7,691,347 Silica removal from pregnant leach solutions

Patent Number/Link:

111111111111111111111111111111111111111111111111111111111111111111111111111

US007691347B2

(12) United States Patent

Gillaspie et al.

(10) Patent No.:

(45) Date of Patent:

US 7,691,347 B2

Apr. 6,2010

(54) SILICA REMOVAL FROM PREGNANT

LEACH SOLUTIONS

6,416,672 Bl 7/2002 Midkiff

(Continued)

FOREIGN PATENT DOCUMENTS

(75) Inventors: James D. Gillaspie, Gilbert, AZ (US);

David R. Baughman, Golden, CO (US);

Dennis D. Gertenbach, Lakewood, CO

(US); Wayne W. Hazen, Lakewood, CO

(US); George Owusu, Thornton, CO

(US); John C. Wilmot, Anthem, AZ

(US)

CA 2295066 2/1999

(73) Assignee: Freeport-McMoran Corporation,

Phoenix, AZ (US) (Continued)

OTHER PUBLICATIONS

(Continued)

Cooper, R.M.G., "Silica Precipitation From Electrolyitc Zinc Solutions

(Doctor Thesis)," Curtin University of Technology, School of

Applied Chemistry, Perth, AU, Dec. 1998 (XP002502895) (20 pgs).

Primary Examiner-Melvin C Mayes

Assistant Examiner-Stefanie Cohen

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

Mar. 19,2009

Prior Publication Data

Filed: Sep. 19, 2007

US 2009/0074640 Al

( *) Notice:

(22)

(65)

Subject to any disclaimer, the term ofthis

patent is extended or adjusted under 35

U.S.c. l54(b) by 40 days.

(21) Appl. No.: 11/857,941

U.S. PATENT DOCUMENTS

Int. Cl.

C22B 11/00 (2006.01)

U.S. Cl. 423/34

Field of Classification Search None

See application file for complete search history.

References Cited

13 Claims, 7 Drawing Sheets

The present invention relates generally to a process for

removing dissolved or colloidal silica from a pregnant leach

solution ("PLS"). More particularly, an exemplary embodiment

ofthe present invention relates to a process which mixes

PLS with an acid source, preferably lean electrolyte, to

induce formation ofcolloidal silica that can then be collected

and removed. Additionally, in an exemplary embodiment of

the present invention, at least one silica seeding agent is added

to induce formation ofcolloidal silica, at least one flocculant

is added to induce aggregation of the colloidal silica, and a

solid-liquid separation process is utilized to remove advantageous

amounts or substantially all of the colloidal silica,

thereby providing relief from supersaturation of dissolved

silica in the metal recovery processes.

(57) ABSTRACT

4/1972 Matthew et al.

5/1974 Slusarczuk et aI.

5/1976 Bodson

9/1982 Ishiwata et al.

8/1983 Her et al.

3/1984 Rex

8/1988 Featherstone

3/1991 Browne

9/1995 Browne

6/2002 Cifuentes et al.

6/2002 White

3,656,941 A

3,810,843 A

3,954,937 A

4,349,513 A

4,399,109 A

4,437,995 A

4,765,913 A

4,997,573 A

5,453,206 A

6,409,799 Bl

6,409,979 Bl

(52)

(58)

(56)

(51)

RELIEF FROM SUPERSATURATION USING GALACTOSOL-CIBA-SILICA SEEDING AGENT

./'

I ' ...... 2S;ILSOlidS r- I 1....29i/Lsolids

o 10 "

Sample Time, hr •• ..

Note: 45 mg/L Si equilibrium concentration assumed; no PEO treatment

US 7,691,347 B2

Page 2

u.s. PATENT DOCUMENTS

FOREIGN PATENT DOCUMENTS

0851034

1650163

Matthew, I.G., et aI., "The Hydrometallurgical Treatment of Zinc

Silicate Ores," Metallurgical Transactions B, vol. 8B, Mar. 1977, pp.

73-83 (XP009108278).

International Search Report and Written Opinion for corresponding

PCT Application No. PCTIUS2008/075043 dated Dec. 15,2008.

* cited by examiner

7/1927

111988

10/1996

9/2006

4/2004

5/2006

OTHER PUBLICATIONS

274297

63001496

8276191

2006-257540

WO 2004029306

WO 2006/049632

7/1998

4/2006

9/2002 Marsden et al.

5/2004 Balliett et al.

5/2005 Marsden et al.

5/2003 Balliett et al.

4/2004 Fugleberg et al.

112005 Balliett et al.

6/2005 Marsden et al. 205/580

7/2006 Marsden et al.

6,451,088 Bl

6,730,279 B2

6,893,482 B2

2003/0086864 Al

2004/0074340 Al

2005/0019247 Al

2005/0126923 Al *

2006/0144717 Al

u.s. Patent Apr. 6,2010 Sheet 1 of? US 7,691,347 B2

100

SOLIDS

BLEED

117 OR 127

CONDITIONING (OPTIONAL)

f201

~01

) 101

)202 302

REACTIVE PROCESSING ~

)102

CONDITIONING (OPTION) lr 203

)103

L~S.r204 SECONDARY

METAL

RECOVERY/

)104 DISPOSAL )

208

SILICA REMOVAL CIRCUIT

)111

216

ELECTROLYTE RECYCLE

TANK

) 118

f218

ELECTROWINNING

METAL PRODUCT

120

) 121

~ ~

BLEED

108 119

FIG. 1

u.s. Patent Apr. 6,2010 Sheet 2 of? US 7,691,347 B2

208~

PREGNANT LEACH

SOLUTION

104

108

212

210

114

MIXING TANKS(S)

112

FLOCCULANT REAGENT DOSING

ACID SOURCE ---.L=--..r-------L....---L....-~

SEEDING AGENT-.--+!L...-- ..---- ----'

109

113

214

111

TO ELECTROLYTE RECYCLE

TANK

FIG. 2

107 OR 108 ACID

7J).

•

~=~

rFJ =('

(..'D...

(.H

o....

......:J

rJl

......:J

0-.,

W"""'"

......:J =N

:-:

~Cl\

.... o

CLEANED

ELECTROLYTE

TO TANK

REMOVED OR

FORMED SILICA

BLEED

FIG. 3

-IU4

.~ SEEDING 109

~ AGENT + 1

MIXING TANK + 1)2 1)3 FLOCCULANT

MIXING TANK + ~

~ 1)4

210 REAGENT DOSING ~

2~0 TANK ~2

2~2

2~4

)10 ?17

rFJ =('

(..'D...

,j;o,.

o....

......:J

7J).

•

~=~

:-:

~Cl\

.... o

CLEANED

ELECTROLYTE

TO TANK

REMOVED OR

FORMED

SILICA BLEED

.~ 109 ~t:t:UINlj

~ AGENT

1+ 1

MIXING TANK ...

MIXING TANK 113 FLOCCULANT

2~0

MIXING TANK ... )14

2~0 hJ6 REAGENT ..

2~ DOSING TANK ~11

115 2{;

)10

2(4

107 OR 108 ACID

10' ..J SOURCE

FIG. 4

rJl

......:J

0-.,

W"""'"

......:J =N

RELIEF FROM SUPERSATURATION USING FUMED SILICA SEEDING AGENT

100 , • i , , i

7J).

•

~=~

rFJ =('

(..'D...

o....

......:J

:-:

~Cl\

.... o

rJl

",......:I

0'1

W"""'"

......:I =N

15 20 2S

Sample Time, hr

5 10

Note: 45 mg/L Si equilibrium concentration assumed; no PEO treatment

FIG. 5

-0-3 wt%, 1:1 SPLS:LE @ 122 gIL acid

....-- 5 wt%, 1:1 SPLS:LE @ 122 gIL acid

II F "F= I I _ 3 WI%, 2: 1 SPLS:LE @ 122 gIL acid

-)IE- 5 wt%, 2:1 SPLS:LE@ 122 gIL acid

____ 5 wt%, SPLS:LE @ 122 gIL acid

-0-5 wt%, 1:1 SPLS:LE@ 122 gIL acid

00 '.J' , • ,

'if!.

~ 60

III

:::J

(/) --0 -40 .!!1

0::

RELIEF FROM SUPERSATURATION USING (PEO)- SILICA SEEDING AGENT

:-:

~Cl\

.... o

rFJ =('

(..'D...

Cl\

o....

......:J

7J).

•

~=~

-+- 25 gil solids SPLS @ 13 gil acid

-II- 1: 1 SPLS:LE, 117 gIL acid, 25 gil solids

....- 1:2 SPLS:LE, 153 gIL acid, 23 gIL solids

_~ 1: 1 SPLS: LE, 118 gIL acid, 21 gil solids

___ 1: I SPLS: LE, 118 gil acid, 23 gil solids

20 I , V,C I I I I

1001 :;k= l i if· f e 1

80 I "F< ¥ I I I I

co~

.a 60 i -i# L.' C~ll B I I

(])

::::J

.C..J.) o

]1 40 ,Jr'---t----=E~~;~:::~:::~===~·- ~ I I I =::;00-"'--::: I I

rJl

",......:I

0'1

W"""'"

......:I =N

s 10 15 20 2S

o~ ~ f , I I I

Note: 45 mg/L Si equilibrium concentration assumed; no PEO treatment

FIG. 6

Sample Time, hr

:;::::;

l1l

.... 60

.:..l. l1l

I..I.).

Q) a.

(J) ...... 010

0 ...... .m

0::

RELIEF FROM SUPERSATURATION USING GALACTOSOL-CIBA-SILICA SEEDING AGENT

t.-.

..... 25 gIL solids

...29 gIL solids

7J).

•

~=~

:-:

~Cl\

.... o

rFJ =('

(..'D...

......:J

o....

......:J

FIG. 7

Note: 45 mg/L Si equilibrium concentration assumed; no PEO treatment

o , ~o

Sample Time, hr

IS ~. cs d

rJl

......:J

0-.,

W"""'"

......:J =N

US 7,691,347 B2

SILICA REMOVAL FROM PREGNANT

LEACH SOLUTIONS

FIELD OF INVENTION

The present invention relates generally to a process for

removing dissolved or colloidal silica from a pregnant leach

solution ("PLS"). More particularly, an exemplary embodiment

ofthe present invention relates to a process which mixes

PLS with an acid source, preferably lean electrolyte, to

induce formation ofcolloidal silica that can then be collected

and removed. Additionally, in an exemplary embodiment of

the present invention, at least one silica seeding agent is added

to induce formation of colloidal silica, at least one flocculent

is added to induce aggregation of the colloidal silica, and a

solid-liquid separation process is utilized to remove advantageous

amounts or substantially all of the colloidal silica,

thereby providing relief from supersaturation of dissolved

silica in the metal recovery processes.

one flocculent is added to induce aggregation ofthe formatted

colloidal silica, and a solid-liquid separation process is utilized

to remove advantageous amounts or substantially all of

the colloidal silica, thereby providing relief from supersaturation

of dissolved silica in the metal recovery processes.

For example, in accordance with the various embodiments

of the present invention, the silica removal process can be

implemented after any reactive processing (discussed in

greater detail hereinbelow), resulting in enhanced silica

10 removal and various other advantages over prior art metal

recovery processes.

Additionally, in accordance with the various embodiments

of the present invention, the reduction in the total dissolved

silica and colloidal silica in the PLS reduces impurities in the

15 metal value deposited on the cathode during an electrowinning

step and reduces colloidal silica in any subsequent solvent

extraction step.

BRIEF DESCRIPTION OF THE DRAWING

DETAILED DESCRIPTION OF EXEMPLARY

EMBODIMENTS

The detailed description ofexemplary embodiments ofthe

invention herein shows various exemplary embodiments and

the best modes, known to the inventors at this time, of the

55 invention are disclosed. These exemplary embodiments and

modes are described in sufficient detail to enable those skilled

in the art to practice the invention and are not intended to limit

the scope, applicability, or configuration of the invention in

any way. Additionally, all included figures are non-limiting

60 illustrations of the exemplary embodiments and modes,

which similarly are not intended to limit the scope, applicability,

or configuration of the invention in any way.

Various embodiments of the present invention exhibit significant

advancements over prior art processes, particularly

65 with regard to metal recovery and process efficiency. Moreover,

existing metal recovery processes that utilize a reactive

process for metal recovery/solution extraction/electrowin-

A more complete understanding of the present invention,

however, may best be obtained by referring to the detailed

description when considered in connection with the figures,

wherein like numerals denote like elements and wherein:

FIG. 1 illustrates an exemplary flow diagram of a metal

recovery process with a silica removal circuit in accordance

with one exemplary embodiment ofthe present invention;

FIG. 2 illustrates an exemplary flow diagram of a silica

removal circuit in accordance with one exemplary embodi30

ment of the present invention;

FIG. 3 illustrates an exemplary flow diagram of a serial

silica removal circuit in accordance with one exemplary

embodiment of the present invention;

35 FIG. 4 illustrates an exemplary flow diagram of a parallel

silica removal circuit in accordance with one exemplary

embodiment of the present invention;

FIG. 5 illustrates exemplary lab data where fumed silica is

used as the seeding agent in accordance with an exemplary

40 embodiment of the present invention;

FIG. 6 illustrates exemplary lab data where polyethylene

oxide (PEO)-silica agglomerates are used as the seeding

agent in accordance with an exemplary embodiment of the

present invention; and

FIG. 7 illustrates exemplary lab data for Galactosol-Cibasilica

is used as the seeding agent in accordance with an

exemplary embodiment of the present invention.

SUMMARY OF THE INVENTION

BACKGROUND OF THE INVENTION

In general, according to exemplary embodiments of the

present invention, the present invention relates generally to a

process for removing dissolved or colloidal silica from a

pregnant leach solution ("PLS"). More particularly, an exemplary

embodiment ofthe present invention relates to a process

which mixes PLS with an acid source, preferably lean electrolyte,

to induce formation ofcolloidal silica that can then be

collected and removed. Additionally, in an exemplary

embodiment ofthe present invention, at least one silica seeding

agent is added induce formation ofcolloidal silica, at least

Hydrometallurgical treatment of metal-bearing materials,

such as metal ores, metal-bearing concentrates, and other

metal-bearing substances, has been well established for many 25

years. Moreover, leaching of metal-bearing materials is a

fundamental process utilized to extract metals from metalbearing

materials. In general, the first step in this process is

contacting the metal-bearing material with an aqueous solution

containing a leaching agent which extracts the metal or

metals from the metal-bearing material into solution. For

example, in copper leaching operations, especially copper

from copper minerals, such as chalcopyrite and chalcocite,

sulfuric acid in an aqueous solution is contacted with copperbearing

ore. During the leaching process, acid in the leach

solution may be consumed and various soluble components

are dissolved thereby increasing the metal content of the

aqueous solution. Other ions, such as iron may participate in

the leaching of various minerals as these ions participate in

dissolution reactions.

Additionally, under these current leaching processes, especially

copper from copper sulfides such as chalcopyrite and

chalcocite, large concentrations ofdissolved silica are generated.

This dissolved silica is gradually transformed to colloidal

silica. Large amounts of this colloidal silica can agglom- 45

erate within process equipment, which may lead to

inefficiencies in subsequent solvent extraction steps and low

overall process yields. Additionally, this colloidal silica residue

can result in impurities in the extracted metal (i.e. impurities

in metal deposited during electrowinning steps).

Accordingly, a process that enables efficient metal recovery

and provides relief from supersaturation of dissolved

silica in pregnant leach solutions, thereby reducing silica

within the metal recovery process, would be advantageous.

US 7,691,347 B2

3 4

(2)

(1)

4CuFeS2+1702+4H20~2Fe203+4Cu2++8H++

8soi-

Thus, in accordance with one aspect of the present invention,

in order to maintain preferable leaching temperature, a

cooling liquid 301 may be introduced into the leaching vessel

during leaching. In accordance with one aspect of this

embodiment ofthe present invention, a cooling liquid 301 is

preferably contacted with the feed stream in leaching vessel

during leaching. Cooling liquid 301 may comprise any suitable

cooling fluid from within the process or from an outside

source, such as recycled liquid phase from the product slurry,

make-up water, or a mixture ofcooling fluids. Cooling liquid

may be introduced into leaching vessel through the same inlet

as metal-bearing inlet stream 101, or in any marmer that

effectuates cooling of metal-bearing inlet stream 101. The

amount of cooling liquid added during leaching may vary

according to the pulp density of the metal-bearing inlet

stream 101, as well as other parameters of the leaching process.

In an exemplary aspect ofthis embodiment ofthe invention,

a sufficient amount of cooling liquid 301 is added to

reactive processing step 202 to yield a solids content in product

slurry 102 on the order of less than about 50% solids by

weight, more preferably ranging from about 3 to about 35%

solids by weight, and most preferably ranging from about

10% to about 20% solids by weight.

Moreover, in accordance with one aspect of the present

invention, reactive processing step 202 may occur in any

At lower temperatures, acid is generally consumed and

elemental sulfur is fonned according to the following reac40

tion:

metal, such as cobalt, iron, or manganese, recovery process

streams, to fonn a metal-bearing inlet stream 101.

Moreover, in an exemplary embodiment of the present

invention, after metal-bearing inlet stream 101 has been suitably

prepared for metal recovery processing, it may be forwarded

to a reactive processing step 202, for example, metal

extraction. The reactive processing step 202 may be any suitable

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

material 100 in a condition such that it may be subjected to

10 later metal recovery processing. For example, exemplary

suitable processes include reactive processes that tend to liberate

the desired metal value or values in the metal bearing

material 100 from the metal-bearing material 100. In accordance

with a preferred embodiment ofthe present invention,

15 as described in greater detail below, reactive processing step

202 may comprise a leaching process.

Furthermore, in an exemplary embodiment of the present

invention, the leaching process may comprise any leaching

process suitable for extracting the metal in metal-bearing

20 material 100 into a PLS 102. In accordance with one aspect of

the present invention, the leach step comprises atmospheric

leaching, pressure leaching, agitation leaching, heap leaching,

stockpile leaching, pad leaching, thin-layer leaching and/

or vat leaching, at either ambient or elevated temperatures.

25 Preferably, pressure leaching is a pressure leaching process

operating at a temperature in the range of about 1400 C. to

about 2500 C. and more preferably in the range ofabout 1500

C. to about 2200 C.

In accordance with an aspect of the present invention, the

30 optimum temperature range selected for operation will tend

to maximize the extraction of copper and other metals, minimize

acid consumption, and thereby minimize make-up acid

requirements. That is, at higher temperatures, sulfide sulfur

generally is converted to sulfate according to the following

35 reaction:

ning process sequence may, in many instances, be easily

retrofitted to exploit the many commercial benefits the

present invention provides.

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

the present invention, a metal-bearing material 100 is provided

for processing. Metal-bearing material 100 may be an

ore, a concentrate, or any other material from which copper

and/or other metal values may be recovered. Metal values

such as, for example, copper, gold, silver, zinc, platinum

group metals, nickel, cobalt, molybdenum, rhenium, uranium,

rare earth metals, and the like, may be recovered from

metal-bearing materials in accordance with various embodiments

of the present invention. The various aspects and

embodiments of the present invention, however, prove especially

advantageous in connection with the recovery of copper

from copper-bearing materials, such as, for example, ores

and/or concentrates containing chalcopyrite (CuFeS2), chalcocite

(Cu2S), bornite (CusFeS4), and covellite (CuS), malachite

(CU2C03 (OH)2), pseudomalachite (CuS[(OH)2P04]2),

azurite (CU3(C03MOH)2), chrysocolla ((Cu,Al)2H2Si20s

(OH)4.nH20), cuprite (Cu20), brochanite (CuS04.3Cu(OH)

2), atacamite (Cu2[OH3 Cl]) and other copper-bearing minerals

or materials and mixtures thereof. Thus, metal-bearing

material 100 preferably is a copper ore or concentrate containing

at least one other metal value.

Metal-bearing material 100 may be prepared in conditioning

step 201 for metal recovery processing in any manner that

enables the conditions of metal-bearing material 1OO-such

as, for example, composition and component concentration-

to be suitable for the chosen reactive processing

method, as such conditions may affect the overall effectiveness

and efficiency of metal recovery 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, as

discussed in some detail hereinbelow, metal-bearing material

100 may undergo combination, flotation, blending, and/or

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

in conditioning step 201 before metal extraction.

In accordance with one aspect of the present invention,

metal-bearing material 100 may optionally be prepared in a

conditioning step 201, wherein conditioning step 201 may

comprise controlled, fine grinding. More precisely, u.s. Pat. 45

No. 6,676,909 describing controlled grinding is contemplated

herein and the subject matter of that patent is hereby

incorporated by reference. Preferably, a uniform particle size

distribution is achieved. It should be understood that a variety

ofacceptable techniques and devices for reducing the particle 50

size of the copper-bearing material are currently available,

such as ball mills, tower mills, grinding mills, attrition mills,

stirred mills, horizontal mills and the like, and additional

techniques may later be developed that may achieve the

desired result of reducing the particle size of the copper- 55

bearing material to be transported.

Referring again to FIG. 1, in an exemplary embodiment of

the present invention, after metal-bearing material 100 has

been suitably prepared for metal recovery processing, optionally

by controlled grinding, and other physical and/or chemi- 60

cal conditioning processes 201, including but not limited to a

thickening process, it may be combined with any number of

liquid feed streams, including but not limited to process

water, but any suitable liquid may be employed, such as, for

example, recycled raffinate, pregnant leach solution ("PLS"), 65

lean electrolyte, and/or other recycled streams from the metal

recovery processes, including but not limited to secondary

US 7,691,347 B2

5 6

present invention, conditioning step 203 comprises atmospheric

flashing. Further, flashed gases, solids, solutions, and

steam may optionally be suitably treated, for example, by use

of a Venturi scrubber wherein water may be recovered and

hazardous materials may be prevented from entering the environment.

As discussed above, under the current reactive and conditioning

processes for metal recovery, especially copper from

copper sulfides such as chalcopyrite and chalcocite, large

10 concentrations of dissolved silica are generated. This dissolved

silica is gradually transformed into colloidal silica.

Large amounts ofthis colloidal silica can agglomerate within

process equipment, which may lead to inefficiencies in subsequent

solvent extraction steps and low overall process

yields. Additionally, this colloidal silica residue can result in

impurities in the extracted metal (i.e. impurities in metal

deposited during electrowinning steps 218).

Accordingly, the present invention teaches a process for

relief from supersaturation ofdissolved silica in PLS. Typical

PLS can contain between about 600 mg/L and about 1500

mg/L dissolved silica depending on the reactive temperatures

and/or processes utilized in the metal extraction processes.

This dissolved silica can create impurities in the final metal

product and systemic problems in the metal extraction process

by creating colloidal silica, which can agglomerate

within processing equipment including, but not limited to

tanks, pipes, and solvent exchange apparatus. The silica

removal process ofthe present invention can be implemented

after any reactive processing, such as by medium or high

temperature pressure leaching, resulting in a PLS.

In accordance with an exemplary embodiment of the

present invention, the process for providing relieffrom supersaturation

ofdissolved silica in PLS comprising: (i) providing

a feed stream containing metal-bearing material; (ii) subjecting

at least a portion of the metal-bearing feed stream to at

least one reactive process, wherein a PLS is formed; (iii)

adding acid to the PLS; (iv) adding at least one seeding agent

to the PLS; (v) forming colloidal silica from dissolved silica

in the PLS; (vi) adding at least one flocculant to the formed

colloidal silica, such that the colloidal silica agglomerates;

(vi) removing at least a portion ofthe agglomerated colloidal

silica; and (vii) recovering metal from the remaining PLS by

electrowinning.

In accordance with another exemplary embodiment ofthe

present invention, a process for recovering metal and providing

relief from supersaturation of dissolved silica in PLS

comprising: (i) providing a feed stream containing metalbearing

material; (ii) subjecting at least a portion ofthe metalbearing

feed stream to at least one reactive process, wherein

a PLS is formed; (iii) adding acid to the PLS; (iv) adding at

least one seeding agent to the PLS; (v) forming colloidal silica

from dissolved silica in the PLS; (vi) adding at least one

flocculent to the formed colloidal silica, such that the colloidal

silica agglomerates; (vii) removing at least a portion ofthe

55 agglomerated colloidal silica; (viii) recovering metal from

the remaining PLS by electrowinning; (ix) and providing at

least a portion ofthe lean electrolyte from the electrowinning

step to supply some or all ofthe acid used. In this way, the use

ofrecycled acid-containing solution, rather than concentrated

sulfuric acid, is economically advantageous.

In an exemplary embodiment illustrated by FIG. 1, after

metal-bearing material 100 has been suitably prepared for

reactive processing, for example, by other physical and/or

chemical conditioning processes 201, optionally, controlled

fine grinding, it is subjected to at least one reactive process

step 202 to yield a PLS 102. By way of example, reactive

process step 202 can be a high temperature or a medium

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. In accordance with one aspect of an exemplary

embodiment of the invention, the pressure leaching vessel

used in leaching step is an agitated, multi-compartment pressure

leaching vessel. However, it should be appreciated that

any pressure leaching vessel that suitably permits metal-bearing

material 100 to be prepared for metal recovery may be

utilized within the scope of the present invention.

During reactive processing step 202, copper and/or other

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 15

example, where copper is the metal being recovered, an acid,

such as sulfuric acid, may be contacted with the copperbearing

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 prepara- 20

tion for later metal recovery steps may be utilized within the

scope of this invention.

In accordance with one aspect of the present invention,

reactive processing step 202 comprises pressure leaching,

sufficient oxygen 302 is injected into a pressure leaching 25

vessel to maintain an oxygen partial pressure from about 50 to

about 200 psi, preferably from about 75 to about 750 psi and

most preferably from about 100 to about 400 psi Furthermore,

due to the nature of medium temperature pressure leaching,

the total operating pressure in leaching vessel 201 is generally 30

superatmospheric.

The residence time for the pressure leaching process can

vary, depending on factors such as, for example, the characteristics

of the copper-bearing material and the operating

pressure and temperature of the pressure leaching vessel. In 35

one aspect ofan exemplary embodiment ofthe invention, the

residence time for the pressure leaching ranges from about 30

to about 180 minutes, more preferably from about 60 to about

120 minutes.

Subsequent to metal-bearing material 100 undergoing 40

reactive processing step 202, the metal values that have been

made available by reactive processing step 202 undergo one

or more of various conditioning steps 203. In one exemplary

embodiment, the product stream 102 from leaching step 201

may be conditioned to adjust the composition, component 45

concentrations, solids content, volume, temperature, pressure,

and/or other physical and/or chemical parameters to

desired values and thus to form a suitable metal-bearing solution.

Generally, a properly conditioned metal-bearing solution

will contain a relatively high concentration of soluble 50

metal, for example, copper sulfate, in an acid 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 copper product ultimately recovered.

In one aspect of an exemplary embodiment of the present

invention, conditioning of a metal-bearing solution for metal

recovery begins by adjusting certain physical parameters of

the product slurry 102 from the reactive processing step 202.

Optionally, in an exemplary aspect ofthis embodiment ofthe 60

invention, wherein the reactive processing step 202 is pressure

leaching, it is desirable to reduce the temperature and

pressure of the product slurry, in some instances to approximately

ambient conditions. An exemplary method of so

adjusting the temperature and pressure characteristics of the 65

product slurry 102 is a conditioning step 203 comprising

flashing. In one aspect of an exemplary embodiment of the

US 7,691,347 B2

7 8

Moreover, under normal medium-temperature pressure

leaching conditions, the dissolved silica concentration of the

PLS 102 is usually in the range of300 mg/L to 400 mg/L, a

concentration that exceeds the solubility limit at room temperature.

Over an extended period of time and under these

conditions, the dissolved silica monomer (Si(OH)4) gradually

polymerizes and transforms to colloidal particles, or

silica gel. This colloidal silica can be responsible for silica

agglomeration and silica residue throughout the metal extraction

processes. The rate of polymerization is catalyzed by

hydrogen ions and fluoride ions (if any). When the dissolved

silica experiences a higher acid, the monomer polymerizes

much more quickly and precipitates as colloidal particles

according to:

nSiCOH)4",CSi02)n+2nHp

Generally, silica polymerization is often temperature

dependant. For example, reducing the temperature increases

the rate of silica polymerization and vice versa.

In addition to dependence on temperature, the conversion

from dissolved silica to colloidal silica is dependant on the

acid concentration or pH of the PLS. Similarly, a decreased

pH value will tend to give higher polymerization rates. Thus,

by controlling the pH, one has an additional degree of freedom

for controlling the rate of silica polymerization. For

instance, increasing the pH to about 2 will result in a sharp

decrease in the rate of silica polymerization.

While dissolved silica is a problem in the metal extraction

process, the use of one or more solid-liquid phase separation

steps are unsatisfactory to remove advantageous amounts of

dissolved silica and colloidal silica from the PLS, 102. This is

due in part because typical metal recovery processes do not

form colloidal silica by addition ofa seeding agent to assist in

forming colloidal silica after any conditioning steps and prior

to metal recovery, preferably by electrowinning. Thus they do

not remove advantageous amounts or substantially all dissolved

silica, as the present invention does.

Accordingly, illustrated in FIG. 2 and in accordance with

an exemplary embodiment of the present invention, silica

40 removal circuit 208 utilizes any process suitable for causing

silica dissolved in a pregnant leach solution to form colloidal

silica and removing the formed colloidal silica. Preferably, in

accordance with an exemplary embodiment of the present

invention, silica removal circuit 208 utilizes the addition ofat

least one seeding agent to assist in forming colloidal silica.

More specifically, again with reference to FIG. 2, in an

exemplary embodiment of the present invention, silica

removal circuit 208 uses a process which PLS 104 with an

acid source 108, preferably lean electrolyte, to induce forma-

50 tion ofcolloidal silica that can then be collected and removed.

Additionally, in an exemplary embodiment of the present

invention, at least one silica seeding agent 109 is added to

induce formation of colloidal silica and a solid-liquid separation

process is utilized to reduce colloidal silica throughout

metal recovery processes.

In an exemplary embodiment ofthe present invention with

reference to FIG. 2, silica removal circuit 208 may comprise

one or more mixing tanks 210 suitable for mixing the PLS 104

with an acid source 108 to begin forming colloidal silica.

Furthermore, in an exemplary embodiment of the present

invention, silica removal circuit 208 may comprise one or

more mixing tanks 210 suitable for mixing the PLS 104 with

a seeding agent 109 to begin forming colloidal silica. Additionally,

in an exemplary embodiment of the present invention,

silica removal circuit 208 may comprise one or more

solid-liquid phase separation steps 214 to collect and/or

remove colloidal silica. It should be understood, as will be

temperature pressure leaching step. Preferably, pressure

leaching is a pressure leaching process operating at a temperature

in the range of about 1400 C. to about 2500 C. and

more preferably in the range ofabout 1500 C. to about 2200 C.

Most preferably, the pressure leaching process operates at a

temperature in the range of about 1500 C. to about 1600 C.

Further, referring again to FIG. 1, in one aspect of an

exemplary embodiment of the present invention, conditioning

ofa metal-bearing solution after reactive process step 202

begins by adjusting certain physical parameters in condition- 10

ing step 203. For example, as discussed in some detail herein

below, after reactive processing 202 metal-bearing material

100 may undergo reagent additions, flashing processes, one

or more solid-liquid phase separation steps including use of

filtration systems, counter-current decantation (CCD) cir- 15

cuits, thickeners, clarifiers, or any other suitable device for

solid-liquid separation, in conditioning step 203 to prepare

the metal solubilized therein for recovery.

In accordance with further aspects of this exemplary

embodiment, the slurry product 102 from the reactive process 20

step 202, or further conditioned slurry product stream 103,

may be further conditioned in preparation for later metalvalue

recovery steps in one or more solid-liquid phase separation

steps 204 may be used to separate solubilized metal

solution from solid particles. This may be accomplished in 25

any conventional manner, including use offiltration systems,

counter-current decantation (CCD) circuits, thickeners, clarifiers,

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 30

decision whether to employ a CCD circuit, a thickener, a

filter, a clarifier, or any other suitable device in a solid-liquid

separation apparatus. In one aspect ofan exemplary embodiment

of the invention, one or more solid-liquid phase separation

steps 204 may be carried out with a conventional CCD 35

utilizing conventional countercurrent washing ofthe residue

stream to recover leached metal values to one or more solution

products and to minimize the amount of soluble metal

values advancing with the solid residue to further metal

recovery processes or storage.

Additionally, referring again to FIG. 1, in one aspect of an

exemplary embodiment of the present invention, the separated

solids from one or more solid-liquid phase separation

steps 204 may further be subjected to later processing steps,

including secondary metal recovery, such as, for example, 45

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

zinc, nickel, cobalt, uranium, rhenium, rare earth metals,

and the like, by sulphidation, cyanidation, or other techniques.

Alternatively, the separated solids may be subject to

impoundment or disposal.

Referring to FIG. 1, in an exemplary embodiment of the

present invention, after PLS 104 has been suitably conditioned

in 203 or 204 it may be forwarded to a desired metal

recovery step. The metal recovery step may include any suitable

conditioning and/or copper recovery method or methods, 55

for example, electrowinning, formation, solution extraction

(sometimes referred to as solvent extraction or liquid ion

exchange), ion exchange, and/or ion flotation, and preferably

results in a relatively pure copper product.

Further, referring again to FIG. 1, in an exemplary embodi- 60

ment of the present invention, the resulting PLS 104 may be

forwarded to a silica removal circuit 208. In accordance with

an exemplary embodiment ofthe present invention as focused

onthe removal ofsilica, it is here, after the reactive processing

steps 202, any optional conditioning steps 203, and/or any 65

solid-liquid separation steps 204, when removal ofdissolved

or colloidal silica is most advantageous.

US 7,691,347 B2

discussed in greater detail below, that causing dissolved silica

to form colloidal silica reduces the overall concentration of

colloidal silica residue and agglomeration throughout metal

recovery process, thereby enabling efficient metal recovery

and providing relief from supersaturation of dissolved silica

in the PLS.

More specifically, in an exemplary embodiment of the

present invention with reference to FIG. 3 exemplifying silica

removal circuit 208, colloidal silica can be formed from dissolved

silica in PLS, 104, by feeding PLS 104 to one or more

mixing tanks 210, adding an acid source, 107 or 108, wherein

the acid source is preferably a fresh acid feed 107 and/or a

lean electrolyte recycle 108 from the electrowinning step 218.

In accordance with an exemplary embodiment ofthe present

invention, the acid, 107 or 108, is added in any amount suitable

to induce the fonnation of colloidal silica, preferably

greater than about 80 giL ofacid is added. In accordance with

an exemplary embodiment of the present invention, preferably

80 giL to 180 giL of acid is added.

In accordance with an exemplary embodiment of the

present invention, the acid can be added to the PLS 104, either

through the addition ofconcentrated H2S04 and/or by blending

PLS 104 with lean electrolyte (LE) 108. In an exemplary

embodiment, the acid is supplied from LE 108 recycled from

the electrolyte recycle 216 and/or electrowinning circuit 218.

Moreover, in accordance with an exemplary embodiment of

the present invention, any PLS 104 to LE 107 volume ratio

providing a acid concentration greater than 80 giL can be

employed and are contemplated in this disclosure. Based on a

225 giL acid concentration of LE, in accordance with an

exemplary embodiment of the present invention, a 2: 1 PLS

104 to LE 107 volume ratio is preferable.

Also, in an exemplary embodiment ofthe present invention

with reference to FIG. 3, contemporaneous with or after the

addition of acid, 107 and/or 108, to PLS 104 at least one

seeding agent, 109 and/or 110, may be added, wherein the

seeding agent is preferably a seeding agent supplied by an

external feed 109 and/or provided by a seeding agent recycle

from one or more solid-liquid phase separation steps 214.

Regarding the seeding agent, in accordance with an exemplary

embodiment ofthe present invention illustrated in FIG.

3, at least one seeding agent, 109 and/or 110, is added into one

or more mixing tanks 210 to increase the rate ofsoluble silica

transfonnation to the colloidal state. Preferably, in one exemplary

embodiment ofthe present invention, the concentration

of the seeding agent added is 16 giL or higher. Most preferably,

in one exemplary embodiment ofthe present invention,

the concentration of the seeding agent added is 30 giL. or

higher.

In accordance with an exemplary embodiment of the

present invention illustrated in FIG. 3, at least one seeding

agent, 109 and/or 110, can be provided from silica precipitates

collected anywhere in the metal recovery process (i.e.

the electrowinning circuit 218-not shown), or by providing

external seeding agents 109 into the metal recovery process.

For example, in an exemplary embodiment of the present

invention, seeding agents, 109 and/or 110, can be any silica

based seeding agents including, but not limited to fumed

silica, polyethylene oxide (PEO)-silica agglomerates, and/or

a silica agglomerates fonned by treating colloidal silica rich

PLS with Galactosol 40HD4CD (from Hercules, Inc.), guar

gum, and Ciba 7689 (from Cytec Corporation).

For example, in an exemplary embodiment of the present

invention, at 5% fumed silica and greater than 80 giL acid,

about 60-80% relief of silica supersaturation was achieved

within a 4 to 6 hour retention time. After 24 hours, the extent

ofsupersaturation reliefwas 80-90%, indicating that the bulk

of the silica polymerization takes place within a 6 hour residence

time.

Similarly, in accordance with an exemplary embodiment of

the present invention, the PEO-silica agglomerates were very

effective in promoting supersaturation relief, with faster polymerization

at higher seed loadings. The concentration of

PEO-silica agglomerates ranged from 4-40 giL (dry weight).

The kinetics of the supersaturation relief process was fast in

10 the presence of excess acid (greater than 80 giL acid).

Between 80 and 90% relief of supersaturation was attained

within a 6 hour retention time. After a 24 hour retention time,

the extent ofsupersaturation reliefwas 98-99%; thus, the bulk

of the silica polymerization takes place within a 6 hour resi-

15 dence time.

Additionally, in accordance with an exemplary embodiment

ofthe present invention, silica agglomerates fonned by

treating colloidal silica rich PLS with 30 mg/L Galactosol

40HD4CD and 10 mg/L Ciba 7689 resulted in similar kinet-

20 ics when added as seed material. In a 6 hour residence time,

about 80% of the supersaturated silica was relieved from

solution; in a 24 hour residence time, 95% of the excess

soluble silica was removed from solution by the seed material,

again indicating that the bulk of the polymerization

25 chemistry takes place within a 6 hour residence time at an

operating temperature of 50° C. Additionally, the rate of

supersaturation relief was found to be independent of temperature

within the 25-80° C. range.

In accordance with an exemplary embodiment of the

30 present invention illustrated in FIG. 3, the seeding agent can

be repeatedly recycled from different parts of the metal

extraction process, wherever colloidal silica is formed. For

example, in one embodiment of the present invention, the

seeding agent can be recycled from the solid-liquid separa-

35 tion process, 214 (with reference to FIG. 2, FIG. 3, and FIG.

4) and/or the electrowinning effluent 108 (with reference to

FIG. 1).

In an exemplary embodiment of the invention with reference

to FIG. 2 and FIG. 3, the PLS 104, acid, 107 and/or 108,

40 and at least one seeding agent, 109 and/or 110, are fed into

one or more mixing tanks 210. This mixture is then mixed

and/or stored for a predetennined amount ofresidence time to

induce further nucleation and formation ofcolloidal silica. In

accordance with one embodiment, this mixture can be trans-

45 ferred between multiple mixing tanks 210 in series or parallel

for additional mixing and residence time to induce further

nucleation and fonnation of colloidal silica. Furthermore, in

accordance with another exemplary embodiment of the

present invention, after the acid, 107 and/or 108, and at least

50 one seeding agent, 109 and/or 110, are mixed with the PLS

104 and colloidal silica is fonned, the colloidal silica slurry

112 may be forwarded to one or more reagent dosing tanks

212 and a flocculent 113 may be added. In accordance with

another exemplary embodiment of the present invention,

55 flocculant 113 may any substance that promotes flocculation

by causing silica colloids and/or other silica particles in the

colloidal silica slurry 112 to aggregate, or form floccules.

For example, in accordance with another exemplary

embodiment of the present invention, flocculant 113 may

60 comprise any multivalent cation, including but not limited to

any aluminum, iron, calcium, and/or magnesium, or any polymer,

including but not limited to polyacrylamides, compound

suitable for promoting flocculation of colloidal silica. Furthennore,

in accordance with another exemplary embodiment

65 ofthe present invention, flocculent 113 may comprise at least

one of polyethylene oxide (PEO), Galactosol 40HD4CD,

guar gum, Ciba 7689, and Scifloc C2733.

US 7,691,347 B2

11 12

dosing tanks 212 and a flocculent 113 may be added. The two

exemplary configurations described herein and depicted in

the drawings are serial and parallel configurations, respectively,

and numerous configurations are contemplated within

the scope of this disclosure to remove dissolved silica and

colloidal silica from the PLS.

With regard to FIG. 3 and FIG. 4, in an exemplary embodiment

ofthe present invention, the flocculated slurry 114 now

contains concentrated amounts of flocculated colloidal silica

10 and substantially less dissolved silica is transferred to the

solid/liquid separation step 214 to remove the colloidal silica

and, thus, metal-rich solution, or rich electrolyte solution 111,

is forwarded to the electrolyte recycle tank 216. Preferably, in

an exemplary embodiment, the final solid-liquid separation

15 step 214 is a thickener with most of the underflow 110

recycled to enhance fonnation and removal ofcolloidal silica.

Experimental results for some ofthe exemplary processes are

provided in the Example Section below.

In addition to the underflow or bottoms of the solid/liquid

20 separation step 214 being recycled to one or more mixing

tanks, 210, 220, and/or 222, the bottoms can be split into a

residue stream, including removed colloidal silica, 117 (FIG.

3) or 127 (FIG. 4), and depending on the stream, 117 (FIG. 3)

or 127 (FIG. 4), composition, may be neutralized,

25 impounded, disposed of, or subjected to further processing,

such as, for example, precious metal recovery, treatment to

recover other metal values, such as, for example, recovery of

gold, silver, platinum group metals, nickel, cobalt, molybdenum,

zinc, rhenium, uranium, rare earth metals, and the like.

30 Optionally, in accordance with an exemplary embodiment

illustrated in FIG. 1 and FIG. 2, a portion of the residue

stream, including removed colloidal silica, 117 (FIG. 3) or

127 (FIG. 4), can be recycled to other steps of the metal

recovery process.

Lastly, again with reference to FIG. 1, in an exemplary

embodiment, after one or more silica removal circuit 208,

metal-rich solution, or rich electrolyte solution 111 is substantially

free from supersaturated silica. The stream may

then be sent to electrolyte recycle tank 216. Electrolyte

40 recycle tank 216 suitably facilitates process control for electrowinning

circuit 218, as will be discussed in greater detail

below. Metal-containing solution stream 111, is preferably

blended with a lean electrolyte stream 108 in electrolyte

recycle tank 216 at a ratio suitable to yield a product stream

45 118, the conditions of which may be chosen to optimize the

resultant product of electrowinning circuit 218. With continued

reference to FIG. 1, metal from the product stream 118 is

suitably electrowon to yield a pure, cathode metal product

120.

For the sake of convenience and a broad understanding of

the present invention, an electrowinning circuit useful in connection

with various embodiments ofthe invention may comprise

an electrowinning circuit, constructed and configured to

operate in a conventional manner. The electrowinning circuit

55 may include electrowinning cells constructed as elongated

rectangular tanks containing suspended parallel flat cathodes

of metal alternating with flat anodes of lead alloy, arranged

perpendicular to the long axis of the tank. A metal-bearing

leach solution may be provided to the tank, for example at one

60 end, to flow perpendicular (referring to the overall flow pattern)

to the plane of the parallel anodes and cathodes, and

metal can be deposited at the cathode and water electrolyzed

to form oxygen and protons at the anode with the application

of current. Other electrolyte distribution and flow profiles

65 may be used.

The primary electrochemical reactions for electrowinning

ofmetal from acid solution is believed to be as follows:

After sufficient colloidal silica has been fonned and

agglomerated by the flocculant 113 in reagent dosing tank

212, in accordance with another exemplary embodiment of

the present invention, the flocculated slurry 114 may be forwarded

to one or more solid/liquid separation steps 214 to

remove advantageous amounts of colloidal silica. As mentioned,

one or more solid-liquid phase separation steps 214

may be used to separate flocculated colloidal silica and to

form metal-rich solution 111 prepared for metal recovery

processes. This solid-liquid phase separation may be accomplished

in any conventional manner, including use offiltration

systems, counter-current decantation (CCD) circuits, thickeners,

clarifiers, centrifuges, and the like. In accordance with

further aspects of this preferred embodiment, solid-liquid

phase separation step 214 comprises a dissolved-air flotation

(DAF), pinned-bed clarification, colunm flotation, air-encapsulated

flocculation, vibrating Sweco screening, stationary

Kason screening, or Trommel screening.

In another exemplary embodiment ofthe present invention,

the flocculated slurry 114 is fed to the solid/liquid separation

step 214 at a temperature less than about 100° C. Most preferably,

in another exemplary embodiment of the present

invention, the flocculated slurry 114 is fed to the solid/liquid

separation step 214 at a temperature greater than 25° C. and

less than about 85° c., most preferably 50° C.

Preferably, in another exemplary embodiment of the

present invention, between all the mixing tanks, 210, the

solution is mixed continuously or intermittently for four (4)

hours or more and allowed to be aged for a residence time of

six (6) hours to remove an advantageous amount of silica

from the metal extraction process. It should be understood

that numerous variations on mixing times and aging or residence

times are contemplated within this invention.

In one exemplary embodiment of the present invention,

removing advantageous amounts of colloidal silica means 35

removing more silica than would be removed in a solid/liquid

separation step without the addition of a seeding agent at the

same temperature, acidity, and with the same mixing and

residence time.

In one exemplary embodiment of the present invention,

removing advantageous amounts of colloidal silica means

removing greater than about 60% of the total silica in the

metal extraction process. In another exemplary embodiment

ofthe present invention, removing advantageous amounts of

colloidal silica means removing greater than about 70% ofthe

total silica in the metal extraction process. In another exemplary

embodiment ofthe present invention, removing advantageous

amounts of colloidal silica means removing greater

than about 90% of the total silica in the metal extraction

process. In another exemplary embodiment of the present 50

invention, removing advantageous amounts ofcolloidal silica

means removing about 98% of the total silica in the metal

extraction process.

In an alternative exemplary embodiment with reference to

FIG. 4, after the PLS 104 is mixed with acid, 107 and/or 108,

and a seeding agent, 109 and/or 110, in one or more mixing

tanks 210, as described above. Preferably, in accordance with

another exemplary embodiment ofthe present invention, PLS

104 is mixed with acid, 107 and/or 108, and a seeding agent,

109 and/or 110, in two or more mixing tanks, 220 and 222, in

parallel with one another. Similarly, in accordance with

another exemplary embodiment ofthe present invention, after

the acid, 107 and/or 108, and at least one seeding agent, 109

and/or 110, are mixed with the PLS 104 and the desired

amount ofcolloidal silica is fonned, the colloidal silica slurry

115 from mixing tank 220 and colloidal silica slurry 116 from

mixing tank 222 may be forwarded to one or more reagent

US 7,691,347 B2

2CUS04+2H20~2CuO+2H2S04+02

Cathode half-reaction: Cu2++2e---""Cuo

Turning again to FIG. 1, in a preferred embodiment of the

invention, product stream 118 is directed from electrolyte

recycle tank 216 to an electrowinning circuit 218, which

contains one or more conventional electrowinning cells. It

should be understood, however, that any method and/or appa- 10

ratus currently known or hereinafter devised suitable for the

electrowinning of metal from acid solution, in accordance

with the above-referenced reactions or otherwise, is within

the scope of the present invention.

In accordance with a preferred aspect of the invention, 15

electrowinning circuit 218 yields a cathode metal product

120, optionally, an offgas stream (not shown), and a relatively

large volume of metal-containing acid solution, herein designated

as lean electrolyte stream 121. As discussed above, in

the illustrated embodiment of the invention, a portion oflean 20

electrolyte stream 121 (FIG. 1) is preferably recycled to various

places in the metal extraction process including, but not

limited to reactive processing step 202 and/or to electrolyte

recycle tank 216. Optionally, a portion of metal-containing

solution stream 111 from silica removal circuit 208 is com- 25

bined with lean electrolyte recycle stream 108 and is recycled

to reactive processing step 202. Moreover, in accordance with

one aspect of an exemplary embodiment of the invention, a

portion oflean electrolyte stream 121 (lean electrolyte bleed

stream 119 in FIG. 1) is removed from the metal recovery 30

process, exemplified in FIG. 1, for the removal of impurities

and acid and/or residual metal recovery operations.

Preferably, lean electrolyte recycle stream 108 comprises

at least about 50 percent by weight of lean electrolyte stream

121, more preferably from about 60 to about 95 percent by 35

weight of lean electrolyte stream 121, and most preferably

from about 80 to about 90 percent by weight of lean electrolyte

stream 121. Preferably, lean electrolyte bleed stream 119

comprises less than about 50 percent by weight oflean electrolyte

stream 121, more preferably from about 5 to about 40 40

percent by weight of lean electrolyte stream 121, and most

preferably from about 10 to about 20 percent by weight of

lean electrolyte stream 121.

Metal values from the metal-bearing product stream 120

are removed during electrowinning step 218 to yield a pure, 45

cathode metal product. It should be appreciated that in accordance

with the various aspects of the invention, a process

wherein, upon proper conditioning ofthe metal-bearing solution,

a high quality, uniformly-plated cathode metal product

may be realized without subjecting the metal-bearing solu- 50

tion to solvent/solution extraction prior to entering the electrowinning

circuit is within the scope ofthe present invention.

As previously noted, careful control of the conditions of the

metal-bearing solution entering an electrowinning circuitespecially

maintenance of a substantially constant metal 55

composition in the stream-can enhance the quality of the

electrowon metal by, among other things, enabling even plating

ofmetal on the cathode and avoidance of surface porosity

in the cathode metal, which degrades the metal product and

thus may diminish its economic value. In accordance with 60

this aspect of the invention, such process control can be

accomplished using any ofa variety oftechniques and equipment

configurations, so long as the chosen system and/or

method maintain a sufficiently constant feed stream to the

electrowinning circuit. A variety of methods and apparatus 65

are available for the electrowinning ofmetal and other metal

values, any of which may be suitable for use in accordance

with the present invention, provided the requisite process

parameters for the chosen method or apparatus are satisfied.

The Example set forth hereinbelow is illustrative ofvarious

aspects of a preferred embodiment of the present invention.

The process conditions and parameters reflected therein are

intended to exemplifY various aspects of the invention, and

are not intended to limit the scope of the claimed invention.

ACID ADDITION EXAMPLES

Example I

Aged (3-week-old) medium-temperature PLS containing

330 mg/L total Si was obtained. After 6 weeks of aging and

maintaining the PLS at 50° c., the soluble silicon concentration

decreased to 143 mg/L and was blended with LE. After

blending with 223 giL of acid at a I :2.5 volume ratio and

treating with 20 mg/L PEO, the soluble silicon concentration

was reduced from 75 to 34 mg/L. The addition of the LE

catalyzed the relief of silica supersaturation. This example

indicates that concentration of acid is crucial to remove

advantageous amounts of colloidal silica.

Example 2

Concentrated H2S04 was added to fresh PLS samples and

allowed to age over a three day period. Samples were taken

periodically and treated with the equivalent of 20 mg/L PEO

to remove colloidal silica. After 10 to IS min at 50° c., treated

samples were filtered on 0.45 flm media. Filtrates were analyzed

for soluble silica (as silicon). Table I shows that

increasing the acid concentration of the blend solution promotes

removal advantageous amounts of colloidal silica.

TABLE I

Soluble Si

Acid Analyses. mg/L

Experiment ID Addition, giL Day 1 Day 3

2938-133-1 0 165 158

2938-136-1 117 154 101

2938-136-2 143 152 82

2938-136-3 182 149 75

2938-136-4 219 145 76

2938-136-5 257 142 71

USE OF SEEDS TO FORM COLLOIDAL SILICA

EXAMPLES

Example I

Samples of fresh PLS were slurried with fumed silica to

promote the reliefof silica supersaturation. The slurries were

stirred at 50° C. over a period oftime. Samples were taken at

1,2, 4, 6, and 24 hours, filtered, and analyzed for soluble silica

(as silicon). FIG. 5 shows the extent of silica supersaturation

relief from PLS, with and without LE addition, when fumed

silica is used as seed. The rate of the process increases with

increasing solid load and/or acid concentration. Comparison

with data generated show that the supersaturation reliefkinetics

was fast with fumed silica, most likely due to the higher

specific surface area. At 5% solids loading, 60-80% relief of

supersaturation was achieved in a 4- to 6-hr retention time.

After a 24-hr residence time, close to 80% reliefofsupersaturation

was achieved in the presence ofLE with sufficient acid.

US 7,691,347 B2

15 16

The data shows that fumed silica can be successfully used as

seed material to remove advantageous amounts of colloidal

silica.

air-encapsulated flocculation is possible method to remove

advantageous amounts of colloidal silica.

Example 2

TABLE 2

Example 4

Example 3

After 22 recycles, the slurry was transferred to a I-L graduated

cylinder equipped with a mechanical rake, spiked with

the equivalent of 4 mg/L PEO, and subjected to a settling

procedure.

The settling characteristics ofthe slurry are summarized in

Table 2. This example illustrates that thickening is a possible

method to remove advantageous amounts of colloidal silica.

A continuous bench-top trommel screen was constructed

to test recovery ofPEO-silica agglomerates from LE.

The initial experiments showed that the liquor passing

through the screen was very clear, indicating little remaining

colloidal silica. This example illustrates that trommel screen

is a possible method to remove advantageous amounts of

colloidal silica.

A pilot-size stationary Kason screen with an adjustable

screen angle was employed to process PEO treated LE to

recover PEO-silica agglomerates. The screening was continuous

and was fed with two mix tanks in series to provide an

10 approximately 3-min retention time in each tank. A 10-mg/L

PEO dose, which was effective in bench-top experiments,

gave a silica concentration of 75 mg/L Si. This example

illustrates that Kason screen is a possible method to remove

advantageous amounts of colloidal silica.

Example 2

Fresh silica agglomerates generated from 10-15 mglL PEO

treatment of colloidal silica-rich LE was recycled as seed

material to relieve supersaturation of silica from fresh PLS

with and without LE addition. The slurries were stirred at 50°

C. over a period oftime. Samples were taken at I, 2, 4, 6, and

24 hours, filtered, and analyzed for soluble silica (as silicon).

There was no further PEO treatment of the solutions.

FIG. 6 illustrates that 80-90% reliefofsupersaturation was

attained within a 6-hr retention time. After 24-hr contact,

98-99% relief of supersaturation was attained. The data

shows that agglomerated silica from PEO treatment ofLE can

be recycled as seed material to fresh PLS to remove advan- 20

tageous amounts of colloidal silica.

FIG. 7 shows the extent of supersaturation relief achieved

when the recycled seed material was generated by treating

colloidal silica-richLE with a combination of30 mg/L Galactosol40HD4CD

and 10 mg/L Ciba 7689. The data show that 25

the silica agglomerates generated from the treatment of LE

with combined Galactosol40HD4CD and Ciba 7689 initiated

soluble silica removal effects similar to those of the PEOsilica

agglomerates; greater than 80% and 95% supersatura- 30

tion reliefwas attained after 6 and 24 hours, respectively. The

data generated from these experiments suggest that Galactosol

and Ciba-coagulated silica agglomerates can be recycled

as seed material to remove advantageous amounts ofcolloidal

silica from a blend of fresh PLS and LE without prolonged 35

aging of the PLS.

SOLID-LIQUID PHASE SEPARATION

EXAMPLES

Example I

Feed PEO Solids Initial Thickener

Slurry Solids Settled Overflow Settling Capacity,

Solids, % Dose, glt Solids, % TSS,mg/L Rate,m/hr m2/(t/day)

1.8 190 13.5 37 0.7 4.98

A method for encapsulating air during flocculation was

attempted in 16 batch scoping experiments, feed solution

assaying 158 mg/L total Si, was used for these experiments.

High-speed mixing created a large vortex capable of temporarily

suspending fine air bubbles in solution. When flocculant

was added to the stirred solution, the suspended air

bubbles were trapped within the silica floccules. When agitation

was stopped, the resultant floccule masses instantly rose

to the top of the solution and remained stable for many hours

after formation.

An initial experiment used a I giL stock solution ofPolyox

WSR-301(PEO) at doses oflO, 20, and 30 mg/L of solution,

and gave post-flocculation solution silica values of96, 44, and

30 mg/L Si, respectively. Subsequent testing with freshly

prepared I giL WSR-301 solution at 10 and 20 mglL dosages

gave solution silica values of86 and 66 mg/L Si, respectively.

Other PEO formulations used were Ucarfloc 302, 304, and

309 ("UCF"), which correspond to increasing molecular

weights. Each of the formulations was tested at doses of 10

and 20 mglL. These showed reductions in silica concentrations

with increasing doses. UCF-309 gave the best results,

resulting in a treated solution concentration of 38 mg/L Si

after a polymer dose of20 mglL. This example illustrates that

As used herein, the terms "comprise", "comprises", "comprising",

"having", "including", "includes", or any variation

45 thereof, are intended to reference a non-exclusive inclusion,

such that a process, method, article, composition or apparatus

that comprises a list of elements does not include only those

elements recited, but can also include other elements not

expressly listed and equivalents inherently known or obvious

50 to those of reasonable skill in the art. Other combinations

and/or modifications of structures, arrangements, applications,

proportions, elements, materials, or components used

in the practice ofthe instant invention, in addition to those not

specifically recited, can be varied or otherwise particularly

55 adapted to specific environments, manufacturing specifications,

design parameters or other operating requirements

without departing from the scope ofthe instant invention and

are intended to be included in this disclosure.

Moreover, unless specifically noted, it is the Applicant's

60 intent that the words and phrases in the specification and the

claims be given the commonly accepted generic meaning or

an ordinary and accustomed meaning used by those of reasonable

skill in the applicable arts. In the instance where these

meanings differ, the words and phrases in the specification

65 and the claims should be given the broadest possible, generic

meaning. If it is intended to limit or narrow these meanings,

specific, descriptive adjectives will be used. Absent the use of

US 7,691,347 B2

17 18

* * * * *

6. The method of claim 5, wherein said advantageous

amount ofremoved colloidal silica is greater than about 60%

ofthe total silica in the metal extraction process.

7. The method of claim 3, wherein the silica based seed is

recycled from the electrowinning step.

8. The method of claim 1, wherein acid is added until the

acid concentration is greater than about 80 grams per Liter

and less than about 180 grams per Liter.

9. The method of claim 1, wherein said acid, said seeding

agent, and said pregnant leach solution is aged for at least

about 6 hours prior to removal of colloidal silica.

10. The method ofclaim 1, wherein said acid, said seeding

agent, and said pregnant leach solution is aged at a temperature

greater than about 25 degrees Celsius and less than about

80 degrees Celsius.

11. A method for providing relieffrom dissolved silica in

pregnant leach solutions comprising:

providing a feed stream comprising a metal-bearing material;

subjecting at least a portion of the metal-bearing feed

stream to at least one reactive process, wherein a pregnant

leach solution is formed;

subjecting at least a portion of said pregnant leach solution

to at least one mixing tank, wherein acid and at least one

seeding agent are added to said pregnant leach solution,

such that dissolved silica forms colloidal silica;

transferring said colloidal silica to at least one reagent

dosing tank, wherein at least one flocculant is added to

said colloidal silica, such that said colloidal silica

agglomerates; and

removing at least a portion of said agglomerated silica in a

solid-liquid separation step.

12. The method ofclaim 11, wherein the solid-liquid separation

step comprises at least one of a filtration system, a

35 counter-current decantation (CCD) circuit, a thickener, a centrifuge,

a screen, a flotation method, a clarification method,

and a flocculation method to remove colloidal silica.

13. A method for providing relief from dissolved silica in

pregnant leach solutions comprising:

providing a feed stream comprising a metal-bearing material;

subjecting at least a portion of the metal-bearing feed

stream to at least one reactive process, wherein a pregnant

leach solution is formed;

adding at least one seeding agent to said pregnant leach

solution;

adding acid to the seeding agent and said pregnant leach

solution;

forming colloidal silica from dissolved silica in said pregnant

leach solution;

adding at least one flocculant to said formed colloidal

silica, such that said colloidal silica agglomerates;

removing at least a portion of said agglomerated silica in a

solid-liquid separation step;

recovering metal from said pregnant leach solutionby electrowinning;

and

providing at least a portion of the lean electrolyte from the

electrowinning step to supply some or all of said acid to

form colloidal silica.

these specific adjectives, the words and phrases in the specification

and the claims should be given the broadest possible

meaning. If any other special meaning is intended for any

word or phrase, the specification will clearly state and define

the special meaning.

The use ofthe words "function", "means" or "step" in the

specification or claims is not intended to invoke the provisions

of35 USC 112, Paragraph 6, to define the invention. To

the contrary, if such provisions are intended to be invoked to

define the invention, then the claims will specifically state the 10

phrases "means for" or "step for" and a function, without

recitation of such phrases of any material, structure, or at in

support ofthe function. Contrastingly, the intention is NOT to

invoke such provision when then claims cite a "means for" or

a "step for" performing a function with recitation of any 15

structure, material, or act in support of the function. If such

provision is invoked to define the invention it is intended that

the invention not be limited only to the specific structure,

materials, or acts that are described in the preferred embodiments,

but in addition to include any and all structures, mate- 20

rials, or acts that perform the claimed function, along with any

and all known or later-developed equivalent materials, structures,

or acts for performing the claimed function.

What is claimed is:

1. A method for providing relief from dissolved silica in

pregnant leach solutions comprising:

providing a feed stream comprising a metal-bearing material;

30 subjecting at least a portion of the metal-bearing feed

stream to at least one reactive process, wherein a pregnant

leach solution is formed;

adding at least one seeding agent to said pregnant leach

solution;

adding acid to said pregnant leach solution;

forming colloidal silica from dissolved silica in said pregnant

leach solution;

adding at least one flocculant to said formed colloidal

silica, such that said colloidal silica agglomerates;

removing at least a portion of said agglomerated silica in a

solid-liquid separation step; and

recovering metal from said pregnant leach solutionby electrowinning.

2. The method ofclaim 1, wherein the reactive process step 45

comprises pressure leaching at least a portion of the feed

stream at a temperature of from about 1400 C. to about 2500

C. and at a total operating pressure of from about 50 psi to

about 750 psi.

3. The method ofclaim 1, wherein the seeding agent com- 50

prises any silica based seed.

4. The method ofclaim 1, wherein the seeding agent comprises

at least one of a fumed silica and a polyethylene oxide

(PEO)-silica agglomerates.

55 5. The method of claim 1, wherein said portion of the

colloidal silica removed is an advantageous amount, wherein

said advantageous amount is more silica than would be

removed in a solid/liquid separation step without the addition

ofsaid seeding agent and said flocculant at the same temperature,

acidity, and with the same mixing and residence time.