U.S. patent number 3,901,776 [Application Number 05/523,588] was granted by the patent office on 1975-08-26 for process for the recovery of copper from its sulfide ores.
This patent grant is currently assigned to Cyprus Metallurgical Processes Corporation. Invention is credited to Duane N. Goens, Paul R. Kruesi.
United States Patent |
3,901,776 |
Kruesi , et al. |
August 26, 1975 |
Process for the recovery of copper from its sulfide ores
Abstract
An improvement in the process for recovering copper from its
sulfide ores or concentrates thereof which comprises treating the
ore with cupric chloride and/or ferric chloride to form a copper
chloride electrolyte and a residue, electrolytically recovering
copper from the electrolyte and further treating the residue with
ferric chloride to solubilize substantially all of the copper
remaining therein for conversion to copper chloride electrolyte,
with ferrous chloride from the electrolyte being regenerated to
ferric chloride for leaching the residue, the improvement which
comprises conducting the electrolysis without the conversion of any
cuprous copper to cupric copper, using a separator between the
anolyte and catholyte compartments of the electrolytic cell to
prevent passage of ions of copper and iron between the catholyte
and anolyte, continuously further treating the residue with
regenerated ferric chloride of a concentration to insure there is
no cuprous copper in the resulting solution and regenerating ferric
chloride from ferrous chloride in the solution free of cuprous
chloride by passing the solution through the anolyte compartment of
the electrolytic cell as copper is continuously being recovered at
the cathode of the cell.
Inventors: |
Kruesi; Paul R. (Golden,
CO), Goens; Duane N. (Golden, CO) |
Assignee: |
Cyprus Metallurgical Processes
Corporation (Los Angeles, CA)
|
Family
ID: |
24085603 |
Appl.
No.: |
05/523,588 |
Filed: |
November 14, 1974 |
Current U.S.
Class: |
205/582 |
Current CPC
Class: |
C22B
15/0069 (20130101); C25C 1/12 (20130101); Y02P
10/20 (20151101) |
Current International
Class: |
C25C
1/12 (20060101); C22B 15/00 (20060101); C25C
1/00 (20060101); C22d 001/16 () |
Field of
Search: |
;204/107 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Andrews; R. L.
Attorney, Agent or Firm: Sheridan, Ross & Fields
Claims
What is claimed is:
1. A process for the recovery of copper from copper sulfide ores
and their concentrates comprising:
a. leaching the ore or concentrate feed with a material comprising
cupric chloride in a first leaching stage with separation of the
solids from the resulting solution and sending the solids to a
second leaching stage;
b. reducing substantially all of the copper chloride content of the
solution from said first leaching stage to cuprous chloride;
c. recovering copper from the solution of step (b) by subjecting
the solution to electrolysis in the cathode compartment of an
electrolytic cell having an anode and a cathode and a separator
therebetween to keep ions of copper and iron from travelling from
the cathode to the anode, with the ferrous chloride ions in the
cathode unaffected by the electrolysis;
d. leaching the solids from said first leaching stage with
materials comprising ferric chloride and cupric chloride with
separation of the solids and spent leach solution and sending the
latter to said first leaching stage and the solids to a third
leaching stage;
e. oxidizing the ferrous chloride in the spent catholyte from said
electrolysis to ferric chloride and sending the ferric chloride to
said third leaching stage to leach the solids from said second
leaching stage followed by separation of the resulting solids and
spent leach solution, and
f. introducing the spent leach solution of step (e) containing
ferrous, ferric and cupric chlorides into the anode compartment of
said cell to oxidize said ferrous chloride to ferric chloride with
the cupric chloride being unaffected by the electrolysis, and
transferring said electrolytically oxidized solution to said second
leaching stage; whereby the electrolytic cell is operated without
the conversion of any cuprous ions to cupric ions.
2. The process of claim 1 in which the solution from said second
leach is returned to leach (1).
3. The process of claim 1 performed as a continuous process.
4. The process of claim 1 performed in multiple steps and
stages.
5. The process of claim 1 in which in step (b) the reduction is
performed with metallic copper.
6. The process of claim 1 in which the leaching materials in step
(a) include ferric chloride.
7. The process of claim 1 in which in step (f) up to about 85% of
the ferrous chloride is oxidized to ferric chloride.
8. In the process for recovering copper from copper sulfide ores or
their concentrates in which the ore or concentrate is leached with
cupric chloride and/or ferric chloride, the resulting solution and
residue separated, substantially all of the copper chloride in the
solution reduced to cuprous chloride, the resulting cuprous
chloride solution electrolyzed to recover copper, and the ferrous
chloride in the spent electrolyte oxidized to ferric chloride which
is recycled for leaching at least part of the chalcopyrite residue,
the improvement which comprises: conducting said electrolysis in an
electrolytic cell having an anode and a cathode divided by a
separator to keep ions of copper and iron from travelling from the
cathode to the anode, to recover substantially all of the copper in
solution at the cathode without the formation of cupric copper in
the cell.
9. The improved process of claim 8 including solubilizing at least
a part of the copper in said residue with said recycled ferric
chloride to produce cupric chloride and ferrous chloride in
solution, introducing said latter solution into the anode
compartment of said electrolytic cell to oxidize the ferrous
chloride therein to ferric chloride as metallic copper is being
simultaneously recovered at the cathode and using the ferric
chloride regenerated by the electrolytic oxidation of ferrous
chloride in the anode to leach additional chalcopyrite residue.
10. The improved process of claim 9 in which up to about 85% of the
ferrous chloride in solution is converted to ferric chloride in the
anode compartment.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to hydrometallurgical processes for
recovering copper from its sulfide ores in which the sulfide sulfur
is recovered as elemental sulfur so that the sulfur dioxide
pollution problem characteristic of pyrometallurgical processes is
eliminated. Particularly, the invention is related to those
processes wherein the copper in copper sulfide is solubilized by
treating the ore with cupric chloride and/or ferric chloride with
the copper being recovered from the resulting copper chloride
solution by electrolysis. The present process results in the
recovery of high yields of commercial grade copper with economic
consumption of power in the electrolysis step due to an improvement
by which no cuprous copper is converted to cupric copper during
electrolysis and the anode of the cell is utilized for the
conversion of ferrous chloride from spent ferric chloride leach
solution to ferric chloride for further leaching while
substantially all of the copper is being continuously plated from
the electrolyte.
2. Prior Art
As is well known, the main source for copper today is copper
sulfide ores, principally, chalcopyrite. Conventional
pyrometallurgical processes by which the copper was formerly
recovered from its sulfide ores are objectionable today because of
the polluting effect of the sulfur dioxide produced by these
processes. Accordingly, there is a great deal of activity in the
copper industry to develop pollution-free processes for the
recovery of copper from its sulfide ores.
A large number of hydrometallurgical processes are being developed
in which the copper in its sulfide ores is solubilized by treatment
of the ore with ferric chloride and/or cupric chloride with the
formation of elemental sulfur followed by recovery of the copper
from the resulting solution or electrolyte by electrolysis. The
sulfur dioxide pollution problem is eliminated in these processes
in which the sulfide sulfur is converted to elemental sulfur.
The steps for solubilizing copper in chalcopyrite usually include
the procedure of first reacting the raw ore with cupric chloride
followed by further reaction of the resulting solution with a
reducing agent such as metallic copper to provide an electrolyte
which is essentially all cuprous chloride. The residue from the
cupric chloride reaction step is then treated with ferric chloride
to solubilize essentially all of the remaining copper. In order for
these processes to be commercially feasible, they must be highly
efficient in the consumption of electrical energy, regeneration of
reagents, removal of impurities, recovery of other metals contained
in the ore, and they must not generate undesirable amounts of
sulfate ions with the consequent prohibitive consumption of
electrical energy or reagents.
It is well known that for the economic recovery of copper by
electrolysis the copper in the electrolyte must be in the cuprous
form. It is also well known that the presence of ferric or cupric
ions at the cathode where copper is being plated from cuprous
chloride interferes with the plating of the copper. An expedient to
keep these ions away from the cathode is the use of a separator to
prevent the circulation of electrolyte from cathode to anode as the
plating is in progress. Another expedient is to avoid the presence
of ferric ions in the anolyte by leaving enough cuprous copper in
the electrolyte for oxidation to cupric copper to prevent any
oxidation of ferrous ion to ferric ion as the first oxidation has
precedence over the latter. This procedure eliminates ferric ions
in the electrolyte which might travel to the cathode, but it also
requires circulation of the electrolyte from cathode to anode or
some other procedure to prevent cupric ions from coming in the
vicinity of the cathode. An objection to the latter procedure is,
of course, that large amounts of copper are being recirculated in a
continuous process when only a portion of the copper entering the
cell is being recovered.
In these procedures in which electrolysis is performed on an
electrolyte resulting from initially leaching the copper sulfide
ores with ferric chloride and/or cupric chloride, the ferrous
chloride entering the cell in the electrolyte passes on through the
cell unaffected and is conventionally oxidized to ferric chloride
in the spent electrolyte and the resulting ferric chloride
recirculated to leach chalcopyrite residue from the initial cupric
chloride leaching step. Ordinarily, only one effective leaching can
be performed with the recirculated ferric chloride without
regeneration as it is substantially reduced to ferrous chloride in
the leaching of the chalcopyrite residue. An efficient means
utilizing the electrolytic cell for regenerating the ferric
chloride after leaching the chalcopyrite residue for further
leaching of residue is desirous. In accordance with this invention
a process is provided by which the anode of the electrolytic cell
is used to regenerate spent ferric chloride from chalcopyrite
residue leaching while copper is being continuously recovered at
the cathode in the absence of ferric and cupric ions.
U.S. Pat. No. 333,815 discloses an electrolytic process for the
recovery of copper from ferric chloride leach solutions of copper
sulfide ores in which ferric chloride is regenerated at the anode.
However, this process is performed with cuprous ions in the
presence of the anode and would obviously be inefficient to
regenerate ferric chloride because of the precedence of the
oxidation of cuprous to cupric ions over the oxidation of ferrous
to ferric ions. Also, no procedure is provided for preventing
cupric and ferric ions from contacting the cathode of preventing
the conversion of cuprous to cupric ions during the cell
operation.
U.S. Pat. No. 3,767,543 discloses the regeneration of ferric
chloride from ferrous chloride at the anode as copper is being
electrolytically recovered at the cathode from a ferric chloride
leach solution of chalcopyrite. However, since cuprous ions are
present in the anolyte an inefficient regeneration of ferric
chloride will result. Further, no provision is made to prevent the
conversion of cuprous to cupric ions.
U.S. Pat. Nos. 3,764,490 and 3,776,826 both disclose the conversion
of cuprous to cupric copper at the anode and the processes of these
patents are not concerned with the regeneration of ferric chloride
from ferrous chloride at all as ferric chloride is not used in
leaching the copper sulfide ores.
U.S. Pat. No. 3,785,944 discloses a process in which copper in
chalcopyrite is initially solubilized by treatment with cupric
chloride and/or ferric chloride with ferric chloride being used to
treat residue from the initial treatment of the chalcopyrite ore
concentrate. An electrolyte is produced in a second reduction stage
with metallic copper in which essentially all of the copper is
reduced to cuprous chloride and the iron reduced to ferrous
chloride. The only regeneration of ferric chloride is by oxidation
of the ferrous chloride in the spent electrolyte, the resulting
ferric chloride being used to oxidize chalcopyrite residue from the
initial cupric chloride treatment of the chalcopyrite concentrate.
The patent teaches against the formation of ferric chloride at the
anode and to prevent this only a portion of copper is recovered
from the cuprous chloride electrolyte with enough being left in
solution for the express purpose of preventing the oxidation of
ferrous to ferric chloride at the anode. Electrolyte is circulated
from cathode to anode to prevent the cupric chloride being formed
at the anode from contacting the cathode where copper is being
plated from cuprous chloride electrolyte. The process does not
provide for regeneration of ferric chloride in the cell and is
expressly directed to the conversion of cuprous ions to cupric ions
during electrolysis.
Accordingly, the principal object of this invention is to provide
an improvement in the step for electrolytically recovering copper
from cuprous chloride electrolyte produced by treatment of
chalcopyrite ores with metal chlorides by which efficient
utilization of the cell is obtained by using the anode to
regenerate ferric chloride from spent ferric chloride leach
solution while copper is being simultaneously plated at the cathode
of the cell cuprous chloride electrolyte without the conversion of
cuprous ions to cupric ions.
BRIEF SUMMARY OF THE INVENTION
In accordance with the invention, finely ground chalcopyrite ore
concentrate is treated with cupric chloride in a first leaching
step followed by separation of the solution and chalcopyrite
residue. The copper in the solution is further reduced with
metallic copper or other reducing agent to provide an electrolyte
in which the copper is essentially all in the cuprous form. The
electrolyte is subjected to electrolysis in an electrolytic cell in
which the anode and cathode compartments are separated by a
separator which prevents passage of ions of iron and copper from
the cathode to anode. The spent electrolyte goes to purification
for recovery of the metals other than copper followed by
electrolytic recovery of iron, with simultaneous regeneration of
ferric chloride at the anode. An alternative procedure at this
point is the removal of excess iron by hydrolysis with oxidation of
ferrous chloride to ferric chloride for recirculation. The
regenerated ferric chloride in both instances is circulated to
leaching and the spent ferric chloride leach solution is circulated
through the anode of the cell as copper is being plated at the
cathode for regeneration of ferric chloride for use in further
leaching. The result is that all of the copper can be recovered
from the electrolyte without the conversion of cuprous to cupric
ions with simultaneous use of the cathode for plating copper and
the anode to regenerate ferric chloride for multiple leachings with
overall effective utilization of electrical energy.
BRIEF DESCRIPTION OF THE DRAWING
The single drawing is a flow diagram of the process of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the flow diagram, feed of chalcopyrite ore concentrate
ground to an average particle size preferably 90% -- 200 mesh is
subjected to a cupric chloride leach in leach 1. The leaching
solution may or may not contain ferric chloride. The reactions
between chalcopyrite and ferric chloride and cupric chloride are as
follows:
4FeCl.sub.3 + CuFeS.sub.2 .fwdarw. CuCl.sub.2 + 5FeCl.sub.2 + 2S
(1)
3cuCl.sub.2 + CuFeS.sub.2 .fwdarw. 4CuCl + FeCl.sub.2 + 2S (2)
the solids are separated as chalcopyrite residue and the solution
subjected to a reduction stage with recycled copper from the
electrolysis in which cupric chloride is reduced to cuprous
chloride in accordance with the following reaction.
Cu + CuCl.sub.2 .fwdarw. 2CuCl (3)
The solution containing ferrous chloride and substantially all of
the copper as cuprous chloride is introduced into the cathode
compartment of an electrolytic cell for recovery of copper. The
ferrous chloride is not affected by the electrolysis and passes on
through the cell in the spent electrolyte.
The electrolytic cell is provided with a separator between the
anode and cathode separating it into anolyte and catholyte
compartments. The separator used prevents ions of copper and iron
from travelling from the cathode to the anode. The separator also
prevents the direct flow of catholyte to anolyte or vice versa. An
example of a suitable membrane is a microporous polypropylene film
sold under the trademark "CELGARD" by the Celanese Plastics
Company, Newark, N.J.
The electrolyte is about 2.5 molar in ferrous chloride at a pH of
0.5. A cell temperature of about 80.degree.C is used. An anode
current density of about 80-120 amps per sq. ft. and a cathode
current density of about 50-100 amps per sq. ft. are used. Some of
the copper recovered at the cathode is recycled to the reduction
stage for reducing cupric to cuprous chloride. These are preferred
but not limiting process limitations.
Sulfate ion is removed from the electrolyte after electrolysis by
precipitation with barium or calcium in the purification step. The
elemental sulfur formed in leach 1 is separated with the solids and
is eventually removed in the tails from which it is recovered by a
conventional procedure.
As will be seen from the flow diagram, the chalcopyrite residue
from leach 1 is subjected to two leaching steps, that is, leach 2
and leach 3. This is done to insure that substantially all of the
copper is removed from the chalcopyrite concentrate. Solution from
leach 2 containing some copper is continuously recirculated to
leach 1. Leach 3 is performed with ferric chloride resulting from
oxidation of ferrous chloride in the spent electrolyte. The spent
ferric chloride leach solution from leach 3 is not recirculated to
leach 1 but is passed through the anode compartment of the cell for
conversion of the ferrous chloride therein to ferric chloride. This
solution entering the anode compartment is substantially depleted
of ferric chloride which will have been converted to ferrous
chloride in the oxidation of the chalcopyrite residue from leach 2.
The cuprous copper present is oxidized to cupric chloride before
the solution enters the anode. The chalcopyrite residue received in
leach 3 from leach 2 is heavily depleted in copper. The process is
operated so that leach 3 will always be conducted with a
substantial excess of ferric chloride so that all of the copper in
the chalcopyrite will be completely solubilized and no copper will
be lost in the tails. The reaction is preferably conducted at a
temperature between 105.degree.-110.degree.C.
The leach solution entering leach 3 from leach 2 with residue will
contain some cuprous ions in addition to ferrous and cupric ions.
However, as leach 3 is done with a substantial excess of ferric ion
the following reaction occurs:
FeCl.sub.3 + CuCl .fwdarw. FeCl.sub.2 + CuCl.sub.2 (4)
The result is that the solution leaving leach 3 for the anode
contains substantially all of the iron as ferrous iron with some
little ferric iron, and all of the copper as cupric chloride with
no cuprous chloride being present. This is essential for the
economical conversion of ferrous chloride to ferric chloride at the
anode as the oxidation of cuprous to cupric chloride takes
precedence over the oxidation of ferrous to ferric chloride and if
any cuprous copper is present it will be oxidized to cupric
chloride before any ferrous chloride will be oxidized to ferric
chloride and this will substantially diminish the efficiency of the
cell in converting ferrous chloride to ferric chloride.
As a precautionary measure, not more than about 85% of the ferrous
chloride is oxidized to ferric chloride at the anode because it is
advisable to always maintain some ferrous chloride in the solution
so that if the cell operation is upset at any time there will
always be some ferrous ion at the anode for conversion of ferric
ion to keep the cell from discharging oxygen or chlorine.
The solution leaving the anode for leach 2 preferably contains not
more than about 85% ferric chloride, 15% ferrous chloride and the
remainder cupric chloride. This means that the solution is high in
ferric chloride for effective leaching in leach 2 of the
chalcopyrite residue from the reduction step. Reactions 1 and 2
above occur in leach 2. The solution from leach 2, which is
recirculated to leach 1, contains ferrous chloride plus some cupric
and cuprous ions.
In leach 1 the solution containing ferrous, cuprous and some cupric
ions is contacted with fresh feed so that reaction 2 above occurs.
Thus most of the cupric ions are reduced to cuprous ions. However,
chalcopyrite is insufficiently active to reduce all of the cupric
ion present to cuprous ion so that the solution overflowing the
first stage thickener contains ferrous plus cuprous ions plus some
cupric ions. Since it is required that the cupric ions in the
solution from leach 1 be at a minimum during electrolysis, the
solution is contacted with recycled copper powder to reduce the
remaining cupric ions to cuprous ions in accordance with equation 3
above. The result is that the solution which becomes the
electrolyte contains iron and copper almost exclusively as ferrous
and cuprous ions.
At the cathode, copper powder is plated in three stages. The copper
from stage 1 is product copper and may be sold as such or further
refined for sale. Copper further depleted from the electrolyte in
electrolytic stages 2 and 3 may be recycled to the reduction stage
for the reduction of cupric ion. The electrolyte depleted in copper
is sent to the purification stage where sulfate ion is removed as
explained above.
In the purification stage, the last residue of copper and undesired
impurities such as zinc, lead, arsenic, antimony, bismuth, etc.,
are removed from spent electrolyte which then proceeds either to
iron plating or hydrolysis as shown in the flow diagram.
If the solution is sent to iron plating, iron is plated at the
cathode for sale. The iron plating cells are equipped with the same
separators as the copper plating cells thereby preventing the
mixing of catholyte and anolyte and preventing migration of ferric
ions from the anolyte to the catholyte. The depleted (anion)
catholyte goes to the anode of the iron cell where ferrous iron is
oxidized to ferric iron which is circulated to leach 3.
If the solution is sent to hydrolysis as an alternate procedure,
the purified ferrous solution is treated with oxygen to regenerate
ferric chloride and precipitate hydrated iron oxide in accordance
with the following equation:
3FeCl.sub.2 + 0.75 O.sub.2 .fwdarw. 1/2 Fe.sub.2 O.sub.3 +
2FeCl.sub.3 (5)
The ferric chloride formed is then circulated to leach 3.
Based on the chemical reactions of the process set forth above and
the use of the separator between anolyte and catholyte it is
apparent that there is no possibility for the conversion of cuprous
to cupric ions in the electrolytic cell. No cuprous ions from the
catholyte reach the anolyte to be converted to cupric ions as the
separator prevents the travel of cuprous ions from catholyte to
anolyte. In order to demonstrate that no cuprous ions are
introduced into the anolyte from leach 3, and to demonstrate the
efficient conversion of ferrous ions from leach 3 to ferric ions
with economical use of electrical power during cell operation, the
following procedure was carried out using the flow sheet of the
invention with the results given below being obtained. All
percentages are given as weight percentages.
LEACH 3
Partially reacted chalcopyrite residue from leach 2 gave the
following analysis:
Element Weight % ______________________________________ Fe 14.1 Cu
7.1 Zn 0.028 Pb 0.008 S.degree. 34.2
______________________________________
Two hundred grams of the above residue entered Leach 3 where the
solution from the cathode operation also entered after purification
and regeneration. One liter of this purified solution which
contained mainly ferric chloride in excess (118.2 g/l
Fe.sup.3.sup.+) encountered the reacted residue for a thorough
leach. The leaching operation of Leach 3 was aimed at a complete
depletion of the copper in chalcopyrite to produce tails ready to
be discarded. The leaching was performed at 106.degree.C and at pH
0.5.
It was found that the system allowed no possibility of formation of
cuprous ions, the solution leaving Leach 3 having the following
analysis:
Fe.sup.3.sup.+ Fe.sup.2.sup.+ Cu.sup.+ Cu.sup.+.sup.+ S.sup.= 42.5
g/l 69.5 g/l 0 13.7 g/l 1.44 g/l
Clear solution from Leach 3 with the above composition was fed to
the cell anode during cell operation for anodic oxidation whereby
the ferrous ions were converted to additional ferric ions at the
anode.
The tails from Leach 3 ready for disposal were analyzed to contain
the following:
Fe Cu S.degree. 7.18% 0.34% 52.4%
The overall recovery of copper after Leach 3 is shown by the
following metallurgical balance:
______________________________________ Copper in Copper Copper in %
Copper Feed Solubilized Tails Leaching Recovery 104 g 103.52 g 0.48
g 99.54 ______________________________________
Cell Anode Conversion
The cell anode received from the thickener overflow of Leach 3 a
clear solution with composition as indicated above. The cell anode
was operated at 120 amperes per square foot of graphite anode area.
At total power input of 27 ampere-hours was used for the anodic
oxidation of ferrous ion to ferric ion at 75.degree.C.
It was found that 54.9 grams of iron in ferric form was produced
through anodic oxidation of ferrous iron. The rate of power
consumption was 0.49 ampere-hours per gram of Fe.sup.+ .sup.+.sup.+
processed. This FIGURE compared with 0.48 ampere-hours per gram
Fe.sup.+ .sup.+.sup.+ (Fe.sup.+ .sup.+ to Fe.sup.+ .sup.+.sup.+)
theoretical. The current efficiency for the process was 98
percent.
After completing the desired anodic reaction the solution with the
following composition was advanced to leach 2:
Fe.sup.+.sup.+.sup.+ Fe.sup.+.sup.+ Cu.sup.+ Cu.sup.+.sup.+ S.sup.=
97.4 g/l 15.2 g/l 0 13.7 g/l 0
As stated previously, it is preferred not to oxidize all of the
ferrous ion to ferric ion in the cell operation.
LEACH 2
Leach 2 received the anode processed solution having the above
composition from the cell anode. Partially reacted chalcopyrite
containing 26.4% Fe; 18.8% Cu and 6.88% S.degree. from Leach 1
entered Leach 2. The leaching operation was conducted at
80.degree.-90.degree.C and at pH 0.5. This leach consumed the
available ferric ion in the anode processed solution leaving a
heavily copper depleted chalcopyrite to be proceeded to Leach 3
with a composition as follows:
Fe Cu S.degree. 14.1% 7.1% 34.7%
The leach liquor from Leach 2 was advanced to Leach 1 as an
overflow from thickener 2.
LEACH 1
The fresh feed of chalcopyrite with head assay of:
Fe Cu Zn Pb S 26% 26% 0.126% 0.063% 28.2%
was contacted with leach liquor from Leach 2, through thickener 2
which contained essentially ferrous, cuprous and some cupric ions
with the following analysis:
Fe.sup.+.sup.+.sup.+ Fe.sup.+.sup.+ Cu.sup.+ Cu.sup.+.sup.+ 0 120
g/l 11.5 g/l 28.2 g/l
The leach was conducted at 80.degree.C and at ph 0.5. This leach
produced the partially reacted chalcopyrite which entered Leach 2
with the composition indicated earlier (see Leach 2 for the
partially reacted chalcopyrite analysis). As shown in the flow
sheet, the leach liquor was filtered and advanced to the cathode
operation whereby the solution contacted recycled copper powder
from the cathode during the reduction process to reduce cupric to
cuprous copper. As a result the solution entered the cathode as
catholyte bearing mainly ferrous and cuprous ions.
From the above data it is seen that the process of the flow sheet
operates with no cuprous ions being converted to cupric ions in the
cell operation and with the use of the anode of the cell to convert
ferrous chloride in spent ferric chloride leach solution to ferric
chloride, with economical consumption of electrical power as copper
is being plated at the cathode.
The process is not restricted to any particular number of
electrolysis of leach stages, as more or less than the three stages
of each used for illustrating the invention can be utilized. The
spent ferric chloride from any leaching stage can be sent to the
anolyte for regeneration so long as all of the copper in it is in
the cuprous stage. Each of the leaching stages may contain any
number of leaching steps.
From the above description of the invention, it will be noted that
the advantage provided is that the cell anode can be used for
regeneration of ferric chloride while copper is being
simultaneously plated at the cathode. The advantage of this is that
the ferric chloride regenerated in the spent electrolyte can be
used for a number of oxidation steps with regeneration to insure
complete removal of copper from the chalcopyrite concentrate, the
additional oxidation steps being possible because of regeneration
of the ferric chloride between steps in the anode of the cell. It
is obvious that this is much more economical than using oxygen in
separate oxidation steps for continued oxidation of the spent
ferric chloride leach solution from Leach 3 to regenerate ferric
chloride.
Although the invention has been disclosed with the use of cupric
chloride alone in Leach 1, it includes the use of ferric chloride.
Other reductants than metallic copper can be used to reduce the
cupric chloride to cuprous chloride in the reduction stage. Any
excess sulfate ions generated in the electrolysis process can be
removed from the spent electrolyte by precipitation with barium or
calcium. The process can be conducted with multiple stages of cells
and may be conducted batch or continuous.
While the invention has been illustrated by its application to
chalcopyrite, a common copper sulfide mineral, it is equally
applicable to other copper sulfide minerals, such as, covellite and
chalcocite.
* * * * *