111111111111111111111111111111111111111111111111111111111111111111111111111
US007041152B2
(12) United States Patent
Marsden et al.
(10) Patent No.:
(45) Date of Patent:
US 7,041,152 B2
*May 9, 2006
References Cited
U.S. PATENT DOCUMENTS
C01G 3/12 (2006.01)
B01F 1/00 (2006.01)
U.S. Cl. 75/743; 75/744; 423/27;
423/658.5; 423/522
Field of Classification Search 75/743,
75/744; 423/522,27, 658.5
See application file for complete search history.
(54) METHOD FOR PROCESSING ELEMENTAL
SULFUR-BEARING MATERIALS USING
HIGH TEMPERATURE PRESSURE
LEACHING
(75) Inventors: John O. Marsden, Phoenix, AZ (US);
Robert E. Brewer, Park City, UT (US);
Joanna M. Robertson, Thatcher, AZ
(US); Wayne W. Hazen, Lakewood,
CA (US); Philip Thompson, West
Valley City, UT (US); David R.
Baughman, Golden, CO (US)
(73) Assignee: Phelps Dodge Corporation, Phoenix,
AZ (US)
(52)
(58)
(56)
6,451,089 B1 *
6,497,745 B1 *
6,663,689 B1 *
6,890,371 B1 *
9/2002 Marsden et al. 75/744
12/2002 Marsden et al. 75/743
12/2003 Marsden et al. 75/744
5/2005 Marsden et al. 75/743
* cited by examiner
Primary Examiner-Roy King
Assistant Examiner-Kathleen McNelis
(74) Attorney, Agent, or Firm-Snell & Wilmer L.L.P.
( *) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 0 days.
This patent is subject to a terminal disclaimer.
(57) ABSTRACT
250 260
--l
" I
13 Claims, 3 Drawing Sheets
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 ofthe
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.
..-,0" .
.......
32 .....
/
/<-34
, /r
a/
luI. 21, 2005
if
TO 16OC, 0.7% YIELD. 15% SANDS
30 +----+--~-+_---+----I----_+_---j
200 210 220 230 240
AUTOCLAVE TEMPERATURE, DEG. C
(2006.01)
(2006.01)
1°°1
901
80
70
60
, ,
50
,
Filed: Mar. 29, 2005
Prior Publication Data
Related U.S. Application Data
Continuation of application No. 10/328,633, filed on
Dec. 23, 2002, now Pat. No. 6,890,371, which is a
continuation of application No. 09/912,945, filed on
luI. 25, 2001, now Pat. No. 6,497,745.
Provisional application No. 60/220,677, filed on luI.
25,2000.
US 2005/0155459 Al
Int. Cl.
C21B 15/00
C22B 11/00
(63)
(60)
(51)
(22)
(65)
(21) Appl. No.: 10/907,318
---{}.•-._. 5% SULFUR IN REACTOR --0-- 5% SULFUR, 5% SANDS IN REACTOR
u.s. Patent May 9, 2006 Sheet 1 of 3 US 7,041,152 B2
106
108
'~r- PRESSURE OXIDATION -- ~.-- O'ISPEHSING AGE
1 18
PRECIOUS
"- LIQUID-SOLID ; METAL
PHASE SEPARATION RECOVERY
1
(FIG. 2)
\
SULFURIC ACID SOLUTION 200
FIG. 1
NT
u.s. Patent May 9, 2006 Sheet 2 of 3 US 7,041,152 B2
iQG
- / -~-' ~ -----,
. LIQUID-SOLID
PHASE
SEPARATION
Hl
J ---l-- _
212
206
204
214
202
208
210
----- ..
I
1
NEUTRALIZATION & /-
pH ADJUSTMENT
HOT LIME BOIL
(OPTIONAL)
1
PRECIOUS METALS
CYANIDE LEACHING
PRECIOUS METALS
RECOVERY
(LIQUID) llQUlo.SOLID PHASE
SEPARATION
------------
CYANIDE V DESTRUCTION
j..-------------
TAILINGS V DISPOSAL
200/":
j I
I __ ~ -------------------------------------
FIG. 2
u.s. Patent May 9, 2006 Sheet 3 of 3 US 7,041,152 B2
250 260
,LT
....,
~"--------l
.......-..~ I
.'
."..-,..
/<-34 ..-
.;I' ..,. ......./
"" .. ' a.-'
,. ..
it
TO 16OC. 0.7% YIELD, 15il/ll SANDS
70
40
50
3O+-----I,-.-~--+----+-----+----+-----1
200 210 220 230 240
AUTOCLAVETEMPERATURE,DEG.C
60
100r 901 80
- ..0.... - 5% SULFUR, 5% SANDS IN REACTOR
FIG. 3
US 7,041,152 B2
2
SUMMARY OF THE INVENTION
process slurry, including precious metals and unreacted
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 subsequent
recovery of such metal values extremely difficult
using conventional processing techniques. U.S. Pat. No.
6,676,909 disclose that while pressure leaching under
medium temperature conditions offers many advantages,
10 prior medium temperature pressure leaching processes characteristically
have suffered from 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. Proper
15 control of such pressure leaching processes, as described
therein, enables the formation of elemental sulfur in addition
to the desired metal recovery (e.g., copper). This patent is
hereby incorporated by reference. However, recovery of
metal values that may be contained in the elemental sulfur-
20 containing residue, such as, for example, precious metals,
may be 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
25 in connection with transportation of the residue or handling
ofthe 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.,
30 about 1400 C. to about 1800 C.) is needed. Moreover, an
effective and efficient method to enhance recovery of any
metal values encapsulated within the sulfur-bearing material
would be advantageous.
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
sulfur-bearing materials, preferably at high temperatures,
not only to facilitate the recovery of a sulfuric acid solution,
but also to enhance recovery ofmetal values contained in the
45 sulfur-bearing materials. The acid produced, preferably a
relatively dilute sulfuric acid solution, advantageously can
be used in other metal extraction processes often with
significant cost savings.
As will be described in greater detail hereinbelow, the
50 methods and processes of the present invention are particularly
suited for use in connection with sulfur-bearing materials
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
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
60 stream to high temperature pressure leaching in a pressure
leaching vessel, optionally in the presence of a suitable
dispersing agent. In accordance with a preferred aspect of
this embodiment of the invention, the sulfur-bearing material
feed stream comprises residue from medium tempera-
65 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
35
(1)
(2)
FIELD OF INVENTION
CROSS-REFERENCE TO RELATED
APPLICATIONS
BACKGROUND OF THE INVENTION
4CuFeS2+4H2S04+502~4CuS04+2Fe203+8SC+
4H20
1
METHOD FOR PROCESSING ELEMENTAL
SULFUR-BEARING MATERIALS USING
HIGH TEMPERATURE PRESSURE
LEACHING
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
ofthese 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 40
temperatures above about 2000 c., the dominant leaching
reaction in dilute slurries may be written as follows:
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.
This application is a continuation of U.S. patent application
Ser. No. 10/328,633, filed on Dec. 23, 2002 now U.S.
Pat. No. 6,890,371, which is a continuation of U.S. patent
application Ser. No. 09/912,945, filed on luI. 25, 2001 and
issued as U.S. Pat. No. 6,497,745 on Dec. 24, 2002, which
claims priority to U.S. Provisional Patent Application Ser.
No. 60/220,677, filed on luI. 25, 2000, the disclosures and
contents of which are hereby incorporated by reference.
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 ofthe sulfide converts to elemental sulfur (S0) rather
than sulfate (S04-2). According to the reaction:
For example, experimental results show that at about 1600
C. and about 100 psi oxygen overpressure in the pressure 55
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
US 7,041,152 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 materials,
basic iron sulfate may be fonned during pressure
leaching according to the following reaction:
Fe203+2Sol-+4H+~2Fe(OH)S04+H20
When basic iron sulfate is fonned, 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.
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 tenn is used in FIG. 1, is used interchangeably
with the tenn "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
ofthe 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. U.S. Pat. No. 6,676,909
15 teaches that, 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 (Cu2 S), bornite
(CusFeS4 ), and covellite (CuS). The sulfur-containing resi-
20 dues 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
25 for processing in any suitable marmer. For example, desired
composition and/or component parameters can be achieved
through a variety of chemical and/or physical processing
stages, the choice of which will depend upon the operating
parameters of the chosen processing scheme, equipment cost
30 and material specifications. For example, feed stream 102
may undergo comminution, blending, and/or slurry fonnation,
as well as chemical and/or physical conditioning. Such
preparation efforts may include, for example, sulfur-bearing
material feed stream 102 being combined with solution, for
35 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 process to
produce a slurry.
With continued referenced to FIG. 1, preferably sulfur-
40 bearing 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,
optionally with one or more dispersing agents 16 to facilitate
pressure leaching (step 104) of sulfur-bearing material feed
45 stream 102. In accordance with one aspect of the present
invention, the feed slurry containing sulfur-bearing material
102 may be fonned in any suitable mixing vessel or by
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
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention exhibits significant advancements
over prior art processes, particularly with regard to process 50
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 the 55
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 60
the context ofthe present invention, the tenn "sulfur-bearing
material" refers to elemental sulfur, elemental sulfur-bearing
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 65
addition, the tenn "sulfur-bearing material" refers to other
sulfur compositions that may include sulfur together with
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 ofthis 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 10
separated from the resultant acid stream and subjected to
metal recovery processing. Such metal recovery processing
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.
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.
US 7,041,152 B2
5 6
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
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
10 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
15 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
20 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
25 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 ranging from
30 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 slurry is preferably obtained
35 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
40 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
50 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 com-
55 position, 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 solid-liquid separation
stage. However, it should be appreciated that any
technique for conditioning the product slurry is within the
60 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
65 accomplished through the use of multiple stages of counter
current decantation (CCD) washing. Wash solution and a
suitable flocculant may be added as desired.
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 ofthe material in pressure leaching vessell 04
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 tenn "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 235 0 C. to about 2750
c., and optimally in the range of about 2500 C.
The duration of pressure leaching in any particular appli- 45
cation depends upon a number of factors, including, for
example, the characteristics ofthe 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,
and preferably is sufficient to suitably disperse sulfur-bearing
material feed stream 102, as well as any other additives
within the pressure leaching vessel.
The present inventors have found that to prevent the
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
dispersants and/or particulate matter, for example, ground
7
US 7,041,152 B2
8
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
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. 10
On the other hand, the solid residue 18 obtained from
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 15
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 20
too low to justifY further treatment, the residue may be sent
to an impoundment area (not shown).
reflected therein are intended to exemplifY various aspects of
the invention, and are not intended to limit the scope of the
claimed invention.
EXAMPLE I
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 I. 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 H2S04 /g sulfur).
As can be seen from the results shown in Table I,
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.
TABLE I
O2 Usage
g °ig % of H2 SO4
Temp. Time % reacted theoretical Strength Yield
Test (0 C) (min.) % SO Sand SO 1.5 gig So (giL) gig So %
A 160 65 15 5.08 339 1.6 0.02 0.7
B 220 60 0 1.88 126 69 1.55 50.8
C 220 60 5 1.78 nla 84 1.75 57.1
D 235 55 0 1.88 126 114 2.38 77.4
E 235 60 5 1.82 122 121 2.63 86.0
F 250 60 0 1.92 128 129 2.70 88.4
G 250 60 5 2.08 139 134 2.83 92.4
40 Referring now to FIG. 2, residue 18 from liquid-solid
phase separation step 106 (FIG. 1) may be subjected to
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 charac- 45
teristics of residue 18, it may be advantageous to subject it
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, 50
an optional hot lime boil (step 204) followed by precious
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 55
elsewhere in connection with a hydrometallurgical process,
for example as a sulfur dispersant, (not shown), typically
after the cyanide is destroyed (step 212). Alternatively, the
tailings may be disposed (step 214). As those skilled in the
art will recognize, any number of precious metal or other 60
metal recovery methods may be suitable to achieve the
objective ofrecovering metals, such as precious metals (e.g.,
silver and gold) from residue stream 18, and therefore
alternative processing routes may be successfully utilized.
The Examples set forth hereinbelow are illustrative of 65
various aspects of certain preferred embodiments of the
present invention. The process conditions and parameters
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 lOA wt % solids
with synthetic raffinate and water. The feed was provided to
a stirred 2.0 liter Parr pressure leaching vessel at 225° 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 increasing
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.
An 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
US 7,041,152 B2
9 10
* * * * *
cess 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 elemental sulfur-bearing solid residue
from the pressure leaching process carried out at a
temperature in the range ofabout 1400 C. to about 1800
C. to produce a feed material;
b) forming a feed slurry by combining said feed material
with a dispersant wherein said dispersant comprises at
least one of a surfactant, ground sand, mineral processing
tailings, or combination thereof, and a sufficient
amount of fluid medium;
c) pressure leaching at least a portion of said feed slurry
at a temperature in the range of about 2200 C. to about
275 0 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
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
solution in connection with other processing operations.
10. The process of claim 6 wherein said step of pressure
leaching at least a portion of said feed slurry is conducted at
a temperature in the range in excess of about 2350 C.
11. A process for the production of sulfuric acid and
recovery of precious metals from an elemental sulfur-bearing
material comprising the steps of:
a) providing an elemental sulfur-bearing material wherein
said elemental sulfur-bearing material comprises an
elemental sulfur-containing residue from a pressure
leaching operation;
b) pressure leaching said elemental sulfur-bearing material
at a temperature in the range of about 2200 C. to
about 275 0 C. in an oxygen-containing atmosphere in
an agitated multiple-compartment pressure leaching
vessel to form a product slurry comprising a sulfuric
acid solution;
c) adding a dispersant during said pressure leaching step
wherein said dispersant comprises at least one of a
surfactant, ground sand, mineral processing tailings, or
combination thereof;
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. The process ofclaim 11 wherein said step of providing
an elemental sulfur-bearing material comprises providing an
elemental sulfur-containing residue from a pressure leaching
60 operation carried out at a temperature in the range of about
1400 C. to about 1800 C.
13. The process of claim 11 wherein said step of pressure
leaching comprises pressure leaching at a temperature of
about 2350 C.
40
20
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 10
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 15
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 a feed stream comprising an elemental
sulfur-bearing material and a dispersant wherein said
dispersant comprises at least one of a surfactant,
ground sand, mineral processing tailings, or combination
thereof, and wherein said elemental sulfur-bearing 25
material comprises an elemental sulfur-containing residue
from a pressure leaching operation carried out at a
temperature in the range of about 1400 C. to about 1800
c.;
b) pressure leaching at least a portion of said feed stream 30
at a temperature in the range of about 2200 C. to about
275 0 C. in an oxygen-containing atmosphere in an
agitated multiple-compartment pressure leaching vessel
to form a product slurry comprising a sulfuric acid
solution;
c) separating at least a portion of said sulfuric acid 35
solution from said product slurry to yield a residue;
d) recovering at least one metal value from said residue.
2. The process of claim 1 wherein said step of recovering
at least one metal value from said residue comprises recovering
at least one precious metal from said residue.
3. The process of claim 1 wherein said step of pressure
leaching at least a portion of said feed stream comprises
pressure leaching at temperatures above about 2350 C.
4. A treatment process comprising the steps of:
a) providing a feed stream comprising an elemental 45
sulfur-bearing material-wherein said elemental sulfurbearing
material comprises an elemental sulfur-containing
residue from a pressure leaching operation
carried out at a temperature in the range of about 1400
C. to about 1800 c.; 50
b) pressure leaching at least a portion of said feed stream
in the presence of a dispersant wherein said dispersant
comprises at least one of a surfactant, ground sand,
mineral processing tailings, or combination thereof, at
a temperature in the range of about 2200 C. to about
275 0 C. in an oxygen-containing atmosphere in an 55
agitated multiple-compartment pressure leaching vessel
to form 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.
5. The process of claim 4 wherein said step of recovering
at least one metal value from said residue comprises recovering
at least one precious metal from said residue.
6. A process for recovering metal values from an elemental
sulfur-bearing solid residue of a pressure leaching pro
='fo�`�ie�^D��nt-family:"Times New Roman","serif";mso-fareast-font-family: HiddenHorzOCR'>at a temperature in the range of about 220° C. to
about 275° C. in an oxygen-containing atmosphere in
an, agitated multiple-compartment pressure leaching
vessel to form a product slurry comprising a sulfuric
acid solution;
c) adding a dispersant 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.
17. The process of claim 16 wherein said step of providing
an elemental sulfur-bearing material comprises providing an
5 elemental sulfur-containing residue from a pressure leaching
operation carried out at a temperature in the range of about
140° C. to about 180° C.
18. The process of claim 16 wherein said step of pressure
10 leaching comprises pressure leaching at a temperature of
about 235° C.
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