6,626,979 Method for improving metals recovery using high temperature pressure leaching

Patent Number/Link:

111111111111111111111111111111111111111111111111111111111111111111111111111

US006626979B2

(12) United States Patent

Marsden et al.

(10) Patent No.:

(45) Date of Patent:

US 6,626,979 B2

*Sep. 30, 2003

(54) METHOD FOR IMPROVING METALS

RECOVERY USING HIGH TEMPERATURE

PRESSURE LEACHING

(56) References Cited

U.S. PATENT DOCUMENTS

(73) Assignee: Phelps Dodge Corporation, Phoenix,

AZ (US)

( *) Notice:

OTHER PUBLICATIONS

Ed. By Fathi Habashi: "Handbook of Extractive Metallurgy,"

1997, Wiley-Vch, Germany XP002224090 p.

741-p.743, p. 757-p. 758.

(List continued on next page.)

Primary Examiner-Melvyn Andrews

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

4,338,168 A * 7/1982 Stanley et al. 137/268

4,399,109 A 8/1983 Her et al.

(List continued on next page.)

FOREIGN PATENT DOCUMENTS

3/1982

1/2002

0047076

WO 02/08474

Subject to any disclaimer, the term of this

patent is extended or adjusted under 35

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

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

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

Joanna M. Robertson, Thatcher, AZ

(US); David R. Baughman, Golden,

CO (US); Philip Thompson, West

Valley City, UT (US); Wayne W.

Hazen, Lakewood, CO (US); Roland

Schmidt, Golden, CO (US)

(75)

19 Claims, 2 Drawing Sheets

The present invention is directed to a process for recovering

metal values from metal-bearing materials. During a reactive

process, a seeding agent is introduced to provide a

nucleation site for the crystallization and/or growth of solid

species which otherwise tend to passivate the reactive process

or otherwise encapsulate the metal value, thereby

reducing the amount of desired metal values partially or

completely encapsulated by such material. The seeding

agent may be generated in a number of ways, including the

recycling of residue or the introduction of foreign substances.

Processes embodying aspects of the present invention

may be beneficial for recovering a variety of metals

such as copper, gold, silver, nickel, cobalt, molybdenum,

zinc, rhenium, uranium, rare earth metals, and platinum

group metals from any metal-bearing material, such as ores

and concentrates.

This patent is subject to a terminal disclaimer.

(21) Appl. No.: 10/238,088

(22) Filed: Sep. 9, 2002

(65) Prior Publication Data

us 2003/0019330 A1 Jan. 30, 2003

Related U.S. Application Data

(63) Continuation of application No. 09/912,967, filed on Jul. 25,

2001, now Pat. No. 6,451,088.

(51) Int. CI? C22B 3/06

(52) U.S. Cl. 75/739; 75/740; 75/743;

75/744; 205/560; 423/122; 423/658.3

(58) Field of Search 75/739, 740, 743,

75/744; 423/122, 658.3; 205/560

(57) ABSTRACT

, METAL-BEARING MATERIAL

, ! PROCESSING

, 1 METAL RECOVERY

US 6,626,979 B2

Page 2

U.S. PATENT DOCUMENTS

OlliER PUBLICATIONS

Das G K et al: "Acid pressure leaching of nickel--eontaining

chromite overburden in the presence of additives" Hydrometallurgy,

Elsevier Scientific Publishing Cy. Amsterdam,

NL, vol. 39, No.1, Oct. 1, 1995 (1995-10--01), pp. 117-128,

XP004040725, ISSN: 0304-386X, p. 118 ("Experimental")

abstract.

Database Compendex online! Engineering Information,

Inc., New York, NY, US; Greer Raymond T et al: "Characterization

of Solid Reaction Products From Wet Oxidation of

Pyrite in Coal Using Alkaline Solutions" Database accession

No. EIX82040002261 XP002224019 abstract & Scanning

Electron Microsc 1980 Scanning Electron Microsc, Amf

O'Hare, Chicago, ILL, USA, 1980, pp. 541-550.

PCT International Search Report.

* cited by examiner

Horton et al. 423/20

Landolt et al.

Kerfoot et al. 423/26

Collins et al. 75/728

Jones 75/743

Marsden et al. 75/739

* 11/1989

1/1994

9/1994

3/1998

2/1999

9/2002

4,880,607 A

5,281,252 A

5,348,713 A *

5,730,776 A *

5,869,012 A *

6,451,088 B1 *

u.s. Patent Sep. 30, 2003 Sheet 1 of 2 US 6,626,979 B2

METAL-BEARING MATERIAL

PROCESSING

METAL RECOVERY

FIG. 1

METAL-BEARING MATERIAL

4~ \

1 /5

\ 10"{ PRESSURE LEACHING

V 18

ATMOSPHERIC FLASHING

V 24

20~ LIQUID-SOLID ;

PHASE SEPARATION TO FIG. 3

/28 \ /29 32

30 I ;

SOLVENT EXTRACTION

/34

\ 40"{ SOLVENT STRIPPING r- I

/42 V 48

\ 44"{ ELECTROLYTE RECYCLE TANK r-

/50

ELECTROWINNING r-

FIG. 2

u.s. Patent

Sep. 30, 2003 Sheet 2 of 2

US 6,626,979 B2

! 22

LIQUID-SOLID !

PHASE !---L------,

SEPARATION

NEUTRALIZATION & V 60

pH ADJUSTMENT

HOT LIME BOIL V 62

(OPTIONAL)

PRECIOUS METALS V 64

CYANIDE LEACHING

PRECIOUS METALS V 66

RECOVERY

(LIQUID) LIQUID-SOLID PHASE V 68

SEPARATION (OPTIONAL)

------------------,

CYANIDE V 70

DESTRUCTION

~-----------------

TAILINGS 72

DISPOSAL

FIG. 3

US 6,626,979 B2

BRIEF DESCRIPTION OF THE DRAWING

DETAILED DESCRIPTION OF EXEMPLARY

EMBODIMENTS

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 metal recovery

process in accordance with an exemplary embodiment of the

present invention;

FIG. 2 illustrates a flow diagram of an exemplary metal

recovery process in accordance with an alternative embodiment

of the present invention; and

FIG. 3 illustrates a flow diagram of further aspects of the

exemplary metal recovery process of FIG. 2.

The present invention relates to a metal recovery process

that implements pressure leaching vessel seeding. Generally,

a material bearing a metal value is subjected to a pressure

leaching process wherein a seeding agent is utilized. Metal

values may then be recovered and processed in accordance

60 with various recovery processes.

Referring to FIG. 1, in accordance with various aspects of

the present invention, a metal-bearing material 2 is provided

for processing. Metal-bearing material 2 may be an ore, a

concentrate, or any other material from which metal values

65 may be recovered. Metal values such as, for example,

copper, gold, silver, zinc, platinum group metals, nickel,

cobalt, molybdenum, rhenium, uranium, rare earth metals,

In accordance with an exemplary embodiment of the

present invention, a process for recovering metal from a

metal-bearing material generally includes the steps of: (i)

subjecting a concentrate containing a metal value to a

5 pressure leaching process, wherein the pressure leaching

vessel is seeded with a seeding agent; and (ii) extracting the

metal value from the product of the reactive process. In one

aspect of an alternative embodiment of the invention, the

seeding agent may be recycled residue that is introduced to

10 the pressure leaching vessel. In general, the seeding agent is

selected to enable the formation of a nucleation site for the

crystallization and/or growth of solid species derived from

the solution in which the reactive process occurs. In a further

aspect of the present invention, other foreign material may

15 be used as a seeding agent during pressure leaching. In an

additional aspect of the present invention, a combination of

seeding agents may be used during pressure leaching.

In yet another embodiment of the present invention,

copper is recovered from a metal-bearing material. The

20 copper-containing material is subjected to high temperature

pressure leaching in a pressure leaching vessel, wherein a

seeding agent is introduced into the pressure leaching vessel,

which preferably is a multi-compartment pressure leaching

vessel. The pressure leaching product may then undergo one

25 or more subsequent conditioning and/or refining processes

such that copper and/or other metal values may be recovered

from the pressure leaching product or products.

The advantages of a process according to the various

aspects of the present invention will be apparent to those

30 skilled in the, art upon reading and understanding the

following detailed description with reference to the accompanying

drawing figures.

FIELD OF THE INVENTION

SUMMARY OF THE INVENTION

BACKGROUND OF THE INVENTION

METHOD FOR IMPROVING METALS

RECOVERY USING HIGH TEMPERATURE

PRESSURE LEACHING

CROSS REFERENCE TO RELATED

APPLICATIONS

Smelting is one approach for recovering metals, such as

copper, from metal-bearing sulfide materials. Due to the

high cost of smelting, the copper sulfide minerals in the ore

body typically are first concentrated by flotation techniques

to provide a smaller volume for smelting. The concentrate is

then shipped to a smelter, which processes the concentrate

pyrometallurgically at high temperatures to form a crude

copper product that is subsequently refined to a highly pure

metal.

The recovery of copper from copper sulfide concentrates

using pressure leaching has proven to be a potentially

economically attractive alternative to smelting. Pressure

leaching operations generally produce less fugitive emissions

than smelting operations, and thus, environmental

benefits may be realized. Further, pressure leaching circuits 35

may be more cost-effectively constructed on-site at a

concentrator, eliminating the expense associated with concentrate

transportation that smelting operations may require.

Further, any by-product acid produced in the pressure leaching

circuit may be used in adjacent heap leaching operations, 40

thus offsetting the costs associated with purchased acid.

On the other hand, the application of pressure leaching

may result in unacceptably high copper and precious metal

losses. A significant cause of such metal losses has been

identified when metal values become occluded by materials 45

present in the pressure leaching vessel, such as, for example,

hematite and/or other materials, rendering these metal values

unavailable to subsequent processing, which results in

these metal values being lost.

An effective and efficient method to recover copper from 50

copper-containing materials, especially copper from copper

sulfides such as chalcopyrite and chalcocite, that enables

high copper recovery to be achieved at a reduced cost over

conventional processing techniques and that enhances the

recovery of precious metals from metal-bearing materials 55

would be advantageous.

This process relates generally to a process for recovering

metals from metal-bearing materials, and more specifically,

a process for recovering copper and other metals through

high temperature pressure leaching in a pressure leaching

vessel wherein a seeding agent is added to the pressure

leaching vessel during the oxidation process.

This application is a continuation of U.S. Ser. No. 09/912,

967, filed on Jul. 25, 2001, now U.S. Pat. No. 6,451,088 the

disclosure of which is hereby incorporated by reference.

While the way in which the present invention addresses

the deficiencies and disadvantages of the prior art is

described in greater detail below, in general, according to

various aspects of the present invention, a process for

recovering copper and other metal values from a metalbearing

material includes various reactive and recovery

processes. In a preferred aspect of the invention, a seeding

agent is introduced to the metal recovery process, most

preferably, during a pressure leaching process.

US 6,626,979 B2

and the like may be recovered from metal-bearing materials

in accordance with various embodiments of the present

invention. Various aspects and embodiments of the present

invention, however, prove especially advantageous in connection

with the recovery of copper and gold from goldbearing

copper sulfide ores, such as, for example, goldbearing

chalcopyrite (CuFeS2 ), chalcocite (Cu2 S), bornite

(CUsFeS4 ), and covellite (CuS). Thus, metal-bearing material

2 preferably is a gold-bearing copper ore or concentrate,

and most preferably, is a gold-bearing copper sulfide ore or

concentrate.

Metal-bearing material 2 may be prepared for pressure

leaching processing in any manner that enables the conditions

of metal-bearing material 2-such as, for example,

particle size, composition, and component concentrationto

be suitable for the chosen processing method, as such

conditions may affect the overall effectiveness and efficiency

of processing operations. Desired composition and component

concentration parameters can be achieved through a

variety of chemical and/or physical processing stages, the

choice of which will depend upon the operating parameters

of the chosen processing scheme, equipment cost and material

specifications. For example, metal-bearing material 2

may undergo comminution, flotation, blending, and/or slurry

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

Referring again to FIG. 1, after metal-bearing material 2

has been suitably prepared for processing, it is subjected to

a processing step 4. Processing step 4 may be any suitable

process or reaction that puts a metal value in metal-bearing

material 2 in a condition such that it may be subjected to

later recovery steps. For example, exemplary suitable processes

include reactive processes which tend to liberate a

desired metal value in the metal bearing material 2 from the

metal-bearing material 2. In accordance with one embodiment

of the present invention, processing step 4 comprises

pressure leaching, either at medium temperatures (e.g., from

about 120° C. to about 190° C.) or high temperatures (e.g.,

greater than about 200° C.).

In accordance with another embodiment of the invention,

processing step 4 comprises a high temperature pressure

leaching process operating at a temperature in the range of

about 170° C. to about 235° C., more preferably from about

200° C. to about 230° c., and optimally above about 200° C.

Processing step 4 may occur in any pressure leaching

vessel suitably designed to contain the pressure leaching

mixture at the desired temperature and pressure conditions

for the requisite pressure leaching residence time.

Preferably, the pressure leaching vessel used in processing

step 4 is an agitated, multi-compartment pressure leaching

vessel. However, it should be appreciated that any pressure

leaching vessel that suitably permits metal-bearing material

to be prepared for metal recovery may be utilized within the

scope of the present invention.

During processing step 4, metal values may be solubilized

or otherwise liberated in preparation for later recovery

processes. Any substance that assists in solubilizing the

metal value, and thus releasing the metal value from a

metal-bearing material, may be used. For example, in a

metal recovery process wherein copper is the metal being

recovered, an acid, such as sulfuric acid, may be contacted

with the copper-bearing material such that the copper may

be solubilized for later recovery steps. However, it should be

appreciated that any suitable method of solubilizing metal

values in preparation for later metal recovery steps may be

utilized within the scope of this invention.

In accordance with a preferred aspect of the present

invention, a seeding agent is introduced to the reactive

process during processing step 4, prior to metal value

recovery. While a seeding agent may be utilized, care should

be taken to ensure that it does not negatively impact the

overall metal recovery process. A suitable seeding agent

5 preferably comprises any material capable of forming a

nucleation site for the crystallization and/or growth of solid

species. For example, in accordance with various aspects of

the present invention, as discussed hereinabove, a metal to

be recovered is liberated in connection with the reactive

10 process. The present inventors have found that often materials

that precipitate or crystallize from solution tend to

passivate the reactive process and/or encapsulate a metal or

metals to be recovered. Through use of the inventive seeding

agent, such species are urged to crystallize, precipitate or

15 otherwise form at or in proximity to the seeding agent,

instead of the metal value, thus leaving the metal value

exposed and amenable to subsequent leaching or other

recovery.

Accordingly, the seeding agent may be any particle which

20 acts as a site for particle accumulation and/or precipitation,

and may originate from recycled materials from other stages

of the metal recovery process or may be provided by the

addition of substances that are foreign to the metal recovery

process. In some cases, the seeding agent comprises any

25 material that promotes crystallization, precipitation, and/or

growth of unwanted materials-for example in the preferred

case of copper recovery, hematite, gangue, and the likethat

may otherwise tend to partially or completely encapsulate

the desired metal values, rendering the desired metal

30 values (e.g., copper and gold) generally unavailable or less

accessible to a lixiviant solution. As is known, in

precipitation, seed particles tend to grow in size through

deposition of materials from solution. Accordingly, nonpreferential

precipitation onto other (i.e., non-seed) material

35 surfaces may also occur.

One source of suitable seeding agents useful in accordance

with various aspects of the present invention are those

materials which can be found in the pressure leaching vessel

discharge, which materials may be recycled for seeding

40 purposes. Use of the recycled pressure leaching vessel

discharge may be desirable for economic reasons, and using

a seeding agent that is similar or identical to unwanted

particles in the pressure leaching process slurry may tend to

encourage the accumulation of unwanted material. For

45 example, in metal recovery processes where an unwanted

material, such as hematite, is either present in the metalbearing

material or is produced as a by-product, introduction

of recycled hematite-containing residue from previous pressure

leaching processes likely will tend to provide newly

50 formed or liberated hematite a preferential nucleation site. In

the absence of this nucleation site, unreactive particles may

occlude the desired metal values to solubilization by precipitating

on the surface of the metal values, rendering the

metal values unrecoverable. Therefore, introducing a seed-

55 ing agent to prevent such occlusion may assist in providing

better metal recovery.

Another source of suitable seeding agents useful in accordance

with various aspects of the present invention are other

by-products of the recovery process. For example, in cases

60 where the metal-bearing material selected for use in connection

with the recovery process of the present invention

comprises multiple metal values, for example, copper, gold,

and/or silver, it may be desirable to recover the metals in

sequential recovery steps. For example, if copper is initially

65 recovered through a pressure leaching process, gold and

silver may be thereafter recovered, for example, through the

use of cyanide leaching. In such a case, the cyanideUS

6,626,979 B2

5 6

solid-liquid phase separation stages may be used to separate

solubilized metal solution from solid particles. This may be

accomplished in any conventional manner, including use of

filtration systems, counter-current decantation (CCD)

5 circuits, thickeners, centrifuges, and the like. A variety of

factors, such as the process material balance, environmental

regulations, residue 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

10 in a solid-liquid separation apparatus. However, it should be

appreciated that any technique of conditioning the product

slurry for later metal value recovery is within the scope of

the present invention.

As further discussed hereinbelow, the separated solids

15 may further be subjected to later processing steps, including

precious metal or other metal value recovery, such as, for

example, recovery of gold, silver, platinum group metals,

nickel, cobalt, molybdenum, zinc, rhenium, uranium, rare

earth metals, and the like. Alternatively, the separated solids

20 may be used for seeding purposes during reactive processing

as described above, or may be subject to disposal.

The liquid separated from a liquid-solid separation apparatus

may also undergo a series of conditioning steps to

prepare the metal values solubilized therein for metal recov-

25 ery. For example, the separated liquid may undergo various

reagent additions and/or solvent extraction stages to put the

metal values in a state such that the metal values are

susceptible to metal recovery techniques. Further, subsequent

conditioning and/or processing steps may be under-

30 taken such that recovery rates are as efficient as possible.

After any desired preparation steps, the pressure leaching

product stream may undergo the desired metal recovery step.

The metal value recovery method may include any suitable

35 conventional method of removing the desired metal values

from solutions, such as, for example, electrowinning,

precipitation, solvent extraction, cyanidation, ion exchange,

and/or ion flotation, and preferably results in a relatively

pure metal product.

In an exemplary embodiment of the present invention

illustrated in FIG. 2, a copper-containing feed stream 4

containing a copper-containing material 2 is provided for

metal value recovery. The copper in copper-containing

material 2 may be in any form from which copper may be

45 extracted, such as copper oxide or copper sulfide, for

example chalcopyrite (CuFeS2 ), chalcocite (Cu2 S), bornite

(CusFeS4), and covellite (CuS). Copper-containing material

2 also may include any number of a variety of other metals,

such as gold, silver, platinum group metals, zinc, nickel,

50 molybdenum, cobalt, rare earth metals, rhenium, uranium,

and/or mixtures thereof.

In accordance with one embodiment of the present

invention, feed stream 4 is combined with a liquid 6, which

may comprise water, to form a feed slurry 5. Feed slurry 5

55 is then subjected to a pressure leaching step 10.

Alternatively, feed stream 4 may be directly fed into a

pressure leaching device (step 10), such as a pressure

leaching vessel, together with other feed streams, namely

feed stream 6.

In one embodiment (not shown in FIG. 2), coppercontaining

material feed stream 4 is prepared for pressure

leaching by comminuting a copper-containing material and

subjecting it to flotation. In this case, feed stream 4 is

combined with a liquid, preferably water, to form feed slurry

65 5, is subjected to pressure leaching (step 10 in FIG. 2). The

combination of liquid with feed stream 4 can be effectuated

using anyone or more of a variety of techniques and

attenuated cyanide leach tailings may suitably be used as a

seeding agent in accordance with the present invention.

A seeding agent suitable in accordance with a further

aspect of the present invention may also be a material that

is not a by-product of any reactive processing. For example,

particles that are foreign to the recovery process, such as

hematite, sand, silica sand, clays, and/or jarosite may be

used. Still further, generally unreactive particulate materials

such as, for example, low grade concentrate, tailings, or

intermediate product streams from mineral processing

activities, may be added to the pressure leaching vessel. It

should be appreciated, however, that in accordance with

various aspects of the present invention, any material that is

capable of forming a nucleation site for the crystallization

and/or growth of solid species is within the scope of the

invention.

In accordance with still further aspects of the present

invention, the seeding agent may be suitably selected and

varied during operation of a continuous recovery process.

For example, again for purposes of illustration only, in cases

where the metal-bearing material selected contains copper

and other precious metals, such as gold and/or silver, the

seeding material initially may be a generally unreactive

additive, for example, hematite, and thereafter processing

by-products, such as, for example solid-liquid separation

residue, cyanide-attenuated cyanide leach tailings, and the

like, may be recycled to the reactive process and serve as the

seeding agent during continued operation of the recovery

process.

Subsequent to metal-bearing material 2 undergoing the

reactive processing of step 4, the metal values that have been

made available by the reactive process may undergo various

recovery processes. Referring again to FIG. 1, recovery

process 6 may be any process for recovering metal values,

and may include any number of preparatory or conditioning

steps. For example, a metal-bearing solution may be prepared

and conditioned for metal recovery through one or

more chemical and/or physical processing steps. The metalbearing

solution may be conditioned to adjust the 40

composition, component concentrations, solids content,

volume, temperature, pressure, and/or other physical and/or

chemical parameters to desired values. Generally, a properly

conditioned metal-bearing solution will contain a relatively

high concentration of soluble metal, for example, copper

ions and sulfate in solution and preferably will contain few

impurities. Moreover, the conditions of the metal-bearing

solution preferably are kept substantially constant to

enhance the quality and uniformity of the metal product

ultimately recovered.

In one aspect of a preferred embodiment of the present

invention, conditioning of a copper-containing solution for

copper recovery in an electrowinning circuit begins by

adjusting certain physical parameters of the product slurry

from the reactive processing step. In a preferred aspect of

this embodiment of the invention, wherein the reactive

processing step is high temperature pressure leaching, it is

desirable to reduce the temperature and pressure of the

product slurry. A preferred method of so adjusting the

temperature and pressure characteristics of the copper- 60

containing product slurry from a high temperature pressure

leaching stage is atmospheric flashing.

In accordance with further aspects of this preferred

embodiment, after the product slurry has been subjected to

atmospheric flashing using, for example, a flash tank, the

product slurry may be further conditioned in preparation for

later metal-value recovery steps. For example, one or more

US 6,626,979 B2

apparatus, such as, for example, in-line blending or using a

mixing tank or other suitable vessel. The combined material

may then be subjected to a flotation processing step (not

shown), and the flotation product thereafter may be filtered,

air dried, and repulped before being subjected to pressure

leaching.

With continued reference to FIG. 2, feed slurry 5 is

suitably introduced to a pressure leaching vessel to undergo

high temperature pressure leaching; as such, the pressure

leaching vessel preferably comprises a sealed, multicompartment

pressure leaching vessel 10. Feed slurry 5 may

have a solid particle size on the order of less than about 100

microns, preferably ranging from about 45 to about 60

microns. More preferably, the solid particle size of feed

slurry 5 is suitably dimensioned such that the size distribution

of no more than about 20% of the concentrated coppercontaining

materials is larger than about 60 microns. In

accordance with a preferred aspect of this embodiment, feed

slurry 5 has a preferred solid-liquid ratio ranging from about

5 percent to about 50 percent solids by weight, and preferably

from about 10 percent to about 35 percent solids by

weight.

Any agent capable of assisting in the solubilization of the

metal value to be recovered (e.g., copper), such as, for

example, sulfuric acid, may be provided during the pressure

leaching process in a number of ways. For example, such

acids may be provided in a cooling stream provided by the

recycle of the raffinate solution 32 from the solvent extraction

step 30 (before or after solubilization, see FIG. 3),

and/or the recycle of a portion of the liquid phase of the

product slurry 18, and/or by the production during pressure

leaching of a sulfuric acid from the oxidation of the sulfide

minerals in the feed slurry. However, it should be appreciated

that any method of providing for the solubilization of

copper is within the scope of the present invention.

In accordance with one aspect of this exemplary

embodiment, the high temperature pressure leaching process

in pressure leaching vessel 10 preferably occurs in a manner

suitably selected to promote the solubilization of the metal

value to be recovered (e.g., copper). Various parameters may

influence the high temperature pressure leaching process.

For example, during pressure leaching, it may be desirable

to introduce materials to enhance the pressure leaching

process. In accordance with one aspect of the present

invention, during pressure leaching in the pressure leaching

vessel, sufficient oxygen 14 may be injected into the vessel

to maintain an oxygen partial pressure from about 50 to

about 200 psi, preferably from about 75 to about 150 psi, and

most preferably from about 100 to about 125 psi.

Furthermore, due to the nature of high temperature pressure

leaching, the total operating pressure in the pressure leaching

vessel is generally superatmospheric, preferably from

about 250 to about 750 psi, more preferably from about 300

to about 700 psi, and most preferably from about 400 to

about 600 psi.

The residence time for the high temperature pressure

leaching process can vary, depending on factors such as, for

example, the characteristics of the metal-bearing material

and the operating pressure and temperature of the reactor. In

one aspect of the invention, the residence time for the high

temperature pressure leaching process ranges from about 30

to about 120 minutes.

Control of the pressure leaching process, including control

of the temperature in pressure leaching vessel 10, may

be accomplished by any conventional or hereafter devised

method. For example, in accordance with one aspect of the

invention, the temperature of the pressure leaching vessel 10

is maintained at from about 200° C. to about 235° c., and

more preferably from about 215° C. to about 230° C. Due to

the exothermic nature of pressure leaching of many metal

5 sulfides, the heat generated by high temperature pressure

leaching is generally more than that needed to heat feed

slurry 5 to the desired operating temperature. Thus, in order

to maintain preferable feed slurry temperature, a cooling

liquid may be contacted with the feed slurry during pressure

10 leaching. In accordance with one aspect of this embodiment

of the present invention, a cooling liquid is preferably

contacted with the feed stream in pressure leaching vessel 10

during pressure leaching. Cooling liquid may comprise

make-up water, but can be any suitable cooling fluid from

15 within the process or from an outside source, such as

recycled liquid phase from the product slurry, neutralized

raffinate solution 32, or a mixture of cooling fluids. Cooling

liquid may be introduced into pressure leaching vessel 10

through the same inlet as feed slurry, or alternatively in any

20 manner that effectuates cooling of feed slurry 5. The amount

of cooling liquid added to feed slurry 5 during pressure

leaching may vary according to the amount of sulfide

minerals in and the pulp density of the feed slurry 5, as well

as other parameters of the pressure leaching process. In a

25 preferred aspect of this embodiment of the invention, a

sufficient amount of cooling liquid is added to pressure

leaching vessel 10 to yield a solids content in product slurry

18 on the order of less than about 50% solids by weight, and

more preferably ranging from about 3 to about 35% solids

30 by weight.

In accordance with one aspect of the present invention, an

unreactive seeding agent is introduced into a high temperature

pressure leaching process to assist in metal recovery.

Referring to FIGS. 2 and 3, in accordance with a preferred

35 aspect of this embodiment of the present invention, residue

22 may be recycled to pressure leaching vessel 10 and used

as a seeding agent. Residue 22 may be divided such that a

portion is directed back to pressure leaching vessel 10 and

the remainder may be either discarded or subjected to further

40 metal recovery (such as, for example, as illustrated in an

exemplary fashion in FIG. 3). For example, and as is shown

in FIG. 3, the portion of residue stream 22 that is not

recycled as a seeding agent to pressure leaching vessel 10

may undergo precious metal recovery using cyanidation or

45 any other metal recovery technique. Particles in the portion

of residue stream 22 that are recycled to pressure leaching

vessel 10 may act as accumulation sites for precipitation of

other materials, such as hematite, as described above, thus

enhancing the amount of copper that may be recovered.

50 Recycled residue 22 may be delivered to pressure leaching

vessel 10 by pumping and piping to the pressure leaching

vessel, a feed tank, or other suitable intermediate location. It

should be appreciated that numerous other unreactive and/or

reactive materials may be used as seeding agents in accor-

55 dance with the present invention and may be used in

combination with the feed stream to the pressure leaching

vessel.

In accordance with a preferred aspect of the embodiment

of the invention illustrated in FIG. 2, product slurry 18 from

60 pressure leaching vessel 10 may be flashed in an atmospheric

flash tank 16 or other suitable vessel to release

pressure and to evaporatively cool product slurry 18 through

the release of steam to form a flashed product slurry 24.

Depending upon the specific process equipment configura-

65 tions and specifications, more than one flash stage may be

employed. Flashed product slurry 24 preferably has a temperature

ranging from about 90° C. to about 105° c., a

US 6,626,979 B2

copper concentration of from about 35 to about 60 grams/

liter, and an acid concentration of from about 10 to about 60

gramslliter.

Referring still to FIG. 2, flashed product slurry 24 may be

directed to a solid-liquid separation apparatus 20, such as a

counter-current decantation (CCD) circuit. Alternatively, the

solid-liquid separation apparatus may comprise, for

example, a thickener or a filter. In one aspect of a preferred

embodiment of the invention, solid-liquid phase separation

step 20 may be carried out with a conventional CCD

utilizing conventional counter-current washing of the residue

stream to recover leached copper to the coppercontaining

solution product and to minimize the amount of

soluble copper advancing to precious metal recovery processes

or storage. Preferably, large wash ratios are utilized to

enhance the effectiveness of the solid-liquid separation

stage-that is, relatively large amounts of wash water are

added to the residue stream in CCD circuit 20. Preferably,

flash product slurry 24 is diluted by the wash water in CCD

circuit 20 to form a copper-containing solution having a

copper concentration of from about 15 to about 60 grams/

liter.

Depending on its composition, residue stream 22 from

solid-liquid separation apparatus 20, as discussed above,

may be used as a seeding agent during pressure leaching,

may be disposed of or subjected to further processing, such

as, for example, precious metal recovery. For example, if

residue stream 22 contains an economically significant fraction

of gold, it may be desirable to recover this gold fraction

through a cyanidation process or other suitable recovery

process. If gold and/or other precious metals are to be

recovered from residue stream 22 by cyanidation

techniques, the content of contaminants in the stream, such

as elemental sulfur, iron precipitates, and unreacted copper

minerals, is preferably minimized. Such materials generally

promote high reagent consumption in the cyanidation process

and thus increase the expense of the precious metal

recovery operation. Additionally, as mentioned above, it is

preferable to use a large amount of wash water or other

diluting solution during the solid-liquid separation process

to maintain low copper and acid levels in the CCD residue

in an attempt to optimize the residue stream conditions for

precious metal recovery.

Referring now to FIG. 3, residue 22 from solid-liquid

separation step 20 may be subjected to various further

processing. Depending on the characteristics of residue 22,

it may be advantageous to subject it to neutralization and/or

pH adjustment, such as is illustrated in step 60. The residue

once so treated may be recycled to pressure leaching 10, or

subjected to further processing.

Such processing may include, with continued reference to

FIG. 3, an optional hot lime boil (step 62) followed by

precious metal recovery (step 66), such as through the use of

conventional cyanide leaching (step 64) followed by liquidsolid

phase separation (step 68). If cyanide leaching is used,

the resultant tailings may be recycled to pressure leaching

10, as shown, to be used as a seeding agent, preferably after

the cyanide is destroyed or attenuated (step 70), or alternatively

disposed of (step 72). As illustrated in FIG. 3, various

alternative processing routes may be utilized.

In accordance with various aspects of the present

invention, even when there is little gold present in the

residue, use of a seeding agent in the pressure leaching

process can increase the recovery of the gold present in the

residue stream. For example, although extraction of gold

from the residue in pilot plant experiments was on the order

of from about 73 to about 82% when a seeding agent was not

introduced into the pressure leaching vessel, use of a seeding

agent (e.g., hematite) during pressure leaching enabled laboratory

gold extractions from the residue ranging from about

5 89 to about 91%.

Referring back to FIG. 2, in accordance with various

aspects of the present invention, the recovery of the desired

metal value (e.g., copper) may be accomplished through

conventional solvent extraction/electrowinning (SXIEW)

10 techniques. For example, a diluting solution 26 may be

contacted with the separated liquid 28 from solid-liquid

separation apparatus 20 to reduce the acid concentration of

the separated liquid 28 sufficiently to provide desirable

equilibrium conditions for solvent extraction 30. Solution 26

15 may be any suitable liquid, for example, water or atmospheric

leach efiluent solution, that sufficiently reduces the

copper and acid concentrations to desired levels. In a preferred

aspect of this embodiment of the invention, sufficient

amount of solution 26 is contacted with the separated liquid

20 stream 28 to yield an acid concentration in the diluted

copper-containing solution preferably ranging from about 2

to about 25 grams/liter, and more preferably from about 4 to

about 7 grams/liter and a pH preferably ranging from about

pH 1.5 to about pH 2.5 and more preferably from about pH

25 1.8 to about pH 2.2, and optimally in the range of about pH

2.0.

The diluted copper-containing solution 29 may be further

processed in a solvent extraction step 30. During solvent

extraction 30, copper from copper-containing solution 29

30 may be loaded selectively onto an organic chelating agent,

for example, an aldoximelketoxime blend, resulting in a

copper-containing organic stream 34 and a raffinate solution

32. Raffinate 32 from solvent extraction step 30 may be used

in a number ways. For example, all or a portion of raffinate

35 32 maybe recycled to pressure leaching vessel 10 for temperature

control or may be used in heap leaching operations,

or may be used for a combination thereof. The use of

raffinate 32 in heap leaching operations may be beneficial

because the acid and ferric/ferrous iron values contained in

40 raffinate 32 can act to optimize the potential for leaching

oxide and/or sulfide ores that commonly dominate heap

leaching operations. That is, the ferric and acid concentration

of raffinate 32 may be used to optimize the Eh and pH

of heap leaching operations. It should be appreciated that the

45 properties of raffinate 32, such as component concentrations,

may be adjusted in accordance with the desired use of

raffinate 32.

Copper-containing organic stream 34 is then subjected to

a solvent stripping phase 40, wherein more acidic conditions

50 may shift the equilibrium conditions to cause the copper in

the reagents to be exchanged for the acid in a highly acidic

stripping solution. As shown in FIG. 2, an acid-bearing

reagent 38, preferably sulfuric acid, and optionally, lean

electrolyte 48, are contacted with copper-containing organic

55 stream 34 during solvent stripping phase 40. Sulfuric acid is

a preferred acid-bearing reagent and is a desirable copper

matrix for electrowinning operations. The acid-bearing

reagent is contacted with the copper-containing organic

stream to effectuate the exchange of acid for copper to

60 provide copper for metal recovery 46.

Referring still to FIG. 2, copper-containing solution

stream 42 from solvent stripping phase 40 may be sent to an

electrolyte recycle tank 44. The electrolyte recycle tank may

suitably facilitate process control for electrowinning stage

65 46, as will be discussed in greater detail below. Coppercontaining

solution stream 42, which generally contains

from about 35 to about 50 grams/liter of copper and from

US 6,626,979 B2

about 160 to about 180 grams/liter acid, is preferably

blended with a lean electrolyte 48 (i.e., electrolyte that has

already been through the metal recovery phase and has had

a portion of its dissolved copper removed) and make-up

fluid 52, such as, for example, water, in the electrolyte 5

recycle tank 44 at a ratio suitable to yield a product stream

50, the conditions of which may be chosen to optimize the

resultant product of metal recovery 46.

Preferably, the copper composition of product stream 50

is maintained substantially constant at a value from about 20 10

to about 60 grams/liter, more preferably at a value from

about 30 to about 50 grams/liter. Copper values from the

copper-containing product stream 50 are removed during

metal recovery step 46, preferably using electrowinning, to

yield a pure, cathode copper product. It should be appreci- 15

ated that in accordance with the various aspects of the

invention, a process wherein, upon proper conditioning of

the copper-containing solution, a high quality, uniformlyplated

cathode copper product may be realized without

subjecting the copper-containing solution to solvent extrac- 20

tion prior to entering the electrowinning circuit is within the

scope of the present invention. As those skilled in the art are

aware, a variety of methods and apparatus are available for

the electrowinning of copper and other metal values, any of

which may be suitable for use in accordance with the present 25

invention, provided the requisite process parameters for the

chosen method or apparatus are satisfied.

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 30

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 embodi- 35

ments without departing from the scope of the present

invention. For example, although reference has been made

throughout to various metal value recovery examples, it is

intended that the invention also be applicable to the recovery

of other materials that may be recovered through reactive 40

processing that incorporate use of a seeding agent. Further,

although certain preferred aspects of the invention, such as

materials for seeding the reactive process, for example, are

described herein in terms of exemplary embodiments, such

aspects of the invention may be achieved through any 45

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 claims.

What is claimed is:

1. A process for recovering a metal value from a metalbearing

material comprising the steps of:

subjecting a metal-bearing material to a reactive process

to liberate at least one metal value from said metal- 55

bearing material;

incorporating at least one seeding agent into said reactive

process, said seeding agent capable of forming a nucleation

site for the crystallization and/or growth of solid

species from said reactive process;

obtaining a product from said reactive process, wherein at

least one metal value is present in said product; and

extracting said at least one metal value from said product.

2. A process for recovering a metal value from a metalbearing

material according to claim 1, wherein said seeding 65

agent comprises at least a portion of a residue from said

reactive process.

3. A process for recovering a metal value from a metalbearing

material according to claim 1, further comprising the

step of recovering metals which are present in said residue

from said reactive process before using said residue as said

seeding agent.

4. A process for recovering a metal value from a metalbearing

material according to claim 1, wherein said seeding

agent is not a by-product of said reactive process.

5. A process for recovering a metal value from a metalbearing

material according to claim 1, further comprising the

step of adding a plurality of seeding agents to said reactive

process.

6. A process for recovering a metal value from a metalbearing

material according to claim 1, wherein said metal

value is selected from the group consisting of copper, gold,

silver, nickel, cobalt, molybdenum, zinc, rhenium, uranium,

rare earth metals, and platinum group metals.

7. A process for recovering a metal value from a metalbearing

material according to claim 2, wherein said metal

present in said residue is selected from the group consisting

of copper, gold, silver, nickel, cobalt, molybdenum, zinc,

rhenium, uranium, rare earth metals, and platinum group

metals.

8. A process for recovering a metal value from a metalbearing

material according to claim 1, further comprising the

step of extracting said metal value from said product of said

reactive process using electrowinning.

9. A process for recovering a metal value from a metalbearing

material according to claim 1, wherein said reactive

process comprises pressure leaching.

10. A process for recovering a metal value from a metalbearing

material according to claim 9, wherein said reactive

process comprises pressure leaching at a temperature of

about 170° C. to about 235° C.

11. A process for recovering a metal value from a metalbearing

material according to claim 1, wherein said step of

subjecting a metal-bearing material to a reactive process

produces acid, and further comprising the step of utilizing at

least a portion of the acid produced by said reactive process

in a heap leaching operation or an agitated leaching operation.

12. A process for recovering a metal value from a metalbearing

material according to claim 1, wherein said step of

extracting at least one metal value from said product comprises

extracting at least one precious metal from said

product.

13. A process for recovering a metal value from a metalbearing

material according to claim 1, wherein said step of

extracting at least one metal value from said product comprises

extracting gold from said product.

14. In a process for recovery of a precious metal from a

copper-containing material comprising subjecting the

copper-containing material to a reactive process to liberate

the copper from said copper-containing material and to form

a residue comprising the precious metal, wherein materials

are present or generated in said reactive process that either

passivate said reactive process or encapsulate the precious

metal, thus preventing later liberation of the precious metal

from said residue,

the improvement comprising introducing a seeding agent

into said reactive process to prevent said materials

present or generated during said reactive process from

passivating said reactive process or encapsulating the

precious metal.

15. The improved process of claim 14 wherein said

seeding agent comprises a material capable of forming a

nucleation site for the crystallization and/or growth of solid

species from the reactive process.

US 6,626,979 B2

16. The improved process of claim 14, wherein said

seeding agent comprises a material capable of forming a

nucleation site for iron and other metal precipitation products.

17. The improved process of claim 16, wherein said 5

seeding agent comprises a material capable of forming a

nucleation site for hematite.

18. A metal recovery process comprising the steps of:

(a) providing a metal-bearing material including at least

one metal value and at least one precious metal;

(b) subjecting said metal-bearing material to a reactive

process to liberate said at least one metal value;

prevent said reactive process from passivating or

encapsulating said at least one metal value;

(d) recovering said at least one metal value.

19. The process of claim 18 further comprising the step of

(e) recovering at least one precious metal from said metalbearing

material.

* * * * *