EPA-650/2-74-085-a
SEPTEMBER 1974
Environmental Protection Technology Series
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EPA-650/2-74-085-0
CONTROL OF SULFUR DIOXIDE EMISSIONS
FROM COPPER SMELTERS:
VOLUME I - STEAM OXIDATION
OF PYRITIC COPPER CONCENTRATES
by
C.A. Rohrmann, H.T. Fullam, and P.P. Roberts
Battelle Pacific Northwest Laboratories
Battelle Boulevard,
Richland, Washington 99352
Contract No. 68-02-0025
Program Element No. 1AB013
ROAP No. 21ADC-056
EPA Project Officer: L. Stankus
Control Systems Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
September 1974
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This report has been reviewed by the Environmental Protection Agency and
approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Agency, nor does mention
of trade names or commercial products constitute endorsement or recommen-
dation for use.
11
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CONTROL OF SULFUR DIOXIDE EMISSIONS FROM
COPPER SMELTERS BY STEAM OXIDATION
OF PYRITIC COPPER CONCENTRATES
Prepared for
THE ENVIRONMENTAL PROTECTION AGENCY
CONTROL SYSTEMS LABORATORY
DEVELOPMENT ENGINEERING BRANCH
and
THE PHELPS DODGE CORPORATION
Under Contract Number 68-02-0025
June 1972
BATTELLE
Pacific Northwest Laboratories
Chemical Technology Department
. RICHLAND, WASHINGTON 99352
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CONTENTS
Page No.
ABSTRACT 1
INTRODUCTION 2
1. Copper-Bearing Minerals and Their Relationship to
Study 3
2. Previous Work 4
3. Objective of the Study 4
PROJECT TASK SUMMARIES 4
Task I - Background Information 4
Task II - Laboratory Investigations 5
Task III - Economic Assessment of the Process 6
Task IV - Identification of Additional Work 6
SECTION 1 6
Background Information and Evaluation 6
SECTION II 11
Experimental Laboratory Investigations 11
1. Copper Concentrates 11
2. Equipment 12
a. Steam Oxidation 12
b. Desulfurization 18
3. Analytical Methods 19
4. Experimental Results 21
a. Differential Thermal Analysis of
Concentrates 21
b. Labile Sulfur Removal 23
c. Hydrogen Sulfide Yields 27
d. Reaction Kinetics 41
e. Fate of Concentrate Impurities 46
5. Interpretation of Experimental Results 47
a. Process Limiting Factors 47
SECTION III 49
Economic Assessment of the Process Concept 49
1. Basis 49
2. Material Balances 49
3. Major Equipment Sizing 50
4. Capital Cost Comparison 52
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CONTENTS (contd)
Page No.
5. Comparison of Fuel and Depreciation Costs 53
6. Estimate of Lower Limit of Hydrogen Sulfide
Concentration in Steam Leaving Oxidizer 53
SECTION IV 54
Recommendations 54
SECTION V 55
Identification of Additional Work Required 55
1. Suggested Additional Work 56
2. Impact on Conventional Smelting Practices 57
3. Advantages 58
REFERENCES 60
APPENDIX 63
World Primary Copper Smelters and Smelting Capacity 64
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LIST OF FIGURES
FIGURE 1.
FIGURE 2.
FIGURE 3.
FIGURE 4.
FIGURE 5.
FIGURE 6.
FIGURE 7.
FIGURE 8.
FIGURE 9.
FIGURE 10.
FIGURE 11.
FIGURE 12.
FIGURE 13.
Page No.
Diagram of Experimental Setup Used in Steam
Oxidation Tests 15
Steam Oxidation Reactor and Furnace 16
Differential Thermal Analysis of Air-Dried
Copper Concentrates in Helium 22
Differential Thermal Analysis of Air-Dried
Concentrates Heated in Air 24
The Iron-Sulfur System (Rosenqvist) 25
H2S Yield as a Function of Reaction Time 29
Effect of Reaction Temperature on the
Equilibrium H~S Yield (Experimental) 30
Comparison of Experimental and Calculated
(Thermodynamic) H^S Yield at Various
Reaction Temperatures 35
Calculated Equilibrium Gas Composition as
a Function of Reaction Temperature 40
H?S Yield as a Function of Reaction Time
for a Batch Reactor 43
H?S Yield as a Function of the Pyrrhotite
Reacted for Various Water Flow Rates 44
Contact Time Required to Reach the Equilibrium
Hydrogen Sulfide Concentration as a Function of
the Pyrrhotite Reacted - at 800°C
.45
Steam Oxidation Process Material Balance Flow-
sheet 51
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LIST OF TABLES
Page No.
TABLE 1. Description of Copper Concentrates Used
in the Steam Oxidation Studies 13
TABLE 2. Weight Loss of Concentrates on Vacuum
Drying at 110°C 13
TABLE 3. Chemical Analyses of Copper Concentrates
Used in Steam Oxidation Studies 14
TABLE 4. Equilibrium Hydrogen Sulfide as a Function
of Temperature 32
TABLE 5. Calculated Equilibrium Gas Compositions 34
TABLE 6. Equilibrium Constants as a Function of
Reaction Temperatures 39
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CONTROL OF SULFUR DIOXIDE
EMISSIONS FROM COPPER SMELTERS BY
STEAM OXIDATION OF PYRITIC COPPER CONCENTRATES
ABSTRACT
This project to study the chemistry, engineering and economics of
steam oxidation as a means for the large-scale, low-cost preparation
of hydrogen sulfide for use as an intermediate in the production of
elemental sulfur from the gaseous effluents from conventional copper
smelters was initiated in June of 1971 by means of a contract between
Battelle and the sponsors, the Environmental Protection Agency and the
Phelps Dodge Corporation. The laboratory studies showed that hydrogen
sulfide was produced in relatively high yield and rapid rate from the
iron sulfide obtained in a first step of neutral or non-oxidizing roast-
ing of pyritic copper concentrates. In addition, the copper sulfides
were found to be non-reactive with the high temperature (700-800°C)
water vapor. However, equilibrium conditions limit the concentration
of hydrogen sulfide to less than about 1% in the water vapor. No prac-
tical means could be foreseen which would significantly increase this
concentration. At such a concentration the energy requirements needed
for the supply of high-temperature water vapor assures that the pro-
cess could not compete economically with a more conventional process.
A change in scope of this project to study alternate means of hydrogen
sulfide production without need for a reductant is recommended. An
aqueous process based on the use of regenerable hydrochloric acid which
still maintains the copper in the form of an enriched sulfide concen-
trate is the preferred route proposed for further study.
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INTRODUCTION
The conventional processes for smelting copper sulfide ores and con-
centrates involve successive steps or combinations of roasting in air to
remove part of the sulfur, melting and iron slagging in reverberatory
furnaces to yield fused copper-iron sulfides (matte) and reduction of the
matte to blister copper in converters. In all of these steps the sulfur
in the original ores and concentrates is released as sulfur dioxide gas
at various dilution levels from which it is not readily recoverable, par-
ticularly at low concentrations. Furthermore, once recovered, usually as
sulfuric acid from the waste gases of higher concentration, this low-valued
compound has limited use and marketability.
For many years it has been known that water vapor at high temperatures
can also oxidize sulfides to yield a large fraction of the sulfur in the
form of hydrogen sulfide. However, in contrast with sulfur dioxide, hydro-
gen sulfide is very readily concentrated and easily converted to elemental
sulfur by means of existing, coirmon, large-scale technology. Furthermore,
with hydrogen sulfide at hand, it can also be made to react very readily
with sulfur dioxide to produce elemental sulfur.
In the past few years Battelle supported preliminary laboratory inves-
tigations of the steam oxidation process as it might be applied to a number
of mineral sulfides. Its application to representative and typical pyritic
copper concentrates appeared to be unique. Although the removal of sulfur
via conversion to hydrogen sulfide was not found to be complete, it was suf-
ficiently high to justify further intensive study.
In the conventional (Claus) process for the conversion of hydrogen
sulfide to elemental sulfur, about one-third of the hydrogen sulfide is
burned to form sulfur dioxide, or the latter may be provided from other
sources. These two gases are then reacted catalytically to yield elemental
sulfur. The Battelle laboratory work indicated that the steam oxidation
reaction was probably complete enough to provide sufficient hydrogen sul-
fide for reaction with the residual sulfur dioxide which would be expelled
in subsequent smelter operations.
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In June of 1971 Battelle was awarded a contract to conduct research on
the steam oxidation concept for the Environmental Protection Agency, Control
Systems Laboratory, Development Engineering Branch. The Phelps Dodge Corpo-
ration, the next to the largest producer of copper from domestic sources in
the U.S., was a joint sponsor of this project.
Although other means could be considered for the production of the de-
sirable hydrogen sulfide, such processes generally require the use of a re-
ductant such as natural gas, hydrogen or coke for direct reaction with sulfur
or with sulfur dioxide. The steam oxidation concept is unique in that hydro-
gen sulfide may be produced directly from processed concentrates without the
need for a reductant. However, the energy requirements for production of
the high-temperature water vapor were recognized as the principal unknown
which would have an important bearing on the realization of a practical pro-
cess.
1. Copper-Bearing Minerals and Their Relationship to this Study
Although there are sources of copper existing as so-called oxidized
copper in the form of oxides, silicates, carbonates and sulfates, by far
the most important copper minerals are the sulfides. Two of the principal
copper sulfide mineral resources are chalcopyrite and chalcocite. These
are usually recovered as concentrates which are mixtures with varying
amounts of pyrite, iron disulfide. However, some of the chalcopyrite
concentrates (the most important copper mineral) may be quite low in
pyrite (10% or less). There are also a few very important commercial ore
bodies that are extremely complex in their copper sulfide mineralization
and comprise, in addition to those minerals mentioned above, significant
fractions of bornite, enargite, tetrahedrite, covellite, digenite and
tennantite. In addition, economically significant amounts of precious
metals (gold and silver) and molybdenum are also present in some pyritic
copper sulfide concentrates. By way of clarification, the identifica-
tion "pyritic copper sulfides" is meant to cover all copper sulfide con-
centrates in which iron sulfide exists in significant amounts. This
iron sulfide content would include pyrite as well as any iron sulfide
which is bound up in other important sulfide mineral forms such as in
calcopyrite and bornite. On the other hand, if a concentrate were pure
chalcocite, it could not be classed as a pyritic copper sulfide because
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pure chalcocite would contain no iron sulfide. However, most chalcocite
concentrates contain rather high levels of pyrite with some of this being
in very close mineralogical association. The only exception in the U.S.
is the White Pine concentrate of the Copper Range Company which is char-
acteristically very low in pyrite.
To provide reasonably good coverage of the major pyritic copper con-
centrates and their behavior in the steam oxidation process requires that
most of the work be concentrated on representative chalcopyrite and high
pyrite chalcocite concentrates. In addition, a few confirmatory tests
were conducted on concentrates of more complex mineralization and on con-
centrates in which precious metals (silver) and molybdenum are significant
by-products to be certain that the process will not adversely influence
the ultimate recovery of these values.
2. Previous Work
Although extensive previous work on the steam oxidation of pyrite and
neutral-roasted pyrite (pyrrhotite) was noted, essentially no such work
directed at similar treatment of pyritic copper concentrates was uncovered.
3. Objective of the Study
It was the objective of this project to investigate the chemistry and
to appraise the kinetics and engineering and economic feasibility of the
steam oxidation process as a means of air pollution abatement for copper
smelters.
PROJECT TASK SUMMARIES
Task I - Background Information
1. The concept of oxidation of iron sulfide with high-temperature water
vapor is old as evidenced by literature references dating back to as early
as 1836. Many expired patent references to processes based on the reaction
exist.
2. The references do not provide an adequate basis for assessing the real
technical and economic feasibility of a practical application of the
reaction, particularly to typical pyritic copper concentrates.
3. The use of hydrogen sulfide to react with sulfur dioxide is a well-known
and extensively applied means for the large-scale production of elemental
sulfur.
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Task II -Laboratory Investigations
1. This study has shown that hydrogen sulfide can be produced from the
iron sulfide in copper concentrates by exposure to water vapor, pref-
erably in the range of 700 to 800°C.
2. Essentially all of the iron sulfide can thus be converted to magnetite
without attack on the copper sulfide.
3. It was observed, however, from the laboratory studies backed up by
thermodynamic considerations that the concentration of hydrogen sulfide
in the off-gas will never exceed about 1% by volume. Although slightly
higher concentrations would be expected at temperatures higher than 800°C,
sintering of the concentrate mixtures is encountered at which time a
rapid fall off of reactivity was observed.
4. Although the equilibrium yields would be expected to be similar for any
composition involving water and pyrrhotite, significant differences in
yields for concentrates from various sources were shown in the results.
It is concluded that the reactions are more complex than anticipated.
At this time the exact nature of these reactions is not known.
5. On the basis of the present laboratory and thermodynamic studies, no
means are apparent to assure the achievement of an improvement in reaction
gas concentration required to assure a competitive steam oxidation process.
6. The reaction rate appears to be quite rapid (even after 90% of the
pyrrhotite has been reacted, a contact time of only 3 seconds at 800°C
is required to achieve the equilibrium ^S concentration); however,
the low equilibrium composition makes it essentially impractical to take
advantage of this rapid rate since a reactor of very large cross-sectional
area with only a small depth of concentrate would appear to be required.
7. Although some concentrates appear to have too low an iron content to
provide sufficient hydrogen sulfide, we do not regard this as a general
problem because pyritic copper concentrates are prepared from ores
generally high in pyrite. This excess pyrite, over that required for the
production of a preferred matte composition, is rejected in the flota-
tion circuit. Most of such pyrite could be retained if there were a
need for it—such as to assure sufficient hydrogen sulfide production.
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Task III - Economic Assessment of the Process
Preliminary economic studies made on the basis of the laboratory results
show that construction and operating costs are not competitive with a conven-
tional natural gas-SCL reduction process without about a sixty percent in-
crease in hLS concentration in the reaction off-gas.
Ta^sk IV - Identification of Additional Work
Steam oxidation as studied here appears to hold little or no prospect as
the means of economic hydrogen sulfide production on which to base a practi-
cal air pollution control process for copper smelters. No additional work
on the steam oxidation concept is suggested. However, the study has provided
a firm basis on which more attractive alternative concepts for hydrogen sul-
fide production may be developed. Continuation of the work to achieve adequate
hydrogen sulfide production by reaction of neutral-roasted pyritic copper con-
centrates with a non-oxidizing, regenerable acid such as hydrochloric acid is
proposed. The extensive work already done under this study with representa-
tive concentrates, the understanding of their primary characteristics and the
apparent simplicity and near state-of-the-art technology of most of the process
steps to be involved in this alternative concept supports the suggested con-
tinuation of the work.
SECTION I
Background Information and Evaluation
The reaction of steam with metallic sulfides has been a subject of chemical
as well as industrial interest for many years. Regnault^ ' about 135 years
ago studied the reaction in a qualitative manner for a number of metal sul-
fides. In this work Regnault clearly observed the distinctive difference
in the reactivity of iron sulfide and copper sulfide with the former being
more easily reacted to yield hydrogen sulfide, hydrogen and magnetic iron
oxide. No equations, rates of reaction or temperatures other than "red heat"
(2}
or "white heat" were reported. Gautierv ' 70 years later acknowledged the
iron sulfide-water vapor reaction to be as follows after observing that the
ratio of hydrogen sulfide to hydrogen was about 3:1
3FeS + 4H0 -»• Fe0 + 3H$ + H
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He also observed that copper sulfide was reduced to metal at high tempera-
ture with formation of sulfur dioxide rather than hydrogen sulfide. Tem-
perature measurements were not specified.
In the following 40 years (1910-1950) there were some widespread efforts
at gaining a better understanding of the steam oxidation reaction; however,
a clear realization of the thermodynamics, equilibria, and kinetics suitable
for determining whether or not realistic applications were possible does not
appear to have resulted from these works. This period was also a time of
rather intense patent activity relating to the steam oxidation concept.
Likewise in this period the patents also indicated a great deal of ac-
tivity aimed at the commercial applications of the steam oxidation reaction
with iron sulfides for the production of hydrogen sulfide and as a means for
the recovery of elemental sulfur.
In an early patent (U.S. 987,156), McLarty^ ' proposed the conversion of
nickel sulfide ores to oxides by means of pressurized steam.
The Hall process and patents^ '*' almost exclusively related to the
techniques and devices to produce hydrogen sulfide and sulfur from pyrite
via some combination of what is now called neutral roasting and steam oxida-
tion. The Bacon patents^ ' emphasized the advantage in hydrogen sulfide
production achievable by the introduction of alkaline material to the ores
being oxidized by steam. Bacon also includes the reaction between sulfur
fa\
dioxide and pyrite. The patent by Leesev ; mentions that at the preferred
operating temperature the steam oxidation reaction is complete in a few
seconds.
(g\
As late as 1958 deJahn was granted a U.S. patent^ ' that involved treat-
ment of pyrite with "very hot steam" to yield sulfur and iron oxide.
Among the patent literature there is also frequent reference to the use
of steam along with oxidizing, reducing or acidic gases to achieve specific
separations or conversions with metal sulfides generally. It was felt that
these were not sufficiently relevant to the principal reactions and objec-
tives being studied in this project and thus were not detailed in this
review. References of Moltereck,^10^ Arnold,(11^ Hooten,(12) Perkins,(13)
Petersen,(14) Lindemann,(15) Goetz,(16) Horakova,(17) Birkeland,(18) and
Millar^ ' are representative of these.
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The patents by Hall, Bacon, and Leese and others are all of interest and
provided a basis for optimism for the realization of a process; however,
there does not appear to be any direct commercial application of any of these
inventions. Most of these patents are repeated in patents granted in foreign
countries. Thus, although the body of patent literature is quite large,
there is much repetition with the same inventions covered by patents in more
than one country.
After about 1940 there began to appear some fairly detailed theoretical
and laboratory studies of the reaction.(20~29) Uno^28^ conducted a mathema-
tical study of the equilibria for the reaction:
3 FeS + 4 H20 + Fe304 + 3 H2S + H2
The results indicated that an H2S concentration of about 1% would be expected
at 800°C. Frey^ also studied the same reaction from the standpoint of
thermodynamics data and calculated that 1.8% of the water as required by the
equation would be converted to hydrogen sulfide and hydrogen at equilibrium
at a temperature of 800°C.
Much earlier Thompson and Tilling^ ' did laboratory work on the de-
sulfurization of pyrite with steam, other gases and mixtures of gases.
Although these authors established that the reaction of interest began at
580°C and that it continued at higher temperatures, they also concluded that
steam was catalytic in promoting the decomposition of pyrite at lower tem-
peratures. Their results also indicated that the steam - FeS reaction was
rapid. Quantitative, and kinetic data were not presented.
The work of Kirillov and Makarov^ ' was more extensively experimental.
Their data also indicated that maximum yield or conversion of sulfur from
the FeS to H2S required many times the stoichiometric amount of steam. Al-
though their methods of analysis were not reviewed in detail their results
indicated favorable practical prospects for the reaction. The H2S content
of the gas was high. The H2S to S02 ratio was also generally high. In fact,
most of such data appeared to yield higher concentrations than one would
normally expect. The gas analysis data appeared to be reported on a water-
free basis which would emphasize these high figures.
(24)
Rama Murthiv ' also did experimental work but with limited results
reported, such as a one-hour exposure of pyrite to hydrogen mixed with steam
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at 600°C yielded a 69% recovery of the sulfur in the form of both
and S02.
/or OC\
Inaba and Konov ' did extensive laboratory study and thermodynamic
calculations on the reactions involved. They observed that although FeS
could be completely desulfurized with water vapor, the thermodynamics were
not very favorable. However, it appears that they also anticipated practi-
cal applicability, if improvements could be made in equipment and techniques.
No quantitative data on the reaction of steam with copper sulfide
minerals have been reported although Parlr ' observed very slow reactions
taking place between steam and various copper minerals at temperatures in
the range of 200-460°C.
Studies of the thermodynamics and kinetics of the reaction of steam with
iron sulfides have been made but no equivalent studies for copper sulfide
minerals at the temperatures of interest were found.
(29)
Diev, et al.,v ' using steam and oxygen in the converting step for
copper smelting, released up to about one-third of the total sulfur in the
elemental form. They studied the reactions thermodynamically using pub-
lished data to determine the equilibrium composition of the gases. Since
fluid silica slags as well as molten iron and copper sulfides were involved
at temperatures far above those where steam oxidation is known to proceed,
these results do not appear to have a direct relationship to the steam oxida-
tion concept as being studied under this present project.
In the application of a steam oxidation process for the conversion of
pyritic materials to hydrogen sulfide, it is probable that a preliminary
step involving simply the thermal decomposition of pyrite to yield elemental
sulfur and pyrrhotite (FeS) would be adopted. This step is generally termed
"neutral roasting," since it does not involve oxidation of the pyrite or
pyrrhotite to yield sulfur dioxide. Also, since it does involve essentially
present state-of-the-art technology, no exhaustive effort was made to review
the extensive background literature. A few references, however, provide some
useful information and contribute to an understanding of this well-known pro-
cedure.
(32) (33)
Kunda, et al. and Mehta, et al. provide extensive.data on the
large-scale thermal decomposition and economics of pyrite processing. These
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two papers are concerned with the hydrometallurgical approach to the problem
of ultimate iron and sulfur recovery from neutral-roasted pyrite.
Graves and Heatlv ' also covered the economics of sulfur recovery from
the large-scale processing of pyrite including the step of neutral roasting.
It should be noted that all of these latter references were presented
at a time of sulfur shortage and high sulfur prices in the U.S. and Canada.
This situation has decidedly changed since that time.
(35)
Another useful reference is that of Kassila. ' In this paper the
flash smelting process as developed by Finland's Outokumpu Company is de-
scribed.
Also included is a description of the process as used at the Kokkola
plant to produce elemental sulfur via the thermal decomposition of pyrite.
This process was used on a large scale for at least about five years in the
mid-19601s. Although similar processes have been used and proposed for use
throughout the world, this plant probably represents the most recent practical
application of the thermal decomposition of pyrite for large-scale elemental
sulfur production. Guccione^ ' provides additional details on the process
used at the Kokkola plant.
Very little of the works cited above are strictly relevant to the present
study which is focused on the reaction between steam and the principal copper
sulfide material concentrates of the U.S. Most of the previous work deals
with reactions of the iron sulfides alone. While it is true that the expected
reaction to produce hydrogen sulfide from copper concentrates will be with
the pyrite and probably also the copper-iron sulfides present, the composi-
tion of the concentrates vary and the effect of the various components on
the steam oxidation are unknown.
In prior unpublished work at Battelle-Northwest, tests were carried out
to demonstrate the potential of the steam oxidation reaction to produce hydrogen
sulfide using representative minerals and copper concentrates. Included in
these tests are pyrite, copper sulfide flotation concentrates, zinc sulfide
(sphalerite or marmatite), tetrahedrite and galena. The data can be sunmarized
up to the present time on the results of these tests as follows:
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1. Pyrite after conversion to pyrrhotite by the usual heating step
in the absence of air (neutral roasting) reacted readily with water
vapor at atmospheric pressure and at about 850°C. The reaction
appears to follow that described by Thompson and Tilling'^0', as
3FeS + 4H20 •+ Fe.,0. + 3H2S + Hp.
Sulfur and hydrogen sulfide were determined in the off-gas. Hydro-
gen was not sought. Sulfur dioxide was absent. The pyrrhotite
(FeS) was not noticeably magnetic. The solid residue was highly
magnetic and was assumed to be mainly magnetite, Fe^O^. Weight
changes, without resort to chemical analyses, indicated about a
90% conversion. Chemical analysis subsequently obtained showed
that 97.5% of the sulfur in the pyrite sample had been removed.
2. Similar results were obtained with the copper concentrate; however,
it was concluded that only the iron sulfide fraction reacted. Cop-
per sulfide is not considered to be reactive with steam at the con-
ditions of the tests.
3. Zinc sulfide was unreactive under similar conditions.
In the neutral-roasting step, which would probably be used as a pretreat-
ment step to convert the pyrite to pyrrhotite and thereby also remove volatile
contaminants as well as part of the sulfur as elemental sulfur, some rather
direct and uncomplicated reactions can be visualized, such as the following
for the decomposition of chalcopyrite, the most conmon copper mineral:
2 CuFeS2 -> 2 FeS + S + Cu2S
However, in view of the complex thermochemical mineralogy of the copper-
iron-sulfur system, such a desirable result for chalcopyrite or other copper-
iron-sulfur mineral decompositions is probably never obtained.
SECTION II
Exjaer i men t a 1 L,a bg_rat ory Investigations
1. Copper Concentrates
The steam oxidation studies were carried out using copper concentrates
recovered from pyritic copper deposits. Most of the work was concentrated
on representative chalcopyrite and chalcocite-type copper concentrates
containing significant amounts of pyrite. In addition, a few confirmatory
tests were conducted with concentrates of more complex mineralization and
on concentrates containing precious metals to be certain that the steam
oxidation process will not adversely affect the ultimate recovery of these
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values. Table 1 gives a description of the six concentrates selected
for use in this study.
The six selected concentrates were obtained from the various copper
producers. About four pounds of each were vacuum dried 24 hours at 100°C.
The vacuum drying resulted in weight losses varying from ^0.5% to over
11% for the different concentrates as shown in Table 2.
The vacuum-dried material was carefully mixed to minimize hetero-
geneity, sampled and stored in sealed bottles for use in the bench scale
experiments.
The samples were analyzed for Cu, S, Fe, insolubles and other metals.
The results of these analyses are given in Table 3.
2. Equipment
a. Steam Oxidation
The steam oxidation studies were carried out by passing steam in
a helium carrier gas through a heated bed of the copper concentrate
and analyzing the reaction products. A schematic diagram of the ap-
paratus used for most of the experiments is shown in Figures 1 and 2.
High-purity helium was used as a carrier gas and was passed over
copper metal turnings to remove traces of oxygen.
The steam generator consisted of a Vycor vessel heated by a small
furnace to approximately 400°C. Water was injected into the vessel
by a syringe pump capable of highly reproducible water flow rates.
The pump was calibrated at all of the flow rates used in the experi-
ments by weighing water collected over a measured pumping time interval,
In some of the early experiments water vapor was injected into the
reactor by bubbling the carrier gas through a series of gas purifier
bottles containing water at a constant known temperature and calculat-
ing the water content from vapor pressure data. The latter technique
was satisfactory only for Tow steam flow rates. In both methods the
lines leading to the reactor were held at ^200°C by heating tapes.
The reactor consisted of a small Vycor vessel 50 mm I.D. x 50
mm high with a porous quartz frit on the bottom to support the
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TABLE 1. Description of Copper Concentrates Used
in the Steam Oxidation Studies
Source
1. Pima Mining Co., Arizona,via
Phelps Dodge Corporation
2. Morenci, Arizona, Phelps
Dodge Corp.
3. Tyrone, New Mexico,
Phelps Dodge Corp.
4. Lavender Pit-Bisbee, Arizona,
Phelps Dodge Corp.
5. Battle Mountain, Nevada,
Duval Corp.
6. Butte, Montana,
Anaconda, Co.
Principal Minerals
Chalcopyrite
Pyrite & Chalcocite
Pyrite & Chalcocite
Comments
Low in pyrite,
contains silver
Contains Mo
Contains Mo
Complex CuFe sulfides
(bornite, chalcopyrite)
and pyrite
Chalcopyrite,Chalcocite, High in pyrite
pyrite and silver
Very complex CuFe
Sulfide minerals
including enargite
Contains As, Zn,
Cd, Bi and Pb
TABLE 2. Weight Loss of Concentrates on Vacuum Drying at 110 C
Concentrate Source
Pima
Morenci
Tyrone
Lavender Pit
Battle Mountain
Anaconda
weight Loss, %
6.7
2.6
1.4
0.4
11.4 .
0.8
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TABLE 3. Chemical Analyses of Copper Concentrates Used in Steam Oxidation Studies
Source Cu
Pima i 27.14
Morenci
Tyrone
Lavender
Pit
Battle
Mtn.
20.82
20.31
12.65
24.50
Anaconda j 26.93
i
Weight %
S Fe Insol As Sb Zn
29.6 27.3 10.16 0.06 0.025 0.3
36.2 27.3 9.12 0.06 0.025 1.5
40.0 30.1 6.48 0.39 0.05 0.3
39.7 32.0 8.88 0.36 0.03 1.8
31.3 25.0 13.12 0.06 0.063 0.70
34.7 19.4 6.64 1.86 0.037 6.2
Pb
0.04
0.04
0.04
0.20
0.03
0.05
Mo
0.020
0.030
0.085
0.025
0.018
0.05
Bi
0.016
0.008
0.012
0.024
0.020
0.03
i
Cd
0.002
0.001
0.001
0.004
0.003
Se
380
320
280
360
510
i
0.12
290
i
PPM
Te
42
68
58
110
64
250
.Troy Oz/Ton
Hq ! Ag
280 ! 2.8
280
310
1.82
1.54
240 1.94
i
380
10.79
1
240 10.42
1
Au
00.010
. Q.020
i
0.01
0.07 !
0.31
0.07 :
-------
ROTOMETER
SHUT-OFF
HELIUM GAS TANlT) VALVE
SYRINGE WATER
PUMP
HEATED COPPER
TURNINGS
MANOMETER
FLASH BOILER
C7vr>
WET TEST METER
GAS TRAPS WITH CuSO,
RECORDER
CONDENSATE
RESERVOIR
REACTION VESSEL
IN FURNACE
WATER TRAP
GAS CHROMATOGRAPH
FIGURE 1. Diagram of Experimental Setup Used in Steam Oxidation Tests
-------
-16-
REACTION
PRODUCTS
THERMOCOUPLE
TO RECORDER
THERMOCOUPLE
TO CONTROLLER
REACTANT
QUARTZ
FRIT
FURNACE
STEAM &
CARRIER GAS
FIGURE 2. Steam Oxidation Reactor and Furnace
-------
-17-
reactant bed and disperse the incoming gas. The capacity of the
reactor was 100 g of copper concentrate. A thermocouple well was
fitted through the top in such a way that the thermocouple junctions
were surrounded by the charge. The gas inlet tube was 9 rnn I.D. and
the outlet tube was 20 rrni I.D. The charge was loaded into the
reactor through the outlet tube.
The reactor was heated in a 2-1/4 in. diameter by 12 in. long
tube furnace. The temperature was monitored and controlled by use
of two chromel-alumel thermocouples, a proportioning controller and
a strip chart recorder. Temperature control was maintained within
± 2°C of the set point.
The gas stream leaving the reactor contains helium, hydrogen,
water, hydrogen sulfide, sulfur dioxide and sulfur. The sulfur and
water were removed by use of a water-cooled condenser. The remaining
gases passed through two or three traps containing solutions of
copper sulfate-sodium chloride to remove the hydrogen sulfide and
sulfur dioxide, and finally through a wet test meter. The sampling
valve for the gas chromatograph was between the condenser and the
first trap.
The helium used as a carrier gas was controlled by a gas flow-
meter and a small needle valve placed at the inlet of the system.
In the normal operating, procedure a weighed amount of the cop-
per concentrate was placed in the reactor and spread to give the
charge a level surface. The apparatus was assembled and purged with
high-purity helium until the gas chromatograph indicated the absence
of air. The reactor furnace was turned on, and when the desired
temperature was reached, the water flow to the steam generator was
started. The exit gas stream was analyzed for hydrogen sulfide and
sulfur dioxide at frequent intervals throughout the run. The flow
rate of the helium plus any hydrogen was monitored by periodically
recording the wet test meter reading. The pressure of the system
and the temperature of the hood housing the gas chromatograph and
wet test meter were noted.
-------
-18-
b. Desulfurization
In any application of the steam oxidation concept it is likely
that the pyritic copper concentrates would first be neutral-roasted
to remove primarily the labile sulfur from the pyrite and also to
remove other major volatile contaminants such as arsenic and antimony.
Furthermore, such separation would minimize the significant reaction
between water vapor and sulfur which also yields hydrogen sulfide and
sulfur dioxide. In addition, since pyrite decomposition takes place
at temperatures substantially below that at which the steam oxidation
reaction is optimum, the neutral-roasting operation should be con-
ducted separately. Otherwise, the hydrogen sulfide produced con-
currently would be evolved with the other volatiles such as sulfur,
arsenic, antimony and possibly lead, plus major dilution with the
neutral-roasting gases. Additional clean-up of the hydrogen sulfide
may then also be required in order to produce high-quality sulfur.
For other minerals in the copper-iron-sulfur system, such as
chalcopyrite, decomposition into rather simple components may also
be visualized, such as:
2 CuFeS2 -v 2 FeS + Cu2$ + S.
However, the complexity of this system suggests that such a direct
and desirable result would probably not be achieved. Instead, some
mineral forms of lower sulfur content could be expected along with
the products as indicated by the above simplified reaction concept.
Although the scope of the study did not provide for a detailed study
of these possible reactions, it is likely that in the subsequent
steam oxidation step, oxidation is sufficiently extensive to assure
that all iron-sulfur compounds are converted to iron oxides with the
sulfur evolved largely as hydrogen sulfide.
The reactor used for neutral roasting of the copper concentrates
consisted of a 2 in. I.D. by 30 in. long Vycor tube closed at one end
with a rubber stopper at the open end. A 9 mm I.D. tube inserted
through the rubber stopper extending nearly to the closed end served
as an inlet for the helium used to maintain a non-oxidizing atmosphere.
A second 9 mm Vycor tube closed at one end was used as a thermocouple
-------
-19-
well. The exit line was a 20 mm glass tube leading to a 500 cc
flask to trap the bulk of the sulfur.
The reactor was heated in a 2-1/4 in. I.D. by 16 in. long tube
furnace. The temperature was controlled manually with a variable
transformer and monitored with a chromel-alumel thermocouple and a
strip chart recorder.
The desulfurization was carried out by placing a weighed amount
of the vacuum dried copper concentrate in the reactor tube and the tube
placed in the furnace so the charge was centered in the hot zone and
the helium flow started. When all the air was purged from the reactor
tube, the furnace was adjusted to the desired operating temperature
(usually 800°C) and maintained at that temperature for 16 hours. The
system was then cooled, the charge removed, pulverized, weighed and
stored for future use in capped jars.
3. Analytical Methods
The gas produced in the steam oxidation reaction will contain hydro-
gen, hydrogen sulfide, sulfur dioxide, sulfur, water and carrier gas
(helium in our experiments). As the gases cool, the sulfur and water
condense. In the presence of water and a catalytic surface, the follow-
ing reaction also takes place:
2 H2S + S02 -»• 1.5 S2 + 2 H20.
Because of this reaction the determination of the composition of the gas
leaving the reactor is a difficult analytical problem. From the practi-
cal standpoint, it is essential to know only the net hydrogen sulfide
and sulfur dioxide resulting from the steam oxidation reaction(s). The
net hydrogen sulfide and sulfur dioxide after removal of the condensed
water and sulfur were determined by gas chromatography or absorption
followed by a chemical method described below. The total sulfur used
up in the reactions was determined by measuring the sulfur content of
the copper concentrate, both before and after the reactions.
The chromatograph used in all the measurements was an Aerograph
Autoprep Model 700 with a thermal conductivity detector. A 1/4 in. O.D.
x 5 ft long stainless steel columns of Poropak Q provided excellent
-------
-20-
separation of hydrogen sulfide and sulfur dioxide. At a column
operating temperature of 100°C the retention time for hydrogen sul-
fide was 2 min., 45 sec., and for sulfur dioxide 5 min., 20 sec. The
chromatograph was equipped with a gas sampling valve which was con-
nected in-line with the gas stream to be monitored. A 2-ml sample
of the gas stream could be injected into the chromatograph without
interrupting the process flow.
The chromatograph was calibrated for hydrogen sulfide and sulfur
dioxide by injecting samples of known hydrogen sulfide or sulfur di-
oxide concentration using the gas sampling valve to measure the
volume. The chromatograms were recorded on a Hewlett-Packard recorder.
Calibration curves were obtained by plotting gas concentration
versus peak height times peak width at half-maximum. The minimum
measurable concentration was 0.1% hydrogen sulfide and 0.25% sulfur
dioxide.
In some experiments, the total hydrogen sulfide and the total
sulfur dioxide evolved in the steam oxidation run were determined
by a method based on the absorption of these gases in a solution
(*)
containing a known amount of copper sulfate and sodium chloride.
In this method hydrogen sulfide is quantitatively precipitated as
cupric sulfide and sulfur dioxide is oxidized to sulfur trioxide.
In both reactions a stoichiometric amount of hydrogen is released.
By measuring the amount of copper precipitated and the amount of
hydrogen ion formed after absorption of the gas being analyzed, the
hydrogen sulfide and sulfur dioxide can be calculated.
The analyses for copper, iron, gold, silver, molybdenum, cad-
mium, zinc, arsenic, antimony, and sulfur in the copper concentrates
and in the solid reaction products from the steam oxidation process
were made by a commercial laboratory using standard wet-chemistry
methods. However, for the analysis for the trace constituents such
as selenium, tellurium and mercury, an atomic absorption spectro-
metric method was used by the same commercial laboratory.
(*) Schwartz, Arthur, "Determination of Hydrogen Sulfide,Sulfur Dioxide,
Carbonyl Sulfide,Carbon Desulfide and Carbon Dioxide in a Gas Mixture,"
Anal. Chem. 43, pp. 389-392 (1971).
-------
-21-
4. Experimental Results
a. Differential Thermal Analysis of Concentrates
Differential thermal analysis (DTA) was performed on the various
copper concentrates. The analyses were made using a du Pont Model 900
DTA unit. Samples of the air-dried concentrates were heated in helium
and air at controlled rates to about 1000°C. The samples heated in
helium each exhibited an endothermic reaction beginning between 450
and 570°C which is due to the liberation of labile sulfur from the
pyrite and chalcopyrite. Figure 3 shows typical DTA scans obtained
with Morenci and Lavender Pit concentrates in helium. The tempera-
tures at which sulfur evolution began are as follows for the various
concentrates:
Concentrate T,°C
Morenci 458
Tyrone 459
Lavender Pit 457
Battle Mountain 470
Pima 457
Anaconda 570
The temperature at which the endothermic reaction begins is about
100°C higher for the Anaconda concentrate than for the other concen-
trates. The reasons for this difference are not known but are
probably related to the complex mineralogy of the Anaconda concentrate.
When the concentrate samples, which had been heated in helium,
were reheated in air, each exhibited a very large exothermic reaction
which began between 310 and 538°C. With each concentrate the reaction
occurred over a temperature range of at least 200°C. In each case
the exothermic reaction was followed by a strong endothermic re-
action which began between 630 and 750°C depending on the concen-
trate. The exothermic reaction is due to oxidation of the metal
sulfides. The endothermic reaction is probably due to (1) the de-
composition of any copper sulfate formed during the oxidation reaction,
and (2) a change in crystal structure of the metal oxides present.
All of the DTA curves obtained with the various concentrates are
similar in their general character to those reported in the litera-
ture for the sulfides of iron and copper when heated in air.
i
-------
-22-
o
X
<
o
MORENCI CONCENTRATE
o
X
o
o
LAVENDER PIT CONCENTRATE
L
0
1
I
1
1
200 400 600 800
REACTION TEMPERATURE, (
1000
1200
FIGURE 3. Differential Thermal Analysis of Air-Dried
Copper Cencentrates in Helium
-------
-23-
When air-dried concentrate samples were heated directly in
air the DTA scans obtained were very similar to those obtained with
samples which were heated in helium, and then air. However, for the
samples heated directly in air, the exothermic reaction began at a
lower temperature and was of much greater magnitude. Typical DTA
traces for copper concentrates heated in air are shown in Figure 4.
b. Labile Sulfur Removal
When copper concentrates containing pyrite or chalcopyrite are
heated to an elevated temperature in a vacuum or inert atmosphere
the pyrite decomposes with the evolution of sulfur vapor. In a
static system the extent of the decomposition is determined by the
reaction temperature and the sulfur partial pressure. If the sulfur
vapor is removed from the reaction vessel as it forms, the extent of
the pyrite decomposition will depend on the reaction temperature and
time at temperature. The products of the pyrite decomposition reaction
are sulfur vapor and pyrrhotite. The composition of the sulfur vapor
will depend on the vapor temperature and pressure, and will contain
a mixture of $2, 83, 84, 85, Sg, S7, and Sg molecules. At extremely
high temperatures, some dissociation of $2 molecules to sulfur atoms
occurs, but this occurs far above the temperature region of interest
in this study.
Both pyrite and pyrrhotite are non-stoichiometric sulfides.
They can be approximated by the formulas Fe$2 and FeS. However, the
iron-to-sulfur ratio for each compound can vary over a substantial
range, depending on the sulfur partial pressure. Figure 5 shows a
(37)
portion of the iron-sulfur phase diagram/ ' and the range of homo-
geneity that exists for each compound. For example, the diagram
shows the wide range of composition which exists for the so-called
beta form of iron sulfide (FeS-^ ). Furthermore, this form is
stable up to very high temperatures. Thus, one could not expect to
obtain constant iron-to-sulfur ratios when thermally decomposing
pyrite. The ultimate composition would be determined by the dura-
tion of exposure and the partial pressure of sulfur over the material.
In a flowing gas system, equilibrium conditions could be reached
only after very prolonged periods.
-------
-24-
MORENCI CONCENTRATE
o
X
o
o
UJ
LAVENDER PIT CONCENTRATE
J
200
400
600
800
1000
1200
REACTION TEMPERATURE, UC
FIGURE 4. Differential Thermal Analysis of Air-Dried
Copper Concentrates Heated in Air
-------
-25-
1600 -
60
SULFUR, ATOM PERCENT
70
FIGURE 5. The Iron-Sulfur System (Rosenqvist)
-------
-26-
If the steam oxidation reaction is carried out with the copper
concentrate as received from the producer, the labile sulfur is
evolved as the concentrate is heated to the reaction temperature.
This sulfur condenses in the downstream sections of the equipment
and can interfere with the equipment operation. It was decided,
therefore, that the labile sulfur would be removed from the various
concentrates, and the desulfurized products would be used for the
steam oxidation reactions^ The desulfurization reactions were
carried out in the equipment discussed in the previous section. The
desulfurization temperature, in each case, was 800°C and the concen-
trate was held at temperature for 16 hours in a stream of flowing,
high-purity helium.
A large quantity of each concentrate was desulfurized. A
1-2 kg quantity of each desulfurized concentrate was thoroughly
blended and analyzed. In all subsequent experiments involving a
specific concentrate, the feed material was taken from the blended
and analyzed batch of desulfurized product.
The six concentrates showed the following weight losses due
to sulfur evolution.
Initial Sulfur Weight Weight Loss as %
Concentrate Wt% Loss, % of Initial Sulfur
Morenci 36.2 16.8 46.4
Tyrone 40.0 19.0 47.5
Pima 29.6 9.6 32.5
Lavender Pit 39.7 18.4 46.4
Battle Mountain 31.3 15.2 48.5
Anaconda 34.7 17.6 50.7
It is impossible to assign a specific formula to the iron sulfide
product from the desulfurization reactions. However, if one assumes
that the copper is present as Cu£S and any other metal sulfides
(other than iron) are present as the normal sulfides, the iron-
sulfur ratios for the various desulfurized concentrates are approxi-
mately as follows:
-------
-27-
Desulfurized Iron Sulfide
Concentrate Composition
Moreno i FeSi.i6
Tyrone FeS1-OB
Pi ma FeS^Q
Lavender Pit FeS^ 12
Battle Mountain FeSi.ii
Anaconda FeS1>01
Except for the desulfurized Anaconda concentrate, the iron sulfide
compositions are about what one would predict from thermodynamic
considerations.
When the concentrates were desulfurized at 800°C, sintering of
the product did not appear to be a problem. Only the Pima concen-
trate showed a tendency to sinter. The Pima product formed large
partially-sintered lumps at 800°C which were easily broken up.
The other products formed loosely-bonded agglomerates which were
readily broken up by shaking the product in a glass jar. Subsequent
experiments showed that only the desulfurized Pima concentrate
presented sintering problems during the steam oxidation reaction at
temperatures of 800°C or less. Above 800°C all of the concentrates
showed a tendency to sinter during steam oxidation, and at 900°C
sintering became a severe problem.
When the various concentrates were desulfurized, the off-gas
always contained some h^S and S02 in addition to elemental sulfur;
however, the amounts produced were quite small. The reactions which
result in the ^S and S02 formation are unknown, but could involve
bound water which is not removed during the drying step.
c. Hydrogen Sulfide Yields
In the experiments designed to measure the ^S yield, 80-100
grams of desulfurized concentrate were placed in the vertical reactor
tube and the system was purged with high-purity helium. When all
oxygen was removed from the system, the concentrate was heated to
the desired temperature. When the reaction temperature was reached,
the water flow was started while maintaining the helium flow. The
-------
-28-
off-gas, after cooling to room temperature to condense most of the
water, was analyzed for h^S and S02 by gas chromatography (GC).
Then the gas was scrubbed with a copper sulfate-sodium chloride
solution to remove the h^S and S02, and the residual gas flow
(principally helium and hydrogen) was measured using a wet-test
meter. From the gas flow, GC analysis and water flow, the h^S
yield as a function of water fed to the reactor could be calculated.
In most of the experiments very little S02 could be detected
in the off-gas by gas chromatography. This indicates that if any
S02 was present in the off-gas leaving the reactor, it reacted with
H2S as the gas cooled, to form elemental sulfur according to the
reaction
2 H2S + S02 2 2 H20 + 3 S (1)
The h^S content of the gas stream, as determined by gas chronato-
graphy, represents, therefore, the net h^S yield after any S0£
initially present has reacted.
Figure 6 shows the results of a typical steam oxidation run
using desulfurized Morenci concentrate. The h^S yield is essentially
constant for the first portion of the run, and then decreases with
time as the sulfur content of the concentrate is depleted. This
indicates that the composition of the off-gas leaving the reactor
is constant during the first portion of the run. By carrying out
similar runs at various water flow rates it was established that,
during the initial phase of each run, the off-gas leaving the reactor
was in thermodynamic equilibrium with the fresh desulfurized concen-
trate. The length of time in which the H2S yield was constant was
a function of the water flow and volume of concentrate used.
By carrying out a series of runs at various temperatures with
a desulfurized concentrate, it is possible to obtain a measure of
the equilibrium H2S yield as a function of temperature. This was
done for each of the six concentrates. Figure 7 shows the results
obtained with three of the concentrates: Morenci, Anaconda, and
Lavender Pit. The results obtained with the other three concentrates
-------
-29-
o
CO
0.9
0.8
0.7
0.6
0.5
o
o
z:
ce.
O
"Is, °-4
LU
_J
O
0.3
0.2
0.1
- o
TEMPERATURE
CONCENTRATE
WATER FLOW
HELIUM FLOW
800°C
DESULFURIZED MORENCI
0.585 g/MINUTE
118 cc/MINUTE
I
I
I
20 40 60 80 100
REACTION TIME, MINUTES
FIGURE 6. H2S Yield as a Function of Reaction Time
120
140
-------
-30-
o
o
1 .0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1 -
400
O MORENCI
O ANACONDA
A LAVENDER PIT
500
600
700
800
REACTION TEMPERATURE, °C
900
FIGURE 7. Effect of Reaction Temperature on the
Equilibrium H^S Yield (Experimental)
-------
-31-
are similar to those obtained with the Morenci concentrates as can
be seen by referring to Table 4. It must be remembered that the
equilibrium H»S yields presented in Figure 7 and Table 4 are the
net yields after any hl,S and SO,, in the cooled gas have reacted to
form sulfur.
If copper concentrate, which has not been desulfurized, is
used in the steam oxidation reaction, the initial H?S yield is in-
creased. However, the HLS yield decreases rapidly with time and
after about 50 minutes reaction time the H2S yield approximates
that obtained with a desulfurized concentrate. The off-gas from
the reaction contains both H^S and SO- and as the gas cools ele-
mental sulfur is formed. The reaction is incomplete however, and
the GC analysis shows that cooled off-gas contains both SOp and
H^S. The HpS-SO- ratio in the gas is approximately 2:1. It is
hypothesized that the SO- and the bulk of the H?S is formed by a
reaction between the labile sulfur vapor and water vapor:
2 H20 + 3/2 S2 t 2 H2S + S02
During the initial stage of the run, the release of labile sulfur
is high and the SO- and H-S yields are high. As the release of
labile sulfur decreases to zero, the H?S yield decreases until it
equals the H~S yield from the steam oxidation reaction.
To determine if the sulfur-water reaction could account for the
high H~S yield, experiments were performed in which sulfur vapor and
water vapor were heated together at 300-500°C, cooled to room tempera-
ture, and the gas stream analyzed by GC. The results show the gas
stream contained high concentrations of both S02 and H-S, indicating
that the water-sulfur reaction is responsible for the high H-S yields
observed when untreated copper concentrate is steam oxidized.
Reports in the literature indicate that the addition of lime
or other alkaline agents to the copper concentrate can increase the
yield of H?S obtained during steam oxidation. However, in a number
of tests in which calcium hydroxide (10 wt%) was added to the con-
centrate, no increase in hLS yield was observed. This was true
using both untreated and desulfurized concentrate. A substantial
-------
TABLE 4, Equilibrium H^S Yield As A Function Of Temperature
Temperature
Morenci
H?S Yield, Moles H?S / 100 Moles of Water Fed
lyrone
Pi ma
Battle Mountain
Lavender Pit
Anaconda
450
500
550
600
650
700
750
800
850
900
-
0.07
0.14
0.23
0.35
0.49
0.62
0.82
0.89
1.05
-
0.07
-
0.22
0.35
0.51
0.60
0.77
0.81
1.09
0.02
0.07
0.12
0.20
0.33
0.51
0.65
0.82*
_
0.08
0.14
0.23
0.32
0.61
0.85
0.90
0.96
0.07
0.16
0.28
0.42
0.57
0.68
0.90
0.86
0.94
0.08
0.14
0.23
0.33
0.47
0.54
0.64
0.71
0.72
0.74
CO
ro
i
Concentrate bed partially sintered at 800°C.
-------
-33-
amount of S0?, however, was detected in the off-gas when the lime
was added to the desulfurized concentrate.
The steam oxidation of desulfurized copper concentrate is pre-
sumed to occur by the reaction
3 FeS + 4 H90 t Fe70, + 3 H~S + H, (2.)
L. yield, as
a function of temperature, is given in Figure 8. The H2S yields
obtained with Morenci and Lavender Pit concentrates are also shown.
-------
-34-
TABLE 5. Calculated Equilibrium Gas Compositions*
Basis: 3FeS(s) + 4H20(g)
&F
Temp
°C
400
600
800
1000
1200
1400
AFR'
kcal
31.46 6.11x10
35.96 1.00x10
-11
-9
-9
40.53 5.578x10
45.12 1.779xlO"8
49.61 4.370x10-8
54.19 8.355xlO-8
>(r\
^9 1 o
Kp
1 C0U« ' ~>"o-J/n
34(s) 2(g
Gas Composition, atm
) 2(g)
H2S H2 H20
0.00366
0:00734
0.01121
0.01495
0.01856
0.02173
0.00122
0.00245
0.00374
0.00498
0.00619
0.00724
0.99512
0.98021
0.98505
0.98007
0.97575
0.97103
* Assuming ideal gas behavior, unit activity of solid constituents, and
no side reactions which affect the gas composition.
-------
-35-
1 .8
1.6
1 .4
1 .2
O CALCULATED H2$ YIELD
A DESULFURIZED MORENCI CONCENTRATE
D DESULFURIZED LAVENDER PIT CONCENTRATE
o
o
400
500
600
700
800
900
1000
1100
REACTION TEMPERATURE, UC
FIGURE 8. Comparison of Experimental and Calculated
(Thermodynamic) H^S Yields at Various
Reaction Temperatures
-------
-36-
The experimentally measured hLS yields are much less than the
calculated yields. There are several possible explanations for this:
1. Inaccuracies in the free energy data which affect the cal-
culated yields.
2. The calculated equilibrium yield assumes ideal behavior of
reactants and products, which may not be the case even at
the low pressure (^ 1 atm) of the reaction system.
3. Thermodynamic equilibrium is not attained in the reaction
system due to kinetic limitations.
4. The steam oxidation reaction does not proceed as written.
5. Other reactions occur which affect the H~S yield.
(38)
The compilation of free energy data by Rosenqvist^ appears
to be the best source of data available. Even so, the suggested
accuracy of the data is such that the AF°R for Reaction (2) could
+
be in error by as much as - 14.5 kcal at the various temperatures.
An error of this magnitude would have a drastic effect on the cal-
culated H2S yields. At 800°C, the calculated H2$ yield could vary
from 0.207 - 5.745 moles H2$/100 moles H20 fed to the reactor,
depending on the error in the calculated free energy of reaction.
At the low reaction pressures involved (about one atmosphere
absolute), the deviation from ideal gas behavior would be slight.
Corrections for non-ideal gas behavior would have only a slight ef-
fect on the calculated H2S yield. Deviations from unit activity
for the solid constituents could have a substantial effect on the
calculated H2S yield, but not to the same degree that inaccuracies
in the free energy data would have.
The experimental data indicate that the off-gas composition
does approach the thermodynamic equilibrium during the initial stages
of each run. Since decreasing the water flow to very low levels
does not increase the initial H,,S yield, the off-gas from the
reactor must be at equilibrium.
All experimental evidence indicates the steam oxidation re-
action proceeds as written as shown above (2) and as supported by
-------
-37-
the work of Thompson and Tilling. ' However, to prove or dis-
prove that the reaction proceeds as assumed would require a study
beyond the scope of this program.
There are a number of other reactions which could occur in
the reaction system and affect the H2S yield. These include the
following:
AFj
- R — |/o
(kcal) KP
2 H2S — 2 H2 + S2 17.7 2.534 x 10"4 (3)
K4
2 H20 + 3/2 S2 ; - ^ 2 H2$ + S02 4.34 0.1307 (4)
K5 5
2 H20 + 1/2 S2 ~^-" S02 + 2 H2 22.0 3.31 x 10"D (5)
3 Fe,0.. + FeS — ^ 10 FeO + S0? 36.6 3.51 x 10"° (6)
0 H \ ^
K7
Fe.O. + FeS - * 4 FeO + 1/2 S? 19.2 1.23 x 10~4 (7)
*5 H ~\ ~ ^-
K8 5
3 FeS + 2 S02 " - " Fe304 + 5/2 S2 22.8 2.27 x 10"s (8)
K9 ,
FeS + H00 - " FeO + H9S 12.3 3.13 x 10"J (9)
L. ^ t-
K10
Fe304 + H2 " - ' 3 FeO + H20 -2.3 2.94 (10)
3 FeS + 10 H20 " — ^ Fe304 + 3 S02 + 10 H2 132 1.33 x 10"27 (11)
Calculated at 800°C
Similar reactions can be written involving copper. If Si02, MgO and
CuO are present in the concentrate, the formation of complex oxides
must also be considered.
-------
-38-
Because of many possible reactions which could be involved in
the steam oxidation of desulfurized copper concentrate, a rigorous
thermodynamic analysis of the reaction system is impossible. How-
ever, it is known that under certain conditions sulfur and SOp are
reaction products in addition to magnetite, hLS and hL; also that
some HpS decomposition could occur at the reaction temperatures in-
volved. Therefore, the equilibrium off-gas compositions were cal-
culated assuming that reactions 2, 3 and 4 occur in the reaction
system. The equilibrium constants for the three reactions were
determined and the results are given in Table 6. The equilibrium
gas composition was calculated as a function of temperature. The
calculated gas compositions and H2$ yields are shown in Figure 9.
The calculations show the hL and S02 concentrations, at equi-
librium, increase rapidly with temperature. The sulfur concentration
is low at all temperatures, while the HpS concentration remains
relatively constant. Assuming all of the SCL formed reacts with
KUS as the gas cools, the net H2S yield decreases with increas-
ing temperature, and would become zero at about 875°C. This is
in complete disagreement with the experimental data which shows the
net HLS yield increases with increasing reaction temperature.
At reaction temperatures above 800°C, the amount of SCL formed
increases rapidly. At 800°C all of the S02 formed reacts with HL.S
to form sulfur as the gas cools, and analysis of the cooled off-gas
shows no residual S02. Above 800°C the cooled off-gas contains
H?S plus some unreacted SOp. If the residual SO,, was reacted with
H2S, the net H2S yield would be lower than shown in Figure 9, and
could possibly approach the predicted value. Even so, the dis-
crepancy between the experimental and calculated gas compositions
show either the free energy data used for the calculations are in
error or the assumed reactions are incorrect. A costly and time-
consuming experimental program would be required to determine why
the calculated and experimental gas compositions do not agree.
-------
-39-
Table 6. Equilibrium Constants* As A Function Of Reaction Temperatures
Reactions Considered
3FeS
K,
^t
V '
K.
3H2S
2H20 + 3/2S2 ---^ 2H2S + SC>2
K3 = (PH/(PY/(V2
Temp, °C
400
600
800
1000
1200
1400
6.11 x 10
-11
1.003 x 10
5.578 x 10
1.179 x 10
4.370 x 10
8.355 x 10
-9
-9
-8
-8
-8
1.393 x 10
2.206 x 10
2.534 x 10
6.453 x 10
0.06964
0.4206
-9
-6
-4
-3
3.901 x 10
0.3585
0.1307
0.05283
0.02569
0.01520
-3
* Assuming ideal gases and unit activity of solid constituents.
-------
-40-
0.020
0.015
UJ
Of
Of.
a.
<£
O_
o:
CD
0.01
0.005
PARTIAL PRESSURES OF S2+H20 NOT SHOWN)
PS IS LOW: <0.001 ATM. AT ALL TEMPS)
P ' =1-P -P -P -P
SO,
\NET H2S
\ / NET SO-
I \Xl _\
600
FIGURE 9.
700
800
900
1000
REACTION TEMPERATURE, UC
Calculated Equilibrium Gas Composition as
a Function of Reaction Temperature
-------
-41-
d. Reaction Kinetics
The kinetics of the steam oxidation reaction were evaluated
using the fixed bed reactor shown in 2. The nature of the reaction
system and the uncertainty of the reaction mechanism makes a rig-
orous analysis of the reaction impractical. Instead it was neces-
sary to make empirical estimates of the steam oxidation reaction
kinetics based on the fixed bed data.
If the HpS is produced by Reaction (2) and the reaction pro-
ceeded to completion, one mole of water would yield 0.75 moles of
H~S. However, the thermodynamic equilibrium apparently limits the
H2S yield that can be obtained. At 800°C, about 0.0082 moles of
hLS per mole of water fed is the thermodynamic limit. As the steam
oxidation reaction proceeds in the fixed bed reactor, the pyrrhotite
concentration in the concentrate bed decreases continuously with
time. The reactor system is, therefore, in an unsteady state through-
out the course of the reaction. In addition, at any given time the
pyrrhotite concentration will vary from the top to the bottom of
the concentrate bed.
It can be visualized that for a given concentrate particle, a
layer of magnetite builds up on the particle as the pyrrhotite reacts.
The HpS yield from the single particle will decrease with time as
magnetite layer builds up and the pyrrhotite concentration (or re-
active surface area) decreases. In a fixed bed reactor the off-gas
leaving the reactor will approach the equilibrium composition if
the gas-solid contact time (residence time) is sufficient. The con-
tact time required will, in turn, depend on the pyrrhotite concen-
tration with the time increasing as the concentration decreases.
The contact time is determined by the gas (water) flow rate and the
concentrate bed depth. For a given experimental run, in which both
the water flow and bed volume are fixed (thus fixing the contact
time), the H-S yield will be constant as long as the gas is in
equilibrium with the concentrate. However, a point is reached in
time at which the contact time required to maintain the equilibrium
exceeds (due to the decrease in the average pyrrhotite concentra-
tion) the actual contact time and the H2$ yield drops below the
-------
-42-
equilibrium level. The HpS yield will continue to decrease until
all of the pyrrhotite is consumed. For a given experiment, the
water flow and concentrate volume will determine the length of
time the H^S yield is constant. Figure 10 shows typical steam
oxidation runs at 800°C using desulfurized Morenci concentrate.
With a small volume of concentrate and a high water flow, the H?S
yield is below the equilibrium level even at the start of the run.
For the three runs shown in Figure 10 the gas flows corresponded
to superficial gas velocities of 0.09-0.44 ft/sec at 800°C. With
the Morenci concentrate fluidization of the bed began at a superfi-
cial gas velocity of about 0.82 ft/sec (at 800°C) which corresponded
to a water flow of 6.14 g/min.
From the fixed bed experiments it is possible to calculate the
HpS yield, under various conditions, as a function of the pyrrhotite
concentration if one assumes an average pyrrhotite concentration
across the bed. This assumption is not completely valid for a fixed
bed system, but the error introduced by the assumption should not be
excessive. Figure 11 shows the results of such calculations for de-
sulfurized Morenci concentrate which was steam oxidized at 800°C.
By making a number of runs with a given concentrate at various
contact times, it is possible to estimate the contact time required
to reach the equilibrium hLS yield as a function of the pyrrhotite
concentration (process economics dictate that the ^S content of
the reactor off-gas should be a maximum, and it is necessary to know
the contact time required to reach equilibrium in order to estimate
production costs). This was done with the desulfurized Morenci con-
centrate and the results are shown in Figure 12. The estimate assumes
the pyrrhotite concentration is uniform throughout the bed. This
would be approximately true for a fluidized bed reactor, but not for
a fixed or moving bed system. Similar estimates can be made for
other reaction temperatures and concentrates, but this was not done
in the current study.
An attempt was made to determine the effect of temperature on
the kinetics of the steam oxidation reaction. The problem is com-
plicated by the fact that at reaction temperatures above 800°C a
-------
-43-
EQUILIBRIUM H-S YIELD
(EXPERIMENTALLY DETERMINED)
20 g DESULFURIZED MORENCI
0.585 g/MINUTE H20
CONTACT TIME -0.37
10 g DESULFURIZED MORENCI
0.825 g/MINUTE H20
CONTACT TIME -0.13 SECONDS
10 g DESULFURIZED MORENCI
3.12 g/MINUTE H20
CONTACT TIME -0.034
REACTION TEMPERATURE=800
100 200
REACTION TIME, MINUTES
300
FIGURE 10. H9S Yield as a Function of Reaction
TTme for a Batch Reactor
-------
-44-
0.8
THERMODYNAMIC EQUILIBRIUM
(EXPERIMENTALLY DETERMINED
CONTACT TIME=0.33 SECONDS
CONTACT TIME
0.13 SECONDS
CONTACT TIME=0.017 SECONDS
REACTION TEMPERATURE - 800"C
I I I 1
20 30 40 50
PYRRHOTITE REACTED, PERCENT
FIGURE 11. H?S Yield as a Function of the Pyrrhotite
Reacted for Various Water Flow Rates
-------
-45-
2.0
REACTION TEMPERATURE=800UC
J_
I
20 40 60 80 100
AMOUNT OF PYRRHOTITE REACTED, PERCENT
FIGURE 12. Contact Time Required to Reach the Equilibrium H
Concentration as a Function of Pyrrhotite Reacte
at 800°C
-------
-46-
substantial fraction of the pyrrhotite may be consumed in the
formation of SCL which reduces the net hLS production. Therefore,
while the experimental data show that pyrrhotite reacts more
rapidly at 900°C than at lower temperatures, the increased rate is
of no benefit because the net yield of hLS is greatly decreased at
the higher reaction temperatures. The optimum reaction temperature
for the steam oxidation reaction appears to be in the range of 700-
800°C.
Fate of Concentrate Impurities
The various concentrates contain certain impurities whose
presence must be considered in the steam oxidation process. The
impurities of interest are gold and silver (for their economic
value) and arsenic and antimony (for their potential health hazards
and detrimental effects on the process and resulting by-products
such as sulfur and iron oxide).
Arsenic and antimony are present in the concentrates as sul-
fides. These sulfides are quite volatile, however, and should be
eliminated from the concentrates during the desulfurization reaction.
Analysis of the various desulfurized concentrates showed only trace
levels of arsenic and antimony, indicating the sulfides had vola-
tilized as expected. During the desulfurization of arsenic-antimony
containing concentrates, yellow orange solids condensed as thin films
in the cold sections of the system. These solids were not analyzed,
but were found to be soluble in aqua regia as are the arsenic and
antimony sulfides.
The various concentrates studied contained up to about 11 troy
ounces of silver per ton and 0.3 oz of gold/ton. Analysis of the
desulfurized concentrates and steam oxidation residues indicated
that the gold and silver remained with the solid residue through-
out the process. This is to be expected since the gold and silver
are not volatile at the temperatures under consideration. While
exact material balances for the gold and silver were not obtained
due to analytical inaccuracies, there was no experimental evidence
to show that the gold and silver did not stay with the concentrate
residue. These analytical results were as follows:
-------
-47-
Suppl^er of Concentrate
Battle Mountain (Duval)
In Troy Ounces - Ag
Per Ton - Au
Anaconda
Weight % - As
Sb
Concentrate Desulfurized Residue After
Dry Basis Concentrate Steam Oxidation
10.79
0.31
1.86
0.037
12.3
0.39
trace
trace
12.8
0.56
trace
trace
5. Interpretation of Experimental Results
Process Limiting Factors
The objective of the steam oxidation concept is to produce H2S
from iron sulfides (pyrrhotite) without need for a specific chemical
reductant so that the H2$ can be used to react with S02 to produce
elemental sulfur. Any source of iron sulfide could be used, but
copper concentrates containing pyrite or chalcopyrite were used as
the iron source in this study. The commercial value of the steam
oxidation process would be determined by the cost of producing the
H2S.
The experimental study has shown that FLS can be produced from
pyritic copper concentrates by the steam oxidation reaction. Es-
sentially all of the iron sulfide in desulfurized concentrate can
be converted to H^S and magnetite by the reaction, while the copper
sulfide is unchanged. There are, however, several limitations to
the process which reduce its potential value.
The most serious problem concerning the steam oxidation process
is the limit placed on the hLS concentration of the off-gas leaving
the reactor by thermodynamic considerations. All of the tests show
that the H2$ concentration in the off-gas will never exceed about 1.1%.
This corresponds to a consumption of about 1.5% of the water fed to
the reactor. The low equilibrium hLS concentration of the off-gas
places severe limitations on the heat economy of the process and on
the reactor design. It means that at least 90 moles of water must
be fed to the reactor to produce one mole of H2$. Unless very high
waste heat recovery can be accomplished, the heat load required to
produce the H?S will be extremely large.
-------
-48-
The tests show the initial hLS yields increase with increasing
temperature. However, at reaction temperatures above 800°C, the
rate of SCL formation increases and much of the pyrrhotite is con-
sumed in S(L production. As a result the optimum temperature for
the steam oxidation reaction appears to be between 700 and 800°C.
At 800°C the equilibrium H~S concentration of the off-gas is only
about 0.82%, which places even more restrictions on the process.
If the steam oxidation reaction involves only the water and
pyrrhotite, the equilibrium hLS yields should be about the same
for all the desulfurized concentrates. Variations in factors such
as surface area, crystal modifications, pyrrhotite concentrations,
etc., should not affect the equilibrium hLS yield to any degree.
However, the results show that there is a significant difference
in the equilibrium H^S yields for the various concentrates (see
Table 4). This would seem to indicate that the reaction(s) which
produce the H2S is more complex than anticipated. This view is
further substantiated by the fact that the equilibrium H~S yields
are much different from those calculated on a basis of available
thermodynamic data. The one major conclusion that can be drawn from
the H2S yield data is that the mechanism(s) by which H^S is pro-
duced in the steam oxidation process is not known. The apparent
complexity of the process indicates that a time-consuming experimental
program would be required to define accurately the reaction mechanism;
however, such work should yield results useful in understanding the
process.
The rate of the steam oxidation reaction(s) appears to be quite
rapid at temperatures of 700°C and above. However, the low equilib-
rium H2S yield makes it quite difficult to take advantage of the
rapid reaction rates. At a temperature of 800°C the contact time
required to achieve the equilibrium HpS concentration is less than
3 seconds even when 90% of the pyrrhotite in the concentrate has been
reacted. As a result, any reactor design considered which is to
produce substantial quantities of H2$ will require a very large cross-
sectional area and only a small depth of concentrate. The cost of
building and operating reactors of the required cross-sectional area
-------
-49-
will make the cost of producing H2S by the steam oxidation reaction
much higher than desirable. Operation at higher temperatures does
not improve the situation due to the formation of S0~. At reaction
temperatures above 800°C a substantial fraction of the pyrrhotite
is consumed in the formation of SCL which greatly reduces the HLS
yield obtainable.
In summary, the major limitation of the steam oxidation process
is the low concentration of H,,S in the reactor off-gas. Since this
low concentration is due to thermodynamic limitations, it does not
appear possible to increase the HUS concentration without changing
the reaction(s) involved.
SECTION III
Economic Assessment of the Process Concept
In view of the rather unfavorable prospects for achieving the hydrogen
sulfide yields and concentrations desired for a likely process involving the
steam oxidation concept, it was considered unnecessary to make a detailed
economic analysis. Instead a preliminary evaluation based on a comparison
with another likely method of achieving elemental sulfur production for which
data were at hand was regarded as suitable. The following evaluation com-
pares the steam oxidation concept with the ASARCO process for very large-
(42)
scale sulfur dioxide reduction as reviewed in the A. G. McKeex report.
1. Basis
As the basis for this evaluation, an arbitrary figure of 676 tons
of sulfur (about 400 tons of copper per day) in a concentrate of a com-
position representative of Morenci material was selected (Table 3) which
on a weight basis was:
Cu 20.82%
S 36.2 %
Fe 27.3 %
Other, including moisture 6.56%
Inerts 9.12%
2. Material Balances
Assumptions
a. All sulfur was assumed to exist only as chalcocite (CU2S) and
pyrite (FeS2).
-------
-50-
b. The following principal reactions were assumed for the overall
process:
FeS2 -»• FeSj^ + 0.9 S (labile sulfur evolution durinq
neutral roasting and pyrrhotite
formation)
3 FeSul + 4 H20 -> Fe304 + 3.3 HZ$ + 0.7 \\2 (the steam oxi-
dation reaction)
2 H?S + S09 + H90 + 3 S (the Glaus reaction for elemental
d * * sulfur)
c. The equilibrium composition of gas leaving the steam oxidation step
of the process was assumed to be one mole of hUS per 99 moles of H?0.
On the basis of these assumptions, the distribution of the sulfur
from 100 tons of concentrate was calculated to be as follows:
Labile sulfur 13.95 tons
Chalcocite sulfur 5.20 -tons
Pyrrhotite sulfur 17.05 tons
In order to balance the H2S and S02 input to the Claus reaction
for elemental sulfur production, two-thirds of the sulfur remaining in
the residue after neutral roasting of the concentrate must be evolved
as H2S in the steam oxidation step. It is assumed that the sulfur re-
maining in the residue after steam oxidation would be evolved in the
converting step as S02. Therefore, the residue from the steam oxi-
dizing step would contain about 7.42% sulfur.
The results of the material balance calculations are shown in
Figure 13.
3. Major Equipment Sizing
Fluidized Beds
The total cross-sectional area of the fluidized beds needed for the
steam oxidation process was estimated to be 28,246 square feet, as
follows:
The volumetric flow rate of steam at 800°C and atmospheric pres-
sure would be 28,246 cubic feet per second.
The gas velocity needed for fluidization was taken as 1 foot per
second based on laboratory experience. Therefore, the total
-------
BASIS: PROCESSING OF 1867 SHORT TONS PER DAY OF PYRITIC COPPER CONCENTRATE
(QUANTITIES GIVEN ARE TONS/DAY EXCEPT AS NOTED)
CD
73
O> rt-
r+ O>
CD cu
-S 3
CD CL
dl QJ
— ' rt-
o> -i.
3 O
O 3
-n -s
— ' O
o o
S. fD
V)
3" in
ft)
n>
CONCENTRATE (1867)
S (676)
w/
1
1
1
S (260.5)
1
1
1
k NEUTRAL
~* ROASTING
H2S (2
, H20 (1
1 H2 <
1
STEAM
^ OXIDI Z ING
806°C
1
^ STEAM
~~w GENERATOR
1
1
D4'4) CLAUS
5430) -^CONVERTER
i T\ 270°C
?> *
S(676)
H20 (15586)
INERT GAS
(3.4xl05SCFM)
S02 (277.2)
INERT GAS (2. lx!05SCFM)
1
SMELTING
PROCESS
-------
-52-
po 246
cross-sectional area required would be -^ — - = 28,246 square feet.
The bed depth is estimated to be 2.75 feet based on the follow-
ing calculations:
The estimated time for conversion of pyrrhotite to magnetite is
900 minutes.
The amount of sulfur needed to be retained as unconverted pyrrho
tite per hundred parts of steam oxidation residue would be:
7.42-5.20 = 2.22 parts
The degree of pyrrhotite conversion in the steam oxidation step
would then be:
17.05-2.22 x 10Q = BJ%
17.05
Assuming ideal or perfect backmixing in the fluid bed, the re-
quired holdup time for conversion of the pyrrhotite in the neutral -
roasted residue to 87% is about twice the conversion time or about
1.25 days. This holdup time corresponds to about 2334 tons in the
total fluidized beds. Assuming a bulk density of 60 pounds per cubic
foot, the total bed volume would be:
2334 x 200° = 77,700 cubic feet
60
thus the average bed depth would be:
(The reference for these calculations is the book by Levenspiel (43).)
4. Capital Cost Comparison
The capital cost of the ASARCO process for 676 tons of sulfur per
day is estimated to be $49.0 million based on the following calculations:
The capital cost of ASARCO process processing feed gas containing
4 vol% S02 at a rate of 116.6 tons of sulfur/day is $12 million
(1969). Costs increase on the basis of 0.8 power of capacity.
-------
-53-
Therefore, the cost of a plant processing 676 tons of sulfur per day
would be $49.0 million (1969).
The minimum capital cost of a steam oxidation plant is $60.3
million based on the following calculations:
Forty 30-ft-diameter fluid-bed units are needed. The 1969 cost
of one unit = |Z2. (230,000) = $285,000. The installed cost of forty
t.ob
units would then be $11.4 million (1969). The heat requirement for
the 28,246 cubic feet per second of 800°C steam is 2.27 x 109 Btu/hr.
Steam-generating furnaces are assumed to produce 10^ Btu/hr each.
9OC
The estimated cost of each furnace is (360,000) or 380,000. Twenty-
three furnaces are required for steam production. The cost of twenty-
three furnaces would then be 23(380,000) or $8.7 million (1969). These
cost data are adjusted to 1969 using Marshall and Stevens cost indices.
The cost data source was a book by Dryden and Furlow. '
Thus, the minimum installed equipment cost is $20.1 million and
the total minimum plant cost is (3.0) (20.1) or $60.3 million (1969)
for the steam oxidation process. The factor (3.0) in the above calcu-
lation represents the ratio of total plant cost to equipment cost and
is used to arrive at total minimum plant cost.
5. Comparison of Fuel Plus Depreciation Cost of Process
On the basis of plant costs as estimated above and on an estimate
of fuel costs, the annual fuel and depreciation costs of the two pro-
cesses are as follows:
Millions of Dollars Per Year
ASARCO Steam Oxidation
Depreciation (Linear 15 yr) 3.27 4.02
Fuel Cost/Yr ($0.40/mil lion 4.12 7.91
Btu)
Fuel + Depreciation 7.39 11.93
6. Estimate of Lower Limit of H2S Concentration in Steam Leaving the
Oxidizer
The following calculation was made to show the minimum h^S con-
centration which would have to be attained to make the steam oxidation
-------
-54-
process competitive (or equivalent) in cost with the ASARCO process as
estimated above. Since many equipment units in parallel are assumed to
be required, the process capital and fuel costs should be proportional
to the steam throughput. To reduce the cost of the steam oxidation pro-
cess to that of the ASARCO process, the steam throughput would have to
be reduced by at least a factor of 7.39 or 0.62. To maintain the pro-
TT753"
duction rate of H?S, the mole % H?S in the steam leaving the steam
oxidation units would then have to be raised to 1 or 1.61 mole %.
In other words, if the oxidizer can be operated to produce more than
1.61% H?S in steam, the process may be as economical as the ASARCO process.
However, the ASARCO process has not been operated beyond the large
pilot-plant scale and is expected to be superceded by improved processes
'in the future. Thus the comparison is realistically even more unfavorable
than indicated here.
SECTION IV
Recommendations
In view of (1) the lack of expectations for the steam oxidation process
to provide a competitive means for sulfur dioxide air pollution abatement,
(2) the desirability of a means of producing hydrogen sulfide on a large
scale and at characteristically low cost for use in sulfur dioxide air pol-
lution abatement, (3) the encouraging possibilities of an alternative process
for such production and (4) the full utilization of existing background and
experience developed to date in this important facet of air pollution control,
the following recommendations are made:
1. Further consideration of the steam oxidation process as a means of
air pollution abatement for copper smelters under the present pro-
ject should be abandoned.
2. The scope and objective of the present study should be broadened
to cover the production of hydrogen sulfide from pyritic copper
concentrates without the use of a reductant.
3. The area of study recommended for investigation would be on a concept
involving the following combination of processes:
(a) The neutral roasting of pyritic copper concentrates.
-------
-55-
(b) The reaction of hydrochloric acid with the neutral roasted
concentrates to produce hydrogen sulfide and an enriched con-
centrate via iron dissolution and removal.
(c) The conversion of the enriched concentrates to blister copper
by conventional means thus recovering the precious metals also.
(d) The production of pure elemental sulfur by the reaction of the
hydrogen sulfide from step (b) with the sulfur dioxide from
step (c).
(e) The regeneration of the hydrochloric acid from the ferrous
chloride solution by step (b) and the concurrent recovery of
pure iron oxide for sale.
SECTION V
Identification of Additional Required Work
It is reasonably clear from the results of this present study that the
steam oxidation process concept does not provide an economical means for
sulfur dioxide air pollution abatement at copper smelters and furthermore
holds little promise for improvements in the process chemistry to assure a
more favorable view. However, this conclusion does not in any way detract
from the overall desirable objective of producing hydrogen sulfide from
pyritic copper concentrates as an attractive possibility for sulfur dioxide
air pollution abatement at copper smelters. This observation gains consid-
erable support when the rather major work being done by others to achieve
a similar result is noted. For example, the U.S. Bureau of Mines Citrate
process^ ' for elemental sulfur production from smelter flue gas involves
the reduction of a major fraction of the recovered sulfur by use of natural
gas to produce hydrogen sulfide which is essential to operation of the pro-
cess. This process is scheduled to be demonstrated on a large scale.
Similarly, the co-sponsor of this present study, The Phelps Dodge Corporation,
is also concurrently engaged in a substantial cooperative effort with others
to demonstrate an improved process for sulfur dioxide reduction with natural
gas also to yield elemental sulfur. ' Thus these two efforts which are
of considerable magnitude have two common, general features—each is directed
at the conversion of smelter waste sulfur dioxide to elemental sulfur. Al-
though each accomplishes this in different ways, the end result is achieved
by use of natural gas as the reductant. With increasing concerns about the
-------
-56-
efficient use of fuels in general and natural gas in particular, availability
and economics may dictate the use of reductants other than natural gas with
accompanying complications in the overall reduction process and processing
economics.
1. Suggested Additional Work
Continuation of the present study along the lines of an alternative
approach which will produce the required amount of hydrogen sulfide but
still without need for a chemical reductant is suggested. The work would
involve the laboratory study of the chemistry of the less familiar of
the following steps which would comprise the overall process:
(a) Neutral roasting of pyritic copper concentrates to remove
volatiles including a large portion of the sulfur as ele-
mental sulfur and to convert the iron sulfides to acid-solu-
ble forms.
(b) Acid leaching of the residue from step (1) to yield concen-
trated hydrogen sulfide gas and to separate the iron in a
soluble form.
(c) Regeneration and recovery of the acid for recycle and the con-
current production of a fairly pure iron oxide residue.
(d) Converting of the enriched insoluble copper sulfide residue
to blister copper containing the usual level of precious
metals.
(e) Reacting of the sulfur dioxide from the converting step with
the hydrogen sulfide from the leaching step to yield elemental
sulfur.
Only step (b) among the above is regarded as an area which requires
substantial laboratory study and development. All of the other steps
are regarded as near present state-of-the-art processing requiring only
a small amount of laboratory development.
The studies of the neutral roasting step as applied to a variety of
representative pyritic copper concentrates as detailed in this present
report are directly applicable to the follow-on work proposed here.
Means of copper recovery involving hydrogen sulfide production to-
gether with nearly conventional means for blister copper production with
or without subsequent electrorefining appears to have been suggested in
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-57-
(41)
the literature, ' but a detailed presentation of such a process has
not been noted. It is this area in which further efforts should be
directed. Specifically, the work should comprise a laboratory and pre-
liminary economic study of a process involving the steps as listed above.
At this time the preferred acid for hydrogen sulfide production by pref-
erential dissolution of the iron appears to be hydrochloric. Regeneration
of this acid from the corresponding ferrous chloride is already practiced
on a substantial scale in the steel pickling industry. The principal
problems to be studied would be concerned with (a) assuring the effective-
ness of both hydrogen sulfide production and preferential dissolution of
the iron, (b) development of suitable means of satisfactorily removing
or assuring the minimum carryover of copper into the iron chloride solu-
tion, (c) establish the fate of the precious metals, (d) investigation
of the response to the process of representative concentrates on the
basis of their copper mineralization: chalcocite, covellite, chalcopy-
rite, enargite, tetrahedrite, bornite, etc., (e) determine the
preliminary economics of the preferred process.
A few scouting tests have been conducted in the laboratory on the
hydrochloric acid dissolution process on desulfurized (neutral roasted)
Morenci concentrate. These tests showed that the evolution of hydrogen
sulfide is rapid and apparently fairly complete. These tests, in which
no effort was made to assure the exclusion of air, also showed that less
than 10% of the copper was dissolved with over 90% of the iron being
solubilized. A copper sulfide concentrate containing over 50% by weight
copper was obtained after removal of this iron by this simple treatment
with the hydrochloric acid. The dissolution of some of the copper is
attributed to the presence of ferric iron presumably formed by air
oxidation. It is believed that essentially all of this dissolved copper
can be reprecipitated by contacting the solution with hydrogen sulfide or
by cementation with scrap iron.
Impact on Conventional Smelting Practices
Assuming a successful outcome from the proposed research, the follow-
ing impact or significant changes would be required for adoption of the
process in place of conventional smelting processes:
-------
-58-
(a) Neutral roasting with sulfur recovery instead of oxidative
roasting would be required.
(b) Hydrogen sulfide production via the aqueous acid dissolution
of the soluble iron sulfides as produced in (a) above,
together with
(1) conversion of hLS to elemental sulfur,
(2) regeneration of the acid and recovery of fairly
pure iron oxide which should be marketable and
(3) recovery of potential dissolved copper.
(c) Reverberatory furnaces would be eliminated.
(d) Converters and the converting process would be changed to ac-
commodate the very rich and very low iron content concentrates.
(e) S0?-containing gases from the converters would be combined
with excess hLS in step (b-1) above to produce marketable
elemental sulfur.
3. Advantages
Although firm advantages cannot be claimed without confirmation
resulting from further laboratory work, some apparent significant ad-
vantages can be visualized on the assumption that hoped-for results
of the laboratory work will be realized.
(a) For those concentrates characterized by high pyrite content,
a substantial fraction of the total sulfur will be obtained
as elemental sulfur from the neutral roasting step.
(b) The hydrogen sulfide obtained in the acid dissolution of the
pyrrhotite produced in (a) above would be more than enough to
react with the sulfur dioxide obtained from the converting
step. If the quantity is marginal, it is probable that more
pyrite could be retained with the copper at the concentrator.
It is understood that most sulfide concentrators are operated
to reject pyrite which exists in the ore.
(c) The essentially iron-free copper concentrate obtained after
acid treatment and anticipated to contain over 50% copper,
would be unique as a feed to most conventional converters.
Although the converting procedure would probably be changed,
the changes could result in very high capacity from a converter,
with a greatly reduced requirement for slag-forming agents
such as silica and limestone. Electro-converting may also be
attractive with concurrent production of a rich and low-volume
sulfur dioxide off-gas.
-------
-59-
(d) No reverberatory furnaces with their high fuel and slag-forming
material requirements would be needed. At present the rever-
beratories comprise the principal source of low-strength, large-
volume sulfur dioxide-containing waste gases.
(e) Waste heat from neutral roasters and converters may contribute
substantially to the evaporation economy of the acid regenera-
tion step. The net heat (fuel) requirements for this alterna-
tive smelting process may even be less than that for a conven-
tional smelter.
(f) The lower total off-gas load and minimum concentration of waste
sulfur dioxide in these off-gases may make unnecessary the
requirement for the costly very tall stacks at smelters, with
their attendant and also costly electrostatic precipitators.
(g) The process should yield high-quality sulfur and iron oxide
by-products from which significant sales value should be realized.
-------
-60-
REFERENCES
1. Regnault, V., "Research Relative to the Action of Water Vapor on Metals
and Metal Sulfides," Annales de Chim. et de Ph.ys.. 378-88 (.1836).
2. Gautier, M. A., "Effect of Water Vapor at Red Heat on Sulfides, Formation
of Native Metal - Application to Volcanic Phenomenon," Comptes rendu,
94, 1465-70 (1906).
3. McLarty, J. A., U.S. Patent 987,156, "Treating Nickel Sulfide Ores With
Steam Under Pressure Without Roasting."
4. Hall, W. A., "A New Desulfurization Method, Eng. Mag., 4_5 876-8 (1913).
5. Wilson, A. W. G., "Hall Process for Desulfurizing Ores," Summary Report.
Mines Branch, Canada Dept. Mines, 27-30 (1913).
6. Hall, W. A., U.S. 1,083,247, "Process for the Production of Sulfureted
Hydrogen" (1913).
U.S. 1,083,248, "Process for the Extraction of Sulfur from
Metallic Sulfides" (1913).
U.S. 1,083,249, "Process for the Production of Sulfur" (1913).
U.S. 1,083,250, "Process for Recovering Sulfur" (1913).
U.S. 1,083,251, "Process of Obtaining Sulfur from Sulfides" (1913).
U.S. 1,083,252, "Process of Desulfurizing and Briquetting Ores" (1913)
U.S. 1,083,253, "Process for Extracting Sulfur" (1913).
7. Bacon, R. F., U.S. 1,235,953, "Production of Hydrogen Sulfide" (1917).
U.S. 1,731,516, "Recovery of Sulfur from Iron Pyrites" (1929).
U.S. 1,782,226, "Recovery of Sulfur from Iron Pyrites" (1930).
U.S. 1,939,033, "Recovery of Sulfur" (1933).
8. Leese, L. F. W., U.S. 1,947,529, "Sulfur Recovery from Sulfides" (1932).
9. deJahn, F. W., U.S. 2,851,349, "Obtaining Iron and Sulfur from Iron Sulfide
Ore Without Fusion" (1958).
10. Woltereck, H. C., Ger. 275,503, "A Process of Separating Zinc and Other Metals
Oxidizable by Steam."
11. Arnold, F. P. and Wideman, G. F., U.S. 1,104,239 and 1,104,287, "Removing
Sulfur and Arsenic with Alkalies and Superheated Steam."
12. Hooten, W. M., Brit. 18,007, "Treatment of Metallic Sulfides with Steam
Mixed with Other Gases."
-------
-61-
13. Perkins, W. G. , U.S. 1,478,295, "Selective Treatment of Ores Containing
Fe Pyrite with Steam."
14. Petersen, E. F. and Field, S., Brit. 206,207, "Sulfide Ores are Treated
with Steam to Recover h^S with a Limited Quantity of Air."
15. Lindemann, L., Norw. 53,577, "Freeing Ores and Oxides from Sulfur with
Hydrogen and Superheated Steam."
16. Goetz; C., Ger. 636,773 (Also Ger. 589,448) "Treatment of Sulfidic or
Arsenical Ores with Steam and a Reducing Gas."
17. Horakova, J. and Rajecky, F., Czech., 90,809, "Separating Elements from
Ores by Roasting in Steam and Inert Gases."
18. Birkeland, K. , U.S. 1,121,606, "Process for Treating Sulfid Ores and
Other Metallic Sulfids" (1914).
19. Millar, W. S., U.S. 1,567,378, "Desulfurizing Sulfide Iron Ores with
Sul fur Dioxide. "
20. Thompson, F. C. and Tilling, N., "The Desulfurization of Ores," J. Soc.
Chem. Ind., «, 27-46T (1924).
21. Ruhrmann, J., "Elimination of Sulfur from Spathic Iron Ore by Roasting,"
Stahl u. Eisen, 4£, 1118-9 (1926).
22. Grunnert, E. , "Desulfurization of Coal," J. Pract. Chem., 122, 1-120 (1929).
23. Kirillov, I. P. , and Makarov, M. M., "Preparation of H£S from Pyrite by
the Action of Water Vapor," J. Applied Chem. (USSR) ^9, 71-8 (1946).
24. Rama Murthi , R. K. , "Decomposition Studies of the Iron Pyrites of Bihar
with a View to Their Utilization," J. Indian Inst. Set., 3£, 32-5 (1954).
25. Inaba, T. and Kono, K., "Research on the Reaction of Iron Sulfides,"
J. Chem. Soc. Japan, 57_, 1-21 (1954).
26. Inaba, T., and Kono, K. , "Mechanism of Wet Roasting of Pyrrhotite,
J. Chem. Soc. Japan, 58^, 952-9 (1955).
27. Budon, V. D. , "Interaction Between Water Vapor and Metal Sulfides," Bulletin
from the Institute of Metallurgy and Enrichment, Academy of Sciences of the
Kazhak Socialist Republic, 2_, 36-46 (1960).
28. Uno, T., "Equilibrium Between FeS and Mixed Gas of H2 and I-^O," Mem. Fac.
Eng. Hokaido Univ., 9_, 84-90 (1952).
29. Diev, N. P., Paduchev, V. V., and Toporova, V. V., "Use of Steam in the
Bessemerization of Copper Mattes in Oxygen, Acad of Sci . of the Soviet
Union, Reports from Eastern Branch, 6, 79-84 (1957).
-------
-62-
30. Frey, W. H., "Production of Hydrogen Sulfide (Thermodynamics)," Chimia,
2., 265-88 (1948).
31. Park, C. F. Jr., "Hydrothermal Experiments with Copper Compounds, Econ.
Geol., 26, 857-83 (1931).
32. Kunda, W., Mackiw, V. N. and Rudyk, B., "Iron and Sulfur from Sulfidic
Iron Ores," The Canadian Mining and Metallurgical (CIM) Bulletin for
July, 1968, pp. 819-835.
33. I'iehta, B. l\. , and O'Kane, P. T./'Economics of Iron and Sulfur Recovery
from Pyrites," ibid pp. 836-845.
34. Graves, J. T., and Heath, T. D., "Sulfur Dioxide and Sulfur from Fluosolids
Systems," presented at a meeting of the American Institute of Mining,
Hetal1urgical and Petroleum Engineers in Los Angeles, Calif., Feb. 2, 1967.
Technical Preprint No. 7008-P by Dorr-Oliver Incorporated.
35. Kassila, K., "Flash Smelting Process," a paper presented at the "Seminar
on Copper Production and Group Study Tour of Copper Plants in the USSR,"
Tashkent, USSR 1-15 October, 1970, United Nations Industrial Development
Organization.
36. Guccione, E., "From Pyrite: Iron Ore and Sulfur Via Flash Smelting,"
Chemical Engineering, Feb. 14, (1966), pp. 122-24.
37. Rosenqvist, T., J. Iron Steel Inst.. 175, pp. 37-56 (1954).
38. Rosenqvist, T., "Thermochemical Data for Metallurgists," Tapir Forlag (1970).
39. Rosenbaum, J. B. et. al., U.S. Bureau of Mines Report of Investigations
(RI-7774), "Sulfur Dioxide Emission Control by Hydrogen Sulfide Reaction
in Aqueous Solution—the Citrate System," 1973.
40. Henderson, J. M., "Reduction of SO, to Sulfur," Mining Congress Journal,
March 1973, pages 59-62. L
41. Levy, S. I., U.S. Patents 1746313 (1930), "Treatment of Copper-Rich
Material," and 1980809 (1934), "Production of Ferric Oxide and Other
Metal Values from Pyrites."
42. PB-184885, "Systems Study for Control of Emissions—Primary Non-Ferrous
Smelting Industry—Volume II," Arther 6. McKee & Co., June 1969.
43. Levenspiel, 0., "Chemical Reaction Engineering," John Wiley and Sons,
Inc., (1962), page 367.
44. Dryden & Furlow, "Chemical Engineering Costs," (1966).
-------
-63-
APPENDIX
WORLD PRIMARY COPPER SMELTERS AND SMELTING CAPACITY
-------
WORLD PRIMARY COPPER SMELTING CAPACITY
COUNTRY
EUROPE
Austria
Belgium
Bulgaria
Finland
France
Germany F.R.
Italy
Netherlands
Norway .
Rumania
Spain
Sweden
Yugoslavia
COMPANY
Montanwerke BMxlegg G.m.b.h.
Metal lurgle Hoboken
Metallo-Chimique S.A.
George Damijanov Copper
Medet Copper Works
Outokumpu Oy
Societe Francais d/Affinage du Culvre
Norddeutsche Affinerie
Berliner Kupfer-Raffin G.m.b.H.
Duisburger Kupferhutte
Metallhutte Kail G.m.b.H.
Huttenwerke Kayser A.G.
AMMI
Alcu Metaal N.V.
Orkla Metal Aktieselskap
A/S Sulitjelma Gruber
Combinatul Chimico
Metallurgic "Georghin Dej"
Rio Tinto Patino S.A.
Rio Tinto Patino S.A.
Electrolysis del Cobre S.A.
Industrie Reunidas Minera-
Metalurgicas S.A.
Boliden Aktiebolag
Rudarsko Tapionicarsk Bazen Bor
SMELTER
Brixlegg
Hoboken
Beerse
Harjavalta
Polssy
Hamburg
Berlin-WUlmersdorf
Duisburg
Kail (Eifel)
Lunen
Aussa-Corno
Thamshamm
Sulitjelma
Bor
Bara Mare
Huelva
Rio Tinto
Barcelona
Asua
Ronnskar
Bor
1971 CAPACITY
(METRIC TONS)
12,000
45,000
25,000
20,000
50,000
11,000
75,000
15,000
30,000
20,000
42,000
10,000
4,000
6,000
40,000
18,000
15,000
18,000
65,000
105,000
POTENTIAL
CAPACITY
(METRIC TONS)* DATE
18,000
100,000
60,000
200,000
75,000
1975
1972
1975
n.a.
1972-73
i
CT>
-P.
140,000
1974
TOTAL
643,000
-------
USSR
Government
1965 CAPACITY
(METRIC TONS)
Pechenga 12,000
(Kola Peninsula)
Monchegorsk 11,000
(Kola Peninsula)
Munusinsk 50,000
(Central Siberia)
Pitkaryanta 10,000
(Karelo-Finnish Republic)
Mednogorsk (Urals) 55,000
Balkhash (Kajakhatan) 125,000
Dzezhkazgan-Karsakpai 200,000
Combine (Kazakhsdan)
Almalyk (Uzbekistan) 100,000
Norilsk 5,000
(North Central Siberia)
Srednyevralsk (Urals) 50,000
Krasnovralsk (Urals) 45,000
Kirovgrad (Urals) 25,000
Yuspenskiy (Kazakhstan) 5,000
Karabash (Urals) 30,000
Blyava (Urals) 50,000
Sibay (Urals) 25,000
Kadzharan (Azerbaldzhan) 25,000
Zangezur (Azerbaidzhan) 10,000
Allaverdi (Armenia) 15,000
100,000
300,000
i
en
en
i
TOTAL
848,000
1,085,000** (1971)
1,389,000**
1977
-------
AFRICA
Rhodesia
S. African Rep.
S. W. Africa
Uganda
Zaire
Zambia
Messina-Rhodesia Smelting &
Refining Co., Ltd.
Messina Transvaal Development Co.
Palabora Mining Co., Ltd.
O'OKiep Copper Co., Ltd.
Tsumeb Corporation, Ltd.
Kilembe Mines Ltd.
Gecamines
Gecamines
Gecamines
Roan Consolidated Mines
Roan Consolidated Mines
NCCM (Nchanga Consolidated Copper
NCCM Mines)
Alaska
23,000
Messina
Palabora
Nababeep
Tsumeb
Jinja
Likasi-Shituru
Lubumbashi
Liulu
Mufulira
Luanshya
Chingola\
N'Kana [
20,000
89 ,500
40,000
35,000
18,000
185,000
125,000
125,000
230,000
122,000
420,000
170,000
155,000
247,001
500,000
1972
1973
1973
1974-75
TOTAL
1,432,500
01
i
ASIA
India
Iran
Japan
Indian Copper Corp.
Hindustan Copper Corp.
Hindustan Copper Corp.
Government
Mitsubishi Metal Mining (2 p
Onahama Smelting & Refining
Furukawa Mining Co.
Dowa Mining Co.
Dowa Mining Co.
Hibikyodp Smelting Co.
Mitsui Mining Co.
Nippon Mining Co.
Nippon Mining Co.
Sumitomo Metal Mining Co.
Sumitomo Metal Mining Co.
Sumitomo Metal Mining Co.
Rasa Industry.
Toho Zinc
Moubhander
Khetri
Ingladhal
Sar Chesmeh
Naoshima
Onahama
Ashio
Kosaka 1
OkayamaJ
Tawanao
Hibi
Hitachi
Saganosekl
Kuni tomi
Besshi
Toyo
Miyaki
Onahama
10,000
146,000
90,000
38,000
54,000
47,000
60,000
120,000
16,000
108,000
96,000
24,000
18,000
31,000
n.a.
n.a.
288,000
84,000
120,000
240,000
1974
n.a.
n.a.
n.a.
1972
1972
n.a.
-------
Korea S.
Philippine Republic
Turkey
Government
Government
Etibank
Etibank
Black Sea Copper Mines
Musan
Murgul
Erganl
Samsun
TOTAL
11,000
19,000
857,000
15,000
60-100,000
n.a.
1974
n.a.
NORTH/CENTRAL AMERICA
Canada
Mexico
Puerto R1co
U.S.A.
Inco
Inco
Falconbridge Nickel Mines, Ltd.
Gaspe Copper Mines, Ltd.
Hudson Bay Mining & Smelting Co.,Ltd.
Noranda Mines, Ltd.
Asarco Mexicana S.A.
Asarco Mexicana S.A.
Campania Minera de Cananea S.A.
Cia Minera Macocozac S.A.
Cia Minera de Santa Rosalia
Ponce Mining (Kennecott-Arnax)
American Metal Climax, Inc.
Asarco
Asarco
Asarco
Anaconda
Inspiration Consolidated
Kennecott Copper Corp.
Kennecott Copper Corp.
Kennecott Copper Corp.
Kennecott Copper Corp.
Magma
Phelps Dodge
Phelps Dodge
Phelps Dodge
Phelps Dodge
Copper Range
Bagdad (electrowinning)
Copper CUff j
Coniston J
Falconbridge (Ont.)
Murdochville (Que.)
Flin Flon
Noranda (Que.)
San Luis Potosi
La Cavidad
Cananea
Conception del Oro
Santa Rosalia
Ponce
Cartaret
Tacoma
El Paso
Hayden
Anaconda
Miami
Garfield (Utah)
Hurley (Chino)
McGill (Nev.)
Hayden (Ray)
San Manuel
Douglas
Morenci
Ajo
Southern Hidalgo
White Pine
Arizona
TOTAL
170,000
30,000
63,000
45,000
204,000
30,000
37,000
25,000
10,000
40,000
105,000
77,000
80 ,000
170,000
70,000
300,000
100,000
100,000
100,000
85,000
140,000
80,000
70,000
81,000
6,500
2,218,500
200,000
254,000
42,000
n'.a.
n.a.
135,000
91,000?
1974-75
1973-74
n.a.
n.a.
n.a.
1974
1974
-------
SOUTH AMERICA
Brazil
Chile
Peru
AUSTRALIA
Plgnatari Group
Pignatari Group
Andes Copper Mining Co.
Chile Exploration
Sociedad Minera El Teniente S.A.
Cia Minera Disputada de las Condes
S.A.
ENAMI
ENAMI
Mantos Blancos
Southern Peru Copper Corp.
Cerro de Pasco Corp.
Mt. Isa Mines, Ltd.
Electrolytic Refining & Smelting Co.
Peko
Caraiba
Caraiba
Potrerillos
Chuquicamata
Caletones
Chagres
Las Ventanas
Paipote
Mantos Blancos
Ilo
La Oroya
---•
100,000
319,000
Z55.000
30 ,000
43,000
33,000
30,000
160,000
50,000
TOTAL
TOTAL
GRAND TOTAL 1971
GRAND TOTAL 1977
1,020,000
35,000
70,000
100,000
n.a.
1973?
1976?
n.a.
n.a.
Mt. Isa
Port Kembb
Tennant Creek
100,000
40,000
— v_ —
150,000
25,400
1974
1972
OO
I
140,000
7,369,100
8,899,800 (1,530,700 increase) = >21% increase
in next 6 yr =. 3.5%/yr growth
* For major increases
** Assumes 4%/yr increase in capacity from 1965 to 1977
Data are obtained from the following sources:
(1) Survey of Free World Increases in Copper Mine, Smelter and Refinery Capacities 1971-1977, International Wrought Copper
Council, April 1972.
(2) Nonferrous Metal Works of the World, First Edition 1967, H. G. Cordero, Editor.
(3) A. D. McMahon, Copper—A Materials Survey, U. S. Dept. of the,Interior, Bureau of Mines IC-8225, 1965.
(4) Metal Statistics 1971, 64th Annual Edition, The American Metal Market Co.
(5) Yearbook of the American Bureau of Metal Statistics, 50th Annual Issue for the year 1970, Issued June 1971.
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
i. REPORT NO.
.
EPA-650/2-74-085-a
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE Control of ^^^ Dioxide Emissions
from Copper Smelters; Volume I--Steam Oxidation of
Pyritic Copper Concentrates
5. REPORT DATE
September 1974
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
C. A.Rohrmann, H.T.Fullam, and F. P.Roberts
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORONIZATION NAME AND ADDRESS
Battelle Pacific Northwest Laboratories
Battelle Boulevard
Richland, Washington 99352
10. PROGRAM ELEMENT NO.
1AB013; ROAP 21ADC-056
11. CONTRACT/GRANT NO.
68-02-0025
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
NERC-RTP, Control Systems Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 6/71-7/72
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
is. ABSTRACT The report presents results of a laboratory study on production of hydrogen
sulfide by reaction between water vapor at 700-800°C and iron sulfide contained in
neutral-roasted pyritic copper ore concentrate. Hydrogen sulfide thus obtained was
to be reacted with sulfur dioxide emitted from copper smelter converters. In this
manner sulfur emissions from a smelter could be controlled and recovered in the
form of elemental sulfur. It was determined that the above treatment of copper ore
concentrate could yield necessary quantities of hydrogen sulfide. The concentration
of yielded hydrogen sulfide, however, was limited in the stream to less than 1.0 per-
cent by reaction equilibrium conditions, thus implying excessively high energy
requirements and causing this control approach to be significantly more expensive
than known conventional processes. Alternative means of hydrogen sulfide production
are dealt with in the second volume of the report.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Air Pollution
Sulfur Dioxide
Copper Ores
Smelters
Smelting
Hydrogen Sulfide
Air Pollution Control
Stationary Sources
Steam Oxidation
Pyritic Copper
13B
07B
11F
13H
8. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
74
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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