UNIVERSITYo/tALIFORNIA 
 COLLEGE of MINING 
 
 DEPARTMENTAL 
 LIBRARY 
 
 * * 
 BEQUEST OF 
 
 SAMUELBENEDICTCHRISTY 
 
 PROFESSOR OF 
 
 MINING AND METALLURGY 
 1885-1914 
 
CYANIDE PROCESSES. 
 
 BY 
 
 E. B. WILSON, E.M. 
 it 
 
 FIRST EDITION. 
 
 FIRST THOUSAND. 
 
 NEW YORK: 
 
 JOHN WILEY & SONS. 
 
 LONDON- CHAPMAN & HALL, LIMITED. 
 
 1896. 
 
Copyright, 1895, 
 
 BY 
 
 E. B WILSON. 
 
 BRAUNWORTH, MUNN A BARBER, PRINTERS AND BOOKBINDERS, NEW YORK. 
 
CONTENTS. 
 
 PAGE 
 
 INTRODUCTION iii 
 
 CHAPTER I. STAMP-MILL WORK i 
 
 II. AMALGAMATION 7 
 
 III. FOUNDATION OF CYANIDE PROCESS 10 
 
 IV. CHEMISTRY OF THE OPERATION 21 
 
 V. LEACHING THE ORE 29 
 
 VI. ZINC AS A PRECIPITANT , 38 
 
 VII. TREATMENT OF BULLION 43 
 
 VIII. THE RECOVERY BY THE CYANIDE PROCESS 48 
 
 IX. LABORATORY WORK 54 
 
 X. GOLD AND SILVER SOLVENTS COMBINED WITH 
 
 ELECTRICAL ACTION 72 
 
 XI. CYANIDE SOLUTION WITH VARIOUS ELECTRODES ... 80 
 
 XII. THE CURRENT 87 
 
 XIII. ANODES 92 
 
 XIV. CATHODES 97 
 
 XV. VARIOUS PROCESSES AND CONCLUSIONS , 103 
 
 AUTHORITIES in 
 
 USEFUL INFORMATION. 113 
 

INTRODUCTION. 
 
 THE author's investigations of the Cyanide Process 
 were first confined to Patent Office literature, together 
 with such extracts as appeared from time to time in 
 technical journals and society periodicals. For his own 
 benefit he grouped the numerous articles which gave 
 but a passing insight into the subject. His investiga- 
 tions upon the subject made to verify the results as 
 set forth by the various writers convinced him that by 
 grouping the items of importance in connection with 
 the subject considerable light could be thrown on the 
 process and much time saved. 
 
 This grouping may also have the effect of bringing 
 out new ideas upon the subject, and the one point 
 mastered will not be forgotten while examining the 
 next article on the subject. The writer is indebted 
 to many for the ideas here advanced, and takes this 
 occasion to express his gratitude to them for their 
 valuable contributions. He has not attempted to go 
 into the mechanical arrangements for the process, be- 
 cause on the one hand circumstances will vary at each 
 plant, and on the other the arrangement of details 
 belongs to the engineer of the company controlling 
 and promoting the patents. The author's object has 
 
 in 
 
IV INTRODUCTION. 
 
 been to confine the text to the process itself and such 
 points as have special bearing on its success. While 
 the rudiments of this method were known as early as 
 1806, it is only within the past few years that its 
 practical value has been acknowledged, and even at 
 the present time many prefer to use more complicated 
 processes rather than change from a plan they are 
 familiar with to one which is comparatively unfamiliar. 
 
 The writer has endeavored to be unbiassed in his 
 remarks, but after reading and rereading some thirty 
 different patent specifications with their claims, he 
 fears stress enough has not been laid on defective 
 points, and begs the reader's consideration if his 
 opinions as set forth favor any one patentee more 
 than another. 
 
 What he desires to bring out clearly are the points 
 which he considers of value as he sees them, and to 
 avoid those whose value was yet to be demonstrated. 
 An examination of these numerous patents leads him 
 to the conclusion long ago reached by some eminent 
 authority that " there is nothing new under the sun." 
 
 For the benefit of those interested in mines he has 
 dilated somewhat on stamp-mill work ; for the benefit 
 of the miner he has made remarks which he hopes 
 will be of value; and lastly, for the mining engineer 
 he has told all he knows of the subject at the present 
 time. 
 
 THE AUTHOR. 
 
CYANIDE PROCESSES. 
 
 CHAPTER I. 
 
 PRACTICALLY speaking, there are but two classes 
 of ores which contain the precious metals : free-mill- 
 ing, or those which deliver up their gold contents to 
 amalgamation, and refractory, which only do so in a 
 measure or not at all. 
 
 The term " free-milling " is derived from the gold 
 in the ores being in such a state that upon being 
 crushed in a stamp-mill the particles of gold sepa- 
 rate from the rock, free, to be then brought into con- 
 tact with mercury, and from which they can only be 
 freed by distillation. This treatment is termed arnal- 
 gamation. 
 
 The term " refractory ores'* is derived from the 
 fact that all gold-bearing ores are not " free-milling," 
 and will not amalgamate their gold with mercury ; in 
 other words, obstinately refuse to yield up their gold 
 to the easiest method of recovery. 
 
 Free-milling ores do not yield all their gold, and 
 refractory ores will at times yield some of their gold 
 to mercury, but the circumstances connected with 
 
2 CYANIDE PROCESSES. 
 
 such results will not change the names adopted, as 
 will be shown. As we are dealing with ores with ref- 
 erence to their adaptability to the cyanide treatment, 
 and since all ores so treated must be stamped or 
 crushed for this treatment, we will consider that a sur- 
 vey of stamp-mill work should precede the details of 
 the process. 
 
 In all work uniformity of product is desirable, but 
 particularly is this the case in metallurgical work, to 
 obtain the most satisfactory results. Of the two 
 methods of crushing or stamping in use, namely, the 
 wet and the dry, the wet has given the better results 
 both as to uniformity of the grains and speed of 
 crushing. 
 
 When wet crushing is practised, water is allowed to 
 flow into the mortar of the stamp-mill and flow out 
 through a screen ; sometimes two screens are used, 
 one on each side of the mortar, giving a double dis- 
 charge. The sized mesh used on these screens varies 
 from sixty to one hundred for amalgamation, but for 
 the cyanide process it has been in many instances 
 possible to use 3O-mesh screens and even very much 
 coarser. 
 
 The size of the mesh of the screen determines the 
 degree of fineness to which crushing is to be carried, 
 as all fine particles which can pass the mesh are carried 
 through by water, while all that cannot pass through 
 remain in the mortar to be pounded until they can. 
 
CYANIDE PROCESSES. 3 
 
 With dry crushing two discharge-screens can be em- 
 ployed to give more uniform results and faster pulver- 
 ization. 
 
 When crushing dry, the stamps falling on the ore 
 pulverizes it ; there being no water to move it away, 
 the dry powder accumulates in the battery mortar 
 and under the stamps, thus retarding the process and 
 very often forming a cushion for the stamp, not al- 
 lowing it to crush particles uniformly. 
 
 The various machines so far invented have not 
 proved satisfactory for dry crushing ; and while with 
 new rolls a very uniform product can be obtained, 
 it is an endless repetition of screening and returning 
 to the rolls again. 
 
 The best dry crushing so far witnessed by the 
 writer is accomplished by Krupp's pulverizer; but 
 even this is very slow, still there is no elevating and 
 screening. 
 
 This field for inventive genius is open. There is 
 needed very badly a good dry crusher which will 
 crush uniformly, speedily, not clog with damp ores, 
 not break with hard ores, will crush both hard and 
 soft rock equally well, will not round the particles, 
 but leave rough surfaces as do stamps, and will not 
 be too costly for repairs. Any machine that can take 
 up and meet all these requirements will take the place 
 of stamp-mills. One of the obstacles to be overcome 
 in crushing wet for the cyanide process is the amount 
 
4 CYANIDE PROCESSES. 
 
 of water used necessary to do the work of uniform 
 crushing. This water has been in some instances re- 
 turned from settling-tanks back into the mortar to be 
 used again and again. While there are no objections 
 to the use of this water, there are to pumping 
 it. It is understood that with wet crushing water 
 enough must be used to allow the sludge to flow 
 through the screens. It is often to the advantage of 
 the cyanide process that coarse crushing is allowable, 
 both as to amount of water used and time saved in 
 crushing; still even this advantage of time is more 
 than counterbalanced by time lost in treatment of ore 
 by the cyanide solution when coarse crushing is prac- 
 tised. For if we are able to save time in crushing, and 
 subsequent drainage of water and liquor, we must 
 allow the cyanide solution to remain longer in contact 
 with ore being treated. 
 
 On the other hand, when fine crushing is employed, 
 as it must be at times, the water drains slowly from 
 the settling-tanks, leaving the fine ore very firmly 
 packed, and sometimes so firmly packed, if clayey or 
 slimy, as to almost allow of no filtration, even when 
 suction and other devices are employed to assist 
 gravity. The average speed of drainage is about 12 
 inches per hour, which can be increased mechanically ; 
 but even in this case we shall still have the packing to 
 contend with, which will interfere with cyanide leach- 
 ings. 
 
CYANIDE PROCESSES. 5 
 
 The character of the ore will determine the degree 
 of fineness in crushing. 
 
 An open porous ore might be crushed to the size of 
 a pea, while a compact ore with metal disseminated 
 through it in grains may need 6o-mesh or finer. 
 
 If the metal is in porous or loose ore in form of 
 seams or streaks, coarse crushing will answer. 
 
 It is often necessary with refractory ores to use a 
 preliminary treatment of lime to neutralize the 
 acids which usually are found in partially oxidized 
 sulphur pyritous ores, and are more or less dissoluble 
 in water. Attempts have been made to neutralize 
 these ores in the process of stamping by adding 
 lime to the stamp-water. The objection to this pro- 
 ceeding is that a great degree of uncertainty must 
 prevail as to the amount of lime required ; and more- 
 over, as the lime must be leached out of the ore by 
 water later on, not much is to be gained, but consider- 
 able annoyance will be caused if too much lime finds 
 its way into the ore. 
 
 Mr. A. B. Paul used a cyanide solution in the stamp- 
 battery, the object being to take up gold as it was 
 liberated from the ore, thus hastening the operation 
 and lessening the amount of water waste. 
 
 There are several objections to this practice which 
 make it unadvisable, and which summed up are : 
 
 That loss of cyanide takes place ; no coarse gold can 
 
O CYANIDE PROCESSES. 
 
 be taken up ; and that its action is of no great as- 
 sistance to the mercury to be used in such instances. 
 
 Also the amount of gold recovered by this method 
 would be so small that the customary leaching must 
 follow; hence no time is gained. Again, this system 
 would not be feasible if sulphurets were being treated. 
 
 The resume of stamp-mill work for our investiga- 
 tions amounts to this : 
 
 That the more uniform the particles are crushed 
 the more complete will be the extraction results with 
 cyanide ; 
 
 That the degree of fineness required will depend 
 upon the character of the ore and the method of the 
 distribution of metal in the ore ; 
 
 That porous ores require less fineness than compact 
 ores; 
 
 That dry, crushing does not give as uniform particles 
 as wet crushing ; 
 
 That the use of lime or cyanide solution in the bat- 
 teries is not to be commended ; 
 
 That where particles of free gold exist in any 
 appreciable size mercury can be used in the stamp- 
 mortar to facilitate recovery when sulphides are not 
 being stamped. 
 
CHAPTER II. 
 
 AMALGAMATION. 
 
 REFRACTORY ORES TAILINGS AND CONCENTRATES. 
 
 UNDER the heading of refractory ores come those 
 parts of free-milling ores which cannot be delivered 
 of their gold by mercury. With good stamp-mill 
 practice, there will float away in the slimes or tailings 
 a percentage of gold if wet stamping is followed, 
 and the same percentage of loss occurs when dry 
 crushing is practised. The cause of this loss will 
 be stated later on. Ores containing the precious 
 metals, free-milling at the surface very often become 
 refractory when they reach a depth where the elements 
 cannot obtain access to them ; this depth is usually 
 water-level. The cyanide process is particularly 
 adapted to this class of ores. 
 
 To obtain the gold from free-milling ores mercury 
 is placed in the mortar of the stamp-mill batteries, 
 and amalgamated copper plates placed so that the gold 
 going over them with slimes may be captured by the 
 mercury on the plates. This amalgamation, as it is 
 called, will recover by good mill-work 60$ of the gold 
 in the ore. 
 
 7 
 
8 CYANIDE PROCESSES. 
 
 The various reasons advanced why more gold is not 
 recovered are that the particles are too fine, and that 
 others are covered with a film of oxide, sulphide, or 
 tarnish which prevents the mercury from coming in 
 contact with the gold, thus preventing its uniting with 
 it. These fine particles and tarnished gold are virtu- 
 ally then refractory. After they have left the stamps 
 they are termed tailings. It has been customary to 
 grind these tailings in a pan with mercury, or to con- 
 centrate them by vanners, bumping-tables, or other 
 means. The cyanide process acts very readily and 
 completely on most tailings, so that its introduction 
 has been the means of recovering immense quantities 
 of gold from tailings. 
 
 Those ores which carry sulphides, tellurides, ar- 
 senides, antimonides, and base-metal compounds are 
 refractory. When containing considerable gold, if 
 treated with mercury, they make the mercury "flour," 
 or else sicken, so that both mercury and gold are lost. 
 
 Sickened mercury becomes so sluggish by admix- 
 ture of base metals that it will not act upon gold. 
 This mercury can be restored to its normal condition 
 so that it is not a loss, but while it is sickened it is of 
 no practical value for gold recovery. 
 
 Flouring of mercury is a much more serious affair. 
 It is due to sulphides coating the mercury and prevent- 
 ing the globules of mercury from uniting when once 
 separated. Continued working subdivides the mercury 
 
CYANIDE PROCESSES. 9 
 
 more and more until it becomes a black slimy mass 
 which will be found difficult to settle in water, and 
 is carried off in the washings and lost. 
 
 The separation of this metallic slime from the 
 heavier portions of the ore is almost an impossibility. 
 
 Various schemes have been proposed and various 
 chemicals tried to obviate the difficulties encountered 
 by flouring and sickening of the mercury, but we have 
 heard of none which have proved entirely satisfactory 
 to other than the inventor. 
 
 When fine or tarnished gold particles are met with, 
 and the mercury retains its bright appearance and 
 fluidity, amalgamation does not always ' take place. 
 To force the gold to meet the mercury mechanical 
 means, such as grinding with mercury, has been resorted 
 to. If sulphides are present, this will cause the mer- 
 cury to flour; if base metals are present, sickening of 
 the amalgam will result. The proper method for 
 treating such ores before the introduction of the cya- 
 nide process was concentration, or assortment for the 
 smelters. As we are dealing merely with stamp-mill 
 work only as it effects the cyanide process, we refer 
 those who desire further information to Prof. T. A. 
 Rickards' articles in the Engineering and Mining Jour- 
 nal, also to "California Gold Mill Practices" by Ed. B. 
 Preston, which are the most replete with information 
 of any in our language, at least that we have observed. 
 
CHAPTER III. 
 
 FOUNDATION OF CYANIDE PROCESS. 
 
 THAT gold was soluble in cyanide of potassium solu- 
 tions was known to Hagen in 1806. L. Eisner stated 
 in 1844 that gold and silver could be dissolved in 
 potassium cyanide without decomposition of water. 
 He further stated that the dissolution of the metals is 
 the consequence of the action of oxygen, which, ab- 
 sorbed from the air, decomposed part of the cyanides, 
 thus forming a double salt auro-potassic cyanide, 
 which has later been stated in the following equation, 
 known as " Eisner's Equation": 
 
 2Au + 4 KCy + O + H 3 = 2AuKCy 2 + 2KOH. 
 
 The first scientific literature on the subject is by 
 Prince Bagration in 1843. He concluded his paper 
 with the remark that in the future cyanide of potas- 
 sium must be enumerated among the solvents of gold. 
 Faraday made use of a cyanide solution to produce 
 thin films of gold in 1857. Ten years later J. H. 
 Rae took out the first patent for applying cyanide to 
 obtain gold from the ores direct. He was followed 
 by Faucett in 1881 ; He in turn by Sanders in 1881 ; 
 
 10 
 
CYANIDE PROCESSES. II 
 
 then by J. W. Simpson in 1885 ; finally by MacArthur 
 and Forrest in 1889. To these latter men is due the 
 praise, not that they were the first discoverers, but 
 because they pushed their inventions, and enabled the 
 recovery of $14,000,000 in five years by their process 
 which otherwise would be irrecoverably lost. 
 
 It is of no special moment to us who discovered the 
 process or whose process or patent is valid : that 
 MacArthur people proved the way by practical demon- 
 stration is of more value to the world than who owns 
 the patent. After the examination of some thirty or 
 forty patent claims it appears to the writer that the 
 patent offices are more at fault in granting claims than 
 those who make the claims and obtain the patents. 
 
 Eisner's equation has caused such comment as to 
 have led some to jump at conclusions too hastily. 
 Even MacArthur stated that oxygen in the solution 
 was not necessary for the dissolution of gold, but we 
 believe he has repented. A pure solution of potas- 
 sium cyanide will not dissolve gold to any great extent 
 when immersed in it, but dissolves it readily when 
 oxygen is present. 
 
 For example, if gold-leaf is placed on the surface of 
 a cyanide solution, it will dissolve in a few minutes, 
 and the stronger the solution the quicker it will dis- 
 solve ; however, if submerged in the solution it dis- 
 solves but slowly, the strength of the solution effect- 
 ing its rate of dissolution but slightly. 
 
12 CYANIDE PROCESSES. 
 
 MacLaurin of New Zealand made some experi- 
 ments which we quote from. 
 
 He used gold-leaf of uniform thickness, and his de- 
 ductions were that oxygen was necessary for the solu- 
 tion of cyanide if it was to dissolve gold with any 
 rapidity. A piece of gold-leaf placed in a stoppered 
 bottle lost o.i 8$ of its weight in ninety-two hours. 
 
 Another piece placed in open bottle lost 9.1$ of its 
 weight in sixty-two hours. Still another piece placed 
 in a bottle with oxygen lost 24.2$ of its weight in 
 ninety-six hours. The strength of the solutions was 
 identical in every instance. 
 
 Experiments were made by the State Mining Bureau 
 of California with dilute cyanide solution upon metal- 
 lic gold. 
 
 With a i per cent solution it was found possible 
 to dissolve such gold-leaf as is used by sign-painters 
 in one hour. When dentists' foil was used, about six 
 times thicker than painters' foil, it required forty- 
 eight hours to dissolve. 
 
 Mr. J. B. Hanney verified Eisner's equation and 
 MacLaurin's experiments in a practical way. His 
 theory was that dilute cyanide solutions acted more 
 rapidly on gold. He attributed this to the cyanide 
 displacing oxygen by dissolving in the water, and that 
 therefore gold could not dissolve until oxygen had been 
 absorbed from the air. To carry out this theory he 
 treated ores with dilute and then with strong solution. 
 
CYANIDE PROCESSES. 13 
 
 He found that the rate of dissolution of gold in- 
 creased with the strength of the solution, provided 
 oxygen of the air could come in contact with the gold. 
 
 Mr. Hanney invented an electro-chemical apparatus 
 which he used in his experiments. In direct oppo- 
 sition to this Mr. Miller has patented an apparatus 
 to keep the air away from the solution. 
 
 From MacLaurin's experiments we deduce: 
 
 1 . That oxygen is necessary for dissolving gold in 
 a cyanide solution, and that it combines with the 
 potassium of the potassium cyanide in the proportion 
 required by Eisner's equation. 
 
 2. The rate at which gold is dissolved in a solution 
 of potassium cyanide passes through its maximum in 
 passing from dilute to concentrated solution, due to 
 the fact that the solubility of oxygen in a cyanide 
 solution decreases with the concentration. (See " Gen- 
 eral Information.") 
 
 The MacArthur-Forrest patent, May 14, 1889, con- 
 sisted in subjecting the ores to a small quantity of 
 cyanide solution without any other chemically active 
 agent, but they state the process may be expedited 
 by stirring. 
 
 Mr. J. C. Montgomerie added NaHO, then NaO 2 , 
 finally Na 2 O 2 , each oxide being the cause of a separate 
 patent, and, as he says, giving equally good results. 
 
 Carl Moldenhauer claims that in order to extract 
 gold it is necessary to simultaneously oxidize the solu- 
 
14 CYANIDE PROCESSES. 
 
 tion. Instead of depending upon air and agitation 
 he dissolves gold with cyanide of potassium in the 
 presence of permanganate of potash. Later on he used 
 ferricyanide of potassium in connection with cyanide 
 of potassium to make the action more energetic, but 
 states that ferricyanide of potassium will not dissolve 
 gold. 
 
 THE SOLUTION. 
 
 The acknowledged practice for economical results 
 is to use a weak solution of potassium cyanide. Mac- 
 Arthur says regulate the quantity of cyanide so that 
 its cyanogen will be in proportion to the gold and 
 silver in the ore-charge, but in all cases to use suffi- 
 cient water to keep the solution extremely dilute, be- 
 cause when dilute its preference is for gold and silver 
 rather than the baser metals. 
 
 "We find it most advantageous to use a quantity 
 of cyanide the cyanogen of which is equal in weight 
 to from one to four parts for every thousand parts of 
 ore, and we dissolve the cyanide in a quantity of 
 water of about half the weight of the ore." 
 
 In other words, the solution should contain 8 parts 
 of cyanogen to 1000 parts of water by weight. This 
 proportion would give 20 pounds KCy to the 1000 
 pounds water, or 40 pounds to the ton of ore. This 
 amount is not sufficient, except for the weak solution, 
 at the commencement of the operation. The action 
 
CYANIDE PROCESSES. I 5 
 
 of cyanide upon gold is slow at first, but increases 
 with time ; hence by using a weak solution first to com- 
 mence the operation the way is paved for the standard 
 or strong solution, and at the same time the chances 
 are lessened for the strong solution attacking the base 
 metals present. There seems to be no definite rule 
 regarding the amount of cyanide required for taking up 
 one ounce of gold. Eisner's equation theoretically 
 gives the amount as I part cyanogen for every 1.5 
 parts of gold to be dissolved. Practical results require 
 40 parts cyanogen to I part of gold, and from this 
 down according to the care used and safeguards em- 
 ployed to economize its use. 
 
 Good results have been obtained with 0.05 per cent 
 of cyanogen in the solution to the ton of ore. 
 
 The percentage of cyanide required will depend 
 upon the nature of the ore and the methods used. 
 
 Losses must surely occur in treating ores contain- 
 ing acids or not thoroughly oxidized from acid salts. 
 
 They will also occur by Eisner's rule ; again, by 
 absorption of the vats ; by coming in contact with 
 carbonic acid ; they will also occur in the zinc pre- 
 cipitation-boxes. 
 
 There may also some loss occur by coming in con- 
 tact with iron 
 
 Mr. Paul says the proper per cent of the solution 
 should be as testing will show, viz., the proper per 
 cent for extracting the highest per cent of the pre- 
 
l6 CYANIDE PROCESSES. 
 
 cious metals, "say from one half per cent to one and 
 one half per cent, then treating the ore for a given 
 length of time with this solution." 
 
 Mr. Paul's rule is about the only rule we have to go 
 by, and it must be the case from the nature of 
 ores differing so widely in character. 
 
 Time is more an element for the successful opera- 
 tion of this process than a high percentage of cyano- 
 gen. As this depends upon the character of the ore, 
 tests must be employed, as illustrated under head- 
 ing of " Laboratory- work." 
 
 The action of the solution is to penetrate the ore, 
 find the gold, and bring it out ; if, therefore, coarse 
 crushing can be used, time may be gained in crushing 
 and rapidity of leaching, which will compensate for 
 the extra time required for keeping the solution in 
 contact with the ore. 
 
 Time may be saved by agitating the ore with the 
 solution, either by mechanical stirrers or rotating 
 barrels. These agitators are especially valuable for 
 quick work where fine crushing is necessary or clayey 
 slimes and tailings are to be dealt with. To facilitate 
 matters filter-presses and mechanical suction of the 
 liquid from the vats can be employed. In South 
 Africa the vats and charges are so huge that mechan- 
 ical stirrers would require considerable power, and as 
 the vats stand by themselves, requiring no watching, 
 no power is considered necessary. In other words, to 
 
CYANIDE PROCESSES. !/ 
 
 avoid the use of power they increase the size of the 
 vats, saving time by the great charges treated. 
 
 Slimes or tailings from other processes can be 
 readily treated by the cyanide method ; in fact this 
 makes it the most important all-around metallurgical 
 factor yet put in practice, its use not being limited to 
 free-milling or yet refractory ores, but adaptable to 
 many and various phases of gold extraction, and when 
 we say gold we mean silver as well, only using the 
 term gold to avoid repetition of the words gold and 
 silver. 
 
 Coarse gold requiring longer time for treatment by 
 cyanide, it is better if possible to save what can be 
 saved by amalgamation, and this latter would proba- 
 bly be followed because of the ease with which the 
 bullion can be recovered from mercury. 
 
 When such coarse gold occurs in conjunction with 
 fine gold or auriferous sulphurets, it is customary 
 to crush wet, amalgamate in the stamp-mill mortar, 
 pass the tailings into percolators or vats, which 
 are provided with overflow-pipes to conduct the 
 excess of water into a sump, from which it may be 
 returned into the battery to be used again. In order 
 to save a portion of the gold lost by amalgamation it 
 has been customary to use concentrators, which save 
 the metal grains containing gold and allow the sand 
 to run off in the water. Tailings thus greatly re- 
 duced in bulk can be shipped to smelters or treated 
 
1 8 CYANIDE PROCESSES. 
 
 again with mercury; the latter method will not prove 
 very effective, however. 
 
 It is possible to treat these concentrates by cya- 
 nide, but, being generally richer in metal, their treat- 
 ment requires longer time for the best results. As 
 their quantity is limited, the size of the plant need 
 not be as extensive as where the whole mass of tail- 
 ings is to be treated. Agitation will hasten the 
 operation with concentrates. Percolation with con- 
 centrates requires 20 days, because of the difficulty the 
 solution encounters in passing through the coarse par- 
 ticles of ore. " Difficulty sometimes arises, owing to 
 the crystalline form of iron pyrites and galena. These 
 minerals crystallize in cubes, and in fluid arrange 
 themselves face to face, so that a section of such a 
 mass depostied from fluid would resemble a brick wall 
 in structure." Dr. A. Scheidel suggests mixing 
 coarse sand with the cubes to overcome the difficulty. 
 (See "General Information.") 
 
 The results of the experiments made upon tailings 
 containing sulphurets by the State Bureau of Mining 
 of California are here given. A i-per-cent solution 
 of potassium cyanide was used for the experiments. 
 
 The experiments illustrate the effect of time and 
 strength of the solution, while they also illustrate that 
 the solution is not impaired in its action when sul- 
 phides only are present, both of which are important 
 items in considering the scope of the process. 
 
CYANIDE PROCESSES. 19 
 
 Treatment lasting 2 hrs. : tailings retained 35.29$ gold. 
 
 3 " *' , " 31-37* 
 
 4 M 30.37$ 
 6 M " 25.49$ M 
 8 " " " 21.56$ " 
 
 Another portion from the same lot of sulphurets 
 ground and passed through a loo-mesh screen (the 
 former having been passed through 6o-mesh sieve) 
 were then treated six hours. There was left in the 
 tailings after this treatment 17.64 per cent of gold, 
 showing that fineness of the ore in this case materially 
 aided digestion. 
 
 To ascertain whether dilute cyanide would extract 
 all the gold in these sulphurets the ore was ground in 
 an agate mortar to impalpable powder, and digested 
 or 48 hours with three different solutions of I per 
 cent cyanide, after which treatment the tailings were 
 found to contain 9.8 per cent of gold. 
 
 Another lot of sulphurets from which free gold 
 had been removed with great care was subjected to a 
 i-per-cent solution after passing i2O-mesh screen. 
 
 Treatment lasting 2 hrs. : tailings retained 31.2$ gold. 
 
 3 M " 28.5$ H 
 
 4 " " " 15.6$ " 
 -*. 5 " " " 15.5$ " 
 
 8 " " " 10.4$ " 
 
 The deductions to be made by comparison with the 
 
2O CYANIDE PROCESSES. 
 
 6o-mesh screen experiments are that double the fine- 
 ness lessens the time by one half in treatment of ore 
 by cyanide solutions of the same strength. 
 
 We have so far arrived at the following conclusions 
 regarding the necessity for oxygen and the strength 
 of solutions: 
 
 1. That oxygen is necessary for dissolving gold in 
 cyanide of potassium solution, and that it combines 
 with the potassium of the potassium cyanide in the 
 proportions stated in Eisner's equation. 
 
 2. That agitation shortens the process, as does the 
 strength of the solution, but that what is gained in 
 time is lost in power and cyanogen. 
 
 3. That weak solutions of cyanide of potassium are 
 preferable to strong solutions, inasmuch as they are 
 less prone to attack base metals, and are more 
 economical in proportion to loss of cyanide during 
 the operation. 
 
 4. That while theoretically one part of cyanide 
 should dissolve one and one half parts of gold, 
 practically the operation may require forty parts of 
 cyanide to one part of gold. 
 
CHAPTER IV. 
 
 CHEMISTRY OF THE OPERATION. 
 
 BEFORE the introduction of the cyanide process 
 Plattner's method, with its improvements by Messrs. 
 Thies, Rothwell, and others, was the only economical 
 chemical process used on a commercial scale. The 
 Russell process has found some advocates, but the 
 methods of cyanide and chlorination have found 
 more. The cloud which hovered over all chemical 
 operations for the extraction of the precious metals, 
 and which exists to-day, was due to frauds and un- 
 practical schemes. Chemists have also made tests in 
 their laboratories, and have induced parties to adopt 
 their plans, which have proved to be valueless upon a 
 commercial scale. 
 
 To obtain economical and practical methods sim- 
 plicity must be one of the chief objects. 
 
 It is of no value that one can extract all the gold 
 from an ore if the cost of extraction is more than the 
 gold recovered. 
 
 While the cheapest piece of machinery is not 
 always the best, the simplest and cheapest piece of 
 mechanism which will do the work satisfactorily is the 
 
 21 
 
CYANIDE PROCESSES. 
 
 best. The scope of a chemical process is another 
 consideration ; that process which will meet every re- 
 quirement has not been found, but the cyanide proc- 
 ess has approached nearer to the ideal than any we 
 have knowledge of. 
 
 The chemical reaction of the cyanide process is 
 such that after the chemist has determined the pro- 
 portions of chemicals to be used in the treatment of 
 any particular ore the entire work becomes mechanical. 
 
 The process may be adapted to wet or dry crush- 
 ing; to coarse or fine ore, according to the texture of 
 the ore ; to tailings or concentrates from other treat- 
 ment. It is not applicable to every ore, but to what 
 ores it may be applied we can readily determine by 
 analysis. Mr. Paul says that "if laboratory tests 
 were satisfactory on 50 per cent of ore he would not 
 hesitate to build a mill on that test, so uniform are 
 the results to be obtained." 
 
 The chemical reaction expressed by Eisner's equa- 
 tion is for gold : 
 
 2'Au + 4KCy + O + H 2 O = 2AuKCy 2 + 2KOH. 
 For silver: 
 
 2 Ag + 4KCy + O + H 2 O = 2AgKCy 2 + 2KOH. 
 
 From the equations it is seen that double. salts of 
 gold and silver are formed with potassium cyanide, 
 while caustic potash is liberated. It is yet an open 
 
CYANIDE PROCESSES. 23 
 
 question whether gold is found otherwise than in a free 
 state in ores, and it is given as a reason why gold 
 unites so readily with cyanides that it is in a free 
 state. 
 
 Silver is found more in combination with chemical 
 compounds in gold ores, and hence is not recovered 
 as readily as gold. Furthermore, the sulphides of 
 zinc and other base metals generally accompanying 
 gold and silver in refractory ores are not acted upon 
 by cyanide solutions, at least so as to be noticeable. 
 
 There are acid ores containing oxidized pyrites or 
 acid earths which are very destructive to cyanide and 
 must be treated before being introduced to the 
 cyanide solution. Ores or tailings containing sul- 
 phurets subjected to the weather will oxidize, forming 
 metallic sulphates on the earthy constituents. These 
 are only partially soluble in water, so that while water 
 washings will assist in removing them, other treat- 
 ment should follow. The cyanide would partially be 
 absorbed and partially decomposed by these sub- 
 stances if the ore were not freed from their influences, 
 as illustrated in the following equations : 
 
 I. FeSO 4 + 2KCy = FeCy 2 -f K 2 SO 4 . 
 
 Were lime added before the potassium cyanide, we 
 we could expect the following reaction : 
 
 2FeSO 4 + 2CaO = gFeO -f- 20180, . f 
 
24 CYANIDE PROCESSES. 
 
 Ferrous oxide, while a powerful base, and neutral- 
 izing acid, absorbs oxygen readily, passing into ferric 
 oxide, thus: 
 
 2FeO + O= Fe 2 O 3 . 
 
 This being a very feeble base, it will have no 
 further effect, and will undoubtedly be partially 
 removed from the ore by the water wash necessary to 
 carry off the calcium sulphate. [^/MacArthur states 
 that I part of lime is sufficient for 99 parts of ore for 
 this treatment. We would advise, however, labora- 
 tory and litmus-paper tests for surety. 
 
 II. F 
 
 = Fe,0. + 3(K.SO.) + 6HCy. 
 
 From this equation we see that ferric sulphate is 
 converted into ferric oxide, and potassium sulphate 
 with free hydrocyanic acid liberated as well. 
 
 The action of sulphates of alumina and magnesia is 
 practically the same with cyanide, liberating free 
 hydrocyanic acid, which is a loss. To neutralize 
 these sulphates we give the ore a preliminary treat- 
 ment as before, using lime or sodium oxide, 
 
 Fe a3 (S0 4 ) + 3 Na 2 = Fe 2 O 3 + 3 (Na 2 SO 4 ),- 
 
 and then follow it with a water wash to remove the 
 precipitants from the ore, While ferrous salts, solu- 
 
CYANIDE PROCESSES. 2$ 
 
 ble or insoluble, exist in the ore, the lime or soda 
 will combine with the acid to deposit the ferric oxide. 
 The ferric oxide, although a feeble base, woul^l com- 
 bine with cyanogen to a more or less extent, *so that 
 if it can be freed from the ore so much the better. 
 Where sulphates of alkaline earths exist only, the 
 oxidation may take place with the cyanide solution 
 in contact, but this is not advisable where lime is 
 present. The quantity of alkali presented for neu- 
 tralizing acid ores must be determined by laboratory 
 tests of the ore, as demonstrated under "Laboratory- 
 work." The tests having determined the amount of 
 alkali needed, the proper quantity is not added all at 
 once, but little by little, so that its action will be 
 uniform throughout the ore being treated. 
 
 Butters and Clennell advanced the following equa- 
 tions as possible reactions accompanying the action of 
 cyanide on pyrites : 
 
 III. To illustrate the influence of oxygen on ferric 
 sulphides or iron pyrites : 
 
 (a) FeS 2 + H 2 + ;O = FeSO 4 + H 2 SO 4 . 
 
 Iron sulphate and free sulphuric acid are formed by 
 this action. Should the iron sulphate be further 
 attacked by oxygen from the air, we could expect 
 
 (b) 2FeS0 4 +0=Fe 2 3 ,2S0 3 , 
 which is an insoluble basic sulphate (Wittstein). 
 
26 CYANIDE PROCESSES. 
 
 Berzelius gives the action on ferrous sulphate by 
 the oxygen of the air as 
 
 ioFeSO 4 + 5O = 2Fe 2 O 8 ,2SO 3 + 3Fe 2 (SO 4 ) 3 . 
 
 The sulphate being converted into insoluble basic 
 sulphate and soluble ferric sulphate. The cyanide 
 reaction on the ferrous salts is given as follows : 
 
 IV. FeSO 4 + 2KCy = FeCy, + K 2 SO 4 . 
 The reaction then continued results in 
 FeCy, + 4 KCy = K.FeCy., 
 ultimately giving rise to 
 
 = Fe.O, + 6K 2 SO, + Fe,Cy,. . 
 
 Should lime be present, the reaction would not be 
 complete. Taking the double salt, as follows, 
 
 First, FeCy 2 + 4-KCy = K 4 FeCy fl ,- 
 Second, K 4 FeCy 6 +Ca(OH) 2 
 
 = 2KOH + FeCy 2 + 2KCy + CaCy,. 
 
 V. Ferric salts and cyanide give 
 
 Fe 5 (SO,),+ 6KCy = Fe,Cy.+ 3 K 2 SO. and 
 Fe,Cy t + 6H,0 = Fe,(OH) 8 + 6HCy, 
 Fe,(S6 4 ) r +6KCy+6H I 
 
 = Fc,fOH), +6HCy + 3K,SO, . 
 
CYANIDE PROCESSES, 2? 
 
 A mixture of ferrous and ferric salts on addition of 
 cyanide of potassium gives the well-known Prussian 
 blue when ferric salt is in excess, thus: 
 
 VI. iSKCy -f 3FeS0 4 + 2Fe 2 (SO<) 3 
 
 = 9 K,S0 4 -fFe 4 Fe 3 Cy, 8 . 
 
 By mixture of the same salts with ferrous salt in 
 excess we obtain Turnbulls blue : 
 
 VII. i2KCy + 3FeS0 4 +Fe,(S0 4 ), 
 
 = 6K 1 S0 4 + Fe i Fe i Cy H . 
 
 The reactions between iron and potassium cyanide 
 are very complicated and they are not fully under- 
 stood, yet we can understand from the foregoing 
 combinations that loss of cyanide will take place, so 
 that the more safeguards used to prevent loss will 
 prove economical and beneficial. 
 
 If iron be present in the solution of gold and 
 cyanide of potassium, the following possibility may 
 occur: 
 
 6AuKCy 2 + 6KHO + 2Fe + sH.O 
 
 = 6AuKCy + 6HCy + 6KHO + Fe 2 O 3 . 
 
 In this equation, however, the free^ cyanic acid 
 would combine at once with the free alkali to form 
 potassium cyanide : 
 
 6HCy + 6KHO + Fe 2 O 3 = 6KCy + 6H 2 O + Fe f O,. 
 
28 CYANIDE PROCESSES. 
 
 This reaction shows that if a metal be present it 
 may be the means of regenerating potassium cyanide. 
 We are inclined to believe that this action is one 
 cause for so little loss of cyanide when the electro 
 cyanide process is used. 
 
 The more recent practice is to mix with the cyanide 
 solution sodium oxide to reduce any acid present or 
 formed, and thus reduce the amount of cyanide con- 
 sumed. J. C. Montgomerie uses NaOH, Na 2 O, and 
 Na 2 O. 2 with equally satisfactory results. His propor- 
 tions of cyanide potassium to the ore to be treated 
 are 3 Ibs. of cyanide to the ounce of gold ; 3/4 by 
 weight of sodium to the cyanide used. These are dis- 
 solved separately in a little water, then mixed together 
 in water of sufficient quantity to treat the ore. 
 
 Novices should study the subject of sodium before 
 mixing with water. 
 
CHAPTER V. 
 
 LEACHING THE ORE. 
 
 THE original ideas of MacArthur-Forrest were to 
 agitate the ore in the cyanide solution ; when we say 
 ore, tailings are included in the term. They suggested 
 no form of vessel or mechanical means, but simply 
 said that if the pulp were kept in motion by any con- 
 venient mechanical stirrer the operation would be 
 hastened. Agitation should be continued until the 
 gold and silver are nearly all dissolved, when the 
 liquor containing the precious metals is to be drawn 
 off for precipitation. 
 
 Rae's, Simpson's, and nearly every electrical cyanide 
 system for the cyanide process is conducted on the 
 lines of agitation. It is conceded that agitation 
 lessens the time of extraction and expedites the proc- 
 ess. It allows the oxygen of the atmosphere to act 
 on the potassium, freeing the cyanogen so that it may 
 unite with the gold ; it is also probable that by agita- 
 tion the cyanide can come into contact with the metals 
 with greater ease : thus with tarnished particles of 
 gold or gold covered with a sulphide film the slighest 
 
 scratch would admit of the cyanide attacking it, and so 
 
 29 
 
30 CYANIDE PROCESSES. 
 
 dissolving it in quicker time. Where ores are coarse 
 and porous, agitation would assist the operation, but 
 its great practical use will be found with ores hard and 
 fine. Where very low-grade tailings are treated, or 
 where fuel is expensive and unhandy to be obtained, 
 or where very large vats and ore charges are used, 
 mechanical agitation may prove more expensive than 
 simple percolation. 
 
 Ores containing tellurides, arsenides, and sulphides 
 will give better results if agitated than can be obtained 
 by percolation. Barrels with arms, similar in con- 
 struction to chlorinating-barrels, have been used ; also 
 shafts with radiating arms, and barrels simply rotated, 
 for the purpose of agitation. The size of ore- charges 
 treated is limited to the capacity of the barrels in 
 one case and the size of the vats and motive power in 
 the other. 
 
 If time be an element of importance, stronger solu- 
 tions of cyanide may be employed with agitation, but 
 as the loss is proportionally greater, it is the customary 
 practice to use weaker solutions and economize on 
 chemicals. With agitation-barrels it is necessary to 
 introduce chemical oxidizing agents, otherwise no time 
 will be gained, as has been illustrated by MacLaurin's 
 experiments. 
 
 The percolating process is extensively employed in 
 South Africa, where ores, concentrates, and tailings, are 
 worked by it. This process is used as well in other 
 
CYANIDE PROCESSES. 3 1 
 
 countries, and consists in soaking the ores to be 
 treated in cyanide of potassium solutions. After 
 soaking or leaching, as it is called, the solution is 
 drawn off and another stronger solution run on. 
 
 As we have shown, the time required for running 
 or draining these various leaching solutions from the 
 ores depends upon the degree of fineness of the ore 
 and its character for packing tight, which of course 
 would hinder the rapidity of drainage. 
 
 Here it can be seen that uniformity of crushing is 
 advantageous, and that the coarser the ore the quicker 
 will be the drainage. The liquor is run into the 
 vat through the bottom by a pipe connected with a 
 vat holding the solutions of various strengths. The 
 solution rises slowly upwards, percolating the ore in 
 its upward movement, until it has covered the entire 
 charge of ore in the vat. The object of this upward 
 percolation against gravity is that by this means 
 it permeates the mass evenly ; It is run in slowly to 
 avoid making channels in the ore, which would be dis- 
 advantageous to good downward percolation when 
 drainage takes place. The idea is to make the whole 
 quantity of liquor rise and fall through the ore evenly, 
 and not up or down through channels. 
 
 When tailings, especially clayey tailings, are charged 
 intovats, they are apt to remain lumpy. Cyanide solu- 
 tion will have difficulty in penetrating such masses, as 
 channels will be formed and the liquor will naturally 
 
3 2 CYANIDE PROCESSES. 
 
 go the easiest way through the ore. A mixture of 
 clean sand with the ore will assist the percolation in 
 such cases, and this proceeding may be absolutely 
 necessary with clayey tailings which would pack with- 
 out agitation and effectually prevent percolation. The 
 process for cyanide treatment is conducted to this 
 point as follows: 
 
 The ore in every instance is or has been crushed. 
 It is then charged into a vat. If sulphates or other 
 acid salts are present which would be injurious to 
 potassium cyanide, the ore is allowed to stand in 
 water, or water containing enough caustic alkali to 
 neutralize the acid. This water is now drained off 
 and wash-water added. b . 
 
 After the wash-water has drained off, the first solu- 
 tion of cyanide, containing from 0.02 to 0.08 per cent 
 potassium cyanide, is allowed to percolate through 
 the ore and stand some hours before draining. 
 
 The standard or strong solution is next percolated 
 through the ore and drained off. After this another 
 weak solution is percolated through the ore and 
 drained off, and this last solution is followed by a 
 water wash to take up any cyanide containing gold 
 that remains in the ore. 
 
 The first weak solution is allowed to remain in 
 contact with ore 12 hours. 
 
 The standard solution is allowed to remain in contact 
 12 hours, and has a strength from O.J to 1.5 per cent. 
 
CYANIDE PROCESSES. 33 
 
 The final weak solution is run on after the ore has 
 been exposed to the air 4 hours, and is allowed to 
 remain about 12 hours. The final weak solution has 
 a strength of from 0.02 to 0.04 per cent. The 
 quantity of solutions used is one half a ton for each 
 ton of ore. 
 
 The solutions of cyanide and gold are run from the 
 vats into filter-boxes and from there into sumps, to be 
 used again as weak solutions or else brought up to 
 the standard of strong solution by addition of KCy. 
 
 Having obtained the gold from the ore in potas- 
 sium cyanide solution the next step is the recovery of 
 the gold from the solution by precipitation. Mac- 
 Arthur's first patent suggests the evaporation of the 
 solution to dryness, and fusing the resulting saline 
 residue, or by treating the residue with sodium amal- 
 gam. Any one acquainted with evaporation on a 
 small plan knows how tedious such methods are. 
 
 The treating of the residue with sodium amalgam 
 would also be unsatisfactory, as the mercury would 
 oxidize quickly and refuse to unite with the gold. 
 
 MacArthur was quick to see the crudeness of these 
 methods, but by careful experiments with zinc finally 
 ascertained fine filiform threads of zinc would precipi- 
 tate the gold in metallic state. Thin zinc shavings 
 are cut from disks of zinc turned in a lathe. The 
 precipitation-boxes are filled with these zinc shavings, 
 and are so connected together in a series that the 
 
34 CYANIDE PROCESSES. 
 
 solution will go into the first box at the bottom, rise 
 up through the zinc sponge until it reaches an orifice, 
 when it flows into the next box of the series from the 
 bottom up, and so on. The first solution in passing 
 through the zinc filter does not precipitate the gold 
 as fast as the strong solution, but its action on the 
 zinc paves the way for quick precipitation of the gold 
 in the strong solution. The action on zinc is slow, 
 but increases in intensity after it has commenced. 
 Zinc plates or granulated zinc will not answer for 
 precipitation : the zinc must be in thin shavings. 
 Pure zinc will not decompose pure potassium cyanide 
 rapidly until some caustic is formed ; but as soon as 
 iron or gold is in contact with zinc and a cyanide 
 solution, evolution of hydrogen commences at once. 
 
 Hydrogen formed in the precipitation-box shows 
 that electric action is going on between the metal and 
 the solution, in which there is an exchange ; thus, 
 
 2 AuKCy 2 + Zn = K 2 ZnCy 4 + 2 Au. 
 
 Alkali metals will precipitate gold from the cyanide 
 solution. Mr. Malloy patented a process which, if 
 successful, is superior in point of recovery to zinc 
 precipitation, since the potassium cyanide is regener- 
 ated while gold is set free in mercury, from which it 
 can be recovered readily compared with the recovery 
 from zinc. 
 
CYANIDE PROCESSES. 35 
 
 JMalloy uses sodium or potassium amalgam, formed 
 electrolytically from a solution of carbonate in contact 
 with a bath of mercury. The alkali metal combines 
 with cyanogen of the gold compound, forming an 
 alkali salt of cyanogen, while the gold is instantly 
 amalgamated. Thus, 
 
 K 2 CO 3 + elect, current = K 2 + CO, + OH 2 
 KAu + Cy, + K = Au + 2KCy. 
 
 If this method prove successful, it should add 
 greatly to the cyanide process as an economical gold 
 extractor, for it will save cyanide, and also recover 
 finer bullion in a very much easier form to handle. 
 
 Dr. Johnston precipitates the gold and silver from 
 the cyanide solution by pulverized charcoal, through 
 which it is filtered. By one filter he recovers 25 per 
 cent of the gold ; by a series of filters he recovers 95 
 per cent. The gold and silver is recovered by smelt- 
 ing with fluxes after the charcoal has been disposed 
 of by burning. 
 
 Attempts have been made to precipitate the gold 
 by use of zinc and sodium amalgams, the object being 
 to save cyanide and obtain the precious metals in the 
 form of amalgam for recovery. Fairly good results 
 have been obtained this way. 
 
 F. Rinder's process is to precipitate the precious 
 metals by chloride of zinc. The gold is obtained as a 
 grayish powder, by slowly dropping the chloride of 
 
36 CYANIDE PROCESSES. 
 
 zinc into the solution. The precipitate is collected, 
 dried, and finally melted into bullion. To obtain the 
 gold and sjlver separately, the solution is treated first 
 with sulpht?e of iron or sodium to separate the silver 
 and precipitate it. The solution containing the gold 
 is now filtered off fromthis precipitate, and the gold 
 precipitated by *rtripba of zinc. The cyanide liquor 
 can now be reinforced and used again. 
 
 Precipitation by electrical action is considered in 
 the second part, under the proper heading. 
 
 Moldenhauer uses aluminum as a precipitant, which 
 he claims does the work without entering into com- 
 bination with cyanogen. He expresses his process as 
 follows : 
 
 I. 6Au+i2KCy+ 3O 
 
 = 6AuKCy 2 + 6KHO + sH 2 O. 
 
 If to this cyanuret-of-gold solution, which contains 
 free alkali, aluminum is added, the following reaction 
 takes place : 
 
 II. 
 
 = 6Au + 6KCy + 6KHO + A1,O 3 - 
 
 4 : 
 
 The hydrocyanic acid combines at once with the 
 caustic potash to form potassium cyanide. Thus the 
 , second member of equation II would be 
 
 i 
 
CYANIDE PROCESSES. 37 
 
 6Au + i2KCy + 6H 2 O + A1 3 O 3 > 
 
 and cyanide is regenerated. 
 
 In another instance he precipitates the gold and 
 regenerates the cyanide by an alkaline earth, which 
 may be added after precipitation by aluminum, pro- 
 vided a solution is used which contains a free acid and 
 not a free alkali. 
 
CHAPTER VI. 
 
 ZINC AS A PRECIPITANT. 
 
 THE objections to the use of zinc as a precipitant 
 are such as to create considerable comment. It is 
 considered too expensive by some, because of the 
 loss of cyanide in the zinc-precipitating boxes, and 
 because it requires so much zinc. Others consider it 
 from a different standpoint, namely, that the recovery 
 of bullion from its use is too coarse, and the recovery 
 by refining too complicated, together with a certain 
 loss of gold and silver due to refining those metals 
 with zinc. The numerous methods suggested do not 
 seem, however, to have driven the zinc-precipitating 
 process to the wall, although we expect to see it ac- 
 complished in time. 
 
 " Examination of precipitants from a cyanide mill, 
 consisting of gold, silver, copper, calcium carbonate, 
 and fine shreds of zinc, showed that copper was not 
 in a metallic state, because it dissolved with effer- 
 vesence in dilute HC1." Mr. Eichbaum observed 
 that zinc does not precipitate copper from a solution 
 made with potassium cyanide 98 per cent purity ; but 
 
 38 
 
CYANIDE PROCESSES. 39 
 
 on adding iron a brisk evolution of gas took place, 
 but no copper was precipitated. If an impure cyanide 
 solution is used, copper is soon deposited upon the 
 zinc, which is no doubt due to caustic or carbonate 
 in the solution. 
 
 The solution, after gold has been deposited, contains 
 zinc, yet the solution, after being used for months, 
 does not cause inconvenience. By the addition of water 
 the zinc could not saturate the solution, and the same 
 is true of alkali carbonate, which, in the absence of 
 lime, is continually forming. The white precipita*'tf* 
 is the result of alkali on zinc, and the zinc potassic 
 oxide on the double cyanide of zinc and potassium, 
 as shown by the formula, and which is insoluble. 
 This double cyanide of zinc and potassium being used 
 over again in the percolating vats, forms, with the iron 
 salts in the ore, ferrocyanide of zinc. 
 
 Buckland considers this the reason for constant re- 
 moval of zinc from the solution with the residues. 
 
 This double cyanide of zinc and potassium formed 
 during precipitation of gold is not available for dis- 
 solving gold in new operations, but it does not appear 
 to be detrimental to the process when new cyanide 
 solution is added to it. It does not precipitate gold 
 dissolved by a new solution of cyanide. 
 
 Auro-potassium-cyanide seems to be a very stable 
 compound, and not readily decomposed, as is evi- 
 dent when we see that, being once deposited on zinc, 
 
4 CYANIDE PROCESSES. 
 
 the gold does not become redissolved by excess of 
 cyanide so long as zinc is present. 
 
 We should think that if gold is readily deposited 
 from potassium cyanide solution by aluminum, zinc 
 could be as well, in which case the cyanide would be 
 regenerated. Thus, 
 
 6ZnKCy a + 6KHO + sH 2 O + 2A1 
 
 = 6Zn + 6KCy + 6HCy + 6HKO + Al a O 3 
 = 6Zn + i2KCy + 6H a O + A1 S O 3 - 
 
 Zinc for precipitation must not contain arsenic, an- 
 timony, or lead, although a small percentage of the 
 latter is not injurious. MacArthur's results from zinc 
 tests were that fine zinc shavings answered the pur- 
 pose better than zinc in any other form. Granulated 
 zinc and zinc sheets produced unsatisfactory results, 
 due possibly to the limited surface offered for attack, 
 or possibly due to the slow action of cyanide on zinc 
 in compact form, the same as its slow action on gold 
 in grains. 
 
 We are inclined to this latter belief, and consider 
 that it attacks the shavings because they offer numer- 
 ous uneven surfaces or particles which the cyanide 
 can attack readily. As before stated, while the action 
 is slow at first, it becomes quite vigorous and rapid 
 as it proceeds. 
 
 Zinc dust is objectionable, as it would pack and also 
 
CYANIDE PROCESSES. 41 
 
 become mixed with other impurities, which would 
 afford obstacles to refining the bullion. 
 
 Zinc amalgam does not afford surface enough for its 
 weight, and the method of adding it to the solution 
 in small pills, so to speak, is too tedious and faulty. 
 The precipitation of the metals in the zinc-boxes 
 takes place rapidly, and as the first series of boxes 
 do most of the work, the zinc is consumed faster in 
 them. This zinc is replaced by the zinc from the last 
 boxes of the series, and the last boxes filled with 
 fresh zinc. The object aimed at is to have the dep- 
 osition of gold commence at once, which would not 
 be the case with fresh zinc ; besides, the few particles 
 of gold adhering to the zinc in the last boxes are 
 brought to the place where the greater part of the 
 gold is precipitated. 
 
 According to theory, one pound of zinc should pre- 
 cipitate six pounds of gold. However, various losses 
 occurring, such as generation of hydrogen, formation 
 of potassium zinc cyanide, formation of zinc carbo- 
 nate, and the loss which occurs from sifting the gold 
 and ridding it of zinc, makes the total loss of zinc to 
 gold precipitated sixteen to one practically. That the 
 amount of zinc used will vary at different operations 
 we can as readily expect as that different amounts 
 of coal will be consumed under different boilers. 
 One cubic foot of zinc shavings is said to be sufficient 
 for the precipitation of gold from two tons of solu- 
 
42 CYANIDE PROCESSES. 
 
 tion in twenty-four hours at some works. One cubic 
 foot of zinc shavings weighs from three to six pounds, 
 and exposes forty square feet of surface per pound. 
 MacArthur says: "Improvements in detail to in- 
 crease the surface and decrease the weight of the 
 zinc have enabled him to obtain threads so light that 
 one pound will occupy the space of two gallons." 
 The zinc in this form is said to possess enormous 
 chemical activity. 
 
 After passing through the., zinc-boxes the solution 
 should not contain 50 per tent per ton of gold or 
 hardly a trace, since this gold will no doubt be lost 
 by precipitation from the weak solutions. 
 
CHAPTER VII. 
 
 TREATMENT OF BULLION. 
 
 HAVING precipitated the gold and silver from the 
 cyanide solution, the next process is refining the bull- 
 ion. The simplest method of recovering gold from 
 the ore is by amalgamation with mercury. The mer- 
 cury is then pressed through a cloth or chamois-skin, 
 the gold amalgam remaining in the cloth or skin. 
 This is then placed in a retort and the mercury dis- 
 tilled from the gold ; the mercury is condensed and 
 saved for future use. When the cyanide process is 
 used, the operation is much more complicated. The 
 zinc with the gold adhering is shaken in water, when 
 the gold and zinc fall off into the water. The water 
 is then filtered, and the fibrous particles of zinc may 
 be collected in a sieve and shaken again to remove 
 the gold. This last sifting removes the coarse zinc 
 from the mass to be refined. The precipitate will 
 contain gold, silver, and zinc, and if it comes from 
 cleaning up of zinc filter-boxes other metals. 
 
 This precipitate is thoroughly dried and roasted 
 slowly, care being taken that the flame does not come 
 in contact with the mass. After being thoroughly 
 
 43 
 
44 CYANIDE PROCESSES. 
 
 dried it may be refined by the " calcining and roast- 
 ing process" or recovered by the " acid process." 
 
 The roasting process is used where oxidation of 
 base metals has not been complete. At Johnannis- 
 burgh, South Africa, the acid treatment is not em- 
 ployed, as it involves washing and filtration of the 
 slimes, with loss of gold by formation of regulus in 
 melting, if sulphates remain in the slimes, by fault of 
 imperfect washing. "The practice is to dry the 
 slimes to dust nearly; then to thoroughly mix them 
 with powdered nitre, the amount varying from 3 to 
 33 per cent of their weight, and the mass gently 
 heated on a wrought-iron tray. The flames must not 
 come in contact with the slimes, and the gases should 
 be conducted up a flue away from the operator. By 
 the use of nitre everything connected with the pre- 
 cipitate is refined. After this oxidization the roasted 
 mass is placed in plumbago crucibles with the proper 
 fluxes." 
 
 When metallic oxides are present, the flux is: six 
 parts roasted nitre slimes; four parts borax; two 
 parts soda ; one part sand. When only a small amount 
 of metallic oxide is present, the charge may be three 
 parts slimes, one part borax, two parts soda, one part 
 sand. The function of the sand is to form a fusible 
 slag with soda, and protect the pots from metallic 
 oxides and potash formed by the reduction of the 
 nitre. The slag resulting from the melting of these 
 
CYANIDE PROCESSES. 45 
 
 slimes usually contains considerable gold ; it is there- 
 fore crushed and sent to the smelters. It is some- 
 times customary to pan these slags, after crushing, 
 for gold, sending the tailings to the smelter. Fluxes 
 which give clean fluid slag are preferable in this as in 
 any other refining. 
 
 For the sulphuric acid treatment wooden tubs arc 
 sufficient, the temperature created by the action of 
 the acid on the zinc in dissolving it being sufficient to 
 discard the application of artificial heat. After the 
 zinc has dissolved the acid solution is decanted, and 
 the bullion washed to remove all acid traces. 
 
 Should any zinc remain, its presence in melting will 
 cause loss of gold by evaporation, as the zinc volatilizes 
 by heat ; it may be better, therefore, to treat the pre- 
 cipitate first with a weak solution of acid, then follow 
 it by a stronger. 
 
 After washing the mass is dried at a low heat ; when 
 the moisture is driven off, the heat is increased to a 
 dark red. After one hour's roasting all oxidation 
 of the base metals which escaped removal by acid 
 treatment should be complete, the mass presenting a 
 brown-gray appearance. The roasting completed, the 
 bullion is transferred to a wrought-iron box for cool- 
 ing purposes. When cool, it is pulverized. Borax 
 and soda are added to make a clear slag. Plumbago 
 crucibles are well adapted for this treatment, and 
 borax is put into them first ; the mixture of borax and 
 
46 CYANIDE PROCESSES. 
 
 roasted ore is put in from time to time as the mixture 
 melts and sinks down. The melting goes on speedily 
 and in the most satisfactory manner. After the whole 
 quantity is charged the temperature is kept high for 
 some time to give the small bullion globules time to 
 collect. The contents of the crucible are then poured 
 into a heated mould and allowed to cool. It is claimed 
 that this acid treatment has advantages over the cal- 
 cining treatment, being simpler and allowing the 
 plumbago crucibles to be repeatedly used ; also that 
 the bullion is finer and by care can be recovered with- 
 out chemical loss." (Dr. Scheidel.) 
 
 The bullion produced by the cyanide process must 
 necessarily vary according to the grade of ore treated 
 and care taken for its recovery and refining. While 
 one party will recover bullion 950 fine, another will 
 have 750 fine or less. This case is important, since it 
 may be more expensive in the end, as purchasers of 
 bullion pay for its assay value, and refiners' charges 
 are more for base bullion than fine ; under such con- 
 ditions it may be profitable to use care. Bullion pre- 
 cipitated by zinc has objections which, although at 
 times are in a measure unavoidable, can be circum- 
 vented to some extent by close application to details. 
 The loss of bullion from smelting is one of the most 
 objectionable features; the loss of zinc does not 
 amount to much ; the loss of cyanide is a bad 
 feature, but unavoidable we expect, however, to see 
 
CYANIDE PROCESSES. 47 
 
 this reduced and the process carried on with much less 
 cyanide in the future. 
 
 Practice makes perfect, and when the cost has 
 reached as low as $i per ton the method is becoming 
 nearly perfect. We also expect to see the recovery 
 very much simplified, so that the recovered bullion will 
 be finer and the process more readily accomplished. 
 
 The foundation having been laid, the house can be 
 completed. 
 
CHAPTER VIII. 
 
 THE RECOVERY BY THE CYANIDE PROCESS. 
 
 IF by amalgamation of a $40 ore, 70 per cent has 
 been recovered, it is considered excellent work; if now 
 by the cyanide process and use of $12 tailings 90 per 
 cent more is recovered, we can consider it par excel- 
 lent work, since we have recovered all but $1.20 in the 
 ore. 
 
 The Rand Extraction Company of South Africa 
 treats tailings averaging 5 dwt. of gold to the ton 
 equal by our figures to $5 P er ton. They recover 80 
 percent of this, or $4 per ton. The writer has known 
 from personal observation of the recovery of 98 per 
 cent from pure quartz carrying gold, and of another 
 instance of 97^ per cent from clayey ore, while on the 
 other hand, for very good reasons, but 20 per cent of 
 the fire-assay value was recovered. From this we 
 deduce that the character of the ore has much to do 
 with the percentage recovered, and moreover that the 
 cyanide process is not applicable to every ore contain- 
 ing gold and silver. 
 
 If gold can be extracted economically without too 
 great loss of quicksilver, amalgamation should precede 
 
 48 
 
CYANIDE PROCESSES. 49 
 
 the cyanide process, for the cost will be very small, and 
 we can almost surely count on the recovery of 90 per 
 cent of the gold in the tailings by the cyanide process. 
 
 Again, as before mentioned, it requires longer time 
 for cyanide to absorb coarse gold, than it does mercury. 
 These remarks apply only to free-milling gold ores, 
 and not to refractory or tailings ores, but it is in this 
 last instance we appreciate the importance of the 
 process most. Ores charged highly with metallic sul- 
 phides can be treated as before stated, but ores con- 
 taining a high percentage of base metals cannot 
 without first being oxidized. Ores carrying above 5 
 per cent metal are smelting ores ; if they carry that 
 much gold they are bonanzas : in either case if it be 
 possible to send them to the smelters, unless free- 
 milling gold ores, they should be. 
 
 The base and refractory ores generally contain such 
 metals as iron, zinc, lead, and copper, besides such 
 non-metal substances as antimony, bismuth, arsenic in 
 the form of sulphides, arsenides, antimonides, etc. 
 
 Cyanide of potassium dissolves metals more or less, 
 forming generally double salts. When the metals are 
 not free, but are chemically combined with some other 
 substance, such, for example, as sulphur, forming sul- 
 phides, they are not dissolved. It is well known that 
 the affinity of cyanogen for the precious metals is 
 more than for the base metals, but the weaker the 
 solution of cyanogen, is the less likely are the base 
 
50 CYANIDE PROCESSES. 
 
 metals to be attacked. The only sure method of de- 
 termining whether the process is suitable for an ore 
 is by laboratory tests. However, it is stated that should 
 ores contain hydrated copper oxides, copper carbon- 
 ates, or a considerable quantity of antimony, arsenic, 
 etc., the cyanide process will not prove satisfactory. 
 
 Copper compounds physically hard are not acted 
 upon, but when soft, porous, and open the action 
 upon them decidedly interferes with the solution. 
 
 Dr. Scheidel found copper carbonate ore which 
 while hard gave a very marked reaction on cyanide 
 solutions. One fourth ounce of this ore shaken 
 fifteen minutes with 2.73 per cent cyanide of potas- 
 sium solution reduced the strength of the solution to 
 0.05 percent cyanide. "The treatment of the ore 
 in question, notwithstanding the rapid consumption 
 of the cyanide, showed that 70 per cent of the gold 
 was extracted from the ore, while no silver was ex- 
 tracted." 
 
 We would naturally expect that such ores would 
 need preliminary treatment, and he gave it one with 
 sulphuric acid, which he says " had a beneficial effect 
 on the consumption of cyanide, and thereby on the 
 extraction of gold." 
 
 . MacArthur says ''that cyanide solution acts very 
 slightly on antimonial ores, but that these ores hold 
 gold very firmly, and as the compound is impervious, 
 the cyanide is unable to penetrate the mass and thus 
 
CYANIDE PROCESSES. 5 I 
 
 dissolve the precious metal from the base." Both 
 with copper and antimony cyanide solutions will act 
 upon the gold, but with much of the bases present the 
 preliminary treatment, together with the consumption 
 of cyanide, will probably make the process unprofitable. 
 This, however, would depend upon the value of the ore, 
 as some ores can stand considerable expense and then 
 pay. 
 
 An arsenical ore from the Mercur lode, Utah, 
 carrying 20 per cent arsenic was treated at Denver. 
 The results obtained were not such as to warrant the 
 tieatment of this ore by the cyanide process. On the 
 other hand an arsenical ore from Boulder, Col. 
 gave an extraction of 79.4 per cent, and still another 
 gave an extraction of 82 per cent, at a treatment cost 
 of $2.50 per ton. 
 
 Why ores of the same class will not both yield 
 readily to extraction has yet to be ascertained by the 
 aid of the microscope and chemical tests. 
 
 The percentages of recovery depend upon so many 
 things that are not understood that we can only say 
 that the character of the ore is the chief obstacle to 
 high recovery. 
 
 An average of eight concentrates from eight dif- 
 ferent mines gave a recovery of 88.13 per cent. The 
 average quantity treated was 12.38 tons, and its 
 average gold value per ton was 2 oz. 8 dwt. 1 1 grs. 
 
 From 43.5 tons of tailings, the assay value of which 
 
52 CYANIDE PROCESSES, 
 
 was I oz. ii dwt. 4 grs., 89 per cent of the gold was 
 recovered. 
 
 From four samples of ore average weight 1.875 tons 
 each, assaying 2 oz. 7 dwt. 5 grs. gold per ton, and carry- 
 ing 17 oz. 9 dwt. 1 8 grs. silver per ton, the average 
 recovered was 87.21 per cent gold and 62.19 P er cent 
 silver. Highest recovery of gold 91.09 per cent; 
 lowest 8 1. 1 8 per cent. Highest recovery of silver 
 79.78 per cent ; lowest 35.16 per cent. The follow- 
 ing table gives the recovery from different characters 
 of ore, each from different mines G. gold, S. silver : 
 
 Per cent. Per cent. 
 
 Ironstone and kaolin G. 80. 3 
 
 Lead ore G. 88.7 S. 59.58 
 
 Arsenical pyrites G. 82 
 
 Hematite G. 80 S. 61.55 
 
 Silver ore. S. 89.98 
 
 Iron pyrites G. 98 S. 63 
 
 Stephanite G. 90 S. 83.4 
 
 Siliceous ore G. 94 S. 82 
 
 Mixed tailings G. 80 
 
 Quartz and talc G. 86 
 
 Talcose G. 86 
 
 Fifty per cent sulphur pyrites.... G. 92 
 
 Oxidized ore with limonite G. 93 
 
 Sulphuretted copper ore G. 86 
 
 Sulphur, arsenic, antimony G. 80 
 
CYANIDE PROCESSES. 53 
 
 Per C2nt. 
 
 Quartz and fine gold G. 87 
 
 Rusty quartz G. 93 
 
 Ore kaolin G. 100 
 
 Ore quartz G. 100 
 
 The production as reported for five years from 
 South African gold-fields shows the recovery on a 
 grand scale. The process was applied mostly to tail- 
 ings, and is here given in ounces: 1890, 286; 1891, 
 34,862; 1892, 178,688; 1893,330,510; 1894,635,- 
 900. These figures are deserving of more than an 
 ordinary glance, since they represent the progress made 
 in one field since the introduction of the process in 
 1890; but especially are they deserving of considera- 
 tion when they are known to represent ounces of 
 gold discarded, thrown away as of no use, until the 
 introduction of the process made their recovery pos- 
 sible. While it is not exactly in accordance with 
 the ideas of the author to chronicle the cost of treat- 
 ment, yet one comparison may not be amiss. Mr. 
 G. S. Peyton of the Mercur gold mine, Utah, stated 
 in print that while 1500 tons yielded 20 per cent of 
 the assay value of his ore by amalgamation at a cost 
 of $4.25 per ton, 1600 tons treated with cyanide 
 gave an extraction of 88.5 per cent at a cost of $2.25 
 per ton. 
 
CHAPTER IX. 
 
 LABORATORY-WORK. 
 
 HAVING followed the process from the stamps to 
 the bullion, we can now turn our attention to the tests 
 necessary to be made to intelligently conduct the work. 
 Our first inquiry should be, How shall we ascertain the 
 fitness of an ore for cyanide treatment? We must 
 first crush our samples, the finer the better, and pass 
 part of them through a sieve, keeping the remainder 
 or coarser part for duplicate tests if they are needed. 
 
 To ascertain if the ore is acid and needs preliminary 
 treatment, take 400 grams and shake it with water; if 
 the water turns the litmus paper from blue to red, there 
 is acid present. Add now lime, a little at a time, every 
 now and then shaking until the litmus paper no longer 
 turns red. The acid in the ore has become neutralized. 
 Wash this ore thoroughly to remove any traces of 
 lime. The ore is then ready for cyanide treatment. 
 
 There should be at least four tests made of 100 
 grams each of ore. 
 
 The ore is placed in glass bottles with solutions of 
 
 various strengths. 
 
 54 
 
CYANIDE PROCESSES. 55 
 
 These are shaken, some a longer time than others, 
 the time varying, the object being to ascertain the 
 amount of cyanide consumed by the ores in different 
 times, and which strength is best suited for the 
 standard or strong solution, as well as the time neces- 
 sary for the reaction. 
 
 The cyanide consumed, the assay of the ore before 
 treatment, and then again after treatment give the 
 required data. 
 
 These tests will also determine whether an ore is 
 suitable for treatment or not by examination of the 
 amount of cyanide consumed. Percolation tests can 
 now be made with solutions of various strengths and 
 various lengths of time. Analyses now made of the 
 percolations and assays of the well-washed residues 
 will show the best treatment to use. These small 
 tests are excellent guides for treatment on a larger 
 scale. 
 
 Fire assays of ore to be treated should be made as 
 the first step to ascertain the value or weight of the 
 gold per ton ; also that the process may be followed 
 by assay to see how the cyanide is dissolving the 
 gold. We must also measure our cyanide by this 
 assay. We have seen that theoretically I part of cya- 
 nid.e will dissolve 1.5 parts of gold, but that practically 
 we need from 3 to 4 pounds of cyanide for I ounce 
 of gold ; the amount actually necessary therefore can 
 only be determined by the shaking and percolating 
 
56 CYANIDE PROCESSES. 
 
 laboratory tests. One object is to be borne in mind 
 while making these tests: that it is not how much, but 
 how little, cyanide can be used and yet extract all the 
 gold. 
 
 To determine the gold and silver in a solution of 
 cyanide of potassium : Take a known quantity of 
 the liquor and precipitate the silver with a solution 
 of sodium sulphide or iron sulphide. Filter off the 
 remaining liquor, dry, and wrap the precipitate in 
 sheet-lead with a little granular lead and cupel. 
 The remaining solution containing the gold is treated 
 with chloride of zinc, which precipitates the gold. 
 This is then dried, mixed with granular lead, and 
 cupelled. 
 
 If there has been an excess of cyanide solution 
 used, there will be a waste of cyanogen in treating the 
 mass of ore. 
 
 To ascertain the strength of the cyanide solution : 
 Take a burette and pour into it a solution of nitrate 
 of silver, AgNO 3 , whose strength for I c.c. will equal 
 the strength of o. I gram potassium cyanide used. 
 Take a known quantity, 10, 20, or 50 c.c., of the 
 cyanide solution being used, and drop into it the 
 silver nitrate, shaking the cyanide to mix the two 
 solutions. After a time the cyanide solution shows 
 slight turbidity; when it shows distinct turbidity, 
 stop, and read the burette. For example, if 20 c.c. 
 cyanide solution titrated by 1.15 c.c. of the stand- 
 
CYANIDE PROCESSES. 57 
 
 ard AgNO 3 solution, the strength of the cyanide 
 solution would be found by dividing 1.15 by 20 = 
 0.057 P er cent. 
 
 Mr. J. E. Clennell made some investigations 
 which were published in the Chemical News, and 
 again in the Engineering and Mining Journal. Ex- 
 tracts are given from his investigations : 
 
 1. Solutions of cyanide are frequently met con- 
 taining such fine matter in suspension they cannot 
 be filtered clear. If to such solutions lime and agita- 
 tion be applied, they can be filtered clear. 
 
 When soluble double cyanides were present, this was 
 inaccurate, but if only finely divided inert substance 
 was in suspension it was practically correct. 
 
 With double salts such as are obtained from zinc 
 filter-boxes the reactions made by lime are incom- 
 plete, hence valueless. Thus : 
 
 K,ZnCy, + Ca(OH), - Zn(OH) 2 + K,Cy, + CaCy, . 
 
 2. Turbid solutions free form zinc can be titrated 
 without filtering by Fordo's and Gelis' method. The 
 process depends upon the considerations : 
 
 a. That a mixture containing alkaline cyanides, 
 hydrates, and monocarbonates has the hydrates con- 
 verted into neutral salts, and the monocarbonates 
 into bicarbonates, by addition of dilute mineral acid, 
 before any of the cyanides are decomposed. 
 
58 CYANIDE PROCESSES. 
 
 b. That bicarbcmates of the alkali metals do not 
 act on iodine. 
 
 c. When cyanide in such a mixture has been 
 converted into a double silver salt, titration with 
 dilute hydrochloric acid, with phenolphthalein as 
 indicator, shows the quantity required to neutralize 
 the hydrates and convert the carbonates into bicar- 
 bonates. 
 
 Iodine Process. a. A solution of iodide of potas- 
 sium is standardized against a solution of pure po- 
 tassium cyanide, the strength of which has been 
 determined by the silver nitrate method. The end 
 point of the iodine reaction is marked by a permanent 
 yellow tint, or if starch be added by a bluish-yellow 
 color, and is in general sharp and delicate. 
 
 It is essential, however, that the solution shall 
 contain no free caustic alkali or alkaline monocar- 
 bonate, as these bodies react with iodine, rendering 
 the indications too high and indefinite. 
 
 b. Silver nitrate is added to a measured volume of 
 the solution to be tested until a permanent turbidity 
 results, or if the solution was turbid to commence 
 with until a distinct increase is observed. A drop of 
 phenolphthalein indicator is now added to the same 
 liquid and titration is continued with N/io HC1 until 
 the pink color disappears. Another measured por- 
 tion of the original solution is now taken, and a trifle 
 less hydrochloric acid than was necessary to neutralize 
 
CYANIDE PROCESSES. 59 
 
 the alkali in the preceding experiment is added drop 
 by drop with agitation. The solution is now ready 
 for titration with iodine. 
 
 The following experiments illustrate neutralizing 
 the alkali by hydrochloric acid : 
 
 Pure cyanide and caustic potash were mixed so 
 that 10 c.c. of the mixture required 3.7 c.c. of stand- 
 ard iodine, and a like amount required 1.15 c.c. of 
 standard silver nitrate. 
 
 On adding phenolphthalein and titrating with 
 N/io HC1 acid 5.75 c.c. were required. 10 c.c. were 
 then mixed with 5 c.c. of N/io HC1 and the mixture 
 titrated with iodine; 3.3 c.c. were required. 
 
 Next 10 c.c. were mixed with 5 c.c. of N/io HC1 
 and the mixture titrated with standard AgNO 3 ; 
 1.15 c.c. were required. 
 
 In these experiments 
 
 i c.c. standard AgNO 3 = o.oi gram KCy; 
 I c.c. " iodine =0.0035. 
 
 To show that these are practically correct we will 
 calculate them. 
 
 1st. 3.7 c.c. X 0.0035 = - I2 95 percent. 
 
 2d. 1.15 X o.oi = 0.1150 " " 
 
 3d. 3.3 X 0.0035 = 0.1155 " " 
 
 4th. 1.15 X o.oi = 0.1150 " " 
 
 The difference between one and three shows the 
 
60 CYANIDE PROCESSES. 
 
 advantage of neutralizing the hydrate with acid, while 
 the difference between two and four shows no variation 
 when silver nitrate is used. 
 
 When an impure solution of cyanide and caustic 
 were used, the advantage to be gained by the use of 
 acid was in favor of iodine, a trifle. 
 
 A mixture of cyanide and carbonate gave with 
 silver nitrate 0.044 KCy; with silver nitrate and acid 
 the same result 0.044 KCy. With iodine the indi- 
 cated strength was 0.047 KCy. 
 
 The next experiments were made with solutions 
 containing zinc, but satisfactory results were not 
 obtained. 
 
 3. Precipitation by Akaline Sulphides. a. Zinc, 
 silver, or mercury existing as double cyanides are 
 precipitated by sulphuretted hydrogen or an alkaline 
 sulphide, as metal sulphides. 
 
 b. The excess of sulphides may be removed from 
 the cyanide solution without affecting the cyanide by 
 addition of insoluble compounds of lead, such as 
 oxides, carbonates, etc. 
 
 The method to be followed is: 
 
 First. Measure a volume to be tested ; add caustic 
 potash or soda until the cyanide solution is strongly 
 alkaline. 
 
 Secondly. Pass into the now alkaline solution H 3 S 
 until precipitation ceases, or, what is better, a concen- 
 trated solution of pure sodium sulphide. Shake the 
 
CYANIDE PROCESSES. 6 1 
 
 solution well and allow the precipitate to subside. 
 The clear solution after filtering can be freed from 
 excess of sulphide by agitation with litharge added 
 little by little, until a drop of the liquor no longer 
 gives the slightest coloration with a drop of lead 
 acetate solution. A definite volume is now filtered 
 off and tested with silver nitrate. 
 
 The liquid to be tested must give a perfectly white 
 precipitate with a drop of lead acetate. Also it 
 should give no precipitate with sodium carbonate, 
 and moreover it should give no precipitate with sul- 
 phuretted hydrogen. 
 
 In titrating with silver nitrate the point to be 
 noted is the appearance of a distinct permanent tur- 
 bidity pervading the liquid and not disappearing on 
 standing. 
 
 Deductions made were, that wherever a quantity of 
 zinc was present it was necessary : 
 
 First. To remove the precipitation by filtration 
 before adding lead salts, since the precipitated zinc 
 sulphide, although washed, will react upon car- 
 bonate of lead with formation of lead sulphides ; 
 
 Second. A solution of lead acetate is liable to pre- 
 cipitate cyanide of lead ; hence an insoluble com- 
 pound of lead should be added to the solution ; 
 
 Third. To avoid the liberation of hydrocyanic acid 
 considerable alkaline hydrate should be added before 
 precipitating with hydrogen sulphide ; 
 
62 CYANIDE PROCESSES. 
 
 Fourth. Results obtained with alkaline monocar- 
 bonates were not satisfactory. 
 
 The following experiments will illustrate the ap- 
 plication of the method : 
 
 Suppose we take 100 c.c. of the, liquid from what 
 has passed through the zinc-boxes, and which con- 
 tains K 2 Cy 4 Zn. 
 
 We make this strongly alkaline by addition of con- 
 centrated caustic soda, and by addition of hydrogen 
 sulphide precipitate sodium and zinc sulphide. 
 
 This liquor is then filtered, and, if necessary, a little 
 lime is added to make the filtrate clear. 
 
 This filtrate is now shaken with an insoluble lead 
 compound, such as litharge or lead carbonate, and 
 25 c.c. are now filtered off. 
 
 Supposing our pure potassium cyanide is I c.c. 
 = 0.231 KCy, and that i c.c. of zinc sulphate = 0.02 
 gram Zn. Then in the double cyanide K 2 ZnCy 4 
 I c.c. = 0.08, and the free potassium cyanide 0.231 
 0.08 = 0.151 KCy. 
 
 On titrating with AgNO 3 we find it requires from 
 our burette readings 5.7 c.c. AgNO 3 for distinct 
 turbidity. 
 
 5.7-1-25 = .228 per cent KCy ; but four times this 
 gives total cyanide or 0.912 per cent KCy as the 
 indicated strength of the solution. 
 
CYANIDE PROCESSES, 63 
 
 GENERAL INFORMATION. 
 
 Briefly, the cyanide process, leaving out the mechan- 
 ical arrangements for doing the work, is conducted 
 as follows : 
 
 The ore after reaching the mill is crushed, rolled, 
 and stamped. If amalgamation is practised, it takes 
 place during the stamping. If wet crushing is em- 
 ployed, three to five gallons of water per minute will 
 be required. The tailings from the stamps are con- 
 veyed directly into vats by means of launders. 
 
 The vats may be made of iron, coated with tar or 
 asphalt ; or of brick, lined with hydraulic cement ; or 
 of wood coated with asphalt or lined with cement. 
 
 Each vat, if the MacArthur-Forrest process is be- 
 ing used, should be large enough to hold one day's 
 run from the stamp-mills. These vats are made of 
 enormous size, at times fifty feet in diameter, capable 
 of holding five hundred tons of ore and solution. 
 
 Wherever possible, the plant should be so arranged 
 that advantage may be taken of gravity, as this will 
 obviate the use of elevating machinery and much 
 pumping. The leaching-tank, or the first vat of the 
 series which holds the ore and solution, should have a 
 capacity of twice the second tank of the series, which 
 holds only the gold in solution. 
 
 The tank next in order is the precipitating-vat or, 
 as it is termed, the zinc-box, and this should have 
 
64 CYANIDE PROCESSES. 
 
 compartments enough to allow the precipitation of all 
 the gold from the solution. 
 
 Following the precipitating-boxes are the sumps, 
 which receive the weak liquor from them, and should 
 be of such size as to hold the solution from two 
 teachings. 
 
 There is still another tank called the stock-tank 
 which contains a strong solution of potassium cyanide, 
 and there should be yet another to which the weak 
 liquor from the sump may be pumped and brought 
 up to the standard or strong solution by additions 
 from the stock-tank. The sump solutions are used 
 over and over again by making up from the stock-tank 
 the loss of cyanide which took place during the former 
 operations, or they may be used as weak solutions 
 at the commencement of the operation or as wash at 
 the finish. In any case by using the sump liquor 
 cyanide is saved. 
 
 The cost of cyanide 98 per cent pure is fifty cents 
 per pound in New York City. It is costly and worth 
 economizing. Since the process has increased the 
 demand for cyanide of potassium, it is of importance 
 to buy it from some firm which can be relied upon, 
 and which tests it occasionally to ascertain its 
 strength. The tendency, as the subject has been 
 practically worked, is to greatly reduce the amount of 
 cyanide used ; where it was formerly customary to use 
 \\ and more per cent of cyanide in the solution, now 
 
CYANIDE PROCESSES. 65 
 
 equally good results are obtained from the same ore 
 by 1/2 per cent for the strong solutions and 3/10 per 
 cent for the weak solutions. 
 
 Of course the ore and gold to be dissolved will 
 have an influence upon the strength of the solution, 
 also the silver, but the object of the operator should 
 be to keep the solution as low as consistent with the 
 work in hand, bearing in mind that the weaker the 
 solution the less likely it will be to attack any base 
 metals present, and the less loss will occur from oxi- 
 dation and in the zinc-precipitation boxes. In this 
 latter instance the greatest loss takes place, and for 
 that reason inventors have endeavored to find some 
 better method of precipitation. Some establishments 
 instead of allowing the solution to go through the 
 precipitation-boxes pump it back on to the ore or use 
 it upon ore in another vat, thus making two or more 
 treatments with the gold in cyanide solution before 
 precipitating the gold by zinc, thus economizing in 
 the use of cyanide by this means and saving zinc as 
 well. This method, we are informed, is carried on at 
 the Robinson works in South Africa, with extraction 
 results equalling the former practice. 
 
 The numerous methods being devised for saving 
 cyanide and lessening the cost of the process, to- 
 gether with the numerous patents being issued, 
 must impress the thoughtful man, no matter how 
 
66 CYANIDE PROCESSES. 
 
 prejudiced he may be, that there must be some merit 
 in the process worthy consideration. 
 
 It is not claimed by any one we are aware of that 
 all ores can be treated successfully, for such is not the 
 case, but we believe that it can treat any ore where as 
 much care is taken with oxidation as in other proc- 
 esses with equally good results and cheaper. 
 
 There may be given as one reason why better re- 
 sults have not been obtained in the treatment of tail- 
 ings that amalgam on the surface of gold protects it 
 to an enormous extent from the solvent action of 
 potassium cyanide. 
 
 Another reason for bad results may be given, that 
 not enough oxygen from the air was allowed to come 
 in direct contact with the ore and solution. 
 
 The poor results obtained in the treatment of con- 
 centrates may be obviated by allowing more time for 
 the cyanide solution to act upon them, or by finer 
 pulverization. In both cases the action of the cyanide 
 solution can be hastened by agitation. 
 
 In regard to the necessity of oxygen for hastening 
 and carrying on the operation Mr. F. A. Mason de- 
 duced the following from some recent experiments: 
 
 First. That by passing air through solutions of 
 potassium cyanide the solubility of gold was increased. 
 This will be the subject of several more patents. 
 
 Second. That air when forced against a plate of 
 gold in a cyanide solution causes it to dissolve with 
 
CYANIDE PROCESSES. 6? 
 
 more rapidity in that solution. This again proves the 
 truth of Eisner's equation. 
 
 Third. That amalgam on the surface of gold, 
 even when air is forced against it, protects the gold 
 from the action of potassium cyanide. This experi- 
 ment shows the weak action of cyanide upon mercury. 
 
 Ore-sampling. The probabilities are that lean ores 
 will afford the greater bulk of the ores treated by 
 chemical processes, because they will not bear the 
 transportation,- sampling, freight, and other charges 
 to the smelters. 
 
 In some instances, however, when the smelters may 
 need " silica" for a flux so badly as to use pebbles, 
 they will agree to stand one half the expenses, or even 
 buy the ore ; but such instances are likely to prove 
 rare, as the smelters can afford such buying only in 
 extreme cases, and even then only to a limited ex- 
 tent, depending upon the distance and freight charges 
 from the mines to the smelters. 
 
 The smelters being generally situated in a locality 
 suitable for obtaining different classes of ores, and 
 nearer fluxes and coal on which they pay freight than 
 the ore on which the miners pay freight, their useful- 
 ness for low-grade ores is a question, unless the con- 
 centrates of such ores are shipped them. Were the 
 smelters compelled to treat all low-grade .ores, there 
 would be very few smelters, as then the actual run- 
 ning expenses would either bankrupt the smelters or 
 
68 CYANIDE PROCESSES. 
 
 their charges would prohibit the miners shipping their 
 ore. In any case the smelter is more useful for high- 
 grade ores too rich for treatment at the mines, and 
 for this purpose they are a necessity; while those 
 ores, on the other hand, which can be treated at the 
 mines by the chemical processes and yield good re- 
 turns will not go to the furnaces. In both cases 
 where the works are public, that is, buy the ore for 
 treatment from the miners, the public sampling-mill 
 is agent virtually for miner, and smelter, or reduction- 
 works. 
 
 On the returns from the assays made by the 
 sampling-mill the ore is paid for. The ore is not 
 shipped direct to the smelter, but to the sampling- 
 works. Here it is unloaded from the car and weighed. 
 It is then run through crushers; from the crushers it 
 passes through rolls ; from the rolls it is elevated and 
 comes down by gravity through a pipe which auto- 
 matically samples it, by quartering it as it falls, and 
 finally, after this mixing, receives one quarter in a 
 separate bin, while the three quarters are removed to 
 the dumping-bin. 
 
 After the car-load of ore has been sampled auto- 
 matically in this way it would appear to be as accu- 
 rately accomplished as any hand-work could possibly 
 do it. But all the ore is not of the same value; hence 
 the mixing of this sample must be attended to. 
 
 It is now removed from the bin and shovelled in a 
 
CYANIDE PROCESSES. 69 
 
 cone-shaped pile on the floor, the ore always running 
 off the end of the shovel to the apex of the cone, so 
 as to run as evenly as may be down the sides of the 
 cone. Throwing a shovelful of ore on the apex of the 
 cone will not accomplish this result, but easy handling, 
 as mentioned, will. This operation is done once or 
 twice more, after which cutting down the sample is 
 commenced. 
 
 To accomplish the cutting down the pile called the 
 sample is shovelled from the floor on a sampling- 
 shovel, which is made to catch about half of the ore 
 from the floor, the remainder falling into a barrow. 
 This sample thus reduced goes into three separate 
 buckets, first one, then another, and finally the third, 
 when the rotation is commenced over again. The 
 original sample is now cut down one half, but is still 
 very much too large, so that the ore from the three 
 tubs is coned again on the floor as in the first place, 
 and again cut down one half in quantity. 
 
 It is now run through the crushers and sifted, and 
 again cut down, but before this cutting down all that 
 did not pass through the sieve is crushed until it does. 
 These three samples will now weigh about one hun- 
 dred pounds each or less. This is too much, so they 
 are still further mixed until reduced to ten pounds 
 or less, when they are pulverized to pass through 
 a loo-mesh screen. Then one part of each is sent 
 to the assayer. Should there be much variation in 
 
70 CYANIDE PROCESSES. 
 
 the assay returns, the operation of sampling is re- 
 peated when, if the assays tally closely, the average 
 is taken as a basis for settlement. 
 
 It is well to remark that various ores contain more 
 or less moisture, so that a lot of say 100 pounds 
 is weighed, then dried, and weighed again. The 
 total w r eight is now reduced just that much, for if a 
 lot of 100 pounds contains 2 per cent moisture, a car- 
 load of 10,000 pounds will contain 200 pounds, and 
 the smelter objects to paying for that much water. 
 After the assay has proved satisfactory to all con- 
 cerned the sampler settles with the miner but first 
 deducts his charges for sampling with the smelter's 
 charges, and the sampler in turn settles with the 
 smelter. 
 
 The sampling- works have become almost a necessity, 
 as the miner feels better satisfied with his returns, and 
 the smelter is satisfied because he is not accused of 
 fraud. Whether the samplers are satisfied we are not 
 sure, but presume they are, since public sampling is 
 now carried on in every camp of size. 
 
 There are many cases where the miner cannot afford 
 to loose the time and be to the expense of following 
 his ore to the sampler; he therefore hires an agent 
 who attends to the sampling. This man is called the 
 miner's agent; he checks the weights, the moisture, 
 and watches the sampling. 
 
 The sampler's scales are regularly tested by the pub- 
 
CYANIDE PROCESSES. /I 
 
 lie scale inspector, so that every possible safeguard is 
 afforded the miner against loss of values. He can, 
 however, if he wishes sample his ore and have his 
 assay made before shipping, but we consider it 
 doubtful if he did not employ the sampler whether 
 he could have settlements with the smelter on 
 his returns if they differed much from the smelter's 
 assay. The ore to be sampled at the mines is first 
 broken by passing it through a crusher. From the 
 crushed ore every fifth shovel is reserved for sample, 
 the remainder being carried into the railroad car for 
 shipment. This sample is now crushed finer by pass- 
 ing it through the rolls ; it is then coned on the floor 
 as above, flattened out, and divided into four parts, 
 the two opposite being saved as the sample, while the 
 remainder is taken into the car. This is again coned 
 and quartered until the sample is much reduced in 
 size, say to one hundred pounds. It is then weighed, 
 afterwards heated to drive off the moisture, and 
 crushed to go through a very fine sieve, after which it 
 is reduced to size necessary for assay by the same 
 method. This at times gives very accurate results, 
 and is a check upon agent, sampler, and smelter. 
 
CHAPTER X. 
 
 GOLD AND SILVER SOLVENTS COMBINED WITH 
 ELECTRICAL ACTION. 
 
 ACCORDING to Berzelius, " Chemical union of any 
 two substances is an electrical act ; that during contact 
 previous to union the one substance is relatively posi- 
 tive, the other relatively negative, and the act of 
 union is a consequence of the attraction existing be- 
 tween the substances in these two states; also that in 
 the act of uniting the two electrical conditions neutral- 
 ize each other and produce heat." 
 
 Professor Bunsen used to say that electrolysis in all 
 operations marks a great advance on chemical action 
 pure and simple. 
 
 As MacArthur and Forrest were the parties to intro- 
 duce the practical application of cyanide to extraction 
 of gold from ores, Siemens- Halske may be considered 
 the first to introduce electricity into the process to 
 assist its application. Neither of them designed or 
 produced anything new, but, having strength in their 
 convictions, they applied their patents to obtain useful 
 
 results. 
 
 72 
 
CYANIDE PROCESSES. 73 
 
 A good thing laying dormant is of no use to man- 
 kind. 
 
 When Dr. Siemens took the matter up, he found 
 that electrical precipitation was equally effective with 
 either strong or weak solutions of cyanide. This was 
 one step in the right direction, namely, a saving in 
 chemicals. 
 
 Julian Rae of Syracuse, N. Y., patented an appara- 
 tus as early as 1867 for the electrical precipitation of 
 gold from ores, but the patent, like Simpson's, of 
 1885, seems to have been left on the shelf to 
 mould. Mr. Rae did, however, make one practical 
 test, which was not entirely satisfactory, at the 
 Douglas mill, Nevada. His failure to obtain uniform 
 results was due, we believe, to his using an alternating 
 current. Electrolysis with such currents must neces- 
 sarily be very slow, and the slower the reversal of 
 the current the better the results, for if the current 
 alternates quickly there will not be given time for 
 the solution to deposit its metal compound before 
 it is repelled by a reversal of the current. 
 
 The essential conditions necessary for electrolysis 
 are that the substance be a liquid, a definite chemical 
 liquid, and a conductor of electricity. 
 
 Potassium cyanide with gold in solution answers 
 these conditions. 
 
 When potassium cyanide delivers up its gold to the 
 zinc in the zinc-precipitation boxes, it would have its 
 
74 CYANIDE PROCESSES. 
 
 potassium immediately converted into potash by oxy- 
 gen did not potassium cyanide have a definite chemi- 
 cal composition of its own so that it could unite with 
 zinc quickly. The zinc, being the substance liberated, 
 unites with the potassium cyanide to form zinc potas- 
 sium cyanide, and is a secondary product of elec- 
 trolysis. 
 
 Not only precise quantities of current, but definite 
 amounts of electrical energy, are required to decom- 
 pose or separate weights of substances. The amount 
 of electrical energy required to separate from a com- 
 pound a given weight of metal depends upon the 
 strength of the chemical union, the chemical equiva- 
 lent of the substance to be separated, and upon the 
 amount of the conduction resistance of the electrolyte. 
 
 The question of a cyanide solution being increased 
 in dissolving power by becoming an electrolyte is not 
 quite clear to the writer. That gold is positive there 
 can be no doubt, and that cyanide of potassium is 
 negative as an electrolyte there can be no doubt ; 
 but we are told that the solving action takes place at 
 the anode ; hence the gold positive dissolves to the 
 cyanide solution negative, with the result that the 
 gold cyanide solution is positive. The gold is able 
 to keep its electro-positive condition if not its chem- 
 ical condition. 
 
 Whether this electrolyte becomes converted into an 
 electrode by absorbing the gold we are unable to say, 
 
CYANIDE PROCESSES. 75 
 
 but when they become "cations" the gold is in the 
 metallic state and the potassium cyanide is immediately 
 set free. The potassium also should be set free, form- 
 ing caustic potash, but if it be set free the majority of 
 it reunites with hydrocyanic acid, forming potassium 
 cyanide, to go on another round as a negative electro- 
 lyte to collect more gold. Of this much we are 
 confident, but how the electric current stimulates the 
 solution we are unable to comprehend. 
 
 That some potash is set free at the cathode we are 
 sure, but the majority is reconverted into potassium 
 cyanide. 
 
 As the chief amount of conduction resistance is in 
 the electrolyte, and not in the electrodes, and by rise 
 of temperature the resistance of the liquid is de- 
 creased, the effect is to facilitate electrolysis. At 
 the same time this rise in temperature should increase 
 the solubility of the solution. 
 
 The electro-chemical equivalents of gold and po- 
 tassium cyanide are nearly equal. The equivalent 
 weights are: gold 65.4, KCy 65. 
 
 The quantities in fractions of a gram separated by 
 one coulomb of current are: gold .000678, KCy 
 .000684. Grams separated per ampere per hour: gold 
 2.5128, KCy 2.4624. The amount of electrical 
 energy, therefore, required to separate these sub- 
 stances being about equal for each on account of 
 nearly equal atomic weights, we naturally conclude it 
 
? CYANIDE PROCESSES. 
 
 is small, and that an increase of current past a certain 
 point would be a waste of power. 
 
 The object of the electric current, then, as we 
 understand so far, is to decompose a solution of 
 metallic salt, depositing the metal upon the cathode 
 or negative pole, while the metal is dissolved at the 
 positive pole. 
 
 If we use an iron anode with sulphuric acid, we 
 find gold is electro-negative to iron, while if we use 
 the same anode in potassium cyanide, gold is electro- 
 positive to iron. 
 
 If electro-positive and electro-negative metals be 
 connected, as in the case of our gold cyanide solution, 
 they form a galvanic battery of their own, and, being 
 nearly of the same electro-chemical relation, it ap- 
 proaches perfection. Were there any data to go by, 
 we could almost say that this was the reason why 
 potassium cyanide had such an affinity for gold. 
 
 We are not sure that these little galvanic batteries 
 have any action whatever on the results of the other 
 particles of gold and cyanide uniting, or that they are 
 a means of conduction between the electrodes, since 
 there are so few of them in solution, becoming 
 gradually less as deposition at the cathode takes 
 place. 
 
 In a fixed time a given electric current will deposit 
 a certain amount of metal, which will vary for dif- 
 ferent metals in direct proportion to their chemical 
 
CYANIDE PROCESSES. 77 
 
 equivalents. One coulomb or unit of quantity of 
 electrical current will set free 0.0.00162 grams of hy- 
 drogen. Equal weights of different metals in dis- 
 solving will yield unequal amounts of current. If, 
 however, the metals are considered in proportion to 
 their different weights, a very different relation is 
 seen. One gold coulomb is obtained by 
 
 0.000162 X 196.2 
 
 - o. 01061 1 gram of gold. 
 
 One silver coulomb is obtained by 
 
 0.000162 X 107.7 0.01725 gram of silver. 
 
 One potassium cyanide coulomb would be .010530. 
 The rate of deposition of these various substances, or 
 rather their dissolution at the cathodes, would be in 
 one hour by one ampere of current 
 
 0.01061 1 X 3600 38. 19 grains gold ; 
 0.01725 X 3600 . 72.28 " silver; 
 0.01053 X 3600 =37. 90 " KCy. 
 
 To deposit one ounce of the metals or cause their 
 dissolution from an electrolytic condition with the 
 above current would require as many ampere-hours as 
 grains deposited by one ampere is contained times 
 into 480 grains. We can facilitate matters by in- 
 crease of amperes of current up to a certain point, 
 
78 CYANIDE PROCESSES. 
 
 beyond which excess of quantity does not precipitate 
 faster, but injures the electrodes and electrolyte. 
 Laboratory tests are the only sure criterion for the 
 quantity of current necessary, but these tests will be 
 founded on the above facts, with others, which are 
 also is determined in the laboratory. 
 
 Knowing the quantity of solution in which a certain 
 percentage of cyanide of potassium is placed, and then 
 ascertaining the percentage of gold in that solution, we 
 can calculate the necessary amount of current to 
 deposit that metal uniformly. Every different elec- 
 trolyte must be electrolyzed at a particular rate in 
 order to continuously obtain from it the desired quan- 
 tity of metal. 
 
 Increased density of the current is attended by in- 
 creasecTTfeat of conduction resistance in the liquid, 
 which has the effect of dissolving the anode, and in 
 our case nothing more. "It is not by misdirected 
 strength of current, however great, that reducible ele- 
 ments are separated." From a weak solution of a 
 potassium salt even the strongest current will not 
 enable us to obtain the metal ; but by using a cathode 
 of mercury of small surface the metal has been de- 
 posited by the aid of a feeble current. It thus 
 becomes evident that the energy must be intelligently 
 directed. 
 
 To liberate 480 grs. of gold it would require 
 4.80 -f- 38.1 12.6 ampere-hours, and to liberate 
 
CYANIDE PROCESSES. 79 
 
 480 grs. of potassium cyanide from the solution would 
 require 12.7 ampere-hours ; but in our solution, follow- 
 ing Eisner's equation, for every two parts of gold 
 liberated we must liberate two parts of KCy (potas- 
 sium cyanide), hence the number of ampere-hours 
 would be 12.7 X 2 = 25. 4 for potassium cyanide. 
 Thus to liberate one ounce of gold from a solution 
 of 2K 2 AuCy a would require 386 ampere-hours, or if 
 the work was to be performed in 10 hrs. 3.86 amperes 
 perhour for 10 hours. 
 
 By using more amperes we of course waste power, 
 and injure the electrolyte for future use by oxygeniz- 
 ing it so that its potassium is lost, hence free hydro- 
 cyanic acid set free. 
 
CHAPTER XL 
 CYANIDE SOLUTION WITH VARIOUS ELECTRODES. 
 
 ELECTRO-GILDING has been in use over half a 
 century. Dr. Wright of Birmingham, England, used 
 gold cyanide solution for electro-gilding in 1840. 
 
 The principle is that of depositing gold from a gold 
 solution upon a cathode of metal to be plated. 
 
 The current or circuit is made so that electrical 
 action must take place between the electrodes through 
 an electrolytic compound of liquid. The current de- 
 composes the liquid at the cathode, giving up its metal 
 or liberating the electrolyte and its metal constituent 
 from solution. 
 
 Eisner's equation has with electrical action the same 
 features as it possessed where cyanide and zinc pre- 
 cipitation were employed. The oxygen decomposes 
 the potassium of the potassium cyanide as before, 
 except more briskly. 
 
 In this instance agitation is not as important for 
 generating oxygen as it is for moving the ore and liquid 
 so that the electrolyte can come in contact with the 
 electrodes, in one instance receiving life for dissolving, 
 in the other delivering up its metal and, becoming re- 
 generated, and sent on its way to dissolve more gold. 
 
 80 
 
CYANIDE PROCESSES. 8 1 
 
 By electrical action the cyanide can be greatly 
 reduced in the liquor. As we have seen, theoretically I 
 part of cyanide solution should dissolve 1.5 parts of 
 gold, but that practically it requires 48 to 64 times that. 
 
 By the aid of electricity in connection with cyanide 
 the amount needed has been reduced to 16 parts cya- 
 nide to i part gold, and we are of the opinion it will 
 approach nearer the theoretical limit as matters are 
 improved. As the solvent action takes place very 
 much quicker for some cause, and as there is not the 
 loss of cyanide as in percolation and zinc-precipitation, 
 a very great saving in expense and time is recorded. 
 Another item of consideration is that the liquid re- 
 maining will not contain the impurities deleterious to 
 future action in anywhere near the proportions that 
 it must in the former process. When we considered 
 the former plan, we noticed that two or three changes 
 of the solution were practised, with intervals between 
 during which oxygen was allowed to act upon the ore, 
 to furnish the necessary electro-negative element to 
 unite the cyanide and gold. 
 
 By the use of electricity the electro-negative ele- 
 ment is always present at the anode ; this allows of 
 the operation being continued without loss of time for 
 percolation, and of its being continued, so long as any 
 potassium cyanide is in the solution, or any of the 
 precious metals to be dissolved. We have stated that 
 agitation with the current passing is not so necessary 
 
82 CYANIDE PROCESSES. 
 
 as in the former practice, nor would it be as far as 
 oxidation and precipitation go, but there are other 
 considerations which make it desirable that the sludge 
 be kept in motion. 
 
 The solution is very weak, and in order to hasten 
 its action mechanical power should be used. While 
 it is possible, that by liberation of gases, and the ac- 
 tion of gravity due to different densities of the elec- 
 trolytes, either with or without gold in suspension 
 would create circulation, still the fact is that the 
 sludge would settle around and on one or more of the 
 cathodes, thus hindering, if not entirely stopping the 
 deposition of the metals on the cathode. Were the 
 liquid clear or filtered from the sludge, this would not 
 be the case, but by filtering we lose time and can 
 not perform, neither can the cyanide do the work as 
 readily as it is accomplished by agitation. 
 
 One object of using electricity is to save time, 
 cyanide, and zinc ; to do away with several tedious fil- 
 terings or percolations, as they are called ; and to do 
 what leaching is required with one solution, at one 
 time ; and precipitate the gold at the same time that the 
 operation is carried on in the vat. To accomplish this 
 our apparatus, must with the solution satisfy the fol- 
 lowing conditions : There must be a metal anode not 
 easily corroded or dissolved by the solution. The 
 proper position of this anode is above the cathode ; 
 but it can be parallel to it if both are perpendicular. 
 
CYANIDE PROCESSES. 83 
 
 When horizontal and in courses, the oxides from the 
 anode fall away, and being deposited on the cathode 
 will interfere with its action, especially if they can unite 
 chemically with it. Secondly, the cathode must allow 
 the gold to adhere to it, and after the process is 
 completed allow the metal to be easily recovered. 
 When the gold must be dissolved from the cathode 
 by acid, such sheets of thin metal as can be readily 
 removed from the vat should be used, the thin gold 
 can then be removed by scraping the plates. These 
 plates should also be arranged so as to be easily lifted 
 out and returned to the vat, or if mercury is used it 
 must be arranged to run off readily so that it can be 
 strained and returned to the vat. Each inventor has 
 the best mode of accomplishing these results, or at 
 least did have until some one else overtopped him. 
 
 As power must be used for agitation, it must be 
 such as will stir up the whole mass and keep it in 
 motion. It occurs to us, the anode being the dis- 
 solving-point and the cathode the receiving-point, 
 that if the power be applied to either one, that is, the 
 mechanical power, it should be applied to the anocle. 
 If we can apply this power to either electrode, we 
 have simplified matters one step more, by lessening 
 mechanical complications. 
 
 As in the former process, the easiest and best way 
 of recovering the precious metals is in the form of 
 amalgam. 
 
84 CYANIDE PROCESSES. 
 
 The objection offered by Von Gernet to a mercury 
 cathode is impracticability, on account of the large 
 amount necessary to carry on the operation. While 
 we agree to this as far as the large amount goes, 
 we must disagree with him on its being impracticable, 
 considering it also economical as well to use mercury 
 for cathodes. Von Gernet says that ' ' sheets of 
 copper coated with mercury have been used unsuc- 
 cessfully, because the mercury, owing to the action 
 of the current, will penetrate the copper, forming 
 a dry amalgam which does not adhere to the plate." 
 If Mr. Von Gernet will try to get that dry amalgam 
 off from a copper plate, he will find that it does not 
 fall off readily, and will not penetrate the copper 
 more than during ordinary copper-plate amalgama- 
 tion of the gold mills, but it gets against it some way 
 decidedly tighter. 
 
 Of course the mercury will become dry in time, in 
 other words, will wear out ; to avoid this recover the 
 gold once in a while, and put on a fresh coat of mer- 
 cury. The cathode of lead which is used by Sie- 
 mens and Halske has the disadvantage of wearing 
 out, and requires to be as thin as is consistent with 
 mechanical stability. It is used, however, to smelt 
 the gold in recovery or refining of the deposit, and is 
 a very long way ahead of zinc recovery in that re- 
 spect. Siemens and Halske thus made two great im- 
 provements over the old process, viz., saving of cya- 
 
CYANIDE PROCESSES. 85 
 
 nide and zinc, and the attendant troubles in re- 
 fining. 
 
 It is not in our province to criticise any one ; we 
 wish to ascertain just what the improvements are 
 which tend to make the subject more applicable to 
 the extraction of gold from ores, and to point out de- 
 fects as we see them. Should, therefore, an amalga- 
 mated copper plate be placed in a vat with the amal- 
 gam dry on it, the chances for its being scraped off 
 by abrasion or grinding of the ore is possible, espe- 
 cially if the mercury be small in amount and the liquor 
 circulating strong. The electrical current, together 
 with the adhesion of the mercury to the copper plate, 
 keep the gold in contact with the plate. If too much 
 mercury be used, it will be forced into a free state, 
 but if enough is used to keep the amalgam plastic and 
 no more, it will not be rubbed off. However, to avoid 
 such chances as these mercury in large quantities is 
 poured into the vat to act as a cathode. The action of 
 the liquid in circulating may give this liquid mercury 
 the same movement as its own, but as it is denser 
 than the liquid it only partially assumes the motion. 
 Still it is sufficient, where horizontal circular motion 
 is employed to move the mercury, to at times uncover 
 the bottom of the vat in places. Just at this point 
 mercury cathodes fail, for the molecule wishing to 
 deposit its atom of gold may hit a bare spot and 
 the next moment be lifted awav. To overcome this 
 
86 CYANIDE PROCESSES. 
 
 difficulty a copper amalgamated plate can be used 
 in connection with the mercury, so that if the liquid 
 mercury is disturbed the atom of gold may be de- 
 posited on the copper plate. Other cathodes besides 
 mercury and lead have been tried, such as carbon, 
 but of these we will speak in another chapter. 
 
CHAPTER XII. 
 
 THE CURRENT. 
 
 THE quantity and the energy of current required for 
 the electro-cyanide process of dissolving gold and 
 silver from their ores are variously stated. 
 
 If in a fixed time a given electric current will 
 deposit a certain quantity of metal, as we are told, 
 it will be in direct proportion to their electro-chemical 
 equivalents. "This law holds good only for solu- 
 tions strong in metal; but with dilute solutions, as 
 used in the cyanide process, the current does not find 
 sufficient of the metallic compound present at the 
 electrodes, and consequently decomposition of the 
 water takes place. For this purpose to make the 
 efficiency of the precipitation as great as possible 
 constant diffusion of the solution is requisite." 
 (Von Gernet.) 
 
 If we have in our ore one ounce (480 grains) of gold 
 and two ounces (960 grains) of silver, and we wish to 
 precipitate this quantity in 10 hours, we will require 
 
 =1.2 amperes of current for gold, 
 
 38.1 X 10 
 
 87 
 
88 CYANIDE PROCESSES. 
 
 and 
 
 060 
 
 = 1.32 amperes of current for silver; 
 
 but we have the potassium as well to liberate, which 
 for gold in solution will be theoretically I oz. gold = 
 2 oz. potassium ; hence 
 960 
 
 The total amperes would then be for the three metals 
 5.12 amperes per hour, but as the amperes for one 
 are sufficient for all three, the highest, 5.12, may be 
 considered the quantity required. Should we have 
 one hundred tons of such ore to be treated, our volt- 
 age must be considered. Suppose in treatment we 
 used one half horse-power = 275 foot-pounds per 
 second ; as I watt = .7373 foot-pounds per second, we 
 would use 372 watts, but a watt is the product of 
 amperes by volts, hence 372-1-51.2 gives the voltage 
 as 7.2. 
 
 In copper-refining the electrodes, that is, the anodes 
 and cathodes, are given the same superficial surface 
 as nearly as possible. The reason for this is to afford 
 as much dissolving-surface as plating-surface that the 
 result may be uniform. In our instance where the 
 anode is stationary this may be followed, but where 
 the movement of anode relative to the cathode 
 takes place this is not possible. Again, where mer- 
 
CYANIDE PROCESSES. 89 
 
 cury is the cathode, it is well to have it as small as 
 possible, but not smaller than the anode. Von Gernet 
 says ''that a better effect is produced by doubling the 
 surface of electrodes than by increasing the current 
 tenfold." He was speaking of the Siemens-Halske 
 precipitating-vat. 
 
 The iron anodes in that vat or series of vats had 
 14,000 square feet of surface, while the cathodes had 
 12,000 square feet of surface and were of lead. 
 
 The current of electricity used was from a 5 H.P. 
 engine, and yielded 3^ H.P. in electrical energy at 4 
 volts pressure. 
 
 746 watts X 3i H.P. 
 
 4 volts = 652.75 a^res. 
 
 Anodes of iron, carbon and zinc were tried ; the carbon 
 could not stand the action of the current and it was 
 abandoned ; while zinc formed a white precipitate and 
 was otherwise objectionable. Iron was finally adopted, 
 although it precipitated Prussian blue. Iron as an 
 anode is little acted upon by cyanide of potassium, but 
 if the electrolyte is overcharged it acts upon the iron 
 to corrode it. Wrought iron is more readily oxidized 
 than cast iron when used as anodes. It requires a 
 definite amount of current to oxidize a deh'nite amount 
 of iron, and in this instance 1080 Ibs. were oxidized 
 in a month ; the gold percipitated in that time was 
 335,935 grs. in 700 hours, or 4/09 grs. per hour. 
 
90 CYANIDE PROCESSES. 
 
 According to the gold ampere-hour of 38.1 grs., it 
 requires 8817 ampere-hours to deposit this amount. 
 But Butters and Smart say 300 amperes were used, 
 and that is to say 210,000 ampere-hours were ex- 
 pended or 201,283 more ampere-hours were ex- 
 pended than required. The current necessary to 
 deposit this amount of gold was 12.6 amperes. 
 
 Hence the efficiency of the current - = 4.2 per 
 
 cent, and the wasted energy was expended upon the 
 iron. 
 
 As we stated before, the electrodes should be as 
 nearly of a size as possible when we want to obtain 
 equal results. They should be, especially the anode, 
 of a metal or substance not easily acted on by the solu- 
 tion ; iron seems to be suitable to fulfil the conditions 
 of the anode, as it is not readily acted upon by the 
 solution, and when oxidized it is due in great measure 
 to having the current too energetic for the work in hand. 
 
 There must be a certain amount of energy, but not 
 too much. The amount should be determined, as we 
 have tried to show, by the work in hand to be per- 
 formed. If to-day a two-ounce gold ore is to be 
 treated in ten hours, more amperes will be required 
 than if a one-ounce ore were to be treated to-morrow 
 in the same time, and the oxidation of the anode 
 will not be more, since surplus energy has not been 
 expended upon it. 
 
CYANIDE PROCESSES. 9! 
 
 The question of the size of anodes and cathodes, 
 that is, the surface exposed where agitation is used, 
 especially iron and mercury, is purely theoretical. 
 The anode in some cases is not more than one 
 twentieth the surface of the cathode, and yet the iron 
 anode is not very materially oxidized. This may 
 be due to the movement of the anode, which rotates 
 horizontally over the cathode of mercury, but at some 
 distance from it. However, it does not seem possible 
 that this rotation has much to do with it, since the 
 current is continuous, and the voltmeters and ampere- 
 meters do not show any variation of importance. We 
 would suppose that energy would be expended more 
 upon this anode, but we must take the facts as they are. 
 
 It has occurred to me the electrolyte was a good 
 conductor of the current, and that not being often in 
 contact in a state of metalloid with the cathodes, con- 
 ducted the current, which was proportioned right for 
 the work, to the anode and cathode, as if it were part 
 of a circuit. While the heat arising from the con- 
 duction resistance throughout the electrolyte naturally 
 reduces the resistance, it is small, and that leads us 
 again to think that potassium cyanide with pulp is a 
 good conductor. The quantity of energy lost by the 
 corrosion of the cathode is very small, as the mercury 
 does not corrode appreciably. 
 
CHAPTER XIII. 
 ANODES. 
 
 THE anode, or positive pole, is the one by which 
 the current enters the solution, and it is at this pole 
 that the dissolving action takes place. Anodes not 
 readily corroded by chemical action resist the passage 
 of the current. For instance, an iron anode in a solu- 
 tion of potassic cyanide requires considerable elec- 
 tro-motive force to produce electrolysis. Little gas is 
 evolved at the anode, and it is not corroded. Should 
 gas evolve at the anode, the current passes readily, 
 and the anode dissolves rapidly. With an anode com- 
 posed of an alloy, the most easily corroded metal is 
 first attacked. At times the anode does not dissolve, 
 and becomes coated with an oxide, which hinders the 
 current, but that anode which offers the least resist- 
 ance to a current will dissolve most readily. 
 
 Usually the loss of the anode is greater than the 
 gain of the cathode, but very frequently less than 
 theory indicates, because while chemical action is tend- 
 ing to unite the constituents, the electrical action of 
 the current is trying to separate them. We were told 
 
 that when a non-corroded substance is used as anode an 
 
 92 
 
CYANIDE PROCESSES. 93 
 
 elementary substance is set free at that electrode, but 
 these elementary substances set free may unite chem- 
 ically with other substances present and form new 
 compounds. To avoid this in our case an anode 
 should be used which will not form substances detri- 
 mental to the cyanide solution for future use. 
 
 Let us now consider some of the anodes used by 
 the various inventors in their researches to obtain the 
 gold and silver from ores by electrical action with 
 cyanide potassium salts. Julio H. Rea (patent 1867) 
 used as platinum anode. Platinum as an anode offers 
 great resistance to the passage of an electric current ; 
 if silver is taken as i , platinum offers 97 times more 
 resistance. This quality is objectionable at the start, 
 since it causes heat, and offers more resistance to pas- 
 sage of current, thus decreasing the conductivity of 
 the electrolyte. It also takes, on account of resist- 
 ance, more time or more electro-motive force to deposit 
 the same amount of metal in a given time. Owing to 
 the fact that decomposition must take place at the 
 anode of the electrolyte, energy is expended, not on the 
 work, but in setting free oxygen from the electrolyte, 
 with the possibility of decomposing it. Another ob- 
 jection to platinum would be its great cost. Still in 
 an ampere-hour the amount of dissolution of platinum 
 should be, since it is a tetrad, 28.62 grs., or 3/4 as 
 much as gold. There do not seem to be others 
 than Mr. Rae who suggest platinum as an anode, due, 
 
94 CYANIDE PROCESSES. 
 
 no doubt, to its cost, which, for practical work, would 
 be exceedingly large. 
 
 Carbon is suggested by Malloy's process, 1884 and 
 1886. In this case, as with platinum, oxygen escapes. 
 The carbon is, however, practically unacted upon by 
 the anion chemically, but the current or the oxygen 
 mechanically disintegrates the carbon. The greater 
 the current the more rapid the disintegration. 
 
 It is further objectionable because of energy of 
 current lost, and possibly the active energy of the 
 electrolyte. 
 
 Eissler in speaking of the Halske-Siemens process 
 says : " Carbon could be used as an anode, but will not 
 stand the action of the current, and soon crumbles into 
 a fine powder which decomposes cyanide." "This 
 finely divided carbon is in suspension, and cannot be 
 removed from the solution by filtration." On the 
 other hand, Mr. Weightman used arc-light carbons for 
 six months and they were still in good condition. 
 Mr. Weightman's observations do not agree with Mr. 
 Eissler's, but that is not due to error on either side. 
 One undoubtedly had reference to porous carbons, 
 while the other had reference to dense compact car- 
 bons, coated with copper. The copper coating was 
 of very great assistance even to the compact car- 
 bon in counteracting disintegration of the carbon 
 by the current. The great objection to carbon is its 
 lack of conductivity; if silver be 100, then carbon as 
 
CYANIDE PROCESSES. 95 
 
 graphite is .069, and as gas coke .038. An advantage 
 in its use is its small power of dissolution, which is 
 but 1.74 ampere-hours; hence it could cause little 
 deposition without great electrical energy. 
 
 Cassel, H. R., used carbon rods as anodes, as did 
 Fischer and Weber (patents 1883, 1885, and 1887). 
 Mr. J. B. Hanney used a mixture of plumbago and 
 resin as anode, and, as he claims, with very good effect. 
 As a rule, the anodes have been varied but little, but 
 in some patents they have had different arrangements, 
 so as not to conflict. 
 
 Zinc as anode has serious defects, in fact as numer- 
 ous as when used as a cathode. It forms a precipitate 
 of cyanide of zinc in the solution ; also zinc oxide on its 
 surface, which offers resistance to the electro-motive 
 force, making it expensive. Should it precipitate on 
 the cathode, it will also cause future annoyance, and 
 as one of the advantages claimed for electrolysis is that 
 it does away with zinc impurities, should we consider 
 zinc at all in connection with electricity, we have gone 
 backward instead of forward in the perfection of the 
 system. 
 
 Zinc will cause the solution and deposition of 18.95 
 grains in ampere-hour ; hence it is only slightly better 
 than iron as a conductor, while very much inferior as 
 far as by-products from the operation are concerned. 
 Barker's process, 1882, had for anode brass, and did 
 not use cyanide solution, but had for its object the 
 
96 CYANIDE PROCESSES. 
 
 preventing of mercury from sickening. Leaving out 
 the anode and substituting cyanide solution for water, 
 we believe his invention would be successful in a large 
 degree; otherwise we would not mention it here. 
 The subject of anodes for copper-refining and electro- 
 plating is well known ; the conditions of such anodes 
 compared with anodes for the electro-cyanide process 
 are so vastly different that we can only approach them 
 in practice. 
 
 For copper-refining the anode is stationary, and the 
 same may be said for electro-plating in general, but 
 in our case we wish, if possible, to have movable 
 anodes, which do mechanical and electrical work at the 
 same time. Again the ever-changing classes of ore as 
 far as the quantities of gold and silver in the ore are 
 concerned, make the matter of proportioning the size 
 of cathodes very difficult to meet theoretical require- 
 ments. 
 
CHAPTER XIV. 
 CATHODES. 
 
 THE cathodes next require our attention, and these 
 are as important as the anodes, and possibly more so. 
 Upon these the metal from the solution is to be de- 
 posited, and as we wish to obtain that metal in such 
 form as to refine it with least complications and skill, 
 the most satisfactory cathode must fulfil conditions 
 more trying than the anode. It is the pole of the 
 current from which the current passes out of the 
 liquid, so that any chemical decomposition or disinte- 
 gration of the molecules of the electrolyte must take 
 place here. It must be a good conductor of electricity 
 and must not be readily corroded. As a rule, insoluble 
 coatings are less frequent than at the anode, happen- 
 ing generally when highly oxidizable metal is sepa- 
 rated. A film of hydrogen sometimes adheres to the 
 cathode, which will slightly diminish the current. 
 
 The density of the current at the cathode needs to 
 be so regulated as to allow the metals to be deposited 
 as metals, and not as powder, and as we are dealing 
 with compound substances, the cathode should be of 
 such a nature as not to unite readily with the second- 
 ary products of electrolysis. From an impure solution 
 
 97 
 
9 8 CYANIDE PROCESSES. 
 
 the least electro-positive metal should be deposited 
 upon the cathode first; consequently with our solution 
 containing gold and potassium cyanide, silver and 
 potassium cyanide, as double salts of cyanide, the rate 
 of deposition would be silver, gold, potassium ; but it 
 is doubtful under these conditions whether it is neces- 
 sary to use current more than sufficient to liberate the 
 gold and silver, allowing the KCy to remain in solu- 
 tion undisturbed. If this can be accomplished, there 
 will be considerable voltage saved as well as cyanogen. 
 Unable to obtain any reliable information regarding 
 electrolysis of mixed solutions, we can only draw con- 
 clusions from observations. We know, however, that 
 the current will pass through an electrolyte when 
 feeble so as not to cause electrolysis, and that aqueous 
 solutions of the zinc and copper cyanides will dissolve 
 and deposit equally on passage of suitable current ; so 
 we are led to infer from these phenomena, since the 
 electro-motive forces of zinc and copper are equal, that 
 the least abundant metal will deposit least ; but if 
 equally solvent in the solution the least electro-posi- 
 tive will deposit first, and this latter has been proven 
 in the case of silver salt in copper solution. The size 
 of the cathode should be larger than the anode if its 
 conductivity is less, but may be smaller on the reverse 
 of this proposition. It should be of sufficient size, 
 however, to be able to absorb or receive as much 
 metal as is offered for deposition. 
 
CYANIDE PROCESSES. 99 
 
 If the vat is used with agitation, the cathode should 
 be as large as the diameter of the vat, so that every 
 chance for deposition be accorded the solution, and not 
 be contracted by a small cathode, which must focus 
 the current from the electrolyte. 
 
 Julio Rea used copper cathode without amalgamat- 
 ing it ; Mr. Simpson used a zinc cathode ; Michel Body 
 (patent 1894) uses mercury in a contrivance; Mr. 
 Hanney used mercury; Mr. Whitall an iron cathode; 
 Chas. Raleigh employed copper saturated with mer- 
 cury; Mr. Keith uses copper plates preliminarily 
 treated with mercury ; Siemens-Halske use thin sheets 
 of lead ; Barker used mercury, as stated ; Fisher and 
 Weber mercury and metal plates. 
 
 The employment of mercury seems to be the more 
 general for cathodes than any other metal except 
 amalgamated copper plates. Copper makes a good 
 cathode, but as the precious metals are deposited 
 upon its surface dry and hard, there are objections 
 to its use without amalgam. The copper plate is 
 very little wasted by the current. Mr. Simpson's zinc 
 cathode is objectionable for reasons stated. Mr. 
 Whitall's iron cathode was objectionable because the 
 precious metals were deposited as powder, hence no 
 agitation could be used ; and is here further objec- 
 tionable where electricity is concerned on account of 
 impurities in the bullion. 
 
 Chas. Raleigh uses mercury, but his plan of pump- 
 
100 CYANIDE PROCESSES. 
 
 ing mercury through between two active surfaces, as 
 he says, makes the matter dense. (See English 
 patent 14,910, 1893.) 
 
 Mr. Keith's mercury and copper plates will answer 
 admirably, but he follows on the lines of Siemens- 
 Halske, with the bad plan of using porous cells, and 
 circulating the solution after leaching through boxes 
 for precipitation. However, it does away with zinc 
 becoming mixed with the precipitate. 
 
 Lead cathodes used by Siemens-Halske are very 
 thin sheets of lead, and to obtain the gold from them 
 they are smelted with the gold. The process has 
 worked very successfully, but requires smelting skill. 
 
 Pelatan-Clerici process uses both an amalgamated 
 plate and mercury; also carbon cathodes electrically 
 copper-plated, then coated with mercury. 
 
 There are other processes which have peculiarities 
 which we will touch upon in general, using the pat- 
 entees' words, for we have had no chance to prove 
 their claims. There are other electrical processes for 
 different solutions than cyanide, which we do not 
 attempt to follow. 
 
 Wm. Crookes (patent No. 462,535, 1891). 
 
 He says: " In carrying out my combined process I 
 take the gold ore, tailings, etc., and mix with them a 
 solution of nitrate or cyanide of mercury, and pass a 
 rapidly alternating current of electricity through the 
 mass, either when at rest or agitated in any manner." 
 
CYANIDE PROCESSES. IOI 
 
 " The bulk of the mass is not a good conductor of 
 electricity, while the fine particles of gold are excel- 
 lent conductors." " Iron or carbon can be used as 
 electrodes, and each electrode is alternately anode and 
 cathode." " Assuming that sulphate of mercury is the 
 mercurial salt, the current liberates sulphuric acid at 
 one pole and mercury at the other. " " The action now 
 being reversed, the mercury liberated previously has a 
 molecule of acid to unite with it, so that at each pole 
 the mercurial salt is decomposed only to unite again." 
 Since the gold in the wet mass is a better conductor 
 than the surrounding mass, the equipotential lines of 
 force will converge toward them, so that more of the 
 current passes through them than the rest of the 
 mass, and the two sides of each particle of gold act 
 as anode and cathode. On one side sulphuric acid is 
 liberated, on the other mercury, but the arHnity of 
 gold for mercury is so great they instantly amal- 
 gamate on one side, finally on the other side. Thus 
 the size of the particles is not essential, as the finest 
 flour and float gold will be amalgamated. Nor does 
 it matter to what degree of coarseness the ore is 
 crushed so long as the mercurial salt penetrates to 
 one part of the piece of gold locked up in the ore, for 
 the action will then take place and the metal become 
 amalgamated." 
 
 "The advantage incidental to the use of an alter- 
 nating current is that the sudden and violent deconv 
 
IO2 CYANIDE PROCESSES. 
 
 positions and recompositions cause the mass to become 
 hot, and so greatly facilitate the amalgamation." 
 
 "The efficient action is dependent upon several 
 variable factors, viz., current density, area of elec- 
 trodes, rate of alternation per second, and electric 
 conductivity of the crushed ore and liquid." 
 
 We are not aware that this process has had practi- 
 cal application. It may be successful in the laboratory 
 on rich ores, but we have never heard of it beyond 
 the patent specification. We have quoted it because 
 cyanide can be used in connection with it, and it is 
 one process which uses the alternating current. 
 
CHAPTER XV. 
 VARIOUS PROCESSES AND CONCLUSIONS. 
 
 MR. MAcARTHUR said that when cyanide is used 
 in combination with electric current not only is there 
 a larger expenditure of chemicals, but the base metals 
 are dissolved to a large extent along with the gold 
 and silver, and for subsequent separation involve extra 
 expense, which is saved by our process. 
 
 We believe he was afraid of the Siemens-Halske 
 process at the time he said that. However, we must 
 take him at his word. 
 
 Mr. Hanney, a countryman of his, says that when 
 the electric current is used the cyanide solution may 
 be weaker, as its action is increased by the current. 
 He further states that only metal and silver salts are 
 attacked by the solution, and that copper and iron 
 pyrites may be stripped of their gold and not be at- 
 tacked otherwise. 
 
 He uses mercury for a cathode and obtains the gold 
 direct from the ore, which is the easiest method of 
 collecting it for subsequent separation. Another ad- 
 vantage he obtains in this collecting of the precious 
 metals is that no previous treatment, such as amalga- 
 mation, is required for the coarser particles of gold. 
 
 103 
 
IO4 CYANIDE PROCESSES. 
 
 The advantages claimed by Mr. Hanney are so 
 broad that they almost amount to his having an ideal 
 apparatus. 
 
 They are : That the precious metals are extracted 
 direct from the ore. 
 
 That economy is practised in the use of cyanide for 
 extraction, thus approaching more theoretically to 
 the quantity of cyanide necessary for the dissolving of 
 gold. 
 
 That the precipitated metals are at once obtained 
 from the amalgam in the metallic state, thus requiring 
 no chemical or intricate treatment after precipitation. 
 
 That any workable quantity may be treated, so as 
 to dissolve and precipitate the precious metal, and re- 
 cover the bullion in one day. 
 
 That when the process is completed the liquid from 
 the tank may be run off through a rough filter to 
 clear the liquid of sludge so that it may be used over 
 again by being brought up to its standard for re- 
 covery. 
 
 Percentages recovered from three different ores by 
 this process gave 76.2, 86.9, 95.3, an average of 86.1 
 per cent. 
 
 He further hastened the solvent action of the cya- 
 nide solution by agitating the solution by means of 
 a screw propeller placed in the bottom of the vessel, 
 which gave the liquor an upward movement along the 
 sides, then down through the centre of the vessel so 
 
CYANIDE PROCESSES. 10$ 
 
 as to come in contact with his anode of plumbago and 
 resin. 
 
 His planning to obtain all the good points was ad- 
 mirable. Rae's was not quite as good, and Mr. 
 Simpson did not apparently try to improve or push 
 his invention. Siemens and Halske, and Dr. Keith's 
 inventions were only broad enough to deposit the 
 metals after percolation to avoid the trouble incident 
 to zinc precipitation, and what advantage Dr. Keith 
 gained by amalgamated copper plates he lost by using 
 anodes in porous cups I inch diameter, 24 inches 
 long, the cost of which would in all probability equal 
 the cost of the lead by Siemens-Halske's process. 
 
 The most recent process before the public is the 
 Pelatan-Clerici. They put forward the same claims 
 as does Hanney ; they say that while the simple cya- 
 nide process is not capable of universal application, 
 their process is more applicable. 
 
 That where the recovery of gold by amalgamation 
 is from 55 to 60 per cent they are able to recover 85 
 per cent, and more. They say that under the most 
 favorable conditions the common cyanide process 
 saves 68 per cent of the gold, and barely 50 per cent 
 of the silver. 
 
 Their claims are that they use a more efficient so- 
 lution and entirely different method of treating the 
 ore. 
 
 The treatment consists of a single operation which 
 
106 CYANIDE PROCESSES, 
 
 is carried on in a vat. This vat, in the centre of 
 which is a stirrer of metal (iron) and which is com- 
 posed at the bottom of special amalgamated copper 
 plates, is filled with crushed ore or tailings. 
 
 At the same time a diluted solution containing 
 cyanide of potassium, common salt, and some other 
 chemical is added, the portion of each reagent being 
 calculated according to the quality of the material 
 treated. 
 
 The stirrer is then set in motion so as to mix the 
 ore with the solution, and to make a liquid sludge 
 through which an electric current generated from a 
 dynamo is allowed to pass freely. The particles of 
 precious metals are thus brought again and again into 
 contact with quantities of cyanide much more than 
 sufficient to dissolve them entirely. 
 
 Owing to the very efficient dissolving power of the 
 solution on the one hand, and to the action of the 
 electric current on the other hand, the fine gold and 
 silver are readily dissolved, and afterwards electrically 
 deposited on the amalgamated plates in the vat, 
 where they can be recovered in the form of amalgam. 
 
 The coarse grains are amalgamated, so that they 
 are also recovered. 
 
 This process admits of a far smaller quantity of 
 cyanide being used than in any leaching process 
 known. 
 
 The time required for working a charge is from six 
 
CYANIDE PROCESSES. IO/ 
 
 to twelve hours, while by the ordinary method as 
 many days may be consumed under the most favor- 
 able conditions three days. 
 
 This process avoids all the difficulties and complica- 
 tions connected with the leaching and washing of the 
 tailings, the recovery of gold and silver in solutions, 
 and the presence of baser metals. The liquor, i.e., 
 solution and ore, is run out through an opening in the 
 bottom of the vat, and the vat is then ready for an- 
 other charge of ore. The waste liquor is allowed to 
 settle in a tank below the vat, and after a time two 
 thirds of it are drawn off to be used again. The liquor 
 contains from .001 to .002 per cent of cyanide ; it holds 
 in the solution but faint traces of the base metals. 
 
 This process is said to work better with slimes than 
 coarser ore. 
 
 The cost of crushing must be added to the cost of 
 treatment of ore, but as this varies from 50 cents to 
 $2.50 per ton, depending upon circumstances, they do 
 not consider it in making up the cost of the process. 
 This crushing cost must not be considered in compar- 
 ing the cost with tailings treatment which is the 
 result of other treatment, unless the cost of crushing, 
 amalgamating, and tailings treatment be combined, 
 since those operations by the ordinary processes only 
 accomplish as much as this one process. 
 
 The chemicals used are 2 to 3 Ibs. potassium cya- 
 nide per ton of ore or o.ooi to 0.0015 per cent solu- 
 
108 CYANIDE PROCESSES. 
 
 tion ; besides sodium oxide (Na 2 O) as an oxidizing 
 agent, or lime. This reagent is not given, but its cost 
 is placed at 50 cents per Ib. As cyanide potassium is 
 50 cents per Ib. and two thirds are recovered, the 
 total cost of chemicals is $i ; labor and general ex- 
 penses are placed at 80 cents per ton, 10 per cent 
 interest and depreciation on plant placed at 20 cents 
 per ton. Total cost of treatment $2 per ton. The 
 capabilities of this process are as wide as by the older 
 system, with the advantage of recovery of more silver. 
 Conclusions applying to both methods, simple and 
 electrical : 
 
 1. The plant required is comparatively inexpen- 
 sive. 
 
 2. The extraction is arrived at without any previous 
 treatment of ores, except ordinary crushing, which 
 must take place for every treatment. 
 
 3. The extraction is simple, and quite complete; 
 tailings can be treated successfully when failure has 
 attended, other processes. 
 
 4. The precious metals can be precipitated from the 
 solution in various ways to suit the ideas of the oper- 
 ator, but the simplest way is by the electrical current 
 with mercury cathode. 
 
 5. The simple cyanide process extracts only the fine 
 gold, thus necessitating previous amalgamation with 
 free-milling, and longer contact with the solution, and 
 very fine crushing with refractory ore. The electrical 
 
CYANIDE PROCESSES. 1 09 
 
 method with mercury requires no previous amalgama- 
 tion. 
 
 6. The cost of treatment is not so high as to deter 
 the use of either process, and at times is quite reason- 
 able, depending upon circumstances. 
 
 7. The factor time enters into competition with 
 machinery on the one hand, while machinery enters 
 into competition with time on the other. We have 
 neglected previously to state an important factor in 
 favor of agitation, viz., that the tanks can be cleared 
 more readily for another operation ; with percolation 
 they must be shovelled out. 
 
 8. Talcose and clayey ores, such as make leaching 
 difficult even when mixed with sand, are readily treated 
 by agitation and the electric process. 
 
 9. Failure to obtain satisfactory results has occurred 
 from neglect on the part of the operator to properly 
 oxidize the ore before applying the cyanide solu- 
 tion. 
 
 Failure has occurred in other instances because 
 sufficient knowledge of the process was not possessed 
 by the operator. Early experiments proved very 
 unsatisfactory especially in the South Atlantic States, 
 where this process seems to have been tested before 
 it had attained its present state of perfection, or rather 
 before the intelligence now possessed upon the subject 
 had been acquired by experiment. 
 
 Since the early experiments were inaugurated the 
 
110 CYANIDE PROCESSES. 
 
 process has gradually obtained prominence, not so 
 much from writings as from actual results, until now 
 we have come to realize its usefulness in the treatment 
 of ores which we considered formerly of trifling value, 
 and in some instances of no value whatever. When- 
 ever failures are to be recorded in the future of this 
 process, they will be due to the following: first, at- 
 tempting to work ores not suitable for the cyanide 
 process ; and secondly, to the ignorance of the op- 
 erator. Those who intend to erect extraction works 
 in this enlightened age of mining should acquaint 
 themselves with the process, and ascertain if it be 
 applicable to the ores they propose to treat. It is not 
 a difficult matter now to ascertain the fitness of ore 
 for cyanide treatment, and after it has once been de- 
 termined to be suitable for cyanide treatment, nothing 
 but an absolute change in the character of the ore will 
 interfere with its successful work, except, of course, 
 the ignorance of the operator. 
 
 Mr. F. A. Moson's experiment shows that where 
 tailings from amalgamating mills are treated, and the 
 gold particles are coated with mercury, cyanide will not 
 act upon them ; this will account in some measure for 
 not obtaining at times a higher percentage of extrac- 
 tion with the older cyanide method. This objection 
 is removed by electrical cyanide process. 
 
 In the treatment of concentrates care must be used 
 to have them finely pulverized for cyanide treatment 
 
CYANIDE PROCESSES. Ill 
 
 when they do not yield their gold readily by laboratory 
 test. 
 
 The writer is indebted to the following people and 
 publications for information and data (patents U. S. 
 unless otherwise stated) : 
 
 Julio H. Rae ....... No. 61,866, Feb. 5, 1867 
 
 Thos. C. Clark ..... No. 229,586, July 6, 1880 
 
 H. W. Faucett ..... No. 236,424, Jan. u, 1881 
 
 J. F. Sanders ...... No. 244,080, July 12, 1881 
 
 J. W. Simpson ..... No. 323,222, July 28, 1885 
 
 MacArthur-Forrest. No. 403,202, May 14, 1889 
 
 No. 418,138, De4|.24, 1889 
 
 No. 418,137, 
 
 E. D. Kendall. ... No. 482,577, Sept. 13, 1892 
 B. C. Malloy ....... No. 15,206, Nov. 22, 1886 
 
 July 8 
 
 Carl Moldehauer. 
 
 J. C. Montgomerie (English).. . 
 
 j July 22, 1893 
 
 Jan. 2, 1894 
 
 J u ly I0 > l8 94 
 
 Oct. 4, 1894 
 Jan. 8, 1895 
 Carl Pielstecker. .................. Dec., 1894 
 
 Alexis Janin ) 
 
 r MT iv/r -11 f " No ' 515,148, Feb. 20, 1894 
 C. W. Merrill J 
 
 W. D. Johnston ____ No. 522,260, July 3, 1894 
 Pelatan and Clerici .............. Oct. 1 894 
 
112 CYANIDE PROCESSES. 
 
 Wm. Crookes (Eng.). No. 462,535, Nov. 3, 1891 
 
 Siemens-Halske Extracts 
 
 J. B. Hannay 
 
 S. R. Whitall April 18, 1893 
 
 Chas. Raleigh Extracts 
 
 Michel Body Jan. 8, 1 894 
 
 Carl Hoepfner Oct. 24, 1 893 
 
 Baker's Process June 28, 1882 
 
 C. D. Able Jan. 20, 1887 
 
 W. A. G. Birkin Mar. 21, 1893 
 
 W. P. Miller Feb. 6, 1894 
 
 Frederick Rinder June 18, 1895 
 
 -*-**/ 333. 
 
 PUBLICATIONS. 
 
 Engineering and Mining Journal, N. Y. City, Dec. 
 29, 1888. 
 
 Mining and Scientific Press, San Francisco, Cal. 
 
 Mining Journal, Railway and Commercial Gazette, 
 London. 
 
 The Mining Journal, London. 
 
 California State Mining Bureau. 
 
 Journal of Electrical Engineers. 
 
 The various writers whose names appear have 
 written for the above publications, and to those in- 
 terested are probably well known. 
 
C YA NID E PRO CESSES. I 1 3 
 
 USEFUL INFORMATION. 
 
 Area of circle = diameter squared X .7854. 
 
 Circumference of circle = diameter X 3.1416. 
 Cubic inches in gallon imperial = 277.276. 
 
 11 U. S. = 231. 
 " foot = 1728. 
 
 Cubic foot = 6.232 gallons. 
 Cubic yard = 168.264 " 
 Imperial gallon weighs 10 pounds. 
 U. S. " " 8.33 pounds. 
 
 One ton water = 200 imp. gallons. 
 
 " " " 240 U. S. " 
 One cubic foot water weighs 62.5 pounds. 
 Drachm avoirdupois 27.3 grains. 
 
 " fluid water = 54.7 " 
 One cubic inch water = 252.5 " 
 Pennyweight Troy =24 " 
 Ounce avoirdupois = 437.5 " 
 
 11 Troy =480 
 
 Pound " = 5760 " 
 
 *' avoirdupois = 7000 " 
 Gram = 15.432 " 
 
 Grain .0648 gram. 
 
 Ounce = 28.3495 " 
 
 i coulomb = unit of quantity of electric current, 
 
 i ampere " *' flow = I coulomb per sec. 
 
 i ohm = " " conduction resistance. 
 
 i volt = " " electro-motive force. 
 
 Assay ton = 450 grains Troy weight. 
 
 " *' = 29, 1 66 milligrams. 
 
 Avoirdupois ton = 2000 pounds or 32,000 ounces. 
 *' " = 29, 1 66 Troy ounces. 
 

INDEX. 
 
 Acid ores, 54 
 
 Agitation, 15, 29, 82 
 
 Alkali precipitation, 34, 60 
 
 Alkaline sulphides, 25 
 
 Alternating currents, 100 
 
 Aluminum precipitation, 36 
 
 Amalgamation, 7 
 
 Anodes, 92 
 
 Bullion, treatment of, 43 
 
 Ca* ~>des, 97 
 
 C) oal precipitation, 35 
 
 ical treatment of ores, 21 
 'c .entrates, 66 
 rooke's process, 100 
 -ushing ores, 3 
 arrent, 72, 82 
 
 " and cyanide solution, 87 
 yanide and stamp battery, 5 
 " process, 10 
 " " recovery, 48 
 ^termination of gold and silver, 54, 56 
 " " ores, 22, 29, 49 
 
 " " solution, 14, 56 
 
 " zinc by alkaline sulphides, 60 
 " " " " iodine, 58 
 
 41 " " in solution, 60 
 
 lute solutions, 14, 20 
 ainage of ore, 4, 17 
 ectrodes, 80 
 lectro-gilding, 80 
 Jectrolysis, 73 
 Eisner's equation, 10 
 
 US 
 
1 16 INDEX. 
 
 Experiments, n 
 General information, 63 
 Gold recovery by zinc, 33, 38, 51 
 " " " electrolysis, 78 
 
 " refining, 45 
 Hanney process, 12 
 Laboratory-work, 54 
 Leaching, 32 
 Lime treatment, 5 
 Literature, in 
 Mercury cathodes, 98, 105 
 " flouring of, 8, 
 " sickening of, 9 
 Ores, i, 7 
 
 " drainage, 4, I7> 3 2 
 " for cyanide process, 17, 29, 50 
 " leaching of, 29, 32 
 " refractory, 7 
 " tailings, 18, 31 
 Paul's rule, 15 
 
 Precipitation by alkali, 34, 60 
 " " aluminum, 36 
 
 " " charcoal, 35 
 
 " " Peletan-Clerici method, 105 
 
 " " Siemens-Halske method, 99 
 
 " " zinc, 33, 38 
 
 Process, 10, 30 
 
 " chemistry of, 21 
 " ores adapted to, 17, 29, 50 
 " recovery by, 48 
 " scope of, 22 
 Sampling, 67 
 
 Siemens-Halske process, 99 
 Solution, 14, 56, 87 
 Stamp-milling, 2 
 Useful information, 113 
 
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