6,890,371 Method for processing elemental sulfur-bearing materials using high temperature pressure leaching

Patent Number/Link:

111111111111111111111111111111111111111111111111111111111111111111111111111

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)

1..-------'-1- DISPERSING AGENT

ELEMENTAL SULFU~ 14

,----- ----"---1- H20

PRECIOUS

"- LIQUID-SOLID ; METAL

PHASE SEPARATION RECOVERY

(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 -

1...------"-)- DISPERSING AGENT

106 LIQUID-SOLID

PHASE SEPARATION

PRECIOUS

METAL

RECOVERY

(FIG. 2)

10B

SULFURIC ACID SOLUTION 200

FIG. 1

100 ..----------~-----.------~

250 260

.•......

..D ........

......

.••..•.

./·~34

...•.,.-

cr·······

TO 160C, 0.7% YIELD, 15% SANDS

...0

30 +-----/------+-----+-----+---__I------j

200 210 220 230 240

AUTOCLAVETEMPERATURE,DEG.C

(f)

If)

0::: o

--l

0:: o

W:c

llL

...-...{}........ 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 18

)

__-,IC-- ~

r-----r----

106

)

LIQUID-SOLID

PHASE

SEPARATION

NEUTRALIZATION &

pH ADJUSTMENT

202

HOT LIME BOIL

(OPTIONAL)

/204

I ~

PRECIOUS METALS 206

CYANIDE LEACHING

PRECIOUS METALS 208

RECOVERY

(LIQUID) LIQUID-SOLID PHASE

SEPARATION

210

200~

CYANIDE

DESTRUCTION

212

TAILINGS

DISPOSAL

214

FIG. 2

US 6,890,371 B2

SUMMARY OF THE INVENTION

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

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

US 6,890,371 B2

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.

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.

US 6,890,371 B2

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.

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