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US006890371B2
(12) United States Patent
Marsden et al.
(10) Patent No.:
(45) Date of Patent:
US 6,890,371 B2
*May 10,2005
* cited by examiner
PCT/USOl/23469, International Preliminary Examination
Report.
(54) METHOD FOR PROCESSING ELEMENTAL
SULFUR-BEARING MATERIALS USING
HIGH TEMPERATURE PRESSURE
LEACHING
(75) 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)
(73) Assignee: Phelps Dodge Corporation, Phoenix,
AZ (US)
(56) References Cited
U.S. PATENT DOCUMENTS
4,605,439 A * 8/1986 Weir 75/744
6,451,088 B1 * 9/2002 Marsden et al. 75/739
6,497,745 B2 * 12/2002 Marsden et al. 75/743
6,626,979 B2 * 9/2003 Marsden et al. 75/739
6,676,909 B2 * 1/2004 Marsden et al. 423/28
6,680,034 B2 * 1/2004 Marsden et al. 423/24
OTHER PUBLICATIONS
( *) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 0 days.
Primary Examiner-Melvyn Andrews
(74) Attorney, Agent, or Firm---8nell & Wilmer, LLP
(57) ABSTRACT
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.
18 Claims, 2 Drawing Sheets
This patent is subject to a terminal disclaimer.
US 2003/0086849 A1 May 8, 2003
Related U.S. Application Data
Appl. No.: 10/328,633
Filed: Dec. 23, 2002
Prior Publication Data
Continuation of application No. 09/912,945, filed on Jul. 25,
2001, now Pat. No. 6,497,745.
Provisional application No. 60/220,677, filed on Jul. 25,
2000.
(51) Int. CI? COlE 17/69; C22B 3/06
(52) U.S. Cl. 75/743; 75/743; 423/522
(58) Field of Search 75/743, 744; 423/522
(21)
(22)
(65)
(63)
(60)
16
1..-------'-1- DISPERSING AGENT
ELEMENTAL SULFU~ 14
,----- ----"---1- H20
18
PRECIOUS
"- LIQUID-SOLID ; METAL
PHASE SEPARATION RECOVERY
1
(FIG. 2)
\
SULFURIC ACID SOLUTION 200
106
108
104'1. _
(
102
u.s. Patent May 10, 2005 Sheet 1 of 2 US 6,890,371 B2
102
12 ELEMENTAL SULFUR 14
02 ---'------,
104 -
16
1...------"-)- DISPERSING AGENT
106 LIQUID-SOLID
PHASE SEPARATION
18
PRECIOUS
METAL
RECOVERY
(FIG. 2)
10B
SULFURIC ACID SOLUTION 200
FIG. 1
100 ..----------~-----.------~
250 260
.•......
32
..D ........
......
......
.••..•.
.'
./·~34
...•.,.-
cr·······
~
TO 160C, 0.7% YIELD, 15% SANDS
...0
30 +-----/------+-----+-----+---__I------j
200 210 220 230 240
AUTOCLAVETEMPERATURE,DEG.C
40
80
60
70
50
90
a
(f)
E
Ol
a
If)
0::: o
lL
--l
<i
U
IW
0:: o
W:c
llL
o
...-...{}........ 5% SULFUR IN REACTOR --0-- 5% SULFUR, 5% SANDS IN REACTOR
FIG. 3
u.s. Patent May 10, 2005 Sheet 2 of 2 US 6,890,371 B2
------.------------------ --I
I
f
I 18
)
__-,IC-- ~
,
r-----r----
I
I
I
I
106
)
LIQUID-SOLID
PHASE
SEPARATION
NEUTRALIZATION &
pH ADJUSTMENT
202
HOT LIME BOIL
(OPTIONAL)
/204
I
I ~
I
I
I,
PRECIOUS METALS 206
CYANIDE LEACHING
PRECIOUS METALS 208
RECOVERY
(LIQUID) LIQUID-SOLID PHASE
SEPARATION
210
200~
I
CYANIDE
DESTRUCTION
212
TAILINGS
DISPOSAL
214
FIG. 2
US 6,890,371 B2
2
SUMMARY OF THE INVENTION
60
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 of metal values contained in the
50 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
55 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
65 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
molten sulfur may tend to encapsulate metal values in the
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
5 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. As discussed in
applicant's co-pending application entitled "Method for
10 Recovery of Metals From Metal Containing Materials Using
Medium Temperature Pressure Leaching" filed Jul. 25, 2001
and assigned U.S. Pat. Ser. No. 09/915,105, the subject
matter of which is hereby incorporated herein by reference,
while pressure leaching under medium temperature condi-
15 tions offers many advantages, 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
20 molten elemental sulfur. As discussed in greater detail in
applicant's co-pending application, proper 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). However, recovery of metal
25 values that may be contained in the elemental sulfurcontaining
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
30 where the recovery was performed, costs would be incurred
in connection with transportation of the residue or handling
of the acid. An effective and efficient method to manufacture
sulfuric acid from sulfur-bearing material, particularly
elemental sulfur-containing residue resulting from pressure
35 leaching operations operated at medium temperatures (e.g.,
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.
(1) 45
(2)
FIELD OF INVENTION
CROSS-REFERENCE TO RELATED
APPLICATIONS
BACKGROUND OF THE INVENTION
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 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 40
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:
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.
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
This application claims priority to and is a continuation of
U.S. patent application Ser. No. 09/912,945 now U.S. Pat.
No. 6,497,745 entitled "Method for Processing Elemental
Sulfur-Bearing Materials Using High Temperature Pressure
Leaching" filed on Jul. 25, 2001, which claims priority to
U.S. Provisional Patent Application, Ser. 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, both
of which are incorporated by reference herein.
US 6,890,371 B2
3 4
As those skilled in the art will understand, elemental
sulfur is optimally oxidized to sulfuric acid according to the
following reaction:
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
detail in Applicant's co-pending application, U.S. Pat. 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 (Cu2 S),
bornite (CusFeS4), and covellite (CuS). The sulfurcontaining
residues that result from the pressure leaching of
such copper-containing material feed streams may advantageously
be processed in accordance with the various aspects
of the present invention.
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
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.
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.
DETAILED DESCRIPTION
BRIEF DESCRIPTION OF THE DRAWINGS
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.
this embodiment of the invention, the sulfur-bearing material
feed stream comprises residue from medium temperature
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 15
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 20
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 25
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 30
following detailed description with reference to the accompanying
figures.
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
5
US 6,890,371 B2
6
materials, 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 application
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,
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
formation of sulfur agglomerates, the temperature in the
5 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
10 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
15 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
yield. As such, in accordance with an optional aspect of the
20 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
substantially inert particle, such as ground sand or mineral
25 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
recovery residues (e.g., cyanidation tailings) or the like. In
30 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
pressure leaching vessel, preferably substantially
35 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 about 50 to about 150 psig. The total pressure
40 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
from pressure leaching processing 104 in a conventional
45 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
pressure and to evaporatively cool the slurry through the
50 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
55 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
particles in the product slurry. This may be accomplished in
60 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
composition, economic considerations, and the like, may
65 affect the decision whether to employ a CCD circuit, a
thickener, a filter, or any other suitable device in a solidliquid
separation stage. However, it should be appreciated
US 6,890,371 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 H2SOJg 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.
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.,
silver and gold) from residue stream 18, and therefore
5 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
reflected therein are intended to exemplify various aspects of
10 the invention, and are not intended to limit the scope of the
claimed invention.
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).
TABLE 1
O2 Usage H2 SO4
g O:Jg % of
Temp. Time % 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
Referring now to FIG. 2, residue 18 from liquid-solid 50
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 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
metal recovery (step 208), such as through the use of 60
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,
for example as a sulfur dispersant, (not shown), Typically 65
after the cyanide is destroyed (step 212). Alternatively, the
tailings may be disposed (step 214). As those skilled in 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 increasing
temperature. Moreover, the comparison of Curve 32
versus Curve 34 illustrates sulfuric acid yield can be
US 6,890,371 B2
9 10
least a portion of said sulfuric acid
said product slurry to yield a solid
b) pressure leaching at least a portion of said feed stream
in the presence of a dispersant at a temperature in the
range of about 2200 C. to about 2750 C. in an oxygencontaining
atmosphere in an agitated multiplecompartment
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.
7. The process of claim 6, 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.
8. The process of claim 6 wherein said step of recovering
15 metal values from said residue comprises recovering at least
one precious metal from said residue.
9. The process of claim 6 wherein said step of pressure
leaching at least a portion of said feed stream in the presence
of a dispersant comprises pressure leaching at least a portion
20 of said feed stream in the presence of a sufficient amount of
ground sand or mineral processing tailings.
10. A process for recovering metal values from an elemental
sulfur-bearing solid residue of a pressure leaching process
carried out at a temperature in the range of about 1400
25 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 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 dispersant 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
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
solution from
residue;
f) recovering at least one metal value from said solid
residue.
11. The process of claim 10 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.
12. The process of claim 10 wherein said step of reducing
the temperature and pressure of said product slurry comprises
flashing said product slurry.
13. The process of claim 10, said process further comprising
the step of utilizing at least a portion of said sulfuric
55 acid solution in connection with other processing operations.
14. The process of claim 10 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.
15. The process of claim 10 wherein said step of forming
60 a feed slurry comprises combining said feed material with a
sufficient amount of ground sand or mineral processing
tailings.
16. A process for the production of sulfuric acid and
recovery of precious metals from an elemental sulfur65
bearing material comprising the steps of:
a) providing an elemental sulfur-bearing material,
wherein said elemental sulfur-bearing material comenhanced,
on the order of between about 5 and about 10%,
with the addition of a suitable dispersant, for example,
ground sand.
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.
30
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
elemental sulfur-bearing material comprises an 35
elemental sulfur-containing residue from a pressure
leaching operation;
b) pressure leaching at least a portion of said feed stream
at a temperature in the range of about 2200 C. to about
2750 C. in an oxygen-containing atmosphere in an 40
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 45
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 elemental sulfurbearing
material comprises an elemental sulfur-containing
residue from a pressure leaching operation carried out at a 50
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 at least a portion of said feed stream comprises
pressure leaching at temperatures above about 2350 C.
5. The process of claim 1 wherein said step of providing
a feed stream comprising an elemental sulfur-bearing material
and a dispersant comprises providing a feed stream
comprising an elemental sulfur-bearing material and a sufficient
amount of ground sand or mineral processing tailings.
6. A treatment process comprising the steps of:
a) providing a feed stream comprising an elemental
sulfur-bearing material, wherein said elemental sulfurbearing
material comprises an elemental sulfurcontaining
residue from a pressure leaching operation;
An effective and efficient method of producing sulfuric 5
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.
11
US 6,890,371 B2
12
prises 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 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.
* * * * *
s Ne�'�mn��R �T;mso-fareast-font-family: HiddenHorzOCR'>h) applying said acid-containing raffinate solution in a
heap leaching operation.
30 14. The process of claim 13, further comprising the step
of subjecting said residue of step (e) to a further processing.
15. The process of claim 14, wherein said step of further
processing comprises precious metal recovery.
16. The process of claim 14 wherein said step of further
35 processing comprises impounding.
17. The process of claim 13, wherein in said solvent
extracting step, said pH-adjusted copper-containing solution
is contacted with an extraction reagent comprising an
aldoxime/ketoxime mixture.
40 18. The process of claim 13, wherein said step of adjusting
the pH of said copper-containing solution comprises
combining said copper-containing solution with a make-up
diluting solution to yield a pH-adjusted copper-containing
wherein the ratio of said copper-containing solution to said
45 make-up diluting solution is in the range of from about 1:4
to about 1:8 and the pH of said pH-adjusted coppercontaining
solution is from about 1.4 to about 1.8.
19. In a process for recovering copper from a coppercontaining
material comprising the steps of pressure leach-
50 ing a copper-containing material with a liquid to yield a
residue and a copper-containing solution, wherein the copper
in said copper-containing solution is recovered through
solvent extraction of the copper from the copper-containing
solution, the process being improved wherein the copper-
55 containing solution is diluted prior to solvent extraction in a
diluting step, and the ratio by volume of the coppercontaining
solution to the diluting solution is less than about
1:8.
20. The process of claim 19 wherein in said diluting step
60 the ratio by volume of the copper-containing solution to the
diluting solution ranges from about 1:4 to about 1:8.
10
a) pressure leaching a copper-containing material with a 15
liquid to yield a residue and a copper-containing solution;
b) diluting said copper-containing solution with a diluting
solution to form a diluted copper-containing solution,
wherein a ratio of said copper-containing solution to 20
said diluting solution is less than about 1:8 and the pH
of said diluted copper containing solution is less than
about 2.2; and
c) solvent extracting said copper from said diluted copper- 25
containing solution.
2. The process of claim 1, wherein in said diluting step,
the ratio by volume of said copper-containing solution to
said diluting solution ranges from about 1:4 to about 1:8.
3. The process of claim 2, further comprising providing an
extraction reagent for use in said step of solvent extracting
said copper from said diluted copper-containing solution.
4. The process of claim 3, wherein said step of providing
an extraction reagent comprises providing an aldoxime/
ketoxime mixture.
5. The process of claim 3, wherein said step of providing
an extraction reagent comprises providing an extraction
reagent comprising aldoximes, modified aldoximes, or
aldoxime/ketoxime mixtures.
6. The process of claim 2, wherein said pressure leaching
step comprises high temperature pressure leaching at a
temperature from about 210° C. to about 235° C.
7. The process of claim 6, wherein said pressure leaching
step is at superatmospheric pressure at a temperature of
about 225° C. in an oxygen-containing atmosphere.
8. The process of claim 2, further comprising the step of
comminuting said copper-containing material prior to the
step of pressure leaching.
9. The process of claim 8, wherein said comminuting step
comprises comminuting said copper-containing material to a
P8G of less than about 75 microns.
10. The process of claim 2, further comprising the step of
recovering any precious metals contained in said pressure
leaching residue.
11. The process of claim 2, further comprising the step of
electrowinning said copper from said solvent extraction step
to form cathode copper.
12. The process of claim 1, wherein in said solvent
extracting step, said diluted copper-containing solution is
contacted with an extraction reagent comprising an
aldoxime/ketoxime mixture.
The present invention has been described above with
reference to various exemplary embodiments. It should be
appreciated that the particular embodiments shown and
described herein are illustrative of the invention and not
intended to limit in any way the scope of the invention as set 5
forth in the appended claims. For example, although reference
has been made throughout this disclosure primarily to
copper recovery, it is intended that the invention also be
applicable to the recovery of other metal values.
What is claimed:
1. A process for recovering copper from a coppercontaining
material, comprising the steps of:
t;lina��ih �T��l;mso-pagination:none;mso-layout-grid-align:none;text-autospace:none'>material and a solution stream comprising copper
and acid.
4. The method of claim 3, wherein said separating step
comprises reacting at least a portion of the copper in a
copper-containing electrolyte stream in the presence of
sulfur dioxide, whereby at least a portion of said copper in
said copper-containing electrolyte stream precipitates as
copper sulfide onto at least a portion of the coppercontaining
material in said feed stream.
5. The method of claim 1, wherein said leaching step
comprises leaching at least a portion of said pressure leaching
feed stream in a pressure leaching vessel at a temperature
of from about 100 to about 2500 C. and at a total operating
pressure of from about 50 to about 750 psi.
6. The method of claim 1, wherein said leaching step
35 comprises leaching at least a portion of said pressure leaching
feed stream in a pressure leaching vessel and wherein
said leaching step further comprises injecting oxygen into
the pressure leaching vessel to maintain an oxygen partial
pressure in the pressure leaching vessel of from about 50 to
about 200 psi.
7. The method of claim 5, wherein said leaching step
further comprises injecting oxygen into the pressure leaching
vessel to maintain an oxygen partial pressure in the
pressure leaching vessel of from about 50 to about 200 psi.
8. The method of claim 1, wherein said conditioning step
comprises subjecting at least a portion of said product slurry
to solid-liquid separation, wherein at least a portion of said
copper-containing solution is separated from said residue.
9. The method of claim 8, wherein said conditioning step
further comprises blending at least a portion of said coppercontaining
solution with at least a portion of one or more
copper-containing streams to achieve a desired copper concentration
in said copper-containing solution.
10. The method of claim 8, wherein said conditioning step
further comprises blending at least a portion of said coppercontaining
solution with at least a portion of one or more
copper-containing streams to achieve a copper concentration
of from about 20 to about 75 gramslliter in said coppercontaining
solution.
11. The method of claim 1, further comprising the step of
using at least a portion of said acid stream yielded from said
separating step in at least one of heap leaching, vat leaching,
dump leaching, stockpile leaching, pad leaching, agitated
tank leaching, or bacterial leaching operations.
containing suspended parallel flat cathodes of copper alternating
with flat anodes of lead alloy, arranged perpendicular
to the long axis of the tank. A copper-bearing leach solution
may be provided to the tank, for example at one end, to flow
perpendicular to the plane of the parallel anodes and 5
cathodes, and copper can be deposited at the cathode and
water electrolyzed to form oxygen and protons at the anode
with the application of current. As with conventional electrowinning
cells, the rate at which direct current can be
passed through the cell is effectively limited by the rate at
which copper ions can pass from the solution to the cathode 10
surface. This rate, called the limiting current density, is a
function of factors such as copper concentration, diffusion
coefficient of copper, cell configuration, and level of agitation
of the aqueous solution.
The general chemical process for electrowinning of cop- 15
per from acid solution is believed to be as follows:
2CUS04+2H2°---;>2Cuo+2H2S04+02
Cathode half-reaction: Cu2++2e----;>Cuo
Anode half-reaction: 2H20---;>4H++02+4e- 20
Turning again to FIG. 1, in a preferred embodiment the
invention, product stream 107 is directed from electrolyte
recyc~e tank 1060 to an electrowinning circuit 1070, which
contams one or more conventional electrowinning cells.
In accordance with a preferred aspect of the invention,
electrowinning circuit 1070 yields a cathode copper product 25
116, optionally, an offgas stream 117, and a relatively large
volume of copper-containing acid, herein designated as lean
electrolyte streams 108 and 115. As discussed above in the
illustrated embodiment of the invention, lean ele~trolyte
streams 108 and 115 are directed to copper precipitation 30
stage 1010 and electrolyte recycle tank 1060, respectively.
Lean electrolyte streams 108 and 115 generally have a lower
copper concentration than product stream 107, but typically
have a copper concentration of less than about 40 grams/
liter.
The present invention has been described above with
reference to a number of exemplary embodiments. 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 40
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 embodi~
ents .without departing from the scope of the present
mventlon. For example, although reference has been made
throughout to copper, it is intended that the invention also be 45
applicable to the recovery of other metals from metalcontaining
materials. Further, although certain preferred
aspects of the invention, such as techniques and apparatus
for conditioning process streams and for precipitation of
copper, for example, are described herein in terms of exem- 50
plary embodiments, such aspects of the invention may be
achieved through any number of suitable means now known
or hereafter devised. Accordingly, these and other changes
or modifications are intended to be included within the scope
of the present invention, as expressed in the following 55
claims.
What is claimed is:
1. A method for recovering copper from a coppercontaining
material, comprising the steps of:
providing a feed stream comprising a copper-containing 60
material and acid;
separating at least a portion of said copper-containing
material from said acid in said feed stream to yield an
acid stream comprising at least a portion of contami