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US006497745B2
(12) United States Patent
Marsden et al.
(10) Patent No.:
(45) Date of Patent:
US 6,497,745 B2
Dec. 24,2002
OTHER PUBLICATIONS
(54) METHOD FOR PROCESSING ELEMENTAL FOREIGN PATENT DOCUMENTS
SULFUR-BEARING MATERIALS USING
HIGH TEMPERATURE PRESSURE
LEACHING
AU 0219785 12/1958
Assignee: Phelps Dodge Corporation, Phoenix,
AZ (US)
Inventors: John O. Marsden, Phoenix, AZ (US);
Robert E. Brewer, Safford, AZ (US);
Joanna M. Robertson, Thatcher, AZ
(US); Wayne W. Hazen, Lakewood,
CO (US); Philip Thompson, West
Valley City, UT (US); David R.
Baughman, Golden, CO (US)
(75)
(73)
( * ) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 0 days.
Evans, et aI., "International Symposium of Hydrometallurgy,"
Mar. 1, 1973, 2 pages.
Duyesteyn, et aI., "The Escondida Process for Copper Concentrates,"
1998 No Month.
King, et aI., "The Total Pressure Oxidation of Copper
Concentrates," 1993 No Month.
King, J. A., "Autoclaving of Copper Concentrates," paper
from COPPER 95, vol. III: Electrorefining and Hydrometallurgy
of Copper, International Conference held in Santiago,
Chile, Nov. 1995.
Mackis, V. N., "Direct Acid Pressure Leaching of Chalcocite
Concentrate," vol. 19, No.2, Feb. 1967.
(List continued on next page.)
Primary Examiner-Roy King
Assistant Examiner-Tima McGuthry-Banks
(74) Attorney, Agent, or Firm---8nell & Wilmer L.L.P.
(21)
(22)
(65)
Appl. No.: 09/912,945
Filed: Jul. 25, 2001
Prior Publication Data (57) ABSTRACT
U.S. PATENT DOCUMENTS
US 2002/0033076 A1 Mar. 21, 2002
References Cited
Related U.S. Application Data
Provisional application No. 60/220,677, filed on Jul. 25,
2000.
Int. CI? . ... ... ..... ... ... .... C22B 3/08
U.S. Cl. 75/743; 75/744; 423/27;
423/658.5
Field of Search 75/743, 744; 423/658.5,
423/27
The present invention relates generally to a process for the
production of sulfuric acid and liberation of precious metal
values from materials containing sulfur through pressure
leaching operations. In accordance with various aspects of
the present invention, the sulfur-bearing materials may comprise
residues from pressure leaching operations, such as
those carried out at medium temperatures. The process of the
present invention can be advantageously used to convert
such sulfur-bearing materials to sulfuric acid by means of
pressure leaching. The sulfuric acid so produced can be used
beneficially in other mineral processing operations, for
example those at the site where it is produced. Metals, such
as precious metals, that are contained within the sulfurbearing
materials advantageously may be recovered from
processing products by established precious metals recovery
technology.
3/1917 Farup
1/1940 Walthall
7/1966 Zimmerley et al.
1,219,277 A
2,188,324 A
3,260,593 A
(56)
(60)
(51)
(52)
(58)
(List continued on next page.) 18 Claims, 2 Drawing Sheets
02
102
12 ELEMENTAL SULFUR 14
\ ! H2O
1 1 16
104
PRESSURE OXIDATION . ! DISPERSING AGE
18 PRECIOUS
106 ""- LIQUID-SOLID ) METAL
PHASE SEPARATION RECOVERY
(FIG. 2)
108 \
SULFURIC ACID SOLUTION 200
NT
US 6,497,745 B2
Page 2
U.S. PATENT DOCUMENTS Fuller et al.
Duyvesteyn et al.
Schoubye
Jones
Jones 423/24
Alvarez et al.
Brandle et al.
Peng
Virnig et al.
King
Morisaki
Collins et al. 423/27
Klotz
Collins et al.
Allen et al.
King
Jones
Johnson et al.
Seitz et al.
12/1991
1/1993
3/1993
6/1993
5/1994
10/1994
2/1995
1/1997
9/1997
12/1997
1/1998
3/1998
3/1998
6/1998
12/1998
4/1999
5/1999
6/1999
11/2000
5,073,354 A
5,176,802 A
5,198,206 A
5,223,024 A
5,316,567 A *
5,356,457 A
5,389,354 A
5,593,652 A
5,670,035 A
5,698,170 A
5,711,928 A
5,730,776 A *
5,730,950 A
5,770,170 A
5,849,172 A
5,895,633 A
5,902,474 A
5,917,116 A
6,153,168 A
OTHER PUBLICATIONS
* cited by examiner
Hirsch, H. E., "Leaching of Metal Sulphides," Patents, UK,
No. 1,598,454, 1981, 7 pages, No Month.
Chimielewski, T., "Pressure Leaching of a Sulphide Copper
Concentrate with Simultaneous Regeneration of the Leaching
Agent," Hydrometallurgy, vol. 13, No.1, 1984, pp.
63-72.
Dannenberg, R. 0., "Recovery of Cobalt and Copper From
Complex Sulfide Concentrates," Government Report, 20
pages, Report No. BM RI 9138, U.S. Dept. of the Interior,
1987 No Month.
Berezowsky, R.M.G.S., "The Commercial Status of Pressure
Leaching Technology," JOM, vol. 43, No.2, 1991, pp.
9-15 No Month.
Hacki, R. P, "Effect of Sulfur-Dispersing Surfactants on the
Oxygen Pressure Leaching of Chalcopyrite," paper from
COPPER 95, vol. III, pp. 559-577, Met Soc of CIM, Nov.
1995.
Hackl, R.P, "Passivation of Chalcopyrite During Oxidative
Leaching in Sulfate Media," Hydrometallurgy, vol. 39,
1995, pp. 25-48 No Month.
Jim A. King, et aI., paper entitled: "The Total Pressure
Oxidation of Copper Concentrates," vol. I, Fundamental
Aspects, 1993 No Month.
Dreisinger, D. B., "Total Pressure Oxidation of EI Indio Ore
and Concentrate," COPPER 1999, Fourth International Conference,
Phoenix, Arizona, USA, Oct. 1999.
Richmond, G. D., "The Commissioning and Operation of a
Copper Sulphide Pressure Oxidation Leach Process at Mt.
Gordon," ALTA COPPER 1999: Copper Sulphides Symposium
& Copper Hydrometallurgy Forum, Gold Coast,
Queensland, Australia Conference, 1999 No Month.
L.W. Beckstead, et aI., "Acid Ferric Sulfate Leaching of
Attritor-Ground Chalcopyrite Concentrate," vol. II, Extractive
Metallurgy of Copper, Chapter 31, pp. 611-632, Published
by American Institute of Mining, Metallurgical, and
Petroleum Engineers, Inc. in 1976.
Green
Mackiw et al.
Barry et al.
Spedden et al.
Lindblad et al.
Dubeck et al.
Fisher et al. 205/584
Pawlek et al.
Anderson
Parker et al.
Touro
Kunda et al.
Queneau et al.
Novozhilov et al.
Johnson
Ackerley et al.
Domic et al.
Faugeras et al.
Dorr et al.
Wong
Subramanian et al.
Kinoshita
Wong
Riggs et al.
Blanco et al. 205/584
Fountain et al.
Ryabenko et al.
Vaseen
Dain
Weir et al.
Reynolds
Stoddard et al.
Kerner et al.
Cameron et al.
Beczek et al.
Redondo-Abad et al.
Lamb
Dorr et al.
Stanley et al.
Dienstbach
Wilkomirsky et al.
Baglin et al.
Kordosky et al.
Felix et al.
Ditmar et al.
Weir et al.
Weir et al.
Cameron et al.
Cameron
Weir
Salter et al.
Daley
Horton et al.
Lin et al.
Gross et al.
Horton et al.
Horton
Lin et al.
Sawyer et al.
Lin et al.
Lin et al.
Chen
9/1970
1/1972
4/1972
6/1972
2/1975
7/1975
* 11/1975
4/1976
5/1976
6/1976
6/1976
10/1976
11/1976
2/1977
4/1977
4/1977
6/1977
6/1977
6/1977
8/1977
9/1977
11/1977
1/1978
5/1978
6/1978
10/1978
11/1978
2/1979
4/1979
6/1979
8/1979
12/1979
7/1980
7/1980
3/1981
5/1981
6/1981
6/1982
7/1982
9/1983
11/1983
4/1984
3/1985
7/1985
8/1985
2/1986
2/1986
5/1986
5/1986
8/1986
10/1986
2/1987
10/1988
3/1989
10/1989
11/1989
1/1990
1/1990
11/1990
2/1991
7/1991
10/1991
3,528,784 A
3,637,371 A
3,656,888 A
3,669,651 A
3,868,440 A
3,896,208 A
3,917,519 A
3,949,051 A
3,958,985 A
3,961,028 A
3,962,402 A
3,985,553 A
3,991,159 A
4,009,250 A
4,017,309 A
4,020,106 A
4,028,462 A
4,029,733 A
4,029,751 A
4,039,405 A
4,046,851 A
4,057,423 A
4,069,119 A
4,091,070 A
4,093,526 A *
4,120,935 A
4,125,596 A
4,139,596 A
4,150,976 A
4,157,912 A
4,165,362 A
4,178,357 A
4,212,855 A
4,213,958 A
4,256,553 A
4,266,972 A
4,272,341 A
4,333,917 A
4,338,168 A
4,405,569 A
4,415,540 A
4,442,072 A
4,507,268 A
4,526,768 A
4,533,537 A
4,571,263 A
4,571,264 A
4,591,494 A
4,591,495 A
4,605,439 A
4,619,814 A
4,643,887 A
4,775,413 A
4,814,007 A
4,875,935 A
4,880,607 A
4,892,715 A
4,895,597 A
4,971,662 A
4,992,200 A
5,028,259 A
5,059,403 A
u.s. Patent Dec. 24,2002 Sheet 1 of 2 US 6,497,745 B2
102
12 ELEMENTAL SULFUR 14
\ ! H2O 1 1 16
104 PRESSURE OXIDATION / DISPERSING AGE ..
18
PRECIOUS
106 "- LIQUID-SOLID ; METAL
PHASE SEPARATION RECOVERY
(FIG. 2)
108 \
SULFURIC ACID SOLUTION 200
NT
FIG. 1
90
100.,---------------
o
(j)
E
Ol
o
L()
0::: o
LL
....J «u
.E:;
0::: o
LU :r:
lLL
o
80
70
60
50
32
....../ ...i 34
....
cr
40
250 260
~
TO 160C, 0.7% YIELD, 15% SANDS
30 +----+-----j
200 210 220 230 240
AUTOCLAVE TEMPERATURE" DEG. C
6
....J
LU
>=
o
u«
........-0- ......... 5% SULFUR IN REACTOR ----..,:)-- 5% SULFUR, 5% SANDS IN REACTOR
FIG. 3
u.s. Patent Dec. 24,2002 Sheet 2 of 2 US 6,497,745 B2
206
204
212
214
210
208
202
106 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - I
I I ) I
I 18
LIQUID-SOLID II /
PHASE
SEPARATION NEUTRALIZATION & r
pH ADJUSTMENT
I HOT LIME BOIL r
I (OPTIONAL.) I
I
I
I
I I 1
I
I PRECIOUS METALS V CYANIDE LEACHING
PRECIOUS METALS r
RECOVERY
(LIQUID) LIQUID-SOLID PHASE
I SEPARATION I
I
I
I - - - - - - - - - - - -
I
I
I 200~ CYANIDE r
I DESTRUCTION
I
I
I
I ~- - - - - - - - - - - - -
I
I I TAILINGS r
I DISPOSAL. I
I
II
_
FIG. 2
US 6,497,745 B2
1
METHOD FOR PROCESSING ELEMENTAL
SULFUR-BEARING MATERIALS USING
HIGH TEMPERATURE PRESSURE
LEACHING
CROSS-REFERENCE TO RELATED
APPLICATIONS
This application claims priority to u.s. Provisional Patent
Application, Serial No. 60/220,677 entitled "Methods for
Conversion of Sulfur-bearing Material to Sulfuric Acid and
Recovery of Associated Metals by High Temperature Pressure
Oxidation" filed on Jul. 25, 2000, which is incorporated
by reference herein.
FIELD OF THE INVENTION
The present invention relates generally to a process for
manufacturing sulfuric acid, and more specifically, to a
process for manufacturing relatively dilute sulfuric acid
from sulfur-bearing materials using high temperature pressure
leaching processes and recovering metal values from
the sulfur-bearing materials.
BACKGROUND OF THE INVENTION
Hydrometallurgical treatment of copper containing
materials, such as copper ores, concentrates, and the like,
has been well established for many years. Currently, there
exist many creative approaches to the hydrometallurgical
treatment of these materials. The recovery of copper from
copper sulfide concentrates using pressure leaching promises
to be particularly advantageous.
The mechanism by which pressure leaching releases
copper from a sulfide mineral matrix, such as chalcopyrite,
is generally dependent on temperature, oxygen availability,
and process chemistry. In high temperature pressure
leaching, typically thought of as being pressure leaching at
temperatures above about 2000 c., the dominant leaching
reaction in dilute slurries may be written as follows:
(1)
During pressure leaching of copper sulfide concentrates,
such as chalcopyrite containing concentrates at medium
temperatures (e.g., at temperatures in the range of between
about 1400 C. to about 1800 C.), however, a significant
fraction of the sulfide converts to elemental sulfur (SO) rather
than sulfate (SO4-2). According to the reaction:
For example, experimental results show that at about 1600
C. and about 100 psi oxygen overpressure in the pressure
leaching vessel, from about 60 to about 70 percent of the
sulfur in the super-finely ground copper sulfide concentrate
is converted to elemental sulfur, with the remainder being
converted to sulfate.
Elemental sulfur is a hydrophobic substance. In the pressure
leaching process slurry, under certain temperature and
solution conditions, sulfur has a tendency to agglomerate.
Moreover, molten elemental sulfur becomes highly viscous
us at elevated temperatures. For example, the viscosity of
molten sulfur increases from less than 100 centipoise at 1500
C. to more than 90,000 centipoise at 1850 C. As such, the
molten sulfur may tend to encapsulate metal values in the
process slurry, including precious metals and unreacted
2
metal sulfides, and/or stick to various parts of any apparatus
in which processing operations on the molten sulfur are
performed. Encapsulation of the metal values, for example,
copper, precious metals and the like, tends to make subse-
5 quent recovery of such metal values extremely difficult
using conventional processing techniques. As discussed in
applicant's co-pending application entitled "Method for
Recovery of Metals From Metal Containing Materials Using
Medium Temperature Pressure Leaching" filed Jul. 25, 2001
10 and assigned U.S. Ser. No. 09/915,105, the subject matter of
which is hereby incorporated herein by reference, while
pressure leaching under medium temperature conditions
offers many advantages, prior medium temperature pressure
leaching processes characteristically have suffered from
15 incomplete metal (e.g., copper) extraction resulting from
either passivation of the metal sulfide particle surfaces or by
the metal sulfide particles becoming coated with molten
elemental sulfur. As discussed in greater detail in applicant's
co-pending application, proper control of such pressure
20 leaching processes, as described therein, enables the formation
of elemental sulfur in addition to the desired metal
recovery (e.g. copper). However, recovery of metal values
that may be contained in the elemental sulfur-containing
residue, such as, for example, precious metals, may be
25 difficult with use of conventional techniques, and as such
they may be lost. Moreover, if the acid produced by such
processing techniques could not be used at the site where the
recovery was performed, costs would be incurred in connection
with transportation of the residue or handling of the
30 acid. An effective and efficient method to manufacture
sulfuric acid from sulfur-bearing material, particularly
elemental sulfur-containing residue resulting from pressure
leaching operations operated at medium temperatures (e.g.,
about 1400 C. to about 1800 C.) is needed. Moreover, an
35 effective and efficient method to enhance recovery of any
metal values encapsulated within the sulfur-bearing material
would be advantageous.
SUMMARY OF THE INVENTION
40 While the way in which the present invention addresses
the deficiencies and disadvantages of the prior art is
described in greater detail hereinbelow, in general, according
to various aspects of the present invention, a process for
manufacturing sulfuric acid includes pressure leaching of
45 sulfur-bearing materials, preferably at high temperatures,
not only to facilitate the recovery of a sulfuric acid solution,
but also to enhance recovery of metal values contained in the
sulfur-bearing materials. The acid produced, preferably a
relatively dilute sulfuric acid solution advantageously can be
50 used in other metal extraction processes, often with significant
cost savings.
As will be described in greater detail hereinbelow, the
methods and processes of the present invention are particularly
suited for use in connection with sulfur-bearing mate55
rials comprising residues from pressure leaching operations,
such as, for example, those operated at medium temperatures
(e.g., about 1400 to about 1800 C.).
In accordance with an exemplary embodiment of the
present invention, a process for manufacturing sulfuric acid
60 from sulfur-bearing materials generally includes the steps
of: (i) providing a feed stream containing a sulfur-bearing
material, and (ii) subjecting the sulfur-bearing material feed
stream to high temperature pressure leaching in a pressure
leaching vessel, optionally in the presence of a suitable
65 dispersing agent. In accordance with a preferred aspect of
this embodiment of the invention, the sulfur-bearing material
feed stream comprises residue from medium temperaUS
6,497,745 B2
3 4
Further, as those skilled in the art will appreciate, this
reaction may proceed more completely as temperature is
increased. In addition, where the sulfur-bearing material
feed 102 comprises hematite and/or other iron-bearing
30
material generated as a by-product of other metal recovery
processes, materials containing iron sulfides, copper sulfides
and/or other metal sulfides, or any combination of these. In
addition, the term "sulfur-bearing material" refers to other
5 sulfur compositions that may include sulfur together with
any other sulfides and/or metals that might be attendant to or
part of such sulfur compositions. For purposes of this
disclosure, in most instances, the term "elemental sulfur,"
for example as that term is used in FIG. 1, is used inter-
10 changeably with the term "sulfur-bearing material," inasmuch
as, as will be clear from the following disclosure, the
elemental sulfur and sulfide sulfur components of any
sulfur-bearing material 102 are advantageously converted to
sulfuric acid in accordance with the present invention.
In accordance with one aspect of a preferred embodiment
of the present invention, sulfur-bearing material feed stream
102 preferably comprises the sulfur-containing residue produced
in connection with the pressure leaching of coppercontaining
material feed streams. As explained in greater
20 detail in Applicant's co-pending application, U.S. Ser. No.
09/915,105, such copper-containing materials include copper
sulfide ores, such as, for example, ores and/or concentrates
containing chalcopyrite (CuFeS2 ) or mixtures of chalcopyrite
with one or more of chalcocite (Cu2S), bornite
25 (CusFeS4), and covellite (CuS). The sulfur-containing residues
that result from the pressure leaching of such coppercontaining
material feed streams may advantageously be
processed in accordance with the various aspects of the
present invention.
Sulfur-bearing material feed stream 102 may be prepared
for processing in any suitable manner. For example, desired
composition and/or component parameters can be achieved
through a variety of chemical and/or physical processing
35 stages, the choice of which will depend upon the operating
parameters of the chosen processing scheme, equipment cost
and material specifications. For example, feed stream 102
may undergo comminution, blending, and/or slurry
formation, as well as chemical and/or physical conditioning.
40 Such preparation efforts may include, for example, sulfurbearing
material feed stream 102 being combined with
solution, for example, pregnant leach solution (PLS) or
barren raffinate solution from an existing acid heap leaching
operation or an agitated tank leaching operation, in a repulp
45 process to produce a slurry.
With continued referenced to FIG. 1, preferably sulfurbearing
material feed stream 102 (or slurry) is suitably
combined with a fluid 14, preferably water, and suitable
amounts of an oxygenating supply, for example, oxygen 12,
50 optionally with one or more dispersing agents 16 to facilitate
pressure leaching (step 104) of sulfur-bearing material feed
stream 102. In accordance with one aspect of the present
invention, the feed slurry containing sulfur-bearing material
102 may be formed in any suitable mixing vessel or by
55 in-line blending. Other additives, such as wetting agents or
the like, for example, lignosulfonates, may also be used.
As those skilled in the art will understand, elemental
sulfur is optimally oxidized to sulfuric acid according to the
following reaction:
DETAILED DESCRIPTION OF AN
EXEMPLARY EMBODIMENT OF THE
INVENTION
BRIEF DESCRIPTION OF IRE DRAWING
The subject matter of the present invention is particularly
pointed out and distinctly claimed in the concluding portion
of the specification. A more complete understanding of the
present invention, however, may best be obtained by referring
to the detailed description and claims when considered
in connection with the drawing figures, wherein like numerals
denote like elements and wherein:
FIG. 1 illustrates a flow diagram of a process in accordance
with an exemplary embodiment of the present invention;
FIG. 2 illustrates a flow diagram of further processing in
accordance with the embodiment of the present invention
illustrated in FIG. 1; and,
FIG. 3 illustrates a graphical profile of sulfuric acid yield
versus temperature in accordance with various embodiments
of the present invention.
The present invention exhibits significant advancements
over prior art processes, particularly with regard to process
efficiency and process economics. Moreover, existing metal
(e.g., copper) recovery processes that utilize conventional
atmospheric or pressure leaching/solvent extraction/
electrowinning process sequences may, in many instances,
be easily retrofitted to exploit the many commercial benefits 60
the present invention provides.
Referring now to FIG. 1, in accordance with various
aspects of one embodiment of the present invention, a
sulfuric acid production process preferably involves providing
a sufficient supply of a sulfur-bearing material 102. In 65
the context of the present invention, the term "sulfur-bearing
material" refers to elemental sulfur, elemental sulfur-bearing
ture pressure leaching of a copper sulfide mineral, such as
chalcopyrite or a blend of that residue combined with
elemental sulfur. In accordance with a further preferred
aspect of this embodiment of the invention, the use of a
dispersing agent during pressure leaching may aid in alleviating
processing problems caused by the high viscosity
and hydrophobic nature of elemental sulfur at higher temperatures
(e.g., above about 1600 C.
In accordance with a further aspect of this embodiment of
the present invention, metal values contained in the sulfurbearing
material feed stream are liberated from the elemental
sulfur residue during pressure leaching, during which the
elemental sulfur is converted to sulfuric acid, and then
separated from the resultant acid stream and subjected to
metal recovery processing. Such metal recovery processing 15
may include precious metal recovery.
The present inventors have advanced the art of copper
hydrometallurgy by recognizing the advantages of not only
producing a sulfuric acid solution from sulfur-bearing
materials, such as the elemental sulfur by-product of
medium temperature pressure leaching of copper sulfide
minerals, but also of enabling the recovery of metal values
(e.g., precious metals) entrained therein, which otherwise
may have been lost.
These and other advantages of a process according to
various aspects of the present invention will be apparent to
those skilled in the art upon reading and understanding the
following detailed description with reference to the accompanying
figures.
US 6,497,745 B2
5 6
and preferably is sufficient to suitably disperse sulfurbearing
material feed stream 102, as well as any other
additives within the pressure leaching vessel.
The present inventors have found that to prevent the
5 formation of sulfur agglomerates, the temperature in the
pressure-leaching vessel preferably should be maintained
above about 2200 c., and more preferably above about 2350
C. and most preferably about 2500 C. Moreover, the present
inventors have found that the optional addition of certain
10 dispersants and/or particulate matter, for example, ground
sand and the like, facilitates enhanced sulfuric acid recovery
as well as enhanced metal value recovery, especially precious
metal recovery.
With momentary reference to FIG. 3, the difficulties
15 occasioned by sulfur can be addressed through use of
elevated temperature, for example through the use of
elevated temperatures in the range of about 2500 C. and/or
with the use of various dispersants. For example, as shown,
the use of ground sand as a dispersant tends to enhance acid
20 yield. As such, in accordance with an optional aspect of the
present invention, a dispersing agent is added to sulfurbearing
material feed stream 102 either during formation of
the feed slurry or to the pressure leaching vessel used in
pressure leaching step 104. Suitable dispersants include any
25 substantially inert particle, such as ground sand or mineral
processing tailings, or other particles that tend to provide for
the adherence of sulfur and increase the exposed surface area
of the sulfur to be oxidized. Other suitable dispersants may
include recycled pressure leaching residue, precious metal
30 recovery residues (e.g., cyanidation tailings) or the like. In
general, any material now known or hereafter devised by
those skilled in the art which advantageously serve such
purposes may be used.
During pressure leaching 104, oxygen is added to the
35 pressure leaching vessel, preferably substantially
continuously, to maintain the oxygen overpressure at optimal
levels for the desired chemical reactions to proceed.
That is, sufficient oxygen is suitably injected to maintain an
oxygen partial pressure in the pressure leaching vessel
40 ranging from about 50 to about 150 psig. The total pressure
in the sealed pressure leaching vessel is preferably from
about 600 to about 800 psig.
In any event, in accordance with various aspects of the
present invention, a product a slurry is preferably obtained
45 from pressure leaching processing 104 in a conventional
manner. Prior to subsequent processing, the resultant product
slurry is preferably caused to achieve approximately
ambient conditions of pressure and temperature. For
example, the product slurry may be flashed to release
50 pressure and to evaporatively cool the slurry through the
release of steam.
However, the temperature and pressure of the product
slurry may be advantageously reduced in any manner now
known or hereafter devised.
In accordance with various preferred aspects of the
present invention, once the temperature and pressure of the
product slurry is appropriately reduced, preferably, one or
more solid-liquid phase separation stages (step 106) may be
used to separate the sulfuric acid solution from the solid
60 particles in the product slurry. This may be accomplished in
any conventional manner, including use of filtration
systems, counter-current decantation (CCD) circuits,
thickeners, and the like. A variety of factors, such as the
process material balance, environmental regulations, residue
65 composition, economic considerations, and the like, may
affect the decision whether to employ a CCD circuit, a
thickener, a filter, or any other suitable device in a solidmaterials,
basic iron sulfate may be formed during pressure
leaching according to the following reaction:
When basic iron sulfate is formed, acid is consumed and
subsequent metal recovery may be inhibited. As such, to
enable efficient acid production and to optimize metal
recovery, the pulp density of the feed provided to the
pressure leaching vessel should be controlled.
In accordance with various aspects of the present
invention, suitable amounts of water 14 and oxygen 12 are
advantageously provided to feed stream 102 to facilitate the
reaction of elemental sulfur and sulfide sulfur to sulfuric
acid. Further, the feed slurry (i.e., sulfur-bearing material
102) provided for pressure leaching, in accordance with
various aspects of the present invention, preferably contains
sulfur and other materials, including, without limitation,
metal values such as copper, molybdenum, precious metals
and the like.
Sulfur-bearing material feed 102 provided to pressure
leaching vessel 104 preferably has a percent solids ranging
from about 2 to about 20 percent, more preferably on the
order of about 3 to about 8 percent solids. In some cases,
feed 102 may preferably be combined with additional
elemental sulfur, such as from an external source, and in
such cases higher percent solids may be tolerated. Where
feed 102 includes a significant amount of iron, then the acid
concentration of the material in pressure leaching vessel 104
is advantageously controlled to from about 20 to about 50
grams per liter, and more preferably in the range of about 30
to about 40 grams per liter acid.
With continued reference to FIG. 1, after sulfur-bearing
material feed stream 102 has been suitably prepared, it is
subjected to processing, preferably pressure leaching
processing, and more preferably high temperature pressure
leaching. As used herein, the term "pressure leaching" refers
to a process in which the sulfur-bearing material is contacted
with oxygen under conditions of elevated temperature and
pressure. During pressure leaching, the elemental sulfur of
the sulfur-bearing material 102 and many of the metal
sulfides contained in feed 102 are oxidized to form sulfate
and dissolved metal ions in solution. In some cases, significant
metal values may remain in the solid residue including
precious metals, molybdenum and others.
The pressure leaching processes suitably employed in
connection with the present invention are generally dependent
upon, among other things, temperature, oxygen
availability, and process chemistry. While various parameters
of each may be utilized, in accordance with preferred
aspects of the present invention, the temperature during
pressure leaching preferably is maintained above about 2200
c., and more preferably in the range of about 2350 C. to
about 2750 c., and optimally in the range of about 2500 C.
The duration of pressure leaching in any particular appli- 55
cation depends upon a number of factors, including, for
example, the characteristics of the feed material (e.g., sulfurbearing
material feed stream 102) and the pressure leaching
process pressure and temperature. Preferably, the duration of
pressure leaching in accordance with various aspects of the
present invention ranges from about 0.5 to about 3 or more
hours, and optimally is on the order of about one hour.
While any reactor vessel for pressure leaching may be
used, preferably an agitated, multiple-compartment pressure
leaching vessel is employed. For example, any pressure
containment or pressure controlled system may be used.
Agitation may be accomplished in any conventional manner,
US 6,497,745 B2
7 8
EXAMPLE 1
Various sulfur pressure leaching tests were performed. A
Parr batch 2.0 liter pressure leaching vessel was utilized. In
each instance, elemental sulfur was combined in the pressure
leaching vessel with oxygen and water to form a slurry, and
the slurry was contained in a non-adhesive liner. The reaction
temperature was varied as shown in Table 1. In each
instance, the reaction was permitted to operate for one hour.
Fifty grams of sulfur with 100 psi oxygen overpressure were
provided.
Yields were obtained by observing the amount of acid
produced as compared to the amount of elemental sulfur
provided (a theoretical yield of 100% was calculated to
represent 3.06 grams H2 S04/g sulfur).
As can be seen from the results shown in Table 1,
enhanced acid yields were obtainable with enhanced temperature
and the utilization of a dispersant, such as ground
sand, mineral processing tailings, or other suitable material.
tailings may be disposed (step 214). As those skilled in the
art will recognize, any number of precious metal or other
metal recovery methods may be suitable to achieve the
objective of recovering metals, such as precious metals (e.g.,
5 as silver and gold) from residue stream 18, and therefore
alternative processing routes may be successfully utilized.
The Examples set forth hereinbelow are illustrative of
various aspects of certain preferred embodiments of the
present invention. The process conditions and parameters
10 reflected therein are intended to exemplify various aspects of
the invention, and are not intended to limit the scope of the
claimed invention.
liquid separation stage. However, it should be appreciated
that any technique for conditioning the product slurry is
within the scope of the present invention. The product slurry
is subjected to solid-liquid phase separation (step 106) to
yield a resultant liquid phase sulfuric acid solution 108 and
a solid phase residue 18.
Preferably, solid-liquid phase separation (step 106) is
accomplished through the use of multiple stages of counter
current decantation (CCD) washing. Wash solution and a
suitable flocculant may be added as desired.
Sulfuric acid solution 108 may be used in a number of
ways. For example, all or a portion of solution 108 may be
used in other processing operations. The production of
sulfuric acid in this manner may advantageously reduce
costs typically associated with acid procurement for such
processing operations. Such processing operations may 15
include, among other things, acid-consuming heap leaching
operations used in connection with pressure leaching operations
or otherwise, agitated tank leaching, combinations
thereof or other processing operations.
On the other hand, the solid residue 18 obtained from 20
solid-liquid phase separation (step 106) may be further
processed. For example, with continued reference to FIG. 1,
if the metal content of the washed solids from solid-liquid
separation step 106 is sufficiently high to warrant further
processing, the metals contained therein may be recovered 25
through conventional means such as, for example, through
smelting or established metal recovery processing (e.g.,
precious metal recovery), a preferred process for which will
be described in greater detail hereinbelow in connection
with FIG. 2. If, however, the metals content of residue 18 is 30
too low to justify further treatment, the residue may be sent
to an impoundment area (not shown).
Referring now to FIG. 2, residue 18 from liquid-solid
phase separation step 106 (FIG. 1) may be subjected to
TABLE 1
O2 Usage
gOl! % of H2 SO4
Temp. Time % g reacted theoretical Strength Yield
Test CC) (min.) % So Sand So 1.5 gig So (giL) gig So %
A 160 65 5 15 5.08 339 1.6 0.02 0.7
B 220 60 5 0 1.88 126 69 1.55 50.8
C 220 60 5 5 1.78 nla 84 1.75 57.1
0 235 55 5 0 1.88 126 114 2.38 77.4
E 235 60 5 5 1.82 122 121 2.63 86.0
F 250 60 5 0 1.92 128 129 2.70 88.4
G 250 60 5 5 2.08 139 134 2.83 92.4
various further processing to recover metals contained
therein, particularly precious metals, such as gold and silver,
which may exist in the residue. Depending on the characteristics
of residue 18, it may be advantageous to subject it 55
to neutralization and/or pH adjustment, such as is illustrated
in step 202. The residue once so treated may then be
subjected to further processing or otherwise utilized. Such
processing may include, with continued reference to FIG. 2,
an optional hot lime boil (step 204) followed by precious 60
metal recovery (step 208), such as through the use of
conventional cyanide leaching (step 206) followed by
liquid-solid phase separation (step 210). If cyanide leaching
is used, the resultant tailings may be recycled and utilized
elsewhere in connection with a hydrometallurgical process, 65
for example as a sulfur dispersant, (not shown), Typically
after the cyanide is destroyed (step 212). Alternatively, the
EXAMPLE 2
A medium temperature pressure leaching residue containing
23.8 wt % elemental sulfur was prepared for pressure
leaching by making a feed slurry having 10.4 wt % solids
with synthetic raffinate and water. The feed was provided to
a stirred 2.0 liter Parr pressure leaching vessel at 2250 C.
with 50 psi oxygen overpressure for 60 minutes. The resulting
solution contained 55.9 gIL free acid and a bulk residue
(containing 2.9% elemental sulfur and 5.1% sulfate). Precious
metals were recovered from the residue in acceptable
quantities (i.e., 88% gold and 99% silver extraction).
The graphical profile of FIG. 3 further illustrates the
benefits on sulfuric acid yield as a function of temperature
and dispersant addition in accordance with various embodiments
of the present invention. These results generally
indicate that sulfuric acid production increases with increasUS
6,497,745 B2
9 10
least a portion of said sulfuric acid
said product slurry to yield a solid
5
30
c) pressure leaching said feed slurry at a temperature in
the range of about 2200 C. to about 2750 C. in an
oxygen-containing atmosphere to yield a pressure leach
product slurry comprising a sulfuric acid solution;
d) reducing the temperature and pressure of said product
slurry;
e) separating at least a portion of said sulfuric acid
solution from said product slurry to yield a solid
residue;
f) recovering at least one metal value from said solid
residue.
7. The process of claim 6 wherein said step of recovering
at least one metal value from said solid residue comprises
recovering one or more precious metals contained in said
15 residue.
8. The process of claim 6 wherein said step of reducing
the temperature and pressure of said product slurry comprises
flashing said product slurry.
9. The process of claim 6, said process further comprising
the step of utilizing at least a portion of said sulfuric acid
20 solution in connection with other processing operations.
10. The process of claim 6 wherein said step of pressure
leaching said feed slurry is conducted at a temperature in the
range in excess of about 2350 C.
11. A process for recovering metal values from the solid
25 residue of a pressure leaching process carried out at a
temperature in the range of about 1400 C. to about 1800 c.,
the process comprising the steps of:
a) comminuting the solid residue from the pressure leaching
process carried out at a temperature in the range of
about 1400 C. to about 1800 C. to produce a feed
material;
b) forming a feed slurry by combining said feed-material
with a sufficient amount of fluid medium;
c) pressure leaching said feed slurry at a temperature in
the range of about 2200 C. to about 2750 C. in an
oxygen-containing atmosphere to yield a pressure leach
product slurry comprising a sulfuric acid solution;
d) adding a sufficient amount of ground sand or mineral
processing tailings during said pressure leaching step;
e) reducing the temperature and pressure of said product
slurry,
f) separating at
solution from
residue;
g) recovering at least one metal value from said solid
residue.
12. The process of claim 11 wherein said step of recovering
at least one metal value from said solid residue
comprises recovering one or more precious metals contained
50 in said residue.
13. The process of claim 11 wherein said step of reducing
the temperature and pressure of said product slurry comprises
flashing said product slurry.
14. The process of claim 11, said process further com55
prising the step of utilizing at least a portion of said sulfuric
acid solution in connection with other processing operations.
15. The process of claim 11 wherein said step of pressure
leaching said feed slurry is conducted at a temperature in the
range in excess of about 2350 C.
16. A process for the production of sulfuric acid and
recovery of precious metals from an elemental sulfurbearing
material comprising the steps of:
a) providing an elemental sulfur-bearing material;
b) pressure leaching said elemental sulfur-bearing material
at a temperature in the range of about 2200 C. to
about 2750 C. in an oxygen-containing atmosphere in
an, agitated multiple-compartment pressure leaching
ing temperature. Moreover, the comparison of Curve 32
versus Curve 34 illustrates sulfuric acid yield can be
enhanced, on the order of between about 5 and about 10%,
with the addition of a suitable dispersant, for example,
ground sand.
Au effective and efficient method of producing sulfuric
acid from an elemental sulfur-bearing material has been
presented herein. The use of a dispersing agent as well as
elevated temperatures during pressure leaching may aid in
alleviating processing problems caused by the high viscosity
of elemental sulfur. Further, the present inventors have 10
advanced the art of copper hydrometallurgy by recognizing
the advantages of not only producing sulfuric acid solution
from sulfur-bearing materials, such as by-products of
medium temperature pressure leaching of copper sulfide
minerals, but also enabling the recovery of metals, such as
precious metals, entrained therein, which otherwise may
have been lost.
The present invention has been described above with
reference to a number of exemplary embodiments and
examples. It should be appreciated that the particular
embodiments shown and described herein are illustrative of
the invention and its best mode and are not intended to limit
in any way the scope of the invention as set forth in the
claims. Those skilled in the art having read this disclosure
will recognize that changes and modifications may be made
to the exemplary embodiments without departing from the
scope of the present invention. These and other changes or
modifications are intended to be included within the scope of
the present invention, as expressed in the following claims.
What is claimed is:
1. A treatment process comprising the steps of:
a) providing an elemental sulfur-bearing material;
b) pressure leaching said sulfur-bearing material at a
temperature in the range of about 2200 C. to about 2750
C. in an oxygen-containing atmosphere in an agitated
multiple-compartment pressure leaching vessel to form 35
a product slurry comprising a sulfuric acid solution;
c) separating at least a portion of said sulfuric acid
solution from said product slurry to yield a residue;
d) recovering at least one metal value from said residue; 40
e) adding a sufficient amount of ground sand or mineral
processing tailings to said pressure leaching vessel
during pressure leaching.
2. The process of claim 1, wherein said elemental sulfur
bearing material comprises a sulfur product stream from a 45
pressure leaching operation carried out at a temperature in
the range of about 1400 C. to about 1800 C.
3. The process of claim 1 wherein said step of recovering
metal values from said residue comprises recovering at least
one precious metal from said residue.
4. The process of claim 1 wherein said step of pressure
leaching said sulfur-bearing material comprises pressure
leaching at temperature above about 2350 C.
5. The process of claim 1 wherein said step of pressure
leaching said sulfur-bearing material comprises pressure
leaching at temperatures in the range of about 2500 C.
6. A process for recovering metal values from the solid
residue of a pressure leaching process carried out at a
temperature in the range of about 1400 C. to about 1800 c.,
the process comprising the steps of:
a) comminuting the solid residue from the pressure leach- 60
ing process carried out at a temperature in the range of
about 1400 C. to about 1800 C. to produce a feed
material;
b) forming a feed slurry by combining said feed material
with a sufficient amount of fluid medium and by adding 65
a sufficient amount of ground sand or mineral processing
tailings;
US 6,497,745 B2
11
vessel to form a product slurry comprising a sulfuric
acid solution;
c) adding a dispersant comprising a sufficient amount of
ground sand or mineral processing tailings during said
pressure leaching step;
d) separating at least a portion of said sulfuric acid
solution from said product slurry to yield a solid
residue;
e) recovering at least one precious metal value from said
solid residue.
12
17. The process of claim 16 wherein said step of providing
an elemental sulfur-bearing material comprises providing a
sulfur-containing product stream from a pressure leaching
operation carried out at a temperature in the range of about
5 140° C. to about 180° C.
18. The process of claim 16 wherein said step of pressure
leaching comprises pressure leaching at a temperature of
about 235° C.
* * * * *