MATTE SMELTING.
ITS PRINCIPLES
AND
LATER DEVELOPMENTS DISCUSSED.
WITH AN ACCOUNT OF THE
PYRITIC PROCESSES.
BY
HERBERT LANG
FIRST EDITION FOURTH IMPRESSION.
HILL PUBLISHING COMPANY,
505 PEARL STREET, NEW YORK.
6 BOUVERIE STREET, LONDON, E. C.
The Engineering and Mining Journal Power American Machinist
L 3
Q#.
COPYRIGHT, I3S5.
BY
THE SCIENTIFIC PUBLISHING COMPANY.
COPYRIGHT, 1903,
BY
THE ENGINEERING AND MINING JOURNAL.
INTRODUCTION.
IN ITS present development matte-smelting is applied in the
extraction of gold, silver, copper, nickel, cobalt, and lead from
their ores. It is probable that more than one-half of the world's
supply of copper is obtained in this way, while the proportion of
silver thus procured is very large and is yearly increasing. We
do not possess precise statistics bearing on the subject, but
approximate estimates appear to show that the aggregate value of
the metals which are extracted annually throughout the United
States by means of matte-smelting methods has now reached the
magnificent total of thirty millions of dollars. The interest that
is naturally felt in metallurgical processes which are accomplishing
such vast results is increased by the fact that they are in a con*
dition of rapid improvement and expansion, exhibiting at the
present moment a vitality and aprogressiveness as great, perhaps,
as is elsewhere shown in the whole range of metallurgy. We may
confidently expect not only a higher perfection in their application
to the metals of the foregoing list, but also the extension of the
principles of the art of matting to the benefication of ores of
other metals and metalloids. It is not unreasonable to expect that
in the perhaps immediate future we may by such means recover
arsenic, antimony, tin, bismuth, and the metals of the platinum
group; and that by modifications and combinations of already
known processes, sulphur itself may be practically recovered as it
issues from the flues of the matting furnace. Most metallurgists
will doubtless coincide in the assertion that matte-smelting is
therefore nnequaled in the variety and extent of its applications,
as well as in its probable future expansion, by any other process,
or system of processes, known to their art.
Matte-smelting, in common with other departments of ore
337651
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4 INTRODUCTION.
reduction, has undergone changes and improvements of great
magnitude within recent years changes and improvements which
are not fully recorded in our text-books, and of which the
ordinary reader and the merely book-learned individual can have
but slight conception. The smelting of to-day is far different
from the smelting of twenty, of ten, or even of five years ago, and
even those metallurgists who, like the writer, have been actively
employed in such pursuits are themselves as yet hardly able to
realize the full bearing and application of the principles and pro-
cesses so lately worked out.
It may be that a time of transition like the present, when dis-
covery heralds discovery, and improvement merges into improve-
ment, is not the best time for writing the finished treatise which
would mark the closing of an era in metallurgy. But with less
ambition, less leisure, and perhaps less fitness for the task, still
one may doubtless find a great deal to say which would be profit-
able to write and to read. There are many topics connected with
smelting which, being unfitted by their purely practical nature
from discussion in books, we have had no formal instruction upon.
Others there are which have escaped discussion because of their
novelty. It will be the effort in the following essay to touch upon
topics of this practical sort, and to bring those of an isolated or
novel kind into correlation with the underlying principles of
metallurgy, as it is certain that no discussion worthy of the name
can ignore the theoretical basis of the subject. While endeavor-
ing, therefore, to supply the want of present information in partic-
ular lines of work and research, the writer would disclaim any
attempt to produce a complete treatise, or one covering fully the
domain of matte smelting, certain important divisions of which,
as, for example, reverberatory furnace smelting, remaining un-
touched in this writing.
A question having arisen during a year or two past as to the
uses and comparative efficiencies of the matting and the lead
smelting processes, and the query having especial pertinence to
this subject, I think it well to place this discussion before the
reader somewhat in the form of a comparison of the practice,
and incidentally of the principles of the two related arts. As a
basis of an understanding of their salient differences it is conven-
ient to classify them as: 1. Difference in the carrier; 2. Difference
in the slags; 3. Difference in the fuels; 4. Difference in apparatus;
INTRODUCTION. 5
5. Difference in materials treated. Accordingly I shall adopt
such a classification of topics in the ensuing essay.
THEE SHOWING RELATIONS OP THE MATTING PROCESSES.
MATTE SMELTINO.
I
Blast Furnace Matting. Reverberatory Matting
I ; ("Swansea Process ")
German System. Pyritic Smelting.
Gradual Reduction Processes. Austin Older Process.
I
Cold
Blast. Hot blast
CONTENTS.
INTRODUCTION 8
Tree Showing Relations of the Matting Processes ... 5
SECTION ONE. THE CARRIER.
PARAGRAPH.
1. The Carrier De6ned *.... 11
2. Definition of Matte Smelting 11
3._Ho w Mattes are Classified 12
4. The Composition of Mattes 13
5. Views as to Chemical Composition 13
6. The General Problem 15
7. Theoretical Concepts 16
8. Arsenic and Antimony as Matte Formers.. 17
9. The Genera of Matte Constituents 19
10. Wide Dissemination of Favorable Ores 19
11. Excess of Matte Formers 20
12. Conditions Governing the Absorption of Metals 20
13. Summary of the Results of Matting 21
14. Phenomena Respecting Gold and Silver 21
15. The Influence of Copper 23
16. The Carrier Practically Considered. 24
17. Treatment of Molten Mattes 25
Methods of Matte Refining (Table) . 27
18. Coincidences of Smelting Methods 28
19. Conventional Ideas 28
20. Relations with Lead Smelting 30
21. Relative Proportions of Charge and Product 31
22. Proportion of Values 80
23. Possibilities of Concentration 33
24. Practical Advantages. . .. ^ 83
25. Conditions Governing Concentration 34
26. Specific Gravity of Mattes 85
27. Examples.., 85
Illustration of Specific Gravities 36
8 CONTENTS.
SECTION TWO. THE SLAGS.
PAGE.
28. Physical Characteristics of Slags 3?
29. Range of Practicable Slags 38
30. Comparisons with Lead Slags 38
31. The More Acid Slags Preferable 39
32. Specific Gravity of Slags 40
SECTION THREE. PYRITIC SMELTING.
33. The Choice of Fuel 41
34. Definitions and Distinctions. . 42
35. Prime Distinction of Pyritic Smelting . 42
36. Basal Pyritic Reactions 43
37. Deductions from the Foregoing Principles 44
38. Meaning of the Terms Oxidation, Roasting, etc. 44
39. Extent to which Oxidation may be Carried 45
40. Fuel Economy of Smelting Processes 46
41.- Deductions 46
42. Considerations Regarding Heated Blasts 48
43. Temperature of Blast 48
44. Mechanism of the Austin Older Process 49
45. Conditions of Working 51
46. Later Modifications , 52
47. Modes of Feeding Furnaces 53
48. Comparative Tabulation of Effects 53
49. Pyritic Smelting of Simple Ores 53
50. Relation of Blast Temperatures to Fuel 54
51. Adaptation of Processes 55
52. Prevailing Characters of Sulphide Ores 56
53. Uses of the Cold Blast 56
54. Principles Underlying Cold Blast Smelting 57
55. Demonstration of Principles 59
56. Further Demonstration of Principles 59
57. Furnace Construction and Management 60
58. The Furnace Blower 61
59. Comparative Rate of Smelting 62
60. Hearth Activity 62
61. Production of Pyritic Effects 63
62. Secondary Effects 63
63. The Crucible and the Forehearth 64
64. Blasts of Higher Temperature 65
65. Methods of Heating the Blast 66
66. Comparison of the Hot and Cold Blasts 68
67. Direction of Experiment 68
68. Lead in the Pyritic Furnace 69
CONTENTS. 9
SECTION FOUR. LOSSES IN SMELTING, SALE OP PRODUCTS.
TABLES.
PAGE
69. Slag Losses 70
70. Losses in Lead Slags 72
71. Efficiency of Lead and Matte Compared 73
72. Influence of Slag Composition on Losses 74
73. Practical Requirements 74
74. Losses from Volatilization 75
75. Losses in Flue-Dust 79
76. Influence of Various Substances upon Extraction 79
77. Resume" 79
78. Sale of Furnace Products 80
Table Cbaracteristics of Smelting Processes 83
Table of Furnace Effects 85
Table of Work Done 1. The Material Treated 90
Table Showing Peculiarities of Sale 92
Table of Work Done 2. The Products Obtained 93
MATTE SMELTING.
SECTION ONE.
THE CARRIER.
1. THE CARRIER CONSIDERED. ID lead smelting, as all are
aware, the carrier is metallic lead, and the precious metals come
down as alloys with lead, intermingled with the great excee? of
that metal. But inasmuch as other valuable metals which we may
wish to save, as copper, nickel, and cobalt, do not form with lead
the manageable alloys which would enable their simultaneous
extraction, and as the conditions necessarily attending their
reduction to the metallic form are incompatible with the saving
of the lead, we are debarred from the employment of that method
for their extraction. Although all the substances mentioned, as
well as others, cannot be simultaneously produced as metals, their
artificial sulphides may all be produced at one and the same
operation, and the metals won may be separated from each other
and from attending impurities by a series of processes analogous
to and not more difficult or costly than those by which lead bullion
is converted into marketable metals. This smelting operation,
which is called by the Germans " Raw Smelting," and in this
country is indifferently known as "Matting," "Matte Smelting,"
or "Pyritic Smelting," seems to merit better the name "Sulphide
Smelting," as a more distinctive and logical designation. While
preferring the latter term I shall in deference to established
custom continue to use the term "Matte Smelting," as in the
present writing.
2. DEFINITION OF MATTE SMELTING. Matte smelting may-
be defined briefly as the smelting of natural sulphides with the
design of collecting their valuable parts in a quantity of artificial
sulphides. Or, more explicitly, as the smelting of ores composed
12 MATTE SMELTING.
of, containing, or giving rise to, sulphides, for the purpose of
collecting their values in a less quantity of artificial sulphides.
And since, as will be shown, arsenic or antimony cau take the place
of sulphur in the ore mixture with entire success to the operation,
we may and sometimes do have arsenide and antimonide smelting;
for which the above definition, with the obvious changes, will
answer perfectly. Matte, the name by which is designated the
indefinite mixture of artificial sulphides which are the result of
the smelting operation, covers many varieties of product, varying
infinitely in chemical composition and physical characteristics.
One of the most striking features, and one with which the smelter
is very deeply concerned, is the miscibility of mattes; whereby
we fiud sulphides of even considerable differences in specific
gravity, and in fusibility, and of immense difference in chemical
composition, mixing togelher in the liquid state with such
thoroughness that no characteristic peculiar to, or even suggestive
of, either can be recognized in the mingled mass. It may be that
this excessive miscibility partakes Of the nature of solution, one
sulphide being virtuallyilissolved in another, as sugar dissolves in
water. As to this point I shall present a few remarks in another
connection.
3. How MATTES ARE CLASSIFIED. No classification of these
very remarkable compounds has been made other than their
designation according to the predominant metal or oftentimes
according to the metal of predominant value into iron matte,
copper matte, lead matte, silver matte, etc. It will assist the
effort to obtain a logical and scientific view of the subject if we
endeavor to classify them in a manner more consistent with the
present condition of metallurgical science. I would suggest that
there is nothing in the composition of any of the mattes, or even in
the composition of the arsenide and antimonide compounds which
we know by the objectionable term speisses, to prevent their being
brought into a family together, and considered as individual
members of a great class. The classification under which I prefer
for the present purpose to place both the mattes and the speisscs
is as sulphide mattes, arsenide mattes, and antimonide mattes.
Examples of each will be found in their appropriate places in the
Table of Smelting Products accompanying this article. This
classification I shall continue to follow, dropping the term speiss
as distinctive of nothing which we could wish to preserve in our
speech. I shall use the less limited term matte in the general
THE CARRIER.
13
sense of meaning either the sulphide, the arsenide, or the
antimonide compound, or the mixtures of all of them, according to
circumstance.
4. THE COMPOSITION OF ^MATTES. Of the common metals
which play an important part in the chemical composition of mattes,
there are iron, copper, lead, zinc, rickel, and cobalt; while of the
less common ones, the most important are silver,gold,and bismuth.
Occasionally manganese and tin occur; and even the compara-
tively rare elements, vanadium, molybdenum, cadmium, and
platinum have been detected. Even the metals of the alkaline
earths enter at times into the composition of mattes, and, as will
be shown, they sometimes play not unimportant parts therein.
Those chemical analyses of mattes to which I have access demon-
strate profound differences of composition, which I can best illus-
trate by the following citations. Of the various elements which
enter into the composition of certain mattes, I quote the highest
percentages and the lowest which are found therein:
Highest. Lowest.
Platinum 0.0018 0.
Bismuth 1.26 0.
Molybdenum 2.31 0.
Calcium.-. 7. 0.
Barium 22. 0.
Sulphur 44. trace
Arsenic 52. 0.
Antimony 60. 0.
An inspection of this table renders obvious the prodigious
diversity of composition of mattes; whence we may infer the appli-
cation of the matting processes to widely differing ores and
mixtures. We generalize also that no single element of the list
is indispensable in matte formation, but that the place of each
may be taken by others. Even sulphur and iron, which are the
most common and abundant constituents, and which appear in
every matte whose analysis I have encountered, with a single
exception, are in many cases to be considered merely as accidental
impurities, and not as essential to the constitution.
5. VIEWS AS TO CHEMICAL COMPOSITION. Balling and
others have derived from various analyses the formulae Fe 2 S 8 ,
FeS, Fe 3 S, and even Fe 2 S, as representing the various states
in which iron exists in sulphide mattes; while the average of
Highest.
. ...70.47
Lowest.
0.136
80
o
Lead
. 73.
0.
Zinc
11.5
0.
55.
0.
Cobalt
54.
o
Manganese.
... 3
o
Silver
5.
0.
Gold..
.. 0.11
0.
14 MATTE SMELTING.
opinion and experience favors FeS as the usual combination.
Possibly all of these combinations may have been found; but
uncertainty exists which ill accords with the advanced condition
of chemical science.
But if our knowledge as to the mode of combination of the iron
in the sulphide mattes is uncertain and unsatisfactory, it is still
more so in reference to the arsenide compounds of that metal.
Observers have recognized, or claimed to recognize, a long series
of ferrous arsenides of artificial origin, not less than a dozen in
number, differing from each other in well-marked physical as well
as chemical characteristics, and all producible at will by the
instrumentalities of the blast furnace. Arsenide mattes are
especially prone to assume crystalline forms on cooling, and it is
peculiarly pertinent to remark here that a tap of that material
freqently separates into two parts, one thoroughly crystallized at
the bottom and with a massive or incipiently crystallized portion
above.
Analysts are unanimous in ascribing the familiar composition
Cn 2 S to the copper compound which we find in sulphide matte,
and an equivalent ratio to the same metal in its combinations
with arsenic and antimony. In assuming the unvarying
character of its ratio of combination it appears that we stand upon
firm ground, and a safe starting place from which, if we had
analytical evidence enough, we might proceed to the discussion of
the general questions of matte formation. Certain other
elements, as nickel, cobalt, and manganese, as far as is known,
comport themselves with no less strictness than copper, forming
no compounds other than those analogous in composition with
their native mono-sulphides. As to lead; metallurgists have
taken it for granted that this metal possesses but one sulphide,
PbS; but the view of theoretical chemists favors the possi-
bility of the existence of the two lower sulphides s Pb 2 S and
PbS, in matte.
Of metallic substances in matte, we are all familiar with the
existence of copper in the metallic form in rich furnace products
of that kind. Guyard has isolated metallic iron and metallic lead
from the mattes of Leadville; and Mr. Pearce has proved the
existence of metallic gold in certain experimentally formed sul-
phides. I have myself noticed the volatilization of metallic zinc
from molten matte, a phenomenon whose significance I am as yet
unable to grasp.
THE CARRIER. 15
Guyard's view that matte is essentially a combination of ferrous
mono-sulphide (FeS)with the magnetic oxide of iron, has not
found many supporters; but that the latter substance always
exists in matte there is reason for believing. He found 16 and 23
per cent, of magnetic oxide respectively in two samples of Leadville
blast-furnace matte, using methods of separation which were some-
what unusual to chemists and concerning which we scarcely know
enough to enable the proper weight to be attached to his conclu-
sions. His assumption as to the composition of matte was weak-
ened by his parallel one in reference to slag, which he defined as
essentially a combination of silicates with calcium matte (i.e.,
sulphide of calcium plus magnetic oxide of iron), which view
likewise has failed of indorsement since its promulgation.*
6. THE GENERAL PROBLEM. The general problem of the for-
mation of matte in the furnace is an exceedingly important and
interesting one, but is a problem, unhappily, that the present con-
dition of metallurgy does not enable us to solve by any means as
satisfactorily or discuss as luminously as could be wished. The
problem naturally takes a form like this: Given a mixture of heavy
metals and two metalloids, whose affinities at certain temperatures
and under certain conditions are known. Required the resulting
compounds when subjected to a much higher temperature. The
problem, which, in its simplest form is totally incapable of exact
solution in the light of chemistry, becomes vastly more complex
when we realize the solvent power of the innumerable resulting
compounds for uusaturated elements and for other compounds.
In this problem we have a parallel for the well-known astronomical
one of the Three Bodies, which transcends the keenest analysis of the
mathematicians. Experiment long since taught us the respective
affinities of the elements for oxygen; and later the researches of
Fournet demonstrated the relative attractions of the heavy metals
for sulphur; but the more difficult and recondite experimentation
to establish the affinities of those metals toward both elements
and toward each other at the smelting temperature has never been
performed.
Chemical analysis, applied to the study of these interesting
compounds, has not enabled us to fully understand their internal
structure. Even regarding the simplest of them our analysis fails
to substantiate our expectations. We find for example an
* Mining Industry of Leadville, Emmons, p. 724.
16 MATTE SMELTING.
excess of iron in certain ferrous mattes, something beyond the
amount which the doctrine of definite chemical proportions would
teach us to expect; while the heterogeneous character of ferrous
arsenides increases the difficulty of chemical analysis while
diminishing the reliability of its conclusions. Analysis almost
always shows unexpected excesses or deficiences of some elements
not always to be ascribed to the effects of replacement by related
elements. But this fact, be it noticed, does not destroy the
analogy of these artificial compounds to native minerals, for these
also rarely show by analysis the precise proportions demanded by
theory.
7. THEORETICAL CONCEPTS. In attempting to devise a theory
of matte formation it is the most convenient and perhaps the most
rational to conceive of all mattes as derived from the cuprous
sulphide matte by replacement of copper successively by other
metals whereby we obtain all the varieties of sulphide mattes; while
the arsenide and autimonide mattes arise from the replacement of
the sulphur by the two corresponding elements, arsenic and
antimony. At first thought it would seem to the chemist that
the ferrous sulphide matte is more truly typical of the class; and
certain writers have even of late discussed mattes under the
assumption that they are primarily compounds of iron and sulphur
in which the former is replaced in part by lead and copper, and
in less degree by ziuc, silver, nickel, cobalt, manganese, arsenic,
antimony, calcium, barium, and magnesium. In view, as before
remarked, of the variable nature of the combination which iron
forms with sulphur, and the uncertainty and lack of knowledge
of their composition, it appears to me that the ferrous substances
cannot conveniently or logically be taken as the archetype of
mattes, but that the cuproas mattes should be so taken, if we
assume any at all. Of all substances which enter matte, we must
consider iron as one of the most uncertain in its combinations,
and in so far ill calculated to serve as a starting point.
I prefer to look upon matte as a mixture of saturated com-
pounds, each one of them equally important to its existence,
and none of them indispensable to it. Matte would remain matte
if any of its constituents were removed. Accordingly, I do not
look upon the saving, for example, of gold and silver as the result
of those metals becoming in some fortuitous manner entangled in
matte, but rather as the result of the formation of double or
multiple salts, into which the precious metals enter in definite
THE CARRIER. 17
proportion. However, beyond the force of chemical affinity which
tends to definite combination, we are compelled to recognize, as
shown by certain observed phenomena, which 1 need not here
recount, the tendency to solution, which gives rise to indefinite
mixture; and also the attraction of alloyage, or the propensity of
certain regnline metals to form alloys. The subject is of an
undoubtedly difficult and complex nature, such as the materials
and facts at command in nowise enable us to treat adequately.
I may suggest, in this connection, that as chemical analysis has not
given us an adequate comprehension of the matter at issue,
synthesis may do better. By proceeding synthetically in the
direction of Dr. Pearce's experiments, previously cited, or upon a
more ambitious working scale even, if such be found practicable,
one can hardly fail to enlarge the bounds of metallurgical
knowledge, while paving the way for practical results of the
highest value. That experimenter is to be envied whose tastes and
opportunities impel him upon this course of investigation.
It would-be interesting indeed, were our knowledge sufficient, to
trace the progress of a metal through the multifarious forms
which, impelled by. the play of chemical attraction, it assumes, as
the furnace operation proceeds, from the moment when, as crude
ore, it entered upon its baptism of fire until it emerges borne in
fiery matte, or even when freed from "humors and corruptions" it
attains the metallic form and is ready for the service of man;
but for the prese.nt one can do the reader a better service by
frankly declaring that from a reasonable point of view the results
of such speculation, based as it must be upon our too limited
knowledge of the inner harmonies of the smelting furnace, possess
no practical value in comparison with the findings of experience.
8. ARSENIC AND ANTIMONY AS MATTE FORMERS. The
function of arsenic and antimony appears to be misunderstood.
It is difficult to believe that these substances, which resemble
sulphur in their modes of combination, can replace the heavy
metals in mattes. We are familiar with both the native and the
artificial sulphides of the two elements, and we find them
reported in analyses as existing as such in mattes; but what we
know of their physical characters, such as specific gravity, and
volatility, debars us from accepting the conclusion that they
really are found therein. As an invariable rule, the spe'cific grav-
ity increases with the content of arsenic and antimony, while,*
should their sulphides exist, weighing as they do less than any
18 MATTE SMELTING.
mattes, their effect upon the specific gravity would be the
contrary of what is found. Nothing has been proved with more
certainty than that the three elements, arsenic, antimony, and
sulphur, may replace each other entirely in all the combinations
which we meet in practical smelting. It appears most likely that
arsenic in sulphurous mattes does not exist simply as sulphide,
but as the aulpharsenide, the thio-arsenite of the chemists,
formed by the combination of As 8 S 3 , with a sulphide of a heavy
metal (e. g., PbS, As^). The type formula accordingly is
R,S, AS^SS, in which R represents a monatomic metal. Under
the same circumstances antimony acts similarly, forming sulph-
autimonides analogous to the first-mentioned substances, both
series being chemically identical with their mineralogical
relatives.
In ordinary estimation the arsenical and antimonial furnace
products are held as follows:
1. Difficult of treatment by established processes. Especially
is their calcination difficult, owing to the formation of oxidized
nou-volatile substances (arseuiates and antimoniates).
2. Fused they corrode masonry; while those containing lead
Corrode iron through replacement of metals (e.g., PbAs n +Fe =
FeAs n +Pb).
3. They cause losses of values, especially of silver, by volatili-
zation.
4. They deteriorate the quality of associated metals (copper).
5. They, particularly arsenic, are detrimental to the health of
the workmen.
Some of these objections are well taken, but some have lost much
of their force consequent upon late discoveries and improvements
in methods of ore treatment. Notice, for example, that the
corrosive effect of molten arsenides upon iron and upon brick-
work, being a result of chemical action which is now understood,
shows the way to a ready means for decomposing such molten sub-
stances, as well as of resisting their prejudicial effects. Given mol-
ten metallic arsenides with access of air, and contact with siliceous
material, and silicates of metals result, Pursuing the dependent
train of reasoning toward its logical conclusion, and carrying out
the processes indicated, we are led to an application of the pyritic
smelting and bessemerizing principles, and experiments actually
show that under the influence of the air-blast the arsenides are
decomposed with ease, more readily in fact than the sulphide? to
THE CARRIER. fS>
which those principles have been heretofore adapted. Experiments
made by the writer on mixtures of fused sulphides and arsenides show
conclusively the greater facility with which the latter are decom-
posed, and how the elimination of arsenic takes place before that
of the sulphur, and with what high heat it is accompanied.
We are here traversing new and unexplored ground, whereon one*
should tread circumspectly, and I have no desire to hazard pre-
dictions as to the outcome of the application of principles in fields
to which they have not as yet been applied, nor. to anticipate the
results which others may be better entitled to announce; but it
seems to me that we have in this habit of the arsenides, and prob-
ably of the antimonides, so amenable to the influences of the
blast of air, a characteristic which will go far to offset their
injurious behavior in other respects, and that will probably make
their native minerals among the easiest of all substances to smelt.
9. THE GENERA OF MATTE CONSTITUENTS. We have, then,
the following list of substances occurring in mattes:
1. Simple sulphides.
2. Sulpharsenides.
3. Sulphantimonides.
4. Arsenides.
5. Antimonides.
6. Magnetic oxide of iron.
7. Metallic iron, lead, copper, and gold.
More than tifty different compounds and simple substances have
been reported at one time and another as existing in matto; but
not one of them was essential to its existence as such; any ono
could have been removed and still leave matte. Matte, it would
seem, must be made up of a mixture of definite chemical com-
pounds, each of which has or may have its analogue in the
rnineralogical world. Double or multiple salts may exist among
them, as is further suggested by the common phenomenon of the
crystallization of even very complex mattes.
10. WIDE DISSEMINATION OP FAVORABLE ORES. It is self-
evident, and I need not argue the point, that we cau always secure
a mixture of ores which will on melting give rise to an effective
carrier; for it is probably quite impossible to name, and almost
as difficult to conceive of, a mining region where there are neither
sulphur, arsenic, nor antimony; neither iron, lead, nor copper.
From this consideration I think it may fairly be claimed that in
this respect matting has an unimpeachable advantage over a rival
20 MATTE SMELTING.
process which requires a large proportion of lead in order to
become effective. This truth, important and far-reaching as it is,
is of so obvious a nature that I arn scarcely warranted in enlarging
upon it. I prefer rather to leave it to the decision of those
familiar with the conditions prevailing in our mining regions as
to which process is likely to prove most generally practicable.
11. EXCESS OF MATTE FORMERS. It is true that in matting
we can usually obtain the necessary matte constituents with great
facility; but we may and generally do have too much of them.
That is to say: we often have ores which contain not only the
heavy metals named, but also so much sulphur, arsenic, or
antimony in combination, that it becomes necessary to get rid of
the excess above the proportion needed for forming the carrier. It
is then that the resources and skill of the metallurgist are most
heavily taxed. We may get rid of the excess in either of two
ways: the one, outside the furnace, by roasting as if preparatory
to lead smelting; the other inside the blast furnace, when the
operation is called pyritic smelting, being the latest developed and
most interesting branch of matting.
It is the useful peculiarity of matte smelting, that we need be
at no pains to cause the sulphur, the arsenic and the antimony to
combine with the various valuable metals which may be present;
for those obliging elements always unite of their own volition with
the most intrinsically valuable metal, not directly, perhaps, in
every case, but if not, the absorbing it by means of directly formed
mattes or speisses. Provided that a sufficient number of matte-
forming substances are present, all the values are certain to be
saved, excepting of course, the unavoidable and usually small
losses of the operation.
12. CONDITIONS GOVERNING THE ABSORPTION or METALS.
The useful result of the matting fusion in the presence of
sulphur and arsenic is the saving of the valuable metals about in
this order, beginning with that one which is found to be extracted
most completely: Gold, copper, nickel, cobalt, silver, lead.
These, with iron, which is always present, constitute the metallic
portion of the matte. The iron appears to be present only to take
up whatever excess of metalloid there may be, its percentage
diminishing with the increase of the other metals brought down.
Excepting lead, neither of the metals named are crowded out of
the matte by iron, but on the contrary that metal itself is pre-
vented by them from combining with sulphur and arsenic under
THE CARRIER. 21
the conditions prevailing in the furnace. This is fortunate; for
not only are copper, nickel, and cobalt valuable in themselves, but
the mattes in which they are contained are probably more generally
efficacious in extracting the precious metals, than the matte com-
posed only of sulphide of iron.
13. SUMMARY OF THE KESULTS OF MATTING. It follows
from the foregoing considerations that matting, as the result
of several more or less tangible reactions, saves each one of
the several valuable metals at one operation, concentrating
them in one or sometimes two substances, of varying composition,
often almost as complex as the ores from which they were derived.
Again, as a corollary, if we diminish the relative proportion of
matte formed, as compared with the amount of ore smelted, the
composition of the product will be changed. We shall find less
and less iron in it as we concentrate more, and also less sulphur;
but we shall discover an increasing percentage of gold, silvery
copper, cobalt and nickel, and to a certain extent, lead. In the
common case of treating sulphur-bearing gold, silver and copper
ores, if we keep on decreasing the proportion of matte (which in
practice we effect by diminishing the proportion of available
sulphur in the charge) we arrive eventually at a copper-silver-gold
alloy, having passed successively through the various stages of
copper-matte known as coarse metal, blue metal, white metal, and
perhaps pimple metal, the important members of the copper-matte
series, and beyond which, as we proceed to higher degrees of con-
centration, we pass from the domain of matte-smelting into that
of metallic copper smelting, of which we have examples in Arizona
and elsewhere.
While noticing the divergence of the two processes at this point,
let it be added in correction of a misapprehension that seems to
have arisen in some minds, that the copper-silver-gold alloy which
has been mentioned, if made in a blast furnace, would be called
black copper; if produced in a reverberatory, blister copper; and
that the two products differ in important particulars.
14. PHENOMENA RESPECTING GOLD AND SILVER. The
experiments of Mr. Pearce (Trans. A. I. M. E., XVIIL, p. 454)
demonstrate that plain ferrous sulphide exercises no solvent action
on pure gold, the latter when melted with such a matte becoming
diffused irregularly through it in the form of globules; and this
finding is well supported by the matting experiments at the Boston
Institute of Technology, recounted by Mr. Spilsbury (Trans. A. I.
22 MATTE SMELTING.
M. E., XV., p. 767), where it was shown that the gold of pyrites con-
centrations was not absorbed in the matte arising from their
fusion. This evidence is conclusive as to the lack of absorbing power
of ferrous matte toward gold alone; and the further experiments of
Mr. Pearce upon the effects of the same kind of matte upon that
metal in the presence of silver are hardly less so. In brief, he
finds that an alloy of gold and silver is formed, which is dissolved
iii the matte instead of being physically disseminated in it. One
would think that the solution of the alloy in the matte would be
similar to the solution of similar alloys in lead bullion; and from
this point of view the problem of saving the precious metals would
resolve itself into the saving of the matte and separating it from
the other products of fusion. As corroborative evidence of the
efficiency of ferrous matte as an absorbent of gold in the presence
of silver I shall cite the work done at the Toston and Dead wood
matting plants, where many thousand tons of pyritic ores have
been successfully treated with the production of such a matte.
Unfortunately, the details of their work have not been published
as fully as could be wished ; but if we may accept the assurances
of the managers, which I for one do not doubt, the extraction in
each case has been exceptionally complete. However, as bearing
on the technical point at issue, the evidence supplied by their con-
tinued practical success is not as satisfactory as could be wished,
for analyses are lacking to show that the matte is really entirely
free from other metals that might exercise an independent absorb-
ing effect that cannot be disregarded. I think that the tendency
of what evidence we have is to prove the important effect of
relatively small quantities of elements: of stray and unconsidered
substances, as it were. Chemical analysis shows the extreme
complexity of what have been thought pure ores. Iron pyrites
often contains half a dozen of impurities which might have an
important chemical effect upon gold, while in the products of the
smelting furnace we find concentrated a surprising number of well-
known and even some rare elements; and as to those mattes which
have been reported as pure iron sulphide, it is very much to be
doubted that they do not contain at least a small proportion of
hitherto unnoticed substances; for it would be remarkable that a
deposit of ore of such character as to give rise to an absolutely
pure matte were found to exist. The influences particularly of
bismuth, arsenic and tellurium on gold contained in mattes may
THE CARRIER. 23
be anticipated in advance of experiment, and form a fertile subject
of study and deduction.
15. THE INFLUENCE OF COPPER. The influence of copper,
which plays no part in the experiments cited, is of great impor-
tance in practical work throughout almost the entire domain of
matte smelting. It has been deemed essential to the perfect
extraction of the precious metals that a proportion of copper
should be present in the charge, and it is difficult to make some
individuals believe that practical work can be carried on without
it. It may well be that under some circumstances that metal is
imperatively necessary to a good extraction; but that under certain
other circumstances good work can be done in its absence there is
no doubt. I need cite no evidence save that afforded by the two
plants mentioned to prove the point, nor will I venture upon a
generalization of my own concerning the conditions under which
it is safe to rely upon a non-cupriferous matte for the extraction
of both the precious metals; but I feel under the necessity of
quoting the language of an eminent metallurgist whose name I am
unable to use, who sums up tersely the belief to which he has
come through years of experience: "Copper is not necessary in
mattes which accompany acid slags; with basic slags it may be
necessary."
The first clause of this dictum is amply proved by the gentle-
man's own work in producing such matte; and the second I find
to agree with such evidence as I have been able to examine. I
conjecture that there may be substances possessing as great or
greater an influence than copper: but in their absence I regard
that metal as essential to a clean extraction in all the cases which
have come under my notice, where basic or even slightly acid slags
were being produced. The beneficial effect seems to increase up
to an uncertain limit with the percentage of the copper, for I have
repeatedly found that a very low-grade copper matte failed to ex-
tract as high a proportion of silver as a matte richer in copper. I
presume the extraction of gold too would be influenced in the
same manner, but of this I have no evidence to offer. It was no-
ticed at Anaconda, however, that mattes of a certain comparatively
high tenor in copper left more silver in the slags, the expression
there being that " the copper crowded the silver out of the matte."
This observation is not inconsistent with the preceding, inasmuch
as the Anaconda mattes are of much higher tenor in copper than
those used mainly for the extraction of the precious metals, and it
24 MATTE SMELTING.
may be that the very rich mattes do not possess the extractive
powers of the poorer ones. Besides, it is generally considered that
silver exists in such mattes as an integral part thereof, combined
with the sulphur, and so far analogous to the native copper-silver
sulphides; and bearing in mind the greater affinity of sulphur for
copper than for silver, it could hardly be expected that the latter
would be taken up by the metalloid to the exclusion of the former.
We may consider the condition of things as they apparently exist
in a reverberatory matting furnace toward the end of the smelting
operation, when the boiling has ceased and the excess of sulphur
has passed away; or, more to the purpose, that prevailing during
the concentration of argentiferous matte, when sulphur is being
eliminated and iron and copper successively oxidized. Should not
the silver, which is held, as Fournet teaches, by a tenure weaker
than the two base metals, be removed from the matte before the
others, did it there exist only as a sulphide intermixed with other
sulphides? But on the contrary it outlasts the iron and the sul-
phur and eventually separates as a copper-silver alloy. Gold is
somewhat more prone to leave the matte, but it too invariably does
so in combination with some other metal, and we do not often
hear of either of the precious metals having been seen in their
native form in or about any smelting-furnace product. These con-
siderations iippear to indicate that aside from their existence as
definite chemical compounds in matte, which we cannot help ad-
mitting, the precious metals possess other modes of combination
and diffusion, as I have previously indicated.
16. THE CARRIER PRACTICALLY CONSIDERED. There are some
practical considerations connected with the formation of matte
which are of more immediate importance than the theoretical
points heretofore advanced. These relate either to the behavior
of the product in the smelting furnace, or to the subsequent oper-
ations of refining and parting. Generally speaking, the ferrous
matte would prove most favorable to the proper running of the
furnace, owing in part to its beneficial effect upon the hearth.
If, however, such a matte were produced in very large quantities,
special arrangements would be necessary to obviate its corrosive
effects. Under some circumstances we might find the arsenide
more advantageous than the sulphide mattes, on account of their
greater specific gravity, which allows them to settle out of
slags with more readiness. They might, for example, be profit-
ably used in connection with a slag that runs high in zinc, which
THE CARRIER. 25
often interferes prejudicially with the separation of matte; or
when the slag is extremely heavy from a preponderance of iron or
baryta. This point I will discuss in another connection.
If we consider the subsequent treatment of the carrier for the
extraction of the precious metals, pure iron matte would generally
prove most convenient, its refining being quite within the range of
simple and inexpensive processes and plants. In fact I may say
that plain ferrous sulphide is as easily treated as any ordinary
sulphureted gold or silver ore, and for all practical purposes may
be regarded as a simple ore. For its beneficiation we have a choice
of several methods: 1. Re-smelting, raw or roasted, with lead
ores; 2. Lixiviation with chemical solutions; 3. Amalgamation
with quicksilver in pans or barrels. More complex products
require, as a rule, more complicated and difficult treatment.
Such extractive processes, whatever be their nature, are almost
invariably preceded by calcination of the mattes an operation
which is made much more difficult by their complexity. I have
indicated in the accompanying table the refining methods which
are made use of in the several cases cited. Obviously the choice
depends upon the surrounding conditions. If, for example, we
have the use of an amalgamating mill close by our furnace, our
endeavor will be to adapt that process to our wants. The succes-
sive lixiviation of the several valuable metals by means of chemical
solutions is practiced to a great extent, and affords peculiar advan-
tages toward the attainment of pure end products. Various
methods whereby the valuable metals are sought to be extracted
from the molten matte or speiss have been proposed, and some
have been adopted with great success. The most important of
these is the Manhes process of bessemerizing a method which
is of vast and increasing importance in copper metallurgy, and is
being rapidly extended to other metals.
17. TREATMENT OF MOLTEN MATTES. Davies successfully de-
silverizes melted arsenide mattes (Engineering and Mining Journal
(?) 1888) by means of melted lead added to a bath of the matte,
kept in ebullition by means of an air blast applied as in the Manhes
process. Probert proposes the use either of lead or litharge, the
latter of which is decomposed by the materials of the bath, while
the mixing, which appears to be essential to these processes,
is effected in Probert's by the ascending bubbles of carbon dioxide
from lime carbonate in the lining of the containing vessel. That
these methods are imperfect, extracting only a moderate percen-
26 MATTE SMELTING.
tage of the gold and silver values, is not particularly prejudicial,
inasmuch as provision for returning the material to the furnace
always exists. Heretofore the matte has been allowed to cool and
solidify before being returned to the smelting furnace; but the
writer has proposed its return while still molten, whereby its
sensible heat is utilized and other important advantages gained.
This process, which is applicable more particularly to the pyritic
furnace, will be adverted to again in the proper connection.
It would seem that the Davies and Probert processes, which have
proved useful in the treatment of arsenide mattes containing gold
and silver, have not been practically applied to the treatment of
sulphide mattes, although there would not appear to be any
particular reason why they should not prove equally as advan-
tageous therein. It is the opinion of those who have studied them
that they will be found applicable to such mattes, in which case
their sphere of usefulness would be much increased. On the other
hand, the Manhds process, which has effected such wonderful
results in the domain of copper extraction, has not within the
writer's knowledge been practically applied in the decomposition
of the arsenide mattes, which alone are the objects of the two other
processes. However, the arsenides are broken up by the bessemer-
izing blast with the greatest facility, and their oxidation and con-
centration is, as far as the writer's experimental trials show, one of
the easiest operations that confront the metallurgist.
The most interesting of the arsenide mattes are those containing
cobalt and nickel, metals which have a strong affinity for arsenio
an affinity which is taken advantage of sometimes in the benefici-
ation of their ores when these metals are sought in the presence of
substances which exercise an opposing influence. It has been
found advisable under some circumstances to make such an addition
of arsenic-bearing materials to cobalt or nickel ore as serves to
bring about the formation of nickel or cobalt arsenide, while other
heavy metals in the mixture separate therefrom as sulphides. In
this manner it is possible to effect a useful separation of the two,
even from very complex and difficult combinations. The nickel
and cobalt arsenides are still very impure, and comparatively
troublesome to deal with, requiring a prolonged succession of
operations to obtain the metals in reguline form. The metallurgy
of nickel has undergone great improvements within late years, con-
sequent upon the increased demand for that metal. Lately the
German system of matting has been applied to its extraction from
2 fl a
fill
02 SI < CX,
27
28 MATTE SMELTING.
the roasted copper-nickel-irou sulphides of Slid bury, where the
product of smelting is copper-nickel matte, whose average com-
position is given in the table. As for the principles of the art as
carried on at Sudbury there is nothing novel; but grand results
are reached through the skillful application of old and well-known
means. Much of the success arises undoubtedly from the extraor-
dinarily rapid driving of the blast furnaces, which smelt twice
the average amount to be expected from their size.
18. COINCIDENCES OF SMELTING METHODS. Owing to the
usual presence of sulphur in the mixture fused in lead blast
furnaces, a quantity of matte is the almost invariable accompani-
ment of the operation, it being produced along with the metallic
lead, in proportions depending upon the amount of sulphur
present. Should the percentage of sulphur be increased, the
matte-fall is also increased, until eventually the lead quite fails of
reduction and enters the matte, as do the gold and silver, when
present in the charge. Instead of lead smelting, the operation
has now become matting of the German system, which can be
and sometimes is carried on in furnaces similar to or even identical
with the prevailing type of lead blast furnace. Note that the
operation of lead smelting as carried on in the West is really a
mixture or combination of the two methods, which therein over-
lap each other. In smelting a charge suitable for lead smelting
except as containing sulphur enough to convert the heavy metals
into sulphides, we transform lead smelting into matting. And
conversely, by abstracting from a lead- bearing matting charge the
sulphur, we bring about ihe necessary conditions for the produc-
tion of metallic lead, and in so far the result is lead smelting.
The same furnace and accessory apparatus answer in both cases.
The production of metallic lead marks the one, that of matte the
other process.
19. CONVENTIONAL IDEAS. In these hypothetical cases, where
the two methods approach so closely, neither has any decided
advantages over the other. Matting a lead furnace charge plus
sulphur is easily done, but the utility of the operation may be but
slight. It is not matte smelting in its newest developments, nor
are any of the more valuable features of the art exhibited. It is
only when we get away from lead smelting, discarding its mixtures,
its slags, and to a large extent its apparatus, that we begin to
realize the extent and variety of application and the suitability in
diverse circumstances that characterize matte smelting. It is for
THE CARRIER. 29
this reason if for no other, that the application of the methods of
lead smelting to the art have not been found to succeed, and why
metallurgists of that school have not been and are not likely to
be successful in their experimenting.
Speaking from the experience gathered in several years of ex-
periment and research, I must say that it appears to me there is
no possibility of successful matte smelting when following the
lines laid down by the lead smelters. In fact it is only when we
leave the beaten track and strike out upon a road of our own that
we put ourselves in the way of successful achievement; and
furthermore it appears at present that the most noteworthy
successes have been and are destined to be reached by going in
many respects contrary to tradition and to ordinary practice.
There are very few occasions, and I think none, where a charge
suited for the lead furnace can be more profitably matted. The
great and manifold advantages of matting do not appear at such
times, but principally when there is stress in procuring lead or
fluxes or particular descriptions of fuel. Several instances are on
record where results deemed satisfactory have been achieved by
smelters who have run down charges in the lead furnace, inten-
tionally producing matte instead of lead bullion: but it is difficult
to see in any such accounts, however complacently told, the in-
dication of a proof that any advantages were gained, and there
must have been some lost. Clearly there is no object in making
matte when we can with more profit make bullion.
Certain smelting men, identified perhaps with lead extraction,
and very likely impressed with the perfection to which that art
has attained of late, have endeavored to extend the principles and
practice thus acquired to matting gold and silver ores. Their
success and the results of their work can be summed up by saying
that they appear to have achieved a gratifying measure of success
on very easy lines of effort, smelting, for example, a great deal of
old lead slags along with a little ore, and getting the gold and
silver in the form of matte. Such results, satisfactory as they may
be from a business point of view, throw little light upon the im-
portant questions of ore treatment, and only seem to confirm the
position of those who maintain the erroneous yet not uncommon
view that matting is inferior and subsidiary to lead smelting.
There are those whose position in the world of metallurgy should
forbid it, still perpetuating the error of thus subordinating mat-
ting, for which they patronizingly predict a career of usefulness,
30 MATTE SMELTING.
limited probably, in connection with the other branch of smelting.
But matte smelting stands alone. It is not connected necessarily
either in principles or in uses with copper or lead smelting or any
other branch of metal production. The field of its application is
vastly wider than theirs, and in its adaptability to diverse condi-
tions no other branch of metallurgy can ever be expected to rival it.
20. RELATIONS WITH LEAD SMELTING. Returning from this
digression to the subject in hand, it occurs to me to say, that if
matting a lead-smelting charge, plus sulphur be an easy thing, it
does not follow that lead-smelting a lead-bearing matting charge
minus sulphur is always an easy, an economical, or even a possible
thing. For not only may we have present such metals as copper,
nickel, and cobalt, which it is desirable to recover, but our ores may
be of so acid a composition that the loss of lead by scorification as
silicate, and by volatilization on account of the high temperatures
necessary to form acid slags, would make lead smelting ineffective
at least. We are consequently debarred from the use of lead
smelting, first, in the frequent cases where valuable metals other
than lead, silver, and gold are to be won; second, where sulphur
is a constituent; and, third, where the resulting slag would contain
more than 38 per cent., or thereabouts, of silica. Casually read,
my " second " might be excepted to by those familiar with the
character of the ore treated by lead smelters; but it should be
borne in mind "that lead blast furnaces are engaged, as a rule, in
making matte as well as lead bullion, and are equally as well cal-
culated for the one as .for the other. The extraction of the lead
by that method entails the almost equally perfect saving of the
sulphur, with the production olmatte, which requires additional
processes for its, reduction. These processes have become so
recognizedly a part of the duty of lead plants that the term lead
smelting now signifies the production and reduction of mattes as
fully as 'the production of lead bullion. Blast-furnace mattes,
whether produced alone (German system) or in conjunction with
lead bullion (lead smelting), follow frequently enough the same
course of reduction, namely: oxidizing roastings alternated with
re smelting with lead-bearing substances, producing an alloy of
lead with gold and silver (bullion), and a concentrated matte con-
taining copper, fin perhaps cobalt and nickel, with small quanti-
ties of the precious metals. The presence of sulphur, therefore,
which makes the theoretical difference of the processes, entails in
THE CAKRIER. 31
each case the requirement of the decomposition of the resulting
matte.
Since the. inception of the Austin process, and incited by its
success, many ideas of novelty and importance have been evolved
by those working on parallel lines of inquiry, inventions are
multiplying, and research, experiment, and practice go hand in
hand. The subject presents itself in a much broadened aspect. No
longer from the narrow standpoint of the "process man" can we
embrace the unbounded prospect that lies before us. No longer is
it tolerable to regard pyritic smelting as the exclusive domain of a
single great virtuoso, but rather as the property of those who can
master and add to it.
KELATION8 OP PROCESSES.
PYRITIC SMELTING.
I
Gradual Reduction Processes. Austin Older Process
j (Hot Blast).
Cold Blast. Hot Blast.
DEFINITIONS.
Gradual Reduction System. The application of oxidizing cur-
rents of hot or cold air to ore mixtures fed in the ordinary way
(layer feeding). Examples: Bartlett Works,* Canyon City, Colo-
rado; Porphyrite Works, Mineral, Idaho; Bi-Metallic Works,
Leadville, Colorado.
Austin Older Process. The application of oxidizing currents
of hot air to unmixed ores. Example : Toston, Montana.
21. RELATIVE PROPORTIONS OF CHARGE AND PRODUCT. Be-
fore considering the relative weights of material charged and matte
or bullion produced in furnace practice, it will be useful to con-
template the proportion of valuable metals in the material which
it is proposed to treat. In the accompanying table will be found,
under the appropriate heads, some information on this point. We
notice that the proportion of the metals to be saved varies widely
in different cases. For example, the copper in the concentrates at
Butte forms about one- fifth of the charge of the reverberatories.
The lead and silver in the customary charge at Tacoma aggregate
* Mr. Bartlett's efforts have been directed mainly to the treatment of mixed
ores of zinc, lead, and copper, with silver and gold, recovering zinc-lead pigment
and copper-gold-silver matte. For description see the Engineering and Min-
ing Journal, Vol. LVL, pp. 3, 366, 594.
3% MATTE SMELTING.
one-eighth; the copper and silver at Mineral fr^- 7 one-fortieth to
one-sixty-fifth; the silver and gold, which made up the sole values
at Toston, together constituted but one twenty-two-hundredth
part of the mass of the charge. Further inspection of the
data will reveal the like interesting facts concerning the work at
other establishments. It is evident that the necessities of the case
when there are certain proportions of copper, nickel, lead or other
weighty substances to extract will govern the percentage of prod-
uct, which is therefore uncontrollable in so far. Again, having
supposedly to drench the slags with a vast proportion of matte
when we work only for gold and silver, furnishes a second instance
of the practical requirements of matting. And finally come those
necessities imposed on our work by the presence of significant
amounts of sulphur, arsenic and antimony, whose influence upon
the proportion of matte formed is uncontrollable in the lead-smelt-
ing and German systems of reduction, but are partially controllable
in the pyritic system, whose influence thereupon I will later describe.
22. PROPORTION OF VALUES. From- other columns of the
table may be derived the proportions of the valuable metals to the
whole weight of product. At Tacoma and all other lead smelters
the bullion product contains practically 100 per cent, of valuable
metals, or its whole weight. At Mineral it is from 15 to 41 per
cent.; at Butte and Anaconda about 50 per cent.; at Sudbury, 42
per cent.; at Toston, slightly over f nir-tenths per cent. The
purpose of this is to show indirectly what an overpowering propor-
tion of practically worthless iron, sulphur, antimony, etc., it has been
found necessary in many cases of matte-smelting to extract and
subsequently to still further reduce preparatory to the removal of
the valuable metals which we design to win. In these respects we
may look for improvements in matting practice in two directions.
First, in the diminution of the proportion of matte produced to
gold and silver or other valuable substances saved in the treatment
of appropriate ores; and second, in the possible utilization under
favorable circumstances of some of the accompanying elements
which are now deemed worthless or even prejudicial.
That important improvements will take place in the latter
regard there seems no reason to doubt, for, as indicated in the
introductory remarks, it seems that no insuperable obstacles
exist to prevent the direct manufacture of ' sulphuric acid from
the gases evolved in matting, especially, as will be pointed out,
in that form known as pyritic smelting. A great deal might be
THE CARRIER. 33
said at this time and in this connection concerning the utilization
of the several now valueless elements which enter the matte
in precious metal smelting, but as such remarks would be in
large measure anticipatory of practical results, I will at present
refrain.
23. POSSIBILITIES OF CONCENTRATION. Regarding the propor-
tion of matte necessary to bring down the gold and silver of such
charges as I have worked, I may say I have not obtained results of
a satisfactory definiteness, nor am I aware that the minimum
proportion is known to have been attained in any case. I have
used experimentally as small a proportion as two and a half per
cent, of matte, as reckoned on the charge, while the average in
my regular work has been five to seven per cent. I have also pro-
duced at times 20 per cent., or one-fifth of the weight of the
materials charged. It might reasonably be supposed that condi-
tions so diverse would give rise to somewhat varying degrees of
extraction of the values; but the experience gathered may be
summed up by saying that the savings were as high in one case as
in another, the like conditions prevailing as to temperature, and
especially as to the composition of the products. It seemed to me
when producing clean slags by the aid of a given proportion of
matte, that I could still get the same clean slags with a less
quantity of matte. To what extent it would be possible to reduce
the matte production and continue to do good work it is difficult
to say, although it would evidently depend on the chemical
character of the slag formed, and doubtless, within certain limits,
of that of the matte. A friend, in whom I have great confidence,
tells me that his rate of matte production is 5 per cent., and that
his slags are as well cleaned as with a higher ratio. The evidence,
therefore, is to the effect that a very great degree of concentration
is practicable; greater in fact than has been generally known,
but additional practice is necessary to set bounds thereto.
24. PRACTICAL ADVANTAGES. This very important feature,
which is not enough known or studied, constitutes one of the
greatest claims to usefulness of this branch of metallurgy, espe-
cially in its application to gold and silver extraction. It is obvious
that the remark is not applicable to the matter of the saving of
copper, lead or any other substance which forms a considerable
part of the weight of the ore. Scientific students of the art will
on reflection comprehend the full bearing and importance of the
principle, as a property of matting which makes it of the greatest
34 MATTE SMELTING.
utility in the treatment of gold and silver ores in regions particu-
larly remote, where the costs of transportation tell heavily as againsl
the production and shipment of weighty products, such, foi
example, as lead bullion.
25. CONDITIONS GOVERNING CONCENTRATION. When put-
ting forty tons of charge into one ton of matte, in one operation,
I had not necessarily reached the utmost limit of concentration:
on the contrary I think that even that high rate might undei
appropriate circumstances be profitably exceeded. But practical
difficulties intervene; the minute amount of matte produced may,
by faulty manipulation of the furnace, be stopped altogether; or,
on the other hand it may by other agencies be unduly increased.
The most delicate and skillful handling, far beyond anything
required or practiced in ordinary smelting, is essential to maintain
the regularity of the matte-fall at such minute proportions. Thus
the mechanical difficulties of smelting interfere to prevent the
full attainment of those great advantages which are found to flow
from the very highest concentration. On the whole, under ordinary
conditions, I do not regard it as advisable to seek a higher rate
than twenty-five into one, and this of course only when dealing
with gold and silver ores. I need hardly remark that copper
matting allows no such rate of concentration, the whole aspect of
the problem being different, nor need I enlarge upon the conditions
under which our lead smelting is carried on, as to the employment
of a percentage of lead which must not fall below eight or there-
abouts, but generally reaches twelve. I do not doubt that the fair-
minded metallurgist has already conceded those advantages which
advocates of the matting processes claim in this direction.*
There are no matting plants running in America, and probably
none in the world, under conditions which make such an extreme
degree of concentration advisable or necessary, and therefore we
cannot point to examples which would illustrate to the full the
advantages which flow from the very highest rates of concentration.
We can imagine, however, the not uncommon conditions under
which such high rates would possess the maximum of advantages,
and they are in many respects similar to those prevailing in the ex-
ample cited. The most stringent conditions, such, for example, as
those which prevail in many mining regions in Mexico, while in
* Compare Kerl, "Metallurgy of Silver " who asserts that the raw smelting
of silver ores should be accompanied by the production of from 30 to 50 per
cent, of matte, thus concentrating two to three into one.
THE CARRIER. 35
many respects unpropitious to smelting of any sort, may not be
fatal to matting when it is carried on with a view to this highest
concentration of product.
26. SPECIFIC GRAVITY OF MATTES. Upon this important
subject I will venture but few remarks, first referring the reader to
the appropriate text-books for information as to the specific grav-
ity of the simple substances which compose mattes. It would
seem that although the lightest sulphides which enter into a mix-
ture may not, as in the cases of calcium, zinc, and manganese
sulphides, exceed a specific gravity of 4 or thereabouts, the heavi-
est of the arsenides reach a greater weight than cast iron, and even
approach nearly to the gravity of copper, which is above 8.5.
Their specific gravities are such that we can arrange the various
compounds in three groups having well-marked differences iu
several respects, but differing mainly in gravity. The arrange-
ment is as follows :
Group 1. (Substances having a specific gravity not greater than
4.7.) The sulphides of zinc, molybdenum, calcium, and man-
ganese.
GroupS. (Specific gravity between 4.7 and 5.5.) The sul-
phides of barium, iron, cadmium, nickel, cobalt, and copper, and
the magnetic oxide of iron.
GroupS. (Specific gravities ranging from 6 to 9.) The sul
phides of silver, lead and bismuth; the arsenides and antimonides,
and the sulpharsenides and sulphantimonides of silver, copper,
bismuth, lead, iron, cobalt, and nickel, and metallic lead, iron,
and copper.
The intermixture of these compounds necessarily produces a
matte of intermediate specific gravity,orit may produce two or even
three substances of vary ing gravity, which separate in the hearth of
the furnace. I have prepared the annexed table (see p. 36) for the
purpose of showing graphically the influence of various elements
upon the specific gravity of mattes, and enabling the student to
deduce the relative density of any proposed product. I need hard-
ly remark that the matter is of great practical importance in its
bearing upon the separation of the matte from the refuse materials
in smelting, and will repay close study and attention, but the
results obtainable by use of the chart are only to be considered
approximative.
27. EXAMPLES. The commonest description of matte which is
produced by the lead smelters would probably be of about the fol-
36
MATTE SMELTING.
lowing composition: Lead, 15 per cent.; copper, 6 per cent.;
sulphur, 23 per cent., the remainder mostly iron, with small quan-
tities of zinc and arsenic, and minute amounts of a dozen or more
of subordinate elements. Experiment shows that the specific
gravity of such a matte is about 5.3. An increased proportion of
zinc lightens it very much, and increased iron lightens it some-
SPECIFIC GRAVITIES OF THE MATTE FORMERS.
As
Sb
Ca
Zn
Mo
Ni
Co
Cu
Bi
Pb
9
_8.6
8.0
.6.5
_3.5
3.0
QSULPHIDES B ARSENIDES AND ANTIMONIDES (@) SULPHARSENIDES
AND SULPHANTIMONIDEIT
what, but in a less degree. Increased copper, and especially lead,
add to the gravity; and obviously the substitution of arsenic or
antimony for the sulphur also renders it more dense. The heaviest
matte with which I have had practical experience is an antimonial
substance containing 25 per cent, of lead and 20 per cent, of
copper, and whose specific gravity was 8.07. Accompanying it
were small quantities of a still weightier matte having a gravity of
8.3, but the composition of which I did not ascertain.
THE SLAGS. 37
SECTION TWO.
THE SLAGS.
28. PHYSICAL CHARACTERISTICS OF SLAGS. Any sort of slag
that will melt at all may be used in one or the other department
of matte smelting, notwithstanding any peculiarities of its chem-
ical constitution; but we are compelled to attend none the less
closely to these peculiarities when we seek to do thorough or eco-
nomical work, and above all when we would rival the best per-
formances of the scientific lead smelter. Slags have been and are
being made in practice which contain as much as 65 per cent, of
silica; or 40 of lime; or 23 of alumina; and manifesting what
appear to be the most abnormal qualities. Some slags have the
color and texture of stoneware; others are black, and very heavy
and brittle; some slack and fall to pieces like lime; others with-
stand the heaviest blows of the sledge-hammer. Some are thick
with unmelted fragments of quartz, like raisins in a pudding
such cannot be handled in the blast furnace at all; while others of
more favorable composition fuse easily and drive fast. Some run
beautifully, keeping the furnace in good condition, while others
necessitate blowing out almost daily. Some contain nearly a fourth
part of alumina, a difficult constituent; while others are made up
largely of baryta and magnesia, which lead smelters abhor. Yet
all these slags, notwithstanding their peculiarities, serve their
especial purpose -capitally, being made under conditions which
render them both economical and profitable. In discussing the
peculiarities of slags, it is common to characterize the use of some
kinds as "good practice," or "not good practice." We hear a
a great many such opinions advanced with no foundation other
than some preconceived idea of what is fitting in metallurgy.
Apparently, however, there is no real test of good or bad practice
in metallurgy except the financial test. It is good practice when
we make the most money; it is bad when we lose. Any particular
operation is good practice so far as it pays only. In this view the
examples of slags presented herewith are representative of the
38 MATTE SMELTING.
"best practice," being made under conditions which rendered
them practically the best that could be made.
29. KANGE OF PRACTICAL SLAGS. Compare the diverse ex-
amples given in the Table of Work Done with those slags made in
our best lead-smelting works, to gain a commensurate idea of the
vastly wider scope and applicability of the matting processes. From
these examples, the best attested which it is possible to procure, it
will be seen what striking diversity is permissible in the composi-
tion of slags in this type of smelting. Thus we may have basic
or sub-silicates; singulo-silicates, sesqni-silicates, bi-silicates and
tri- or even quadri-silicates, when the atomicity of the bases will
allow. And none of these, I may add, are incompatible with
economical work. Experience shows that we may have in
different cases:
Silica from 25 to 70 per cent.
Alumina " to 23
Ferrous oxide " to 70 "
Manganous oxide " to (?) "
Lime " to 40
Magnesia " to 12 "
Zinc " Oto22
Baryta " to 52
30. COMPARISONS WITH LEAD SLAGS. We have therefore the
largest liberty in choosing the slag for our projected operations,
compared with which the lead smelter finds himself confined
within very narrow limits. It lias been laid down by one of the
foremost lead smelters of the day that in order to do the best work
the lead slags should not contain less of silica than 28 per cent.,
nor more than 37 per cent. Lime, he insists, should not go below
10 per cent., while the highest percentage of this base in any
recognized slag-type is 28 per cent. They eschew magnesia en-
tirely whenever possible, although one of our foremost metallur-
gists uses it extensively in matting and says he likes it as a flux.*
Heavy spar, which has been hitherto a great bugbear to all blast
furnace managers, is found now to be a valuable flux, almost as
desirable as lime, excepting for its lower saturating power and greater
* Dr. Carpenter at his Deadwood works has been signally successful in
adapting the German system to the treatment of highly siliceous gold ores,
which he fluxes with magnesian limestone, producing very acid slags, whose
bases are alkaline earths a course of procedure to which this country affords
no parallel.
THE SLAGS. 39
specific gravity. It is very easily eliminated in the pyritic fur-
nace, where with proper management it can, as I believe, be
largely driven unchanged into the slag, mixing therewith, but
without decomposing. Under other conditions of temperature,
basicity of slag, etc., sulphuric tri-oxide is volatilized and the
baryta unites with silica as in the reverberatory process. Still
another result, but as a rule a less useful one, is brought about in
the German process and in lead smelting, where heavy spar being
reduced to sulphide of barium, by double decomposition with
metallic bases, adds largely to the matte fall.*
31. THE MORE ACID SLAGS PREFERABLE. As a consequence
of our ability to handle the greater variety of slags, it follows that
on the whole less flux is required than is found necessary in lead
smelting, and, speaking in general, less slag is produced. We can
matte a given quantity of average ores by the aid of less fluxes
than we can lead-smelt them. The production of a less quantity
of sl;ig entails less expense for handling, as well as less loss from
en trained f matte particles in the slag, and less heat carried away
by it. That it is possible by skillful composition of charge, and
watchful care in running, to make slags, especially acid ones, freer
from the precious metals than are known in lead smelting, we have
the word of more than one able metallurgist familiar with the
practice of both methods. I believe that certain probably excep-
tional slags have been made in the matting furnace which are
cleaner than have been reported in lead smelting, running as low
as 30 cents per ton, or even less. But in general it is only safe to
claim that under similar conditions the lead and matte slags will
pratically assay the same in gold and silver. In other words, the
conclusion is that there is no practical difference in the extractive
effects of lead bullion and matte. The recognized types of lead
slags may be quite as easily formed in the matting furnace, and
where the nature of the ore mixture seemed to demand they might
be profitably made. To make special efforts to achieve particular
types of lead slag, however, would be impolitic under most cir-
* Kerl (Metallhuttenkunde) describes the intentional formation of matte by
the reduction of heavy spar in connection with iron ores. See also Mineral
Resources, 1874, p. 417.
f I take the liberty of using this word, taken in the sense in which it is used
by mechanical engineers, because there seems to be a certain analogy between
water carried by and included in steam and matte carried by and included in
the slag.
40 MATTE SMELTING.
cumstances, and a matter of doubtful utility in all. It should be
remembered that the recovery of metallic lead, which is the most
exacting requirement in lead smelting, plays no part in matting,
so that because of this dissimilarity of conditions the writer has
discarded lead slags in the matting furnace, finding in the more
acid ones, unknown to the lead smelter, a more promising subject
of experiment and research.
32. SPECIFIC GRAVITY OF SLAGS. Those questions of specific
gravity which so profoundly affect the subject of matte-production
enter not less prominently into that of slags. In the effort to
maintain such differences in the densities of the concurrent pro-
ducts as will entail an adequate separation, we may take measures
to increase the gravity of the matte or diminish that of the slag.
The substances which enter into the composition of slags are prin-
cipally the following, having a specific gravity (fused specimens,
mainly artificial), approximately of:
The singulo-silicates of iron, manganese, and zinc, about 4.
The bi-silicates of iron, manganese, and zinc, about 3.5.
The basic silicates of alumina, from 3.2 to 3.4.
The acid silicates of alumina, from 3 to 3.2.
The silicates of magnesia, from 3 to 3.3.
The silicate? of lime, from 2.6 to 3.
The alkaline silicates, about 2.5.
Uncombined silica, 2.6.
The bi-silicate of baryta, 4.4.
The silicate of lead, 7.
Ferrous sulphide, 4.8.
Calcium sulphide, 4.
Magnetic oxide of iron, 5.
Sulphate of baryta, 4.5.
As regards these silicates the rule which governs specific gravity
is that it suffers a decrease with the increase of silica. Or in other
words the more acid the slag the lower its density, the same bases
remaining. According to this the tri-silicates should be still
lighter than those mentioned a supposition which is borne out by
facts. Slags can be and very likely have been formed having a
gravity of less than 3, and possibly as low as 2.6, as mentioned by
Balling: but materials for such a formation are, and must con-
tinue, very scarce and impracticable. The highly siliceous slags
of Swansea (see table) have a density of 3.21, and rank among the
lightest which are made in the regular way of smelting.
PYRITIC SMELTItfGo 41
SECTION THREE.
PYRITIC SMELTING.
33. THE CHOICE OF FUEL. What is mainly sought in smelt-
ing is cheap heat. Those who contemplate matting operations,
looking about for a source of heat, are quick to recognize the ad-
vantage which they have over the lead smelters in virtue of the very
wide liberty of choice of fuel ; for while the latter are usually
restricted to the use of the blast furnace, with coke or charcoal
(and coal experimentally) as fuel, both blast and reverberatory
furnaces are employed in matting, fired with wood, coal, charcoal,
coke, or gas, according to circumstances. We have furthermore
an important and very interesting source of heat from which the
lead smelter is necessarily debarred, in that in pyritic smelting
we are able to burn certain ores themselves as fuel. It is in its
application to the treatment of highly sulphureted compounds that
matte smelting has received its latest and widest development.
Such substances as pyrite, chalcopyrite, pyrrhotite, arsenopyrite,
etc., which in lead smelting are invariably roasted before fusion
and in the ordinary form of matting frequently are, have been
discovered to possess the most valuable properties as fuels, and
through the efforts of American metallurgists have been brought
into practical use as such in smelting. This process is a new one,
having been in practical existence for but a very few jears,
although it is probable enough that its germs may have existed for
a much longer period. I have no wish to forestall whatever may
be said as to the history of the idea of pyritic smelting, but I am
glad to be first to assert its standing as a distinct art, to define it,
and also to place the credit of its inauguration as a distinctive
process where it justly belongs. There can be no doubt that the
honor of first putting pyritic smelting on a practically useful
basis belongs to Mr. W. L. Austin, whose experiments at Toston,
Montana, first demonstrated the utility of the hot blast in this
line of ore reduction, and eventually paved the way to the success-
ful introduction of the pyritic principle as an important feature
42 MATTE SMELTING.
of metallurgy. This language would appear to be entirely justifi-
able in view of the fact that plants on the pyritic system are now
(June, 1894) in successful operation in direct competition with
older methods of beneficiation, and that the process is being
rapidly introduced in other localities. The pyritic system has
thus attained along with an excellent measure of success a deserved
and considerable celebrity which, naturally enough, lacks a good
deal in discrimination, because attaching to methods by no means
understood even by metallurgists, among whom not half a dozen
in the United States have ever had an opportunity of becoming
practically familiar with any one of the various pyritic methods.
It is even imagined by many that only one pyritic method exists,
and that it covers the whole field of pyritic smelting ; but
I hope to correct this misapprehension, the tendency of which is
injurious to the progress of metallurgy, and show that abundance
of unoccupied space is left for the efforts of other inventive
spirits.
34. DEFINITIONS AND DISTINCTIONS. In order to remove the
uncertainties and misapprehensions connected with the term
pyritic smelting, it should be restricted to that department of
blast-furnace matting wherein a portion of the heat required for
reduction and fusion comes from the oxidation of apart of the ore.
Or, more briefly, wherein ore is burned for fuel. The term pyritic
is not specially descriptive of any matting process; but since it has
become familiar in metallurgy it may well be retained if properly
restricted in its application. That it has not previously been so
restricted every one who has been familiar with recent technical
literature will admit.
35. PRIME DISTINCTION OF PYRITIC SMELTING. It is, then,
the prime distinction of pyritic smelting that ore itself is burned
therein in the furnace. It has long been known that certain of
the metallic sulphides which accompany or contain so large a pro-
portion of our mineral wealth will, under favorable conditions of
exposure to the atmosphere, absorb oxygen spontaneously, pro-
ducing an elevation of temperature, and even incandescence, and
become imperfectly oxidized. This tendency is taken advantage
of in the operation of roasting these ores in furnaces, wherein the
end sought is the same, but the process is hastened by applying a
rapid air current, supplemented by heat, which is the familiar
operation of roasting or calcining. The same tendency to absorb
oxygen is the foundation of pyritic smelting, wherein the operation
PYRITIC SMELTING. 43
is brought about in a more rapid way, with intenser heats and
more powerful air currents, the net results aimed at being the
roasting of a part of the sulphides, plus the smelting of the roasted
material along with the unroasted part and the remaining gangue
constituents of the charge all in one operation. This very sum-
mary and effective treatment has two results bearing directly upon
its metallurgical economy, namely: it obviates in so far the
necessity for a preliminary roasting, and it reduces to an important
extent the proportion of costly fuel required in the smelting.*
36. BASAL PYRITIC REACTIONS. It will be useful at this point
to call attention to some of the reactions which are presumed to
go on inside a blast furnace. We are accustomed to the frequent
use of the terms "oxidizing atmosphere" and " reducing atmos-
phere," both of which have important places in technical and
scientific literature. Both these, in spite of their wide use, are
indefinite, if not misleading, when applied to the conditions pre-
vailing inside smelting furnaces. No furnace atmosphere can be
unqualifiedly reducing or oxidizing in its effects. For example:
in an iron blast furnace the atmosphere is oxidizing toward the
fuel (carbon), and reducing toward the iron ores present. In the
like manner, in the copper blast furnace, it is oxidizing toward the
fuel and reducing toward the copper and iron oxides. In the lead
furnace, while oxidizing the fuel, it tedns to reduce (using the
word in its chemical sense) all the heavy metallic oxides present,
and also the other oxidized compounds, including those of sulphur.
In the German system of matting we find similar conditions pre-
vailing, the oxidizing effects extending only to the fuel, while all
the higher oxides are reduced, some suffering conversion into sul-
phides, the remainder into silicates. But in the pyritic system
the oxidizing effects predominate. Not only is the carbonaceous
fuel burned, but the excess of oxygen beyond what is required for
that purpose enters into combination with the various metals and
metalloidsof the charge, according to the play of chemical affinity,
producing oxides, some of which enter the slag, while others, more
volatile, pass out with the smoke and spent gases. The blast,
which in the iron and lead furnaces produced only a combustion
incomplete and imperfect, of the coke and charcoal, in the pyritic
* The percentage of sulphur eliminated in various operations is approximately
as follows : In roasting preparatory to lead and matte smelting, about 85 per
cent.; in re verberatory smelting of ordinary charges, 13 per cent. (Vivian); in
pyritic smelting, from 65 to 85 per cent.
44 MATTE SMELTING.
furnace tends to burn more thoroughly the fuel, and more or less
completely the oxidizable constituents of the ore also. It may be
said that the complement of the oxidation is the sulphidation; and
the complement of the scorification of the heavy metals is the
formation of matte. Sulphur in the pyritic furnace performs
functions entirely similar to those of carbon in the high iron fur-
nace. Carbon abstracts oxygen from oxides; by uniting with iron
it forms cast-iron, a fusible substance; by uniting with oxygen it
generates heat. Sulphur abstracts oxygen from oxides; by uniting
with the heavy metals it forms matte, a fusible compound; by uniting
with oxygen it generates heat. In these respects arsenic and anti-
mony also act in a manner not dissimilar to sulphur, by their oxi-
dation generating heat and carrying out the other reactions on
which the process depends.
37. DEDUCTIONS FROM THE FOREGOING PRINCIPLES. From
the foregoing considerations it appears that the efficiency of
pyritic over plain matting (German system) in any given case will
be in proportion to the relative amount of oxidizable constituents
in the ore charge; or, more strictly speaking, it will be proportion-
ate to the absolute amount of heat units made available through
the decomposition of the sulphides. What the available heat from
this source will be in any particular case depends on the extent to
which oxidation is carried and upon the heat equivalents of the
various sulphides, etc. The latter may be computed from the
heat equivalents of their elementary constituents, which are known.
The problem in this aspect is identical with that referred to as
" the heat balance of the blast furnace" a subject which has
been so profoundly treated by the iron smelters in its applica-
cation to their own pursuits.
38. MEANING OF THE TERMS OXIDATION, BOASTING, ETC.
We must not lose sight of the fact that it is to the oxidation of the
heavy metals that may be in combination with the sulphur, the
arsenic and the antimony that we are indebted for a large propor-
tion of the heat evolved in pyritic smelting a fact liable to be
overlooked in the general view. Pyritic smelting burns more than
the sulphur; and roasting is more than desulphurizing. Mr.
Austin even attempts to show that the heat evolved by the burning
of the iron is better for his purpose than that produced by the
burning of the sulphur, the latter largely becoming latent in gas-
eous products, while that produced by the formation of ferrous
PYRITIC SMELTING. 45
oxide remains therein during the critical period of the scorification
of that substance.
As it is probable that no charge is ever smelted in a matting fur-
nace without being indebted for apart of the heat to the oxidation
of some sulphur or iron, however little this amount may be, it fol-
lows that the systems of blast-furnace matting are in this respect only
different in the degree to which the oxidation is carried. In the
German system this is so inconsiderable that it may be disregarded,
considering the function of the sulphur, etc., to be only to form
matte, while that of the blast is merely to oxidize carbon, whereby
the necessary heat is evolved. It would appear to some that as a
necessary corollary to this proposition the only difference between
the two rests upon the amounts of air blown in; and that to mutu-
ally transform the German and the pyritic systems we need only
vary the power of our blowing engines. And I may add that it is
upon this assumption that a good many experimental trials of the
latter system have been carried on. That the assumption is errone-
ous and that failure inevitably followed the experiments are
equally certain.*
39. EXTENT TO WHICH OXIDATION MAY BE CARRIED. As a
necessary result of the fact that the atmosphere in the pyritic
furnace is so far oxidizing as to burn sulphur and iron, it follows
that it will also burn all the combustible compounds of carbon and
hydrogen which may be present, including carbonic oxide, the
hydro-carbons, and also, presumably, free hydrogen. These sub-
stances, let it be noticed, are among the usual products of the
imperfect combustion which takes place in iron and other furnaces,
where a reducing action has to be maintained. The ordinary
course of blast-furnace smelting gives rise to gaseous products
which are susceptible of being still further oxidized with the
generation of much heat. The pyritic system, producing fully
oxidized gases, lays claim to a more complete utilization of the
* The principal beat equivalents with which we have to deal are : Coke and
charcoal, about 8,000 units ; olefiant gas, 12,000 ; marsh gas, 13,000 ; carbonic
oxide, 2.400 ; sulphur, 2,300 ; iron, 1,576 ; zinc, 1,300. The assumption that
the calorific efficiencies of different substances in the blastfurnace are in direct
proportion to their heat equivalents is not apparently borne out by observation.
For example, the calorific efficiency of metallic iron should be about one fifth
that of carbon ; but experience shows that it is much higher. We have, how-
ever, to consider the latent and specific heats of the resulting compounds, and
also the extent of the oxidation effected. On the smelting efficiency of metallic
iron, see Raymond, Mineral Resources, 1870, p. 443.
46 MATTE SMELTING.
fuei There passes from an iron blast furnace a great deal of
inflammable gas; the lead, copper, and German matting furnaces
eao 1 1 give off gases in considerable quantities which contain un-
oxidizt'd constituents possessing a high heating power; but the
gaseous products of the pyritic furnace, like those of the rever-
beratory, should be so oxidized as to be incapable of further heat-
proilnciug reactions. In this connection I may mention that
sulphur, which is volatilized so largely, appears to me to be con-
verted partly into sulphuric acid (sulphur trioxide) instead of wholly
into sulphurous anhydride. I base my opinion on the qualitative
tests of the condensed matters, and upon the corrosive properties
<f the fumes rather than upon any profound chemical investigation
of the subject. Inconclusive as my observations are, I find them
much at variance with those of Mr. Austin, who speaks of the
sublimation of elemental sulphur as an accompaniment of his
work. I should be very much surprised to be shown the existence
of unburned sulphur or any other oxidizable substance in the fumes
of my pyritic furnaces, the phenomenon being entirely at variance
with the conditions. I am so convinced of the copious formation
of sulphuric acid in the pyritic furnace, at least under conditions
familiar to me, that I somewhat expect to see the phenomenon
made use of in the direct manufacture of that most valuable
re-agent; for no great difficulties would appear to stand in the
way of condensing the volatilized acid in cooling chambers or in
towers, and its subsequent purification from the solid and liquid
impurities which would naturally accompany it.*
40. FUEL ECONOMY OF SMELTING PROCESSES. Regarding the
relative economy of fuel by the various processes under discussion,
it is evidently fair to assume a priori that that one which results
in a complete combustion of the fuel will, other things being equal,
surpass in economy those in which the combustion is incomplete.
This assumption appears to be borne out by the experience had
in pyritic smelting, where the fuel percentage is much diminished,
irrespective even of the sulphides which may be burned.
41. DEDUCTIONS. Upon the consideration that combustible
matters generally are burned, including the volatile combustible
products of the distillation of coal and wood, it follows that other
* It may be objected that sulphuric anhydride formed in the shaft would be
broken up in volatilizing into dioxide, and oxygen. This may be true in regard
to the major part; but that a considerable evolution of the stronger gas take*
place is certain.
PYKITIC SMELTING. 47
fuels than coke and charcoal may be used in this form of smelting.
Even the most volatile gases may probably be made use of, such,
for example, as ordinary illuminating gas, natural gas, etc. Follow-
ing this train of reasoning I was led to experiment with wood,
which eventually I used, not as a mere makeshift, but regularly
and successfully in practical work. The innovation evoked the
criticisms of certain metallurgical acquaintances, who, not under-
standing the drift of my work, and perhaps imagining that their
own experience and knowledge covered the whole field, were dis-
posed to sneer at what they considered a pitiable makeshift. The
advantages in its use were threefold: first, obviating the waste by
inferior oxidation, which advantage is inherent in pyritic smelting;
second, the employment of a fuel cheaper per unit of calorific
power; third, a useful mechanical effect in rendering the charge
less dense and thereby facilitating the passage of the blast. In
order not to mislead the reader I will add that I have not been
able to replace more than half the coke with wood.* My experi-
ments in the use of coal in the pyritic furnace have been but
slight and inconclusive, nor am I aware of others of a more
thorough nature; but from analogy there should be important
economies in the use of proper kinds of coal, and no technical
difficulties therein. My conclusion, however, was that a portion of
the fuel should be of a strong dense kind, not burning too freely,
but passing well down into the tuyere region, so as to burn there
and produce the hearth temperature needed to perform the work
of melting. The use of too light and fragile a fuel, which is con-
sumed high up in the furnace, will in every case give rise to a
cooling of the hearth and the formation of incrustations which
defeat the intentions of the smelter. Then is required the applica-
tion of greater heat to rectify the disturbance. We may get this
by increasing the percentage of fuel, more particularly of coke.
But the addition of more coke, while it increases the hearth
temperature, decreases the amount of oxygen available for combi-
nation with the sulphides of the charge. Consequently more matte
is formed, and with equal steps iron is withdrawn from the slag.
*See Erdmann's Journal. XVII., p. 471, for description of the practice at
Niscbui Tagilsk, where raw copper ores are smelted, and roasted matte re-
smelted, by the use of wood in the blast furnace. Two hundred and fifty cubic
feet are required to about 4 tons of mixture. This instance, unknown to the
writer until of late, clearly antedates his practice, while the objects are different
in part.
48 MATTE SMELTING.
We are receding then from pyritic work and approaching plain
matting, wherein higher hearth temperature is obtained at the ex-
pense of low concentration of product. We have a better resource
against the emergency in the hot-air blast, which has been applied
to this form of smelting with great success by Mr. Austin, whose
older process depends mainly on the increased oxidizing effects
of hot instead of cold air.
42. CONSIDERATIONS REGARDING HEATED BLASTS. Hot blast
means less blast. For the heated air brings with it the heat which
would otherwise have to be generated by burning fuel at the
expense of a part of the oxygen of the blast; and the loss of this
oxygen diminishes the oxidizing power of the resulting atmosphere,
contaminated as it is with the products of combustion. From the
higher oxidizing power of the hot blast follow the use of higher
sulphur contents of the charge; increased hearth temperature; lower
position of the zone of fusion; increased silica contents of the slag,
and hence les: flux. A diminution of the oxidizable contents of the
charge brings about a diminution of the efficiency of the hot-blast
processes. For when the sulphides become scarce, the lack has to
oe made up by the addition of carbon, and we reach a point where
the process becomes virtually plain matting. Three kinds of fuel
are used at once in the Austin Older Process: coal, wood or oil to
heat the blast, where the fuel cannot be burned so economically as
within the shaft; sulphides, whose fuel efficiency costs nothing
and which are better burned than not; and coke, to make up a
customary, or perhaps only occasional deficiency of heat in the
shaft. Th' heal; from these three sources combined is sufficient to
carry on the re luction and fusion of a charge considerably more
refractory, it is reasonably claimed, than can be handled in the
ordinary blastfurnace. This, f course, would be a very important
advantage in itself. The fu ior heating the blast is usually cheap,
and there is an additional but d i:Vl:ul advantage claimed in the
unusual capacity of tho furnace. Under ,'dinary working con-
ditions this process has proved ffective and ;heap. Under more
favorable conditions it might and probably wouir prove one of the
cheapest in existence.
43. TEMPERATURE OF BLAST. The foregoing considerations
relate mainly to those cases of pyritic smelting wherein the air for
the blast is heated by means of fuel burned in blast-heating con-
trivances outside of the furnace. The apparatus made use of in
such cases is similar in design and effect to the hot-blast stoves
PTRITIC SMELTING. 49
used in connection with iron-smelting plants, but differing there-
from in the character of the fuel used. For whereas, in iron pro-
duction in blast furnaces, the gases evolved from the smelting
contain a large proportion of combustible ingredients and are made
use of as the fuel for the air-heating, we are in the pyritic processes
debarred from this source of heat in consequence of the character
of the products of combustion, which contain no substances
susceptible of further oxidation. The practice has, therefore, been
to employ ordinary fuels for this purpose, which are consumed upon
grates beneath the cast-iron pipes of the blast stove. This is the
course of procedure followed thus far by the pyritic plants on the
Austin system. We have, however, a valuable and costless source
of heat in the waste slags which flow constantly or intermittently
from the furnace, which is entirely sufficient, if properly utilized,
to heat the blast; and several plans have been proposed to this end,
which will be adverted to in the proper connection.
I need hardly add that the methods of heating the blast are in
no case distinctive of any process of pyritic smelting; and I may
say further that the application of the hot blast to this form of
smelting has not been patented to any person in the United States,
and doubtless cannot be so patented. Metallurgists, therefore, are
not debarred from the employment of the heated blast as a means
of pyritic smelting, the only patented features of any process being
solely those novel mechanical principles which distinguish the
different processes.
Having provided ourselves with a costless source of heat for the
blast, the limiting conditions of the discussion in part disappear,
and the question of the availability of the hot blast becomes in the
majority of instances a question of the cost of installing the
apparatus. There are cases, however, where the hot blast from its
intenser oxidizing power might leave no undecomposed sulphides
for the matte; and here the cold blast would prove clearly the
more serviceable. Accordingly, assuming that the blasts of low
temperature comport best with quite small proportions of sulphides,
it follows equally from other considerations that high sulphide con-
tent admits and even demands hotter blasts. Experience may yet
establish the rule that the temperature of the blast should vary
directly with the content of sulphides.
44. MECHANISM OF THE AUSTIN OLDER PROCESS. As shown
in the published drawings of the Patent Office the mechanism of
the Austin Older Process presents some interesting peculiarities.
50 MATTE SMELTING.
It consists principally of a shaft furnace of normal outward appear-
ance, provided with a central tube inside the shaft, extending
downward from the feed floor perhaps three-fourths of the distance
to the tuyere level, and ending in the vicinity of the smelting
zone, affording a means by which the pyritous portion of the ore
may be fed directly into the smelting zone without having to
undergo the usual course of downward travel along with the re-
mainder of the charge, and consequently without undergoing the
usual preheating which is an incident of the descent of the mate-
rials in other furnaces. The object in thus delivering the pyritous
material is twofold. First, to avoid the incipient fusion and con-
sequent sticking to the walls which would ensue were the charge
to be fed as usual; and second, to prevent the partial oxidation
which would also ensue with deterioration of the fuel value of the
pyritous material. The annular space between the inner wall
proper of the stack and the tube is, or may be utilized to feed the
infusible portion of the charge, should it be required. It is to be
understood that the smoke and gases pass up and out of the fur-
nace by way of this annular space, there being no particular
movement of air or gas within the central tube, although for con-
venience the function of the tube and annular space may be re-
versed and the gases allowed to pass out by way of the tube, while
the fusible constituents of the charge are fed into the furnace by
way of the annular space. Hot air is used for the blast, the heat-
ing apparatus consisting of a hot-blast iron-pipe stove or equiva-
lent device. These modifications and additions to the customary
apparatus and process make the plant more costly beyond a doubt,
though it is denied by the patentee that it is more costly per unit of
smelting capacity. What I would moi e particularly call the
reader's attention to is the fact that the Austin Older Process
operates at the smelting zone on cold masses of base-metal sul-
phides, virtually burning them as lumps of coal are burned in the
blacksmith's forge, or in the boilers of a man-of-war under forced
draft. Under these circumstances a very high temperature can,
it is said, be attained, though this might appear to some incon-
sistent with the feeding of cold material directly into the zone of
fusion. It is consequently claimed for the process that difficultly
fusible slags may be successfully produced, which could not be
handled in a iy furnace blown with cold air. The advantages of
being able to make bi-silicate and still more acid slags have been
touched upon in another connection. Where an almost absolutely
PYRITIC SMELTING. 51
clean slag is required it is undoubtedly a certain class of bi-silicates
which most nearly meets the requirements, and in those numerous
cases where silica preponderates there is clearly the greatest advan-
tage in having at command a furnace and process capable of deal-
ing with the acid slags resulting.
45. CONDITIONS OF WORKING. If the reader will reflect
upon the necessary condition of things in the smelting zone of
this furnace he will be struck with its novelty. First he will
perceive good reason why the smelting space cannot rise, produc-
ing fire-tops, insrnuch as there is no fuel in the upper part to take
fire, the only combustible materials of any sort being preserved
from chemical action by being pent up in the interior tube away
from the heat and the oxygen, until the time comes for their dis-
charge into the fiery zone immediately below. They reach the
active zone while as yet unchanged; and there is the best of
reasons why a gradual oxidation of the combustible would not
answer in this system of smelting. The sulphides might indeed
be hot when at the moment of feeding into the smelting space with
good advantage in one respect; but this would presuppose a
partial decomposition, with escape of sulphur and oxidation of
metals and consequent loss of calorific power, which Mr. Austin
seeks to avoid. Again, we need no hint from the inventor to
enable us to discover that an ore consisting of sulphides dissemi-
nated in a stony gangne would be ill suited for this style of furnace.
For the requisite rapidity of combustion could not take place with
an ore whose combustible particles are hidden and protected by
non-conducting material of this nature. Nor need we seek further
for the reason why fine-grained substances are not successfully
treated. We are entitled to assume that only solid, coherent
masses of sulphides or arsenides, undiluted by gangue, especially
gangue of an intractable, stony sort, are calculated to work with
the best success in the Austin furnace, and that fine ores and dis-
seminated sulphides, no matter even if the latter are chemically
unexceptionable, will not serve the requirements of the process.
It would also seem that a reasonably fine comminution of the
remaining part of the charge, that portion in fact which comes
down the annular ring and through which the waste gases pass,
heating it and preparing it for combining with the other compo-
nents, might be a very good precaution, considering how short the
time for complete reduction and combination is, and the highly
siliceous character of the ore which it is an especial purpose of
5x5 MATTE SMELTING.
this furnace to slag. We may venture another assumption,
namely, that the success of the operation depends very largely
upon the separation of the components of the charge into two
parts, the one of combustible matter, of sulphides without gangue,
the other of gangue without sulphides; and that as these become
mixed, or are naturally mixed, the operation is less successful.
As the inventor has published little about the theoretical principles
which underlie his ingenious process, we are entitled to these
assumptions and to as full and free a criticism as we may wish to
pass. We are not entitled, however, to assume that, as charges of
a certain description are likely to give the best results, noth-
ing can be done with less favorable ores. On the contrary
mixtures of quite a decidedly unfavorable appearance have
been treated, hitherto impossible of profitable utilization, among
others the sulphides of a Leadville mine, which are described as
" a kind of blue mud." Mineralogically this description is doubt-
less inexact; but witness the proficiency of American metallurgists,
in whose hands blue mud becomes at once a valuable ore and an
esteemed fuel !
46. LATER MODIFICATIONS. It is to be observed that the re-
sults achieved of late by Mr. Austin have not been in line with his
earlier efforts. He has recently discarded the inner feeding tube,
and in lieu thereof resorts to feeding the fusible materials into the
center of the stack, while the infusible substances are placed
around the periphery so as to separate the sulphides from the
walls and so prevent them from sticking on when they reach a state
of partial fusion. The supposition evidently is that the particles
maintain their relative position during the downward passage,
mixing together finally after arriving in the zone of fusion. One
may be skeptical as to the value of the expedient for preventing
the materials from attaching themselves to the walls, even when a
considerable portion of the charge is composed of infusible matters;
but we may disregard the query as unimportant. It is more per-
tinent to inquire what is to be done when the charge is largely or
entirely made up of sulphides. For in such not unprecedented
cases there would be nothing to prevent the fusible particles from
coming in direct contact with the walls, when the distinctive
features of the Austin process would disappear and the operation
would become identical with those which I describe as the Gradual
Reduction processes. I have accordingly classified Mr. Austin's
newer process with them. Having discarded the central tube, the
PYRITIC SMELTING.
53
only novelty lies in the patented method of feeding as before de-
scribed, which is not sufficient to constitute a different system of
smelting, and indeed does not vary practically from other methods
now known and used.
47. MODES OF FEEDING FURNACES. I advocate and practice
the method of feeding by layers, as in lead and copper smelting,
while I attach little importance to exactness in placing the materi-
als so long as they are in position to become mingled during the
fusion. Mr. Austin adopts such a method of feeding as will in his
opinion prevent the commingling of the materials and the contact
of the sulphides with the walls. Should incrustations form, which
are inevitable under most circumstances, I find no difficulty in re-
moving them by mechanical means, the furnaces which I employ
being of slight depth and easily accessible from the feed floor
through all their interior.
It is apparent that no great differences exist between methods of
smelting described, whence it follows that there can be no great
differences in the effects produced. By discarding the feeding
tube the Austin new method loses wholly the peculiarity of feeding
cold unchanged sulphides directly into the zone of fusion, substi-
tuting therefor the gradual heating and oxidizing effects common
to other methods, and loses likewise in part the other peculiarity
of retaining the sulphides in a central column.
48. COMPARATIVE TABULATION OF EFFECTS.
AUSTIN OLDER PROCESS.
Characterized by
Sudden oxidation.
Contraction of smelting zone.
Concentration of beating effects.
Rapid transference of heat.
Evolution of sulphur and sulphur-
ous anhydride. (?)
Favors hard blowing and rapid
driving.
GRADUAL REDUCTION PROCESSES.
Characterized by
Gradual oxidation.
Expansion of smelting zone.
Diffusion of heating effects.
Slower transference of heat.
Evolution of sulphurous and sul-
phuric anhydrides.
Favor lighter blast and slower
running.
49. PYRITIC SMELTING OF SIMPLE ORES. In its simplest
form pyritic smelting consists in charging a mixture of quartz and
pyrite, and oxidizing so much of the latter that the resulting oxide
of iron will suffice to take up the quartz, forming a slag, while the
unoxidized pyrite is reduced by it to ferrous sulphide by the vola-
tilization of one equivalent of its sulphur, and separates as matte,
along with the gold and silver. It was said to have been in this
VATTE SMELT1NO.
t&at the Austin process was first woiked ont at Toston,
Montana, where it was carried on subsequently in a commercial
way. We are informed by the inventor that the charge which
best brings out its advantages contains about twenty-five per cent,
of sulphur and in the neighborhood of fifty per cent, of siliceous
vein matter, which furnishes silica enough to make a bi-silicate
slag, which he regards as possessing peculiar advantages. To deal
with a mixture of this description a hot blast is justly considered
indispensable. For while we could, no doubt, increase our fuel
ratio and the height of our furnace to enable us to handle a bi-
silicate of iron slag, under these conditions the slag would surpass
the bi-silicates in acidity in fact, we would get little or no base
formed, the oxidation of sulphides ceasing, and hence practically
no slag could be formed at all. There has also been recommended a
mixture of even greater acidity, to wit: equal parts of quartz and iron
pyrites. Now, I imagine that this charge (which would give rise
to a quadri-silicate of iron, if all the iron were to become oxidized
in the operation) would prove impracticable even with the very hot
blast whicli the inventor prescribes.
Recapitulating slightly, we can distinguish two different uses of
the hot blast: first, for its sensible heating effect; and second, for
its chemical effect aside from heating. The pyritic smelter's use of it
is primarily for its chemical effect in burning the sulphides, which
it performs efficiently. The sum total of the different heating effects
goes to fuse and slag some of the solid constituents and to matte
the others. This is pyritic smelting in its extremest development,
to carry out which to the fullest extent requires a charge composed
of coarse pieces of raw pyrites and quartz, the sulphur contents
preferably reaching twenty-five percent., or over. A highly heated
blast must be employed. Under such circumstances it has been
found possible, writes Mr. Austin, to run continuously for a time
without using any ordinary fuel in the furnace shaft. Under less
favorable, and as I understand it, ordinary circumstances, the
fusion cannot be effected without the regular addition of fuel
say two or three per cent, of coke to the charge.*
50. RELATION OF BLAST TEMPERATURES TO FUEL. As we
* The writer would not like to be quoted as affirming or denying the allega-
tions of those who have exploited the Austin processes, but he is abundantly
satisfied that their claims to work at times without the usef any carbonaceous
fuel in the furnace are well founded; as no doubt exists that the blast, if
PYRITIC SMELTING. 55
decrease the amount of sulphides in the mixture, a greater and
greater addition of fuel becomes necessary, until we reach a point
where the sulphides become too small in quantity to have much
effect as fuel, and indeed have to be preserved unoxidized to form
matte. In this exigency the hot blast ceases to perform the
particular chemical function allotted to it and becomes useful for its
direct heating power alone. But as fuel expended in heating the
blast outside the furnace can never in the nature of things be so
economically expended as in heating it inside, it becomes evident
that the hot blast may be no longer economical, unless indeed the
fuel used in heating it in the hot-blast stove be very considerably
cheaper per unit of calorific power than that which we are accus-
tomed to use in the shaft. I do not present this last consideration
as of great weight since, as previously indicated, I have found by
experiment that some of even the cheapest and crudest fuels may
under proper conditions be profitably employed in the pyritic
furnace, taking the place, at least to some extent, of the more
costly artificial fuels in common use. While, therefore, no one can
deny the utility in appropriate circumstances of the hot blast, it is
not to be indiscriminately recommended, in view of the character
of much of the ores, which makes its application superfluous.
51. ADAPTATION OF PROCESSES. Mr. Austin's idea of the proper
functions of pyritic smelting might be esteemed somewhat radical
by those familiar with existing conditions in the mining regions,
for his intent has apparently been to devise a means of treating
ores or ore mixtures carrying a very high proportion of sulphur,
much higher in fact than are found to occur as a general rule.
The experience is that base metal ores of so high a tenor in sulphur
are rather the exception in our Western mining districts, and that
the bulk of the so-called base or refractory ores of gold, silver, and
copper will not exceed 15 per cent, sulphur, and possibly will not
average 10 per cent. It is probable that a metallurgical plan
which is adjusted to the treatment of such moderately pyritous
material will prove more generally advantageous than any attempts
to meet extraordinary conditions by extraordinary means.
heated enough, can take the place of such, fuel and produce all the effects
desired ; but that it is feasible to treat the average run of base metal sulphides
without fuel is more than doubtful. In fact the language now used by Mr.
Austin in reference to his invention would indicate that he has abandoned his
former claims in this regard and now makes no pretense to smelt without fuel.
56 MATTE SMELTING.
52. PREVAILING CHARACTER OF SULPHIDE ORES. It is
seldom that we find very large quantities of pure sulphides of any
sort; pure pyrite, pure chalcopyrite and pure blende rarely exist in
nature uncontaminated by other substances, but are found inter-
mingled in the most heterogeneous way with each other and with
the other sulphides, with arsenides and with the various gangue
matters. The prevailing characters of base metal ores which seek
beneficiation.are mixtures, most commonly silver-but occasionally
gold-bearing, with or without copper, which exists often in small,
but not unfrequently in important proportions, and which is saved
with the same facility, of course, as the precious metals. The very
important subject of gangue merits attention. We find a large
proportion on the average of stony matter, perhaps not less than
two- thirds, in those ores under consideration, and we classify those
of a still lower content in base metals as concentrating ores, as being
best adapted to water treatment. The gangue is prevailingly
quartz, but in more favored localities is calcite, spathic iron
(seldom), heavy spar (less seldom), and not unfrequently is some
felspathic rock, usually somewhat decomposed. Here is indeed a
formidable list of substances, difficult enough formerly to deserve
the opprobrious epithets rebellious, refractory, base, etc., which our
metallurgical predecessors with good reason showered upon them.
But while difficult and intractable enough when taken singly, or
when dealt with by inefficient means, their difficulties vanish when
assailed by the overpowering forces of the pyritic furnace, which
conquer and dispel every opposing element and combination. The
rebellious qualities, or what were deemed such, of the ore are the
foundation of pyritic smelting, which utilizes hitherto objection-
able elements in its essential reactions, making use of the very
characteristics which make all other processes inoperative or highly
expensive, and rendering those substances which by their nature
are the most difficult of beneficiation by other methods, the very
cheapest and best adapted to the pyritic treatment. It is, or will
be, the rule that those ores which are the most intractable to other
processes are the easiest to treat by pyritic smelting.
53. USES OF THE COLD BLAST. Cold blast methods of
pyritic smelting, which I put forward not as rivals of, nor substi-
tutes for the hot-blast methods, furnish a rational and efficient
means of dealing with those classes of base metal ores which da
not contain the highest percentages either of sulphur or silica, but
which are so rich in the former that they are not susceptible of
PYRITIC SMELTING. 57
direct treatment by other processes. An ore mixture containing
10 per cent, of sulphur, combined mainly with iron, might in the
presence of sufficient metallic bases be expected to produce,
roughly speaking, about 30 per cent, of matte, if run down in a
furnace with strong reducing action. This would be the custom-
ary result of the treatment of such a charge by the German
system. The 10 per cent, mixture, however, may be fused in a
furnace in accordance with the principles of what I have called
the cold-blast pyritic system, and the amount of matte reduced to
10, 8, or even a less percentage, the work being attended with the
oxidation of a corresponding proportion of metals and the volatil-
ization of sulphur. Thus, while the German system, applied to
certain pyritic ores, eifects a concentration of three into one, or
thereabouts, the cold-blast method of pyritic work puts ten into
one, or twelve into one a result that necessitates burning off three-
fourths or more of the sulphur and the oxidation of nearly half
the iron. That such results can be regularly and systematically
effected without the agencies of the hot blast, but simply by changes
in furnace construction and manipulation may seem incredible
at first glance, but practical experience amply confirms the asser-
tion. I was first led to experiment in this direction by noticing
the variations in the amount of matte produced by furnaces at
different times, which variations I traced to the influence of the
incrustations formed in the hearth and upon the walls. The
amount of matte produced is to that extent an index of the
chemical changes, and hence of the condition of the atmosphere
within the furnace. Recognizing the relation between the form
of the furnace shaft and the oxidizing or reducing effect, I was
enabled to apply those modifications and improvements in process
and apparatus which constitute what I have called, I hope
justifiably, a praticable cold-blast pyritic process.
54. PRINCIPLES UNDERLYING COLD BLAST SMELTING. This
form of smelting depends upon the circulation of free oxygen
through the charge, making it necessarry to so apply the blast that
such circulation is assured. For this purpose I admit the air into
the blast furnace in a particular manner and in various quantities,
as may be required for the" particular kind of ore in hand, the
amount of sulphur being the principal determining factor. Hav-
ing this active circulation of air, especially in the upper part of
the charge, it becomes possible to effect a striking degree of oxida-
tion and consequently of concentration. The best results that I
58 MATTE SMELTING.
have thus far secured in practice are when treating charges con-
taining a medium amount of sulphur, say from 8 to 15 per cent.,
although there is no necessary reason why still higher percentages
should not be successfully dealt with. While eminently successful
on ore of this medium description, the lack of higher sulphureted
kinds has thus far prevented the demonstration of what the cold-
blast apparatus can do with those excessively base compounds which
are preferred for the hot-blast methods. A further improvement
recently projected and not yet put in practice, will, I am confident,
furnish a powerful means of reduction, suitable to either the hot
or cold-blast processes.* In the most successful work the slag was
of a fusible sort, the bases being largely protoxides of iron and
manganese, for average analyses of which see the accompanying
table. These slags ran freely, the charge requiring 7 to 9 per
cent, of fuel for complete reduction. As shown, the slag contained
on the average one and a half ounces of silver per ton not as clean
as many that can be made, but the most economical possible under
the conditions. Whereas Mr. Austin finds it possible to produce
bi-silicate slags whose base is almost exclusively iron, I found that
slightly acid silicates of the same base (and manganese), or
sesqui-silicates of mixed bases best satisfied the conditions, except-
ing probably as to the freedom from gold and silver, in which
respect information is somewhat lacking. By employing these
means we may, without the help of the heated blast, free the
smelting mixture from much the larger part of the sulphur, and
oxidize an equivalent proportion of the bases; but this must be
done under conditions which, so far as I can see, preclude the em-
ployment of more than moderately refractory slags. It becomes
necessary to maintain such a composition that the slags are not
greatly less fusible than the ordinary lead slags. On the other
hand we can treat fusible basic mixtures with great facility.
* This is the writer's invention of concentration of matte by returning it
while molten to the blast furnace. It is adapted to blasts of any temperature.
Poured upon tha charge in the shallow furnace it comes immediately into contact
with active gases which decompose it partially, with evolution of sulphur
gases, and production of oxides. This is mainly practicable where the charge
is shallow, and hot nearly to the surface. The furnace atmosphere must
necessarily be oxidizing in its effects. Besides the concentration of the matte,
there are secondary results of value, first in supplying a portion of matte to
desilverize the slags in the event of the momentary cessation of matte forma-
tion ; and second, a useful effect upon the furnace hearth whenever obstruc-
tions tend to collect.
PYRITIC SMELTING. 59
55. DEMONSTRATION OF PRINCIPLES. I will endeavor to explain
the principle which governs the case. The function of the
boshes in a furnace is well understood. They are to concentrate
the heat and the chemical action within a small space, whereby
intensity of combustion and reduction result. The air from the
tuyeres is brought into contact with the fuel and materials of the
charge, whereby the oxygen is entirely consumed, with great in-
tensity of heat but with imperfect combustion of the fuel. A
matting furnace having a contracted zone of fusion volatilizes
little or no sulphur, but reduces oxides powerfully and makes much
matte; and, I may add, is able to produce very hot slag. We
may infer from this that to remove the boshes so as to enlarge the
zone of fusion horizontally would have the effect of diminishing
the reduction of oxides, and of volatilizing sulphur, and conse-
quently diminishing the production of matte. This is, in fact,
what does take place; for the oxygen of the air, instead of being
forced into contact with white-hot carbon and thus consumed,
finds spaces in the enlarged zone of chemical activity through
which it can escape upward, whereby it is enabled to combine
with sulphur and other components of the charge for which it is
avid, and so carry on those reactions which are the distinction of
the pyritic process. But notice that the enlargement of the zone
has also the effect of reducing temperature, bringing in the evil
of cooler slag, and consequently debarring us from the employ-
ment of difficult mixtures.
56. FURTHER DEMONSTRATION OF PRINCIPLES. The most
rapid and efficient reduction of ore in a blast furnace takes place
after the smelting zone has been so narrowed by the formation of
incrustations upon the wall and about the tuyeres (noses) that the
air, first warmed by passing through the slag which has collected
about the inlets, is forced into contact with the white-hot fuel,
when the latter burns with powerful intensity of action, creating
a great heat within a comparatively small space. In a round
furnace smelting a hundredweight of materials in a single minute
the melting may all be performed within a space the size of a flour
barrel. Within a certain limit a narrowing of the active space
is accompanied by a rise of the temperature; and a horizontal in-
crease of the smelting area is followed by a decrease of th tem-
perature. But such an increase or decrease of the horizontal sec-
tion of the active smelting space is also accompanied by a corre-
sponding though inverse change in the production of matte. Now,
60 MATTE SMELTING.
matte production we know varies inversely as the oxidizing action
of the furnace upon the sulphur and other matte-forming sub-
stances in the charge. We may also note in this connection the
dependent consequences of the addition to, and withdrawal from
the slag of the bases which result from the varying oxidizing effects
described. I noticed that a certain matting furnace, when freshly
blown in and therefore perfectly free from crusts, yielded very
little matte; while after the accumulation of crusts began the pro-
portion of matte rose rapidly, in strict accord with the contraction
of the smelting area, until when the latter had been reduced to
about one-third of the space it at first occupied, the output of matte
had grown fourfold at least. The temperature of the slag, which
at first was lower than favored the requirements of good work, rose
also, while it increased perceptibly in acidity, owing to the ab-
straction of iron oxide. It follows from these considerations that
oxidation can be furthered in blast furnaces by simply retaining
the normal smelting area, by preventing or removing the wall
incrustations which have so strong a tendency to form.
57. FURNACE CONSTRUCTION AND MANAGEMENT. In design-
ing furnaces for cold-blast pyritic work the metallurgist will of
course eschew the bosh, and with it the downward tapering circu-
lar stack of the Arizona copper furnace type, as being possessed
of qualities opposed to those desired. For this form he will sub-
stitute a prismatic shaft whose width is such as to allow the blast
to penetrate all parts; whose length is proportioned to the quantity
of work desired; and whose depth, being governed by the fact
that fusible slags are to be made, need be but slight. The sides
are vertical plane surfaces upon which obstructions do not readily
collect, or having collected, may be easily removed by means of
tools worked from the feed floor above. These simple means
serve perfectly the purpose intended, and the principal re-
quirement of this kind of smelting, namely, the preservation of
the original interior form of the furnace, is accomplished, whereby
the work is kept under control, the production of matte remains
normal, and the results of the operation, thus rendered certain,
respond in all respects to anticipation. To the experienced metal-
lurgist I need hardly remark that a process whose results cannot
be closely foreseen as we pursue it step by step is not apt to prove
of any great value in the arts. I may say of the pyritic processes
that their value and availability depend upon the skill of
the attendants and the watchfulness of the persons in charge to
PYKITIC SMELTING. 61
a higher degree than any others with which I am acquainted. I
cannot commend those processes as being easy to conduct. Chemical
analysis, which gives so perfect a control over the lead and iron
smelting, is a far less reliable guide in pyritic smelting, and is far
from enabling us to predict the results of contemplated operations.
In the absence of actual experience (of which nothing can take
the place) calculations based on analysis are in a measure untrust-
worthy. At the same time I would not be understood as propos-
ing to dispense with chemical work, which is from my point of
view indispensable. To bring out the full advantages of the pro-
cesses, there is required an extensive experience supplemented by
watchful care and the assistance of chemical analysis. Without
these failure, or at least a long and costly term of experimentation,
is inevitable. Considering the small number of metallurgists who
have thus far had actual experience in pyritic work it will be safe
to prophesy occasional failures, much dissatisfation, and loss of
time before a sure foundation for success is reached.
58. THE FURNACE BLOWER. Returning again to the subject
of furnace construction, I have to remark that to attain efficiency
in pyritic smelting the requirements of the blowing apparatus
have to be modified to correspond with the furnace. The
depth of the charge being but slight there is no need of the power-
ful apparatus to which we are accustomed in other branches of
smelting. We need, however, a very great volume of air; and
this, at the low pressure necessary, is best supplied by the
Sturtevant blower, or some similar centrifugal fan. With much
fine ore it might be advisable to use a very large rotary blower in-
stead. Throughout the designer will have borne in mind espe-
cially the proportion of oxidizable materials in the proposed mix-
ture and provided such means for supplying the air for oxidation
as will be necessary in the given case. Should the sulphur exceed
the proportion supposed to be manageable by ordinary means he
has the choice of several methods for its removal. Mr. Bartlett
and myself have practiced the introduction of an auxiliary blast at
a suitable level, to be determined by, and adjusted in accordance
with the condition of the interior of the stack. One may, probably,
also very expeditiously concentrate the matte by returning it while
still liquid to the charge, it being then in the best condition for
burning in the blast from the tuyeres. This conception, previ-
ously adverted to, seems to possess great advantages from its sim-
62 MATTE SMELTING.
plicity and probable effectiveness. It, however, has not got
beyond the incipient stage as yet.
59. COMPARATIVE RATE OF SMELTING. It has been held by
some that the smelting capacity of pyritic furnaces is greater than
that of ordinary furnaces of equal size of hearth. The writer
must dissent from such views, which are contrary to experience
and reason. It may be that furnaces intended to work on the
pyritic plan have been driven at a faster rate than other furnaces
have been on the same description of charge. But this degree of
speed is inconsistent with the attainment of those concentration
effects which are our aim. In fact the work could hardly be
called pyritic smelting at all, but would fall into the category of
the German system, wherein no oxidation of the ore is expected.
Time is an important element of pyritic work, and there exists a
direct relation between the oxidizing effects produced and the
duration of exposure of the ore to the air currents, and on the
other hand an inverse relation of both to the amount of matte
formed. All the experience yet had, so far as I am aware, con-
firms this view, and I have no hesitation in saying that pyritic
smelting (excepting possibly the Austin older process, of which I
do not here speak) is necessarily a slower method than the German
system of smelting.
This fact, which to some might appear to injure the efficacy of
the system, is not in reality a vital nor even an important objec-
tion. Granted that it be slower even in the proportion of one to
two, it is only necessary then to double the hearth area in order to
restore the smelting capacity. Nothing else about the works need
be changed; blower, power plant, working force, all remain at
the normal.
60. HEARTH ACTIVITY. We must remember, however, that as
there is a limit beyond which a furnace cannot be driven, there is
also one below which it cannot fall without injury to the smelting
process. The diminished rate of smelting which favors oxidation
and high concentration ultimately reaches a point where no smelt-
ing at all can take place and the process comes to an end. The
minimum amount which can be treated in a blast furnace in a given
length of time, still keeping the slag and hearth hot enough to
work acceptably, is an interesting question which we cannot afford
to leave undiscussed. We can compare the smelting powers of
furnaces as to their total capacity in units of charge, or, better and
more scientifically, as to their capacity in units per square foot of
PYRITIC SMELTING. 63
tuyere section. We may designate this intensity per square foot
as hearth activity; and I obtain its value in each particular case by
dividing the consumption in tons of all solid materials which go
into the furnace in twenty-four hours by the tuyere area of the
furnace. Thus I find the hearth activity of the Sudbury furnaces
to be about 7; that of a matting furnace at Mansfeld, 5; at Min-
eral, 3 to 4; Orford, 2f; Bisbee, Arizona (copper), 7; while the
hearth activity of the Edgar Thomson furnace "I," making iron,
reached 14. The lowest feasible rate is probably about one ton per
foot, of which the old European stacks furnish several examples.
No modern furnace either here or abroad runs so slowly, nor can
good clean smelting be done at such a rate. Probably the needs
of the pyritic system would be best subserved by a rate of driving
of from two to four tons per foot, according to the condition of
the charge, etc. Since it is an indispensable requirement in this
style of work to drive slowly, which has a tendency to cool the
hearth, I have suggested as a means of keeping up the temperature
of that part of the furnace the return of the molten matte accord-
ing to my heretofore described invention. By this means the very
slowest rate of smelting could probably be achieved whenever
deemed desirable, and the hearth kept sufficiently hot for the pur-
pose by the repeated passage of the matte.
61. PRODUCTION OF PYRITIC EFFECTS. When we use an air
blast of large volume and low pressure, especially if it be cold, the
conditions are favorable for the formation of slag crusts about the
tuyeres, and a partial filling up of the hearth with the hardened
masses, which are perforated with holes through which the air
currents pass upward. In such a case the tuyeres usually show no
light. The conditions are now favorable for pyritic work, as long
as the fuel is kept at a minimum. They are also good for chilling
up, which has to be guarded against, not as being a serious calam-
ity, however, which it is not, for properly constructed furnaces are
easily and quickly relieved of a chilled charge. The ease with
which the crucible can be removed, the charge dropped, incrusta-
tions knocked off, a hot spare crucible placed in position, some
fuel given, followed by a few hundredweight of slag and matte,
and then the ordinary charge, and operations resumed by letting
on the wind, is such that it becomes cheaper sometimes to blow
out than to bar down, although the barring is proportionally
easy.
62. SECONDARY EFFECTS. The large volume of cold air at low
64 MATTE SMELTING.
pressure produces secondary effects which have an important bear-
ing on furnace construction. A good proportion of the blast fails
to enter the charge to any distance, but finds its way to the surface
by following up the walls where the charge lies loosest, and pro-
ducing a cooling effect there which prevents fusion, while the
excess of oxygen serves to effectually roast a proportion of the ore.
In the next inward layer the air is less abundant, a higher heat
prevails, and smelting takes place combined with oxidation of the
combustibles of the charge. Further inward the tendency to com-
bustion becomes still less, owing to the scarcity of air, and the
roasting and smelting effects both cease, the former first. Were
the furnace wide enough, a core of inert matter, unacted upon by
the blast, would exist in the center, and to avoid that result such
furnaces are made narrow. It will be evident that the most
thorough oxidation will take place in contact with the walls,
or a little way in. Therefore if we desire the highest concentra
tion we must increase the extent of the wall area by lengthening
the furnace, while we diminish the breadth at the tuyeres to get
rid o-f the inert space. This is the principle of peripheral extent,
which cuts an important figure in pyritic work. Mr. Bartlett has
shown his appreciation of its value by designing a furnace having
an interior length of sixteen feet, with a breadth at the tuyeres
of two.
It also follows from what I have said about the effects of the
copious air blast, that water jackets are not necessary in all cases
to protect the furnace wall. The cooling influences of the blast
causing the deposition of slag incrustations on the surfaces most
exposed to danger, and protecting the walls above by cooling below
the fusing point the ore which rests against them, there is no
reason for the employment of other than brickwork constructions.
It is my firm conviction that water jackets are used in many
situations where brick or stone work would answer better; and
that their use is a fashion which is carried to excess, in an age
when the properties and usefulness of fire-resisting materials are
so thoroughly understood.
63. THE CRUCIBLE AND THE FOREHEARTH. The forehearth,
which plays an important part in the German system of smelting,
is in some respects superfluous in pyritic work. In performing the
separation of matte from slag outside the furnace the thing aimed
at is to avoid the deposition of "sows" or " salamanders " of
metallic iron in the crucible. But as there is no tendeucv toward
PYRITIC SMELTING. 65
the precipitation of any metallic substance whatever in pyritic
work, we have reason to discard the forehearth and return to the
use of the interior crucible, which answers the purpose better in
most respects. We lose less heat by radiation, and the apparatus
is easier for the men to handle. It is conceded also that the separa-
tion is better, as it certainly should be, as it has the advantage of
a higher temperature. I have not been able by experiment to
satisfy myself that it really is better, however. I much prefer the
movable form of crucible, which admits of being changed about
with as much facility as the forehearth, whenever reason exists,
but as a rule it does not require it so often.
There should be a tap-hole each for slag ana matte, in the end
or side of the crucible, and the matte tap should be at least twelve,
and better fifteen inches below the slag tap-hole. With a less dis-
tance it is difficult to obtain pure material at each tapping, as the
vortex caused by the rapid flow of matte drags the overlying slag out
with it, even when abundance of matte remains in the crucible.
The aim at a well-conducted matting plant should be to make two
products: pure matte and pure slag; and the proper management
of the products as they issue from the furnace is a subject that
will repay hard study. The slipshod practices at some lead
smelters, and also, I am sorry to say, 'at some matte smelters,
where immense quantities of mixed slag and matte are undergoing
sorting, and unlimited amounts of foul slag are forever on their
way to be re-smelted, should have no place in modern practice.
"Sorting "and "cinder picking "are only necessary when the
furnace work is badly done, or when the plant is ill-arranged. The
re-treatment of slags can ordinarily be confined to that small pro-
portion which, by reason of its favorable action on the furnace, or
from its accidental richness in valuable metals, it becomes advisable
to re-smelt. But the wholesale re-smelting of slags in order to
recover mechanically mixed matte is a practice far behind the age.
64. BLASTS OF HIGHER TEMPERATURE. The effect of the
heated blast upon charges high in sulphureted constituents is
remarkable and quite beyond anticipation. Even air blasts only
warm to the touch produce effects so much more intense than
cold ones that the difference is almost unaccountable. It has long
been remarked that from the heat of summer to the cold of winter,
blast furnaces engaged, for example, on lead smelting, fall off
much in their duty per unit of fuel; and the difference in the py-
ritic furnace is much more striking still. In fact, the possible
66 MATTE SMELTING.
difference of a hundred degrees Fahrenheit in blast temperature is
of great significance in this kind of smelting, where the object ia
to secure the greatest possible production of heat at the lowest
attainable level in the furnace, and with the least contamination
of the internal atmosphere by inert gases. Not only the temper-
ature but the purity of the air blown in exercises an important in-
fluence. The active agent being the oxygen of the air, it is
evident that deterioration in this regard will be followed by in-
jurious consequences, and those inventors who have proposed to
use the partially deoxidized and exhausted air which has once'
supported combustion will here find themselves much at fault.
There is exhibited a very inadequate understanding of the means
which are required and the changes which are wrought in a smelting
furnace, when it is gravely proposed to heat the blast by means of
a jet of oil burning in the delivery pipe at the expense of the oxy-
gen of the air which is being blown; and equally so to attempt to
derive a hot blast by blowing in the exhausted and vitiated gases
from another furnace, worthless and ineffective as the expedient
must be.
Touching the increased oxidizing power of the heated blast, we
may discuss some statements taken from Kerl showing the effects,
relatively considered, of blasts in use at two foreign works where
the matting is of the old or German blast-furnace description,
(German system). Thus, at Mansfeld it was found that the
heated blast of highest temperature favored a more complete
oxidation of the carbon, producing in consequence a greater pro-
portion of carbonic acid and less carbonic oxide than the cold
blast. The gases from the cupolas of Reicheldorf, where a warm
but not hot blast was in use, contained about 25 per cent, of com-
bustible substances and a total calorific efficiency of 58 per cent,
was attained, while the blast of unheated air gave but 50 per cent.*
Such a result as the latter should have afforded every encourage-
ment to the inquiring metallurgist to proceed further on this line,
reducing the fuel ratio and increasing the blast temperature until
the experimental results had developed something of importance.
Pyritic smelting lay dormant in this ground, but Reicheldorf was
not destined to be the scene of its discovery.
65. METHODS OF HEATING THE BLAST. The obvious advan-
tages of the heated blast as applied to various forms of cupola
*Kerl, C. & R. translation, Copper, p. 197.
PYRITIC SMELTING. 67
smelting have led to many new suggestions for, and improvements
in its production. Several schemes have been devised for securing
a hot blast by intercepting the waste heat from the walls of the
furnace, the upper part of the stack, the crucible, or the fore-
hearth, as the case may be. Some of these are obviously inopera-
tive from complexity of parts; while others are so from the fact
that the heat radiated from the apparatus is too small in amount
to be practically useful, even if all of it were absorbed by the air
blast. The forehearth and crucible of a blast furnace may, and
often do radiate enough heat to make the bystanders uncomfortable;
but all of the heat so lost to the process is hardly enough to make
it worth while to take measures for its recovery. Again, it has
been proposed to subject air in pipes to the influence of the heat
contained in the melted materials in the forehearth, v/ith the hope
of thus providing a heated blast. But we must not forget that
the loss of heat by the mingled matte and slag would be fatal to a
proper separation of the two. We dare not abstract heat from the
forehearth, which in ninety-nine cases in a hundred is too cold
rather than too hot, notwithstanding all the nursing which we can
give it; nor from the crucible, which is hardly more likely to
afford the requisite supply of heat. This being the case, it has
seemed to me that the only available source lay in the slags after
their discharge from the furnace or forehearth into the pots, where
they are exposed to cooling by radiation. Here is a supply of
heat, which, could it be thoroughly utilized and recurned to the
furnace, would enable smelting to be carried on witnout any fuel
whatever other than the due proportion of combustible ore. My
device for heating the blast by means of the waste heat of the slag
consists in an arched heating chamber of considerable length built
between the furnace and the slag dump, and so located that the
pots as they are filled are enabled to pass longitudinally through
the chamber, losing their heat as they proceed. The chamber
contains in its lower part a railway track on which the slag cars
run, and in its upper an air main, both being parallel to the axis
of the chamber. This arrangement would be inoperative were it
not that it is divided into successive compartments by vertical
partitions so as to be heated to different degrees, that compartment
nearest the furnace being hottest, whereby the air in the main is
subjected to an increasing temperature and the slag is enabled
to cool effectually before it finally leaves the chamber. The rate
68 MATTE SMELTING.
of travel of the cars and the length of the chamber determine what
amount of heat is communicated to the air in the main.
66. COMPARISON OF THE HOT AND COLD BLASTS. Briefly
comparing the advantages and disadvantages of the hot and cold
blasts, I should say that there appear to be two situations wherein
the hot blast is indispensable in pyritic work. The first is when
the slag is of a difficultly fusible sort; the second when the
sulphur contents are very high. In either case the hot blast will
undoubtedly confer benefits far beyond the cost and complexity of
its installation. There are likewise two cases in which the cold
blast may perform its work best. The first of these is where the
sulphur contents are low, say not above 8 per cent, or where the
oxidizable constituents are so small in quantity that they have
mainly to be preserved nnburned to form matte. Second, in the
absence of experiments bearing directly upon the matter, I can
only suggest as something probable that the cold air blast will
admit of the saving of a larger proportion of lead than the heated
blast. I take it for granted that it is so, and that it is a matter of
some significance.
67. DIRECTION OF EXPERIMENT. It may be of interest to the
reader to learn under what conditions of pressure, temperature,
etc., the various successful forms of pyritic smelting were con-
ceived and worked out. Thus, Mr. Austin's former process was
carried on by the use of a very hot blast (perhaps 1,000 degrees
F.), of moderate or small volume, and rather high pressure. His
present tendency appears to be to lower temperature of blast and
the regular use of inside fuel. Mr. Bartlett, who formerly used a
nigh pressure and moderate volume of cold or slightly heated air,
nas, as evinced by his adoption of furnaces of great peripheral
area, increased the volume of blast. His practice has tended
10 the use of two rows of tuyeres a characteristic which has
evoked much criticism, but which is founded in reason and experi-
ence. Those who have witnessed the performances of such an
apparatus are amazed at its powers of oxidation. My own work
was principally done under these conditions: a cold blast of
moderate pressure (generally eight ounces) and large volume.
Enlarged experience and opportunities lead me to prefer high
temperature, large volume, and low pressure; although as to the
question of temperature in particular, it would have to be settled
by practical considerations quite outside of the desired furnace
effects. For example: an exalted temperature of bkst attained
PYRITIC SMELTING. 69
by the use of outside fuel, however advantageous its effects might
be, would very probably prove less economical than a more moderate
temperature produced by the waste heat of slag or by other cost-
less means.
68. LEAD IN THE PYRITIC FURNACE. We have seen that in
the German system and in lead smelting, the lead is saved, in the
first as a constituent of matte, in the second as metallic lead, in
consequence of the strong reducing action of the furnaces. I need
say no more upon the subject of lead in the pyritic furnace than
to remark upon the absence of those reducing agencies and to call
the reader's attention again to the presence of those conditions
which ensure the oxidation of so many substances. The conditions
are, as might a priori be foretold, adverse to the recovery of lead,
as that metal is scorified and driven into the slag, or even, under
certain circumstances, volatilized in an oxidized form, and this
in proportion to the relative oxidizing power of the apparatus and
blast. I would like to be thoroughly understood upon the latter
point. A very high degree of oxidation, assisted, for example,
by a blast of high temperature, produces from lead-bearing ores a
matte carrying but a small part of the contained metal. A blast
of lower temperature, involving the use of inside fuel, and conse-
quently producing a less intense oxidation, allows a higher percent-
age of lead to go into the matte. In general, the loss is owing to
the formation of oxide of lead, which necessarily becomes the
silicate, and mingles with the other silicates as slag. Mr. Bartlett,
by means of special appliances, which secure a more intense oxi-
dation, has carried the operation a step farther in this direction,
and has succeeded in volatilizing his lead (and I may add, his zinc
also) in a form which renders the sublimate of commercial value.
I again call the reader's attention to the description of this
interesting process which appeared in the Engineering and Mining
Journal as previously cited. Mr. Bartlett's work as described
therein is not strictly pyritic smelting it is more than that. It
is pyritic smelting combined with the intentional sublimation of
a large proportion of the valuable ingredients of the charge, and is
practically the combination of two processes the volatilization
of the lead and zinc, and the matting of the copper (and silver
and gold if present) in one operation. I will not enter upon
any observations in this ingenious, and, I believe, successful
process, other than to point out (what the inventor does not wish
to conceal) a considerable loss in silver from volatilization.
70 MATTE SMELTING.
In the other pyritio methods we have evidence of greater or
smaller lead losses, according to the conditions prevailing. Under
some circumstances the conditions are not incompatible with the
saving of a considerable proportion of that metal perhaps even a
satisfactory amount. We would have generally to consider this
question along with such attendant circumstances as the cost of
transportation, etc., in order to determine the advisability of
recovering all the lead, a part of it, or none at all. As a rule,
however, the presence of significant amounts of lead, which we do
not wish to sacrifice, is a bar to the employment of the pyritic
processes. I regret the inability to furnish statistics showing the
lead losses in pyritic work, and can only say that in those charges
(comparatively low in lead) which I have worked, the absolute
loss seemed to reach from one-third to three-fourths of the whole,
and this during the use of the comparatively mild pyritic agencies
employed at Mineral.
LOSSES IN SMELTING.
The public are doubtless sufficiently familiar with the principal
sources of loss in lead smelting; the same causes are in operation
in matting, producing quite similar results. These causes are
usually classified as 1, Loss in slags; 2, Loss in flue dust; 3, Loss
by volatilization. It is worth while to examine rather closely
into the comparative magnitudes of these different losses.
69. SLAG LOSSES. In the treatment of gold and silver ores the
slags carry away on the average as much in the one process as in
the other. It is difficult, to be sure, to ascertain exactly what is
lost in any given case; the more so, as those conversant with the
facts are disinclined to make them public. Without overlooking
the natural tendency on the part of smelting people to conceal or
NOTE. 1. Without an explicit statement to the contrary, it might be sup-
posed that the pyritic processes are less well adapted to the extraction of cop-
per than of gold and silver, to which they have thus far been principally
directed. But in fact, as far as experience shows, it is extracted quite as
advantageously. It is probable that the pyritic furnace is able to produce
purer mattes than other blast-furnace methods, on account of its greater effects
in eliminating arsenic and antimony.
2. The principal advantage of the pyritic treatment of sulphides may be
summarized as : First, getting rid of roasting apparatus, and the cost and
trouble of running it. Second, getting heat out of the sulphides. Third,
getting flux out of them. Fourth, getting matte out of them, which brings
down the valuable metals of the charge.
PYRITIC SMELTING. 71
at least minimize their slag losses a tendency which forewarns
us not to attach too much credence to stories of abnormally clean
slags we should endeavor to do the fullest credit to the remarkable
performances of the skilled and progressive metallurgists of the
day in their efforts to reduce these sources of loss to the lowest
practicable point. Of absolutely clean slags there are none. Even
the carefully compounded mixtures of the assayer da not yield
slags which are absolutely devoid of valuable metals. Assays
therefore are never absolutely correct a fact which may not be
known to the assayer, but which the working metallurgist, accus-
tomed to find his silver frequently, and his gold occasionally,
"overrun" at the clean-up after a campaign, has the best of
evidence to prove.* Regarding therefore the fact that slags must
inevitably carry off some portion, however small, of that we work
for, an important question confronts the theorist, of how clean
can slags in any given case be made? And a more important one
arises in the mind of the practical metallurgist, of how clean a slag
will it pay to make? We are led by these inquiries in two direc-
tions, and we have the general question, what can be done
economically in slag formation, which pertains generally to
smelting; and second, the question as between matting and lead
smelting, which makes under the same conditions the cleaner
slags. It is difficult to find examples in real practice where slags
are made under conditions so similar as to afford favorable
examples for comparison. Perhaps the best practical examples to
which I can refer are found in the work of the large lead smelters
of the Rocky Mountain region, and the one matte smelter at
Denver. Confining the comparison to silver losses we have to
compare the loss of one and a half ounces to each ton of slagf at
the Argo works with a loss of one ounce, speaking roundly, at the
other plants. But the proportion of slag produced to ore smelted
would not be more than two-thirds as great in the Argo practice
as at the other establishments, where the necessities of the work
compel the use of a great deal of flux, which is not used at all at
Argo. Accordingly, the silver losses per ton of ore would perhaps
* For example, a pile of matte, or of native sulphides, carefully weighed,
sampled and assayed, will oftentimes show a gross value less than the same
material after roasting, notwithstanding the inevitable losses incident to that
operation.
f Private communication from the manager.
72 MATTE SMELTING.
be Deduced to the same figure. Even cleaner than the lead slags
of Colorado are those of Freiberg, where by dint of running all
their first slags through the furnace the second time they are
reduced to three-tenths of an ounce per ton before being dis-
carded. But the conditions which at Freiberg favor this practice
do not prevail in Colorado, where all the requirements of smelting,
save very large plants and highly skilled metallurgists, are not to be
so easily had; and still less at other localities where smelting has
to be carried on under conditions which preclude the thoroughness
of extraction which characterizes German practice. At Freiberg
and at Swansea it may pay to make exceptionally clean slags, one
ton of which does not carry away even so much as one dollar's
worth of all valuable metals combined. At Denver the best prac-
tice may be to produce slags containing two dollars' worth; while
in isolated camps where fuel, labor, refractory materials, etc., are
very dear, and the smelting mixture perhaps unfavorable, the best
metallurgy may favor comparatively foul slags, carrying perhaps as
much as five or more dollars' worth of metals. If the Swansea slags
are cleaner than those of Butte, and Clausthal's freer from metals
than those made in Eureka or Leadville, it does not follow that
the processes or the metallurgy of the latter were at fault. It is
always pecuniary profit and not the perfection of processes which
is the criterion of metallurgical fitness.
70. LOSSES IK LEAD SLAGS. Aside from the slag assays given
in the Table of Work Done, which are too few to afford decisive
evidence as to the points at issue, I have taken pains to collect a
large number of others, mainly from the statements of smelting
superintendents and chemists, whose truthfulness I assume, from
the mass of which I make these deductions:
Three large establishments, dealing extensively with silver ores,
which may be taken as the type of the best-conducted lead smelters
in the United States, make slags which average, speaking without
any attempt at entire accuracy, an ounce of silver per ton, with
minute amounts of gold and a small quantity of lead, which are
not as significant in this examination. I believe that this class of
excellently conducted works do more than half of the lead smelt-
ing of the United States. The next class, embracing smaller but
not necessarily less well-handled plants, working more restrictedly as
to mixture, smelting costs, etc., make slags averaging two to two
and a half ounces of silver per ton ; and a larger number of concerns,
running for the most part intermittently, and engaged oftentiints
PYRITIC SMELTING. 73
upon private work for local mines, produce still fouler slags, whose
average contents it is impossible to conjecture, but which reaches
in some cases five or more ounces. These examples of bad work
are typical not of the work of to-day, but of ten or twenty years
ago, and are introduced into this discussion with a view of showing
what the tendency of the modern practice of lead smelting is
toward.
Such being the practical results which are being achieved by
the lead smelters, we have to continue our examination and
embrace such data as will enlighten us on what the producers of
matte can do, and what it is to their interest to do.
71. EFFICIENCY OF LEAD AND MATTE COMPARED. It is the
opinion of Mr. Austin, based upon long experience with both forms
of reduction, that the slag losses are practically equal under
ordinary conditions. Others, conversant with matting, and perhaps
over-enthusiastic with its advantages, have been of the opinion
that it saved even a higher proportion, at least of the precious
metals, basing their belief upon abnormal results got by the
assay of certain experimental slags. I would remark, however,
that the lead smelters occasionally produce exceptionally, and even
wonderfully clean slags. But these rare exemplars of what we can
do, but do not care to repeat, must go for naught in the
discussion of such a subject as this. Evidently the skill of the
metallurgist, acting upon materials more than ordinarily favorable,
is alone to be credited with these exceptional results, and we
should not do well to class them with the ordinary run of smelting
operations.
On the whole, I am convinced that matte (assuming that it be
of the proper chemical and physical constitution) will collect the
values (silver and gold) as thoroughly as lead will. But we have
somewhat more trouble in removing the matte, now charged with
the values, from the contact with the slag; and to this is to be
ascribed one of the principal losses which matting is found to
incur. When our matte and slag approach each other in specific
gravity, so that the difference is not enough to admit of the
necessarily complete separation, a loss is bound to take place, and
this loss, which is a purely mechanical one, will bear some relation
to the difference of the specific gravities. There is not the
slightest doubt that the process of sulphidation of the valuable
metals during the matting fusion is complete and perfect; but
the mechanical separation of the so-formed sulphides presents a
74 MATTE SMELTING.
point of inferiority to the separation of lead bullion from its slags
by reason of the greater difference of specific gravity in the latter.
72. INFLUENCES OF SLAG COMPOSITION ON LOSSES. The
influences of an improperly constituted slag or matte may indeed
be exceedingly detrimental to successful work, especially where
ultra-clean slags and high results are necessary; and in entering
upon matting operations we are not by any means entitled to leave
this phase of the matter to chance. The separation of the
matte from slag is influenced mainly by the following considera-
tions:
First, being dependent upon the difference between the specific
gravity of slag and matte, it is facilitated by the increased gravity
of the matte and by the diminished gravity of the slag.
It is to some extent facilitated by the fluidity of the slag and
made more difficult by its viscosity, although not always and under
all conditions to the extent that might bethought, for, given time
enough, the most viscous slags will release the matte globules.
The presence of solid unmelted stony particles in a slag has little
effect in preventing the separation, and some of the cleanest slags
which are commercially made, contain numerous solid particles
which remain unmelted during the whole operation, and it is only
when the minute particles of sulphide are locked up absolutely
within the solid masses that any loss from the non-fusion need
be apprehended; although these masses may exist in such pro-
portion as to make the slag quite thick and viscid from their
presence. Such slags, it is evident, may only be profitably made
in the reverberatory furnace, where their viscid nature and the
time required for the separation of the matte are not incompatible
with the smelting operation.
The practical questions which arise at this juncture are, what
differences of specific gravities between matte and slag are essential
to a thorough separation, and how can we secure such differences.
The subject, which is not altogether a new one, demands much
fuller treatment than I am able to give it now, the most that I
can say being to give, unsupported by exact data, the conclusions
at which I have arrived.
73. PRACTICAL KEQUIREMENTS. I think that a difference of
one is clearly insufficient for even a tolerable separation under
any circumstances. Lead smelters' slags having a gravity of
four or slightly under, fail to separate satisfactorily from mattes
of five, an average weight. Slags of 3.65 separated, as experiment
PYRITIC SMELTING. 75
proved, very fairly from the same matte. There is no absolute
difference of specific gravities which we can assume as essential,
because the separation is to some extent contingent on liquidity
and upon the time allowed for subsidence. Active boiling and
abrupt movements of the fluid mass probably also promote coal-
escence of the globules and subsidence of the matte.* Because I
have never had trouble with the separations when the difference
of specific gravity reached 1.75, and because it is probably always
possible to achieve that difference, I regard it as advisable to
work for it.
An inspection of the list of the slag formers, given previously,
shows gravities ranging from two and a half to four, thus having
a range of one and a half; while the matte formers, also shown in
a previous list, range from four to eight or thereabouts. It ap-
pears then that in the effort to attain desirable differences of
gravity we can usually effect it easier by making the mattes
heavier than the slags lighter. At any rate we are able to control
to a considerable extent that source of loss of values which arises
from the dissemination of matte particles in slag.
The solution of matte in slags, which has also been considered
an important source of loss, has been treated by several writers
on copper metallurgy, to whom I shall refer the reader with the
remark that the subject does not appear to have advanced much
in its theoretic treatment since the days of Le Play, nearly half
a century ago. My own views, which are the result of much
study, are still of too immature a character to find a place in an
essay which is professedly of a practical nature.
74. LOSSES FROM VOLATILIZATION. The question of the vola-
tility of metals, which plays a great part in general metallurgy,
is very important in the various departments of matting, and
especially so in pyritic smelting. Herein we are confronted by
conditions which determine the formation of oxides, anhydrides,
and even of salts,and which favor the sublimation of many of them.
* Slow and placid movements of the mixture have been deemed favorable to
the subsidence of matte particles. But the escape of globules from moving
liquids is conditioned on curvilinear movements, and the tendency to escape
varies as the square of the velocity. A high angular velocity is the ideal con-
dition, giving rise to high tangential force. This is only compatible with
curved interior surfaces of the forehearth. The ideal form of the basin would
therefore approach the spherical, as most conducive to separation, and also the
form which the slowly chilling slag tends to produce.
76 MATTE SMELTING.
The Bartlett zinc-lead process, which is an extreme form of pyritic
smelting, is founded upon the tendency of zinc and lead to vola-
tilize from the furnace, whereby there is formed a sublimate of
mixed zinc oxide and lead sulphate, while of the non-volatile sub-
stances of the charge, the copper and gold remain as constituents
of the matte. We are told that in its practical operation this
process causes a loss of from six to fifteen per cent, of the silver,
for this metal is also volatile under the conditions which are essen-
tial to the sublimation of zinc and lead. These conditions, as far
as we know them, are high temperature and the presence of
gaseous currents containing oxygen. In the roasting of silver ores,
especially in the salt-roasting for chloridation, heavy losses of
the same metal are experienced, at times reaching thirty per
cent., and in these cases the losses are by some ascribed to the
formation of other sublimates, as of arsenic, zinc and antimony,
and of chlorine compounds, etc., which act chemically or mechan-
ically to drag away the silver. Silver losses by volatilization from
roasting furnaces are experienced at comparatively low tempera-
tures, perhaps not above incipient redness, or even lower; which
leads to the question, Is it possible for volatilization to take place
at as low a temperature in the upper part of the shaft furnace? If
so, then the conditions governing the volatilization may be identical
in both processes. In each there is the oxidation of sulphides,
arsenides, and antimonides, with the production of oxides of the
common metals and the volatilization in a gaseous current of
nitrogen and a little oxygen, of sulphurous, arsenious, and anti-
monious oxides, and likewise of oxides of zinc and lead, should
all those elements be present. There is a more rapid gas current
in the pyritic shaft, with a shorter exposure of the ore to its
influence.
In bessemeriziug mattes by the Manhes system, which is an op-
eration chemically identical in principle with pyritic smelting, the
conditions are equally favorable for the volatilization of the same
substances. Accordingly we might expect to find a corresponding
loss of silver, and this in fact is reported to occur in the conversion
of argentiferous mattes, although the writer is unable to present
well-attested evidence as to the extent of the losses suffered.
Now concerning the silver losses in pyritic smelting, which is
an all-important matter in the present connection, I regret being
unable to present full information, which is the reader's due, and
can only urge in apology the difficulty of securing data from the
PYRITIC SMELTING. 7?
managers of works, who as a rule are reluctant to make their
losses known. Rumor, unverified, makes the loss of silver at one
Colorado plant 18 per cent. My own experience in regard to
volatilization was exceedingly varied and instructive. Briefly
stated, I experienced losses of silver in different campaigns as
follows: 15 per cent., 11 per cent., 8. 2 per cent., 3. 8 per cent.;
while in one short campaign the silver recovered "overran" 2.6
per cent. These citations taken by themselves convey no lesson
whatever, unless it be that the pyritic process is exceedingly
uncertain in its results; but taken in connection with the con-
current circumstances as to charge, blast, and method of work,
details upon which I will not dwell, they illustrate a great deal.
It is exceedingly difficult in the ordinary run of work to differ-
entiate the losses by slag, by volatilization and by dusting from
each other and give each its true measure of responsibility. I
may say, however, that at Mineral, where the operations were
carried on with particular reference to ascertaining the losses
incurred, we were enabled to segregate them in a satisfactory
manner, and ray conclusions were that about two-thirds of the
loss in the first campaign were due to volatilization proper. This
great loss was in my opinion the result of experimental and im-
perfect work in an untried field. The loss of 8.2 per cent, in the
third case was about evenly divided between volatilization and slag
losses, as shown by regular and frequent slag assays, while in the
campaign where 11 percent, escaped, 3 per cent, appeared to result
from sublimation, the rest entering the slag.
The different causes to which I refer the losses were these:
First, deficiency of copper in the matte; second, occasional defi-
ciency of the matte, arising from excessive oxidation; third, fire-
tops; fourth, improper composition of the slag; fifth, incomplete
separation of matte and slag. Only the second and third of
these have a direct bearing on the subject of volatilization losses.
Volatilization of silver takes place most copiously when the
furnace is run with a hot top; and as the ore at this point has
not reached the heat of fusion, and furthermore as chemical
action within it has probably not taken place to any extent, at
least not to the extent of sulphidation of the precious metals, I
conjecture that the silver is lost while yet in the metallic or
chloride condition; and I further conjecture that when once in
the condition of sulphide it would resist volatilization. I consider
that the loss of silver by volatilization depends upon the intensity
78 MATTE SMELTING.
of the pyritic agencies, and may also be connected with its chemical
condition in the ore. It seems probable that silver contained as
sulphide intermixed with large quantities of other sulphides in
coarse pieces would be less likely to volatilize from the top of the
charge than other compounds of a less stable nature merely
intermingled mechanically with gangue matter.
It is my impression that neither copper nor gold suffers loss
from volatilization while undergoing the pyritic treatment; and
in the absence of all testimony upon the matter we may allowably
assume from the known characteristics of nickel and cobalt that
they also do not. It would appear then that, so far as losses by
volatilization are concerned, the pyritic process is better adapted
to ores of gold, copper, and probably nickel and cobalt, than to
those of silver. And better to silver than to lead.
The last word upon this subject, however, is not yet said. The
fact of the volatility of lead affording a ready means of separating
that metal from the pyritic charge lets loose a current of specula-
tion as to the possibility of recovering silver also by means of its.
volatility. It would appear easy to cause the escape of all the
silver in the charge by the simple expedient of forming no matte >
and could the condensation of the escaping metal be arranged for
as cleverly as that of the lead fumes, very possibly a practical
process would be established.
I do not find that these volatilization losses differ in cause from
those experienced in lead smelting, nor are they greater in degree
than were formerly quite common in that pursuit. They arise from
ignorance and inexperience, and the very common misconception
of furnace effects; and that growth of knowledge and experience
which has worked such a transformation in the one art will, I
doubt not, do as much for the other. I believe that there is.
nothing in the ordinary matting processes which renders them
intrinsically more liable to volatilization losses than lead smelt-
ing, where they are conducted with equal skill and knowledge.
As to the pyritic processes I consider that their tendency to-
volatilize certain elements, while it may, and probably will at first
prove a stumbling-block for the smelting practitioner, when the
conditions governing the reactions are well understood, so that
its results may be foreseen and guarded against, will prove not an
unmixed evil. The tendency to volatilize may open entirely new
paths in metallurgy, and the lead-zinc process may be the fore-
PYRITIC SMELTING. 79
runner of a group of methods whose object will be the volatiliza-
tion and recovery of numerous substances.
75. LOSSES IN FLUE-DUST. The temporary loss from the for-
mation of flue-dust, which is an unavoidable drawback in lead
smelting, is not less so in blast-furnace matting, and the same
evil is dealt with in the same way. Spacious flues must always be
provided for the recapture of the escaping particles, which are
afterward re-smelted with or without the precaution of bricking.
There need be no more said upon this point, as there is nothing
distinctive in matting practice in this direction.
76. INFLUENCES OF VARIOUS SUBSTANCES UPON EXTRACTION.
Iron. Increases liquidity and specific gravity of slags. De-
creases density of mattes.
Copper. Increases density of some mattes. Within uncertain
limits increases extractive power of mattes for silver and espe-
cially for gold.
Lead. Increases density of slags and mattes. Influence of
lead mattes on extraction of the precious metals probably
beneficial.
Arsenic. Increases density, but under some conditions decreases
fusibility of mattes. Assists extraction of cobalt and nickel. Is
volatilized mainly with formation of arsenious tri-oxide (and
loss of silver).
Zinc. Enters slag as oxide, and matte as sulphide, rendering
the former viscid, the latter light, and by injuring the separation
diminishes very seriously the saving of the precious metals. By
volatilization as metal or oxide causes heavy loss of silver.
Barium. Enters slag as baryta silicate, and matte (slightly) as
sulphide, rendering former heavy though liquid, the latter light,
and diminishing the chances of a good separation.
Lime and the Alkalies. Decrease density of slag, and hence
favor separation.
Alumina. By sometimes rendering slags viscous, prejudices
the separation.
SiUca.&n excess of silica, by rendering the slag light, favors
separation; but by adding to its viscosity injures it. The for-
mer quality far outweighs the latter, and some of the cleanest
of known slags are extremely siliceous.
77. RESUME 1. Lead and properly constituted matte are equally
efficient as absorbents of gold and silver, but matte is in certain
cases more difficult to separate from the slags.
80 MATTE SMELTING.
2. In practical work savings of even 100 per cent, of the assay
values are not impossible.
3. The cleanest (of gold and silver) of all known slags are prob-
ably those of high silica contents and hence of low specific
gravity.
4. Those losses which are caused by the non-separation of
matte and slag may be lessened by increasing the difference of the
specific gravities of those substances.
5. Slags made by either the lead-smelting or matting methods
may carry as little as one dollar per ton in valuable metals (gold,
silver, copper and lead).
6. With inferior skill or in the presence of conditions which for-
bid close work, slags may go as high as five or more dollars per ton.
7. In certain well conducted copper works the slags run but
little over one-half per cent, copper; while in others as well con-
ducted they average three times as much.
8. Under appropriate circumstances it may be good metallurgy
to sacrifice values in the slag. And while clean slags are an
evidence of technical skill, they are not its sole criterion.
9. In smelting practice any important losses of gold by volatili-
zation are unheard of.
10. The volatilization of silver, which may take place in all
forms of smelting, is partially under the control of the furnace
operator.
11. Losses in uurecovered flue-dust may cover many losses
hitherto ascribed to true volatilization.
SALE OF FURNACE PRODUCTS.
78. Dealings in furnace produce present many peculiarities, a
competent knowledge of which is only to be attained by close study
and a practical familiarity with the market. This is hardly the
place to go into a discussion of the whole subject, however
important it may be to the producer of mattes and coppers, but
there is a single phase of it which I wish to illustrate, namely,
the comparative advantages which the market now offers to
the lead smelter and to the matte smelter. To make the points
clear I annex a table which contains the elements of several prop-
ositions for the purchase of furnace material, on some of which
considerable transactions have bee i carried on by the writer.
The matte refiner's charges are of three sorts, which may be
systematically grouped as follows:
PYKITIC SMELTING, 81
1. Arbitrary and variable charges upon the ton of matte, or
pound of copper; as $10 to $20 per ton of matte, or 2 to 4 cents
per pound of copper.
2. Discriminations against composition; as a charge per unit
of arsenic, antimony, lead, zinc, etc.; or a higher charge for
treatment when the value of the precious metals exceeds a certain
sum, as $200 to the ton of matte or copper.
3. Standing deductions against the valuable metals in the matte
or black copper; as 30 ounces of the silver, 5 to 8 per cent, of the
silver, 5 to 13 per cent, of the gold, 1.3 or 1.5 of the copper per-
centage. Also one-eighth or one-fourth ounce of gold.
The examples to which I apply the bids are two mattes, the
one of 50 per cent, copper, with 60 ounces silver and 1 ounce gold
a very common description of product; and the other of 25
copper, with 500 ounces of silver a decidedly uncommon product,
but one with which the writer's practice has made him familiar.
For simplicity's sake we will suppose that these substances are
devoid of the injurious ingredients, such as arsenic, antimony, or
bismuth, upon which additional charges are often based. To
parallel the two mattes and afford materials for comparison of the
superior advantages of the lead bullion market, I imagine two
grades of bullion corresponding to the mattes, one of 60 ounces
silver, and 1 ounce gold, the other of 500 ounces silver, no gold;
the lead in each to reach 98 per cent. Assuming the market
price of copper to be 9i cents, of lead 3J cents, of silver 70 cents,
we can easily ascertain the aggregate market value which the
separated and refined constituents would have, and applying the
figures given in the various bids we can arrive at the point to
which the table tends, that is, how great a percentage of the
total value of the various contained metals would the product
bring in the market. The last column on the right shows the
percentage of its contents which the more valuable matte and bul-
lion would sell for, the preceding one, the corresponding results
for the poorer matte and bullion. It is shown that the selling
price at the various markets named, in the case of the 60 ounce,
50 per cent, matte, varies from 50 to 77 per cerrt. of i'ts total
contents; and the very rich silver matte, from 80 to 90 per cent.
The bullion brings from 85 to 95 per cent, of the market price
of its contained metals. These figures show for one thing that
the offer of 0.77 for the common 50 per cent, matte is the highest
which has ever been made in this country until of late, for this,
82 MATTE SMELTING.
grade of material, as far as I am aware, although there is reason
to believe that very large producers are now able to make better
terms for a p f ated quantity delivered at regular intervals. The
richer mattes cannot always be disposed of so advantageously as
the table indicates, inasmuch as there is a strong disposition on
the part of refiners to discriminate against material very rich in
gold and silver. One heavy firm of refiners in Colorado not only
make no such discrimination, but add to the producer's conven-
ience by paying cash down for all purchases, which is a vast im-
provement upon the far Eastern methods.
Much has been and much might still be said as to the defects of
the present system (if it can be called a system) of dealings in
matte-furnace products; but it is enough at present to declare
that we need and must have a better one. The rational and com-
prehensive methods of the lead bullion buyer may well be our
guide in the introduction of improvements; or, in default of
such, each matte or copper producer must become his own refiner.
With the growth and extension of metallurgical knowledge, and
theintroductonof simpler and more expeditious processes, adapted
to the refining of large or of small outputs, there is more and
more reason why furnace produce should be refined and separated
at the point of production, and be placed upon the market as
finished and purified metals*
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CHARACTERISTICS OF PROCESSES.
SECTION FOUR.
CHARACTERISTICS OF THE REVERBERATORY MATTING PROCESS.
Applicable Chiefly to:
Special Advantages as
Applied to:
Disadvantageous in Case of:
Mixtures containing but
small excess of matte-form-
ing substances.
Finely comminuted material.
Hot material from calcining
High cost or poor quality of
fire bricks, fire clay and flre
sand.
furnaces.
Highly siliceous mixtures.
Mixtures rich in sulphates.
Expensive or scarce coal,
wood or oil, or other flam-
Mixtures rich in the alkaline
ing fuel.
earths.
Copper ores or furnace pro-
duce from which it is desir-
The presence of important
Mixtures rich in alumina.
able to volatilize sulphur,
amounts of lead in the ores
Generally to difficultly fluxed
ores, or to those producing
viscid or highly refractory
slags, and particularly to
those containing a signifi-
arsenic or antimony.
requiring treatment.
Mixtures giving rise to ex-
tremely basic or corrosive
slags.
cant amount of zinc.
CHARACTERISTICS OP THE GERMAN SYSTEM.
Applicable Chiefly to:
Special Advantages as
Applied to:
Disadvantageous in Case of:
Mixtures containing no ex-
cess of matte-forming in-
gredients.
To very siliceous ores where
limestone or dolomite are
abundant and cheap.
Mixtures giving rise to ex-
tremely basic or corrosive
slags.
Ores containing a significant
proportion of lead, in pres-
ence of S, As or Sb.
Costly or scarce coke, char-
coal or anthracite.
Presence of S, As or Sb,
which it is desirable to vol-
atilize.
CHARACTERISTICS OP THE AUSTIN OLDER PROCESS.
Applicable Chiefly to:
Special Advantages as
Applied to:
Disadvantageous in Case of:
Mixtures containing a great
proportion of matte-form-
ing substances.
Siliceous ores capable of
forming bi-silicates, mainly
of iron.
Mixtures containing sul-
phides in lump form.
Elimination of large quanti-
ties of sulphur, arsenic and
antimony.
Substances tending to form
crusts upon the furnace
walls.
Ores containing lead which it
is desirable to recover.
84
MATTE SMELTING.
CHARACTERISTICS OF THE GRADUAL REDUCTION METHODS COLD BLAST. ()
Applicable Chiefly to:
Special Advantages as
Applied to:
Disadvantageous in Ose of:
Mixtures of moderate tenor
in sulphides, etc., and rich
in the heavy metals.
Mixtures containing copper,
with or without gold and
silver.
Mixtures containing lead, a
part of which it is desirable
to save.
Mixtures giving rise to easily
fusible slags.
The use of wood as smelting
fuel.
The volatilization of a large
proportion of the contained
sulphur, arsenic and anti-
mony.
The concentration of molten
matte. (See paragraph 59).
Inability to handle refractory
slags.
Comparative slowness of the
process.
CHARACTERISTICS OF THE GRADUAL REDUCTION METHODS HOT BLAST. (&)
(HYPOTHETICAL.)
Applicable Chiefly to:
Special Advantages as
Applied to:
Disadvantageous in Case of:
Mixtures of higher tenor in
sulphides, etc.
Mixtures containing any or
all of the valuable metals,
excepting lead.
Mixtures, siliceous and other-
wise, of ordinary or ex-
ceptional degrees of fusi-
bifity
The probably economical use
of wood and coal as smelt-
ing fuels.
The volatilization of a larger
proportion of sulphur, ar-
senic and antimony.
Additional cost of apparatus
CHARACTERISTICS OF THE BARTLETT PROCESS.
Applicable Chiefly to:
Special Advantages as
Applied to:
Disadvantageous in Case of:
Mixtures containing lead and
much zinc, little copper,
and with or without gold
and silver.
Blende ores containing over
90 per cent. zinc.
Saving of lead.
Expensive fuel.
Heavy loss of silver.
FURXACE EFFECTS.
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MATTE SMELTING.
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MATTE SMELTING.
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3
ill
111
90
MATTE SMELTING.
TABLE OP WORK DONE. PART 1
Localities.
Metal Sought.
(Important Metal in Italics.)
Assay of Ore Mixture, Per Ton
of 2000 IDS.
Character of Ores Treated.
REVERBERATORY MATTING:
Swansea
calcined fine material
Black Hawk, 1878
Gold, silver, copper, 3#
Miscellaneous custom ores, part
heap roasted
Argo, Colo., 1892
Gold, ^ to 1 oz silver, 40
Miscellaneous custom ores one-half
oz copper 3}t
Mount Dudley 1874
S and devoid of Fe
Butte 1882
Silver gold copper
Mn compounds
Pretoria S A (a) ....
Silver 30 oz copper 3#
taining antimonial oxides and de-
void of S
Pretoria S A (6)
taining antimonial oxides and de-
void of S
Butte 1893
Copper, 20#; silver, 13 oz
Roasted copper concentrates hot
GERMAN SYSTEM:
Lend 1872
Gold, silver, lead
from the automatic calciners
Amalgamation slimes quarteosf*
lump ore, compact pyrites, roasted
matte .
Mount Dudley 1874
Silver gold copper lead
Barytic and calcareous silver ores
low in S and devoid of Fe
Butte
Copper, silver
iron and manganese oxides
Leadville, 1891
Silver, copper
Rich lead slags, 90 parts; copper sul-
phides 10 parts
Butte 1893
Copper silver . .
sLagr etc
Altai 186-
Silver, gold
Barytic and siliceous ores
Deadwood, 1892
Sudbury 1893
Gold, silver
Auriferous quartz, carrying pyrite. .
Heap-roasted pyrrhotite and chal-
copyrite, diorite gangue
Toston 1887 (a)
Gold silver
Siliceous lump ore with pyrite
PYRITIC SYSTEMS:
Leadville, 1892
Silver, copper
Cupriferous and argentiferous py-
rite
Mineral, 1892
Silver, 30 oz.; copper, 1%.
Ferric and manganic oxides and sul-
phides, in felspathic gangue
Mineral 1893
Silver, 38 oz. ; copper, \% . .
Ferric and manganic oxides and sul-
LEAD SMELTING: (aaa)
Leadville, 1880
Silver, lead
phides, in felspathic gangue
' Carbonates," lump form . .
Eureka
Silver, lead
'Carbonates," lump form, neutral
or somewhat basic
Golden 1890
Gold, silver, lead ....
Pueblo, 1891
Silver, gold, lead
Miscellaneous custom ores
Tacoma 1893
Gold silver lead
fine ....
Freiberg 1886
Silver gold lead
Clausthal, 1890
(a) Before the inception of pyritic smelting, (eta) Cold blast was used at Mineral ; the
coke, as shown by experiment, (aaa) Examples of lead smelting introduced to afford
TYPICAL OPERATIONS.
I THE MATERIALS TREATED.
91
Fluxes Used, with Proportion to 100 Parts Ore; Fuel Used, and Parts to 100 Parts of Charge
None.
Fluorspar, 3 parts
None
Pyrites, 18 parts; lime, parts.
None...
River sand, 25 parts.
Siliceous and bituminous vein-stuff.
None...
Iron ore and lime, 6 parts
Roasted pyrites, etc., 40 parts.
None
None...
None
Limestone, 13 to 16 parts
Magnesian limestone, parts.
None.
None.
None.
None.
Limestone, 15 parts
Iron ore, 8 parts; dolomite, 12 parts.
None
Iron ore, limestone.
Iron ore, limestone.
Iron ore, limestone.
Iron ore, 18 parts...
None...
Coal, 45 parts
Wood, 1 cord per ton ore.
Coal, 33 parts.
Wood. 1 cord per ton ore.
Wood.
Coal.
Coal.
Coal, 30 parts.
Charcoal, 35 parts.
Charcoal, 35 parts.
None.
Coke, 10. 9 parts.
Coke, 10 parts.
Charcoal, 70 to 90 parts*
Coke.
Coke, 15 parts.
Coke.
Coal, 4 to 6 parts ; coke parts.
Coke and wood, 7^ parts, (aa.)
Coke and wood, 9.4 parts.
Coke and charcoal, about 24 parts,
Charcoal, 25 to 30 parts.
Coke, 12 to 14 parts.
Coke and coal, 16.3 parts.
Coke and charcoal, 14 parts.
Coke, 8}$ parts.
fuel percentage was calculated on the assumption that 2? Ibs. wood (dry fir) equal 1
additional grounds of comparison with matting processes.
TABLE OF WORK DONE. PAR!
Localities.
Product.
31&
duct tc
Weight
of
Charge
Analyses of Products.
Proi
tion
Val
ab
Met
inP
du<
S.
Sb.
As
Fe.
Cu.
Co
Ni.
Pb
Zn.
Ba.
REVERBERATORY MATTING:
Swansea
Cu matte. . .
Cu matte...
Cu matte...
Cu matte
M
A
A
i.
23
33
x
A
!
$
4
Black Hawk, 1878
30
Argo, Colo., 1892
Mount Dudley 1874
40
30
Butte 1882
Cu matte . . .
CuSb matte
Cu Sb matte
Cu matte...
Fe matte
Cu Pb matte.
Cu matte. . . .
Cu matte
,W*
53
Pretoria, S. A. (a)
Pretoria S A (6)
A
H
9
Va
M
2
22
27.9
38
2
3.6
19
55
52
57
4.3
25
X
|
A
Butte 1893
GERMAN SYSTEM:
Lend 1872
9 1
37
Mount Dudley 1874
Butte
60
(
i
*
Leadville 1891
20
57
7 15
Butte 1893
Cu matte. . . .
H
21.5
20
25-35
Altai 186-
1 R
15-20
Deadwood 1892
Fe matte....
CuNi matte.
Fe matte ....
*
Sudbury 1893
20-30
25-35
20-25
8-23
!
Toston, 1887
PYRITIC SYSTEMS:
Leadville, 1892
Cu matte....
14
42
50
57
Mineral 1892
Cu matte
Cu matte....
Pbbars,
Fe As matte.
:*
A
H
.?!
26
27
0.048
3.34
15
15
0.07
1.06
4.6
i
*
flfe
T% 8 t
Mineral 1893
LEAD SMELTING:
Leadville 1880
.035
.13
0.22
33
98.5
.18
.07
Eureka \
Golden 1890
Pbbars
.Pueblo 1891
Pb bars
Tacoma, 1893
Freiberg 1886
Pbbars
Pb bars
H
Clausthal, 1890
Pbbars
....
0.72
3.06
0.06
0.18
...
0.12
98.8
.128
....
T 9
* 5*Cu 2 S, Fe 4 S 8 b
-THE PRODUCTS OBTAINED.
Assay of
< Product.
Analyses of Slag.
Assay ol
Slag.
Authority.
Jz.
La.
Oz. Ag
Si0 2
FeO
MnO
CaO
MgO
BaO
Al a O 8
ZnO
PbO.
Cu a O.
Cu.
8.
Oz
Au.
Oz.
Ag.
i-8<
.18
600-1000
400
1100
800
464
38
29
60.5
28.5
2
2.9
*>*>
LePlay.
Egleston.
Pearce.
Peters.
Peters.
Jennings.
Bettel.
Uhurch
Peters
Keller.
Kerl.
Browne.
Private notes
Private notes
Guyard.
Raymond.
Clark.
Dwight.
Clark.
Biddle.
Hoffman.
7
1 *5
7.5
41
28
7
7
0.7
3
9
0.5
0.39
....
64 (?)
30
27
33
51
25
70
55.5
57
19.75
15
2
1.5
0.5
5.32
2.80
4.5
7 8
0.45
66
....
15 40
8 57
2 16
18
34
2.6
20
"^l
&
^
40
93
36
50
H^
0.8
0.5
32
50-55
58
10-18
8
2-4
75
7-20
5-15
1
m
a
360
560
231
8
34
40.5
4
23.
~^>
}
50
8
M
4
4.5
3
5
1.5
1.7
2-4
3
.
4.5-2.5
26.12
52.80
12
5.8
2 79
16
100-200
150
42
34
27
31
1
0.3
0.6
40
40.6
7
7
8
1.5-4
1.7
....)
0.2
0.3
0.21
I
0.86
4.39
0.51
) '
3.55
>ositioD
INDEX.
A PAOK
Acid slags, use of 39, 40
Lessened specific gravity of 40
Air blasts, cold, use of, in pyritic work 56, 57
Ores suited to 57
Heated by slag 68
Alumina, influence of, upon extraction 79
Anaconda Works, observation respecting recovery of silver 23
Argo Works, silver contents of slags 71
Arsenic and antimony i n mattes 17, 18
Effect upon specific gravity 18
Practical considerations 18, 24, 26
Influence upon extraction 79
Arsenide (and antimonide) matting 7
Austin, W. L 41, 55
Views as to slag losses 73
Austin processes, definition 31
Ores suited to 51
Older process 48, 49, 62, 83
Description of furnace 50, 51
Later modifications 52
Use of hot blasts 48, 54, 68
Balling, views as to constitution of mattes , 13
Barium, influence of, upon extraction 79
Slags in matting 38, 39
Sulphate. (See Heavy Spar.)
Bartlett, use of two rows of tuyeres 68
Bartlett process 61, 69, 76, 84
Bessemerization of matte. (See Manhes Process.)
Arsenides and antiinon ides 1.18, 19
Black copper, definition of 21
Blister copper, definition of 21
Blower for pyritic furnace 61
Calcium matte, Guyard's 15
Carpenter, Dr. F. R., work at Dead wood (foot-note) 38
Carrier, the, function of 6
Chart of the matte-formers 36
Cobalt and nickel 26
Cold blast pyritic work, principles of - 57-59
Concentration effected by return of rotten nutt 58
Of products 33
96 INDEX.
Copper, influence of, upon extraction .23, 79
Condition of, in matte 14
Found in the metallic form 14
Copper furnace, Arizona type 60, 63
Crucible, internal, use of, in pyritic smelting 64, 65
D
Davies process 25, 26
Deadwood, ore treated 22, 38
Elements occurring in mattes ........................................... 13
Extraction, percentage of, influence of various substances upon ........... 79
Feeding furnaces, methods of ......................... . ................ 53
Flue dust, losses in .................................................... 79
Fore-hearth not essential in pyritic smelting .......................... 64, 65
Freiberg, silver contents of slags ...................................... 72
Furnace products, sale of .......................................... 80-82
Furnace effects, table of .......................................... 85-89
Furnace construction ........................................... 57, 61-65
Fuel, perfect utilization of, in pyritic smelting ................... ... .45, 46
Dense varieties of, required ..................................... 47
G
German system of matting ............................................. 62
Characteristics of ............................................. 83
Gold in matte ................... . . .................................. 20-24
Gradual reduction processes, definition ................................. 31
Tabulation of effects .................... . .................... 53
Characteristics of .............................................. 84
Guyard, views of .................................................. 14, 15
M
Hearth activity, definition of ........................................ 62, 63
Heated blasts, use in pyritic work ............................... 48, 49, 54
Intense effects of ............................................ 65, 66
Means of procuring ......................................... 66, 67
When indispensable ........................................... 68
Heavy spar, behavior of, in furnaces ................................. 38, 39
Hot tops provocative of volatilization losses ........................... 77
Iron, condition of, in mattes 13
In arsenide mattes 14
Influence upon extraction 79
Iron matte, effect upon the hearth 24
Treatment of 25
K
Kerl, excerpts from 66
L.
Lead, condition of, in matte 14
Behavior in pyritic smelting 68-70
Influence upon extraction 79
INDEX. 97
PAGE
Lead smelting related to matting 28-30
Comparison of advantages 34
Slags produced 72
Lime, influence upon extraction 79
Losses in smelting 70, 76, 77
IVI
Magnetic oxide of iron, occurrence in mattes 15
Mankes process J25, 26
Related to pyritic smelting 76
Mansfeld, use of hot blast , , 66
Matte, definition of 6, 7
Classification of 12
Composition 13, 19
Metallic substances in 14
Constituents, genera of 19
Arsenic and antimony in 17-19
Considerations relating to refining 25-27
Methods of refining (table) 27
Specific gravity of 35, 36
Production dependent on smelting area 60
Matte-smelting synonyms 6
Definition 6
Advantages 19, 20
Results 20
Mineral, Idaho, rate of smelting at 63
ISI
Nickel and cobalt 26
O
Oxidation, use of the term 44
Pearce, experiments of 14, 17, 21, 22
Probert's process 25, 26
Pyritic effects in blast-furnace smelting ... .43, 45
Production of , 63
Intensity not dependent on amount of blast 45
Pyritic smelting, relations to other processes 31
The choice of fuel 41
Comparative efficiency of 44
Use of wood in 46, 47
Simplest form of 53, 54
Production of fully oxidized gases 45, 49
Smelting without fuel 55
Dependent on skill of attendants 60, 61
Slowness of operation 62
Losses in 76, 77
R
Relation of sulphide to arsenide and antimonide mattes 16
Refining mattes . ... 25
Reicheldorff, cupola smelting at 66
Reverberatory matting, characteristics of 83
98 INDEX.
Sale of furnace products 80-82
Silica, influence upon extraction 79
Silver in matte 20, 21, 23, 24
Slags produced in matting 37-40
Specific gravity of 40, 75
Losses of valuable metals in 70
Slag composition, influence of, upon smelting losses 74
Slag formers, specific gravity of 40, 75
Specific gravity of matte 18, 35, 36, 75
Effect of arsenic and antimony upon 18
Specific gravity of slags 40, 75
Speiss. or Speise. (See Arsenide and Antimonide Mattes.)
Spilsbury, experiments by , 21
Sudbury, smelting at 28, 63
Sulpharsenides and sulphantimonides contained in mattes 18
Sulphide ores of the West, prevailing characteristics of 56
Sulpliur, extent of elimination of, in various processes 43
Functions of, in pyritic smelting 44
Sulphur (elemental) sublimed in Austin process 53, 46
Sulphur tri-oxide, production of, in pyritic furnaces 46
Sulphuric acid, production of, from pyritic fumes 33, 46
Tacoma, typical lead-smelting practice .............. , . ............... 31, 32
Theoretical views of matte constitution ................................. 16
Toston Smelting Works, character of ore treated ......................... 22
Experiments in matting ..................................... 41, 54
Volatilization, losses from ............................................ 75
Influenced by ........................................... 77, 78
Of elemental sulphur and sulphur tri-oxide ................... 33, 46
Wood, use of, in pyritic smelting 46, 47
z
jinc, influence upon extraction 79
YC 33833
337651
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