6,497,745 Method for processing elemental sulfur-bearing materials using high temperature pressure leaching

Patent Number/Link:

111111111111111111111111111111111111111111111111111111111111111111111111111

US006497745B2

(12) United States Patent

Marsden et al.

(10) Patent No.:

(45) Date of Patent:

US 6,497,745 B2

Dec. 24,2002

OTHER PUBLICATIONS

(54) METHOD FOR PROCESSING ELEMENTAL FOREIGN PATENT DOCUMENTS

SULFUR-BEARING MATERIALS USING

HIGH TEMPERATURE PRESSURE

LEACHING

AU 0219785 12/1958

Assignee: Phelps Dodge Corporation, Phoenix,

AZ (US)

Inventors: John O. Marsden, Phoenix, AZ (US);

Robert E. Brewer, Safford, AZ (US);

Joanna M. Robertson, Thatcher, AZ

(US); Wayne W. Hazen, Lakewood,

CO (US); Philip Thompson, West

Valley City, UT (US); David R.

Baughman, Golden, CO (US)

(75)

(73)

( * ) Notice: Subject to any disclaimer, the term of this

patent is extended or adjusted under 35

U.S.c. 154(b) by 0 days.

Evans, et aI., "International Symposium of Hydrometallurgy,"

Mar. 1, 1973, 2 pages.

Duyesteyn, et aI., "The Escondida Process for Copper Concentrates,"

1998 No Month.

King, et aI., "The Total Pressure Oxidation of Copper

Concentrates," 1993 No Month.

King, J. A., "Autoclaving of Copper Concentrates," paper

from COPPER 95, vol. III: Electrorefining and Hydrometallurgy

of Copper, International Conference held in Santiago,

Chile, Nov. 1995.

Mackis, V. N., "Direct Acid Pressure Leaching of Chalcocite

Concentrate," vol. 19, No.2, Feb. 1967.

(List continued on next page.)

Primary Examiner-Roy King

Assistant Examiner-Tima McGuthry-Banks

(74) Attorney, Agent, or Firm---8nell & Wilmer L.L.P.

(21)

(22)

(65)

Appl. No.: 09/912,945

Filed: Jul. 25, 2001

Prior Publication Data (57) ABSTRACT

U.S. PATENT DOCUMENTS

US 2002/0033076 A1 Mar. 21, 2002

References Cited

Related U.S. Application Data

Provisional application No. 60/220,677, filed on Jul. 25,

2000.

Int. CI? . ... ... ..... ... ... .... C22B 3/08

U.S. Cl. 75/743; 75/744; 423/27;

423/658.5

Field of Search 75/743, 744; 423/658.5,

423/27

The present invention relates generally to a process for the

production of sulfuric acid and liberation of precious metal

values from materials containing sulfur through pressure

leaching operations. In accordance with various aspects of

the present invention, the sulfur-bearing materials may comprise

residues from pressure leaching operations, such as

those carried out at medium temperatures. The process of the

present invention can be advantageously used to convert

such sulfur-bearing materials to sulfuric acid by means of

pressure leaching. The sulfuric acid so produced can be used

beneficially in other mineral processing operations, for

example those at the site where it is produced. Metals, such

as precious metals, that are contained within the sulfurbearing

materials advantageously may be recovered from

processing products by established precious metals recovery

technology.

3/1917 Farup

1/1940 Walthall

7/1966 Zimmerley et al.

1,219,277 A

2,188,324 A

3,260,593 A

(56)

(60)

(51)

(52)

(58)

(List continued on next page.) 18 Claims, 2 Drawing Sheets

102

12 ELEMENTAL SULFUR 14

\ ! H2O

1 1 16

104

PRESSURE OXIDATION . ! DISPERSING AGE

18 PRECIOUS

106 ""- LIQUID-SOLID ) METAL

PHASE SEPARATION RECOVERY

(FIG. 2)

108 \

SULFURIC ACID SOLUTION 200

US 6,497,745 B2

Page 2

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5,593,652 A

5,670,035 A

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5,730,950 A

5,770,170 A

5,849,172 A

5,895,633 A

5,902,474 A

5,917,116 A

6,153,168 A

OTHER PUBLICATIONS

* cited by examiner

Hirsch, H. E., "Leaching of Metal Sulphides," Patents, UK,

No. 1,598,454, 1981, 7 pages, No Month.

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Concentrate with Simultaneous Regeneration of the Leaching

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9-15 No Month.

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Oxygen Pressure Leaching of Chalcopyrite," paper from

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1995.

Hackl, R.P, "Passivation of Chalcopyrite During Oxidative

Leaching in Sulfate Media," Hydrometallurgy, vol. 39,

1995, pp. 25-48 No Month.

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Oxidation of Copper Concentrates," vol. I, Fundamental

Aspects, 1993 No Month.

Dreisinger, D. B., "Total Pressure Oxidation of EI Indio Ore

and Concentrate," COPPER 1999, Fourth International Conference,

Phoenix, Arizona, USA, Oct. 1999.

Richmond, G. D., "The Commissioning and Operation of a

Copper Sulphide Pressure Oxidation Leach Process at Mt.

Gordon," ALTA COPPER 1999: Copper Sulphides Symposium

& Copper Hydrometallurgy Forum, Gold Coast,

Queensland, Australia Conference, 1999 No Month.

L.W. Beckstead, et aI., "Acid Ferric Sulfate Leaching of

Attritor-Ground Chalcopyrite Concentrate," vol. II, Extractive

Metallurgy of Copper, Chapter 31, pp. 611-632, Published

by American Institute of Mining, Metallurgical, and

Petroleum Engineers, Inc. in 1976.

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3,528,784 A

3,637,371 A

3,656,888 A

3,669,651 A

3,868,440 A

3,896,208 A

3,917,519 A

3,949,051 A

3,958,985 A

3,961,028 A

3,962,402 A

3,985,553 A

3,991,159 A

4,009,250 A

4,017,309 A

4,020,106 A

4,028,462 A

4,029,733 A

4,029,751 A

4,039,405 A

4,046,851 A

4,057,423 A

4,069,119 A

4,091,070 A

4,093,526 A *

4,120,935 A

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4,150,976 A

4,157,912 A

4,165,362 A

4,178,357 A

4,212,855 A

4,213,958 A

4,256,553 A

4,266,972 A

4,272,341 A

4,333,917 A

4,338,168 A

4,405,569 A

4,415,540 A

4,442,072 A

4,507,268 A

4,526,768 A

4,533,537 A

4,571,263 A

4,571,264 A

4,591,494 A

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4,605,439 A

4,619,814 A

4,643,887 A

4,775,413 A

4,814,007 A

4,875,935 A

4,880,607 A

4,892,715 A

4,895,597 A

4,971,662 A

4,992,200 A

5,028,259 A

5,059,403 A

u.s. Patent Dec. 24,2002 Sheet 1 of 2 US 6,497,745 B2

102

12 ELEMENTAL SULFUR 14

\ ! H2O 1 1 16

104 PRESSURE OXIDATION / DISPERSING AGE ..

PRECIOUS

106 "- LIQUID-SOLID ; METAL

PHASE SEPARATION RECOVERY

(FIG. 2)

108 \

SULFURIC ACID SOLUTION 200

FIG. 1

100.,---------------

(j)

L()

0::: o

....J «u

.E:;

0::: o

LU :r:

lLL

....../ ...i 34

....

250 260

TO 160C, 0.7% YIELD, 15% SANDS

30 +----+-----j

200 210 220 230 240

AUTOCLAVE TEMPERATURE" DEG. C

....J

u«

........-0- ......... 5% SULFUR IN REACTOR ----..,:)-- 5% SULFUR, 5% SANDS IN REACTOR

FIG. 3

u.s. Patent Dec. 24,2002 Sheet 2 of 2 US 6,497,745 B2

206

204

212

214

210

208

202

106 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - I

I I ) I

I 18

LIQUID-SOLID II /

PHASE

SEPARATION NEUTRALIZATION & r

pH ADJUSTMENT

I HOT LIME BOIL r

I (OPTIONAL.) I

I I 1

I PRECIOUS METALS V CYANIDE LEACHING

PRECIOUS METALS r

RECOVERY

(LIQUID) LIQUID-SOLID PHASE

I SEPARATION I

I - - - - - - - - - - - -

I 200~ CYANIDE r

I DESTRUCTION

I ~- - - - - - - - - - - - -

I I TAILINGS r

I DISPOSAL. I

FIG. 2

US 6,497,745 B2

METHOD FOR PROCESSING ELEMENTAL

SULFUR-BEARING MATERIALS USING

HIGH TEMPERATURE PRESSURE

LEACHING

CROSS-REFERENCE TO RELATED

APPLICATIONS

This application claims priority to u.s. Provisional Patent

Application, Serial No. 60/220,677 entitled "Methods for

Conversion of Sulfur-bearing Material to Sulfuric Acid and

Recovery of Associated Metals by High Temperature Pressure

Oxidation" filed on Jul. 25, 2000, which is incorporated

by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to a process for

manufacturing sulfuric acid, and more specifically, to a

process for manufacturing relatively dilute sulfuric acid

from sulfur-bearing materials using high temperature pressure

leaching processes and recovering metal values from

the sulfur-bearing materials.

BACKGROUND OF THE INVENTION

Hydrometallurgical treatment of copper containing

materials, such as copper ores, concentrates, and the like,

has been well established for many years. Currently, there

exist many creative approaches to the hydrometallurgical

treatment of these materials. The recovery of copper from

copper sulfide concentrates using pressure leaching promises

to be particularly advantageous.

The mechanism by which pressure leaching releases

copper from a sulfide mineral matrix, such as chalcopyrite,

is generally dependent on temperature, oxygen availability,

and process chemistry. In high temperature pressure

leaching, typically thought of as being pressure leaching at

temperatures above about 2000 c., the dominant leaching

reaction in dilute slurries may be written as follows:

(1)

During pressure leaching of copper sulfide concentrates,

such as chalcopyrite containing concentrates at medium

temperatures (e.g., at temperatures in the range of between

about 1400 C. to about 1800 C.), however, a significant

fraction of the sulfide converts to elemental sulfur (SO) rather

than sulfate (SO4-2). According to the reaction:

For example, experimental results show that at about 1600

C. and about 100 psi oxygen overpressure in the pressure

leaching vessel, from about 60 to about 70 percent of the

sulfur in the super-finely ground copper sulfide concentrate

is converted to elemental sulfur, with the remainder being

converted to sulfate.

Elemental sulfur is a hydrophobic substance. In the pressure

leaching process slurry, under certain temperature and

solution conditions, sulfur has a tendency to agglomerate.

Moreover, molten elemental sulfur becomes highly viscous

us at elevated temperatures. For example, the viscosity of

molten sulfur increases from less than 100 centipoise at 1500

C. to more than 90,000 centipoise at 1850 C. As such, the

molten sulfur may tend to encapsulate metal values in the

process slurry, including precious metals and unreacted

metal sulfides, and/or stick to various parts of any apparatus

in which processing operations on the molten sulfur are

performed. Encapsulation of the metal values, for example,

copper, precious metals and the like, tends to make subse-

5 quent recovery of such metal values extremely difficult

using conventional processing techniques. As discussed in

applicant's co-pending application entitled "Method for

Recovery of Metals From Metal Containing Materials Using

Medium Temperature Pressure Leaching" filed Jul. 25, 2001

10 and assigned U.S. Ser. No. 09/915,105, the subject matter of

which is hereby incorporated herein by reference, while

pressure leaching under medium temperature conditions

offers many advantages, prior medium temperature pressure

leaching processes characteristically have suffered from

15 incomplete metal (e.g., copper) extraction resulting from

either passivation of the metal sulfide particle surfaces or by

the metal sulfide particles becoming coated with molten

elemental sulfur. As discussed in greater detail in applicant's

co-pending application, proper control of such pressure

20 leaching processes, as described therein, enables the formation

of elemental sulfur in addition to the desired metal

recovery (e.g. copper). However, recovery of metal values

that may be contained in the elemental sulfur-containing

residue, such as, for example, precious metals, may be

25 difficult with use of conventional techniques, and as such

they may be lost. Moreover, if the acid produced by such

processing techniques could not be used at the site where the

recovery was performed, costs would be incurred in connection

with transportation of the residue or handling of the

30 acid. An effective and efficient method to manufacture

sulfuric acid from sulfur-bearing material, particularly

elemental sulfur-containing residue resulting from pressure

leaching operations operated at medium temperatures (e.g.,

about 1400 C. to about 1800 C.) is needed. Moreover, an

35 effective and efficient method to enhance recovery of any

metal values encapsulated within the sulfur-bearing material

would be advantageous.

SUMMARY OF THE INVENTION

40 While the way in which the present invention addresses

the deficiencies and disadvantages of the prior art is

described in greater detail hereinbelow, in general, according

to various aspects of the present invention, a process for

manufacturing sulfuric acid includes pressure leaching of

45 sulfur-bearing materials, preferably at high temperatures,

not only to facilitate the recovery of a sulfuric acid solution,

but also to enhance recovery of metal values contained in the

sulfur-bearing materials. The acid produced, preferably a

relatively dilute sulfuric acid solution advantageously can be

50 used in other metal extraction processes, often with significant

cost savings.

As will be described in greater detail hereinbelow, the

methods and processes of the present invention are particularly

suited for use in connection with sulfur-bearing mate55

rials comprising residues from pressure leaching operations,

such as, for example, those operated at medium temperatures

(e.g., about 1400 to about 1800 C.).

In accordance with an exemplary embodiment of the

present invention, a process for manufacturing sulfuric acid

60 from sulfur-bearing materials generally includes the steps

of: (i) providing a feed stream containing a sulfur-bearing

material, and (ii) subjecting the sulfur-bearing material feed

stream to high temperature pressure leaching in a pressure

leaching vessel, optionally in the presence of a suitable

65 dispersing agent. In accordance with a preferred aspect of

this embodiment of the invention, the sulfur-bearing material

feed stream comprises residue from medium temperaUS

6,497,745 B2

3 4

Further, as those skilled in the art will appreciate, this

reaction may proceed more completely as temperature is

increased. In addition, where the sulfur-bearing material

feed 102 comprises hematite and/or other iron-bearing

material generated as a by-product of other metal recovery

processes, materials containing iron sulfides, copper sulfides

and/or other metal sulfides, or any combination of these. In

addition, the term "sulfur-bearing material" refers to other

5 sulfur compositions that may include sulfur together with

any other sulfides and/or metals that might be attendant to or

part of such sulfur compositions. For purposes of this

disclosure, in most instances, the term "elemental sulfur,"

for example as that term is used in FIG. 1, is used inter-

10 changeably with the term "sulfur-bearing material," inasmuch

as, as will be clear from the following disclosure, the

elemental sulfur and sulfide sulfur components of any

sulfur-bearing material 102 are advantageously converted to

sulfuric acid in accordance with the present invention.

In accordance with one aspect of a preferred embodiment

of the present invention, sulfur-bearing material feed stream

102 preferably comprises the sulfur-containing residue produced

in connection with the pressure leaching of coppercontaining

material feed streams. As explained in greater

20 detail in Applicant's co-pending application, U.S. Ser. No.

09/915,105, such copper-containing materials include copper

sulfide ores, such as, for example, ores and/or concentrates

containing chalcopyrite (CuFeS2 ) or mixtures of chalcopyrite

with one or more of chalcocite (Cu2S), bornite

25 (CusFeS4), and covellite (CuS). The sulfur-containing residues

that result from the pressure leaching of such coppercontaining

material feed streams may advantageously be

processed in accordance with the various aspects of the

present invention.

Sulfur-bearing material feed stream 102 may be prepared

for processing in any suitable manner. For example, desired

composition and/or component parameters can be achieved

through a variety of chemical and/or physical processing

35 stages, the choice of which will depend upon the operating

parameters of the chosen processing scheme, equipment cost

and material specifications. For example, feed stream 102

may undergo comminution, blending, and/or slurry

formation, as well as chemical and/or physical conditioning.

40 Such preparation efforts may include, for example, sulfurbearing

material feed stream 102 being combined with

solution, for example, pregnant leach solution (PLS) or

barren raffinate solution from an existing acid heap leaching

operation or an agitated tank leaching operation, in a repulp

45 process to produce a slurry.

With continued referenced to FIG. 1, preferably sulfurbearing

material feed stream 102 (or slurry) is suitably

combined with a fluid 14, preferably water, and suitable

amounts of an oxygenating supply, for example, oxygen 12,

50 optionally with one or more dispersing agents 16 to facilitate

pressure leaching (step 104) of sulfur-bearing material feed

stream 102. In accordance with one aspect of the present

invention, the feed slurry containing sulfur-bearing material

102 may be formed in any suitable mixing vessel or by

55 in-line blending. Other additives, such as wetting agents or

the like, for example, lignosulfonates, may also be used.

As those skilled in the art will understand, elemental

sulfur is optimally oxidized to sulfuric acid according to the

following reaction:

DETAILED DESCRIPTION OF AN

EXEMPLARY EMBODIMENT OF THE

INVENTION

BRIEF DESCRIPTION OF IRE DRAWING

The subject matter of the present invention is particularly

pointed out and distinctly claimed in the concluding portion

of the specification. A more complete understanding of the

present invention, however, may best be obtained by referring

to the detailed description and claims when considered

in connection with the drawing figures, wherein like numerals

denote like elements and wherein:

FIG. 1 illustrates a flow diagram of a process in accordance

with an exemplary embodiment of the present invention;

FIG. 2 illustrates a flow diagram of further processing in

accordance with the embodiment of the present invention

illustrated in FIG. 1; and,

FIG. 3 illustrates a graphical profile of sulfuric acid yield

versus temperature in accordance with various embodiments

of the present invention.

The present invention exhibits significant advancements

over prior art processes, particularly with regard to process

efficiency and process economics. Moreover, existing metal

(e.g., copper) recovery processes that utilize conventional

atmospheric or pressure leaching/solvent extraction/

electrowinning process sequences may, in many instances,

be easily retrofitted to exploit the many commercial benefits 60

the present invention provides.

Referring now to FIG. 1, in accordance with various

aspects of one embodiment of the present invention, a

sulfuric acid production process preferably involves providing

a sufficient supply of a sulfur-bearing material 102. In 65

the context of the present invention, the term "sulfur-bearing

material" refers to elemental sulfur, elemental sulfur-bearing

ture pressure leaching of a copper sulfide mineral, such as

chalcopyrite or a blend of that residue combined with

elemental sulfur. In accordance with a further preferred

aspect of this embodiment of the invention, the use of a

dispersing agent during pressure leaching may aid in alleviating

processing problems caused by the high viscosity

and hydrophobic nature of elemental sulfur at higher temperatures

(e.g., above about 1600 C.

In accordance with a further aspect of this embodiment of

the present invention, metal values contained in the sulfurbearing

material feed stream are liberated from the elemental

sulfur residue during pressure leaching, during which the

elemental sulfur is converted to sulfuric acid, and then

separated from the resultant acid stream and subjected to

metal recovery processing. Such metal recovery processing 15

may include precious metal recovery.

The present inventors have advanced the art of copper

hydrometallurgy by recognizing the advantages of not only

producing a sulfuric acid solution from sulfur-bearing

materials, such as the elemental sulfur by-product of

medium temperature pressure leaching of copper sulfide

minerals, but also of enabling the recovery of metal values

(e.g., precious metals) entrained therein, which otherwise

may have been lost.

These and other advantages of a process according to

various aspects of the present invention will be apparent to

those skilled in the art upon reading and understanding the

following detailed description with reference to the accompanying

figures.

US 6,497,745 B2

5 6

and preferably is sufficient to suitably disperse sulfurbearing

material feed stream 102, as well as any other

additives within the pressure leaching vessel.

The present inventors have found that to prevent the

5 formation of sulfur agglomerates, the temperature in the

pressure-leaching vessel preferably should be maintained

above about 2200 c., and more preferably above about 2350

C. and most preferably about 2500 C. Moreover, the present

inventors have found that the optional addition of certain

10 dispersants and/or particulate matter, for example, ground

sand and the like, facilitates enhanced sulfuric acid recovery

as well as enhanced metal value recovery, especially precious

metal recovery.

With momentary reference to FIG. 3, the difficulties

15 occasioned by sulfur can be addressed through use of

elevated temperature, for example through the use of

elevated temperatures in the range of about 2500 C. and/or

with the use of various dispersants. For example, as shown,

the use of ground sand as a dispersant tends to enhance acid

20 yield. As such, in accordance with an optional aspect of the

present invention, a dispersing agent is added to sulfurbearing

material feed stream 102 either during formation of

the feed slurry or to the pressure leaching vessel used in

pressure leaching step 104. Suitable dispersants include any

25 substantially inert particle, such as ground sand or mineral

processing tailings, or other particles that tend to provide for

the adherence of sulfur and increase the exposed surface area

of the sulfur to be oxidized. Other suitable dispersants may

include recycled pressure leaching residue, precious metal

30 recovery residues (e.g., cyanidation tailings) or the like. In

general, any material now known or hereafter devised by

those skilled in the art which advantageously serve such

purposes may be used.

During pressure leaching 104, oxygen is added to the

35 pressure leaching vessel, preferably substantially

continuously, to maintain the oxygen overpressure at optimal

levels for the desired chemical reactions to proceed.

That is, sufficient oxygen is suitably injected to maintain an

oxygen partial pressure in the pressure leaching vessel

40 ranging from about 50 to about 150 psig. The total pressure

in the sealed pressure leaching vessel is preferably from

about 600 to about 800 psig.

In any event, in accordance with various aspects of the

present invention, a product a slurry is preferably obtained

45 from pressure leaching processing 104 in a conventional

manner. Prior to subsequent processing, the resultant product

slurry is preferably caused to achieve approximately

ambient conditions of pressure and temperature. For

example, the product slurry may be flashed to release

50 pressure and to evaporatively cool the slurry through the

release of steam.

However, the temperature and pressure of the product

slurry may be advantageously reduced in any manner now

known or hereafter devised.

In accordance with various preferred aspects of the

present invention, once the temperature and pressure of the

product slurry is appropriately reduced, preferably, one or

more solid-liquid phase separation stages (step 106) may be

used to separate the sulfuric acid solution from the solid

60 particles in the product slurry. This may be accomplished in

any conventional manner, including use of filtration

systems, counter-current decantation (CCD) circuits,

thickeners, and the like. A variety of factors, such as the

process material balance, environmental regulations, residue

65 composition, economic considerations, and the like, may

affect the decision whether to employ a CCD circuit, a

thickener, a filter, or any other suitable device in a solidmaterials,

basic iron sulfate may be formed during pressure

leaching according to the following reaction:

When basic iron sulfate is formed, acid is consumed and

subsequent metal recovery may be inhibited. As such, to

enable efficient acid production and to optimize metal

recovery, the pulp density of the feed provided to the

pressure leaching vessel should be controlled.

In accordance with various aspects of the present

invention, suitable amounts of water 14 and oxygen 12 are

advantageously provided to feed stream 102 to facilitate the

reaction of elemental sulfur and sulfide sulfur to sulfuric

acid. Further, the feed slurry (i.e., sulfur-bearing material

102) provided for pressure leaching, in accordance with

various aspects of the present invention, preferably contains

sulfur and other materials, including, without limitation,

metal values such as copper, molybdenum, precious metals

and the like.

Sulfur-bearing material feed 102 provided to pressure

leaching vessel 104 preferably has a percent solids ranging

from about 2 to about 20 percent, more preferably on the

order of about 3 to about 8 percent solids. In some cases,

feed 102 may preferably be combined with additional

elemental sulfur, such as from an external source, and in

such cases higher percent solids may be tolerated. Where

feed 102 includes a significant amount of iron, then the acid

concentration of the material in pressure leaching vessel 104

is advantageously controlled to from about 20 to about 50

grams per liter, and more preferably in the range of about 30

to about 40 grams per liter acid.

With continued reference to FIG. 1, after sulfur-bearing

material feed stream 102 has been suitably prepared, it is

subjected to processing, preferably pressure leaching

processing, and more preferably high temperature pressure

leaching. As used herein, the term "pressure leaching" refers

to a process in which the sulfur-bearing material is contacted

with oxygen under conditions of elevated temperature and

pressure. During pressure leaching, the elemental sulfur of

the sulfur-bearing material 102 and many of the metal

sulfides contained in feed 102 are oxidized to form sulfate

and dissolved metal ions in solution. In some cases, significant

metal values may remain in the solid residue including

precious metals, molybdenum and others.

The pressure leaching processes suitably employed in

connection with the present invention are generally dependent

upon, among other things, temperature, oxygen

availability, and process chemistry. While various parameters

of each may be utilized, in accordance with preferred

aspects of the present invention, the temperature during

pressure leaching preferably is maintained above about 2200

c., and more preferably in the range of about 2350 C. to

about 2750 c., and optimally in the range of about 2500 C.

The duration of pressure leaching in any particular appli- 55

cation depends upon a number of factors, including, for

example, the characteristics of the feed material (e.g., sulfurbearing

material feed stream 102) and the pressure leaching

process pressure and temperature. Preferably, the duration of

pressure leaching in accordance with various aspects of the

present invention ranges from about 0.5 to about 3 or more

hours, and optimally is on the order of about one hour.

While any reactor vessel for pressure leaching may be

used, preferably an agitated, multiple-compartment pressure

leaching vessel is employed. For example, any pressure

containment or pressure controlled system may be used.

Agitation may be accomplished in any conventional manner,

US 6,497,745 B2

7 8

EXAMPLE 1

Various sulfur pressure leaching tests were performed. A

Parr batch 2.0 liter pressure leaching vessel was utilized. In

each instance, elemental sulfur was combined in the pressure

leaching vessel with oxygen and water to form a slurry, and

the slurry was contained in a non-adhesive liner. The reaction

temperature was varied as shown in Table 1. In each

instance, the reaction was permitted to operate for one hour.

Fifty grams of sulfur with 100 psi oxygen overpressure were

provided.

Yields were obtained by observing the amount of acid

produced as compared to the amount of elemental sulfur

provided (a theoretical yield of 100% was calculated to

represent 3.06 grams H2 S04/g sulfur).

As can be seen from the results shown in Table 1,

enhanced acid yields were obtainable with enhanced temperature

and the utilization of a dispersant, such as ground

sand, mineral processing tailings, or other suitable material.

tailings may be disposed (step 214). As those skilled in the

art will recognize, any number of precious metal or other

metal recovery methods may be suitable to achieve the

objective of recovering metals, such as precious metals (e.g.,

5 as silver and gold) from residue stream 18, and therefore

alternative processing routes may be successfully utilized.

The Examples set forth hereinbelow are illustrative of

various aspects of certain preferred embodiments of the

present invention. The process conditions and parameters

10 reflected therein are intended to exemplify various aspects of

the invention, and are not intended to limit the scope of the

claimed invention.

liquid separation stage. However, it should be appreciated

that any technique for conditioning the product slurry is

within the scope of the present invention. The product slurry

is subjected to solid-liquid phase separation (step 106) to

yield a resultant liquid phase sulfuric acid solution 108 and

a solid phase residue 18.

Preferably, solid-liquid phase separation (step 106) is

accomplished through the use of multiple stages of counter

current decantation (CCD) washing. Wash solution and a

suitable flocculant may be added as desired.

Sulfuric acid solution 108 may be used in a number of

ways. For example, all or a portion of solution 108 may be

used in other processing operations. The production of

sulfuric acid in this manner may advantageously reduce

costs typically associated with acid procurement for such

processing operations. Such processing operations may 15

include, among other things, acid-consuming heap leaching

operations used in connection with pressure leaching operations

or otherwise, agitated tank leaching, combinations

thereof or other processing operations.

On the other hand, the solid residue 18 obtained from 20

solid-liquid phase separation (step 106) may be further

processed. For example, with continued reference to FIG. 1,

if the metal content of the washed solids from solid-liquid

separation step 106 is sufficiently high to warrant further

processing, the metals contained therein may be recovered 25

through conventional means such as, for example, through

smelting or established metal recovery processing (e.g.,

precious metal recovery), a preferred process for which will

be described in greater detail hereinbelow in connection

with FIG. 2. If, however, the metals content of residue 18 is 30

too low to justify further treatment, the residue may be sent

to an impoundment area (not shown).

Referring now to FIG. 2, residue 18 from liquid-solid

phase separation step 106 (FIG. 1) may be subjected to

TABLE 1

O2 Usage

gOl! % of H2 SO4

Temp. Time % g reacted theoretical Strength Yield

Test CC) (min.) % So Sand So 1.5 gig So (giL) gig So %

A 160 65 5 15 5.08 339 1.6 0.02 0.7

B 220 60 5 0 1.88 126 69 1.55 50.8

C 220 60 5 5 1.78 nla 84 1.75 57.1

0 235 55 5 0 1.88 126 114 2.38 77.4

E 235 60 5 5 1.82 122 121 2.63 86.0

F 250 60 5 0 1.92 128 129 2.70 88.4

G 250 60 5 5 2.08 139 134 2.83 92.4

various further processing to recover metals contained

therein, particularly precious metals, such as gold and silver,

which may exist in the residue. Depending on the characteristics

of residue 18, it may be advantageous to subject it 55

to neutralization and/or pH adjustment, such as is illustrated

in step 202. The residue once so treated may then be

subjected to further processing or otherwise utilized. Such

processing may include, with continued reference to FIG. 2,

an optional hot lime boil (step 204) followed by precious 60

metal recovery (step 208), such as through the use of

conventional cyanide leaching (step 206) followed by

liquid-solid phase separation (step 210). If cyanide leaching

is used, the resultant tailings may be recycled and utilized

elsewhere in connection with a hydrometallurgical process, 65

for example as a sulfur dispersant, (not shown), Typically

after the cyanide is destroyed (step 212). Alternatively, the

EXAMPLE 2

A medium temperature pressure leaching residue containing

23.8 wt % elemental sulfur was prepared for pressure

leaching by making a feed slurry having 10.4 wt % solids

with synthetic raffinate and water. The feed was provided to

a stirred 2.0 liter Parr pressure leaching vessel at 2250 C.

with 50 psi oxygen overpressure for 60 minutes. The resulting

solution contained 55.9 gIL free acid and a bulk residue

(containing 2.9% elemental sulfur and 5.1% sulfate). Precious

metals were recovered from the residue in acceptable

quantities (i.e., 88% gold and 99% silver extraction).

The graphical profile of FIG. 3 further illustrates the

benefits on sulfuric acid yield as a function of temperature

and dispersant addition in accordance with various embodiments

of the present invention. These results generally

indicate that sulfuric acid production increases with increasUS

6,497,745 B2

9 10

least a portion of said sulfuric acid

said product slurry to yield a solid

c) pressure leaching said feed slurry at a temperature in

the range of about 2200 C. to about 2750 C. in an

oxygen-containing atmosphere to yield a pressure leach

product slurry comprising a sulfuric acid solution;

d) reducing the temperature and pressure of said product

slurry;

e) separating at least a portion of said sulfuric acid

solution from said product slurry to yield a solid

residue;

f) recovering at least one metal value from said solid

residue.

7. The process of claim 6 wherein said step of recovering

at least one metal value from said solid residue comprises

recovering one or more precious metals contained in said

15 residue.

8. The process of claim 6 wherein said step of reducing

the temperature and pressure of said product slurry comprises

flashing said product slurry.

9. The process of claim 6, said process further comprising

the step of utilizing at least a portion of said sulfuric acid

20 solution in connection with other processing operations.

10. The process of claim 6 wherein said step of pressure

leaching said feed slurry is conducted at a temperature in the

range in excess of about 2350 C.

11. A process for recovering metal values from the solid

25 residue of a pressure leaching process carried out at a

temperature in the range of about 1400 C. to about 1800 c.,

the process comprising the steps of:

a) comminuting the solid residue from the pressure leaching

process carried out at a temperature in the range of

about 1400 C. to about 1800 C. to produce a feed

material;

b) forming a feed slurry by combining said feed-material

with a sufficient amount of fluid medium;

c) pressure leaching said feed slurry at a temperature in

the range of about 2200 C. to about 2750 C. in an

oxygen-containing atmosphere to yield a pressure leach

product slurry comprising a sulfuric acid solution;

d) adding a sufficient amount of ground sand or mineral

processing tailings during said pressure leaching step;

e) reducing the temperature and pressure of said product

slurry,

f) separating at

solution from

residue;

g) recovering at least one metal value from said solid

residue.

12. The process of claim 11 wherein said step of recovering

at least one metal value from said solid residue

comprises recovering one or more precious metals contained

50 in said residue.

13. The process of claim 11 wherein said step of reducing

the temperature and pressure of said product slurry comprises

flashing said product slurry.

14. The process of claim 11, said process further com55

prising the step of utilizing at least a portion of said sulfuric

acid solution in connection with other processing operations.

15. The process of claim 11 wherein said step of pressure

leaching said feed slurry is conducted at a temperature in the

range in excess of about 2350 C.

16. A process for the production of sulfuric acid and

recovery of precious metals from an elemental sulfurbearing

material comprising the steps of:

a) providing an elemental sulfur-bearing material;

b) pressure leaching said elemental sulfur-bearing material

at a temperature in the range of about 2200 C. to

about 2750 C. in an oxygen-containing atmosphere in

an, agitated multiple-compartment pressure leaching

ing temperature. Moreover, the comparison of Curve 32

versus Curve 34 illustrates sulfuric acid yield can be

enhanced, on the order of between about 5 and about 10%,

with the addition of a suitable dispersant, for example,

ground sand.

Au effective and efficient method of producing sulfuric

acid from an elemental sulfur-bearing material has been

presented herein. The use of a dispersing agent as well as

elevated temperatures during pressure leaching may aid in

alleviating processing problems caused by the high viscosity

of elemental sulfur. Further, the present inventors have 10

advanced the art of copper hydrometallurgy by recognizing

the advantages of not only producing sulfuric acid solution

from sulfur-bearing materials, such as by-products of

medium temperature pressure leaching of copper sulfide

minerals, but also enabling the recovery of metals, such as

precious metals, entrained therein, which otherwise may

have been lost.

The present invention has been described above with

reference to a number of exemplary embodiments and

examples. It should be appreciated that the particular

embodiments shown and described herein are illustrative of

the invention and its best mode and are not intended to limit

in any way the scope of the invention as set forth in the

claims. Those skilled in the art having read this disclosure

will recognize that changes and modifications may be made

to the exemplary embodiments without departing from the

scope of the present invention. These and other changes or

modifications are intended to be included within the scope of

the present invention, as expressed in the following claims.

What is claimed is:

1. A treatment process comprising the steps of:

a) providing an elemental sulfur-bearing material;

b) pressure leaching said sulfur-bearing material at a

temperature in the range of about 2200 C. to about 2750

C. in an oxygen-containing atmosphere in an agitated

multiple-compartment pressure leaching vessel to form 35

a product slurry comprising a sulfuric acid solution;

c) separating at least a portion of said sulfuric acid

solution from said product slurry to yield a residue;

d) recovering at least one metal value from said residue; 40

e) adding a sufficient amount of ground sand or mineral

processing tailings to said pressure leaching vessel

during pressure leaching.

2. The process of claim 1, wherein said elemental sulfur

bearing material comprises a sulfur product stream from a 45

pressure leaching operation carried out at a temperature in

the range of about 1400 C. to about 1800 C.

3. The process of claim 1 wherein said step of recovering

metal values from said residue comprises recovering at least

one precious metal from said residue.

4. The process of claim 1 wherein said step of pressure

leaching said sulfur-bearing material comprises pressure

leaching at temperature above about 2350 C.

5. The process of claim 1 wherein said step of pressure

leaching said sulfur-bearing material comprises pressure

leaching at temperatures in the range of about 2500 C.

6. A process for recovering metal values from the solid

residue of a pressure leaching process carried out at a

temperature in the range of about 1400 C. to about 1800 c.,

the process comprising the steps of:

a) comminuting the solid residue from the pressure leach- 60

ing process carried out at a temperature in the range of

about 1400 C. to about 1800 C. to produce a feed

material;

b) forming a feed slurry by combining said feed material

with a sufficient amount of fluid medium and by adding 65

a sufficient amount of ground sand or mineral processing

tailings;

US 6,497,745 B2

vessel to form a product slurry comprising a sulfuric

acid solution;

c) adding a dispersant comprising a sufficient amount of

ground sand or mineral processing tailings during said

pressure leaching step;

d) separating at least a portion of said sulfuric acid

solution from said product slurry to yield a solid

residue;

e) recovering at least one precious metal value from said

solid residue.

17. The process of claim 16 wherein said step of providing

an elemental sulfur-bearing material comprises providing a

sulfur-containing product stream from a pressure leaching

operation carried out at a temperature in the range of about

5 140° C. to about 180° C.

18. The process of claim 16 wherein said step of pressure

leaching comprises pressure leaching at a temperature of

about 235° C.

* * * * *