBLIOGRAPHY 253 Boss, M. P. Fine-grinding. M. & S. P., Feb. 17, 1906, 1 p. "Recent Cyanide Practice," p. 31. BRADLEY, W. W. Tube-mill lining. M. & S. P., Jan. 5, 1907, 1 p. "Re- cent Cyanide Practice," p. 207. BRETT, H. T. Cyanide practice at Kalgoorlie, (Tube mills v. pans.) M. & S. P., Dec. 22, 1906, 2 pp. "Recent Cyanide Practice," p. 189. BROWN, F. C. Importance of fine-grinding in cyanide treatment of gold and silver ores. T. A. I. M. E., vol. 36, 1905, 7 pp. BROWN, J. R. El Oro tube-mill lining. (Patents.) M. & S. P., Feb. 29, 1908, 1 p. "More Recent Cyanide Practice," p. 120. BUTTER, C. Notes on tube-milling at El Oro, Mex. M. & S. P., May 26, 1906, 1 p. "Recent Cyanide Practice," p. 55. BUTTERS (C.) and HAMILTON (E. M.). On cyaniding of ore at El Oro, Mex. Dealing principally with regrinding of sand. Inst. Min. & Met., vol. 14, 1904, 44 pp.; abstract in Eng. & Min. Jour., Dec. 15, 1904, 1 p. CAETANI (G.) and BURT (E.). Fine-grinding of ore by tube mills, and cyaniding at El Oro, Mex. T. A. I. M. E., vol. 37, 1906, 53 pp. CALDECOTT (W. A.) and PEARCE (S. H.). Computation of crushing effi- ciency of tube mills. Jour. Ch., Met., & Min. Soc., S. A., Sept., 1906, 2 pp.; Jan. to Mar., 1907, 7 pp. CHAPMAN, R. W. Calculation of comparative efficiencies of crushing and grinding machines. Proc. Aust. Inst. Min. Engrs., Oct., 1909, 5 pp. CLARKE, R. Pans v. tube mills. (Comparative test.) M. & S. P., Apr. 6, 1907, 1 p. "Recent Cyanide Practice, " p. 245. COLLINS, E. A. All-sliming. M. & S. P., Sept. 18, 1909. "More Recent Cyanide Practice, " p. 300. CRANE, W. R. Bibliography of fine crushing by tube and other mills, "Index of Mining Engineering Literature." 1909, 4 pp. DEL MAR, A. Crushing by stages. M. & S. P., Nov. 5, 1910, 1 p. Efficiency of tube mills. Min. World, Feb. 12, 1910, 1 p. DENNY, H. S. Fine-grinding. Pac. Miner, Apr., 1911, 1 p.; Min. Mag.. Mar., 1911, 3 pp. Fine grinding. Min. Mag., July, 1911. DOVETON, G. Fine-grinding. M. & S. P., Jan. 27, 1906, 1 p. "Recent Cyanide Practice, " p. 16. DOWLING, W. R. Tube-mill practice. Jour. Ch., Met., & Min. Soc., S. A., Apr. to Sept., 1906, 16 pp. Critical moisture in tube-mill feed. Min. Mag., June, 1911. Stationary amalgam plates in tube-mill plants. Jour. Ch., Met., & Min. Soc., S. A., Jan., 1911, 1 p. DROTT, M. Tube mills, wet and dry. Aust. Min. & Eng. Rev., Apr. 5, 1909, 5 pp. DRUCKER, A. E. Tube-milling in Korea. M. & S. P., Sept. 22, 1906, 1 p. "Recent Cyanide Practice," p. 110. Tube-mill lining. M. & S. P., Nov. 17, 1906, 1 p. "Recent Cyanide Practice," p. 166. FISCHER, H. Operation of a tube mill. Eng. & Min. Jour., Nov. 17, 1904, 2 pp. " Notes on Metallurgical Mill Construction." 254 TEXT BOOK OF CYANIDE PRACTICE FOOTE, A. D. W. Tube-mill lining, slime-filters, and patents. M. & S. P., Feb. 1, 1908, 1 p. " Recent Cyanide Practice," p. 111. Fox, H. W. Economics of the tube mill. Mines and Mins., June, 1908, 4pp. Spiral feeder for tube mill. Eng. & Min. Jour., Dec. 14, 1907. GRAHAM, K. L. Notes on some recent improvements in tube-mill practice. Jour. Ch., Met., & Min. Soc., S. A., Apr. to Sept., 1907, 13 pp. GROCH (N. C.) and NAGEL (F. J.). Feeder for tube mill. M. & S. P., Apr. 27, 1907, 1 p. HAMILTON, E. M. All-sliming. M. & S. P., Aug. 21, 1909, 3 pp. " More Recent Cyanide Practice," p. 293. HARDINGE, H. W. Conical tube-mill. M. & S. P., Feb. 15, 1908, 2 pp. "More Recent Cyanide Practice," p. 105. Crushing by stages. M. & S. P., Oct. 8, 1910, 1 p. Hardinge conical pebble-mill. T. A. I. M. E., vol. 39, 1908, 5 pp. Hardinge conical tube-mill. Eng. & Min. Jour., Nov. 16, 1907, 1 p. Hardinge conical tube-mill. West. Ch. & Met., Apr., 1908, 7 pp. Pebble-mill amalgamation. M. & S. P., Apr. 30, 1910, 1 p. Problem of fine-grinding in tube mills. Eng. & Min. Jour., Nov. 26, 1910, Ip. Tube-mill lining. M. & S. P., Nov. 23, 1907, and Mar. 28, 1908, 2 pp. "More Recent Cyanide Practice," p. 108. Tube mills. Eng. & Min. Jour., June 8, 1905. "Notes on Metallurgical Mill Construction." Stage crushing. Eng. & Min. Jour., Jan. 22, 1910, 1 p. HENDERSON, E. T. Laboratory screens. Their use in testing efficiency of grinding machines. Aust. Min. & Eng. Rev., Nov. 5, 1908, 3 pp. JAMES, A. Crushing and grinding practice at Kalgoorlie. M. & S. P., July 28, 1906, 2 pp. "Recent Cyanide Practice," p. 73. Tube-mill notes. Eng. & Min. Jour., Mar. 16, 1905, 1 p. "Notes on Metallurgical Mill Construction." Abstract from Inst. Min. & Met., 1905. KLUG, G. C. Grinding pan practice. Pipe discharge and classification of ground product. Jour. W. A. Cham, of Mines, Sept. 30, 1910, 4 pp. LAMB, M. R. Crushing at cyanide plants. Eng. & Min. Jour., Feb. 4, 1911, 1 p. Crushing machines for cyanide plants. T. A. I. M. E., vol. 41, 1910, 6 pp.; abstract in Min. World, July 30, 1910, 2 pp. Chile mill. Eng. & Min. Jour., June 12, 1909, 1 p. LEUPOLD, H. Tube-mill results. Eng. & Min. Jour., June 8, 1905; ab- stract from S. A. Assn. of Engrs. MACKAY, A. N. Tube-mill lining. (Home made.) Min. Mag., July, 1911. MEGRAW, H. A. Some characteristics of Chilean mills. Eng. & Min. Jour., Nov. 12, 1910, 2 pp. McMiKEN, S. D. Tube-mill lining. M. & S. P., Nov. 3, 1906, 1 p. "Re- cent Cyanide Practice," p. 162. Tube-mill liners. N. Z. Mines Record, Oct. 16, 1907. MITCHELL, D. P. Pans v. tubes. M. & S. P., Aug. 4, 1906. "Recent Cyanide Practice," p. 78. CLASSIFIED BIBLIOGRAPHY 255 NEAL, W. Diaphragm cones and tube-milling. M. & S. P., Apr. 2, 1910, 2 pp. "More Recent Cyanide Practice," p. 389. RHODES, C. E. Tube-mill lining. M. & S. P., Dec. 21, 1907. "More Recent Cyanide Practice, " p. 109. RICHARDS, R. H. Bibliography for pulverizers other than gravity stamps. Vol. 1, "Ore Dressing," 1903, p. 289. Bibliography of grinders other than gravity stamps. Vol. 3, "Ore Dress- ing," 1909, p. 1323. Complete bibliography for pulverizers other than gravity stamps. Vol. 4, "Ore Dressing," 1909, p. 2013. ROBERTSON, G. A. Distribution of pulp in tube-milling. Min. World, Oct. 29, 1910; abstract from Jour. Ch., Met., & Min. Soc., S. A. Lay-out of a tube-mill plant. S. A. Eng. Jour., Mar. 18, 1911, 1 p. ROTHERHAM, G. H. New tube-mill lining. Min. World, Apr. 23, 1910, lp. SCHWERIN, M. Notes on some regrinding machines. Eng. & Min. Jour., Mar. 10, 1904, 3 pp. "Notes on Metallurgical Mill Construction." SHAPELY, C. Method of returning pulp to classifier from tube mill. Eng. & Min. Jour., Feb. 4, 1911. SHARPLEY, H. Feeder for tube mill. Eng. & Min. Jour., July 8, 1911. SHERROD, V. B. Grinding tests at Pachuca, Mex. M. & S. P., Mar. 5, 1910, 3 pp.; abstract in Trans. Mex. Inst. Pulp classification and tube-mill efficiency. Met. & Chem. Eng., Mar., 1910, 5 pp. SIMPSON, W. E. Grinding machines used at Kalgoorlie. Eng. & Min. Jour., Nov. 14, 1903. "Notes on Metallurgical Mill Construction." SMART, G. O. Tube-mill circuit and classification. Jour. Ch., Met., & Min. Soc., S. A., May, 1910, 4 pp.; abstract in Min. World, May 7, 1910, 3 pp. STADLER, H. Efficiency of fine-grinding machines. Mines & Mins., June, 1910, 2 pp.; M. & S. P., June 18, 1910, 1 p.; abstract from Jour. S. A. Assn. of Engrs. STANLEY (G. H.) and WEBBER (M.). Laboratory comparison of tube- mill pebbles. Jour. Ch., Met., & Min. Soc., S. A., June, 1908, 2 pp. STEWART, J. A. Increased milling capacity at small cost. (Lane slow- speed mill.) M. & S. P., Feb. 2, 1907. TOD, S. Conical tube-mill grinding. M. & S. P., Aug. 20, 1910. URBITER, W. H. Efficiency of fine-grinding machinery. Eng. & Min. Jour., Aug. 5, 1911, 3 pp. VAN LAW, C. W. Tube mills at Guanajuato. M. & S. P., Aug. 17, 1907. "Recent Cyanide Practice," p. 329. , VON BERNEWITZ, M. W. Concentration of slime. (Tube-milling.) M. & S. P., Dec. 10, 1910, 1 p. BaU mill practice at Kalgoorlie. M. & S. P., July 15, 1911, 2 pp. WAINWRIGHT (W. E.) and MCBRIDE (W. J.). Tube-mill and grinding pans at Broken Hills South mine. (Comparative test.) Proc. Aust. Inst. Min. Engrs., Feb., 1909, 23 pp. WANN, E. E. Fine-grinding. M. & S. P., Dec. 16 and 30, 1905; Feb. 10, 1906. 256 TEXT BOOK OF CYANIDE PRACTICE WARWICK, A. W. Influence of fine-grinding on metallurgy of precious metals. West. Ch. & Met., Mar. and Apr., 1905, 48 pp. WEST, H. E. Tube-mill lining. M. & S. P., Mar. 28, 1908, 1 p. "More Recent Cyanide Practice, " p. 137. W^HITE, H. A. Theory of tube mill. Jour. Ch., Met., & Min. Soc., S. A., May to Oct., 1905; abstract in Eng. & Min. Jour., Sept. 23, 1905, 2 pp.; abstract in " Notes on Metallurgical Mill Construction." WHITMAN, P. R. All-sliming. M. & S. P., Sept. 18, 1909. "More Recent Cyanide Practice, " p. 299. WILSON, E. B. Tube-mill crushing. Mines & Mins., Aug., 1908, 3 pp. YATES, A. Screen analysis and grinding efficiency. M. & S. P., May 1, 1909, 1 p.; abstract from Jour. Ch., Met., & Min. Soc., S. A. Engineering and Mining Journal. Abbe tube-mill. Dec. 20, 1904. El Oro tube-mill lining. Apr. 18, 1908. Lane slow speed mill. May 23, 1908, 1 p. Smooth lining for tube mills. Apr. 30, 1910. Tube-mill lining in use on the Rand. Aug. 6, 1910, 1 p. Giesecke ball-tube mill. Eng. & Min. Jour., Sept. 20, 1911; Min. & Eng. World, Aug. 5, 1911; Mines & Mins., Sept., 1911; M. & S. P., Sept. 30, 1911. Mines and Minerals. Successful tube-mill lining. Vol. 27, p. 507, 1 p. Mining Magazine. Cobbe-Middleton grinding pan. Nov., 1909, 2 pp. Mining and Scientific Press. Regrinding. Apr. 7, 1906, 1 p. "Recent Cyanide Practice," p. 29. Tube mill. Mar. 24, 1906. Tube-mill liner. Mar. 5, 1910. Tube-mill lining. July 28, 1906, 1 p. "Recent Cyanide Practice," p. 69. Mining World. Tube-mill practice in Mexico. July 3, 1909. South African Mines. Economics of tube-mills. Oct. 27 to Nov. 10, 1906. South African Mining Journal. Stamps and tube-mills, Apr. 30, 1910, 1 p. Tube-milling practice. Jan. 2, 1909, 2 pp. Review of present day tube-mill practice on Rand. Sept. 2, 1911. W. Cyanidation of Silver Ores, and in Mexico BOYD, T. K. Cyanidation of silver ores. Mex. Min. Jour., Oct., 1909, 2pp. Milling practice at Altixtac, Mex., Mex. Min. Jour., Sept., 1911, 1 p. BRODIE, W. M. Milling of Batopilas native silver ore. Mex. Min. Jour., Jan., 1911, 3 pp.; abstract in Pac. Miner, Jan., 1911, 2 pp. BROWNE, R. S. Cyaniding silver ores. M. & S. P., vol. 85, p. 338, 1 p. BORDEAUX,, A. F. J. Cyaniding of silver ores in Mexico. T. A. I. M. E., vol. 40, 1909, 11 pp.; vol. 41, 1910, 16 pp. BURGGROF, J. Loreto cyanide plant of Cia. del Real Monte y Pachuca. Mex. Min. Jour., Aug., 1910, 1 p. BURT, E. Milling practice at El Oro mill, Mex. Min. World, Oct. 26, 1907, 4 pp. CLASSIFIED BIBLIOGRAPHY 257 BURT (E.) and CAETANI (G.). Fine-grinding of ore by tube mills, and cyaniding at El Oro, Mex. T. A. I: M. E., vol. 37, 1906, 53 pp. BUTLER, J. S. Milling and cyanide practice, San Prospero mill, Guana- juato. M. & S. P., July 25, 1908, 3 pp. "More Recent Cyanide Practice," p. 158. CHIDDY, A. Cyanidation of silver. Eng. & Min. Jour., June 1, 1905, 1 p. CLARK, J. E. Cyaniding base silver ores. M. & S. P., Aug. 7, 1911, 1 p. DAUE, E. O. Notes on cyanide practice at Pachuca. Mex. Min. Jour., Oct., 1908, 2 pp. DRISCOLL, G. E. Cyaniding silver ores in Honduras. Min. Jour., Jan. 29, 1910, 2 pp.; M. & S. P., Mar. 13, 1909, 2 pp. "More Recent Cyanide Practice, "p. 253. EDMONSON, H. W. Treatment at Rio Plata mining company. Mex. Min. Jour., Aug., 1910, 2 pp. ELWES, H. G. Cyanidation of silver in Mexico. Eng. & Min. Jour., Mar. 16, 1905, 2 pp. EMPSON, J. B. Silver cyaniding in Mexico. Eng. & Min. Jour., Oct. 3, 1908, 1 p. FERRIS, W. S. Moore filter at San Rafael. Mex. Min. Jour., Aug., 1910, 3pp. FIELD, H. C. Practice at Pinguico mill, Guanajuato. Mex. Min. Jour., July, 1911, 1 p. FLYNT, A. Cyanide practice at Compania Minera de los Reyes. Mex. Min. Jour., Aug., 1910, 4 pp. FULTON, C. A. Cyanide practice at Guanajuato. Mex. Min. Jour., Aug., 1910, 9 pp. GIRAULT, E. San Rafael cyanide mill, Pachuca. Trans. Mex. Inst., Dec., 1909, 21 pp.; abstract in Eng. & Min. Jour., July 9 and Oct. 1, 1910, 5 pp.; abstract in Met. & Chem. Engr., Mar., 1910, 5 pp. Methods, results, and costs at San Rafael y Anexas Co., Pachuca. Mex. Min. Jour., June, 1911, 2 pp. GONZALES (F.), GROTHE (A.), and SALAZARS (L.). San Rafael mill at Pachuca, Mex. Min. & Eng. World, Aug. 26, 1911, 2 pp. GRIFFITHS (A. P.) and OLDFIELD (F. W.). Cyaniding some silver ores by percolation. Inst. Min. & Met., vol. 12, 1903, 10 pp.; abstract in Eng. & Min. Jour., July 18, 1903, 1 p. HOBSON, F. J. Cyanide process at Guanajuato. M. & S. P., Jan. 6, 1906, 1 p. " Recent Cyanide Practice," p. 12. Peregrina mill, Guanajuato. Eng. & Min. Jour., May 19, 1906, 2 pp. HOYLE, C. New Esperanza mill and milling practice. Mex. Min. Jour., Aug., 1910, 5 pp. JANIN, L. Cyanide of potassium as a lixiviation agent for silver ores and minerals. Eng. & Min. Jour., Dec. 29, 1888. KLINE, R. C. Treatment of silver ores at Guanaceva, Mexico. M. & S. P., Mar. 18, 1911, 2 pp. KNIFFEN, L. B. Cyanidation of silver ores. M. & S. P., Feb. 2&, 1910, 1 p. "More Recent Cyanide Practice," p. 382. Cyanide experiences in Northern Mexico, Mex, Min. Jour,, Aug., 1910, 258 TEXT BOOK OF CYANIDE PRACTICE 3 pp.; abstract in Pac. Miner, Sept., 1910; abstract in Jour. Ch., Met., & Min. Soc., S. A., Mar., 1911. Deadwood mill at Mongollon, N. Mex. (Silver sulphide ore.) Eng. & Min. Jour., Oct. 14, 1911, 1 p. LAMB, M. R. Cyanide operations in Mexico during 1908. Min. World, Feb. 6, 1909, 4 pp. Metallurgy in Western Chihuahua. Mex. Min. Jour., Nov., 1908, 1 p. Milling and cyaniding methods in Mexican camps. Min. World, Apr. 11, 1908, 3 pp. Minas Prietas Reduction Works. M. & S. P., Aug. 4, 1906, 2 pp. Present cyanide practice in Mexico. Eng. & Min. Jour., Apr. 4, 1908, 7 pp. Table of practice in Mexican cyanide mills. Eng. & Min. Jour., Apr. 3, 1909. LINTON, R. Silver ore treatment in Mexico. (Referring to manganese ore.) Jour. Ch., Met., & Min. Soc., S. A., Aug., 1908, and Mar., 1909. MACDONALD, B. Cyanidation of silver ores at Guanajuato. Eng. & Min. Jour., Apr. 4, 1908, 8 pp. Development of cyanide process for silver ores in Mexico. Eng. & Min. Jour., Apr. 18, 1908, 2 pp. Inauguration of cyanide era in Parral district. Mex. Min. Jour., Aug., 1910, 5 pp. MEGRAW, H. A. Reconstruction of Angustias cyanide mill. Eng. & Min. Jour., Aug. 13, 1910, 2 pp. MENNELL, J. L. Recent advance in cyanidation in Mexico. Min. World, Oct. 26, 1907, 2 pp. NARVAEZ, F. Metallurgical practice at Hacienda de la Union. Eng. & Min. Jour., Nov. 21, 1908, 3 pp. NICOL, J. M. Metallurgical methods at Pachuca. Min. Mag., Feb., 1910, 9 pp. OXNAM, T. H. Cyaniding silver-gold ores of Palmarejo mine, Chihuahua, Mex. T. A. I. M. E., vol. 36, 1905, 54 pp.; abstracts in Eng. & Min. Jour., Aug. 19 to Sept. 9, 1905, 11 pp.; in M. & S. P., July 29 to Sept. 9, 1905, 10 pp.; in Hoffman's " Hydrometallurgy of Silver," 42 pp. PAUL, W. H. Cyanide practice at Dolores mine in Mexico. Bull. Colo. Sch. of Mines, May, 1910, 4 pp. QUARTANO, A. Cyanide year at Dos Estrellas. Mex. Min. Jour., Aug., 1910, 1 p. REID, J. A. Cyanidation of silver-gold ores at Guanajuato. Min. World, Apr. 9, 1910, -2 pp. RICE, C. T. Cyanidation of silver ores, Pachuca. Eng. & Min. Jour., Oct. 3, 1908, 7 pp. Cyanide mills of Guanajuato Development Co. Eng. & Min. Jour., Nov. 14 and 21, 1908, 9 pp. El Rayo gold mine and mill, near Santa Barbara, Mex. Eng. & Min. Jour., July 11, 1908, 3 pp. Jesus Maria and Flores mills, Guanajuato. Eng. & Min. Jour., Sept. 26, 1908, 5 pp. Milling and cyanide practice at El Oro. Eng. & Min. Jour. ; Apr. 3, 1909, 8 pp. CLASSIFIED BIBLIOGRAPHY 259 New Esperanza mill at El Oro. Eng. & Min. Jour., Oct. 17, 1908, 3 pp. Some metallurgical processes at Pachuca, Mexico. Eng. & Min. Jour., Sept. 19, 1908, 4 pp. Veta Colorado cyanide mill, Parral, Mex. Eng. & Min. Jour., July 18, 1908, 3 pp. RICKARD, T. A. Cyanide practice at El Oro. M. & S. P., Sept. 29 and Oct. 6, 1906, 7 pp. "Recent Cyanide Practice, " pp. 114 and 125. Old and new methods at Guanajuato. M. & S. P., June 29, 1907, 2 pp. "Recent Cyanide Practice," p. 296. Metallurgical development at Guanajuato. M. & S. P., May 18, 1907, 2 pp. "Recent Cyanide Practice, " p. 254. SCOBEY, J. Ore treatment at Virginia and Mexico mill, Jalisco. Eng. & Min. Jour., Oct. 2, 1909, 1 p. SEAMON, W. H. Yoquivo mine and mill, Western Chihuahua. Eng. & Min. Jour., Oct. 22, 1910, 2 pp. SHAPELY, C. Slime treatment at Santa Natalia mill. Eng. & Min. Jour., Aug. 20, 1910, 1 p. SHAPELY, E. All-slime cyanide plant at Guanajuato, Mex. Eng. & Min. Jour., July 10, 1909. SHERROD, V. B. Some features in work of Guerrero mill, Pachuca. Trans. Mex. Inst., Dec., 1909, 4 pp. Some notes on combination processes for treatment of silver ores. Mex. Min. Jour., Apr., 1911, 1 p. SWEETLAND, E. J. Treatment of silver-lead tailing by cyanide process. Eng. & Min. Jour., Aug. 25, 1906, 2 pp. THOMAS, K. Guerro mill at Real del Monte, Hidalgo. Mex. Min. Jour., Jan. 9, 1909, 2 pp. TWEEDY (G. A.) and BEALS (R. L.). Cyanide plant and practice at Minas del Tajo, Sinaloa, Mex. T. A. I. M. E., vol. 41, 1910, 44 pp.; abstract in Eng. & Min. Jour., Mar. 12, 1910, 4 pp.; abstract in Min. World, Mar. 12, and 19, 1910, 9 pp. VAN LAW, CARLOS W. Cyanide plant for treating Guanajuato ores. Eng. & Min. Jour., Apr. 6, 1907, 3 pp. VAN SUAN, P. E. Cyaniding at Guazapaies, Mex. Eng. & Min. Jour., Oct. 7, 1911, 2 pp. WESTON, W. Santa Gertrudis cyanide mill. Eng. & Min. Jour., July 15, 1911, 2 pp. WILLIS, H. T. Cyanidation of Parral silver ores. M. & S. P., Apr. 3, 1909, 2 pp. Mex. Min. Jour., May, 1909, 2 pp. Engineering and Mining Journal. Cyanide practice at El Tajo mine, Jalisco, Mex. Jan. 29, 1910, 1 p. Mining and Scientific Press. Dos Estrellas mill. (Costs and method.) Feb. 8, 1908, 2 pp. "More Recent Cyanide Practice," p. 118. Metallurgical chart of operations in Butters Copala mill, Mex. (No text.) Feb. 16, 1907, 1 p. Recent cyanide mill of Guanajuato R. and M. Co. May 23, 1908, 1 p. "More Recent Cyanide Practice," p. 143. Mining World. Mining and milling at Guanajuato. Oct. 26, 1907, 5 pp. 260 TEXT BOOK OF CYANIDE PRACTICE X. Cyanidation in United States and Canada 1. NEVADA ADAMS, W. S. Cyanide practice at the Darby, Nevada, Ore Reduction Co. Mex. Min. Jour., Aug., 1910, 1 p. AYRES, E. R. Bullfrog cyanide mill. Eng. & Min. Jour., Feb. 23, 1907. BARBOUR, P. E. Goldfield Consolidated 600-ton mill. Eng. & Min. Jour., Sept. 5, 1908, 8pp. BOSQUI, F. L. Milling v. smelting in treatment of Tonopah-Goldfield ores. M. & S. P., Mar. 31, 1906, 1 p. "Recent Cyanide Practice," p. 33. Ore treatment at Combination mine, Goldfield. M. & S. P., Oct. 6 and 13, 1906, 6 pp. "Recent Cyanide Practice," p. 136. Treatment of Desert ores. M. & S. P., May 26, 1906, 1 p. "Recent Cyanide Practice," p. 51. BROWNE, R. S. Cyanidation in Nevada. M. & S. P., Nov. 30, 1907. "More Recent Cyanide Practice," p. 39. CAMPBELL, B. P. Windfall mine and mill. Pac. Miner, Sept., 1909, 2 pp. COLLINS, E. A. Cyanidation in Nevada. M. & S. P., Jan. 11, 1908= "More Recent Cyanide Practice," p. 40. CREHORE, L. W. Modern cyanide mill at Mazuma, Nev. Min. World, Sept. 11, 1909, 1 p. GAYFORD, E. Details of cyaniding at Fay, Nevada. M. & S. P., Oct. 25, 1902, 1 p. HANSON, H. Mines and plants of Pittsburgh-Silver Peak. M. & S. P., May 8, 1909, 5 pp. "More Recent Cyanide Practice," p. 263. Pittsburgh-Silver Peak mill. Mines & Mins., July, 1909, 4 pp. HUNT, B. Cyanidation in Nevada. M. & S. P., Feb. 22, 1908, 1 p. " More Recent Cyanide Practice," p. 48. Treatment of Desert ores. M. & S. P., Apr. 28 and June 23, 1906. "Re- cent Cyanide Practice," pp. 65 and 247. HUTCHINSON, J. W. Operations of Goldfield Consolidated Mill, Nevada. M. & S. P., May 6 to June 10, 1911. Reprinted in pamphlet form. KING, L. M. Cyanidation in Nevada. M. & S. P., Jan. 25, 1908, 3 pp. "More Recent Cyanide Practice," p. 41. Treatment of Desert ores. M. & S. P., Aug. 25, 1906, 1 p. "Recent Cyanide Practice, " p. 82. KIRBY, A. G. Cyanidation in Nevada. M. & S. P., June 20, 1908, 4 pp. "More Recent Cyanide Practice," p. 50. KIRCHEN, J. C. Tonopah-Extension mill. M. & S. P., Apr. 9, 1910, 2 pp. LAMB, M. R. Stamp-mill and cyanide plant of Combination Mines Co. Eng. & Min. Jour., June 30, 1906, 2 pp. LEAVER, E. S. Milling practice in Nevada-Goldfield Reduction Works. M. & S. P., Aug. 22, 1908, 1 p. "More Recent Cyanide Practice, " p. 198. MAGENAU, W. Cyaniding stamp-mill tailing at Tuscarora, Nev. Mines & Mins., vol. 21, p. 299, 2 pp. MARTIN, A. H. Goldfield Consolidated mill. Min. Sci., Feb. 11, 1909, 2pp. CLASSIFIED BIBLIOGRAPHY 261 Hundred-stamp Deseret mill at Millers, Nev. Min. World, May 1, 1909, 3pp. Milling conditions in Goldfield district, Nev. Min. World, Mar. 13, 1909, 5 pp. Milling methods at Grass Valley and Nevada City. Pac. Miner, Aug., 1909, 3 pp.; Min. World, Dec. 4, 1909, 3 pp. Mill of Tonopah Mining Co. Min. Sci., Feb. 24, 1910, 2 pp. Montana-Tonopah mine and mill. Min. World, Mar. 12, 1910, 2 pp. Montgomery-Shoshone mill. M. & S. P., Feb. 19, 1910, 2 pp. Pittsburgh-Silver Peak mill. Min. World, Sept. 10, 1910, 2 pp. Silver Peak mill. Min. Sci., Nov. 18, 1909, 1 p. Tonopah Extension mine and mill. Pac. Miner, Oct., 1910, 2 pp. Treating low grade ore at Comstock lode. (Butters plant.) Min. Sci., Jan. 21, 1909, 2 pp. MORRIS, H. G. Equipment and practice at Florence-Goldfield mill. Eng. 6 Min. Jour., Feb. 12, 1910, 3 pp. PARSONS, A. R. Deseret mill, Millers, Nev. M. & S. P., Oct. 19, 1907, 4 pp. "More Recent Cyanide Practice," p. 9. Nevada cyanide practice. Mex. Min. Jour., Aug., 1911, 1 p. RICE, C. T. Butters cyanide plant, Virginia City, Nev. Eng. & Min. Jour., Feb. 9, 1907, 5 pp. Milling at the Florence-Goldfield. Eng. & Min. Jour., Apr. 15, 1911, 2 pp. Tonopah-Belmont cyanide plant. Eng. & Min. Jour., July 15, 1911, 4 pp. Tonopah-Belmont surface plant. Eng. & Min. Jour., Apr. 29, 1911, 3 pp. RICKARD, T. A. Metallurgical development at Goldfield, Nevada. M. & 5. P., June 20, 1908, 3 pp. "More Recent Cyanide Practice," p. 151. ROTHERHAM, G. H. Milling plant of Montana-Tonopah Mining Co. M. & S. P., Sept. 5, 1908, 4 pp. "More Recent Cyanide Practice," p. 201. TYSSOWSKI, J. Goldfield Consolidated mill operations. Eng. & Min. Jour., June 11, 1910, 1 p. VAN SAUN, P. E. Cyaniding at Montgomery-Shoshone mill. Eng. & Min. Jour., Jan. 22, 1910, 3 pp. Mines & Mins., Mar., 1908, 2 pp. Nevada Wonder Co.'s new mill. Min. & Eng. World, Nov. 11, 1911, 4 pp. WOLCOTT, G. E. Mines and mills of Tonopah, Nev. Eng. & Min. Jour., Mar. 20, 1909, 3 pp. Engineering and Mining Journal. New mill of Tonopah Extension Min- ing Co. May 21, 1910, 1 p. Montana-Tonopah stamp and cyanide mill. May 9, 1908, 3 pp. Wet-crushing cyanide plant at Ely, Nevada. (Chainman mine.) Dec. 7, 1901, 2 pp. Mining Science. Goldfield Consolidated mill. May 7, 1908, 1 p. 2. BLACK HILLS BOSQUI, F. L. Cyanide practice at Homestake Mills. M. & S. P., July 6, 1907, 3 pp. "Recent Cyanide Practice," p. 302. CLARK (A. J.) and SHARWOOD (W. J.). Notes on cyaniding methods at Homestake. Min. World, Mar. 26, 1910, 2 pp.; abstract from Jour. Ch., Met., & Min. Soc., S. A. 262 TEXT BOOK OF CYANIDE PRACTICE FULTON, C. H. Crushing in cyanide solution as practiced in Black Hills. T. A. I. M. E., vol. 35, 1904, 28 pp.; M. & S. P., vol. 89, pp. 207, 224, 243, 260, 273, 290, and 310, 7 pp. Cyanide process in Black Hills. Bull. No. 5 of South Dakota Sch. of Mines, Feb., 1902, 87 pp. Metallurgical practice in Black Hills. Bull. No. 7 of South Dakota Sch. of Mines, June, 1904, 63 pp. Metallurgical practice in Black Hills. Mines & Mins., Apr., 1905, 3 pp. GROSS, J. Cyanide practice at the Maitland properties. T. A. I. M. E., vol. 35, 1904, 20 pp.; abstract in Eng. & Min. Jour., Oct. 20, 1904, 1 p.; abstract in M. & S. P., Dec. 10 to 31, 1904. HENTON, J. H. Wet-crushing and cyaniding siliceous ores of Black Hills. M. & S. P., vol. 80, p. 261. Some further mill practice in cyaniding siliceous ores of Black Hills. M. & S. P., vol. 81, p. 284 (Sept. 8, 1900), 1 p. MAGENAU, W. Present practice of cyanidation in Black Hills. Eng. & Min. Jour., Aug. 11 and 18, 1904, 6 pp. MERRILL, C. W. Metallurgy of Homestake ores. T. A. I. M. E., vol. 34, 1903, 14 pp.; abstracts in M. & S. P., Oct. 3 to 24, 1903, 3 pp.; Eng. & Min. Jour., Mar. 7, 1903, 2 pp.; Mines & Mins., Dec., 1903, 1 p.; M. & S. P., Mar. 7, 1903, 1 p. MILLIKEN, J. T. Cyaniding in Black Hills. M. & S. P., vol. 89, p. 176, lp. O'BRIEN, B. D. Cyaniding Black Hills "blue ores." Mines & Mins., Apr., 1909, 5 pp. SAWYER, E. B. Direct wet-crushing cyanide mill of Black Hills. M. 63.54 1.62 60.78 63.79. 39.22 36.21 .65 .57 19.75 101.25 32.50 30.97 61.54 64.59 1.63 61.38 64.42 38.62 35.58 .63 .55 19.63 101.87 31.98 30.48 62.54 65.63 1.64 61.97 65.04 38.03 34.96 .61 .54 19.51 102.50 31.48 30 63.53 66.67 1.65 62.56 65.66 37.44 34.34 .60 .52 19.39 103.12 31 29.54 64.52 67.72 1.66 63.14 66.27 36.86 33.73 .58 .51 19.28 103.75 30.53 29.10 65.51 68.76 1.67 63.71 66.87 36.29 33.13 .57 .50 19.16 104.37 30.07 28.66 66.51 69.80 1.68 64.28 67.46 35.72 32.54 .56 .48 19.05 105 29.63 28.24 67.50 70.84 1.69 64.84 68.05 35.16 31.95 .54 .47 18.93 105.62 29.20 27.83 68.49 71.88 1.70 65.39 68.63 34.61 31.37 .53 .46 18.82 106.25 28.79 27.44 69.48 72.93 1.71 65.93 69.20 34.07 30.80 .52 .45 18.71 106.87 28.38 27.05 70.48 73.97 1.72 66.47 69.77 33.53 30.23 .50 .43 18.61 107.50 27.99 26.67 71.47 75.01 1.73 67.02 70.33 32.98 29.67 .49 .42 18.50 108.13 27.60 26.31 72.46 76.04 1.74 67.56 70.88 32.44 29.12 .48 .41 18.39 108.75 27.22 25.95 73.45 77.08 In part from W. A. Caldecott. Proc. Chemical and Metallurgical Society, S. A. Vol. 2. TABLES 281 Slime Pulp Table * Concluded Specific gravity of dry slime, 2.7. Upper set of figures. Specific gravity of dry slime, 2.5. Lower set of figures. Single set of figures refer to any specific gravity. Specific Gravity of Slime Pulp. Per Cent by Weight of Dry Slime in Wet Pulp. Per Cent by Weight of Solution in Wet Pulp. Ratio by Weight of Solution tolof Dry Slime. Volume in Cu. Ft. of 1 Ton Wet Pulp. Weight in Lbs. of 1 Cu. Ft. of Wet Pulp. Volume in Cu. Ft. of Wet Pulp Containing 1 Ton Dry Slime. Weight in Lbs. of Dry Slime in 1 Cu. Ft. Wet Pulp. 1.75 68.07 71.43 31.93 28.57 .47 .40 18.29 109.38 26.86 25.61 74.45 78.13 1.76 68.58 71.97 31:42 28.03 .46 .39 18.18 110 26.51 25.26 75.44 79.17 1.77 69.09 72.50 30.91 27.50 .45 .38 18.08 110.63 26.16 24.93 76.43 80.21 1.78 69.60 73.03 30.40 26.97 .44 .37 17.98 111.25 25.83 24.61 77.43 81.25 1.79 70.10 73.56 29.90 26.44 .43 .36 17.88 111.88 25.50 24.30 78.42 82.29 1.80 70.59 74.07 29.41 25.93 .42 .35 17.78 112.50 25.19 24 79.41 83.33 1.81 71.08 74.58 28.92 25.42 .41 .34 17.68 113.13 24.88 ! 23.71 80.40 84.37 1.82 71.56 75.09 28.44 24.91 .41 .33 17.58 113.75 24.57 23.41 81.40 85.41 1.83 ! 72.04 75.59 27.96 24.41 .39 17.48 .32 1 114.38 24.27 23.13 82.39 86.46 1.84 72.51 76.09 27.49 23.91 .38 .31 17.39 115 24 22.86 83.38 87.50 1.85 72.97 76.58 27.03 23.42 .37 .31 17.30 115.63 23.70 22.59 84.37 88.54 1.86 73.43 77.06 26.57 22.94 .36 .30 17.20 116.25 23.43 22.33 85.37 89.58 1.87 73.89 77.54 26.11 22.46 .35 17.11 .29 116.88 23.15 22.07 86^36 90.63 1.88 : 74.34 78.01 25.66 21.99 .35 17.02 117.50 22.89 .28 21.83 87.35 91.67 1.89 74.79 78.48 25.21 21.52 .34 .27 16.93 118.13 22.64 21.57 88.35 92.71 1.90 75.23 78.95 1.91 75.67 79.41 24.77 21.05 24.33 20.59 .33 .27 .32 .26 16.84 16.75 118.75 119.38 22.40 21.32 22.14 21.10 89.34 93.75 90.33 94.79 1.92 76.10 79.86 23.90 20.14 .31 16.67 120 20.90 .25 20.87 91.32 95.83 * In part from W. A. Caldecott. Proc. Chemical and Metallurgical Society, S. A. Vol. 2. INDEX A. Acid cyanide solutions, 34. Acidity of cyanide solutions, test for, 33. Acid slag, 185, 190. solutions, standard. (See Solu- tions.) treatment. (See Precipitate.) treatment and roasting, chapter on, 179. treatment of concentrate, pre- liminary, 23, 204. Adair-Usher cyanide process, 129. Aeration, 11, 13, 47, 57, 58, 93, 96, 102, 103, 199. method in percolation, 102, 104, 199. Agitation, 113. amount and strength of solution, 114. and slime treatment, 108. extraction tests, 71. increased consumption of cyanide and lime, 124. intermittent and continuous, 115. of concentrate, 201. Agitators for laboratory, 71. Agitators, types of, 118. Alkaline sulphides or sulphocyanides in silver ore, 19, 46. sulphides or sulphocyanides, oc- currence, 23, 24, 45. sulphides and sulphocyanides, re- moval by lead acetate, 46, 47. sulphides and sulphocyanides, re- moval by mercury, 13, 25, 47, 171. sulphides and sulphocyanides, re- moval by zinc, 46. sulphides, test for, 48. Alkalinity and lime, chapter on, 54. A Ik- Alia and alkalinity. (See Lime.) Alkali solutions, standard. (See So- lutions.) Aluminum, effect of, 26. Amalgamation of concentrate, 201. tests, 77. Ammonia, use in cyaniding, 23. Ammonium cyanide, 9. Annealing graphite crucibles, 192. Antimony, effect of, 24. Arsenic, effect of, 24. Arseniureted hydrogen in precipitate treatment, 181, 211. Assay of base metals in cyanide solu- tion, 53. of gold and silver in cyanide solu- tion, 50. of zinc precipitate, 195. Atomic weights, 273. Available cyanide, definition and test, 48. B. Barium cyanide, 9. Base metals in cyanide solutions, assay of, 53. Basic slag, 185, 190. Bibliography, classified, 213. Bisulphate of sodium treatment of precipitate, 182, 183. Borates in precipitate melting, 185, 187, 189. Borax and borax glass as fluxes, 185, 187, 189, 190. Bottle tests in ore-testing, 69, 71, 72.. Bromocyanide, Use of, 12, 204, 206. Brown air-agitator, 116, 121. Burt rapid filter, 152. revolving filter, 152. Butters and Mein sand distributor, 3,92. filter, 140. 283 284 INDEX C. Calcium. (See Lime.) cyanide, 9. Capacity of tanks, formulae and table, 274, 275. Carbon and carbonaceous matter, effect of, 26, 64. Carbonic acid neutralized by lime and alkalinity, 59. acid of air in agitation, 124. Caustic alkalis. (See Lime.) soda and potash, standard solu- tions, 39, 41. Causticity of lime, determination of, 63. Center-washing in Merrill filter press, 137, 155. Centrifugal pumps in agitation, 119, 120, 121. Chemistry of cyanide solutions, chap- ter on, 28. Chiddy-method .assay of cyanide solutions, 51. Clarifying cyanide solutions, 127, 161, 162. Classification of leaf filters, 140, 154. of ores in cyaniding, 21. of sand and slime, 91, 111. Classified bibliography, 213. Clay liners in graphite crucibles, 191. Cleaning-up, chapter on, 176. Cobalt, effect of, 26. solution for cyanide poisoning, 209. Concentrate cyaniding,, aeration, 199. cyaniding, agitation and fine grind- ing, 201. cyaniding, chapter on, 197. cyaniding, filtration, 201. cyaniding, general considerations, 202. cyaniding, lime and alkalinity in, 198, 200. cyaniding, percolation, 197. cyaniding, preliminary acid treat- ment, 204. testing by cyanide, 78. Continuous agitation, 115. decantation, 129. Copper, effect of, 23. in solution, 170. Crucibles. (See Graphite crucibles.) Crushing, effect of size of, 16. testing for fineness required, 72. Cyanates, 49. Cyanic acid, 49. Cyanicides, 14. Cyanide, action on sulphides, 19, 45. addition in agitation, 113. consumption, increased by agita- tion, 124. consumption, test for cause of, 83. decomposition of, 10, 49. definition of, 7. difference between potassium, sodi- um, and other cyanides, 9. discovery and early use, 1. double, action of, 36. how added to solution, 100. manufacture of, 9. mechanically lost in percolation, 106. poisoning, chapter on, 207. poisoning in precipitate refining, 210. poisoning, prevention, 211. poisoning, treatment with cobalt solution, 209. poisoning, treatment with ferrous salts, 209. poisoning, treatment with hydro- gen peroxide, 208. process, development, 3. process, discovery, 2. properties and reactions, 7. regeneration by lime, 36. regeneration by mercury, or mer- cury salts, 12, 44. regeneration in zinc box, 173. simple and double, 8. solubility of potassium, 9. solution, action of weak and strong, in precipitation, 58, 160. solution, assay of base metal in, 53. solution, assay of gold and silver in, 50. solution, chemistry of, 28. INDEX 285 Cyanide, solution, clarifying, 127, 161, 162. solution, determining strength to be used, 69. solution, handling and control of, during percolation, 96-107. solution, heating, 15. solution, how standardized, 99. solution, nature of acid, 34. solution, quantity necessary, 17, 114. solution, selective action, 14. solution, strength required, 13. solution, test for acidity, 33. solution, test for alkaline sul- phides, 48. solution, test for available cya- nide, 48. solution, test for double cyanides, 35. solution, test for ferri- and ferro- cyanides, 44. solution, test for free cyanide, 29. solution, test for hydrocyanic acid, 32. solution, test for protective alka- linity, 38. solution, test for reducing power, 49. solution, test for total alkalinity, 43. solution, test for total cyanide, 35. solution, zinc in, 172. testing solid, 32. various simple cyanides, 9. Cyanogen, definition of, 7. greater affinity for certain metals, 8. source of, 8. D. Decantation by mechanical means, 129. chapter on, 125. continuous, 129. imperfections of, 126. preceding filtration, 125, 130. in practice, 126, 127. theory of, 125. Decomposition of cyanide, 10, 49. Dehne plate-and-frame filter press in Australia, 133. Depth of sand vats, 93, 199. Development of cyanide process, 3. Direct-filling of sand vats, 90. Discovery of cyanide process, 2. Dissolution of gold and silver, chap- ter on, 11. time required, 18. Distributor for sand vats, 90, 91. Dorr classifier, 91, 111. pulp-thickener, 112, 129. Double cyanides, action of, 36. cyanides, definition of, 8. cyanides, test for, 35. Dressing zinc boxes, 165, 167. Dry-crushed ore, percolation of, 89. Drying ore, 205. E. Electrical precipitation, 5, 159. Electrolytes in slime settlement, 110. Extraction, test for cause of poor, 82. tests. (See Ore-testing.) F. Ferri- and ferrocyanides, decomposi- tion by mercury salts, 12, 44. and ferrocyanides, occurrence, ac- tion and test, 43, 44. Ferrous salts in cyanide poisoning, 209. Filter, leaf, building-up of solution, 157. leaf, Burt rapid, 152. leaf, Burt revolving, 152. leaf, Butters, 140. leaf, classification of, 140, 154. leaf, comparison of types, 156. leaf, encrustation by lime, 59, 158. leaf, general considerations, 137, 154. leaf, granular material for cake, 137, 155. leaf, Hunt, 146, 157. leaf, Kelly, 148, 201. leaf, Moore, 140. 286 INDEX Filter, leaf, Oliver, 143, 157. leaf, Ridgeway, 148, 156. press, plate-and-frame, centerwash- ing in Merrill type, 137. press, plate-and-frame, Dehne type in Australia, 133. press, plate-and-frame, descrip- tion, 131. press, plate-and-frame, in prac- tice, 133. press, plate-and-frame, Merrill type, 135, 155. press, plate-and-frame, use of monteju, 133. Filtration, chapter on, 131. of concentrate, 201. Fine-grinding, 16, 202. Fluor spar as a flux, 186, 190. Fluxes in melting, borax and borax glass, 185, 187, 189, 190. in melting, manganese dioxide, 186, 189, 191. in melting, niter, 186, 189, 191, 195. in melting, silica, 186, 187, 189, 190. in melting, sodium and potassium carbonates, 185, 187, 189, 190, 191. Fluxing, 185, 187, 190. and melting, chapter on, 184. preparation of precipitate and flux, 192. variations due to zinc, 188. Foul solutions, 15. Free acidity in ore, test for, 68. acidity, removal in plant prac- tice, 97. cyanide, definition and test, 29. Furnace, melting, 192. G. Gold and silver, dissolution by cy- anide, 11. and silver mechanically lost in percolation, 106. Graphite crucibles, action of oxi- dizers on, 186, 189. crucibles, annealing, 192. crucibles, clay-liners, 191. Graphite crucibles, composition, 189. crucibles, treatment after use, 194. effect in cyaniding, 26. H. Heating cyanide solution, 15. Hendryx agitator, 121. History and development of cyanide process, chapter on, 1. Hunt filter, 146, 157. Hydrocyanic acid, occurrence, 26, 32, 56, 59, 124, 181, 207,210,211. poisonous effects, 207, 210, 211. acid, test for, 32. acid treatment of precipitate, 180, 182. Hydrogen in precipitation, 26, 59, 167. peroxide in cyanide poisoning, 208. I. Indicator, potassium iodide, 29, 31. Indicators of acidity and alka- linity, 39. Interfering substances, 21. Iron, effect of, 23, 43, 56. oxidation and neutralization by alkali, 56, 200. J. Just silica-sponge brick agitator, 117, 123. K. Kelly filter, 148, 201. L. Latent acidity of ore, test for, 68. acidity, removal in plant practice, 97. Law of mass action, 46. Leaching. (See Percolation.) Leaching rate, definition and test, 80. Lead acetate, use in ore-testing, 70, 78. acetate, use in precipitating alka- line sulphides, 46, 47. acetate, use in zinc-lead couple, INDEX 287 Lead, effect of, 24. in precipitate, fluxing of, 189. smelting of zinc precipitate, 195. tray assay of cyanide solution, 50. Leaf filter. (See Filter, leaf.) Lime, action on sulphide, 37, 45, 60, 200. action on zinc and use in precipita- tion, 58, 160, 167, 169. amount required in practice, 60, 63. and alkalinity, chapter on, 54. and caustic soda compared, 63. as a flux, 190. as neutralizer of carbonic acid, 59. as neutralizer of iron and other salts, 55. determining amount required, 68, 69, 82. determining causticity of, 63. dissolving effect on metals, 60. in slime settlement, 110, 112. method of application, 61, 98, 102, 113, 198. on filter leaves, 59, 158. precipitation of gold by carbon of, 64. properties, varieties, and uses, 54. reducing agents in, 64. regeneration of cyanide by, 36. solubility of, 54, 274. water, 54. Litharge, use in precipitating alka- line sulphides, 47. M. MacArthur-Forrest process, 2. Magnesium cyanide, 9. effect of, 26. Manganese dioxide as a flux, 186, 189, 191. dioxide as an oxidizer in ore treat- ment, 12. effect of, in ore, 26. Manufacture of cyanide, 9. Matte from precipitate melting, 191. treatment of old, 194. Mechanical agitators, 118, 128, 201. decantation processes, 129. Melting and fluxing, chapter on, 184. furnace, 192. with litharge and cupellation, 195. Mercury, effect of, in ore, 25. and mercury salts, use of, in de- composing ferrocyanides, 12, 44. and mercury salts, use of, in pre- cipitating alkaline sulphides, 13, 25, 47, 171. in precipitation, 25, 171. Merrill filter press, 135, 155. Methyl orange indicator, prepara- tion, 39. Milk-of-lime, 54. Moisture retained in percolation, 105. Moore filter, 140. Monteju with filter press, 133. N. Nickel, effect of, 26. Niter, use in melting, 186, 189, 191, 195. use in roasting, 180, 182. Nitric acid treatment of precipitate, 180, 181. O. Oliver filter, 143, 157. Ore testing, agitation extraction tests, 71. testing, amalgamation tests, 77. testing and physical determina- tions, chapter on, 65. testing, bottle tests, 69, 71, 72. testing by percolation, 71. testing, cause of cyanide consump- tion, 83. testing, cause of low extraction, 82. testing, determining cyanide strength required, 69. testing, determining lime re- quired, 68, 69. testing during plant operation, 83. testing for fineness of crushing, 72. testing for leaching rate, 81. testing for slime settling rate, 82. testing, free acidity test, 68. testing, latent acidity test, 68. 288 INDEX Ore testing, methods of, 65, 79. testing of concentrate, 78. testing on large scale, 80. testing, physical examination of ore, 67. testing, precipitation tests, 83. testing, samples for, 66. testing, sizing tests, 73. testing, specific gravity deter- minations, 84. testing, total acidity test, 68. Oxidation of iron salts, 57, 103, 200. Oxidizers in melting and roasting, 180, 182, 186, 189, 191, 195. in ore treatment, 12, 43. Oxidizing roast of ore, 205. Oxygen in cyanide process, 11, 13, 15, 17, 23, 45, 57, 102, 103, 114, 199, 200. P. Pachuca tanks, 116, 121. Percolation, aeration, 102. application of lime, 97. application of solution, 96. arrangement of leaching plant, 93. chapter on, 87. classification for, 91, 111. continuous or alternative wash- ing, 103. cyanide and dissolved metal dis- charged, 106. depth of charge, 81, 93, 199. determining progress of dissolu- tion, 102. direct-filling, 90. fineness of ore, 93. handling and control of solutions, 96-107. leaching rate, 80. moisture retained by sand, 105. of dry-crushed ore, 89. strength of solution, 14. tailing deposit treatment, 87. tests in laboratory, 71. transfer after direct-filling, 92. variation of space due to settle- ment or transfer, 92, 96, 272. Percolation, water-washing and re- moval of cyanicides, 97. Phenolthalein indicator, prepara- tion, 39. Physical determinations and ore testing, chapter on, 65. Plate-and-frame filter press. (See Filter press.) Plant arrangement in percolation, 93. Poisoning, cyanide. (See Cyanide poisoning.) Potassium carbonates as fluxes, 185, 187, 189, 190, 191. cyanide. (See Cyanide.) iodide in free cyanide test, 29, 31. nitrate in roasting and melting, 180, 182, 186, 189, 191, 195. permanganate as an oxidizer in ore treatment, 12. Precipitate, assay of, 195. constituents for melting, 184. fluxing and melting, chapter on, 184. melting with litharge and cupella- tion, 195. refining, arseniureted hydrogen, 181. refining by acid, 180. refining by bisulphate of sodium, 182, 183. refining by hydrochloric acid, 180, 182. refining by nitric acid, 180. refining by sulphuric acid, 181. refining by sulphurous acid, 183. refining, cyanide poisoning in, 210. refining, hot and cold washings, 182. roasting, 179, 182. Precipitation by carbon in ore or lime, 26, 64. care of, 165, 167. chapter on, 159. clarifying solutions, 127, 161, 162. cleaning-up, 176. copper in solution, 23, 170. electrical, 5, 159. hydrogen in zinc boxes, 26, 59, 167. INDEX 289 Precipitation, lime and alkalinity in, 58, 160, 167, 169. mechanical and chemical con- sumption of zinc, 171. mercury in, 25, 171. poor, 168. reactions in, 159. regeneration of cyanide and alkali, 173. tests in ore testing, 83. weak and strong solution in, 160. white precipitate, 58, 160, 168. zinc box, 161. zinc box, packing and dressing, 165, 167. zinc dust, 173. zinc-lead couple, 170. zinc shavings, amount required and consumption, 163, 172. zinc shavings, cutting, 171. zinc shavings, size required, 163. Pressure leaf filters. (See Filter, leaf.) Protective alkalinity, definition and test for, 38. alkalinity, uses of. (See Lime.) Prussian blue, 57. Pulp thickening, 112, 113. R. Rate of leaching, 80. Reducing power of cyanide solution, test for, 49. Refining precipitate. (See Precipi- tate refining.) Refractory ores, nature of, 21. Regeneration of cyanide and alkali in zinc box, 173. of cyanide by alkali, 36. of cyanide by mercury and mer- cury salts, 12, 44. Ridgeway filter, 148, 156. Roasting and acid treatment of pre- cipitate, chapter on, 179. ore, chapter on, 205. ore, test in, 206. use of niter, 180, 182. S. Samples for ore testing, 66. Sand and rock, table of weight, 272. and slime separation, 91, 111. filters for clarifying, 127, 161. treatment. (See Percolation.) Selective action of cyanide, 14. Settlement of slime. (See Slime settlement.) Shavings, zinc. (See Zinc shavings.) Short zinc, cause of, 171. zinc, disposal in clean-up, 177. Silica as a flux, 186, 187, 189, 190. Silicates in precipitate melting, 185, 186, 187, 189. Siliceous slag, 185, 190. Silver, dissolution by cyanide, 11, 19. nitrate test for free cyanide, 29. nitrate test for total or double cyanides, 35. ores amenable to treatment, 27. treatment for, 19. Simple cyanides, definition, 8. Size of metal particles, effect of, 16. Sizing tests, 73. Slag, basic and siliceous, 185, 190. pouring and latter treatment, 194. Slime agitation. (See Agitation.) definition and characteristics, 108. in tailing deposits, 88. pulp, specific gravity table of, 276-281. separation, 91, 111. settlement, 109. settlement, influence of depth, 110. settlement, lime in, 109. settling rate, test for, 82. thickening, 112, 113. treatment and agitation, chapter on, 108. Sluicing-bar of Merrill filter press, 136. Smelting. (See melting.) Sodium carbonates as fluxes, 185, 187, 189, 190, 191. cyanide. (See Cyanide.) peroxide as oxidizer, 12. 290 INDEX Solubilities of various chemicals, table, 274. Solubility of lime, 54, 274. of potassium cyanide, 9. Soluble sulphides. (See Alkaline sul- phides and sulphocyanides.) Solution, cyanide. (See Cyanide so- lution.) Solutions, standard acid and alkali, preparation, 39. standard acid and alkali, tables of equivalents, 42. standard acid and alkali, theory, 39. standard caustic soda and potash, 39, 41. Specific gravity determinations, 84. gravity of slime pulp, table, 276- 281. Standard solutions. (See Solu- tions.) Strength of cyanide solution re- quired, 13, 115. Strong solution in plant practice, 94-105. Strontium cyanide, 9. Sulphides. (See Concentrate.) Sulphocyanides. (See Alkaline sul- phides and sulphocyanides.) Sulphur, effect of, in melting, 189, 191, 195. effect of, in ore, 23. Sulphuric acid treatment of precipi- tate, 181. Sulphurous acid treatment of pre- cipitate, 183. T. Tables, chapter of, 269. Tailing deposits, treatment by per- colation, 87. settlement in ponds, 88. Tanks, classification of, 87, 94. volume of, formulae and table, 274, 275. Tellurium, effect of, 25. Test for complete roast, 206. Test for cyanide and dissolved gold mechanically lost in percolation, 107. Testing for precipitate flux, 186. ore. (See Ore testing.) solid cyanide, 32. solution. (See Cyanide solution.) Thickening of pulp, 112, 113. Thiocyanates. (See Alkaline sul- phides and sulphocyanides.) Time required for dissolution, 18. required in agitation, 115. Total acidity in ore, test for, 68. acidity in plant practice, 97. alkalinity, definition and test for, 43. cyanide, definition and test for, 35. cyanogen, 49. Treatment of concentrate. (See Concentrate cyaniding.) of matte, 194. of slag and old crucibles, 194. Trent agitator, 121. V. Vacuum leaf filter. (See Filter, leaf.) Volume of tanks, table and formulae, 274, 275. W. Water, table of weight and measure, 272. washing in percolation, 97, 105, 106. Weak solution in plant practice, 94, 105. White precipitate of zinc boxes, 58, 160, 168. Z. Zincates, how formed in precipita- tion, 160. Zinc box, 161. box, packing and dressing, 165, 167. dust precipitation, 173. effect of, in ore, 25. INDEX 291 Zinc in precipitate, fluxing, 188. Zinc precipitate, assay of, 195. in solution, accumulation, 171. precipitation. (See Precipitation.) in solution, action on alkaline sul- shavings, amount required and phides, 46. consumption, 163, 172. lead couple, 170. shavings, cutting, 171. potassium cyanide as a solvent, 36. shavings, size required, 163. RETURN TO the circulation desk of any University of California Library or to the NORTHERN REGIONAL LIBRARY FACILITY Bldg. 400, Richmond Field Station University of California Richmond, CA 94804-4698 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS 2-month loans may be renewed by calling (510)642-6753 1-year loans may be recharged by bringing books to NRLF Renewals and recharges may be made 4 days prior to due date DUE AS STAMPED BELOW HOY 3 1992 YC 18752 THE UNIVERSITY OF CALIFORNIA LIBRARY