U.S. patent application number 13/604428 was filed with the patent office on 2013-01-03 for method and apparatus for electrowinning copper using an atmospheric leach with ferrous/ferric anode reaction electrowinning.
This patent application is currently assigned to FREEPORT-MCMORAN CORPORATION. Invention is credited to James D. Gillaspie, John O. Marsden, John C. Wilmot.
Application Number | 20130001093 13/604428 |
Document ID | / |
Family ID | 40377654 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130001093 |
Kind Code |
A1 |
Marsden; John O. ; et
al. |
January 3, 2013 |
METHOD AND APPARATUS FOR ELECTROWINNING COPPER USING AN ATMOSPHERIC
LEACH WITH FERROUS/FERRIC ANODE REACTION ELECTROWINNING
Abstract
The present invention relates, generally, to a method and
apparatus for recovering metal values from a metal-bearing
materials, and more specifically, a process for recovering copper
and other metals through leaching, electrowinning using the
ferrous/ferric anode reaction, and the synergistic addition of
ferrous iron to the leach step.
Inventors: |
Marsden; John O.; (Paradise
Valley, AZ) ; Gillaspie; James D.; (Gilbert, AZ)
; Wilmot; John C.; (Anthem, AZ) |
Assignee: |
FREEPORT-MCMORAN
CORPORATION
Phoenix
AZ
|
Family ID: |
40377654 |
Appl. No.: |
13/604428 |
Filed: |
September 5, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12355624 |
Jan 16, 2009 |
8273237 |
|
|
13604428 |
|
|
|
|
61021694 |
Jan 17, 2008 |
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Current U.S.
Class: |
205/261 ;
205/580; 205/593 |
Current CPC
Class: |
C25C 1/00 20130101; Y02P
10/234 20151101; C22B 15/0084 20130101; Y02P 10/20 20151101; C22B
11/04 20130101; C22B 3/02 20130101; C22B 3/20 20130101; C25C 1/12
20130101; Y02P 10/236 20151101; C22B 3/04 20130101; C22B 15/0095
20130101; C22B 15/0067 20130101 |
Class at
Publication: |
205/261 ;
205/593; 205/580 |
International
Class: |
C25C 1/06 20060101
C25C001/06; C25C 1/12 20060101 C25C001/12; C25D 3/38 20060101
C25D003/38 |
Claims
1. A method of recovering a metal value from an ore comprising:
leaching an ore to yield a metal bearing slurry comprising a metal
value and ferrous iron; separating said metal bearing slurry into a
metal bearing solution comprising said metal value and a first
portion of said ferrous iron and a metal bearing solid comprising a
second portion of said ferrous iron; recycling said second portion
of said ferrous iron to be combined with said ore; and
electrowinning said metal bearing solution by oxidizing said first
portion of ferrous iron to ferric iron at an anode of an
electrowinning cell and reducing said metal value at a cathode of
said electrowinning cell.
2. The method according to claim 1, further comprising recycling
said ferric iron to be combined with said ore.
3. The method according to claim 1, further comprising reducing at
least a portion of said ferric iron to said ferrous iron during
said leaching said ore.
4. The method according to claim 1, further comprising grinding
said ore before said leaching said ore.
5. The method according to claim 1, further comprising plating said
metal value onto a cathode substrate.
6. The method according to claim 1, wherein said metal value is
copper.
7. The method according to claim 1, further comprising a precious
metal recovery step.
8. A method comprising: leaching an ore to yield a metal bearing
slurry comprising ferrous iron, wherein said leaching occurs at
atmospheric pressure; separating said metal bearing slurry into a
metal bearing solution comprising a first portion of said ferrous
iron and a metal bearing solid comprising a second portion of said
ferrous iron; recycling at least a portion of said second portion
of said ferrous iron to said leaching step; extracting a metal
value and said ferrous iron from said metal bearing solution to
yield a rich electrolyte; and electrowinning said rich electrolyte
by oxidizing said first portion of ferrous iron to ferric iron at
an anode of an electrowinning cell and reducing said metal value at
a cathode of said electrowinning cell.
9. The method according to claim 8, further comprising conditioning
said metal bearing solution before said oxidizing said metal
bearing solution.
10. The method according to claim 8, further comprising recycling
said ferric iron to said leaching step.
11. The method according to claim 10, further comprising reducing
said ferric iron to said ferrous iron during said leaching
step.
12. The method according to claim 8, further comprising grinding
said ore before said leaching said ore.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of and claims priority to
U.S. patent application Ser. No. 12/355,624 entitled "METHOD AND
APPRATUS FOR ELECTROWINNING COPPER USING AN ATMOSPHERIC LEACH WITH
FERROUS/FERRIC ANODE REACTION ELECTROWINNING" which was filed on
Jan. 16, 2009. The '624 application claims priority to U.S.
Provisional Application Ser. No. 61/021,694 entitled "METHOD AND
APPRATUS FOR ELECTROWINNING COPPER USING AN ATMOSPHERIC LEACH WITH
FERROUS/FERRIC ANODE REACTION ELECTROWINNING" which was filed on
Jan. 17, 2008. All the aforementioned applications are is
incorporated herewith by reference.
FIELD OF INVENTION
[0002] The present invention relates, generally, to a method and
apparatus for recovering metal values from metal-bearing materials,
and more specifically, to a process for recovering copper and other
metals through leaching, electrowinning using the ferrous/ferric
anode reaction, and the synergistic addition of ferrous iron to the
leach step.
BACKGROUND OF THE INVENTION
[0003] Efficiency and cost-effectiveness of copper electrowinning
is and for a long time has been important to the competitiveness of
the domestic copper industry. Past research and development efforts
in this area have thus focused--at least in part--on mechanisms for
decreasing the total energy requirement for copper electrowinning,
which directly impacts the cost-effectiveness of the electrowinning
process.
[0004] Conventional copper electrowinning, wherein copper is plated
from a rich electrolyte to a substantially pure cathode with an
aqueous electrolyte, occurs by the following reactions:
[0005] Cathode Reaction:
Cu.sup.2++SO.sub.4.sup.2-+2e.sup.-.fwdarw.Cu.sup.0+SO.sub.4.sup.2-(E.sup-
.0=+0.345 V)
[0006] Anode Reaction:
H.sub.2O.fwdarw.1/2O.sub.2+2H.sup.++2e.sup.-(E.sup.0=-1.230 V)
[0007] Overall Cell Reaction:
Cu.sup.2++SO.sub.4.sup.2-+H.sub.2O.fwdarw.Cu.sup.0+2H.sup.++SO.sub.4.sup-
.2-+1/2O.sub.2(E.sup.0=-0.855 V)
[0008] Conventional copper electrowinning according to the above
reactions, however, exhibits several areas of potential improvement
for, among other things, improved economics, increased efficiency,
and reduced acid mist generation. First, in conventional copper
electrowinning, the decomposition of water reaction at the anode
produces oxygen (O.sub.2) gas. When the liberated oxygen gas
bubbles break the surface of the electrolyte bath, they create an
acid mist. Reduction or elimination of acid mist is desirable.
Second, the decomposition of water anode reaction used in
conventional electrowinning contributes significantly to the
overall cell voltage via the anode reaction equilibrium potential
and the overpotential. The decomposition of water anode reaction
exhibits a standard potential of 1.23 Volts (V), which contributes
significantly to the total voltage required for conventional copper
electrowinning. The typical overall cell voltage is approximately
2.0 V. A decrease in the anode reaction equilibrium potential
and/or overpotential would reduce cell voltage, and thus conserve
energy and decrease the total operating costs of the electrowinning
operation.
[0009] One way that has been found to potentially reduce the energy
requirement for copper electrowinning is to use the ferrous/ferric
anode reaction, which occurs by the following reactions:
[0010] Cathode Reaction:
Cu.sup.2++SO.sub.4.sup.2-+2e.sup.-.fwdarw.Cu.sup.0+SO.sub.4.sup.2-(E.sup-
.0=+0.345 V)
[0011] Anode Reaction:
2Fe.sup.2+.fwdarw.2Fe.sup.3++2e.sup.-(E.sup.0=-0.770 V)
[0012] Overall Cell Reaction:
Cu.sup.2++SO.sub.4.sup.2-+2Fe.sup.2+.fwdarw.Cu.sup.0+2Fe.sup.3++SO.sub.4-
.sup.2-(E.sup.0=-0.425 V)
[0013] The ferric iron generated at the anode as a result of this
overall cell reaction can be reduced back to ferrous iron using
sulfur dioxide, as follows:
[0014] Solution Reaction:
2Fe.sup.3++SO.sub.2+2H.sub.2O.fwdarw.2Fe.sup.2++4H.sup.++SO.sub.4.sup.2-
[0015] The use of the ferrous/ferric anode reaction in copper
electrowinning cells lowers the energy consumption of those cells
as compared to conventional copper electrowinning cells that employ
the decomposition of water anode reaction, since the oxidation of
ferrous iron (Fe.sup.2+) to ferric iron (Fe.sup.3+) occurs at a
lower voltage than does the decomposition of water.
[0016] The recovery of copper via electrowinning can also be
limited by processes that prepare the copper containing material
for optimal recovery. Leaching is one such processing step. The
mechanism by which leaching processes effectuate the release of
copper from sulfide mineral matrices, such as chalcopyrite, is
generally dependent on temperature, oxygen and/or oxidizing agent
availability, pressure, and process chemistry. In atmospheric
leaching in ferric sulfate media, the dominant oxidation reaction
is believed to be as follows:
CuFeS.sub.2(s)+2Fe.sub.2(SO.sub.4).sub.3(a)->CuSO.sub.4(a)+5FeSO.sub.-
4(a)+2S.sup.0(s)
[0017] Thus, it is advantageous to use a copper preparation
process, such as leaching, that produces ferrous iron (Fe.sup.2+)
to allow for electrowinning of the prepared copper with a
ferrous/ferric anode reaction process.
SUMMARY OF THE INVENTION
[0018] The present invention relates, generally, to a method and
apparatus for recovering metal values from metal-bearing materials,
and more specifically, to a process for recovering copper and other
metals through leaching, electrowinning using the ferrous/ferric
anode reaction, and the synergistic addition of ferrous iron to the
leach step. This improved process and apparatus disclosed herein
achieve an advancement in the art by providing a metal value
recovery system that enables significant enhancement in energy
consumption and consumption of raw materials as compared to
conventional metal value recovery processes and previous attempts
to apply the ferrous/ferric anode reaction to electro winning
operations. As used herein, the term "alternative anode reaction"
refers to the ferrous/ferric anode reaction, and the term
"alternative anode reaction process" refers to any electrowinning
process in which the ferrous/ferric anode reaction is employed.
[0019] In an exemplary embodiment, ferrous iron is recycled in a
leach step. Preferably, in an exemplary embodiment of this
invention, the ferrous iron, species is pyrite, most preferably,
pyrite is recycled from a solid/liquid phase separation stage or
from a size or gravity based separation process after the leaching
step. In various embodiments, ferric iron from a downstream
electrowinning may also be recycled into a leach step. This
improved process and apparatus disclosed herein achieves
advancement in the art by producing increased amounts of ferrous
iron in the leached product slurry, thereby allowing for direct
electrowinning in connection with a ferrous/ferric anode reaction
process.
[0020] Furthermore, in an exemplary embodiment of this invention,
one or more leach steps may be subjected to a ferrous iron addition
and a subsequent direct electrowinning using an alternative anode
reaction process. Again, in one aspect of this exemplary embodiment
of the present invention the ferrous iron species can be pyrite,
most preferably, pyrite which is recycled from a solid/liquid phase
separation stage after the leaching step.
[0021] In various embodiments, a method is provided comprising
providing an ore comprising a metal value and iron, leaching the
ore to yield a metal bearing slurry comprising the metal value and
ferrous iron, separating the metal bearing slurry into a metal
bearing solution comprising the metal value and a first portion of
the ferrous iron and a metal bearing solid comprising a second
portion of the ferrous iron, recycling the second portion of the
ferrous iron into the ore, electrowinning the metal bearing
solution, oxidizing the first portion of ferrous iron to ferric
iron, recovering the metal value from the metal hearing solution
and recycling the ferric iron to the ore.
[0022] In still other embodiments, a method is provided comprising
providing an ore comprising a metal value and iron, leaching the
ore to yield a metal bearing slurry comprising the metal value and
ferrous iron, separating the metal bearing slurry into a metal
bearing solution comprising the metal value and a first portion of
the ferrous iron and a metal bearing solid comprising a second
portion of the ferrous iron, recycling the second portion of the
ferrous iron into the ore, extracting the metal value and the
ferrous iron from the metal bearing solution to yield a rich
electrolyte, electrowinning the rich electrolyte, oxidizing the
first portion of ferrous iron to ferric iron, recovering the metal
value from the rich electrolyte, and recycling the ferric iron into
the ore.
[0023] In further embodiments, a method is provided comprising
providing a material comprising a metal value and pyrite, leaching
said material to yield a metal bearing slurry, separating said
metal bearing slurry into a metal bearing solution and a solids
component comprising at least a portion of said pyrite, recycling
at least a portion of said solids component into said material,
electrowinning said metal bearing solution, recovering said metal
value from said metal bearing solution, and recycling iron into
said material.
[0024] In various embodiments, a metal value recovery system is
provided comprising a leaching apparatus, a solid-liquid separator
in communication with the leaching apparatus, a first recycle feed
configured to recycle pyrite from the solid-liquid separator to the
leaching apparatus, an electrowinning cell comprising at least one
cathode and at least one flow through anode, the electrowinning
cell is configured to oxidize ferrous iron to ferric iron at the at
least one flow through anode, the electrowinning cell configured to
recovery a metal value on the at least one cathode, the
electrowinning cell in communication with the solid-liquid
separator, and a second recycle feed configured to recycle the
ferric iron from the electrowinning cell to the leaching
apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] 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 drawing figures,
wherein like numerals denote like elements and wherein:
[0026] FIG. 1 illustrates a flow diagram illustrating a process in
accordance with an exemplary embodiment of the present
invention;
[0027] FIG. 2 illustrates a flow diagram illustrating a process in
accordance with an exemplary embodiment of the present
invention;
[0028] FIG. 3 illustrates a flow diagram illustrating a process in
accordance with an exemplary embodiment of the present
invention;
[0029] FIG. 4 illustrates a flow diagram illustrating a process in
accordance with an exemplary embodiment of the present
invention;
[0030] FIG. 5 illustrates a flow diagram illustrating a process in
accordance with an exemplary embodiment of the present
invention;
[0031] FIG. 6 illustrates a flow diagram illustrating a process in
accordance with an exemplary embodiment of the present
invention;
[0032] FIG. 7 illustrates a flow diagram illustrating a process in
accordance with an exemplary embodiment of the present
invention;
[0033] FIG. 8 illustrates a flow diagram illustrating a process in
accordance with an exemplary embodiment of the present
invention.
[0034] FIG. 9 illustrates a flow diagram illustrating a process in
accordance with an exemplary embodiment of the present
invention.
[0035] FIG. 10 illustrates a flow diagram illustrating a process in
accordance with an exemplary embodiment of the present
invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0036] This detailed description of exemplary embodiments shows
various exemplary embodiments of the invention known to the
inventors at this time. 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.
Rather, the following disclosure is intended to teach both the
implementation of the exemplary embodiments and modes and any
equivalent modes or embodiments that are known or obvious to those
of reasonable skill in the art. Additionally, all included figures
are non-limiting illustrations of the exemplary embodiments and
modes, which similarly avail themselves to any equivalent modes or
embodiments that are known or obvious to those of reasonable skill
in the art.
[0037] Aspects of various embodiments may provide significant
advancements over prior art processes, particularly with regard to
process efficiency and economics. Moreover, existing copper
recovery processes that utilize conventional electrowinning process
sequences may, in many instances, easily be retrofitted to exploit
the many commercial benefits the present invention provides.
[0038] With reference to FIG. 1, a metal recovery process is
illustrated according to various embodiments of the present
invention. Metal recovery process 1 comprises leach step 52,
conditioning step 55, recovery step 75, ferric iron recycle 101,
and ferrous iron recycle 100. Leach step 52 can be any method,
process, or system that enables a metal value to be leached from a
metal bearing material. Typically, leach step 52 utilizes acid to
leach a metal value from a metal bearing material. For example,
leach step 52 can employ a leaching apparatus such as for example,
a heap leach, a vat leach, a tank leach, a pad leach, a leach
vessel or any other leaching technology useful for leaching a metal
value from a metal bearing material. In accordance with various
embodiments, leach step 52 may be conducted at any suitable
pressure, temperature, and/or oxygen content. Leach step 52 can
employ one of a high temperature, a medium temperature, or a low
temperature, combined with one of high pressure, or atmospheric
pressure. Leaching step 52 may utilize conventional atmospheric or
pressure leaching, for example but not limited to, low, medium or
high temperature pressure leaching. As used herein, the term
"pressure leaching" refers to a metal recovery process in which
material is contacted with an acidic solution and oxygen under
conditions of elevated temperature and pressure. Medium or high
temperature pressure leaching processes for chalcopyrite are
generally thought of as those processes operating at temperatures
from about 120.degree. C. to about 190.degree. C. or up to about
250.degree. C. In accordance with, an exemplary embodiment, leach
step 52 enables leaching of at least a copper value and an iron
value from a chalcopyrite/pyrite ore or a chalcopyrite/pyrite
concentrate.
[0039] In accordance with a preferred embodiment of the present
invention, and as will be described in greater detail hereinbelow,
leach step 52 preferably comprises a conventional atmospheric
leaching operation.
[0040] In various embodiments, leach step 52 provides a metal
bearing slurry 13 for condition step 55. In various embodiments,
condition step 55 can be for example, but is not limited to, a
solid liquid phase separation step, an additional leach step, a pH
adjustment step, a dilution step, a concentration step, a metal
precipitation step, a filtering step, a settling step, and the
like, as well as combinations thereof. In an exemplary embodiment,
condition step 55 can be a solid liquid phase separation step
configured to yield a metal bearing solution 14 and a metal bearing
solid. In an aspect of this exemplary embodiment, metal bearing
solution 14 can comprise a copper value and ferrous iron
(Fe.sup.2+). In an aspect of this exemplary embodiment, a metal
bearing solid can comprise ferrous iron, and in a preferred aspect,
the ferrous iron can be in the form of pyrite or incompletely
leached chalcopyrite.
[0041] In other various embodiments, condition step 55 may be one
or more leaching steps. For example, condition step 55 may be any
method, process, or system that further prepares metal bearing
material for recovery. In various embodiments, condition step 55
utilizes acid to leach a metal value from a metal bearing material.
For example, condition step 55 may employ a leaching apparatus such
as for example, a heap leach, a vat leach, a tank leach, a pad
leach, a leach vessel or any other leaching technology useful for
leaching a metal value from a metal bearing material.
[0042] In accordance with various embodiments, condition step 55
may be a leach process conducted at any suitable pressure,
temperature, and/or oxygen content. In such embodiments, condition
step 55 may employ one of a high temperature, a medium temperature,
or a low temperature, combined with one of high pressure, or
atmospheric pressure. Condition step 55 may utilize, conventional
atmospheric or pressure leaching, for example but not limited to,
low, medium or high temperature pressure leaching. Medium or high
temperature pressure leaching processes for chalcopyrite are
generally thought of as those processes operating at temperatures
from about 120.degree. to about 190.degree. C. or up to about
250.degree. C.
[0043] In various embodiments, condition step 55 may comprise
dilution, settling, filtration, solution/solvent extraction, ion
exchange, pH adjustment, chemical adjustment, purification,
concentration, screening, and size separation. In various
embodiments, condition step 55 is a high temperature, high pressure
leach. In other embodiments, condition step 55 is an atmospheric
leach. In further embodiments, condition step 55 is a solid liquid
phase separation. In still further embodiments, condition step 55
is a settling/filtration step. In such embodiments, depending on
the ore body used, pyrite and chalcopyrite may be heavier and/or
larger than the other constituent particles, enabling a
settling/filtration/screening step to select for at least a portion
of pyrite and chalcopyrite contained in a solid phase.
[0044] In various embodiments, ferrous iron recycle 100 can be
configured to transfer at least a portion of metal bearing solid
comprising ferrous iron from condition step 55 to leach step 52.
Ferrous iron recycle 100 recycles a portion of ferrous iron that
was not leached into metal bearing solution 14. In an aspect of the
present invention, the ferrous iron that is recycled back to leach
step 52 can include iron that is still trapped in metal bearing
solid, for example pyrite. In an exemplary embodiment, the ferrous
iron that is recycled back to leach step 52 can be exposed to an
acid to leach the recycled ferrous iron into a solution. In an
exemplary embodiment, ferrous iron may be added to leaching step 52
by recycling ferrous iron from condition step 55 downstream of
leaching step 52. Preferably, in an exemplary embodiment of this
invention, the ferrous iron species is pyrite, most preferably,
such pyrite comprises pyrite recycled from a solid/liquid phase
separation stage after leaching step 52.
[0045] With further reference to FIG. 1, metal bearing solution 14
is suitably treated in recovery step 75 to advantageously enable
the recovery of a metal value, such as, for example, a copper
value. In one exemplary embodiment, recovery step 75 comprises
direct electrowinning. In another exemplary embodiment, recovery
step 75 comprises a solvent extraction and electrowinning. In
various embodiments, recovery step 75 can employ an electrowinning
step configured to cause the ferrous/ferric (Fe.sup.2+/Fe.sup.3+)
couple to become the anode reaction, which as used herein, can be
referred to as the alternative anode reaction ("AART"). In so
doing, the ferrous/ferric anode reaction replaces the decomposition
of water anode reaction. Because oxygen gas is not produced in the
ferrous/ferric anode reaction, the generation of "acid mist" as a
result of the reactions in the electrochemical cell can be
eliminated. In addition, because the equilibrium potential of the
Fe.sup.2+/Fe.sup.3+ couple (i.e., E.sup.0=-0.770 V) is less than
that for the decomposition of water (i, E.sup.0=-1.230 V), the cell
voltage is decreased, thereby decreasing cell energy consumption.
Furthermore, in accordance with one aspect of the invention,
ferrous iron can be created in leach step 52 and used in the
ferrous/ferric electrowinning anode reaction in recovery step
75.
[0046] The alternative anode reaction ("AART") as well as general
cell configurations, operating parameters and flow and cell
characteristics of such process which may be employed in connection
with various embodiments and aspects of the present invention are,
for the purpose of clarity, discussed in greater detail
hereinbelow. As such, it should be appreciated that as used in
connection with the following description of the exemplary
embodiments made with reference to the drawing figures the AART
process referred to is that which is more fully described
hereinbelow.
[0047] Further with reference to FIG. 1, in accordance with a
preferred embodiment of the invention, ferric iron recycle 101 can
be configured to permit ferric iron (Fe.sup.3+) generated in
recovery step 75 to be recycled to leach step 52. In this manner,
ferric iron from ferric iron recycle 101 can be reduced to ferrous
iron in leach step 52. This improved process and apparatus
disclosed herein achieves an advancement in the art by producing
increased amounts of ferrous iron in the leached product slurry,
thereby allowing for electrowinning with a ferrous/ferric anode
reaction process.
[0048] As leaching step 52 consumes ferric iron by reducing ferric
iron to ferrous iron, in accordance with various aspects of the
present invention, leaching step 52 may be used to reduce the
ferrous iron needed for downstream recovery step 75, such as for
example, through use of an electrowinning cell configured for AART.
As noted above, for clarity, exemplary embodiments of an
electrowinning cell and the various parameters associated therewith
configured for AART are described in detail below. Synergistically,
ferric iron produced from the AART may be recycled into leach step
52 for reduction to ferrous iron. For example, ferric iron recycle
101 illustrates the flow of ferric iron into leach step 52 so that
ferric iron may be reduced to ferrous iron.
[0049] With reference now to FIG. 2, metal recovery process 2 is
illustrated in accordance with an exemplary embodiment of the
present invention. Metal-bearing material 11 may be an ore, a
concentrate, or any other material from which 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 a
metal-bearing material 11 in accordance with various embodiments of
the present invention. Various aspects and embodiments of the
present invention, however, prove especially advantageous in
connection with the recovery of copper from copper sulfide ores,
such as, for example, chalcopyrite (CuFeS.sub.2), chalcocite
(Cu.sub.2S), bornite (CusFeS.sub.4), and covellite (CuS). Thus,
metal-bearing material 11 may be a copper ore or concentrate, and
preferably, is a copper sulfide ore or a concentrate. Various
aspects and embodiments of the present invention, however, prove
especially advantageous in connection with the recovery of copper
and gold from gold hearing copper sulfide ores, such as, for
example, gold bearing chalcopyrite (CuFeS.sub.2), chalcocite
(Cu.sub.2S), bornite (CusFeS.sub.4), and covellite (CuS). Thus,
metal-bearing material 11 may be a gold-bearing copper ore or
concentrate, and preferably, is a gold-bearing copper sulfide ore
or a concentrate.
[0050] Metal-bearing material 11 may be prepared for leaching step
10 in any manner that enables the conditions of metal-bearing
material 11 such as, for example, particle size, composition, and
component concentration to be suitable for the chosen processing
method, as such conditions may affect the overall effectiveness and
efficiency of processing operations. Desired composition and
component concentration parameters can be achieved through a
variety of chemical and/or physical processing stages, the choice
of which will depend upon the operating parameters of the chosen
processing scheme, equipment cost and material specifications. For
example, metal-bearing material 11 may undergo comminution, fine
grinding, flotation, blending, and/or slurry formation, as well as
any chemical and/or physical conditioning including, but not
limited to metal precipitation and/or a solid/liquid phase
separation step. As used herein, metal bearing material 11 may be
interchangeably referred to as ore or concentrate. In various
embodiments, metal bearing material can comprise at least one metal
value and pyrite.
[0051] In various aspects of this embodiment of the present
invention, metal bearing material 11 is moved to leach step 10 via
metal bearing stream 12. In various embodiments, leach step 10 is
conducted at near about atmospheric pressure (i.e., 1 atm or 101.3
kPa). Such a leaching apparatus useful for leach step 10 may be,
for example but not limited to, a heap leach, a vat leach, a tank
leach, a pad leach, a simultaneous grind/leach, or any other
similar operation. In an exemplary embodiment, the leach step 10
can be performed using oxides of metal values. In an exemplary
embodiment, ferric sulfate media may be used.
[0052] In accordance with one preferred embodiment of the present
invention, atmospheric leach step 10 may be carried out under
conditions whereby the pyrite is not materially oxidized. For
example, leach step 10 may include the application of an oxidizing
agent, e.g. oxygen in the form of air or O.sub.2 gas. Typically,
the operating solution potential of the atmospheric leach step 10
is less than about 500 mV (with reference to Ag/AgCl electrode),
preferably, between about 350 mV and 520 mV and more preferably
between about 380 mV and 480 mV.
[0053] In various embodiments, atmospheric leach step 10 includes a
bulk concentrate containing a chalcopyrite:pyrite ratio of between
about 3:1 and about 1:20 is subjected to the leaching process.
Alternatively, the chalcopyrite:pyrite ratio is between about 1:1
and about 1:10, or between about 1:2 and about 1:4. In exemplary
embodiment, the chalcopyrite:pyrite ratio is between about 1:4.
Additional pyrite may be added.
[0054] Leach step 10 may be performed at temperatures between about
50.degree. C. and about 250.degree. C. In various embodiments,
leach step 10 may be performed at temperatures between about
190.degree. C. and about 250.degree. C. In other embodiments, leach
step 10 may be performed at temperatures between about 120.degree.
C. and 190.degree. C. In still other embodiments, leach step 10 may
be performed at temperatures between about 50.degree. C. and about
120.degree. C., although a temperature of about 60.degree. C. and
about 90.degree. C. is preferable. In various embodiments, a leach
step 10 is performed under about atmospheric, pressure.
[0055] In accordance with one aspect of the present invention,
atmospheric leach step 10 may include ferric iron among the metal
values to be processed. As discussed above, it is advantageous to
use a leach step, exemplified in FIG. 2 as atmospheric leaching
step 10, which produces ferrous iron to allow for electrowinning of
the copper value utilizing a ferrous/ferric anode reaction process.
Thus, in accordance with this exemplary embodiment of the present
invention, ferrous iron recycle 100 can be configured to recycle
ferrous iron to atmospheric leaching step 10 to increase the
production of ferrous iron in the metal bearing slurry 13 from the
atmospheric leaching step 10.
[0056] The solid liquid phase separation step 30 is suitably
configured to separate metal slurry 13 into a metal bearing
solution 14 and a metal bearing solid comprising ferrous iron. In
an exemplary embodiment, metal bearing slurry 14 comprises a metal
value, such as for example a copper value and ferrous iron.
Preferably, at least a portion of metal bearing solid comprising
ferrous iron is transferred via ferrous iron recycle 100 to
atmospheric leach step 10. In an exemplary embodiment, ferrous iron
may be added to atmospheric leaching step 10 by recycling ferrous
iron from solid-liquid phase separation step 30 of the atmospheric
leaching step 10. Preferably, in an exemplary embodiment of this
invention, the ferrous iron species is pyrite, most preferably,
pyrite which is recycled from a solid/liquid phase separation stage
30 after atmospheric leaching step 10.
[0057] In various embodiments, a metal value 99 can be recovered
from metal bearing solution 14 by direct electrowinning step 40
configured to utilize. AART. In an exemplary embodiment, metal
value 99 can be copper. In various embodiments, ferric iron is
recycled from direct electrowinning step 40 to increase the
production of ferrous iron in the product slurry from an
atmospheric leaching step 10. As atmospheric leaching step 10
consumes ferric iron by reducing ferric iron to ferrous iron,
atmospheric, leaching step 10 may be used to reduce the ferrous
iron needed for downstream direct electrowinning step 40 that
utilize AART. Synergistically, ferric iron produced in the AART
reaction may be recycled into atmospheric leach step 10 for
reduction to ferrous iron. For example, ferric iron recycle 101
illustrates the flow of ferric iron into an atmospheric leach step
10 so that ferric iron may be reduced to ferrous iron. Also in
accordance with exemplary embodiments, ferric iron is recycled from
direct electrowinning step 40 to increase the production of ferrous
iron in the metal bearing slurry 13 from the atmospheric leaching
step 10.
[0058] With reference now to FIG. 3, metal recovery process 3 is
illustrated in accordance with an exemplary embodiment of the
present invention. As illustrated in FIG. 3, metal bearing material
11, metal bearing stream 12, atmospheric leach step 10, metal
bearing slurry 13, solid-liquid phase separation step 30, ferrous
iron recycle 100, metal bearing solution 14 and ferric iron recycle
101 are as described hereinabove.
[0059] However, in accordance with this exemplary embodiment of the
present invention, metal-bearing solution 14 from solid-liquid
phase separation step 30 may be further processed in a solvent
extraction step 200. In accordance with various aspects of this
embodiment of the present invention, solvent extraction step 200
can be configured to selectively extract both a metal value, such
as for example copper, and ferrous iron. During solvent extraction
step 200, a metal value, such as for example copper, from metal
bearing solution may be loaded selectively onto an organic
chelating agent, for example, an aldoxime/ketoxime blend, resulting
in a metal value containing organic stream and a raffinate solution
201. In various embodiments, the metal value containing organic
stream may comprise a copper compound and ferrous iron. Solvent
extraction step 200 can be configured to select for both a metal
value, such as copper, and ferrous iron by the selection of an
appropriate mixture of ketoximes and/or aldoximes. Solvent
extraction step 200 can produce a raffinate solution 201 and a rich
electrolyte 15. In various embodiments, solvent extraction step 200
can yield a rich electrolyte 15 comprising a metal value and
ferrous iron.
[0060] Raffinate 201 from solvent extraction step 200
advantageously may be used in a number of ways. For example, all or
a portion of raffinate 201 may be recycled to atmospheric leaching
step 100, such as for example to aid with temperature control or
solution balancing, or it may be used in other leaching operations,
or it may be used for any combination thereof. The use of raffinate
201 in atmospheric leaching step 10 may be beneficial because the
acid and ferric/ferrous iron values contained in raffinate 201 may
act to optimize the potential for leaching oxide and/or sulfide
ores that commonly dominate heap leaching operations. That is, any
ferric iron and acid remaining in raffinate 201 may be used to
optimize the Eh and/or pH of atmospheric leaching step 10. It
should be appreciated that the properties of raffinate 201, such as
component concentrations, may be adjusted in accordance with the
desired use of raffinate 201.
[0061] In various embodiments, a metal value 99 can be recovered
from rich electrolyte 15 by electrowinning step 210 configured to
utilize AART. In an exemplary embodiment, metal value 99 can be
copper. In various embodiments, ferric iron is recycled from
electrowinning step 210 to increase the production of ferrous iron
in the product slurry from an atmospheric leaching step 10. As the
atmospheric leaching step 10 consumes ferric iron by reducing
ferric iron to ferrous iron, the atmospheric leaching step 10 may
be used to reduce the ferrous iron needed for downstream
electrowinning step 210 that utilize AART. Synergistically, ferric
iron produced from the AART reaction may be recycled into an
atmospheric leach step 10 for reduction to ferrous iron. For
example, ferric iron recycle 101 illustrates the flow of ferric
iron into an atmospheric leach step 10 so that ferric iron may be
reduced to ferrous iron. Also in accordance with exemplary
embodiments, ferric iron is recycled from electrowinning step 210
to increase the production of ferrous iron in the metal bearing
slurry 13 from the atmospheric leaching step 10.
[0062] As illustrated in FIG. 4, metal recovery process 4 can be
configured for recovery of a metal value and a precious metal
value, in accordance with another exemplary embodiment of the
present invention. As illustrated in FIGS. 2 and 3, metal bearing
material 11, metal bearing stream 12, atmospheric leach step 10,
metal bearing slurry 13, solid-liquid phase separation step 30,
ferrous iron recycle 100, metal bearing solution 14 and ferric iron
recycle 101 are as previously described above.
[0063] Hydrometallurgical processes, particularly pressure leaching
processes, may be sensitive to the particle size of the metal
bearing material to be treated, such as for example metal bearing
material 11. Thus, it is in the area of extractive hydrometallurgy
it may be desirable to finely divide, grind, and/or mill mineral
species to reduce particle sizes prior to leaching. It generally
has been appreciated that reducing the particle size of a mineral
species, such as, for example, a copper sulfide, enables leaching,
such as for example pressure leaching, under less extreme
conditions of pressure and temperature to achieve the same metal
extraction as achieved under conditions of higher temperature and
pressure. The particle size distribution can also affect other
leaching conditions, such as, for example, acid concentration and
oxygen overpressure.
[0064] A variety of acceptable techniques and devices for reducing
the particle size of the metal-bearing material are currently
available, such as ball mills, tower mills, superfine 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 increasing the surface area of the
material to be processed.
[0065] For example, metal-bearing material 11 may be prepared for
metal recovery processing by controlled fine grinding. Preferably,
it is advantageous not only to reduce the size of the metal-bearing
material 11 particles in the process stream, but also to ensure
that the weight proportion of the coarsest particles is minimized.
Significant advantages in processing efficiency and copper recovery
are achievable by enabling substantially all particles to react
substantially completely. In exemplary embodiments, fine grinding
step 90 preferably results in metal bearing material 11 being
finely ground, such that the particle size of the metal bearing
material II being processed is reduced such that substantially all
of the particles are small enough to react substantially completely
during leaching.
[0066] Ground metal bearing material 21 can comprise various
particle sizes and particle size distributions may be
advantageously employed in accordance with various aspects of the
present invention. For example, in accordance with one aspect of
the present invention grinding step 90 results in metal bearing
material 11 being finely ground to a P80 on the order of less than
about 25 microns, and preferably on the order of a P80 between
about 13 and about 20 microns. In accordance with another aspect of
the present invention, the copper-containing material has a P80 of
less than about 250 microns, preferably a P80 from about 75 to
about 150 microns, and more preferably a P80 on the order of from
about 5 to about 75 microns. In accordance with yet another aspect
of the present invention, a particle size distribution of
approximately 98 percent passing about 25 microns is preferable,
and more preferably, the metal-bearing material stream has a
particle size distribution of approximately 98 percent passing from
about 10 to about 23 microns, and optimally from about 13 to about
15 microns.
[0067] Fine grinding step 90 may be conducted in any manner,
satisfactory controlled fine grinding may be achieved using as fine
grinding apparatus, such as, for example, a stirred horizontal
shaft mill with baffles or a vertically stirred mill without
baffles. Such exemplary apparatus include the Isamill developed
jointly by Mount Isa Mines (MIM), Australia, and Netzsch
Feimnahltechnik, Germany and the SMD or Detroit Mill, manufactured
by Metso Minerals, Finland. Preferably, if a horizontal mill is
utilized, the grinding medium would be 1.2/2.4 mm or 2.4/4.8 mm
Colorado sand, available from Oglebay Norton Industrial Sands Inc.,
Colorado Springs, Colo. However, any grinding medium that enables
the desired particle size distribution to be achieved may be used,
the type and size of which may be dependent upon the application
chosen, the product size desired, grinding apparatus manufacturer's
specifications, and the like. Exemplary media include, for example,
sand, silica, metal beads, ceramic beads, and ceramic balls.
[0068] In various embodiments, ground metal bearing material 21 can
optionally be subjected to a separation step, such as, for example,
a precipitation step 80 shown in FIG. 4, which, in accordance with
this exemplary process, serves to precipitate solubilized metal
value from as recycled lean electrolyte stream 204 onto the
surfaces of solid particles in the ground metal bearing slurry 22.
In an exemplary embodiment, precipitation step 80 can involve
ground metal bearing material 21 being combined with a sulfur
dioxide (SO.sub.2) stream, lean electrolyte stream 204, and/or
recycled liquid phase 203 in a suitable processing vessel.
Preferably, precipitation step 80 is carried out such that the
metal value from the lean electrolyte 204 precipitates, at least in
part, onto the surface of ground metal bearing slurry 22. Optional
precipitation step 80 can be carried out at a slightly elevated
temperature, such as from about 70.degree. C. to about 180.degree.
C., preferably from about 80.degree. C. to about 100.degree. C.,
and most preferably at a temperature of about 90.degree. C.
Heating, if necessary, can be effectuated through any conventional
means, such as electric heating coils, a heat blanket, process
fluid heat exchange, external exothermic reaction, and other ways
now known or later developed. In an exemplary process, steam may be
generated in other process areas, and may be directed to the
processing vessel in optional precipitation step 80 to provide the
heat desired to enhance the precipitation process.
[0069] In exemplary embodiments, optional precipitation step 80
produces ground metal bearing slurry 22, which can be processed by
solid liquid phase separation 1030. Solid liquid phase extraction
1030 may be similar to solid liquid phase separation step 30 as
described hereinabove. Solid liquid phase separation step 1030
yields a rough metal bearing solution 24 and a rough metal bearing
solid 23. Rough metal bearing solid 23 can be processed by
atmospheric leaching step 10 to yield metal bearing slurry 13.
Solid liquid phase separation step 30 can be configured to separate
metal bearing slurry 13 into metal bearing solution 14 and metal
bearing solid 26, as described herein. In accordance with this
exemplary embodiment, metal bearing solution 14 is advantageously
processed by a direct electrowinning step 40 to yield a metal value
99. Direct electrowinning step 40 may be configured with AART, as
described hereinabove. Lean electrolyte 204 from direct
electrowinning step 40 can be recycled to precipitation step 80, or
recycled and mixed with metal bearing solution 14 and/or recycled
as ferric iron recycle 101 back into atmospheric leaching step 10.
As described herein, atmospheric leaching step 10 can reduce ferric
iron from ferric iron recycle 101 into ferrous iron.
[0070] Moving back to solid liquid phase separation step 30, metal
bearing solid 26 may be split such that at least a portion of metal
hearing solid 26 may provide ferrous iron to atmospheric leaching
step 10 via ferrous iron recycle 100. The remainder and/or at least
a portion of metal bearing solid 26 may be added to second
atmospheric leaching step 50. In various embodiments, second
atmospheric leaching step 50 can utilize any leaching process
described herein. In an aspect of the exemplary embodiments,
atmospheric leaching step 50 can be configured to conditions as
described herein for atmospheric leaching step 10.
[0071] Moving to solid liquid phase separation step 1030, in
accordance with various aspects of this exemplary embodiment, rough
metal bearing solution 24 may be added to a leaching step 20.
Leaching step 20 may be any leaching process described herein. In
accordance with one aspect of this exemplary embodiment, leaching
step 20 may include the addition of air or oxygen to help
facilitate leaching. Second metal bearing material 111 may be added
to leach step 20. In various embodiments, second metal bearing
material 111 may be equivalent to metal bearing material 11
described herein. Second metal bearing material 111 may be
transferred to leach step 20 via second metal bearing material
stream 112.
[0072] In exemplary embodiments, leach step 20 can yield slurry 28.
Second solid liquid phase separation step 2030 can be configured to
process slurry 28 to yield solid portion 29 and liquid portion 202.
In accordance with one aspect of this exemplary embodiment, solid
portion 29 may be added to second atmospheric leach step 50, and
liquid portion 202 from solid liquid phase separation step 2030 may
be recycled to leach step 20. In various aspects of this exemplary
embodiment, second atmospheric leach step 50 can yield a precious
metals slurry 27. In such case, solid liquid phase separation step
3030 can process precious metal slurry 27 into a recyclable liquid
phase 203 and a precious metals residue 31. A portion of precious
metal residue 31 may be recycled back to second atmospheric leach
step 50 via precious metal recycle 120. Precious metal residue can
be processed by precious metal recovery step 33 to recover precious
value 95. Precious metal recovery step 33 can be electrowinning,
ion exchange, electrorefining and/or any other recovery process
useful for the recovery of a precious metal. Precious metal value
can be for example but not limited to gold, silver, nickel,
rhenium, or molybdenum, and is preferably gold.
[0073] Depending on its composition, precious metal residue 31 from
solid liquid phase separation step 3030 may be disposed of or
subjected to further processing, such as, for example, precious
metal recovery. For example, if precious metal residue 31 contains
an economically significant fraction of gold, it may be desirable
to recover this gold fraction through a cyanidation process or
other suitable recovery process. If gold or other precious metals
are to be recovered from precious metal residue 31 by cyanidation
techniques, the content of contaminants in the stream, such as
elemental sulfur, iron precipitates, and unreacted copper minerals,
is preferably minimized. Such materials generally promote high
reagent consumption in the cyanidation process and thus increase
the expense of the precious metal recovery operation. Additionally,
as mentioned above, it is preferable to use a large amount of wash
water or other diluent during the solid-liquid separation process
to maintain low copper and acid levels in the CCD residue in an
attempt to optimize the residue stream conditions for precious
metal recovery.
[0074] As illustrated in FIG. 5, metal recovery process 5 can be
configured for recovery of a metal value and a precious metal
value, in accordance with an exemplary embodiment of the present
invention. For the sake of brevity, as illustrated in FIGS. 2, 3,
and 4, metal bearing material 11, metal bearing stream 12,
atmospheric leach step 10, metal bearing slurry 13, solid-liquid
phase separation step 30, ferrous iron recycle 100, metal bearing
solution 14 and ferric iron recycle 101 are as described
hereinabove. Also as illustrated in FIG. 4, second metal bearing
material 111, second metal bearing material stream 112, and lean
electrolyte 204 are as described hereinabove.
[0075] With reference to FIG. 5, solid-liquid phase separation step
30 can be configured to separate metal bearing slurry 13 into metal
bearing solution 14 and a precious metal residue comprising ferrous
iron 121. In exemplary embodiments, a first portion of precious
metal residue comprising ferrous iron 121 can be recycled to
atmospheric leach step 10 via ferrous iron recycle 100. In
exemplary embodiments, a second portion of precious metal residue
comprising ferrous iron 121 can be process by residue treatment
step 34 and optionally by precious metal recovery step to yield
precious metal value 95. Precious metal recovery step and precious
metal 95 have been described in detail above.
[0076] In exemplary embodiments, a first portion of metal bearing
solution 14 can be combined with second metal bearing material 111
and the combination can be processed by high temperature pressure
leaching step 130. In various embodiments, high temperature
pressure leaching step 130 may be configured to utilize a pressure
leaching vessel preferably in a manner suitably selected to promote
the solubilization of the metal value to be recovered, such as for
example copper and/or a precious metal value. Various parameters
may influence the high temperature pressure leaching process. For
example, during pressure leaching, it may be desirable to introduce
materials to enhance the pressure leaching step 130. In accordance
with one aspect of the present invention, during pressure leaching
in the pressure leaching vessel, sufficient oxygen may be injected
into the vessel to maintain an oxygen partial pressure from about
50 to about 200 psi, preferably from about 75 to about 150 psi, and
most preferably from about 100 to about 125 psi.
[0077] Furthermore, due to the nature of high temperature pressure
leaching 130, the total operating pressure in the pressure leaching
vessel is generally superatmospheric, preferably from about 250 to
about 750 psi, more preferably from about 300 to about 700 psi, and
most preferably from about 400 to about 600 psi. The residence time
for the high temperature pressure leaching step 130 can vary,
depending on factors such as, for example, the characteristics of
the combination of metal bearing solution 14 and second
metal-bearing material 111, as well as the operating pressure and
temperature of the reactor. In one aspect of the invention, the
residence time for the high temperature pressure leaching step can
range from about 30 to about 120 minutes. In various embodiments,
high temperature pressure leaching step 130 can produce a second
metal bearing slurry 113.
[0078] Still referring to FIG. 5, second solid-liquid phase
separation step 1030 can be configured to separate second metal
bearing slurry 113 into second metal hearing solution 122 and a
precious metal residue 123. In exemplary embodiments, a second
portion of metal bearing solution 14 can be combined with second
metal bearing solution 122. This combination can be configured to
move an adequate amount of ferrous iron to an electrowinning step.
In exemplary embodiments, precious metal residue 123 can be
processed by second residue treatment step 1034, and, optionally,
by precious metal recovery step 1034 to yield precious metal value
95. Precious metal recovery step 1034 and precious metal 95 have
been described in detail hereinabove.
[0079] In various embodiments, a metal value 99 can be recovered
from the combination of second portion of metal bearing stream 14
and second metal bearing solution 122 by a direct electrowinning
step 40 preferably configured to utilize AART. In an exemplary
embodiment, metal value 99 can be copper. In various embodiments,
ferric iron is recycled from direct electrowinning step 40 to
increase the production of ferrous iron in the product slurry from
an atmospheric leaching step 10. As the atmospheric leaching step
10 consumes ferric iron by reducing ferric iron to ferrous iron,
the atmospheric leaching step 10 may be used to reduce the ferrous
iron needed for downstream direct electrowinning step 40 that
utilize AART. As discussed herein, ferric iron produced from the
AART reaction may be recycled into an atmospheric each step 10 for
reduction to ferrous iron. For example, ferric iron recycle 101
illustrates the flow of ferric iron into an atmospheric leach step
10 so that ferric iron may be reduced to ferrous iron. In an
exemplary embodiment, lean electrolyte bleed 205 can be configured
to provide lean electrolyte to other heap leach or neutralization
processes 280.
[0080] As illustrated in FIG. 6, metal recovery process 6 can be
configured for recovery of a metal value and a precious metal
value, in accordance with an exemplary embodiment of the present
invention. For the sake of brevity, as illustrated in FIGS. 2, 3,
4, and 5 metal bearing material 11, metal bearing stream 12,
atmospheric leach step 10, metal bearing slurry 13, solid-liquid
phase separation step 30, ferrous iron recycle 100, metal bearing
solution 14 and ferric iron recycle 101 are as described above.
Also as illustrated in FIGS. 4 and 5 second metal bearing material
ill, second metal bearing material stream 112, and lean electrolyte
204 are as described above. In addition, as illustrated in FIG. 5,
high temperature pressure leach step 130, second metal bearing
slurry 113, second solid-liquid phase separation step 1030,
precious metal residue comprising ferrous iron 121, second metal
bearing solution 122, precious metal residue 123, direct
electrowinning step 40, and metal value 99 are as described
above.
[0081] With further reference to FIG. 6, a second solid liquid
phase separation step 1030 can be configured to produce second
metal bearing solution 122, precious metal residue 123, and leach
recycle stream 124. In exemplary embodiments, a portion of metal
bearing solution 14 can be combined with second metal bearing
solution 122. This combination can be configured to move an
adequate amount of ferrous iron to an electrowinning step. In
various embodiments, a metal value 99 can be recovered from the
combination of second portion of metal bearing stream 14 and second
metal bearing solution 122 by a direct electrowinning step 40
preferably configured to utilize AART. In an exemplary embodiment,
metal value 99 can be copper. In various embodiments, ferric iron
is recycled from direct electrowinning step 40 to increase the
production of ferrous iron in the product slurry from an
atmospheric leaching step 10.
[0082] In an exemplary embodiment, precious metal residue 123 can
be subjected to a neutralization step 190 and then can be
processed, such as by a cyanide leach step 170. The precious metal
slurry 213 produced by cyanide leach step 170 may comprise gold. A
third solid liquid phase separation step 2030 can be configured to
separate precious metal slurry 213 into a precious metal solid 215
and a liquid portion 214. In an exemplary embodiment, precious
metal solid 215 can processed by precious metal processing step 33
to produce precious metal value 95. Precious metal recovery step 33
and precious metal 95 have been described in detail above.
[0083] Still referring to FIG. 6, a second portion of precious
metal residue comprising ferrous iron 121 can be optionally
subjected to a grinding step 140. In one aspect of this exemplary
embodiment, grinding step 140 may be equivalent to fine grinding
step 90. In another aspect of this exemplary embodiment, grinding
step 140 produces an output material that is courser than that
produced by fine grinding step 90. A ground precious metal residue
comprising ferrous iron material can be subjected to a sulfur
flotation step 150, such as, for example to facilitate removal of
elemental sulfur. A second grinding step 1140 may be optionally
utilized. Second grinding step 1140 may be equivalent to grinding
step 140, and the ground and essentially sulfur-free precious metal
residue may be processed by second cyanide leach step 1170. The
second precious metal slurry 216 second produced by cyanide leach
step 1170 may comprise gold. Solid liquid phase separation step
3030 can be configured to separate second precious metal slurry 216
into second precious metal solid 218 and second liquid portion 217.
In an exemplary embodiment, second precious metal solid 218 can
processed by second precious metal processing step 1033 to produce
precious metal value 95. Second precious metal recovery step 1033
may be equivalent to precious metal recovery step 33, which along
with precious metal 95 have been described in detail above.
[0084] As illustrated in FIG. 7, metal recovery process 7 can be
configured for recovery of a metal value and a precious metal
value, in accordance with an exemplary embodiment of the present
invention. For the sake of brevity, as illustrated in FIGS. 2, 3,
4, 5, and 6 metal bearing material 11, metal bearing stream 12,
atmospheric leach step 10, metal bearing slurry 13, solid-liquid
phase separation step 30, ferrous iron recycle 100, metal bearing
solution 14 and ferric iron recycle 101 are as described above.
Also as illustrated in FIGS. 4 and 5 second metal hearing material
111, second metal bearing material stream 112, and lean electrolyte
204 are as described above. In addition, as illustrated in FIGS. 5
and 6, high temperature pressure leach step 130, second metal
bearing slurry 113, second solid-liquid phase separation step 1030,
precious metal residue comprising ferrous iron 121, second metal
bearing solution 122, and precious metal residue 123 are as
described above. Moreover, as illustrated in FIG. 6, optional
grinding step 140, optional second grinding step 1140, sulfur
flotation step 150, and cyanide leach step 170 are as described
above.
[0085] Moving to FIG. 7 in accordance with a further exemplary
embodiment of the present invention, metal-bearing solution 14 from
solid-liquid phase separation step 30 may be further processed in a
solvent extraction step 200. In certain aspects of this exemplary
embodiment, solvent extraction step 200 can be configured to
selectively extract both a metal value, such as for example copper,
and ferrous iron. During solvent extraction step 200, a metal
value, such as for example copper, from metal bearing solution may
be loaded selectively onto an organic chelating agent, for example,
an aldoxime/ketoxime blend, resulting in a metal value containing
organic stream and a raffinate solution 201. In various
embodiments, the metal value containing organic stream may comprise
a copper compound and ferrous iron. Solvent extraction step 200 can
be configured to select for both a metal value, such as copper, and
ferrous iron by the selection of an appropriate mixture of
ketoximes and/or aldoximes. Solvent extraction step 200 can produce
a raffinate solution 201 and a rich electrolyte 15. In various
embodiments, solvent extraction step 200 can yield a rich
electrolyte 15 comprising a metal value and ferrous iron.
[0086] Raffinate 201 from solvent extraction step 200 may be
combined with second metal bearing slurry 113 and can be used in a
number ways. For example, all or a portion of raffinate 201
combined with second metal bearing slurry 113 may be recycled to
atmospheric leaching step 10 for temperature control and/or balance
water in a metal recovery process. The use of raffinate 201
combined with second metal bearing slurry 113 in atmospheric
leaching step 10 may be beneficial because the acid and
ferric/ferrous iron values contained in raffinate 201 combined with
second metal bearing slurry 113 can act to optimize the potential
for leaching oxide and/or sulfide ores that commonly dominate heap
leaching operations. That is, any ferric iron and acid remaining in
raffinate 201 combined with second metal bearing slurry 113 may be
used to optimize the Eh and/or pH of atmospheric leaching step 10.
It should be appreciated that the properties of raffinate 201
combined with second metal bearing slurry 113, such as component
concentrations, may be adjusted in accordance with the desired use
of raffinate 201.
[0087] In various embodiments, a metal value 99 can be recovered
front rich electrolyte 15 by electrowinning step 210 configured to
utilize AART. In an exemplary embodiment, metal value 99 can be
copper. Lean electrolyte 204 can be recycled from electrowinning
step 210 back to solvent extraction step 200. In various
embodiments, ferric iron is recycled from electrowinning step 210
to increase the production of ferrous iron in the product slurry
from an atmospheric leaching step 10. As the atmospheric leaching
step 10 consumes ferric iron by reducing ferric iron to ferrous
iron, the atmospheric leaching step 10 may be used to reduce the
ferrous iron needed for downstream electrowinning step 210 that
utilize AART. As discussed herein, ferric iron produced from the
AART reaction may be recycled into an atmospheric leach step 10 for
reduction to ferrous iron. For example, ferric iron recycle 101
illustrates the flow of ferric iron into an atmospheric leach step
10 so that ferric iron may be reduced to ferrous iron.
[0088] Still referring to FIG. 7, in exemplary embodiments, a first
portion of precious metal residue comprising ferrous iron 121 can
be recycled to atmospheric leach step 10 via ferrous iron recycle
100. In exemplary embodiments, a second portion of precious metal
residue comprising ferrous iron 121 can be subjected to several
processing step and then can be processed by residue treatment step
34 and optionally by precious metal recovery step to yield precious
metal value 95. In exemplary embodiments, a third portion of
precious metal residue comprising ferrous iron 121 can be subjected
to a neutralization step 235 to yield a residue 94 that may be in
condition for disposal.
[0089] Returning to the second portion of precious metal residue
comprising ferrous iron 121, the second portion can be optionally
subjected to a grinding step 140 then can be subjected to a pH
adjustment step 145. In an exemplary embodiment, pH adjustment step
145 neutralizes a ground second portion. A ground neutralized
second portion can be subjected to a sulfur flotation step 150 to
remove elemental sulfur 96. A second grinding step 1140 may be
optionally utilized. The ground and essentially sulfur-free second
portion can be processed by cyanide leach step 170. The precious
metal slurry 213 produced by cyanide leach step 170 may comprise
gold. Second solid liquid phase separation step 1030 can be
configured to separate precious metal slurry 213 into precious
metal solid 215 and liquid portion 214. In an exemplary embodiment,
precious metal solid 215 can processed by processed by residue
treatment step 34 and optionally by precious metal recovery step to
yield precious metal value 95. Liquid portion 214 may be processed
to produce a liquid that can be further utilized in a metal value
recovery process or can be disposed of Liquid portion 214 can be
processed by a carbon in column 225 then acid washed 230 and
processed by a stripping step 240. In addition, liquid portion 214
can be processed by a sulfide precipitation step 220 to remove
sulfur for the liquid portion 214.
[0090] As illustrated in FIG. 8, metal recovery process 8 can be
configured for recovery of a metal value and a precious metal
value, in accordance to an exemplary embodiment of the present
invention. For the sake of brevity, as illustrated in previous
figures, metal bearing material 11, metal bearing stream 12,
atmospheric leach step 10, metal bearing slurry 13, solid-liquid
phase separation step 30, ferrous iron recycle 100, metal bearing
solution 14, ferric iron recycle 101, high temperature pressure
leach step 130, second metal bearing slurry 113, second
solid-liquid phase separation step 1030, second metal bearing
solution 122, precious metal residue 123, optional grinding step
140, sulfur flotation step 150, cyanide leach step 170, ground
metal bearing material 21, ground metal bearing slurry 22, rough
metal bearing solid 23, direct electrowinning 40, and metal value
99 are as described above.
[0091] With further reference to FIG. 8, preliminary solid liquid
phase separation step 5030 can produce acid bleed 136 and rough
metal bearing solid 23. In an exemplary embodiment, acid bleed 136
can optionally be combined with limestone to produce gypsum 137.
Moving to second solid liquid phase separation step 1030, second
metal bearing solution 122 can be recycled to precipitation step
80. In an aspect of exemplary embodiments, precious metal residue
123 can be processed by a repulp step 135 configured to combine
limestone, acid bleed 136, and precious metal residue 123. In
aspects of this exemplary embodiment, since precious metal residue
123 may comprise ferrous iron, a portion of precious metal residue
123 may be recycled to precipitation step 80 via second ferrous
iron recycle 1100. After repulp step 135, the material can be
optionally subjected to a grinding step 140 and then can be
subjected to a sulfur flotation step 150 to remove elemental sulfur
96. The material can be then can be subjected to a residue step 165
configured to combine the material with lime and/or limestone. The
residue material can be processed by cyanide leach step 170. The
precious metal slurry 213 produced by cyanide leach step 170 may
comprise gold. Third solid liquid phase separation step 2030 can be
configured to separate precious metal slurry 213 into residue 94
and precious metal liquid portion 231. In an exemplary embodiment,
precious metal liquid portion 231 can processed by processed by
precious metal recovery step 33 to yield precious metal value
95.
[0092] As illustrated in FIG. 9, metal recovery process 9 can be
configured for recovery of a metal value and a precious metal
value, in accordance to an exemplary embodiment of the present
invention. For the sake of brevity, as illustrated in previous
figures, metal bearing material 11, metal bearing stream 12,
atmospheric leach step 10, metal bearing slurry 13, solid-liquid
phase separation step 30, ferrous iron recycle 100, metal bearing
solution 14, ferric iron recycle 101, high temperature pressure
leach step 130, second metal bearing slurry 113, second
solid-liquid phase separation step 1030, second metal bearing
solution 122, precious metal residue 123, optional grinding step
140, sulfur flotation step 150, cyanide leach step 170, ground
metal bearing material 21, ground metal bearing slurry 22, rough
metal bearing solid 23, lean electrolyte 204, lean electrolyte
bleed 205, heap leach and neutralization process 280, direct
electrowinning 40, and metal value 99 are as described above.
[0093] Referring to FIG. 9, second solid liquid phase separation
step 1030 can be configured to produce second metal bearing
solution 122 and precious metal residue 123. In an aspect of
exemplary embodiments, second metal bearing solution 122 can be
recycled to atmospheric leach step 10. In another aspect of
exemplary embodiments, precious metal residue 123 can be subjected
to a neutralization step 190 and then can be process by cyanide
leach step 170. Precious metal slurry 233 and residue 94 can be
produce by cyanide leach step 170.
[0094] As illustrated in FIG. 10, a metal recovery process can be
configured for recovery of a metal value and a precious metal
value, in accordance to an exemplary embodiment of the present
invention. For the sake of brevity, as illustrated in previous
figures, metal bearing material 11, metal bearing stream 12,
atmospheric leach step 10, metal bearing slurry 13, solid-liquid
phase separation step 30, ferrous iron recycle 100, metal bearing
solution 14, ferric iron recycle 101, high temperature pressure
leach step 440, direct electrowinning 40, neutralization step 190,
raffinate solution 201, solvent extraction step 200, metal bearing
solid 26, rich electrolyte 15, lean electrolyte stream 204, and
lean electrolyte bleed 205 are as described above.
[0095] Referring to FIG. 10, a metal bearing material 11 may be
configured to enter one or more separate leach steps. In various
embodiments, one or more leach steps include pressure leach step
440 and atmospheric leach step 10. Metal bearing material 11 from
pressure leach step 440 may be flashed in flash/splash step 450 or
otherwise conditioned. Flashed metal bearing material 417 may be
subjected to atmospheric leach step 10. In this manner, heat and/or
steam from flashed metal bearing material 417 may be transferred to
atmospheric leach 10. In an aspect of exemplary embodiments, metal
bearing slurry 13 from atmospheric leach 10 may be processed by
solid liquid phase separation 30 into metal bearing solution 14 and
metal bearing solid 26. Metal bearing solution 14 can be subjected
to direct electrowinning 40 to yield metal value 99. Metal bearing
solid 26 can be subjected to counter current decantation wash (CCD)
step 400. CCD step 400 may be conducted with fresh water and/or
raffinate solution 201. CCD solid material 415 may be disposed
and/or neutralized in neutralization step 190. CCD liquid material
414 may be subjected to solvent extraction step 200. Solvent
extraction step 200 may be useful in extracting any remaining
copper in CCD liquid material 414 for use in subsequent direct
electrowinning 40. Raffinate solution 201 may be used to cool
pressure leach 440. Lean electrolyte bleed 205 may comprise a
portion of raffinate solution 201.
[0096] In an exemplary embodiment, a first portion of precious
metal residue comprising ferrous iron 121 can be recycled to
atmospheric leach step 10 via ferrous iron recycle 100. In
exemplary embodiments, a second portion of precious metal residue
comprising ferrous iron 121 can be subjected to several processing
steps and then can be processed by precious metal recovery step 33
to yield precious metal value 95. Second portion of precious metal
residue comprising ferrous iron 121 can be subjected to a residue
neutralization step 1190 configured to combine the second portion
of precious metal residue comprising ferrous iron 121 with lime
and/or limestone. The combined neutralized material can be
subjected to an optional grinding step 140. The ground combined
neutralized material can be subjected to a sulfur flotation step
150 to remove elemental sulfur 96. In an aspect of exemplary
embodiments, the ground sulfur-free material can be combined with
precious metal slurry 233 to produce a combined material 241. A
second cyanide leach step can be configured to process the combined
material to produce a residue 94 and a precious metal material 242.
The resulting precious metal material 242 can be processed by
precious metal recovery step 33 to yield precious metal value
95.
[0097] In various embodiments of the present invention, one or more
leach steps may be subjected to a ferrous iron recycle 100 and a
subsequent direct electrowinning 40 using an alternative anode
reaction process. Again, in an exemplary embodiment of this
invention, the ferrous iron species is pyrite, most preferably,
pyrite is recycled from a solid/liquid phase separation stage 30
after the leaching step 10. In various embodiments, one or more
leach steps may be subjected to a ferrous iron recycle 100 and a
subsequent solvent extraction step 200 and electrowinning step 210
using an alternative anode reaction process.
[0098] As ferrous iron is oxidized at the anode in the
electrochemical cell of electrowinning 40, 210, the concentration
of ferrous iron in the electrolyte is depleted, while the
concentration of ferric iron in the electrolyte is increased. As
the concentration of ferric iron in the electrolyte is increased,
the ferric iron is delivered to the atmospheric leach step 10 via a
ferric iron recycle 101. The concentration of ferric iron in the
electrolyte in the atmospheric leach step 10 decreases during the
leach process as the concentration of ferrous iron in the
electrolyte increases. In accordance with various embodiments, as
the concentration of ferrous iron in the electrolyte of the
atmospheric leaching step 10 increases, ferrous iron is delivered
to subsequent processing steps. In various embodiments, ferrous
iron is delivered to electrowinning step 40, 210. Where direct
electrowinning is used, the ferrous iron bearing material may be
subjected to one or more conditioning step 55 as described herein.
In various embodiments, ferrous iron is delivered to an
electrowinning step 210 after undergoing solvent extraction
200.
[0099] In accordance with one aspect of the invention, ferrous
iron, for example, in the form of pyrite (FeS.sub.2), is added to
the copper-rich electrolyte to be subjected to electrowinning, to
cause the ferrous/ferric (Fe.sup.2+/Fe.sup.3+) couple to become the
anode reaction in so doing, the ferrous/ferric anode reaction
replaces the decomposition of water anode reaction. Because there
is no oxygen gas produced in the ferrous/ferric anode reaction,
generation of "acid mist" as a result of the reactions in the
electrochemical cell is eliminated. In addition, because the
equilibrium potential of the Fe.sup.2+/Fe.sup.3+ couple (i.e.,
E.sup.0=-0.770 V) is less than that for the decomposition of water
(i.e., E.sup.0=-1.230 V), the cell voltage is decreased, thereby
decreasing cell energy consumption. Furthermore, in accordance with
one aspect of the invention, ferrous iron can be created in an
atmospheric leach step 10 and used in the ferrous/ferric
electrowinning anode reaction in electrowinning 40, 210.
[0100] In accordance with various aspects of the invention,
electrowinning may be performed in a variety of ways under a
variety of conditions. While various configurations and
combinations of anodes and cathodes in the system electrochemical
cell may be used effectively in connection with various embodiments
of the invention, preferably a flow-through anode is used and
electrolyte circulation is provided using an electrolyte flow
manifold capable of maintaining satisfactory flow and circulation
of electrolyte within the electrowinning cell.
[0101] Generally speaking, increasing the operating current density
in an electrowinning cell increases the cell voltage. This
increased voltage demand translates into increased energy costs for
producing copper, which affects the profitability of the
electrowinning operation. On the other hand, certain other
parameters in alternative anode reaction processes--such as, for
example, temperature and iron concentration in the electrolyte--may
be controlled in a manner that mitigates the effect of increased
current density on cell voltage. For instance, as the temperature
of the electrolyte is increased, cell voltage tends to decrease.
Similarly, as the concentration of iron in the electrolyte, and
more specifically concentration of ferrous iron adjacent to the
anode, increases, voltage tends to decrease in electrowinning cells
employing the alternative anode reaction. Nevertheless, the
mitigating effect of increased temperature and increased iron
concentration on high cell voltage is limited.
[0102] In general, processes and systems configured according to
various embodiments of the present invention enable the efficient
and cost-effective utilization of the alternative anode reaction in
copper electrowinning at a cell voltage of less than about 1.5 V
and at current densities of greater than about 26 A/ft.sup.2 (about
280 A/m.sup.2). Furthermore, the use of such processes and/or
systems reduces generation of acid mist and permits the use of low
ferrous iron concentrations in the electrolyte and optimized
electrolyte flow rates, as compared to prior art systems, while
producing high quality, commercially saleable product.
[0103] Generally speaking, as the operating current density in the
electrochemical cell increases, the copper plating rate increases.
Stated another way, as the operating current density increases,
more cathode copper is produced for a given time period and cathode
active surface area than when a lower operating current density is
achieved. Alternatively, by increasing the operating current
density, the same amount of copper may be produced in a given time
period, but with less active cathode surface area (i.e., fewer or
smaller cathodes, which corresponds to lower capital equipment
costs and lower operating costs). However, as the current density
is increased, the conversion rate of ferrous iron to ferric iron
increases.
[0104] As current density increases using the ferrous/ferric anode
reaction, cell voltage tends to increase due in part to the
depletion of ferrous ions at the anode surface. This can be
compensated for by increasing transport of ferrous ions to the
anode as current density increases in order to maintain a low cell
voltage. The prior art was limited to current densities of 26
A/ft.sup.2 (280 A/m.sup.2) and below for copper electrowinning
using the ferrous/ferric anode reaction in large part because of
ferrous iron transport limitations. Stated another way, previous
attempts that increased flow rates and increased iron concentration
in the electrolyte to achieve high current densities were
unsuccessful in decreasing overall cell voltage. Various
embodiments of the present invention allow for operation at current
densities above--and significantly above--26 A/ft.sup.2 while
maintaining cell voltages of less than about 1.5 V.
[0105] In accordance with other exemplary embodiments of the
invention, a system for operating an alternative anode reaction
process includes an electrochemical cell equipped with at least one
flow-through anode and at least one cathode, wherein the cell is
configured such that the flow and circulation of electrolyte within
the cell enables the cell to be advantageously operated at a cell
voltage of less than about 1.5 V and at a current density of
greater than about 26 A/ft.sup.2. Embodiments of the present
invention permit operation of electrochemical cells using the
ferrous/ferric anode reaction at current densities of from about 26
to about 35 A/ft.sup.2 at cell voltages of less than about 1.0 V;
up to about 40 A/ft.sup.2 at cell voltages of less than about 1.25
V; and up to about 50 A/ft.sup.2 or greater at cell voltages of
less than about 1.5 V.
[0106] In an exemplary embodiment of the invention, a current
density of from about 20 to about 50 amps per square foot of active
cathode (about 215 A/m.sup.2 to about 538 A/m.sup.2) is maintained,
preferably greater than about 26 A/ft.sup.2 (280 A/m.sup.2), and
more preferably greater than about 30 A/ft.sup.2 (323 A/m.sup.2) of
active cathode. It should be recognized, however, that the maximum
operable current density achievable in accordance with various
embodiments of the present invention will depend upon the specific
configuration of the process apparatus, and thus an operating
current density in excess of 50 A/ft.sup.2 (538 A/m.sup.2) of
active cathode may be achievable in accordance with the present
invention.
[0107] Various mechanisms may be used in accordance with the
present invention to enhance electrolyte flow, as detailed herein.
For example, an electrolyte flow manifold configured to inject
electrolyte into the anode may be used, as well as exposed "floor
mat" type manifold configurations and other forced-flow circulation
means. In accordance with various embodiments of the invention, any
flow mechanism that provides an electrolyte flow effective to
transport ferrous iron to the anode, to transport ferric iron from
the anode, and to transport copper ions to the cathode such that
the electrowinning cell may be operated at a cell voltage of less
than about 1.5 V and at a current density of greater than about 26
amps per square foot (A/ft.sup.2), is suitable.
[0108] In accordance with one exemplary embodiment of the present
invention, a flow-through anode with an electrolyte injection
manifold is incorporated into the cell. As used herein, the term
"flow-through anode" refers to any anode configured to enable
electrolyte to pass through it. While fluid flow from the manifold
provides electrolyte movement, a flow-through anode allows the
electrolyte in the electrochemical cell to flow through the anode
during the electrowinning process. The use of a flow-through anode
with manifold electrolyte injection decreases cell voltage at low
electrolyte flow rates and at low electrolyte iron concentrations
through enhanced diffusion of ferrous iron to the anode. In
accordance with various aspects of exemplary embodiments of the
invention, electrolyte injection manifolds with bottom injection,
side injection, and/or in-anode injection are incorporated into the
cell to enhance ferrous iron diffusion. Overall cell voltages of
less titan about 1.5 V may be achieved, though it is preferable to
achieve a cell voltage of less than about 1.20 V or about 1.25 V,
and more preferable to achieve a cell voltage of less than about
0.9 V or about 1.0 V.
[0109] Any now known or hereafter devised flow-through anode may be
utilized in accordance with various aspects of the present
invention. Possible configurations include, but are not limited to,
metal wool or fabric, an expanded porous metal structure, metal
mesh, multiple metal strips, multiple metal wires or rods,
perforated metal sheets, and the like, or combinations thereof.
Moreover, suitable anode configurations are not limited to planar
configurations, but may include any suitable multiplanar geometric
configuration.
[0110] While not wishing to be bound by any particular theory of
operation, anodes so configured allow better transport of ferrous
iron to the anode surface for oxidation, and better transport of
ferric iron away from the anode surface. Accordingly, any
configuration permitting such transport is within the scope of the
present invention.
[0111] Anodes employed in conventional electrowinning operations
typically comprise lead or a lead alloy, such as, for example,
Pb--Sn--Ca. One disadvantage of such anodes is that, during the
electrowinning operation, small amounts of lead are released from
the surface of the anode and ultimately cause the generation of
undesirable sediments, "sludges," particulates suspended in the
electrolyte, or other corrosion products in the electrochemical
cell and contamination of the copper cathode product. For example,
copper cathode produced in operations employing a lead-containing
anode typically comprises lead contaminant at a level of from about
1 ppm to about 4 ppm. Moreover, lead-containing anodes have a
typical useful life limited to approximately four to seven years.
In accordance with one aspect of a preferred embodiment of the
present invention, the anode is substantially lead-free. Thus,
generation of lead-containing sediments, "sludges," particulates
suspended in the electrolyte, or other corrosion products and
resultant contamination of the copper cathode with lead from the
anode is avoided.
[0112] Preferably, in accordance with an exemplary embodiment of
the present invention, the anode is formed of one of the so-called
"valve" metals, including titanium (Ti), tantalum (Ta), zirconium
(Zr), or niobium (Nb). The anode may also be formed of other
metals, such as nickel, or a metal alloy, intermetallic mixture, or
a ceramic or cermet containing one or more valve metals. For
example, titanium may be alloyed with nickel (Ni), cobalt (Co),
iron (Fe), manganese (Mn), or copper (Cu) to form a suitable anode.
Preferably, the anode comprises titanium, because, among other
things, titanium is rugged and corrosion-resistant. Titanium
anodes, for example, when used in accordance with various aspects
of embodiments of the present invention, potentially have useful
lives of up to fifteen years or more.
[0113] The anode may also comprise any electrochemically active
coating. Exemplary coatings include those provided from platinum,
ruthenium, iridium, or other Group VIII metals, Group VIII metal
oxides, or compounds comprising Group VIII metals, and oxides and
compounds of titanium, molybdenum, tantalum, and/or mixtures and
combinations thereof. Ruthenium oxide and iridium oxide are
preferred for use as the electrochemically active coating on
titanium anodes when such anodes are employed in connection with
various embodiments of the present invention. In accordance with
one embodiment of the invention, the anode is formed of a titanium
metal mesh coated with an iridium-based oxide coating. In another
embodiment of the invention, the anode is formed of a titanium mesh
coated with a ruthenium-based oxide coating. Anodes suitable for
use in accordance with various embodiments of the invention are
available from a variety of suppliers.
[0114] Conventional copper electrowinning operations use either a
copper starter sheet or a stainless steel or titanium "blank" as
the cathode. In accordance with one aspect of an exemplary
embodiment of the invention, the cathode is configured as a metal
sheet. The cathode may be formed of copper, copper alloy, stainless
steel, titanium, or another metal or combination of metals and/or
other materials. As is generally well known in the art, the cathode
is typically suspended from the top of the electrochemical cell
such that a portion of the cathode is immersed in the electrolyte
within the cell and a portion (generally a relatively small
portion, less than about twenty percent (20%) of the total surface
area of the cathode) remains outside the electrolyte bath. The
total surface area of the portion of the cathode that is immersed
in the electrolyte during operation of the electrochemical cell is
referred to herein, and generally in the literature, as the
"active" surface area of the cathode. This is the portion of the
cathode onto which copper is plated during electrowinning.
[0115] In accordance with another aspect of an exemplary embodiment
of the invention, the anode comprises a titanium mesh (or other
metal, metal alloy, intermetallic mixture, or ceramic or cermet as
set forth above) upon which a coating comprising carbon, graphite,
a mixture of carbon and graphite, a precious metal oxide, or a
spinel-type coating is applied. Preferably, in accordance with one
exemplary embodiment, the anode comprises a titanium mesh with a
coating comprised of a mixture of carbon black powder and graphite
powder.
[0116] In accordance with an exemplary embodiment of the invention,
the anode comprises a carbon foam, graphite foam, or a
metal-graphite sintered material wherein the exemplary metal
described is titanium. In accordance with other embodiments of the
invention, the anode may be formed of a carbon composite material.
Examples of such composite materials include polycrystalline
graphite, polycrystalline graphite coated or densified with a
graphitizable pitch material or pyrolytic carbon, graphite foam
coated or densified with graphitizable pitch or pyrolytic carbon, a
metal-graphite sintered material coated or densified with
graphitizable pitch or pyrolytic carbon, fiber-reinforced
carboncarbon composites, graphite and/or carbon coated metallic
mesh, and the like. In these applications, the coating or
densification seals the structure preventing particle removal,
while increasing strength, toughness, and conductivity. The coating
may contain fiber reinforcement in order to further enhance
performance characteristics.
[0117] In accordance with one aspect of an exemplary embodiment,
the graphite foam is produced from a mesophase pitch material such
as described by Klett et al. in U.S. Pat. No. 6,261,4850 Unlike
polymeric resin-based precursors such as, for example, phenolic
resin, polyvinyledene fluoride resin, polyacrylonitrile resin,
phenol/formaldehyde resin, urethane resin, and the like, mesophase
pitch foam is graphitizable and is highly conductive electrically,
when graphitized, forming an electrically-continuous-low-resistance
structure.
[0118] To increase the mechanical properties and conductivity of
this foam material, it can be coated or densified with a
graphitizable material such as that formed from the pyrolysis of a
hydrocarbon gas, such as methane or a pitch-based material in the
form of petroleum pitch, coal tar pitch, or mesophase pitch formed
by, for example, a heat-soak, solvation, or catalytic
polymerization process.
[0119] In accordance with another aspect of an exemplary
embodiment, a fiber reinforced carbon-carbon composite may comprise
fibers in one or more dimensions that may be positioned in an
oriented fashion by any technique now known or hereafter devised,
such as, for example, weaving, braiding, and filament winding, or
in random fashion (such as in the case of a felt). These fibers
form a preform which is densified with a matrix material that
rigidizes the preform, fills in the porosity thereby increasing the
density, increases the toughness, and increases the conductivity if
it is graphitizabie. It should be noted, however, that different
materials can be employed to rigidize and density the preform. The
carbon fibers employed in the fabrication of fiber-reinforced
composites preferably comprise pitch-based, mesophase pitch-based,
and catalytically-produced carbon and graphite fibers, such as, for
example, those produced by Applied Sciences of Cedarville, Ohio.
However, polyacrilonitrile and rayon-based carbon fibers may also
be employed. The matrix employed in the fabrication of fiber
reinforced composite preferably may comprise a petroleum
pitch-based precursor, a coal tar pitch-based precursor, a
polymeric resin-based polymer precursor, a gas phase
hydrocarbon-based precursor, or a mesophase pitch-based precursor.
In accordance with one exemplary embodiment, the matrix is a
mesophase pitch-based precursor impregnated into the composite.
[0120] It should be noted that to further increase the conductivity
of these composite materials, graphitizable particulates such as
graphitized carbon black, carbon nanotubes, and/or graphite flakes
or particles may also be incorporated in the composite. In
addition, all these carbon-based materials can be heat-treated to
temperatures between about 1500.degree. C. and about 3000.degree.
C., and preferably between about 2500.degree. C. and about
3000.degree. C., to graphitize these materials in order to further
increase their conductivity.
[0121] Moreover, a metal in the metallic mesh or metal-graphite
sintered exemplary embodiment is described herein and shown by
example using titanium; however, any metal may be used without
detracting from the scope of the present invention. Exemplary
embodiments of such anodes are set forth in various of the Examples
herein.
[0122] In accordance with one exemplary embodiment, a wire mesh may
be welded to the conductor rods, wherein the wire mesh and
conductor rods may comprise materials as described above for
anodes. In one exemplary embodiment, the wire mesh comprises of a
woven wire screen with 80 by 80 strands per square inch, however
various mesh configurations may be used, such as, for example, 30
by 30 strands per square inch.
[0123] Moreover, various regular and irregular geometric mesh
configurations may be used. In accordance with yet another
exemplary embodiment, a flow-through anode may comprise a plurality
of vertically-suspended stainless steel rods, or stainless steel
rods fitted with graphite tubes or rings. In accordance with
another aspect of an exemplary embodiment, the hanger bar to which
the anode body is attached comprises copper.
[0124] In accordance with various embodiments of the present
invention, the cathode may be configured in any manner now known or
hereafter devised by the skilled artisan.
[0125] In various embodiments, a flow through cathode may be used.
As used herein, the term "flow-through cathode" refers to any
cathode configured to enable electrolyte to pass through it. While
fluid flow from an electrolyte flow manifold provides electrolyte
movement, a flow-through cathode allows the electrolyte in the
electrochemical cell to flow through the cathode during the
electrowinning process.
[0126] Various flow-through cathode configurations may be suitable,
including: (1) multiple parallel metal wires, thin rods, including
hexagonal rods or other geometries, (2) multiple parallel metal
strips either aligned with electrolyte flow or inclined at an angle
to flow direction, (3) metal mesh, (4) expanded porous metal
structure, (5) metal wool or fabric, and/or (6) conductive
polymers. The cathode may be formed or copper, copper ahoy,
stainless steel, titanium, aluminum, or any other metal or
combination of metals and/or other materials. The surface finish of
the cathode (e.g., whether polished or unpolished) may affect the
harvestability of the copper powder. Polishing or other surface
finishes, surface coatings, surface oxidation layer(s), or any
other suitable barrier layer may advantageously be employed to
enhance harvestability. Alternatively, unpolished or surfaces may
also be utilized.
[0127] An exemplary flow-through cathode suitable for use in
accordance with one aspect of an embodiment of the present
invention generally comprises a flow-through body portion
comprising multiple thin rods that are suspended from a bus bar.
Multiple thin rods preferably are approximately the same length,
diameter, and material of construction, and are preferably spaced
approximately evenly along the length of a bus bar. A bus bar may
be substantially straight and configured to be positioned
horizontally in an electrowinning cell. Other configurations may,
however, be utilized, such as, for example, "steerhorn"
configurations, multi-angled configurations, and the like.
Moreover, a cathode may be unframed, framed, and may comprise
electrical insulators on the ends of thin rods, or may have any
other suitable structural configuration. Thin rods may have any
suitable cross-sectional geometry, such as, for example, round,
hexagonal, square, rectangular, octagonal, oval, elliptical, or any
other desired geometry. The desired cross-sectional geometry of
thin rods may be chosen to optimize harvestability of copper powder
and/or to optimize flow and/or mass transfer characteristics of the
electrolyte within the electrowinning apparatus.
[0128] In certain embodiments of the present invention, the effect
of enhanced electrolyte circulation on the cathode reaction is to
promote effective transfer of copper ions. In order to promote a
cathode deposit that is of high quality, the electrolyte
circulation system should promote effective diffusion of copper
ions to the cathode surface. When the copper diffusion rate is
sufficiently hindered, the crystal growth pattern can change to an
unfavorable structure that may result in a rough cathode surface.
Excessive cathode roughness can cause an increase in porosity that
can entrain electrolyte, and thus impurities, in the cathode
surface. An effective diffusion rate of copper is one that promotes
favorable crystal growth for smooth, high quality cathodes. Higher
current density requires a higher rate of copper transfer to the
cathode surface. For production of high quality, commercially
acceptable cathodes, the maximum practical current density is
limited in part by the copper diffusion rate that promotes
favorable crystal growth patterns. In the present invention, the
electrolyte circulation system utilized in the electrochemical cell
to facilitate the ionic transfer to or from the anode is also
effective at promoting effective diffusion of copper ions to the
cathode. For example, use of the flow through anode enhances the
copper ion transfer to the cathode in a similar manner to the
ferrous and ferric ion transfer to and from the anode.
[0129] Generally speaking, as the operating current density in the
electrochemical cell increases, the copper plating rate increases.
Stated another way, as the operating current density increases,
more cathode copper is produced for a given time period and cathode
active surface area than when a lower operating current density is
achieved. Alternatively, by increasing the operating current
density, the same amount of copper may be produced in a given time
period, but with less active cathode surface area (i.e., fewer or
smaller cathodes, which corresponds to lower capital equipment
costs and lower operating costs).
[0130] In accordance with an exemplary embodiment, the copper
concentration in the electrolyte for electrowinning is
advantageously maintained at a level of from about 20 to about 60
grams of copper per liter of electrolyte. Preferably, the copper
concentration is maintained at a level of from about 30 to about 50
g/L, and more preferably, from about 40 to about 45 g/L. However,
various aspects of the present invention may be beneficially
applied to processes employing copper concentrations above and/or
below these levels.
[0131] Generally speaking, any electrolyte pumping, circulation, or
agitation system capable of maintaining satisfactory flow and
circulation of electrolyte between the electrodes in an
electrochemical cell such that the process specifications described
herein are practicable may be used in accordance with various
embodiments of the invention.
[0132] Injection velocity of the electrolyte into the
electrochemical cell may be varied by changing the size and/or
geometry of the holes through which electrolyte enters the
electrochemical cell. Any number of configurations of differently
directed and spaced injection holes are possible. For example,
although the injection holes are approximately parallel to one
another and similarly directed, configurations comprising a
plurality of opposing injection streams or intersecting injection
streams may be beneficial in accordance with various embodiments of
the invention.
[0133] In accordance with various embodiments of the invention, the
electrolyte flow manifold comprises tubing or piping suitably
integrated with, attached to, or inside the anode structure, such
as, for example, inserted between the mesh sides of an exemplary
flow-through anode. Yet another exemplary embodiment is illustrated
in, wherein a manifold is configured to inject electrolyte between
the mesh sides and of anode. Manifold includes a plurality of
interconnected pipes or tubes extending approximately parallel to
the mesh sides and of anode and each having a number of holes
formed therein for purposes of injecting electrolyte into anode,
preferably in streams flowing approximately parallel to the mesh
sides.
[0134] In accordance with an exemplary embodiment of the invention,
electrolyte flow rate is maintained at a level of from about 0.1
gallons per minute per square foot of active cathode (about 4.0
L/min/m.sup.2) to about 1.0 gallons per minute per square foot of
active cathode (about 40.0 L/min/m.sup.2). Preferably, electrolyte
flow rate is maintained at a level of from about 0.1 gallons per
minute per square foot of active cathode (about 4.0 L/min/m.sup.2)
to about 0.25 gallons per minute per square foot of active cathode
(about 10.0 L/min/m.sup.2). It should be recognized, however, that
the optimal operable electrolyte flow rate useful in accordance
with the present invention will depend upon the specific
configuration of the process apparatus, and thus flow rates in
excess of about 1.0 gallons per minute per square foot of active
cathode (in excess of about 40.0 L/min/m.sup.2) or less than about
0.1 gallons per minute per square foot of active cathode (less than
about 4.0 L/min/m.sup.2) may be optimal in accordance with various
embodiments of the present invention.
[0135] Generally, as the operating temperature of the
electrochemical cell (e.g., the electrolyte) increases, better
plating at the cathode is achievable. While not wishing to be bound
by any particular theory, it is believed that elevated electrolyte
temperatures provide additional reaction energy and may provide a
thermodynamic reaction enhancement that, at constant cell voltage,
results in enhanced copper diffusion in the electrolyte as
temperature is increased. Moreover, increased temperature also may
enhance ferrous diffusion, and can result in overall reduction of
the cell voltage, which in turn results in greater economic
efficiency. Conventional copper electrowinning cells typically
operate at temperature from about 115.degree. F. to about
125.degree. F. (from about 46.degree. C. to about 52.degree.
C.).
[0136] In accordance with one aspect of an exemplary embodiment of
the present invention, the electrochemical cell is operated at a
temperature of from about 110.degree. F. to about 180.degree. F.
(from about 43.degree. C. to about 83.degree. C.). Preferably, the
electrochemical cell is operated at a temperature above about
115.degree. F. (about 46.degree. C.) or about 120.degree. F.'
(about 48.degree. C.), and preferably at a temperature below about
140.degree. F. (about 60.degree. C.) or about 150.degree. F. (about
65.degree. C.). However, in certain applications, temperatures in
the range of about 155.degree. F. (about 68.degree. C.) to about
165.degree. F. (about 74.degree. C.) may be advantageous.
[0137] It should be recognized, however, that while higher
operating temperatures may be beneficial for the reasons outlined
above, operation at such higher temperatures may require the use of
materials of construction designed and selected to satisfactorily
withstand the more rigorous operating conditions. In addition,
operation at higher temperatures may require increased energy
demands.
[0138] The operating temperature of the electrochemical cell may be
controlled through any one or more of a variety of means well known
in the art, including, for example, an immersion heating element,
an in-line heating device (e.g., a heat exchanger), or the like,
preferably coupled with one or more feedback temperature control
means for efficient process control.
[0139] A smooth plating surface is optimal for cathode quality and
purity, because a smooth cathode surface is denser and has fewer
cavities in which electrolyte can become entrained, thus
introducing impurities to the surface. Although it is preferable
that the current density and electrolyte flow rate parameters be
controlled such that a smooth cathode plating surface is
achievable, operating the electrochemical cell at a high current
density may nonetheless tend to result in a rough cathode surface.
Thus, in accordance with one aspect of an exemplary embodiment of
the present invention, an effective amount of a plating reagent is
added to the electrolyte stream to enhance the plating
characteristics--and thus the surface characteristics--of the
cathode, resulting in improved cathode purity. Any plating reagent
effective in improving the plating surface characteristics, namely,
smoothness and porosity, of the cathode may be used. For example,
suitable plating reagents (sometimes called "smoothing agents") may
include thiourea, guar gums, modified starches, polyacrylic acid,
polyacrylate, chloride ion, and/or combinations thereof may be
effective for this purpose. When used, an effective concentration
of the plating reagent in the electrolyte--or, stated another way,
the effective amount of plating reagent required--invariably will
depend upon the nature of the particular plating reagent employed;
however, the plating reagent concentration generally will be in the
range of from about 20 grams of plating reagent per tonne of copper
plated to about 1000 g/tonne.
[0140] In order for the ferrous/ferric couple to maintain a
continuous anode reaction, the ferric iron generated at the anode
preferably is reduced back to ferrous iron to maintain a
satisfactory ferrous concentration in the electrolyte.
Additionally, the ferric iron concentration preferably is
controlled to achieve satisfactory current efficiency in the
electrochemical cell.
[0141] Finally, as used herein, the terms "comprise", "comprises",
"comprising", "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 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 of the instant
invention, in addition to those not 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 of the instant
invention and are intended to be included in this disclosure.
[0142] 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 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, 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.
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