Note: Descriptions are shown in the official language in which they were submitted.
Case K-~4~7-KCC;
10~;864Z
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The invention relates to processes for electro-
inning copper from aqueous sulfuric acid solutions con-
taining dissolved copper values and more particularly to
such processes in which a lead anode is utilized.
Electrowinning processes are widely used to recover
metallic copper from aqueous electrolyte solutions contain-
ing dissolved copper values. Conventional electrowinnin~
processes for copper utilize anodes made of lead or an
alloy of lead and antimony. ~hen an aqueous electrolyte
solution contains a corrosive material, such as sulfuric
acid, the lead or lead-antimony alloy anod~s are subject
to corrosion. Antimonial lead anodes have a generally
satisfactory service life when the sulfuric acid concentra-
; tion in the electrolyte solution is small, i.e~, below
about ~0 grams per liter of sulfuric acid. However, with
electrolytes having higher sulfuric acid concentrations,
the corrosion of conventional antimonial lead anodes is
greatly accelerated, which creates a serious problem not
only from the standpoint of high anoda replacement costs
~20 but also with respect to lead contaminants which are
transmitted to the copper deposited at the cathodes. -~
The alloying of lead with calcium to obtain a
hard lead alloy is known. The hard lead-calcium alloys
` are known to be useful in manufacturing electrical cable
sheaths, ammunition~ and plates in lead storage batteries~
In the last-mentioned use, the lead-calcium alloy plates
were found to be less susceptible to "self-discharge" which
~; is inherent with conventional lead-antimony alloy plates
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' due to transfer of antimony between the plates of the ~ ~
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~ ;864Z ; ::
In accordance with one aspect of the present in~ention,
there is provided a process for electrowinning copper from
an aqueous sulfuric acid electrolyte containing dissolved
copper values comprising immersing at least one anode and at ;;
least one cathode in said electrolyte and impressing an
electrical potential across said anode and cathode to deposit
copper on said cathode, the anode being a lead alloy containing ;
from about 0.025 to about O o lO percent calcium by weight.
; The term lead is meant to include pure lead as well as
commercial lead and chemical lead, which usually contains ~ - -
small quantities of copper, silver, nickel, zinc and bismuth. ~ -
This term is also meant to include lead alloys in which the
alloying elements do not eliminate the corrosion resistance
provided by the calcium addition.
It has been found that the incorporation of the small
` amount of calcium in the lead forms an alloy, which, when
- used as an anode in electrowinning copper from aqueous
sulfuric acid solutions, is remarkably stable and exhibits
exceptionally superior resistance to corrosion in comparison
to conventional lead or lead-antimony alloy anodes. Further,
the use of the lead-calcium alloy anodes results in significant
reduction of lead contaminants in the cathode depositèd
, copper.
The calcium-lead alloy which is used in the anodes of
this inventi~n can be made in any conventional manner, ~ -
` including the procedure described in detail in U.S. Patent ; -
.: . .
Nos. 1,890,014 and 2,042,840.
~ The invention is applicable to all conventional processes
; of electrowinning copper from an aqueous, sulfuric acid
electrolyte. Generally, the electrolyte solution will
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106~364Z
conkain from about 10 to about 300 grams of H2S04 per liter
of solution, and from about 0 5 to about 60 grams o~
dissolved copper per liter of solution The electrolyte
can be passed through conventional electrowinning cells
which contain a large number of alternately disposed cathode
and anode sheets wherein the anode sheets are made from a
lead-calcium alloy according to this invention. The cathodes
can be any of those conventionally used in the electrowinning
of copper For example, the cathodes can be made of stain-
less steel, titanium, or electrolyticall~ deposited copper.
The current density can ~ary over a generally wide range,
; such as from about 5 to about 40 amps per square foot, with
a voltage drop per electrode pair of approximately 2 volts.
The $mproved process of the present invention is
advantageously used in electrowinning copper from dilute,
- sul~uric acid leach solutions which have been used in leach-
ing copper values from copper-bearing material, such as low
grade ores and mine waste dumps. The improved process is
particularly advantageous in electrowinning copper from
somewhat more concentrated sulfuric acid solutions, as
those obtained in multi-step, leach-solvent ex~raction pro-
~, ... .
cesses
In one such multi-step process, copper scrap
and/or cement copper is initially leached with an aqueous ~ -
ammonical leaching solution under oxidizing conditions to
oxidize the copper values to cupric oxide. The cupric `
oxide then reacts with ammonium hydroxide in the aqueous
ammonical leaching solution to form a soluble copper ammonia
complex. Thereafter, the copper-pregnant ammonical leach
solution is passed to an ion exchange zone, wherein it is
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10686~Z
contacted with an organic, ion exchange liquid which generally
contains a liquid organic ion exchange agent dissolved in a
suitable, water immiscible, organic solvent, such as kerosene. ;~ - ;
A suitable liquid organic ion exchange agent is a substituted
2-hydroxy benzophenoxime, such as taught in U.S. Patent No.
3,428,449. The dissolved copper ions are extracted from the
aqueous ammonical leach solution by the organic ion exchange
agent, and the organic and aqueous phases are then allowed
to separate. The copper-pregnant organic ion exchange agent
is thereafter contacted with an aqueous, sulfuric acld
solution to strip the ma~ority o~ the copper therefrom. The
aqueous, sulfuric acid solution obtained from the stripping
step generally contains from 100 to 300 or more grams per
liter of sulfuric acid and from about 20 to about 50 grams
per liter of dissolved copper values. Such an ion exchange
system can also be utilized to transfer copper ions from a
,
dilute acid leach solution, (such as the dilute sulfuric
acid solution mentioned hereinabove) to the more concentrated
.
sulfuric acid solution in a manner similar to that described
for transferring copper from an ammonical leach solution to
` a sulfuric acid solution.
The~ lead-calcium alloy anodes of this invention have
been found to be exceptionally resistant to corrosion even
when the electrolyte is one which contains a substantial
~ concentration of sulfuric acid, such as, for example, the
'`,J electrolyte from the solvent extraction systems discussed
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1 above. In addition, the cooper produced by the process of
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~; this invention contains a minimum amount of lead impurities, ~
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~ usually less than 4 parts per million.
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~6864;~
The invention is further described in connection
with the following example which is intended to illustrate
the invention but not to limit the scope thereof
EXAMPLE
A calcium-lead alloy anode was made containing 0.10
weight percent calcium with the balance being essentially
lead. Two antimony-lead alloy anodes were also made. One
contalning 5 weight percent antimony with the balance being
load, and the second containing lO weight percent antimony
and 0.4 weight percent arsenic with the balance being
essentially lead. Each of these anodes was approximately
170 cm2 in area. Each anode was placed into an electrolytic
cell so as to be positioned between two ca~hodes of equal
dimensions7 with a cathode to anode spacing~of one inch.
The cathodes were made of copper or titanium metal.
An aqueous sulfuric acid electrolyte containing
i 1~0 grams per liter of sulfuric acid, 40 grams per liter of
dissolved copper, and 2 grams per liter of dissolved iron
was introduced into each of the electrolytic cells to
submerge the anode and cathodes of each cell in the electro- ; -
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lyte. An electric potential was applied between the anode
and cathodes o~ each cell so that each anode opsrated under
a current density of 16 amps per square foot, with a voltage ;
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drop of about 2 volts between the anode and cathodes of
each cell. : :
The corrosion rate of each anode was determined by ;
periodically measuring the weight loss thereof. Each anode
exhibited an initial inductance time~ that is to say an
initial period of time after the anode had been put in -
` 30 service, wherein the weight loss was nil. During the
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induction time, a film of Pb02 formed on the anodes. After -
the induction period, the corrosion rate~ or rate of weight
loss was constant The corrosion rates of khe anodes for
the period after the initial induction time ~ shown in
the following table. The induction time for each anode and
the length of the text of each anode is also shown in the
table.
TABLE
Induction Time of
Corrosion Rat~ ~ime Test ;
Ano_e cm2day x 10~ Da~s _ Days
5% SbJ Pb 2.9 3 57
10% Sb, o~4% As, Pb 3.2 3 33 -
0.10% Ca. Pb 0.06~ 20 10
As can be seen from the above da~a, the anodes
; made of the lead-calcium alloys were found to corrode at a
` rate of only 2-3 percent of that of the conventional anodes
made of antimony-lead alloys. Thus, the life of the lead-
calcium anodes would be some twenty to thirty-three times
as long as that of the conventional antimony-lead anodesO -
The process taking place in the three cells that
utilized the three lead-calcium anodes produced copper in
which the lead` impurity did not exceed 4 parts per million.
Whereas this invention is described herein with ~ :
respect to certain preferred procedures thereof, it is to
A be understood that many variations are possible without
departing from the inventive concepts particularly pointed ~
out in the following claims: -
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