Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS AND PLANT FOR ELECTRODEPOSITING COPPER
Technical Field
The present invention relates to a process for the electrochemical winning or
refining of
copper by electrode positing copper from an electrolyte solution containing
the metal in
ionogenic form, in which the electrolyte is passed through an electrolysis
plant compris-
ing at least one electrolytic cell, which in an electrolyte tank for receiving
the electrolyte
has at least two electrodes serving as anode and cathode, which are
alternately ar-
ranged at a distance from each other, and to a corresponding plant.
For producing copper, a multitude of processes are known, in particular
pyrometallurgi-
cal and hydrometallurgical processes. In pyrometallurgical processes, enriched
chal-
copyrite is molten in a suspension furnace or bath-type melting furnace by
adding
oxygen to obtain a copper matrix, in converters is then converted to crude
copper in
two blowing steps, and is purified further in a final electrolytic refining
step. This elec-
trolysis is also referred to as refining electrolysis. In hydrometallurgical
processes, on
the other hand, in particular low-copper oxidic ores with a copper content of
about 0.5
to 1 wt-% are used as starting materials. The starting ore poor in copper,
which due to
its mineralogical composition cannot always be processed economically with
other
processes such as flotation, is leached e.g. with dilute sulfuric acid, and in
an extraction
plant the resulting solution rich in copper is treated with an organic
extractant which
selectively extracts copper ions from the solution. Subsequently, the copper-
containing
extractant is stripped with foul electrolyte with a copper content of about 30
to 40 g/l,
which originates from the succeeding electrolysis plant, the copper from the
extractant
phase passing over into the electrolyte, which upon further purification for
removing
extractant residues and solids typically is recirculated to the electrolysis
plant with a
copper content of 40 to 50 g/l. Such electrolysis is also referred to as
extraction elec-
trolysis.
During operation of the electrolyses, the copper ions are reduced at the
cathodes and
deposited as elementary copper. Conventional electrolysis plants for the
electrometal-
lurgical winning of copper, as they are described for instance in J.A. Wells
and W.R.
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Snelgrove, The Design and Engineering of Copper Electrowinning Tankhouses, Pro-
ceedings of the International Symposium on Electrometallurgical Plant
Practise, Per-
gamon Press, 1990, pp. 57 to 72, comprise up to 188 electrolytic cells, each
of which
has between 20 and 60 cathodes, chiefly made of stainless steel, as well as a
corre-
sponding number of anodes. At predetermined distances, depending on the size
of the
plant, the copper-coated cathodes are withdrawn from the electrolytic cell
manually or
by means of cranes and transferred to a stripping plant, in which the copper
coatings
are peeled (stripped) off the cathodes, before the cathode starting sheets are
returned
to the electrolytic cells after a corresponding aftertreatment. The copper
peeled off is
finally processed in melting furnaces.
For an efficient aftertreatment of the copper-loaded cathodes, in particular
for peeling
off the deposited copper in the stripping machine, a rather uniform deposition
of the
copper on the cathodes, based on the surface area of the cathodes, is
desirable. This
is only ensured with a uniform streamline distribution along the length of the
cathodes.
As is described for instance in A. Schmidt, Angewandte Elektrochemie, Verlag
Chemie
1976, pp. 49 to 51, the uniformity of the streamline distribution with a given
conductivity
of the electrolyte is, however, increasing with decreasing width and in
particular length
of the electrode surface immersed into the electrolyte. In addition, the
streamline distri-
bution depends on the conductivity of the electrode material and on the
current density
applied during electrolysis. Due to these relations, both the refining
electrolysis and the
extraction electrolysis typically employ electrodes with a surface area
maximally im-
mersed into the electrolyte of about 1x1 meter. The melting furnaces for the
further
processing of copper are also adjusted to this size.
Due to the high investment and operating costs of the electrolysis plants and
cathode
processing plants comprising crane and stripping machines, which are combined
in the
so-called tankhouse, attempts have been made for quite some time at increasing
the
economic efficiency of both the refining electrolysis and the extraction
electrolysis. This
largely depends on the efficiency of the electrolysis as well as on the number
of the
cathode movements and therefore on the amount of copper deposited per cathode.
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To increase the efficiency of the electrolysis, it is desirable to increase
the current
density during the electrolysis, in order to achieve a higher deposition of
copper on the
cathodes per unit time. However, the current density on the cathode side is
limited by
the quality of the copper deposited, as due to the increased overvoltage on
the cath-
odes more impurities are deposited with increasing current density. On the
anode side,
the lead alloy used as electrode material for the extraction electrolysis
becomes more
unstable, and the copper anode used for the refining electrolysis becomes
passivated
with increasing current density. As a result of these two effects, present-day
electroly-
ses operate with a maximum current density of about 370 A/m2 electrode
surface. In
the extraction electrolysis, a higher current density can only be achieved by
using
expensive anode materials with a lower quality of the electrodeposited copper.
Therefore, a further reduction of the production costs with a consistent
quality of the
electrodeposited copper can only be achieved by reducing the specific
investment and
operating costs of the cathode processing plants comprising the crane and
stripping
machines, i.e. by decreasing the necessary number of cathode movements based
on
the amount of copper electrodeposited per cathode.
Description of the Invention
It is the object of the present invention to increase the copper loading per
cathode
based on the number of cathode movements with a consistent quality of the
electrode-
posited copper.
In accordance with the invention, this object is solved by' a process for
electrodepositing copper from an electrolyte solution containing the copper in
ionogenic form, said process comprising a step of passing an electric current
across
the electrolyte solution in at least one electrolytic cell provided in a tank
for receiving
the electrolyte solution and provided with electrodes including at least one
anode
and at least one cathode, said at least one anode and at least one cathode
being
alternately arranged at a distance from each other, wherein the electrodes
have a
horizontal hanger bar with a first end and a second end and wherein at an edge
of
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the electrolyte tank two contact bars are provided, which are each connected
to a
power source of electric current, the first end of the hanger bar of said at
least one
cathode resting on one of the two contact bars via a two-line contact and the
first
end of the hanger bar of sais at least one anode resting on the other one of
the two
contact bars via a two-line contact,
characterized in that the second end of the hanger bar of said at least one
cathode
rests on a cathode equalizer bar which is arranged on one of the two contact
bars,
in that the second end of the hanger bar of said at least one anode rests on
an
anode equalizer bar, which is arranged on one of the two contact bars, and
in that during operation of the electrolysis the at least one cathode is
immersed into
the electrolyte solution over a length of at least 1.2 meters.
The object of the invention is also solved by an electrolysis plant for
electrodepositing copper from an electrolyte solution containing the copper in
ionogenic form, by passing an electric current across the electrolyte
solution, said
electrolysis plant comprising at least one electrolytic cell which includes an
electrolyte tank for receiving the electrolyte solution, at least two
electrodes
including at least one anode and at least one cathode, said at least one anode
and
at least one cathode being alternately arranged at a distance from each other
and
each having a substantially horizontal hanger bar, as well as two contact bars
arranged at an edge of the electrolyte tank, each contact bar being
connectable to a
power source of electric current, where the at least one cathode has a first
end of its
hanger bar resting on one of the two contact bars and the at least one anode
has a
first end of its hanger bar resting on the other one of the two-contact bars,
characterized in that during operation of the electrolysis the at least one
cathode is
immersed into the electrolyte solution over a length of at least 1.2 meters,
in that the
first ends of the hanger bars each rest on the contact bars via a two-line
contact,
and in that on at least one of the two contact bars at least one equalizer bar
is
provided, on which rests a second end of each of the hanger bars of the at
least one
cathode and/or at least one anode.
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According to a preferred embodiment, the electrolysis plant defined above is
used
for performing the process of the invention.
Surprisingly, it could be found in accordance with the present invention that -
contrary
to the prejudice existing among experts that electrodes with an electrolyte
immersion
surface of more than 1x1 m, and in particular electrodes with an electrolyte
immersion
depth of more than 1 m, are not suitable for winning copper due to the non-
uniform
streamline distribution necessarily obtained at the electrodes - an
electrolyte immer-
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sion depth of the electrodes of more than 1.2 m leads to a sufficiently
uniform deposi-
tion of copper on the cathodes in processes for electrodepositing copper from
an elec-
trolyte solution containing the metal in ionogenic form also with the cathode
materials
commonly employed in the refining and extraction electrolyses and with the
usually
adjusted current densities. Here as well, an efficient processing of the
loaded cathodes,
in particular a stripping of the copper deposited, is possible with the known
processing
techniques. In the process of the invention, more copper is produced per
cathode
movement than in known processes with a consistent quality of the electrode
posited
copper due to the greater electrolyte immersion depth, so that the costs per
ton of
extracted copper can be decreased drastically.
During operation of the electrolysis, the immersion depth of the electrodes
into the
electrolyte preferably is an integral multiple of the commonly used immersion
depth of
about 1 m and particularly preferably about 2 m with a cathode width of about
1 m
each. The advantage is that the melting furnaces, which because of the active
cathode
surface, i.e. the cathode surface immersed into the electrolyte, normally were
designed
for a size of 1x1 m in the known processes, can be used unchanged, in that the
stripped copper sheets to be obtained with the process in accordance with the
invention
are reduced to the corresponding size of 1x1 m subsequent to the stripping
operation
and before being supplied to the melting furnace. With an active electrode
length of 2
m, this can easily be achieved in that for instance the copper sheets are bent
in the
middle and are folded at the bending surface. It is likewise possible to
obtain two sepa-
rate cathode sheets each of 1x1 m during the stripping operation, e.g. by an
insulated
horizontally circumferential region provided at about the level of half the
cathode height,
so that another folding or reduction in size is made superfluous. Finally, a
mechanical
separation is also possible.
In accordance with a development of the invention it is proposed that the at
least one
electrolytic cell has more than 60 cathodes, particularly preferably more than
100
cathodes, and quite particularly preferably 114 cathodes. As a result, the
efficiency of
the process of the invention is further increased, as the size of the
electrolytic cells
caused by this measure provides for an inexpensive transport while at the same
time
reducing the number of cells per production capacity. This leads to a smaller
tank-
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house, shorter cathode delivery paths and less stray currents. In principle,
the cathodes
can be made of all materials known to the skilled person for this purpose,
stainless
steel cathodes being preferred.
It turned out to be advantageous to perform the electrolysis with a current
density as
used in the known processes, preferably with a current density of more than
200 A/m2,
and particularly preferably with a current density between 250 and 370 A/m2.
In this
way, the deposition of major amounts of impurities on the cathodes is avoided
and
copper is produced with the required quality. Due to the greater active
electrode length
and surface area, higher specific current intensities, i.e. higher current
intensities per
electrode, are obtained in the process of the invention as compared to the
processes of
the prior art. Whereas in the last-mentioned processes with cathodes and
anodes of an
active electrode surface of 1x1 m each, the specific current intensity is 740
A per elec-
trode with a current density of 370 A/m2, the specific current intensity is
doubled in
accordance with the invention to 1,480 A per electrode when using electrodes
with an
active surface of 1x2 m.
In the process of the invention, the electrodes can in principle be positioned
in the
electrolytic cells, be fixed and supplied with current in any way known to
those skilled in
the art. However, electrodes with a horizontal hanger bar known per se, which
has a
first end and a second end and preferably is made of the same material as the
cathode
surface, in particular steel, turned out to be advantageous. For power supply,
one end
of the hanger bar of the cathodes each rests on a first contact bar connected
to a
power source, whereas one end each of the hanger bar of the anodes each is in
con-
tact with a second contact bar connected to the power source. Preferably, the
two
contact bars are arranged on one contact bar each, which are provided at the
edge of
the electrolyte tank. The respectively second ends of the hanger bars of the
electrodes
can rest on a supporting surface of insulating material, which for instance is
likewise
arranged on the contact bars.
In accordance with a particular embodiment of the present invention, the
electrodes
have the first end of their hanger bar each resting on one of the two contact
bars via a
two-line contact. This is advantageous in particular because due to the larger
specific
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current densities in the process of the invention higher currents must be
transmitted
from the contact bars to the electrodes, which can be realized more
effectively with
two-line contacts due to the greater contact surface. For this purpose, a
contact bar
with an at least substantially trapezoidal indentation is used particularly
preferably, onto
which the first end of the hanger bar is applied with a contact surface having
an at least
substantially rectangular cross-section. The two-line contact can of course
also be
effected in any other way known to the skilled person for this purpose.
To ensure a transmission of current rather free of losses between the contact
bars and
the cathodes, which are for instance made of stainless steel, also with high
specific
current intensities, the process of the invention preferably employs cathodes
whose
e.g. steel-sheathed hanger bar has a copper core. Due to the high electric
conductivity
of copper, the current thus transmitted from the contact bar to the hanger bar
is trans-
mitted to the active electrode surface with only minimal losses, whereas the
steel
sheath surface of the hanger bar provides the hanger bar in particular with a
high
mechanical strength and high corrosion resistance. Based on its cross-section,
the
copper core preferably has the same geometry as the hanger bar. In this case,
a
hanger bar made of steel, which for instance is substantially square in cross-
section,
likewise includes a substantially square copper core.
In accordance with a development of the invention it is proposed to have the
respec-
tively second end of the hanger bar of the cathodes rest on an equalizer bar
preferably
arranged on one of the two contact bars, irrespective of whether the contact
of the
other hanger bar ends with the contact bars is effected via a one-line or two-
line con-
tact or any other contact whatsoever. The advantage of this embodiment
consists in
that the cathodes in this way have two electric contacts, namely on the one
hand with a
contact bar and on the other hand with an equalizer bar, whereby the
distribution of
current between the electrodes is rendered more uniform. This is expedient in
particular
with high specific current intensities, in order to minimize the transfer
resistances and
electric losses.
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For the same reasons, it is preferred in the process of the invention to also
have the
second end of the hanger bar of the anodes rest on an anode equalizer bar
separate
from the cathode equalizer bar.
In accordance with a particular embodiment of the present invention, the
contact bars
and/or possibly the equalizer bar or, particularly preferably, the
intermediate contact
bars, on which the contact bars and possibly the equalizer bars are arranged,
are
cooled during the electrolysis, in order to avoid a power loss, which results
from the
higher specific current intensity and the related higher current load, and a
heating of the
corresponding conductor bars. For this purpose, a water cooling of the
conductor bars
turned out to be particularly expedient, which is realized for instance by
passing cooling
water through a cooling water channel provided in the bus bars. Good results
are
achieved in particular with cooling water channels having a diameter of about
15 to 20
mm. Extruded bus bars with embedded cooling channel are preferably used for
this
purpose, although good results are also achieved with bus bars with milled
slots, which
are subsequently covered and welded, or with soldered copper tubes. For
supplying
water to the corresponding bus bars, tubes of PVC or hoses of vinyl material
turned out
to be particularly useful.
To achieve an efficient heat exchange between the bus bars and the cooling
water, it is
proposed in accordance with the invention to pass the cooling water through
the cool-
ing water channels with a velocity sufficient to maintain a turbulent water
flow, where a
velocity of about 1.5 m/s should, however, not be exceeded.
In accordance with the invention, the cooling water supply can also be
effected by two
coolant circuits divided into a primary circuit, which at least partly extends
through the
intermediate bus bars to be cooled, and a secondary circuit, which preferably
extends
completely outside the bus bars to be cooled. The connection of the two
circuits can be
effected in any way known to the skilled person. In particular, shell-and-tube
heat
exchangers as well as plate-type heat exchangers turned out to be useful.
Particularly
preferably, the primary circuit exclusively extends through the bus bars to be
cooled
and is operated with high-purity cooling water, for instance water purified by
a reverse
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osmosis plant, whereas the secondary circuit is fed with crude water and is
recooled for
instance by an atmospheric cooling tower.
To ensure that the primary circuit is always filled with cooling water, the
same prefera-
bly includes a water expansion tank.
In accordance with a development of the invention it is proposed to provide a
fluid
distributor in the at least one electrolytic cell, through which during
operation of the
extraction electrolysis a liquid, a gas, a gas mixture or a mixture of gas and
liquid is
introduced, particularly preferably from below, into the electrolytic cell.
Due to the
convection flow generated by such introduction of fluid a better intermixing
of the elec-
trolyte is achieved, which is why the copper is deposited on the cathodes more
uni-
formly. Furthermore, the convection flow effects a reduction in thickness of
the bound-
ary layers at the electrodes, which results in a better and faster mass
transfer of the
copper ions to the electrode surface. An introduction of fluid from below into
the electro-
lytic cell is particularly preferred, because in the upper region of the cell
a certain con-
vection flow is obtained automatically due to the gas bubbles released at the
anode
during the extraction electrolysis, and therefore in particular in the lower
region of the
electrolytic cell an additional convection flow is important.
Preferably, electrolyte solution or a mixture of electrolyte solution and gas
bubbles is
introduced into the electrolytic cell through the fluid distributor. Since
electrolyte con-
tinuously refreshed with copper sulfate from the leaching plant must in any
case be
supplied to the electrolytic cell during operation of the electrolysis, the
fluid supply
system requires no increase in the investment and operating costs in the first
case and
only an insignificant increase thereof in the second case. To increase the
convection,
other liquids, gases or gas mixtures can also be supplied to the electrolytic
cell instead
of electrolyte solution or a mixture of electrolyte solution and gas bubbles,
or other
systems such as mechanical mixing devices or the application of ultrasound can
be
used.
In accordance with a particular embodiment of the present invention, the fluid
distribu-
tor, as it is of simple construction and efficient in terms of operating
costs, consists of
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two tubes arranged substantially parallel to the longitudinal sides of the
electrolytic
cells, which at their surfaces each have one or more fluid outlet holes. The
tubes are
disposed at a small distance from the side wall. The distance is defined by
the fasten-
ing mechanism of the tube at the cell wall and provides for the deposition of
electrolyte
sludge at the cell bottom. Typically, the distance is 10-50 mm. The distance
of the two
tubes from the cell bottom should be chosen such that electrolyte sludge can
be col-
lected below the fluid distributor at the cell bottom. Typically, the distance
from the cell
bottom is 100-200 mm. As fluid supply conduit to the fluid distributor, there
can for
instance be used a tube arranged in the middle of the end face of the
electrolytic cell,
which with respect=to the electrolytic cell extends vertically from the top to
the bottom
and at its lower end branches into two tubes extending horizontally and
parallel to the
end face of the electrolytic cell, one of which tubes is each connected with
one end of
the tubes of the fluid distributor, which extend substantially parallel to the
longitudinal
sides of the electrolytic cells.
To achieve an effective convection flow, the fluid distributor should have a
high enough
number of fluid outlet holes. In accordance with the present invention it was
found that
for this purpose the relative number of the fluid outlet holes with respect to
the total
number of electrode pairs per electrolytic cell is decisive. Preferably, the
fluid distributor
has 1-5, particularly preferably about 1-2 fluid outlet holes per electrode
pair and cell
side provided in the electrolytic cell.
The shape of the fluid outlet holes is less decisive in terms of the
convection flow.
However, it turned out to be advantageous to provide substantially circular
fluid outlet
holes.
However, what influences the quality of the convection flow achieved much more
is the
cross-sectional area of the fluid outlet holes. In the case of circular fluid
outlet holes,
the diameter thereof preferably is 1 to 10 mm, particularly preferably 5 to 7
mm, and in
particular about 6 mm.
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In accordance with a development of the invention it is proposed to provide at
least two
electrolyte outlets per electrolytic cell, in order to achieve a trouble-free
overflow and
promote a uniform distribution of the electrolyte in the electrolytic cell.
In accordance with a particular embodiment of the present invention, the
cathodes used
have an indentation of V-shaped cross-section at their lower longitudinal
edge.
Thereby, a densification of streamlines necessarily occurring at straight
edges, which
leads to an - undesired - increased deposition of copper at the edges, can be
reduced
and optimally even be prevented completely. During stripping, the indentation
further-
more effects a separation of the front and rear sides deposited on the cathode
into two
cathode sheets.
The invention will subsequently be explained in detail with reference to
embodiments
and the drawing. All features, per se or in any combination, constitute the
subject-
matter of the invention, independent of their inclusion in the claims or their
back-
reference.
Brief Description of the Drawings
Fig. 1 shows the basic structure of an electrolysis plant for winning or
refining
copper;
Fig. 2 shows a section along line A-A in Fig. 1;
Fig. 3 schematically shows a section through an electrolytic cell with a
cathode
held by a hanger bar;
Fig. 4 schematically shows a section through an electrolytic cell with an
anode
held by a hanger bar;
Fig. 5 schematically shows two-line contacts between the hanger bar and a con-
tact bar;
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Fig. 6 schematically shows one-line contacts between the hanger bar and a con-
tact bar with equalizer bar; and
Fig. 7 schematically shows the structure of a pilot plant for performing the
process
of the invention.
Description of the Preferred Embodiments
In the electrolysis plant for winning or refining of copper, which is
schematically illus-
trated in Figs. 1 and 2, electrolytic cells 1 (dimensions L x W x H e.g. about
12.5 x 2 x
2.7 m) each with a plurality of e.g. 115 anodes 2 and 114 cathodes 3, which
are each
arranged alternately and are held at the edges of the electrolytic cells 1 via
hanger bars
4, are provided in numerous cell rows.
Via a crane 5, the hanger bar 4 with the electrodes suspended thereon can be
trans-
ported between a maintenance area 6 for the anodes 2, the cells 1 as well as a
strip-
ping machine 7, in which the copper deposited at the cathodes 3 is stripped in
a man-
ner known per se.
Fig. 3 schematically shows a cathode 3 resting on the edges of the
electrolytic cell via
the hanger bar 4. Correspondingly, Fig. 4 shows an anode 2 which is likewise
held 'by a
hanger bar 4. The anode 2 additionally has holes 8 for spacers, which ensure
the
required uniform distance between anodes and cathodes of e.g. 50 mm each.
Via a two-line contact 9, the one end of the hanger bars 4 rests on a contact
bar 10
arranged at the edge of the electrolyte cell(cf. Fig. 5), which is connected
with a non-
illustrated power source via a bus bar. The other end of the hanger bar 4
rests on an
equalizer bar 11. In general, this is effected via a one-line contact (cf.
Fig. 6).
With the process in accordance with the invention, which is characterized by a
high
specific current intensity - based on the electrodes - more copper is produced
than in
the known processes due to the greater electrolyte immersion depth of the
cathodes
per cathode movement with a consistent copper quality. A cathode with an
active
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immersion surface increased to 2x1 m needs only to be withdrawn from the
electrolyte
tank for processing after a copper loading of 200 kg, whereas a conventional
prior art
cathode of 1x1 m must already be processed after a deposition of 100 kg
copper. Thus,
the effort involved in the cathode movements is halved by a factor of 2, so
that, based
on the same amount of copper produced, correspondingly smaller or less crane
sys-
tems are required, for instance one instead of two cranes for handling the
electrodes, a
smaller number of stripping machines and thus less production area and
personnel.
The ground area required for mounting the electrolytic cells in the tankhouse
is also
drastically reduced. In the process in accordance with the invention, on the
other hand,
different contact bars and possibly equalizer bars are required due to the
higher spe-
cific current intensity, and for the subsequent processing of the loaded
cathodes crane
systems with a higher load-bearing capacity are required due to the higher
weight of
these cathodes. The height of the tankhouse between upper cell edge and crane
path
must be adjusted for processing the extended cathodes, and the same is true
for
mounting the electrolytic cells with increased overall height. Due to the
greater cathode
surface, differently sized stripping machines as well as folding or
comminution ma-
chines for folding the larger copper sheets before supplying the same to a
melting
furnace designed for conventional plants are required. As both investment and
operat-
ing costs for the last-mentioned measures are smaller than the corresponding
savings
achieved due to the smaller number of cathode movements, a significant
decrease of
the production costs is achieved on the whole.
Based on an annual production of 120,000 tons, a comparison of the process of
the
invention, which is performed with an active electrode surface of 2x1 m, with
the prior
art process performed with an active electrode surface of 1x1 m, but twice the
number
of electrodes with the same current density, yields the following
characteristics:
Prior art process Inventive process
Amount of copper per m2 cell area (in t) 40 65
Amount of copper per m2 tankhouse (in t) 20 30
Amount of copper per m3 tankhouse (in t) 1.9 2.3
Cathode movements per day 3120 1560
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When using the process of the invention, the investment costs for
corresponding plants
for the electrochemical extraction of copper thus can be decreased by up to
20%, and
the production costs can be decreased by up to 10%.
Example
In the test stand for performing verification tests on a pilot scale as shown
in Fig. 7, two
electrolytic cells 1 a, 1 b connected in parallel with respect to the
electrolyte supply and a
common electrolyte preparation and circulation system are provided. Both
electrolytic
cells are electrically connected in series (not shown). The electrolytic cell
la is
equipped with two lead anodes (A, width of 0.5 m and height of 2 m, immersed
surface)
and a centrally arranged cathode K. The electrolytic cell lb has 3 anodes (A,
width of
0.5 m and height of 1 m, immersed surface) and two cathodes K of equal size.
The
used number and size of the electrodes leads to the fact that in the case of a
series
connection equal current densities are achieved in both electrolytic cells.
Both electrolytic cells are charged with the same amount of fresh electrolyte
(20a and
20b). The inflow of electrolyte is adjusted such that during a stationary
operation of
both electrolytic cells a copper depletion of about 1.5 g/I is obtained. The
depleted
solution 21a and 21b, respectively, is supplied to the electrolyte circuit. It
comprises a
stirred leaching tank 22, in which the depleted amount of copper is
compensated by
adding copper oxide 23. The overflow of the leaching tank 22 (enriched
electrolyte 25)
is introduced into a pump recipient tank 24. The pump recipient tank 24 is
electrically
heated by the heater 26 and stirred by partial recirculation of the enriched
electrolyte
25'. The pump 27 is used for circulating the electrolyte.
In pilot tests, a synthetically produced sulfuric-acid copper sulfate solution
was used as
electrolyte. To improve the cathode morphology, a small amount of guar
solution (not
shown) was added to the pump recipient tank 24. The current density used was
300
A/m2. Several tests were performed, which took 5 to 7 days. In all tests,
cathodes of
very good quality were produced in both cells. The copper quality achieved was
inde-
pendent of the cathode size. In all tests, a current efficiency > 90% was
achieved
(Table 1, all concentrations at the cell inlet, e.g. cell 1a):
CA 02553926 2006-07-13
WO 2005/080640 PCT/EP2005/001127
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Test Cu Content H2SO4 Current density Test Voltage Current
(g/l) (g/I) (A/m2) period (h) (V) efficiency (%)
1 45 120 300 161 2.1 95
2 47 140 300 167 2.05 91
3 55 135 300 189 2.1 94
CA 02553926 2006-07-13
WO 2005/080640 PCT/EP2005/001127
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List of Reference Numerals
1 electrolytic cell
2 anode
3 cathode
4 hanger bar
5 crane
6 maintenance area
7 stripping machine
8 holes
9 two-line contact
10 contact rail
11 equalizer bar
20a,b fresh electrolyte
21a,b depleted solution
22 leaching tank
23 copper oxide
24 pump recipient tank
25,25' enriched electrolyte
26 heater
27 pump
A anode
K cathode
