Note: Descriptions are shown in the official language in which they were submitted.
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ANODE AND METHOD OF OPERATING AN ELECTROLYSIS CELL
Field of the invention
The invention relates to a new kind of anode to be used in electrowinning. The
invention
also relates to a method of operating an electrolysis cell to be used in the
electrowinning
of metals.
io Electrowinning is a process where a metal dissolved in an electrolyte is
reduced on a
cathode by means of an electrical current. In electrowinning a current is
passed through
the anode through the electrolyte solution containing the metal value so that
the metal
value is extracted as it is deposited in an electroplating process onto the
cathode. When
an electrical current is applied to the sulfate based electrolysis system,
metal is
is precipitated on the surface of the cathode and water decomposes on the
anode where
acid and oxygen are formed. Electrowinning takes place in an electrolytic cell
that
contains a number of anodes and a number of cathodes arranged in an
alternating
manner. The commercial use of electrowinning requires a large number of
cathodes
and anodes in a single electrolytic cell. One type of anode used in
electrowinning has
20 been lead based anode, which could have a negative effect on the quality
of copper
deposited. One significant disadvantage of using such lead based anodes is
that during
electrowinning operations small amounts of lead are released from the surface
of the
anode, which causes the undesirable particulates to be suspended in the
electrolyte. In
addition, the lead sludge must be cleaned periodically from the cell bottom
e.g. every 45
25 to 90 days, and during this time the electrowinning cell is not
producing metal.
One issue in electrowinning processes is a rather high cell voltage leading to
increased
energy consumption. Due to high energy consumption in electrowinning and low
corrosion resistance of previous anodes, there has been a need to investigate
better
30 anode materials in electrowinning. Mixed metal oxide (MMO) coated anodes
consist of
conductive mixed metal oxide coatings on valve metal substrates, usually
titanium or
nickel. Dimensionally Stable Anode or DSAO is a well-known type of MMO-coated
anode. When the MMO-coated anodes are used in sulfate based electrowinning the
cell
can be operated at a lower cell voltage than when lead based anodes are used.
One
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type of dimensionally stable anode is presented in patent publication
US4134806,
where the idea is to stabilize current distribution between the DSA anode and
cathode
by thickening the DSA anode structure in the border areas. Publication US
20100276281 presents the anode for use in electrowinning cells. According to
the
publication the electrode includes a hanger bar and an electrode body
including at least
one conductor rod and a substrate, a connection coupling the hanger bar and
the at
least one conductor rod, and a seal isolating the connection. An electrode
comprises a
hanger bar including at least one recessed hole, and an electrode body
comprising at
to least one conductor rod press fit into said at least one recessed hole
and a substrate
coupled to said conductor rod.
Past research and development efforts have focused on ways to increase
production
capacity per plant area for copper electrowinning, which directly impacts on
the cost-
is effectiveness of the electrowinning process. To increase the production
of the
electrolysis plant and cell, it is desirable to increase the current density
during
electrolysis, and achieve a higher deposition rate of copper on the cathodes.
The
current density on the cathode side is limited by the quality of the copper
deposited, as
due to the increased overvoltage on the cathodes more impurities are deposited
with
20 increasing current density. In addition, increasing the current density
also leads to an
increase in the corrosion rate of lead from lead anodes and consequently more
lead
circulates in the electrolyte and lead can be included in the cathodes,
necessitating an
increase in the frequency of cell cleaning to control lead and decreasing the
production
rate.
Due to high investment and operating costs of the electrolysis plants and
cathode
processing plants comprising of a 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
extractionielectrowinning 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. One way to decrease tankhouse capital
expenses is by increasing the length of cathode, thus increasing the
production capacity
per cell without the need to increase the current density, the plant area or
the number of
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electrolytic cells.
Publication WO 2005/080640 presents a process for electrochemically winning or
refining copper, where the idea of the invention is to increase the copper
loading per
cathode. To increase the economic efficiency of such processes and plants, it
is
proposed in accordance with the publication to immerse at least one cathode
into the
electrolyte over a length of at least 1.2 meters during operation of the
electrolysis.
io Still problems can occur when using cathodes with great length. When
using lead
anodes with jumbo cathodes i.e. cathodes of great length, warping of the anode
during
electrowinning may occur and cause short circuits to the process. There can be
problems especially with the first and last anodes in a cell, with current
flowing only on
one side of the anode, which may cause warping or creep deformation of the
anode.
is Warping leads to an increased number of short circuits and a lower
current efficiency. If
lead anodes are used with jumbo cathodes, more frequent cell maintenance is
needed
to remove the lead sludge from the cell. In addition, for an even current
distribution it is
beneficial to position the anodes at equal distances from the cathodes. In
order to avoid
such issues or problems there has been a need to develop a new kind of anode
to be
20 used with long cathodes with a rigid structure and located in the right
position in the cell.
Objective of the invention
An object of the invention is to provide an anode for electrowinning process,
especially
25 when the anode is to be used with "jumbo" cathodes having a great length
(of 1.2 m or
longer) and for avoiding problems stabilizing the position of the anode inside
the
electrolytic cell.
Short description of the invention
The anode and the method of the invention are characterized by the definitions
of
independent claims. Preferred embodiments of the invention are defined in the
dependent claims.
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The invention presents an anode for an electrowinning process in an
electrolytic cell
having cell walls and a bottom cell for holding an electrolyte and electrolyte
feeding
means. The anode comprises of a hanger bar for supporting the anode, a
conducting
rod for distributing the current to the anode, an anode body having at least
partly
conductive structure, which anode body allows the penetration of the
electrolyte and is
at least partly covered by electrocatalytic coating, when in connection with
the anode
there is arranged a non-conductive element, which is restricted to the
conductive
structure of the anode body at least from its one side and which non-
conductive element
is arranged at a distance A from the electrolyte surface level, when the non-
conductive
element provides a means for attaching the anode to the cell. By using of
anode
presented in this invention many problems in a process for electrowinning can
be
avoided. According to the embodiment of the invention the length A is arranged
to be
between 0,3-2 meters, which depends on the size of the electrodes and process
parameters.
According to the one embodiment of the invention the non-conductive element of
the
anode is formed by excluding part of the anode body from electrocatalytic
coating, for
example at least 2 percent of the anode surface is excluded from
electrocatalytic
coating.
According to one embodiment of the invention the non-conductive element is
made of at
least one non-conductive object attached to the anode body.
According to another embodiment of the invention the anode is being attached
into the
electrolytic cell by anchoring elements located in the cell bottom, in the
cell wall, in the
electrolyte feeding means or attached to the cathode next to the anode.
According to the invention the conductive structure of the anode body consists
of a
mesh structure, including preferably at least one of the following; Ti, Ni,
Pb, Ta, Zr or Nb
and the electrocatalytic coating consists of a Pt-group metal oxide or a
mixture of metal
oxides.
According to another embodiment of the invention the height B between the
upper part
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of the non-conductive element and anode bottom surface is arranged to be
between
0.05-0.3 m.
5 The invention also describes a method of operating an electrolysis cell
to be used in the
electrowinning of metal, when metal is electrodeposited on the cathode surface
from an
electrolyte solution in an electrolytic cell having cell walls and a cell
bottom, which cell
contains electrolyte where anodes and cathodes are immersed in alternating
fashion, in
which the anode is supported by a hanger bar on the conducting rod, which
distributes
io the current to the anode, when the anode body has at least a partly
conductive structure
allowing the penetration of the electrolyte and an electrocatalytic coating,
when the
anode is attached inside the electrolytic cell by a non-conductive element
arranged in
connection with the anode, which non-conductive element is restricted to the
conductive
structure of the anode body at least from its one side and which non-
conductive element
is is arranged at a distance A from the electrolyte surface level.
According to the
embodiment of the invention the anode is attached into the electrolytic cell
bottom by
anchoring elements.
According to the different embodiments of the method the anode is attached
into the
20 electrolytic cell wall, into the electrolyte feeding means or the
cathode next to the anode
by anchoring elements.
According to one embodiment of the invention the electrolyte is fed at least
from two
25 manifolds in the cell, when the other one is at the bottom of the cell.
According to one embodiment of the invention the anode could be used in the
electrowinning of the metal copper, Cu.
30 There are many advantages of using the anode according to the invention.
The anode
can easily be attached in the cell, anode warping is avoided, good mixing
effect of
electrolyte inside the cell is reached by using the anode according to the
invention. Also
copper growth on the cathode surface will be more even. When using a flow-
through
anode with electrolyte feeding vertically in the middle of the cell, good
electrolyte mixing
35 is obtained and metal ion concentration gradients can be avoided. Better
anode
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attaching and anchoring in the cell can be achieved by coating only part of
the surface
of the anode with the electrocatalytic coating.
Brief description of the drawings
The accompanying drawings, which are included to provide a further
understanding of
the invention and constitute a part of this specification, illustrate
embodiments of the
invention and together with the description help to explain the principles of
the invention.
io In the drawings:
Fig. 1 schematically shows an anode according to the invention, where the non-
conductive part of the anode is part of the anode body.
is Fig. 2 shows another embodiment of the anode, where the non-conductive
element is
attached to the anode.
Fig. 3a schematically shows an anode according to the invention, where the
anchoring
elements are located on the electrolytic cell bottom.
Fig. 3b schematically shows an anode according to the invention, where the
anchoring
elements are located on the electrolytic cell walls.
Fig. 3c schematically shows an anode according to the invention, where the
anchoring
elements are located on the electrolyte feeding means.
Fig. 3d schematically shows an anode according to the invention, where the non-
conductive element is attached to the anode and attached to the anchoring
elements.
Detailed description of the invention
Reference will now be made in detail to the embodiments of the present
invention,
examples of which are illustrated in the accompanying drawings.
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Figures 1 and 2 shows an anode 1 for electrowinning of metals, such as copper
in an
electrolytic cell 2 having cell walls 3 and cell bottom 4 for holding an
electrolyte 5. The
anode comprises of a hanger bar 7 for supporting the anode on the conducting
rod 8,
which distributes the current to the anode, an anode body 9 having at least
partly
conductive structure allowing the penetration of the electrolyte and an
electrocatalytic
coating. According to the invention there is arranged a non-conductive element
10, 12,
14 in connection with the anode 1 at a distance A from the electrolyte surface
level 11,
when the distance A is arranged to be at an interval 0,3-2 meter. This depends
on the
io size of the anode used. The non-conductive element 10, 12, 14 provides
means for
attaching the anode 1 inside the electrolytic cell 4, which is important when
using long
anodes with long cathodes. When using long cathodes, it is important that the
anode is
fixed and rigid in its place and possible warping of the anode is prevented.
The non-
conductive element consists of any suitable material that is not electrically
conductive
is and could be selected based on the process needs. It is possible that
the non-
conductive element could consist of several pieces or is made from one piece.
Figures 3a, 3b, 3c and 3d describe different ways for attaching the anode
inside the
electrolytic cell 4. The non-conductive element 10, 12, 14 of the anode
provides means
20 for attaching the anode 1 for example in the cell bottom 3, to the walls
2 or to the
electrolyte feeding means 6 by anchoring elements 13, which are attached to
the non-
conductive elements. It is also possible to attach the anode next to the
cathode inside
the electrolytic cell (not shown in figures). When the anode is attached to
the cathode by
using non-conductive element, it means that it acts as a spacer, which is
known to be
25 used to align the electrodes and separate them at a fixed distance from
each other in
order the electrolytic process to function. One way for attaching the anode is
presented
in Fig 3b, when the anchoring elements 13 are located in both sides of the
anode, which
anchoring elements are attached to the non-conductive element 14 and from its
other
side to the electrolytic cell walls 2. By attaching the anchoring elements 13
to the
30 electrolyte feeding means 6, as presented in Fig. 3c, it saves space
inside the
electrolytic cell.
When using a long anode, it is important that the anode is rigid and straight
and
positioned from even distance from the adjacent cathodes. According to the
invention
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the anode can be anchored inside electrolytic cell 4 by supportive anchoring
elements
13, which could be of any shape (e.g. V-neck) and suitable for attaching them
to the
non-conductive elements 10, 12, 14. The electrolytic cell may be used for
electrowinning of several metal values. An electrowinning cell as described
herein may
be configured for the extraction of a variety of metal values. Fig. 3d
schematically shows
an anode, where the non-conductive element 12 is attached to the anode and
attached
to the anchoring elements 13. It is possible that the non-conductive element
is attached
to the cathode next to the anode, when the non-conductive element functions as
a
io cathode guide, i.e. during cathode harvests it guides the cathode into
the correct
position and prevents any contact between the cathode and the anode body.
According to the invention the distance between electrolyte surface level 11
and the
non-conductive element, meaning length A is arranged to be in interval 0,3-2
meter
is when the height B between the upper part 16 of the non-conductive
element 10,12,14
and anode bottom surface 15 is arranged to be between 0.05-0.3 m. Then the
immersion of the anode is enough to be used with long cathodes. One way is to
form
the non-conductive element 10, 12, 14 of the anode 1 is by excluding the anode
body 9
from electrocatalytic coating when at least 2 percent of the anode 1 surface
is excluded
20 from electrocatalytic coating. When part of the surface is left without
conductive
electrocatalytic surface, electric current can be shielded and anode can be
placed on
the cell bottom without problematic edge deposit growth on the cathode bottom.
The
conductive structure of the anode body consists for example of a mesh
structure
allowing the penetration of the electrolyte, when the anode mesh consists of
preferably
25 one of the following metals; Ti, Ni, Pb, Ta, Zr or Nb. Catalytic coating
preferably consists
of Pt-group metal oxide.
It is apparent to a person skilled in the art that as technology advanced, the
basic idea
of the invention can be implemented in various ways. The invention and its
30 embodiments are therefore not restricted to the above examples, but they
may vary
within the scope of the claims.
