Note: Descriptions are shown in the official language in which they were submitted.
~Ls579
PROCE~S ~OR EIEC~ROWINNING OF
COPæER VA~UES FROM SO~ID ~OR~S ~ ~ ~EOF
~ his invention relate~ to improYed ways and means for the
electrolgtic recover~ o~ copper directly from cement copper
and~or copper sul~ide concen~rates in a system using an
~ SO4-base electrolyte into w~ich the solid copper-bearing
ma~erial is introduced.
In elect~olysis, ions in solution will, under the in~luence
of electric current, migrate to an electrode of oppos:ite polarityO; 10 In the case of metal ions9 such aB copper, the metal deposits
on the cathode whence it is recovered.
~ he usual electrolytic system for electrowi~ning o~ copper
starts with a clear solution of CuSO4 which has been formed in
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conventional manner such a~ by reaction between ~ SO4 and
copper oxide. ~o~e workers have proposed direct electrow ~ g
. by treating a sl~rry of crushed copper oxide ores in the cell
itself thus avoiding the cost and e~pense of leach;ng, filtra- :
tion and purification as needed to produce a clear electrolgte.
~ ~ome recently proposed elect:rowinn~ng processes have, under ~ .
: 20 care~ully controlled conditions Or agi~ation, temperature and: .
.
current, proven succes~ul i~ the electrowi~ning of pure copper
directly from slurries of crushed oxiae ores, ~u~ cement copper
and copper ~ul~ideR are not amenable to treatmen~ in accordance
with these propo~al~. .
In el~ctrolytic processes as hereto~ore prac~iced~ it ha~
been desireable to keep the dissolved iro~ conte~t o~ the ~ :
electrolyte below 2 gpl to a~oid sharp drop~ in current
efficiency; and in any event3 the iron content was kept below . . -
9 gpl i~ order to protect the cathode and an~ deposited copper
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from attack by ferric iron which attaek defeats the recover~
of copper.
- It is the primary object of this invention to provide a
- process for the direct electrowinning of copper from slurries
of olid cement copper or copper sulfLde concentrates in an
H2S04 electrolyte.
It is another object to pro~ide an electrowinning process
for direct recovery of high purit~ copper from cement copper
; and copper sulfide concentrates at high current densities and
e~ficiencies; and under conditions such that the cathode is
protected ~rom ferric iron attack without generation of excess
04.
Another object is the provision of an electrowinning
proce~s in which the capital cost and expense of operation is
reduced by elimination of the equipment required for the u~ual
steps of leaching, sedimentation, filtration and puri~ication.
~ he preæent invention is predicated on the discover~ that
by maintaining a high dissolved iron content (above 10 gpl) in
the electrolyte while at the same time high current densities,
on the order of at least 60 amp/~t2, are emplo~ed~ two related
eve~ts take placeO First, there will be sufficient ~ liberated
at the ca~hode to continuously reduce ferric iron to ferrous -
iron in the vicinity of the cathode to thu~ avoid attack on
the depo~ited cathode copper which i~ turn enable~ the ~oluble
iron, under care~ull~ selected ana controlled oper~ting condi-
tions of temperature9 current and electrolyte co~position, to
effect direct winning of pure co~per from a 81urr~ of cement
or ~ulfide copper concentrates.
In brief, the process invention contempla~e~ the violent
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mixing of finely-divided cement copper or sulfide copper
concentrates with a sulfuric acid-copper sul~ate ~olution i~ :
which is mainta~ned a sig~i~icant concentration o~ dis~ol~ed
: iron while subjecting the mi2ture to a current field i~ an
electrolgtic cellO
In the case o~ cement copper, the electrol~te is usually
saturated at about 35-40 gpl iron and the iron concentratio~
is desirably mai~tained in a range of 20-40 gpl.
~lthough the exact ~unction of the dissolved iron is not
known, it is theorized that the high current density employed
in this invention oxidizes ferrous to ferric which then acts
to oxidize or ionize elemental cement copper which, after going
into solution, is in tur~ reduced hy electrolysis to elemental
copper that is deposited at the ca~hodeO ~he iron must be
pre~ent in a sufficient concentra~ion to oxidize the copper
and al~o to provide a reservoir of ferrous iron to be 9imul-
taneou~ly oxidized to ferric iron a~ the anode so that the
proce~s may operate continuousl~ with ~erric iron in solution
being consumed in o~idation of copper while ionized copper is
reduced and plated at the cathode at the same rate that ferrous ~ .
iron i5 oxidized at the anode.
Assuming the reaction is as described, then the cement
copper goes int.o solution in accordance with the equation:
Cu + 2Fe+++ --~ Cu++ + 2Fe+~
but this proceeds at a practical rate onl~ when the voltage ~ .
and current densities as well as ~ ~04 and ~US04 co~centra
tion~ are su~ficientl~ high.
According to our studies, in the case o~ cement coppex
the reactior prooeeds et a practic~l rato wh~n the di~so1ved
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iron concentration is 20-40 gpl, the H2S04 starting concen-
tration is 200-240 gpl, the solution temperature is above 60C,
the DC volta~e is from 2-5 ~olts (measured between the anode
and cathode) the current density is above 60 amp/ft2 but
below that which causes boiling o~ electrolyte and/or forma-
tion of brittle plate, the latter being determined empirically.
(The top llmit we have so far observed is about 300 amp/ft2.)
In order that the reaction proceed properly, it is also necessary
that the slurry of cement copper in electrolyte be agitated
violently. Also, the dissolved copper concentration of the
electrolyte should be maintained in the range of 20-40 gpl.
Below 20 gpl Cu, a brittle and/or powdery plate will be formed.
; ~he upper limit is unimportant. ~his concentration is con-
veniently obtained at the outset by the addition of copper
sulfate, although it will build up by itself as pawer is
supplied to the cell. ~
~he presence of at least 10 gpl of dissol~ed iron is -
mandatory. In the case of cement copper -the minimum content
is about 20 gpl. ~o start operations, it is usually necessary
to add iron. ~his is conveniently done by adding ferric
sulfate. The addition of a soluble copper salt (CuS04) at
the outset is also desirable although, as noted, i~ iron is
; present, the copper concentration will be built up and then
maintained at a selected levelO
In the case of sulfide concentrates, the specific opera-
ting conditions may vary from those required from cement
copper7 however, the basic re~uirements of dissolved iron and
high current densities remain.
In the case of Cu2S a basic reaction is apparently:
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~ 455~
Cu2S -~ 2Fe~+ --~ Cu~ ~ 2Fe++ ~ Cu~+
with the u++ thereafter being reduced~to plate at the cathode
while ferrous iron is reoxidized at the anode.
CuS is only difficultly soluble in the acid electrolyte
yet under the conditions of our process the ore is depleted
; relatively easily which means that some mechanism operates todissolve the copper. Our work shows that the rate of copper
recovery varies directly with the iron content of the electro-
l~te. ~hus, it is believed that the iron does enter into or
perhaps catalyzes rapid dissolving of the copper.
In general, for sulfide concentrates during operation the
electrolyte ~hould contain 10--25 gpl dissolved i:ron and at
least 25 gpl dissolved copper. ~he electrolyte -temperature
should be at least 25 gpl dissolved copper. ~he electrolyte
temperature should be above 60C but below the boiling point
of the solution. Volt~ge should be above about 2.5 volts.
Current densities should be above 60 amp/ft2 cathode area up
to a maximum where brittle pla~e or boiling of electrolyte
occurs. In general, high current densities result in higher
recovery rates. ~;
It is important that the slurry be violently agitated in
the cell during the process. This accomplishes several things.
It insures maximum contact between the solids and electrolyte~
avoids uncontrolled polarization at the electrodes, insures ~ -
contact between liberated h~drogen gas and ferric iron adjacent
~ the cathode to protect the cathode and the depositea copper
; from attack by ferric iron. Also, if the agitation is carried ~`
~ out b~ movement of the cathode, the plate quality will be
. .
~ ~urther enhanced by the moving cathode target.
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Extensive tests were performed on cement copper and
chalcocite concentrates from sev~ral sources.
r~he equipment used comprised an octagonal shaped tank with
its wall serving as the anode. An oscillating cathode was
mounted in the tank. r~he cathode was formed with several
removable stainless steel plates which permitted variati~ in
the cathode area to provide a wide variation of current densi-
ties with a given power source. Paddles were mounted on the ~-~
cathode structure to agitate the slurry as the cathode recipro-
cated. Power was supplied by a conventional full wave
rectifier DC power supply. r~he cell tank was built to contain
about 20 inches slurry and the cathodes were arranged to be
immersed to a maximum depth of about 18 inches. Each cathode
plate thus had an effective single side surface area o~ about
.31 ft . In the test arrangements both sides were plated.
r~hus, each plate had a total effective area of .62 ft2.
The cell was filled and emptied manually. Additional
copper-bearing materials were added and samples -taken as
desired during operating. ~or final analysis of the tails,
the tank was emptied entirely. All tests and assays were
performed in accordance with accepted techniques.
In examples, -the acid content of the electrolyte is
; recited at the start of a test and is based on the known
materials used in making up the solution. r~he acid requirements
are simply tha~ only enough acid is required to keep the
reaction going at an acceptable rate. r~oo much acid will slow
' down reaction rates. r~he current density affects the acid
; concentration. r~oo low a density will cause undesirable acid
build-up in the system with reduction in recovery rates.
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~0145~7g
Increasing current will stop or even reverse acid build-up.
~hus, the current should be adjusted to maintain the acid at
the proper level to maintain optimum recover~ rates without
excess gas-release.
A series of tests was conducted on cement copper to
demonstrate the ef~ect of dissolved iron on the plating process.
~he cement copper contained about 90Yo copper (dry basis). ~he
electrolyte contained 200 gpl H2S0~ at the start. ~he iron
content of the electrolyte was increased b~J the incremental
addition of ferric sul~ate. ~'he dissolved copper content
increased as a result of ~he process1 increasing as iron
content increased.
~est DissolvedDits~olvedVoltageCurrent ~emp
No. Iron Content Cu gpl Densit~2
e~ol Am~s/î t
1.6 10.6 2.8 ~.4 43
2 13.1 19.7 3.0 55.5 55
3 13.4 23.6 3.4 55.5 40
4 13.4 23.5 3.4 66.6 52
13.8 23.9 3.0 44.4 51
6 25.4 2~.4 3.7 66.6 54
In the foregoing tests copper deposited at the cathode, in the
- time indicated, was:
~est 1: A~ter 45 minutes, only unacceptable powder deposited;
25 ~est 2: After 60 minutes brittle plates were formed -total
copper recovered was 399 grams. Power consumption
- . .,
was .853 KWH/lb copper recovered;
~est 3: Af~r 60 minutes a plate o~ improved appearance~ ~ut
still somewhat brittle was harvested--total weig~ o~
copper recovered was 358.4 gram~, power consumption
was 1~09 KWE/lb copper recovered;
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~est 4: After 60 minutes bright flexible plates were
harvested. ~otal weight of copper recovered was 479
grams, power consumption was 967 K~JH/lb copper
recovered; ~
~est 5: After 60 minutes dense bright flexible plates were -
harvested. ~otal weight of copper recovered was 304
grams, power consumption was .925 KWH/lb copper
recovered;
~est 6: After 60 minutes, dense bright flexible plates formed.
~otal weight of copper recovered 407 grams, power
consumption was 1.2L~ KWH/lb copper recovered.
~he tests demonstrate that th6 ability of the sys-tem to
dissolve and plate copper varies directly with the dissolved
iron content and, further, that the quality of deposited plate
- 15 increases as the dissolved iron content increases~ ~he plate
quality is enhanced by the ability of the H2 to reduce corrosive
ferric iron adjacent the cathode and by the constant avail-
ability of ferric ions elsewhere in -the system to oxidize
elemental copper into solution.
Other operating tests were performed in the same test
equipment on various cement copper and chalcocite concentrate
sa~ples. All tests were conducted with vigorous agitation.
All currents are Da.
~XAMPIE I
h wet chalcocite concentrate containing 37.2% copper by
weight (as Cu2S) and ground to pass a 325 mesh screen (~yler)
;~` was mixed in the tank with 45 liters of an electrolyte
initially containing in solution 100 gpl H2S04, 15 gpl ferric
, ~
; iron and 30 gpl of copper. Voltage averaged 3 5 and a steady
3 current density of 75 amps/ft2 cathode area was applied. ~em-
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~J9LS57~
perature was steady at 61C. ~t the end of 2 hours 447.5 grams
of high grade copper plate was strippecl from the cathode.
Power consumption was 1.74 KWH/lb copper recovered. ~he initial
charge was 2419 grams containing 900 grams copper of which 447
5 grams or about 50% was recovered on the cathode.
- EXAr~E II
~ he same setup used in Example I was employed, but an
additional 2419 grams of concentrate was added and the system
operated at an average of 3.6 volts and a steady current density
10 of 74 amps/ft2~ for ~our hours. Temperature was steady at
about 61a. After four hours the pl ates were again stripped.
I!hey were of high guality and weighed 919 grams. Also, a~ter
:l~our hours time the electrolyte contained 33.0 grams OI copper
and 13.8 grams oî ~errous iron in solution. A-t the beginning
15 of this test, the system contained about 1353 grams of copper
as Cu2S and, of this, 919 grams or 68% was recovered at the
cathode at a power consumption OI 1.72 KWH/lb copper.
E~IE III
An 1880 gram sample oî we-t chalcocite containing about
46.8% copper as Cu2S and ground to pass a 200 mesh screen
(~yler) was mixed in 44 liters OI an electrolyte containing
200 gpl H2S04, 27.4 gpl dissolved iron and 39.3 gpl dissolved
copper. I!he system was ~un for 4-1/2 hours during which the
voltage varied Irom 3.9 volts during the îirst hour to 3.35
volts during the last hour. Current density was a constant
66.6 amps/ft2. ~emperature ranged from 47-64C.
At the end o~ the test, the electrolyte still contained
32.7 gpl copper as compared to the start oî 39O3 ~,pl. ~he
weight o~ copper recovered at the cathode was 1179 grams. Of
30 thi~, 291 grams was taken ~rom the electrolgte while the
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balance was recovered from the concentrate. Ignoring experi-
mental error, the recovery was essentially 100%.
The following tests were carried out in a smaller cell
- than the other tests. It was essentially of the same design,
but shallower and with a smaller cathode area.
E~AMPIæ IV
.
A 1691 gram sample of wet cement copper, containing about
~7.~/0 copper was mixed with 27 liters of electrolyte con- -
taining 200 gpl H2S04, 30 gpl dissolved f~rric iron and 30 gpl
dissolved copper. ~he system was operated for a total of four
hours. Additional amounts of cement copper, totalling 3182
grams, were added at about 1/2 hour intervals. ~hus, the cumu-
lative total wet cement copper processed in the cell was 4873
grams containing 2335 grams of copper. Voltage ranged from a
high of 4.9 to a low of 3.7. Current density at the cathode
also varied from a high of 250 amps/ft2 to a low of 150 amps/ft2.
I ~hese values are shown in Table A.
~ABLE A
~ime Voltage Total Current ~emp
_ _ Amp~rage Amps/ft _ -
O(Start) 4.3 320 150 59
1 3-9 320 150 69
1-1/2 3.9 ~20 150 70
2 3.8 320 150 71
*2 4.9 430 200 71
2-1/2 4.2 430 200 76
3 3 7 430 200 78
*3 4.5 535 250 7
3-1/2 ~.2 535 250 82
(*changeover in current made at this time)
~S57~
Samples oî copper plate were taken from one cathode plate at
2 hours (47.6 grams) and from the same cathode plate at 3 hours
(57.5 grams). At -the end of the test, all cathode plates were
stripped, the product sheets weighed and compared with the ;~
product sheets taken during the test. A total of 2150 grams oî
copper was recovered at the cathode. All plates were of high
guality, dense and fle}cible. At the finish, the electrol~te
contained 40.4 gpl ferrous iron and 40.7 gpl copper All oî
the 2150 grams of plate copper plus the 288 grams increase i~ ;
dissolved copper content of the electrolyte during the test was
extracted from the cement copper solids. On the basis of the
weight of copper recovered from ths cathode the percent recovery
is about 92% and if one considers the additional copper in solu-
~; tion as being effectively recovered, and allowing for experimental
error, the recovery is at 100%.
~ ~E V :.
A. 1480 gram sample of wet chalcocite conce~Ltrate co~taining
38.7% (573 grams) copper ground to pass a 325 ~yler nesh screen
was mixed with 27 liters of electrolyte initially containing
lO0 gpl H2S04, 30 gpl copper and 30 gpl iron as ferric sulfate.
q'he test was conducted for a total of six hours. Additional
amounts of concentrate containing another 2074 grams copper
were added in increments during the test. ~hus, a total OI
2647 grams copper as sulfide was processed. Voltage raIlged
from a high of 5.2 to a low of 4.2 volts. Current density at
the cathode was at 150 amp~ît2 during the first hour and 200
,~
amp/ît~ during the balance of the test. ~emperature stæted ;
at 60C and climbed to 79C for the last three howrs. A total
of 26~5 grams of copper was recovered a-t the cathode while the
electrol;yte showed a loss of 10 grams copper. ~hus, 26~5 grams
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of copper was recovered from the concentrate. ~his represents
a recovery of 99.55~/o from the processed concentrate. ~otal
power consumption was 11.249 KWH and 2470 a~llp hours. This is
a power consumption of 1.93 KWH/lb cathode copper. Current
efficience was 90.4Y~-calculated on the basis that a-t 100%
efficiency, one amp. hour will produce 1.185 grams copper.
The electrolyte was sampled at one hour intervals and the
samples analyzed for copper and iron content. '~hese reults are
listed in Table B.
;~ 10 ~ABIE B
Elapsed Copper Iron* Amp/ft2 ~oltage
ime-h s gpl ~pl Cathode DC
O(start) 30. 30.* 150 4.9
1 39.8 25.1 150
1** 39.8 25.1 200 L~.
~, 2 39.8 28.1 200 5.2
3 37-4 29.9 200 5.o
+~-~
~' ~ 35.7 30.5 200 4.3
; 20 5 36-5 32.4 200 4.2
6 30.2 30.1 200 4+.2
*At start iron was as ferric. At all other times values are
for ferrous.
~*Amperage was increased at end of one hour
+++500 ml H2S04 added at end of three hours. (In all work 60
Baume acid was used).
On visual inspection the cathode product was of high qualityO
Many other test$ were made in the same equipment on cement
coppers and chalcocite concentrates from various sourcesO The
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45579
operating conditions were within t~e limits set forth i~ the
foregoing examples and general tex*. In all cases~ it was
possible to produce a good plate when 1;he dissolved iron
content of the electrolyte and current densities were in the
stated ranges.
Due to the cost, only pa~t of the copper product was
subjected to laboratory assay ~or purit~. However, the copper
produced in two additional runs made in accordance with this
invention was assayed. One run was made on an Anaconda cement
copper containing about 85% copper (dry basis), the resulting
plate formally assayed at 99.9965% copper. Another run was
made on a chalcocite concentrate containing only 26.L~% copper.
~he resulting plate ~ormally assayed at 99.9942/o copper. ~his
is remarkable purit~ and clearly demonstrates the ability of
the proce~s to produce high grade copper directly from hereto-
fore difficultly treatable ma~erial~.
Although actual tests are reported only o~ cement copper
and chalcocite sulfides, it is obvious that the process will
apply to any copper-bearing sulfide concentrates.
As used herein, cement copper re~ers to that rinely
~`~ divided copper~ormed in well known manner by ~ of
copper s~lutions on steel whereby the copper replaces the iron
and is recovered.
Copper bearing sulfides amenable to processing in accord-
ance with our process include the common naturally occurringore~, or concentrates thereo~, such as bornite (Cu2FeS2),
chalcocite~Cu2S) chàlcopyrite (CuFeS2) and covellite (CuS~.
Also, act~al tests were conducted on Chrysocolla (CuSiO3-~H20),
under the conditions outlined ~or sulfides; and it reacted
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~ sS79
similarly to the chalcocite concentrate, yielding a high
~uality copper.
An important feature o~ our process is the ~act that it
operates without undesirable release ~rom the cell of gases,
such as 2~ H2 or H2S and the like.
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