111111111111111111111111111111111111111111111111111111111111111111111111111
US006663689B2
(12) United States Patent
Marsden et al.
(10) Patent No.:
(45) Date of Patent:
US 6,663,689 B2
*Dec. 16,2003
(54) PROCESS FOR DIRECT ELECTROWINNING
OF COPPER
(75) Inventors: John O. Marsden, Phoenix, AZ (US);
Robert E. Brewer, Safford, AZ (US);
Joanna M. Robertson, Thatcher, AZ
(US); David R. Baughman, Golden,
CO (US); Philip Thompson, West
Valley City, UT (US); Wayne W.
Hazen, Lakewood, CO (US); Christel
M. A. Bemelmans, Indian Hills, CO
(US)
(52) U.S. Cl. 75/744; 205/367; 423/34
(58) Field of Search 75/744; 205/367;
423/34
(56) References Cited
U.S. PATENT DOCUMENTS
3,917,519 A * 11/1975 Fisher et al. 205/584
4,093,526 A * 6/1978 Blanco et al. 205/584
5,223,024 A * 6/1993 Jones 75/743
6,451,089 B1 * 9/2002 Marsden et al. 75/744
Related U.S. Application Data
(73) Assignee: Phelps Dodge Corporation, Phoenix,
AZ (US)
(63) Continuation of application No. 09/912,921, filed on Jul. 25,
2001, now Pat. No. 6,451,089.
(51) Int. CI? C22B 3/06
(21) Appl. No.: 10/238,399
(22) Filed: Sep. 9, 2002
(65) Prior Publication Data
us 2003/0019331 A1 Jan. 30, 2003
(57) ABSTRACT
11 Claims, 2 Drawing Sheets
A system and process for recovering copper from a coppercontaining
ore, concentrate, or other copper-bearing material
to produce high quality cathode copper from a leach solution
without the use of copper solvent extraction techniques or
apparatus. A process for recovering copper from a coppercontaining
ore generally includes the steps of providing a
feed stream containing comminuted copper-containing ore,
concentrate, or other copper-bearing material, leaching the
feed stream to yield a copper-containing solution, conditioning
the copper-containing solution through one or more
physical or chemical conditioning steps, and electrowinning
copper directly from the copper-containing solution, without
subjecting the copper-containing solution to solvent extraction.
* cited by examiner
Primary Examiner-Melvyn Andrews
(74) Attorney, Agent, or Firm---8nell & Wilmer, LLP
This patent is subject to a terminal disclaimer.
Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 0 days.
( *) Notice:
114
119
118
110
109
Cu SEPARATION
1010
: 1051-., I--~~--I~_L_ 113
112 - - --
111 : 1031
10B
\
u.s. Patent Dec. 16, 2003 Sheet 1 of 2 US 6,663,689 B2
108
1010
Cu SEPARATION
109
102
THICKENER
I
I 1021
1020f:1
1 _
110
103
PRESSURE LEACHING
1030 f :- - - - - - - - - - - - - - - - - - - - - - - - - - - - 104
118
119
1040
FLASH
105
114
CCO
113 : 1051
1050 f :- - - - - - - - - - - - - - - - - - - - - - - - - - - - 106
1060
ELECTROLYTE RECYCLE TANK
108 1070
107
ELECTROWINNING
116
Cu
FIG. 1
u.s. Patent Dec. 16,2003 Sheet 2 of 2 US 6,663,689 B2
( SUBGRADE ORE) (EVAP.)
201 202
ATMOSPHERIC LEACH
203
ELECTROWINNING Cu
206
204
204 !
---------------------- ------1
I
I
I,
I
205 207 I
~_ - - - - - - - - - - - - - - - - - - - - - - - - - - - I
, I
2020
2030
208
I,
I
I
I
I
I
I
I
: 203
:- - .\ - - - - - - - - - - - - - - - - - - - -,
I
~~----------------------
ELECTROLYTE
RECYCLE TANK
107 115
1070
ELECTROWINNING
116
FIG. 2
US 6,663,689 B2
2
SUMMARY OF THE INVENTION
While the way in which the present invention addresses
the deficiencies and disadvantages of the prior art is
described in greater detail hereinbelow, in general, according
to various aspects of the present invention, a process for
20 recovering copper and other metal values from a coppercontaining
material includes obtaining a copper-containing
solution from, for example, a pressure leaching system, and
then appropriately conditioning the copper-containing solution
for electrowinning. In a preferred aspect of the
25 invention, the composition of the copper-containing solution
is similar to the composition of the electrolyte produced by
a solvent extraction circuit, for example, with respect to acid
and copper concentrations. In accordance with the various
embodiments of the present invention, however, the copper-
30 containing solution is not subjected to solvent extraction.
In accordance with an exemplary embodiment of the
present invention, a process for recovering copper from a
copper-containing material generally includes the steps of:
(i) providing a feed stream containing copper-containing
35 material; (ii) subjecting the copper-containing feed stream to
atmospheric leaching or pressure leaching to yield a coppercontaining
solution; (iii) conditioning the copper-containing
solution through one or more chemical or physical conditioning
steps; and (iv) electrowinning copper directly from
40 the copper-containing solution, without subjecting the
copper-containing solution to solvent extraction. As used
herein, the term "pressure leaching" shall refer to a metal
recovery process in which material is contacted with an
acidic solution and oxygen under conditions of elevated
45 temperature and pressure.
In one aspect of a preferred embodiment of the invention,
one or more processing steps are used in order to separate
copper from the acid in a recycled portion of the lean
electrolyte from the direct electrowinning process, thus
50 enabling the rejection of a portion of the acid component
from the process circuit without rejecting a significant
portion the copper. As discussed in greater detail
hereinbelow, a number of conventional or hereafter devised
processes may be utilized to separate copper from acid in the
55 feed stream. For example, in accordance with one aspect of
an exemplary embodiment of the invention, a copper precipitation
step may be utilized to precipitate solubilized
copper from a lean electrolyte stream onto the surfaces of
solid particles in a copper-containing material stream in
60 advance of the pressure leaching step, thus separating the
copper from the acid solution.
In an aspect of another embodiment of the invention, a
recycle circuit is used intermediate to the leaching and
electrowinning steps to facilitate control of the composition
65 of copper-containing solution entering the electrowinning
stage, and to thus enhance the quality of the copper recovered
therefrom.
copper recovered by such so-called direct electrowinning
processes often is too impure for sale or use as is, and thus,
generally must be further refined at an additional cost, or
may be sold at a discount. More specifically, prior art
5 techniques have shown the ability for direct electrowinning
of copper to produce a relatively low-quality copper product.
An effective and efficient method to recover copper from
copper-containing materials, especially copper from copper
10 sulfides such as chalcopyrite and chalcocite, that enables
high copper recovery to be achieved at a reduced cost over
conventional processing techniques would be advantageous.
FIELD OF THE INVENTION
CROSS REFERENCE TO RELATED
APPLICATIONS
BACKGROUND OF THE INVENTION
1
PROCESS FOR DIRECT ELECTROWINNING
OF COPPER
This application is a continuation of U.S. Ser. No. 09/912,
921, filed on Jul. 25, 2001, now U.S. Pat. No. 6,451,089 the
disclosure of which is hereby incorporated by reference.
The present invention relates generally to a process for
recovering copper from a copper-containing ore,
concentrate, or other copper-bearing material, and more
specifically, to a process for producing cathode copper 15
without the use of solvent/solution extraction, ion exchange
of copper, or related processes to refine and concentrate the
copper-bearing solution.
Hydrometallurgical treatment of copper containing
materials, such as copper ores, concentrates, and other
copper-bearing materials, has been well established for
many years. Currently, there exist many creative approaches
to the hydrometallurgical treatment of these materials;
however, common to almost all of the processes either now
known or under development is the use of solvent extraction
and electrowinning (SX-EW) for solution purification and
copper recovery. Although SX-EW is not without its
drawbacks, the proven success in the copper SX-EW field
has made this approach standard for production of high
quality copper products.
The traditional hydrometallurgical process for copper
recovery involves first leaching copper-containing material
with an acidic solution, either atmospherically or under
conditions of elevated temperature and pressure. The resultant
process stream-the so-called pregnant leach solutionis
recovered, and in a solvent extraction (or solution
extraction, as it is sometimes called) stage, is mixed with an
organic solvent (i.e., an extractant), which selectively
removes the copper from the pregnant leach solution. The
copper-loaded extractant is then mixed with an aqueous acid
solution, which strips the copper from the extractant, producing
a solution stream suitable for electrowinning. This
resultant solution stream is highly concentrated and relatively
pure, and typically is processed into high quality
copper cathode in an electrowinning circuit.
In general, electrowinning of copper consists of the electrolytic
deposition (sometimes called "plating") of copper
onto a cathode and the evolution of oxygen at an anode. In
a simple design of an exemplary electrowinning unit, a set
of cathodes and anodes are set in a reaction chamber
containing the copper-containing electrolyte. When the unit
is energized, copper ions are reduced onto the cathode (i.e.,
plated). Plating of copper typically occurs on copper starter
sheets or stainless steel blanks. Anodes are quasi-inert in the
electrolyte and provide a surface for oxygen evolution. The
copper plates produced by the electrowinning unit can be in
excess of 99.99 percent pure.
Purification of copper from the pregnant leach solution by
solvent extraction has proven to be a successful means of
providing a concentrated copper solution suitable for electrowinning
of highly pure copper metal. Direct electrowinning
of copper-that is, plating of copper directly from the
pregnant leach solution without the intervening step of
purification by solvent extraction-is known. However, the
3
US 6,663,689 B2
4
In accordance with various preferred aspects of the
present invention, by providing for the electrowinning of
copper directly from a copper-containing solution without
first subjecting the copper-containing solution to solvent
extraction, the present invention enables lower-cost recovery
of copper and eliminates the expenses associated with
solvent extraction, such as specialized reagents, process
apparatus and equipment, and energy resources.
Furthermore, in accordance with one preferred aspect of the
invention, careful control of the composition of the coppercontaining
solution entering the electrowinning circuit
enables production of high quality, uniformly-plated cathode
copper.
These and other advantages of a process according to
various aspects of the present invention will be apparent to
those skilled in the art upon reading and understanding the
following detailed description with reference to the accompanying
figures.
BRIEF DESCRIPTION OF IRE DRAWING
The subject matter of the present invention is particularly
pointed out and distinctly claimed in the concluding portion
of the specification. A more complete understanding of the
present invention, however, may best be obtained by referring
to the detailed description and claims when considered
in connection with the drawing figures, wherein like numerals
denote like elements and wherein:
FIG. 1 illustrates a flow diagram of a copper recovery
process in accordance with an exemplary embodiment of the
present invention; and
FIG. 2 illustrates a flow diagram of a copper recovery
process in accordance with an alternative embodiment of the
present invention.
DETAILED DESCRIPTION OF EXEMPLARY
EMBODIMENTS
The present invention exhibits significant advancements
over prior art processes, especially other so-called "direct
electrowinning" processes, particularly with regard to product
quality and process efficiency. Moreover, existing copper
recovery processes that utilize a conventional atmospheric
or pressure leaching/solvent extraction/electrowinning process
sequence may, in many instances, be easily retrofitted
to exploit the many commercial benefits the present invention
provides.
In one aspect of a preferred embodiment of the invention,
the relatively large amount of acid generated during the
electrowinning stage as a copper-containing electrolyte
stream is transported out of the copper recovery process
after a separation step in which substantially all of the
copper is removed from the acid stream. It is generally
economically advantageous to utilize this generated acid
stream in some way, rather than to neutralize or dispose of
it. Thus, as discussed in greater detail hereinbelow, the
present invention may find particular utility in combination
with conventional atmospheric leaching operations, such as,
for example, heap leaching, vat leaching, dump or stockpile
leaching, pad leaching, agitated tank leaching, and bacterial
leaching operations, which often require a substantially
continuous acid supply.
In one aspect of an exemplary embodiment of the present
invention, a feed stream containing copper-containing material
is provided for processing. In accordance with the
various embodiments of present invention, the coppercontaining
material may be an ore, a concentrate, or any
other copper-bearing material from which copper and/or
other metal values may be recovered. The copper in the
copper-containing material may be in the form of copper
oxides, copper sulfides or other copper minerals, and the
5 copper-containing material may include any number of a
variety of other metals, such as, for example, gold, platinum
group metals, silver, zinc, nickel, cobalt, molybdenum, rare
earth metals, rhenium, uranium and mixtures thereof. Various
aspects and embodiments of the present invention prove
10 especially advantageous in connection with the recovery of
copper from copper sulfide ores, such as, for example,
chalcopyrite (CuFeS2 ), chalcocite (Cu2 S), bornite
(CusFeS4), and covellite (CuS).
The feed stream of copper-containing material can be
15 provided in any number of ways, such that the conditions of
the feed stream are suitable for the chosen processing
methods. For example, feed stream conditions such as
particle size, composition, and component concentrations
can affect the overall effectiveness and efficiency of down-
20 stream processing operations, such as, for example, atmospheric
leaching or pressure leaching.
In accordance with a preferred aspect of the invention, the
particle size of the copper-containing feed material is
reduced to facilitate fluid transport and to optimize the
25 processing steps of atmospheric or pressure leaching and
subsequent metal recovery processes. A variety of acceptable
techniques and devices for reducing the particle size of
the copper-containing material are currently available, such
as ball mills, tower mills, ultrafine grinding mills, attrition
30 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. With regard to one aspect of a
preferred embodiment of the invention, such a result is
35 desired because the reaction rate during leaching generally
increases as the surface area of the copper-containing material
increases, such that increasing the fineness of the
copper-containing material before subjecting the material
stream to pressure leaching generally will allow for more
40 moderate temperature and pressure conditions to be
employed within the pressure leaching vessel, and may
reduce the residence time of the oxidation reaction during
pressure leaching.
FIG. 1 illustrates an exemplary embodiment of the present
45 invention wherein copper is the metal to be recovered from
a copper-containing material, such as a sulfide ore. In
preparation for froth flotation, the copper-containing material
feed stream is ground to a particle size suitable to
liberate mineral-bearing particles from gangue materials. In
50 one aspect of a preferred embodiment, copper-containing
material is comminuted using, for example, a ball mill, and
subjected to conventional flotation techniques and practices.
In one aspect of the present invention, the copper-containing
material has a PSO of less than about 250 microns, preferably
55 a PSO from about 75 to about 150 microns, with the optimal
size depending on flotation and liberation characteristics.
The product from flotation preferably has a PSO of less than
about 150 microns, and more preferably a PSO on the order
of from about 5 to about 75 microns. Other particle sizes and
60 distributions that facilitate fluid transport and subsequent
processing may, however, be utilized.
In another aspect of a preferred embodiment of the
present invention, the comminuted copper-containing material
is combined with a liquid to form a copper-containing
65 material stream 101. Preferably, the liquid comprises water,
but any suitable liquid may be employed, such as, for
example, raffinate, pregnant leach solution, or lean electroUS
6,663,689 B2
5 6
2CU+2+CuFeS2+4S02+4H20~3CuS+3S04-2+8H++Fe+2CuFeS2+
Cu+2~Fe+2+2CuS(possible side reaction)
Other copper minerals and other sulfides react to varying
degrees according to similar reactions, producing copper
precipitates and a weak sulfuric acid by-product. In accordance
with a preferred aspect of the invention, copper
separation stage 1010 is carried out at a slightly elevated
temperature, such as from about 70° C. to about 180° c.,
preferably from about 80° C. to about 100° c., and most
preferably at a temperature of about 90° C. Heating, if
necessary, can be effectuated through any conventional
means, such as electric heating coils, a heat blanket, process
fluid heat exchange, and other ways now known or later
developed. In the exemplary process of FIG. 1, steam
generated in other process areas, such as stream 119 from
flash tank 1040 or stream 118 from pressure leaching stage
1030, may be directed to the processing vessel in copper
separation stage 1010 to provide the heat desired to enhance
the precipitation process. The residence time for the copper
precipitation process can vary, depending on factors such as
the operating temperature of the processing vessel and the
composition of the copper-containing material, but typically
ranges from about thirty (30) minutes to about 6 hours.
Preferably, conditions are selected such that significant
amounts of copper are precipitated. For example, precipitation
rates on the order of about 98% precipitation of copper
have been achieved in processing vessels maintained at
about 90° C. for about 4 hours.
Other parameters to consider when conditioning the
copper-containing material feed stream for processing are
the fraction of solid particles in the feed stream and the total
volume of the feed stream. Thus, these or other parameters,
such as, for example, temperature, pressure, viscosity,
density, composition, and the like, may be suitably
electrolyte stream that otherwise may have been lost or
would have required additional processing to recover, potentially
resulting in significant economic benefits.
In this preferred aspect of the invention, the precipitation
5 step involves the copper-containing material stream being
combined with a sulfur dioxide (S02) stream 109 and a lean
electrolyte stream 108 in a suitable processing vessel. For
example, in the embodiment illustrated in FIG. 1, lean
electrolyte stream 108 may comprise a recycled acidic
10 copper sulfate stream generated during an electrowinning
operation. Other streams, however, preferably copper-rich
streams, may also be used. In one aspect of this embodiment
of the invention, lean electrolyte stream 108 has an acid
concentration of from about 20 to about 200 gramslliter,
15 preferably from about 30 to about 150 gramslliter, and most
preferably from about 50 to about 120 gramslliter. In a
further aspect of this embodiment of the invention, lean
electrolyte stream 108 has a copper concentration of from
about 20 to about 55 grams/liter, preferably from about 25
20 to about 50 gramslliter, and most preferably from about 30
to about 45 gramslliter. In copper precipitation stage 1010,
copper from lean electrolyte stream 108 precipitates to form
a desired copper-rich concentrate. Preferably, precipitation
is carried out such that the copper from the lean electrolyte
25 precipitates, at least in part, onto the surface of unreacted
copper-containing material particles within stream 101 in
the form of copper sulfides, such as, for example, eus.
While not wishing to be bound by any particular theory, the
chemical reaction during this exemplary copper precipita-
30 tion step-wherein, for example, the copper-containing
material is primarily chalcopyrite-is believed to be as
follows:
lyte. For example, a portion of lean electrolyte stream 108
from the direct electrowinning process may be combined
with comminuted copper-containing material to form
copper-containing material stream 101 (not shown in FIG.
1).
The combination of the liquid with the copper-containing
material can be accomplished using anyone or more of a
variety of techniques and apparatus, such as, for example,
in-line blending or using a mixing tank or other suitable
vessel. In accordance with a preferred aspect of this
embodiment, the material stream is concentrated with the
copper-containing material being on the order less than
about 50 percent by weight of the stream, and preferably
about 40 percent by weight of the stream. Other concentrations
that are suitable for transport and subsequent processing
may, however, be used.
In accordance with one aspect of the present invention, it
is desirable to separate the copper in a recycled stream of
lean electrolyte from electrowinning from the acid, and also
to reduce the amount of contaminants in the portion of the
stream to be subjected to the metal recovery process. In such
a separation process, the acid that is removed from the
recycled lean electrolyte stream may be rejected from the
process circuit, taking with it at least a portion of the metal
contaminants and other soluble impurities from the coppercontaining
feed stream and the recycled lean electrolyte
stream. Any number of conventional or hereafter devised
separation processes and techniques may be useful to
achieve the separation of copper from acid in the feed
stream. For example, separation processes and/or techniques
such as precipitation, low temperature pressure leaching,
acid solvent extraction/ion exchange, membrane separation,
cementation, pressure reduction, sulfiding, and/or the use of
liberator cells may be useful for this purpose.
The separation aspect of a preferred embodiment of the 35
invention contributes to providing a resultant acid stream
that contains a relatively small fraction of copper, which can
be used for leaching, pH control, or other applications.
Moreover, utilization of a separation process in accordance
with this aspect of the invention may be particularly advan- 40
tageous in that it may enable contaminants from the unrefined
copper-containing material stream to be removed from
the copper-containing material stream and incorporated into
the resultant acid stream. Because the resultant acid stream
is preferably removed from the metal recovery process 45
altogether and utilized in remote operations, disposed of, or
neutralized, the contaminants contained therein are likewise
removed from the metal recovery process and are thus
prevented from accumulating in the process stream. This
may be a significant advantage in that such contaminants, 50
particularly metal contaminants, typically have a deleterious
effect on the effectiveness and efficiency of the desired metal
recovery process. For example, metal contaminants and
other impurities in the process stream, if not carefully
controlled and/or minimized, can contribute to diminished 55
physical and/or chemical properties in the cathode copper
produced by electrowinning, and can thus degrade the
copper product and diminish its economic value.
Referring again to FIG. 1, in accordance with one aspect
of a preferred embodiment of the invention, copper- 60
containing material stream 101 is subjected to a separation,
such as, for example, a precipitation step, which, in this
exemplary process, serves to precipitate solubilized copper
from a recycled lean electrolyte stream onto the surfaces of
solid particles in the copper-containing material stream. As 65
discussed in detail above, this aspect offers an important
advantage in that it enables recovery of copper from a lean
US 6,663,689 B2
7 8
stream 203 may not be subjected to solvent extraction, but
may instead be blended with other copper-containing process
streams, and the resultant stream then sent to an
electrowinning circuit. For example, all or a portion of PLS
5 stream 203 (broken line) may be blended with coppercontaining
solution stream 106 and lean electrolyte stream
115 in electrolyte recycle tank 1060 (from FIG. 1) to form
a resultant product stream suitable for electrowinning in an
electrowinning circuit.
In accordance with a further aspect of this embodiment of
the present invention, as previously briefly mentioned, acid
stream 110 advantageously may remove impurities from the
process, for example the electrowinning process. Such
impurities include, without limitation, iron, aluminum,
15 magnesium, sodium, potassium and the like, often present as
sulfates. In the absence of removal, such impurities may
accumulate to deleterious levels, and, as such negatively
impact production efficiencies and product (e.g. copper
cathode) quality. The presence of such impurities in acid
20 stream 110 generally does not negatively impact the aforementioned
handling of acid stream 110.
In accordance with one aspect of a preferred embodiment
of the invention illustrated in FIG. 2, solvent extraction unit
2020 purifies copper-bearing PLS stream 203 from the heap
25 leach in two unit operations-an extraction operation, which
may have multiple stages, followed by a stripping operation.
In the extraction stage, PLS stream 203 is contacted with an
organic phase consisting of a diluent in which a copper
selective reagent (i.e., the extractant) is dissolved. When the
30 solutions are contacted, the organic extractant chemically
removes the copper from the PLS, forming an aqueous
raffinate stream. The raffinate and organic streams are subsequently
separated in a settler. After separation of the
organic and aqueous phases in the settler, a portion of the
35 aqueous phase (stream 206) is typically returned to one or
more leaching operations to be reloaded with copper from
the ore in the atmospheric leach to form the PLS. The
organic stream passes on to the second unit operation of the
solvent extraction process, the stripping operation. In the
40 stripping operation, the organic stream is contacted with a
strongly acidic electrolyte. This acidic solution "strips" the
copper from the extractant, leaving the organic phase substantially
depleted of copper. At least a portion of the loaded
strip solution aqueous phase (stream 204) is advanced to an
45 electrowinning plant 2030 as a copper "rich" solution.
Aqueous stream 204 is processed in electrowinning plant
2030 to yield cathode copper 207 and a copper-containing
lean electrolyte stream 208, which, in one aspect of a
preferred embodiment of the invention, may be recycled in
50 part to solvent extraction unit 2020.
In accordance with one alternative aspect of the invention,
aqueous stream 204 may not be subjected to electrowinning
immediately after leaving the solvent extraction unit, but
may instead be blended with other copper-containing pross
cess streams, and the resultant stream then sent to an
electrowinning circuit. For example, all or a portion of
aqueous stream 204 (broken line) may be blended with
copper-containing solution stream 106 and lean electrolyte
stream 115 in electrolyte recycle tank 1060 (from FIG. 1) to
60 form a resultant product stream suitable for electrowinning
in an electrowinning circuit 1070. In such cases the stripping
solutions used in solvent extraction 2020 likely will be
comprised of spent electrolyte from electrowinning circuit
1070.
If efiluent acid stream 110 is not used as a by-product
reagent or otherwise utilized, the acid may be neutralized
using, for example, acid-consuming gangue (i.e., mineral
addressed. Although these parameters mayor may not be
significant to the overall efficiency of processing operations
downstream in all cases, these parameters can affect equipment
size and material specifications, energy requirements,
and other important aspects of process design. Thus, calculated
adjustment of these stream parameters in advance of
complex or resource-intensive processing stages can positively
affect the economic efficiency of the chosen process.
Solid-liquid separation systems, such as, for example, filtration
systems, counter-current decantation (CCD) circuits, 10
thickeners, and the like are useful in adjusting these parameters
and are widely used in the industry.
In one aspect of the embodiment of the invention illustrated
in FIG. 1, product stream 102, which generally
contains covellite/chalcopyrite particles and acid, contains a
large fraction of acid generated in pressure leaching stage
1030 and electrowinning stage 1070, and the acid generated
in copper separation stage 1010.
In accordance with a preferred aspect of the invention, the
copper-containing material stream entering the pressure
leaching stage contains from about 10 and about 50 percent
solids by weight, preferably from about 20 to about 40
percent solids by weight. To adjust the solids concentration
of product stream 102 in accordance with the desired
parameters, in accordance with an exemplary embodiment
of the invention, product stream 102 is sent to a solid-liquid
separation circuit 1020. In one aspect of a preferred embodiment
of the invention, solid-liquid separation circuit 1020
preferably includes a wash thickener circuit 1021 comprising
multiple thickener stages arranged in a counter-current
decantation (CCD) configuration that effectuate separation
of a substantial amount of the acid in the product stream
from the copper-containing solid particles therein. In the
illustrated embodiment, the underflow of thickener circuit
1021 is pressure leaching feed stream 103 and the overflow
is acid stream 110. Preferably, acid stream 110 contains only
a negligible amount of copper.
Process efiluent acid stream 110 may be utilized,
processed, neutralized, impounded, and/or disposed of in a
variety of ways, the appropriate choice of which is largely
dependent upon economic and regulatory factors. In one
aspect of the illustrated embodiment, the acid stream can be
beneficially used in, for example, an atmospheric leaching
operation, where acid is required to leach copper oxide or
sulfide minerals. Such a leaching operation may be a heap
leach, a vat leach, a tank leach, a pad leach, or any other
similar operation. Acid is consumed in these operations
through reaction with acid-consuming constituents in the
ore.
In FIG. 2, acid stream 110 from thickener circuit 1021
(FIG. 1) is sent to a conventional atmospheric leach operation
2010. In accordance with one aspect of a preferred
embodiment of the invention, atmospheric leach operation
2010 is a conventional acid-consuming heap leach
operation, wherein a subgrade ore 201 is contacted with acid
stream 110 and, optionally, other process streams, such as
raffinate stream 206 from downstream solvent extraction
unit 2020. In heap leach operation 2010, the acid percolates
downward through the ore heap, solubilizing the copper in
the copper-containing ore in the form of copper sulfate, to
form a copper-rich pregnant leach solution (PLS) stream
203. In conventional atmospheric leach operations, PLS
stream 203 is sent to a solvent extraction unit, such as
solvent extraction unit 2020 in FIG. 2, to produce a high
concentration and relatively pure copper sulfate solution 65
suitable for electrowinning. In accordance with an alternative
aspect of the present invention illustrated in FIG. 2, PLS
US 6,663,689 B2
9 10
aspect of one embodiment of the invention, the temperature
of pressure leaching vessel 1031 is advantageously maintained
at from about 140° C. to about 180° C. or in the range
of from about 150° C. to about 175° C. In accordance with
another embodiment of the invention, the temperature of
pressure leaching vessel 1031 is advantageously maintained
between from about 200° C. to about 235° C. or in the range
of from about 210° C. to about 225° C. Furthermore, the
total operating pressure in pressure leaching vessel 1031 is
necessarily superatmospheric, ranging from about 50 to
about 750 psi. In accordance with one aspect of one embodiment
of the invention, the pressure is advantageously in the
range of between from about 200 to about 450 psi, and more
preferably from about 250 to about 400 psi. In accordance
with another embodiment of the invention, the pressure is
advantageously maintained between from about 400 or
about 500 to about 700 psi.
During pressure leaching, it is generally desirable to inject
oxygen into the pressure leaching vessel. In one aspect of a
preferred embodiment of the invention, during pressure
leaching in pressure leaching vessel 1031, sufficient oxygen
112 is injected into the vessel to maintain an oxygen partial
pressure in pressure leaching vessel 1031 of 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.
Because pressure leaching of many metal sulfides is a
highly exothermic process and the heat generated is generally
greater than that required to heat pressure leaching feed
stream 103 to the desired operating temperature, cooling
liquid 111 is preferably contacted with pressure leaching
feed stream 103 in pressure leaching vessel 1031 during
pressure leaching. Cooling liquid 111 is preferably process
water, but can be any suitable cooling fluid from within the
refining process or from an outside source. In a preferred
embodiment of the invention, a sufficient amount of cooling
liquid 111 is added to pressure leaching vessel 1031 to yield
a solids content in the product slurry 104 ranging from about
3 to about 15 percent solids by weight.
The residence time for pressure leaching generally
depends on a number of factors, including the composition
of the copper-containing feed stream and the operating
pressure and temperature of the pressure leaching vessel. In
one aspect of the invention, the residence time for pressure
leaching ranges from about thirty minutes to about three
hours.
In another aspect of the present invention, the coppercontaining
solution is conditioned for electrowinning
through one or more chemical and/or physical processing
steps. In much the same way that the copper-containing
50 material feed stream is conditioned for processing in accordance
with above-described aspects of the invention, the
copper-containing solution intended to be utilized in the
electrowinning circuit of the present invention is conditioned
to adjust the composition, component concentrations,
55 volume, temperature, and/or other physical and/or chemical
parameters to desired values. Generally, a properly conditioned
copper-containing solution will contain a relatively
high concentration of copper in an acid solution and will
contain few impurities. Preferably, the conditions of copper-
60 containing solution entering the electrowinning circuit are
kept at a constant level to enhance the quality and uniformity
of the cathode copper product.
In a preferred aspect of the invention, conditioning of a
copper-containing solution for electrowinning begins by
65 adjusting certain physical parameters of the product slurry
from the previous processing step. In a preferred embodiment
of the invention wherein the previous processing step
4CuFeS2+4H2S04+502~4CuS04+2Fe203+8S0+4H202CuS+
2H2S04+02~2Cu+2+2S04-2+2H20+2So
4CuFeS2+1702+4H20~4CuSO4+4H2S04+2Fe2032Cu2S+502+
2H2S04~4CuS04+2H20CUS+202~CUS04
Pressure leaching, for example in pressure leaching vessel
1031, preferably occurs in a manner suitably selected to
promote the solubilization of copper using these (or other)
processes. In general, temperature and pressure in the pressure
leaching vessel should be carefully controlled. For
example, in accordance with one aspect of the invention, the
temperature of pressure leaching vessel 1031 is maintained
at from about 100° C. to about 250° c., preferably from
about 140° C. to about 235° C. In accordance with one
processing tailings) or a neutralizing agent, such as limestone
or lime. Neutralizing with acid-consuming gangue can
be relatively inexpensive, as the neutralizing reagent is
essentially free. On the other hand, neutralizing with limestone
or lime may be less desirable economically, as both 5
these reagents will incur cost. Nevertheless, should neutralization
be desired, any method for acid neutralization now
known or hereafter devised may be employed.
Referring again to FIG. 1, the underflow slurry from wash
thickener circuit 1021, pressure leaching feed stream 103 in 10
this preferred embodiment of the invention, has a composition
of about 40 to about 60 percent solids by weight, the
balance being a dilute acid solution. The general composition
of the dilute acid solution is dependent upon the ratio of
process water to acid introduced in the thickener circuit (i.e., 15
the wash ratio).
In a further aspect of the present invention, the conditioned
copper-containing feed stream preferably is subjected
to a suitable process, such as pressure leaching, to produce
a product slurry 104, which comprises a copper-containing 20
solution and a residue 114. The process may be selected as
desired, but, in general, enables production of a coppercontaining
solution that exhibits copper and acid concentrations
similar to an electrolyte stream resulting from a solvent
extraction circuit-that is, the copper-containing solution 25
preferably is suitable for processing in an electrowinning
circuit. Any suitable technique or combination of techniques
that yields an appropriate copper-containing solution without
employing solvent extraction techniques may be used. In
a preferred embodiment of the invention, as illustrated in 30
FIG. 1, pressure leaching feed stream 103 is subjected to a
pressure leaching stage 1030 to yield a copper-containing
product slurry 104.
In accordance with one aspect of this embodiment of the
present invention, pressure leaching feed stream 103 is 35
transported to a suitable vessel for pressure leaching, which
can be any vessel suitably designed contain the process
components at the desired temperature and pressure conditions
for the requisite processing residence time. In a preferred
embodiment, a pressure leaching vessel 1031 is 40
employed for this purpose. Pressure leaching vessel 1031 is
preferably a multi-compartment, agitated vessel.
Generally, the chemical conversions that occur during
pressure leaching stage 1030 under certain conditions for the
solubilization of the copper in copper-containing materials, 45
such as chalcopyrite, chalcocite, or covellite are as follows:
If desired, conditions during pressure leaching can be
controlled such that a portion of the sulfide sulfur contained
in the feed stream is converted to elemental sulfur instead of
sulfate. The fraction of chalcopyrite and covellite that form
sulfur instead of sulfate are believed to react according to the
following equations:
11
US 6,663,689 B2
12
is pressure leaching, it is desirable to reduce the temperature
and pressure of the product slurry. A preferred method of so
adjusting the temperature and pressure characteristics of the
preferred product slurry is atmospheric flashing.
Thus, in accordance with a preferred aspect of the
embodiment illustrated in FIG. 1, product slurry 104 from
pressure leaching vessel 1031 is flashed in an atmospheric
flash tank 1040 or other suitable atmospheric system to
release pressure and to evaporatively cool the product slurry
104 through the release of steam to form a flashed product
slurry 105. Flashed product slurry 105 preferably has a
temperature ranging from about 90° C. to about 101°C., a
copper concentration of from about 40 to about 75 grams/
liter, and an acid concentration of from about 20 to about
100 gramslliter. In one aspect of the invention, however,
flashed product slurry 105 also contains a particulate solid
residue containing, for example, the iron oxide by-product
of pressure leaching, other by-products, precious metals and
other components that are undesirable for a feed stream to an
electrowinning circuit. Thus, in accordance with the same
principles discussed above, it is desirable to subject the
flashed product slurry to a solid-liquid separation process,
such that the liquid portion of the slurry-the desired
copper-containing solution-is separated from the solid
portion of the slurry-the undesired residue.
Referring again to FIG. 1, in the illustrated embodiment
of the invention flashed product slurry 105 is directed to a
solid-liquid separation stage 1050, such as a CCD circuit
1051. In an alternative embodiment of the invention, solidliquid
separation stage 1050 may comprise, for example, a
thickener or a filter. A variety of factors, such as the process
material balance, environmental regulations, residue
composition, economic considerations, and the like, may
affect the decision whether to employ a CCD circuit, a
thickener, a filter, or other suitable device in solid-liquid
separation stage 1050. In one aspect of a preferred embodiment
of the invention, CCD circuit 1051 uses conventional
countercurrent washing of the residue stream with wash
water 113 to recover leached copper to the coppercontaining
solution product and to minimize the amount of
soluble copper advancing to either precious metal recovery
processes or residue disposal. Preferably, large wash ratios
are utilized to enhance the effectiveness of solid-liquid
separation stage 1050-that is, relatively large amounts of
wash water 113 are added to the residue in CCD circuit
1051. Preferably, the solution portion of the residue slurry
stream is diluted by wash water 113 in CCD circuit 1051 to
a copper concentration of from about 5 to about 200 parts
per million (ppm) in the solution portion of residue stream
114.
Depending on its composition, residue stream 114 from
liquid/solid separation stage 1050 may be impounded, disposed
of, or subjected to further processing, such as, for
example, precious metal recovery. For example, if residue
stream 114 contains economically significant amounts of
gold, silver, and/or other precious metals, 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 residue stream 114 by
cyanidation techniques, the content of contaminants in the
stream, such as elemental sulfur, amorphous iron
precipitates, and unreacted copper minerals, is preferably
minimized. Such materials may promote high reagent consumption
in the cyanidation process and thus increase the
expense of the precious metal recovery operation. As mentioned
above, it is therefore 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 solids-containing residue stream in an attempt to optimize
the conditions for subsequent precious metal recovery.
As previously noted, careful control of the conditions of
a copper-containing solution entering an electrowinning
circuit---especially maintenance of a substantially constant
copper composition-can enhance the quality of the electrowon
copper by, among other things, enabling even plating
of copper on the cathode and avoidance of surface porosity
5 in the cathode copper, which degrades the copper product
and thus may diminish its economic value. In accordance
with this aspect of the invention, such process control can be
accomplished using any of a variety of techniques and
equipment configurations, so long as the chosen system
and/or method maintains a sufficiently constant feed stream
10 to the electrowinning circuit.
Referring again to FIG. 1, in a preferred aspect of the
invention, copper-containing solution stream 106 from
solid-liquid separation stage 1050 is sent to an electrolyte
recycle tank 1060. Electrolyte recycle tank 1060 suitably
15 facilitates process control for electrowinning circuit 1070, as
will be discussed in greater detail below. Copper-containing
solution stream 106, which generally contains from about 40
to about 70 gramslliter of copper and from about 15 to about
100 grams/liter acid, is preferably blended with a lean
20 electrolyte stream 115 in electrolyte recycle tank 1060 at a
ratio suitable to yield a product stream 107, the conditions
of which may be chosen to optimize the resultant product of
electrowinning circuit 1070.
Referring briefly to an alternative embodiment of the
invention illustrated in FIG. 2, an additional lean electrolyte
25 stream 205 may be blended with lean electrolyte stream 115
and copper-containing solution stream 106 in electrolyte
recycle tank 1060 to produce product stream 107 in accordance
with the process control principles discussed in connection
with the embodiment illustrated in FIG. 1. In one
30 aspect of this alternative embodiment, lean electrolyte
stream 205 preferably has a composition similar to that of
lean electrolyte stream 115. Further, as discussed above,
other streams may be introduced to electrolyte recycle tank
1060 for blending, such as, for example, PLS stream 203
35 (FIG. 2).
Referring again to FIG. 1, preferably, the copper composition
of product stream 107 is maintained substantially
constant. While product stream 107 may contain a copper
concentration up to the copper solubility level under the
prevailing conditions, preferably product stream 107 has a
40 copper concentration of about 20 to about 80 gramslliter, and
more preferably of about 30 to about 60 gramslliter, and
often above 40 gramslliter. In one aspect of an exemplary
embodiment of the invention, control valves are positioned
on each of the pipelines feeding lean electrolyte stream 115
45 and copper-containing solution stream 106 to electrolyte
recycle tank 1060 to facilitate blending control within the
tank.
With reference to FIG. 1, copper from the product stream
107 is suitably electrowon to yield a pure, cathode copper
50 product. In accordance with the various aspects of the
invention, a process is provided wherein, upon proper conditioning
of a copper-containing solution, a high quality,
uniformly-plated cathode copper product 116 may be realized
without subjecting the copper-containing solution to a
55 solvent extraction process prior to entering the electrowinning
circuit.
As those skilled in the art are aware, a variety of methods
and apparatus are available for the electrowinning of copper
and other metal values, any of which may be suitable for use
in accordance with the present invention, provided the
60 requisite process parameters for the chosen method or
apparatus are satisfied. For the sake of convenience and a
broad understanding of the present invention, an electrowinning
circuit useful in connection with various embodiments
of the invention may comprise an electrowinning
65 circuit, constructed and configured to operate in a conventional
manner. The electrowinning circuit may include electrowinning
cells constructed as elongated rectangular tanks
US 6,663,689 B2
13 14
* * * * *
nants and other impurities present in said feed stream
and a pressure leaching feed stream comprising a
copper-bearing material;
subjecting at least a portion of said pressure leaching feed
stream to pressuring leaching to yield a product slurry
comprising a copper-containing solution and a residue;
conditioning said product slurry without the use of solvent
extraction techniques to yield a copper-containing solution
suitable for electrowinning;
electrowinning copper from at least a portion of said
copper-containing solution to yield cathode copper and
a copper-containing lean electrolyte stream.
2. The method of claim 1, wherein said step of providing
a feed stream comprising a copper-containing material comprises
providing a feed stream comprising a copper sulfide
ore or concentrate.
3. The method of claim 1, wherein said step of providing
a feed stream comprising a copper-containing material comprises
providing a feed stream comprising a coppercontaining
material and a solution stream comprising copper
and acid.
4. The method of claim 3, wherein said separating step
comprises reacting at least a portion of the copper in a
copper-containing electrolyte stream in the presence of
sulfur dioxide, whereby at least a portion of said copper in
said copper-containing electrolyte stream precipitates as
copper sulfide onto at least a portion of the coppercontaining
material in said feed stream.
5. The method of claim 1, wherein said leaching step
comprises leaching at least a portion of said pressure leaching
feed stream in a pressure leaching vessel at a temperature
of from about 100 to about 2500 C. and at a total operating
pressure of from about 50 to about 750 psi.
6. The method of claim 1, wherein said leaching step
35 comprises leaching at least a portion of said pressure leaching
feed stream in a pressure leaching vessel and wherein
said leaching step further comprises injecting oxygen into
the pressure leaching vessel to maintain an oxygen partial
pressure in the pressure leaching vessel of from about 50 to
about 200 psi.
7. The method of claim 5, wherein said leaching step
further comprises injecting oxygen into the pressure leaching
vessel to maintain an oxygen partial pressure in the
pressure leaching vessel of from about 50 to about 200 psi.
8. The method of claim 1, wherein said conditioning step
comprises subjecting at least a portion of said product slurry
to solid-liquid separation, wherein at least a portion of said
copper-containing solution is separated from said residue.
9. The method of claim 8, wherein said conditioning step
further comprises blending at least a portion of said coppercontaining
solution with at least a portion of one or more
copper-containing streams to achieve a desired copper concentration
in said copper-containing solution.
10. The method of claim 8, wherein said conditioning step
further comprises blending at least a portion of said coppercontaining
solution with at least a portion of one or more
copper-containing streams to achieve a copper concentration
of from about 20 to about 75 gramslliter in said coppercontaining
solution.
11. The method of claim 1, further comprising the step of
using at least a portion of said acid stream yielded from said
separating step in at least one of heap leaching, vat leaching,
dump leaching, stockpile leaching, pad leaching, agitated
tank leaching, or bacterial leaching operations.
containing suspended parallel flat cathodes of copper alternating
with flat anodes of lead alloy, arranged perpendicular
to the long axis of the tank. A copper-bearing leach solution
may be provided to the tank, for example at one end, to flow
perpendicular to the plane of the parallel anodes and 5
cathodes, and copper can be deposited at the cathode and
water electrolyzed to form oxygen and protons at the anode
with the application of current. As with conventional electrowinning
cells, the rate at which direct current can be
passed through the cell is effectively limited by the rate at
which copper ions can pass from the solution to the cathode 10
surface. This rate, called the limiting current density, is a
function of factors such as copper concentration, diffusion
coefficient of copper, cell configuration, and level of agitation
of the aqueous solution.
The general chemical process for electrowinning of cop- 15
per from acid solution is believed to be as follows:
2CUS04+2H2°---;>2Cuo+2H2S04+02
Cathode half-reaction: Cu2++2e----;>Cuo
Anode half-reaction: 2H20---;>4H++02+4e- 20
Turning again to FIG. 1, in a preferred embodiment the
invention, product stream 107 is directed from electrolyte
recyc~e tank 1060 to an electrowinning circuit 1070, which
contams one or more conventional electrowinning cells.
In accordance with a preferred aspect of the invention,
electrowinning circuit 1070 yields a cathode copper product 25
116, optionally, an offgas stream 117, and a relatively large
volume of copper-containing acid, herein designated as lean
electrolyte streams 108 and 115. As discussed above in the
illustrated embodiment of the invention, lean ele~trolyte
streams 108 and 115 are directed to copper precipitation 30
stage 1010 and electrolyte recycle tank 1060, respectively.
Lean electrolyte streams 108 and 115 generally have a lower
copper concentration than product stream 107, but typically
have a copper concentration of less than about 40 grams/
liter.
The present invention has been described above with
reference to a number of exemplary embodiments. It should
be appreciated that the particular embodiments shown and
described herein are illustrative of the invention and its best
mode and are not intended to limit in any way the scope of 40
the invention as set forth in the claims. Those skilled in the
art having read this disclosure will recognize that changes
and modifications may be made to the exemplary embodi~
ents .without departing from the scope of the present
mventlon. For example, although reference has been made
throughout to copper, it is intended that the invention also be 45
applicable to the recovery of other metals from metalcontaining
materials. Further, although certain preferred
aspects of the invention, such as techniques and apparatus
for conditioning process streams and for precipitation of
copper, for example, are described herein in terms of exem- 50
plary embodiments, such aspects of the invention may be
achieved through any number of suitable means now known
or hereafter devised. Accordingly, these and other changes
or modifications are intended to be included within the scope
of the present invention, as expressed in the following 55
claims.
What is claimed is:
1. A method for recovering copper from a coppercontaining
material, comprising the steps of:
providing a feed stream comprising a copper-containing 60
material and acid;
separating at least a portion of said copper-containing
material from said acid in said feed stream to yield an
acid stream comprising at least a portion of contami