111111111111111111111111111111111111111111111111111111111111111111111111111
US008114365B2
(12) United States Patent
Gillaspie et al.
(10) Patent No.:
(45) Date of Patent:
US 8,114,365 B2
*Feb.14,2012
(52) U.S. Cl. 423/34; 75/330
(58) Field of Classification Search None
See application file for complete search history.
U.S. PATENT DOCUMENTS
7,691,347 B2 * 4/2010 Gillaspie et 31 423/34
* cited by examiner
(54) SILICA REMOVAL FROM PREGNANT
LEACH SOLUTIONS
(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)
(56) References Cited
(73) Assignee: Freepoint-McMoran Corporation,
Phoenix, AZ (US)
Primary Examiner - Melvin Mayes
Assistant Examiner - Stefanie Cohen
( *) Notice: Subject to any disclaimer, the term ofthis (74) Attorney, Agent, or Firm - Snell & Wilmer L.L.P.
patent is extended or adjusted under 35
U.S.c. 154(b) by 0 days. (57) ABSTRACT
(21) Appl. No.: 12/718,796
Related U.S. Application Data
(63) Continuation of application No. 111857,941, filed on
Sep. 19,2007, now Pat. No. 7,691,347.
US 201110000337 Al
(22) Filed:
(65)
(51) Int. Cl.
C22B 3/20
This patent is subject to a tenninal disclaimer.
Mar. 5, 2010
Prior Publication Data
Jan. 6, 2011
(2006.01)
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.
20 Claims, 7 Drawing Sheets
RELIEF FROM SUPERSATURATION USING GALACTOSOL-CIBA-SILICA SEEDING AGENT
20
./
/,
J 1.....25 gIL solids I I'"29 gIL solids ~
o
11 '0
Sample Time. hr
Note: 45 mglL Si equilibrium concentration assumed: no PEO treatment
:0 u
u.s. Patent Feb. 14,2012
100
108 119
Sheet 1 of?
BLEED
FIG.l
US 8,114,365 B2
u.s. Patent Feb. 14,2012 Sheet 2 of? US 8,114,365 B2
208~
PREGNANT LEACH
SOLUTION
104
108
ACID SOURCE
MIXING TANKS(S) 210
SEEDING AGENT
109 112
113
212
FLOCCULANT REAGENT DOSING
L
S
214
TO ELECTROLYTE RECYCLE
TANK
FIG. 2
107 OR 108 ACID
~
7J).
•
~
~
~
~=~
rFJ =('
D
(..'D...
(.H
o....
......:J
""f'j
('D
?...'.
~...
No
....
N
d
rJl
",010
""~""""''""
W
0'1
tit =N
CLEANED
ELECTROLYTE
TO TANK
REMOVED OR
FORMED SILICA
BLEED
FIG. 3
IUq.~
109 SEEDING
,J AGENT
.l- ., , I.
MIXING TANK 1- 1)2 1J3 FLOCCULANT
MIXING TANK ! .r 1)4 ~
210 REAGENT DOSING l
~ TANK 210 l~ ~
2~2
2<4
)10 )17 ~
rFJ =('
D
(...'D.....
o....
......:J
~
7J).
•
~
~
~
~=~
""f'j
('D
?...'.
~...
No
....
N
CLEANED
ELECTROLYTE
TO TANK
REMOVED OR
FORMED
SILICA BLEED
.~ 1J9 ~t:t:UINl.:i
AGENT
n ~ 1
MIXING TANK ~
MIXING TANK 11~ FLOCCULANT
2~O
MIXING TANK + )14
2~O ~J~ REAGENT ~
2~ DOSING TANK ~11 '
L
~ 115 2h
)10
2(4
~7
107 OR 108 ACID
10' .J SOURCE
FIG. 4
d
rJl
",010
""~""""''""
W
0'1
tit =N
RELIEF FROM SUPERSATURATION USING FUMED SILICA SEEDING AGENT
~
7J).
•
~
~
~
~=~
rFJ =('
D
(..'D...
Ul
o....
......:J
d
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",010
""~""""''""
W
0'1
tit =N
s 10 15 20 2S
00 • , • , •
o
-<>-3 wt"Io, I:1SPLS:LE@122 gIL acid
...e-5 wt%,I:1 SPLS:LE@ 122 gIL acid
20 II 7F I 1_3wt%,2:ISPLS:LE@122g1Lacid
-M- 5 wt%, 2:1 SPLS:LE@ 122 gIL acid
....... 5 wt"Io, SPLS:LE@122 gIL acid
-<>-5 wt%, I:1SPLS:LE@122 gil acid
tOO I I I I ~ ~t I ""f'j
('D
SOl :::::_~: === s<FS: I I :::::sa 11 I ?...'.
~...
N
0....
N
L .f ,/ ..........-- I I I I I
$0
Note: 45 mg/L Si equilibrium concentration assumed; no PEO treatment
FIG.S
Sample Time, hr
;:R. D
c:;
o ..~ .a(II
f!?
~
::J
(/)
°~&<4:0111 I I ::::>t=== I I
100
80
;;Ii!
C
.Q
.~a 60
~
Q)
a.
~
'0
~ 40
Qj
a:
20
RELIEF FROM SUPERSATURATION USING (PEO)- SILICA SEEDING AGENT
-+- 25 gIL solids SPLS@13 gIL acid
_ I: I 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
......- I: I SPLS: LE, lIS gIL acid, 23 gil solids
~
7J).
•
~
~
~
~=~
""f'j
('D
?...'.
~...
No
....
N
rFJ =('
D
(..'D...
0\
o....
......:J
Note: 45 mg/L Si equilibrium concentration assumed; no PEO treatment
FIG. 6
5 10
Sample Time, hr
15 20 2S d
rJl
",010
""~""""''""
W
0'1
tit =N
RELIEF FROM SUPERSATURATION USING GALACTOSOL-CIBA-SILICA SEEDING AGENT
~
7J).
•
~
~
~
~=~
---
~ 7
f
.... 25 gIL solids
...29 gIL solids
-1
FIG. 7
Note: 45 mg/L Si equilibrium concentration assumed; no PEO treatment
tCO
:0
'#.
cE~
10 ..:.:.J.
11l
l!?
~
::J e..n.. 010 o
'+-
.!!!
~
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o J ~o
Sample Time, hr
., :.0 u
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....
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~
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US 8,114,365 B2
1
SILICA REMOVAL FROM PREGNANT
LEACH SOLUTIONS
This application is a continuation of U.S. application Ser.
No. 11/857,941, filed Sep. 19,2007 now U.S. Pat. No. 7,691,
347 and entitled "Silica Removal From Pregnant Leach Solutions,"
now U.S. Pat. No. 7,691,347.
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 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.
2
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 to induce formation of colloidal silica, at
least one flocculant is added to induce aggregation of the
formatted colloidal silica, and a solid-liquid separation process
is utilized to remove advantageous amounts or substantially
all ofthe colloidal silica, thereby providing relieffrom
10 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
15 greater detail hereinbelow), resulting in enhanced silica
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
20 silica and colloidal silica in the PLS reduces impurities in the
metal value deposited on the cathode during an electrowinning
step and reduces colloidal silica in any subsequent solvent
extraction step.
25 BRIEF DESCRIPTION OF THE DRAWING
BACKGROUND OF THE INVENTION
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
60 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
65 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.
55
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,
30 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
35 removal circuit in accordance with one exemplary embodiment
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;
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
45 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
Hydrometallurgical treatment of metal-bearing materials,
such as metal ores, metal-bearing concentrates, and other
metal-bearing substances, has been well established for many
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 40
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- 50
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.
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
US 8,114,365 B2
3 4
At lower temperatures, acid is generally consumed and
45 elemental sulfur is formed according to the following reaction:
(1)
(2)
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 prodliquid
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"),
lean electrolyte, and/or other recycled streams from the metal
recovery processes, including but not limited to secondary
metal, such as cobalt, iron, or manganese, recovery process
streams, to form a metal-bearing inlet stream 101.
Moreover, in an exemplary embodiment of the present
invention, after metal-bearing inlet stream 101 has been suit-
10 ably 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
15 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,
20 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
25 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.
30 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
35 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
40 reaction:
Various embodiments ofthe present invention exhibit significant
advancements over prior art processes, particularly
with regard to metal recovery and process efficiency. Moreover,
existing metal recovery processes that utilize a reactive
process for metal recovery/solution extraction/electrowinning
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. 50
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 55
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- 60
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- 65
cal conditioning processes 201, including but not limited to a
thickening process, it may be combined with any number of
US 8,114,365 B2
5 6
sure 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
product slurry 102 is a conditioning step 203 comprising
flashing. In one aspect of an exemplary embodiment of the
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.
Under the current reactive and conditioning processes for
metal recovery, especially copper from copper sulfides such
as chalcopyrite and chalcocite, large concentrations of dissolved
silica are generated. This dissolved silica is gradually
transformed into colloidal silica. Large amounts of this colloidal
silica can agglomerate within process equipment,
whichmay lead to inefficiencies in subsequent solvent extraction
steps and lower 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
45 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
flocculant to the formed colloidal silica, such that the colloidal
silica agglomerates; (vii) removing at least a portion ofthe
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.
uct 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
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 10
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 15
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 20
metal value from a metal-bearing material, may be used. For
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 25
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 one aspect of the present invention,
reactive processing step 202 comprises pressure leaching, 30
sufficient oxygen 302 is injected into a pressure leaching
vessel to maintain an oxygen partial pressure from about 75 to
about 750 psi, preferably from about 100 to about 400 psi, and
most preferably from about 50 to about 200 psi. Furthermore,
due to the nature of medium temperature pressure leaching, 35
the total operating pressure in leaching vessel 201 is generally
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 40
pressure and temperature of the pressure leaching vessel. In
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
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 50
may be conditioned to adjust the composition, component
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 solu- 55
tion will contain a relatively high concentration of soluble
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 60
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. 65
Optionally, in an exemplary aspect ofthis embodiment ofthe
invention, wherein the reactive processing step 202 is presUS
8,114,365 B2
7 8
nSi(OH)4 <----+(Si02)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
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 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 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.
Further, referring again to FIG. 1, in an exemplary embodiment
ofthe 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
solid-liquid separation steps 204, when removal ofdissolved
or colloidal silica is most advantageous.
Moreover, under normal medium-temperature pressure
10 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) gradu-
15 ally 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
20 silica experiences a higher acid concentration, the monomer
polymerizes more quickly and precipitates as colloidal particles
according to:
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
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 conditioning
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) circuits,
thickeners, clarifiers, or any other suitable device for
solid-liquid separation, in conditioning step 203 to prepare 25
the metal solubilized therein for recovery.
In accordance with further aspects of this exemplary
embodiment, the slurry product 102 from the reactive process
step 202, or further conditioned slurry product stream 103,
may be further conditioned in preparation for later metal- 30
value 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
any conventional manner, including use offiltration systems,
counter-current decantation (CCD) circuits, thickeners, clari- 35
fiers, 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, a clarifier, or any other suitable device in a solid-liquid 40
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
utilizing conventional countercurrent washing ofthe residue
stream to recover leached metal values to one or more solu- 45
tion 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 sepa- 50
rated 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,
recovery of gold, silver, platinum group metals, molybdenum,
zinc, nickel, cobalt, uranium, rhenium, rare earth met- 55
als, 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 condi- 60
tioned 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,
for example, electrowinning, formation, solution extraction
(sometimes referred to as solvent extraction or liquid ion 65
exchange), ion exchange, and/or ion flotation, and preferably
results in a relatively pure copper product.
US 8,114,365 B2
9 10
a silica agglomerates formed 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 resi-
10 dence 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
15 PEO-silica agglomerates ranged from 4-40 giL (dry weight).
The kinetics of the supersaturation relief process was fast in
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,
20 the extent ofsupersaturation reliefwas 98-99%; thus, the bulk
of the silica polymerization takes place within a 6 hour residence
time.
Additionally, in accordance with an exemplary embodiment
ofthe present invention, silica agglomerates fonned by
25 treating colloidal silica rich PLS with 30 mg/L Galactosol
40HD4CD and 10 mg/L Ciba 7689 resulted in similar kinetics
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
30 soluble silica was removed from solution by the seed material,
again indicating that the bulk of the polymerization
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 tem-
35 perature within the 25-80° C. range.
In accordance with an exemplary embodiment of the
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
40 example, in one embodiment of the present invention, the
seeding agent can be recycled from the solid-liquid separation
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,
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
50 induce further nucleation and formation ofcolloidal silica. In
accordance with one embodiment, this mixture can be transferred
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
55 accordance with another exemplary embodiment of the
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 colloidal silica is fonned, the colloidal silica slurry
112 may be forwarded to one or more reagent dosing tanks
60 212 and a flocculant 113 may be added. In accordance with
another exemplary embodiment of the present invention,
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
comprise any multivalent cation, including but not limited to
Furthennore, 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
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: I 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 45
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 65
based seeding agents including, but not limited to fumed
silica, polyethylene oxide (PEO)-silica agglomerates, and/or
US 8,114,365 B2
11 12
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 formed, 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
dosing tanks 212 and a flocculant 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
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
step 214 is a thickener with most of the underflow 110
recycled to enhance formation and removal ofcolloidal silica.
Experimental results for some ofthe exemplary processes are
25 provided in the Example Section below.
In addition to the underflow or bottoms of the solid/liquid
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,
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.
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
40 127 (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
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
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 com-
60 prise an electrowinning circuit, constructed and configured to
operate in a conventional manner. The electrowinning circuit
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
end, to flow perpendicular (referring to the overall flow patany
aluminum, iron, calcium, and/or magnesium, or any polymer,
including but not limited to polyacrylamides, compound
suitable for promoting flocculation of colloidal silica. Furthermore,
in accordance with another exemplary embodiment
ofthe present invention, flocculant 113 may comprise at least
one of polyethylene oxide (PEa), Galactosol 40HD4CD,
guar gum, Ciba 7689, and Scifloc C2733.
After sufficient colloidal silica has been formed and
agglomerated by the flocculant 113 in reagent dosing tank
212, in accordance with another exemplary embodiment of 10
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 15
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 20
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 30
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) 35
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
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 45
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 50
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 55
than about 90% of the total silica in the metal extraction
process. In another exemplary embodiment of the present
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 65
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
US 8,114,365 B2
14
Example 2
Example I
Example I
ACID ADDITION EXAMPLES
TABLE I
Experiment Acid Soluble Si Analyses. mg/L
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
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.
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
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
40 increasing the acid concentration of the blend solution promotes
removal advantageous amounts of colloidal silica.
thus may diminish its economic value. In accordance with
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
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
10 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
15 are not intended to limit the scope of the claimed invention.
Cathode half-reaction: Cu2
++2e-~Cuo
13
tern) 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
may be used.
The primary electrochemical reactions for electrowinning
of metal from acid solution is believed to be as follows:
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 apparatus
currently known or hereinafter devised suitable for the
electrowinning of metal from acid solution, in accordance 20
with the above-referenced reactions or otherwise, is within
the scope of the present invention.
In accordance with a preferred aspect of the invention,
electrowinning circuit 218 yields a cathode metal product
120, optionally, an offgas stream (not shown), and a relatively 25
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
electrolyte stream 121 (FIG. 1) is preferably recycled to various
places in the metal extraction process including, but not 30
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 combined
with lean electrolyte recycle stream 108 and is recycled
to reactive processing step 202. Moreover, in accordance with 35
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
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
weight of lean electrolyte stream 121, and most preferably
from about 80 to about 90 percent by weight of lean electro- 45
Iyte 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
percent by weight of lean electrolyte stream 121, and most
preferably from about 10 to about 20 percent by weight of 50
lean electrolyte stream 121.
Metal values from the metal-bearing product stream 120
are removed during electrowinning step 218 to yield a pure,
cathode metal product. It should be appreciated that in accordance
with the various aspects of the invention, a process 55
wherein, upon proper conditioning ofthe metal-bearing solution,
a high quality, uniformly-plated cathode metal product
may be realized without subjecting the metal-bearing solution
to solvent/solution extraction prior to entering the electrowinning
circuit is within the scope ofthe present invention. 60
As previously noted, careful control of the conditions of the
metal-bearing solution entering an electrowinning circuitespecially
maintenance of a substantially constant metal
composition in the stream-can enhance the quality of the
electrowon metal by, among other things, enabling even plat- 65
ing ofmetal on the cathode and avoidance of surface porosity
in the cathode metal, which degrades the metal product and
US 8,114,365 B2
TABLE 2
PEO Settled Solids Initial Thickener
Feed Slurry Solids Solids, Overflow Settling Capacity,
40 Solids, % Dose, glt % TSS,mg/L Rate,m/hr m2/(t/day)
1.8 190 13.5 37 0.7 4.98
Example 4
Example 2
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.
16
after a polymer dose of20 mg/L. This example illustrates that
air-encapsulated flocculation is 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
25 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 con-
10 tinuous and was fed with two mix tanks in series to provide an
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
15 advantageous amounts of colloidal silica.
15
Example 2
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.
The data shows that fumed silica can be successfully used as
seed material to remove advantageous amounts of colloidal
silica.
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 20
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 advantageous
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
the silica agglomerates generated from the treatment of LE 30
with combined Galactosol40HD4CD and Ciba 7689 initiated
soluble silica removal effects similar to those of the PEOsilica
agglomerates; greater than 80% and 95% supersaturation
reliefwas attained after 6 and 24 hours, respectively. The
data generated from these experiments suggest that Galacto- 35
sol 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
aging of the PLS.
SOLID-LIQUID PHASE SEPARATION
EXAMPLES
As used herein, the terms "comprise", "comprises", "com-
45 prising", "having", "including", "includes", or any variation
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
50 expressly listed and equivalents inherently known or obvious
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
55 specifically recited, can be varied or otherwise particularly
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
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
65 meanings differ, the words and phrases in the specification
and the claims should be given the broadest possible, generic
meaning. If it is intended to limit or narrow these meanings,
Example I
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 60
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 fonnulations 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
17
US 8,114,365 B2
18
specific, descriptive adjectives will be used. Absent the use of
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 10
define the invention, then the claims will specifically state the
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 15
a "step for" performing a function with recitation of any
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 embodi- 20
ments, but in addition to include any and all structures, materials,
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: 25
1. A method for providing relief from dissolved silica in
pregnant leach solutions comprising:
reacting a feed stream comprising a metal-bearing material
to yield a pregnant leach solution comprising a metalvalue
and dissolved silica; 30
adding acid and at least one seeding agent to said pregnant
leach solution to yield a pregnant leach solution comprising
a metal-value and colloidal silica;
adding at least one flocculant to said pregnant leach solution
comprising a metal-value and colloidal silica, such 35
that said colloidal silica agglomerates;
removing at least a portion of said agglomerated silica;
recovering at least a portion of said metal-value from said
pregnant leach solution.
2. The method ofclaim 1, wherein said reacting step com- 40
prises pressure leaching operation.
3. The method of claim 2, wherein said pressure leaching
operation is operated at a temperature of from about 1400 C.
to about 2500 C.
4. The method of claim 1, wherein said removing step 45
comprises a solid-liquid separation step.
5. The method of claim 4, wherein said solid-liquid separation
step comprises at least one of a filtration system, a
counter-current decantation (CCD) circuit, a thickener, a centrifuge,
a screen, a flotation method, a clarification method, 50
and a flocculation method to remove colloidal silica.
6. The method ofclaim 1, wherein said at least one seeding
agent comprises any silica based seed.
7. The system of claim 6, wherein the silica based seed is
recycled from the electrowinning step.
8. The method ofclaim 1, wherein said at least one seeding
agent comprises at least one of a fumed silica and a polyethylene
oxide (PEO)-silica agglomerates.
9. The method ofclaim 1, wherein said portion ofthe 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 of said seeding
agent and said flocculant at the same temperature, acidity,
and with the same mixing and residence time.
10. The method of claim 9, wherein said advantageous
amount ofremoved colloidal silica is greater than about 60%
ofthe total silica in the metal extraction process.
11. A method for providing relieffrom dissolved silica in
pregnant leach solutions comprising:
reacting a feed stream comprising a metal-bearing material
to yield a pregnant leach solution comprising dissolved
silica;
adding acid and at least one seeding agent to said pregnant
leach solution to yield a pregnant leach solution comprising
colloidal silica;
adding at least one flocculant to said pregnant leach solution
comprising colloidal silica, such that said colloidal
silica agglomerates;
removing at least a portion of said agglomerated silica.
12. The method of claim 11, wherein said reacting step
comprises pressure leaching operation.
13. The method ofclaim 12, wherein said pressure leaching
operation is operated at a temperature of from about 1400 C.
to about 2500 C.
14. The method of claim 11, wherein said removing step
comprises a solid-liquid separation step.
15. The method of claim 14, wherein said solid-liquid
separation step comprises at least one ofa filtration system, a
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.
16. The method of claim 11, wherein said seeding agent
comprises any silica based seed.
17. The system ofclaim 16, wherein the silica based seed is
recycled from the electrowinning step.
18. The method of claim 11, wherein said seeding agent
comprises at least one of a fumed silica and a polyethylene
oxide (PEO)-silica agglomerates.
19. The method of claim 11, 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.
20. The method of claim 19, wherein said advantageous
amount ofremoved colloidal silica is greater than about 60%
ofthe total silica in the metal extraction process.
* * * * *