Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
Title of Invention: ANODE FOR ELECTROWINNING AND METHOD FOR
ELECTROWINNING USING SAME
Technical Field
[0001] The present invention relates to an anode employed for
electrowinning a desired metal by electrolysis and to a method for
electrowinning using the same. More particularly, the present
invention relates to an anode employed for electrowinning in a
sulfuric acid based electrolytic solution with oxygen produced by
anode reaction and to a method for electrowinning using the same.
Background Art
[0002] Electrowinning of a metal is performed by submerging
and energizing an anode and a cathode in an aqueous solution (hereafter
referred to as the electrolytic solution) which contains ions of
a metal to be extracted, thereby allowing the metal to be deposited
on the cathode. Examples of typical electrowinning may include a
method for electrowinning a metal by electrolysis in an electrolytic
solution. In this case, to prepare an electrolytic solution, an
ore is first crushed which contains anyone or more of copper, zinc,
nickel, cobalt, lead, platinum family metals (such as platinum,
iridium, ruthenium, or palladium) , precious metals ( silver or gold) ,
other transition metal elements, and metal elements collectively
called rare metal or critical metal , etc. Subsequently, for example,
metal ions are dissolved in an adequate acid, etc., and a target
metal ion is then extracted, thereby preparing the electrolytic
solution. Furthermore, in the electrowinning, metals may also be
reproduced and extracted by electrolysis in an electrolytic solution
containing target metal ions. In this case, the electrolytic
solution is prepared by crushing used metal or alloy and allowing
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metal ions to be dissolved therein, etc. This may be performed to
_
recycle metal or alloy used in various applications, e.g., for primary
batteries, secondary batteries, fuel cells, mobile devices such
as cellular phones, other electronic devices, electrical and
electronic components, plated steel plates, or plated ornaments.
Furthermore, in the electrowinning, metal ions may be extracted
from a plating liquid waste so as to prepare an electrolytic solution
containing target metal ions, etc., so that a metal is extracted
by electrolysis in the electrolytic solution. Focusing on a
component other than metal ions in an electrolytic solution employed
for electrowinning, electrolytic solutions may include a sulfuric
acid based electrolytic solution with an electrolyte component
mainly composed of sulfuric acid, a chloride based electrolytic
solution with an electrolyte component mainly composed of
hydrochloric acid or chloride, and in addition to these solutions,
various types of electrolytic solutions based on an aqueous solution
with pH adjusted to acidic or basic.
[0003]
The energy consumed in electrowinning is the product
of electrolytic voltage and the amount of electricity used for
energization, so that the amount of metal obtained on the cathode
is proportional to the amount of electricity. Thus, the amount of
consumed electric energy required for electrowinning a metal per
unit weight of the metal to be extracted (hereafter referred to
as the electric power consumption rate) decreases with decreasing
electrolytic voltages. This electrolytic voltage is the potential
difference between the anode and the cathode, and the cathode reaction
may differ depending on the metal obtained on the cathode, so that
the potential of the cathode may differ depending on the type of
the reaction. On the other hand, when illustrated by the type of
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the electrolytic solutions mentioned above, the anode reaction is
the occurrence of oxygen for the sulfuric acid based electrolytic
solution and the occurrence of chlorine for the chloride based
electrolytic solution. For example, in the electrowinning which
is currently commercially available, the sulfuric acid based
electrolytic solution is used for electrowinning a metal such as
copper, zinc, nickel, or cobalt. When the sulfuric acid based
electrolytic solution is used, the potential of the anode when oxygen
occurs varies depending on the material of the anode. For example,
a comparison between materials with a high and low catalytic activity
for the occurrence of oxygen shows that the higher the catalytic
activity of the material, the lower the potential of the anode.
Thus, to reduce the electric power consumption rate for
electrowinning in the same electrolytic solution, it is critical
and necessary to employ a material of a high catalytic activity
for the anode so as to reduce the potential of the anode.
[0004]
Furthermore, the anode for electrowinning in the sulfuric
acid based electrolytic solution is required not only to have a
high catalytic activity for the occurrence of oxygen but also to
have a low catalytic activity, contrary to the case of the occurrence
of oxygen, for a reaction that possibly occurs on the anode (hereafter
referred to as the side reaction) other than the occurrence of oxygen.
For example, in the electrowinning of zinc, copper, cobalt, or nickel,
etc., the electrolytic solution may contain metal ions other than
an essential component therein such as zinc ions, copper ions, cobalt
ions, or nickel ions. Such metal ions known include, e . g. , manganese
ions and lead ions. In the electrowinning in electrolytic solution
containing manganese ions or lead ions, oxidation of plus divalent
manganese ions occurs so as to deposit, on the anode, a manganese
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;
_ .
compound such as manganese oxyhydroxide (MnO0H) or manganese dioxide
(Mn02) , or oxidation of plus divalent lead ions occurs so as to deposit
lead dioxide (Pb02) on the anode. These reactions occur on the anode
at the same time as the occurrence of oxygen as the anode reaction
in the sulfuric acid based electrolytic solution. However, the
manganese compound or the lead dioxide have a low catalytic activity
for the occurrence of oxygen and a lower electrical conductivity,
thus inhibiting the reaction for the occurrence of oxygen on the
anode. This will lead to an increase in the potential of the anode,
causing the electrolytic voltage to be increased. Furthermore, for
example, suppose that not metal ions to be extracted by the
electrowinning but cobalt ions as an additive component to the
electrolytic solution are added to the electrolytic solution. In
this case, not only does oxygen occur on the anode but also oxidation
of plus divalent cobalt ions occur as the side reaction, causing
cobalt oxyhydroxide (0000H) produced thereby to be deposited on
the anode. This in turn causes an increase in the electrolytic
voltage in the same manner as the aforementioned deposition of the
manganese compound or the lead dioxide on the anode. The
aforementioned deposition and accumulation of metal oxide or metal
oxyhydroxide on the anode by the side reaction cause an increase
in the electrolytic voltage and at the same time, degradation in
service life and durability of the anode.
[0005] For the aforementioned reasons, the anode for
electrowinning in the sulfuric acid based electrolytic solution
is required to be made of a material which is adopted to have the
following features:
1) A high catalytic activity for the occurrence of oxygen;
2) A low catalytic activity for a side reaction of depositing metal
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oxide or metal oxyhydroxide on the anode and for a side reaction
of allowing a deposit to be adhered or accumulated on the anode
even when no metal component is contained;
3) Thus, a high selectivity for the occurrence of oxygen;
4) As a result, the anode is at a low potential, in other words,
the overvoltage for the anode reaction is low, and no increase in
the anode potential is caused by the effects of a side reaction
even when the electrowinning is continued;
5) Thus, the electrolytic voltage is low and the low electrolytic
voltage is maintained even when the electrowinning is continued,
thereby reducing the electric power consumption rate for
electrowinning a target metal;
6) At the same time, no degradation in the service life and durability
of the anode is caused by the effects of a side reaction; and
7) A high durability for the occurrence of oxygen.
[0006] On
the other hand, typical anodes to be used as the anode
for electrowinning in the sulfuric acid based electrolytic solution
may include a lead electrode, a lead alloy electrode, or an electrode
(hereafter referred to as the coated titanium electrode) for which
a titanium substrate is coated with a catalytic layer of a platinum
family metal or a platinum family metal oxide or a mixture or a
composite oxide of these metals or oxides, etc. A specific example
of the coated titanium electrode is a titanium electrode coated
with a catalytic layer containing iridium oxide, and in particular,
a coated titanium electrode has been used which is coated with a
catalytic layer of an oxide mixture of iridium oxide and tantalum
oxide or a catalytic layer of the oxide mixture further mixed with
another metal or metal oxide. Furthermore, taking examples of the
coated titanium electrode not only for the electrowinning but also
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for other fields of application, disclosed in Patent Literature
_
1 to Patent Literature 7 are coated titanium electrodes which are
used as the anode for various types of electrolytic processes in
an aqueous solution, such as electroplating, manufacturing of
electrolytic metal foil, common salt electrolysis, manufacturing
of an electrolytic solution, or manufacturing of an electrolytic
function solution. Note that the anodes disclosed in Patent
Literature 1 to Patent Literature 7 include those that are employed
not only for producing oxygen but also those used for producing
chlorine. Furthermore, disclosed in Patent Literature 8 are a
precursor solution that is used when the coated titanium electrode
for electrowinning is manufactured by thermal decomposition and
a method for preparing the precursor solution. The inventor of the
present application discloses, in Patent Literature 9 and Patent
Literature 10, an anode for electrowinning, including a coated
titanium electrode, and a method for electrowinning using the anode.
Citation List
Patent Literature
[0007] PTL 1: Japanese Published Unexamined Patent Application
No. H06-101083
PTL 2: Japanese Published Unexamined Patent Application No.
H09-87896
PTL 3: Japanese Published Unexamined Patent Application No.
2007-246987
PTL 4: Japanese Published Unexamined Patent Application No.
2008-050675
PTL 5: Japanese Published Unexamined Patent Application No.
2010-507017
PTL 6: Japanese Published Unexamined Patent Application No.
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2011-017084
PTL 7: Japanese Published Unexamined Patent Application No.
2011-503359
PTL 8 : United States Patent Application PublicationNo. 2009/0288958
PTL 9: Japanese Patent No. 4516617
PTL 10: Japanese Patent No. 4516618
Summary of Invention
Technical Problem
[0008] As
described above, in Patent Literature 9, the inventor
of the present application disclosed an anode for electrowinning
zinc with a catalytic layer containing amorphous iridium oxide formed
on a conductive substrate and a method for electrowinning zinc using
the same. It is thereby clearly shown that when compared with a
conventional anode for electrowinning zinc and method for
electrowinning, the anode potential and the electrolytic voltage
may be reduced for the occurrence of oxygen at the time of
electrowinning of zinc and that the deposition of manganese
oxyhydroxide and manganese dioxide that occurs as a side reaction
of the anode may be restrained, etc. Here, the deposition of
manganese oxyhydroxide and manganese dioxide, which is a side
reaction, maybe restrained because the catalytic layer containing
amorphous iridium oxide has a high catalytic activity for the
occurrence of oxygen and thus gives a higher priority to the occurrence
of oxygen than to the side reaction, thus allowing the electric
current at the time of energization to be consumed not for the side
reaction but for the main reaction or the occurrence of oxygen.
That is, the anode for electrowinning in the sulfuric acid based
electrolytic solution could restrain a side reaction by increasing
the catalytic activity for the occurrence of oxygen so as to allow
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oxygen to occur with a higher priority over the side reaction.
Meanwhile, disclosed in Patent Literature 10 are an anode for
electrowinning cobalt with a catalytic layer containing amorphous
ruthenium oxide formed on a conductive substrate and a method for
electrowinning cobalt using the same. It is thereby clearly shown
that when compared with a conventional anode for electrowinning
cobalt in a chloride based electrolytic solution and a method for
electrowinning therein, the anode potential and the electrolytic
voltage may be reduced for the occurrence of chlorine, and the
deposition of cobalt oxyhydroxide that occurs as a side reaction
of the anode may be restrained, etc. In these prior art techniques,
it was found that in the electrowinning of zinc or cobalt in the
sulfuric acid based electrolytic solution, the catalytic layer
containing amorphous iridium oxide selectively has a high catalytic
activity for the occurrence of oxygen on the anode, while in the
electrowinning of cobalt in the chloride based electrolytic solution,
the catalytic layer containing amorphous ruthenium oxide selectively
has a high catalytic activity for the occurrence of chlorine on
the anode.
[0009] However, the electrowinning in the sulfuric acid based
electrolytic solution has been required to further increase the
catalytic activity for the anode reaction, thereby further reducing
the anode potential and accordingly further reducing the
electrolytic voltage. In addition, in the electrowinning of a metal
in the sulfuric acid based electrolytic solution, that is, the
electrowinning with the occurrence of oxygen as an anode reaction,
it has also been required to provide an anode and a method for
electrowinning which may further reduce the electrolytic voltage
even in the electrowinning of other metals, for example, copper
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or nickel, etc. Furthermore, it has also been required to provide
_
a reduced electric power consumption rate for electrowinning in
the sulfuric acid based electrolytic solution as well as to provide
not an anode that has a catalytic layer containing an expensive
metal like iridium as a component but an anode with a catalytic
layer less expensive than that or an anode manufactured at a lower
cost. Furthermore, concerning the method for electrowinning in the
sulfuric acid based electrolytic solution as well, it has been
required to provide a method for electrowinning which may further
reduce the electrolytic voltage and which may reduce the cost of
the anode to thereby perform the electrowinning at a lower cost.
[0010]
The present invention was developed to meet the
aforementioned demands. It is therefore an object of the present
invention to provide an anode for electrowinning in a sulfuric acid
based electrolytic solution, the anode being capable of producing
oxygen at a lower potential when compared with a lead electrode,
a lead alloy electrode, or a coated titanium electrode, thereby
allowing the electrowinning to be performed at a reduced electrolytic
voltage and the electric power consumption rate of a desired metal
to be reduced; being available as an anode for electrowinning of
various types of metals; and at the same time, allowing the catalytic
layer to be provided at a reduced cost and the electrowinning to
be performed in volume with efficiency when compared with the coated
titanium electrode used for electrowinning in the sulfuric acid
based electrolytic solution. It is another object of the present
invention to provide a method for electrowinning in the sulfuric
acid based electrolytic solution, the method being capable of
reducing the potential of the anode and the electrolytic voltage
and thus reducing the electric power consumption rate in the
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electrowinning; and allowing the initial cost and the maintenance
cost of the anode to be reduced, thereby reducing the cost of the
entire electrowinning process.
Solution to Problem
[0011] As a result of intensive studies for solving the
aforementioned problems, the inventor of the present application
has completed the present invention by finding that the
aforementioned problems could be solved by an anode for
electrowinning with a catalytic layer containing amorphous ruthenium
oxide and amorphous tantalum oxide formed on a conductive substrate
and a method for electrowinning using the same.
[0012] That is, to solve the aforementioned conventional
problems, the anode for electrowinning of the present invention
and the method for electrowinning using the same have the following
arrangements.
The anode for electrowinning according to the first aspect
of the present invention is an anode for electrowinning in a sulfuric
acid based electrolytic solution, wherein a catalytic layer
containing amorphous ruthenium oxide and amorphous tantalum oxide
is formed on a conductive substrate.
This arrangement provides the following effects.
(1) The catalytic layer containing amorphous ruthenium oxide and
amorphous tantalum oxide selectively shows a high catalytic activity
for the occurrence of oxygen in the sulfuric acid based electrolytic
solution, allowing the potential of the anode for the occurrence
of oxygen to be considerably reduced.
(2) The anode is capable of producing oxygen at a lower potential
in the sulfuric acid based electrolytic solution than an electrode
with a catalytic layer containing crystalline iridium oxide formed
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.
on a conductive substrate or an electrode with a catalytic layer
_
containing amorphous iridium oxide formed on a conductive substrate;
at the same time, restraining a side reaction and providing a high
catalytic activity for the occurrence of oxygen; when compared with
the case where another anode is used for electrowinning in the sulfuric
acid based electrolytic solution, reducing the electrolytic voltage
irrespective of the type of a metal to be extracted on the cathode.
(3) When compared with the electrowinning in the sulfuric acid based
electrolytic solution using an anode with a catalytic layer
containing amorphous iridium oxide formed and in particular, an
anode with a catalytic layer containing amorphous iridium oxide
and amorphous tantalum oxide formed, the anode of the present
invention is provided with a very high inventive step and novelty
and uniqueness that the potential of the anode may further be reduced
and the electrolytic voltage may also be reduced.
(4) The potential of the anode for electrowinning is reduced for
the occurrence of oxygen and the occurrence of oxygen is given a
higher priority over other side reactions, thereby restraining side
reactions such as the deposition and accumulation of manganese
oxyhydroxide, manganese dioxide, lead dioxide, or cobalt
oxyhydroxide, etc., on the anode for electrowinning.
(5) Since ruthenium is one third or less the price of iridium, a
catalytic activity higher than the catalytic activity for the
occurrence of oxygen in the catalytic layer containing amorphous
iridium oxide and amorphous tantalum oxide may be achieved by a
less expensive catalytic layer that contains amorphous ruthenium
oxide and amorphous tantalum oxide.
[0013]
Here, the conductive substrate may be preferably made
of a valve metal such as titanium, tantalum, zirconium, niobium,
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tungsten, or molybdenum; an alloy predominantly composed of a valve
_
metal such as titanium - tantalum, titanium - niobium, titanium
- palladium, or titanium - tantalum - niobium; an alloy of a valve
metal and a platinum family metal and/or a transition metal; or
an electrically conductive diamond (e.g., boron doped diamond),
but the present invention is not limited thereto. Furthermore, the
conductive substrate may be formed in various shapes such as a
three-dimensional porous structure in which bonded to each other
are metal particles that are plate-shaped, net-shaped, bar-shaped,
sheet-shaped, tubular, linear, porous plate shaped, porous, or
spherical. As the conductive substrate other than the
aforementioned ones, it is also acceptable to employ metals other
than valve metals , such as iron or nickel, or electrically conductive
ceramic which is coatedwith the aforementionedvalvemetals, alloys,
or electrically conductive diamond, etc.
Note that the catalytic layer may contain other components
than amorphous ruthenium oxide and amorphous tantalum oxide so long
as the electrolytic voltage may be reduced in electrowinning.
Such other components may include platinum, iridium, ruthenium,
tungsten, tantalum, iridium oxide, titanium oxide, and niobium
oxide; however, the present invention is not limited thereto.
[0014] The anode for electrowinning according to the second
aspect of the present invention is an anode for electrowinning in
a sulfuric acid based electrolytic solution, wherein a catalytic
layer containing amorphous ruthenium oxide and amorphous tantalum
oxide is formed on a conductive substrate; electrowinning may be
performed at an electrolytic voltage reduced by 0.02 V or greater
when compared with an anode with a catalytic layer of amorphous
iridium oxide and amorphous tantalum oxide formed on a conductive
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substrate, or electrowinning may be performed at an electrolytic
voltage reduced by 0.05 V or greater when compared with an anode
with a catalytic layer of crystalline ruthenium oxide and amorphous
tantalum oxide formed on a conductive substrate.
This arrangement provides the following effect.
(1) Without being affected by a third component (another component)
such as iridium oxide, it is possible to increase the catalytic
activity for the occurrence of oxygen with reliability and reduce
the electrolytic voltage irrespective of the type of a metal to
be extracted on the cathode.
[0015] The anode for electrowinning according to the third
aspect of the present invention is an anode for electrowinning in
a sulfuric acid based electrolytic solution, wherein a catalytic
layer of amorphous ruthenium oxide and amorphous tantalum oxide
is formed on a conductive substrate.
This arrangement provides the following effects.
(1) The catalytic layer of the anode for electrowinning is made
of a mixture of amorphous ruthenium oxide and amorphous tantalum
oxide, thereby providing durability that is applicable to
electrowinning in the sulfuric acid based electrolytic solution.
[0016] Here, in Patent Literature 6, disclosed is one
comparative example in which the coating layer having metal
components of ruthenium and tantalum obtained by thermal
decomposition at 480 C had a very low durability in a sulfuric acid
solution. Such a result is a problem that may occur when crystalline
ruthenium oxide is involved which is obtained by thermal
decomposition at a temperature of at least 350 C or greater. In
contrast to this, the inventor of the present application found
that the anode for electrowinning with a catalytic layer of ruthenium
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oxide made amorphous in a mixture of amorphous tantalum oxide and
the same would not cause a problem with durability to the occurrence
of oxygen, like the one in Patent Literature 6, as the anode for
electrowinning in the sulfuric acid based electrolytic solution.
In particular, the anode for electrowinning of the present invention
provides an outstanding durability in an electrolysis condition
of a current density of 0.1 A/cm2 or less per an electrode area,
the condition being a typical electrolysis condition for the
electrowinning in which the occurrence of oxygen is the anode reaction
in the sulfuric acid based electrolytic solution.
[0017]
Here, the present invention will be described in more
detail below. The catalytic layer containing amorphous ruthenium
oxide and amorphous tantalum oxide may be formed on the conductive
substrate by thermal decomposition, in which a precursor solution
containing ruthenium and tantalum is applied to the conductive
substrate and then heated at a predetermined temperature. Other
than the thermal decomposition, it is also possible to employ various
types of physical vapor deposition and chemical vapor deposition
methods, etc., such as sputtering and CVD. In particular, among
those methods for making the anode for electrowinning of the present
invention, the method for making the anode by thermal decomposition
will be described in more detail. For example, a precursor solution
containing ruthenium and tantalum in a variety of forms such as
an inorganic compound, organic compound, ion, or complex is applied
to a titanium substrate, which is then thermally decomposed at
temperatures in a range lower than at least 350 C, thereby forming
a catalytic layer containing amorphous ruthenium oxide and amorphous
tantalum oxide on the titanium substrate. For example, a butanol
solution in which ruthenium chloride hydrate and tantalum chloride
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=
are dissolved is employed as a precursor solution, which is then
applied to the titanium substrate and thermally decomposed. At this
time, for example, if the molar ratio between ruthenium and tantalum
in the butanol solution is 30:70, the catalytic layer of a mixture
of amorphous ruthenium oxide and amorphous tantalum oxide is formed
at a thermal decomposition temperature of 280 C. Furthermore, by
thermal decomposition at 260 C after the application of the
aforementioned precursor solution, the catalytic layer of a mixture
of amorphous ruthenium oxide and amorphous tantalum oxide may also
be formed in the same manner.
[0018]
When the catalytic layer containing amorphous ruthenium
oxide and amorphous tantalum oxide is formed on a conductive substrate
by thermal decomposition, it varies whether amorphous ruthenium
oxide and amorphous tantalum oxide are contained in the catalytic
layer, depending on the molar ratio between ruthenium and tantalum
contained in the precursor solution to be applied to the titanium
substrate and the thermal decomposition temperature. Furthermore,
when a metal component other than ruthenium and tantalum is contained
in the precursor solution, it also varies depending on the type
of the metal component and the molar ratio of the metal component
to all metal components contained in the precursor solution, etc.
For example, when the same components other than metal components
are contained in the precursor solution and only ruthenium and
tantalum are contained as metal components, a lower molar ratio
of ruthenium in the precursor solution would tend to show a greater
range of thermal decomposition temperatures in which the catalytic
layer containing amorphous ruthenium oxide and amorphous tantalum
oxide is obtained. Furthermore, the conditions for forming the
catalytic layer containing amorphous ruthenium oxide and amorphous
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tantalum oxide also vary depending not only on the molar ratio between
such metal components but also on the method for preparing and the
material of the precursor solution, for example, raw materials of
ruthenium and tantalum used to prepare the precursor solution, the
type of a solvent, and the type and concentration of an additive
that may be added to accelerate thermal decomposition.
[0019] Thus, for the anode for electrowinning of the present
invention, the conditions for forming, by thermal decomposition,
the catalytic layer containing amorphous ruthenium oxide and
amorphous tantalum oxide are not limited to the use of the butanol
solvent in the thermal decomposition method mentioned above, the
molar ratio between ruthenium and tantalum, and the range of thermal
decomposition temperatures associated therewith. The
aforementioned conditions are only an example, and the method for
manufacturing the anode for electrowinning of the present invention
may include any methods other than those mentioned above so long
as the methods are available to forming the catalytic layer containing
amorphous ruthenium oxide and amorphous tantalum oxide on the
conductive substrate. For example, as a matter of course, such
methods may include one which is disclosed in Patent Literature
8 that involves a heating step in the preparation process of the
precursor solution. Note that the formation of the catalytic layer
containing amorphous ruthenium oxide and amorphous tantalum oxide
may be known from the fact that by a typically employed X-ray
diffraction method, the diffraction peak corresponding to ruthenium
oxide is not observed and the diffraction peak corresponding to
tantalum oxide is not observed.
[0020] The invention according to the fourth aspect is the anode
for electrowinning according to any one of the first to third aspects,
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,
..
..
wherein the molar ratio between ruthenium and tantalum in the
_
catalytic layer is 30:70.
This arrangement provides the following effect in addition
to those obtained by any one of the first to third aspects.
(1) When the same components other than metal components are contained
in the precursor solution and only ruthenium and tantalum are
contained as metal components, a lower molar ratio of ruthenium
in the precursor solution would tend to show a greater range of
thermal decomposition temperatures in which the catalytic layer
containing amorphous ruthenium oxide and amorphous tantalum oxide
is obtained, thus providing an outstanding mass productivity.
[0021]
The invention according to the fifth aspect is the anode
for electrowinning according to any one of the first to fourth aspects,
wherein an intermediate layer is formed between the catalytic layer
and the conductive substrate.
This arrangement provides the following effects in addition
to those obtained in any one of the first to fourth aspects.
(1) The intermediate layer is formed between the catalytic layer
and the conductive substrate and at the same time, the surface of
the conductive substrate is coated, thereby preventing the
electrolytic solution from reaching the conductive substrate even
when the electrolytic solution penetrates into the catalytic layer.
Thus, the conductive substrate will never be corroded by the acidic
electrolytic solution, thereby preventing an unsmooth current flow
caused by corrosion between the conductive substrate and the
catalytic layer.
(2) When an intermediate layer is formed which is made of oxide
or composite oxide and which is different from the catalytic layer
of the anode for electrowinning of the present invention, the
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catalytic activity for the occurrence of oxygen is low when compared
with the catalytic layer containing amorphous ruthenium oxide and
amorphous tantalum oxide. Thus, even when the electrolytic solution
penetrates the catalytic layer and reaches the intermediate layer,
the intermediate layer has a higher durability than the catalytic
layer and thus protects the conductive substrate because oxygen
does not occur on a priority basis in the intermediate layer as
compared to the catalytic layer. At the same time, the conductive
substrate is coated with such an oxide or composite oxide having
a higher durability, thereby further preventing the corrosion of
the conductive substrate by the electrolytic solution when compared
with the case of no intermediate layer provided.
[0022]
Here, the intermediate layer has a low catalytic activity
for the occurrence of oxygen when compared with the catalytic layer,
but sufficiently coats the conductive substrate, thus restraining
the corrosion of the conductive substrate. The intermediate layer
may be made of, for example, metal, alloy, a carbon based material
such as boron doped diamond, a metal compound such as an oxide and
sulfide, or a composite compound such as a metal composite oxide.
For example, the intermediate layer would be formed of a metal,
in the case of which a thin film of tantalum or niobium, etc., may
be preferably employed . The intermediate layer would also be formed
of an alloy, in the case of which preferably employed are, for example,
tantalum, niobium, tungsten, molybdenum, titanium, or platinum.
Furthermore, an intermediate layer made of a carbon based material
such as boron doped diamond also has the same effects. The
intermediate layer made of the aforementionedmetal, alloy, or carbon
based material may be formed by various types of physical vapor
deposition or chemical vapor deposition methods such as thermal
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decomposition, sputtering, and CVD, etc., or by a variety of methods
_
such as hot dipping or electroplating, etc. For example, the
intermediate layer made of a metal compound such as an oxide or
sulfide or a metal composite oxide may be preferably an intermediate
layer made of an oxide containing crystalline iridium oxide, etc.
In particular, when the catalytic layer is made by thermal
decomposition, it is advantageous, from the viewpoint of simplifying
the manufacturing process of the anode for electrowinning, to form
the intermediate layer of an oxide or composite oxide in the same
manner by thermal decomposition.
[0023] The invention according to the sixth aspect is the anode
for electrowinning according to the fifth aspect and is adopted
such that the intermediate layer is made of tantalum, niobium,
tungsten, molybdenum, titanium, or platinum or any one of alloys
of these metals.
This arrangement provides the following effect in addition
to those obtained in the fifth aspect.
(1) The intermediate layer may be formed in volume with efficiency
by various types of physical vapor deposition or chemical vapor
deposition methods such as thermal decomposition, sputtering, and
CVD or by a variety of methods such as hot dipping and electroplating.
[0024] The invention according to the seventh aspect is the
anode for electrowinning according to the fifth aspect, wherein
the intermediate layer contains crystalline iridium oxide and
amorphous tantalum oxide.
This arrangement provides the following effect in addition
to those obtained in the fifth aspect.
(1) Since ruthenium oxide in the catalytic layer and iridium oxide
in the intermediate layer belong to the same crystalline family
19
CA 02831273 2013-11-18
and have a close interatomic distance, the intermediate layer and
the catalytic layer formed thereon have a good adhesion therebetween,
thus providing a distinctively improved durability.
[0025] Here, the intermediate layer containing crystalline
iridium oxide and amorphous tantalum oxide may be manufactured by
thermal decomposition, in which a precursor solution containing
iridium and tantalum is applied to the conductive substrate and
then heated at a predetermined temperature. The intermediate layer
may also be manufactured by, for example, various types of physical
vapor deposition or chemical vapor deposition methods such as by
sputtering or CVD. For example, in the case of the thermal
decomposition, preferable is such an intermediate layer which is
made of crystalline iridium oxide and amorphous tantalum oxide that
are obtained by thermally decomposing the precursor solution
containing iridium and tantalum at a temperature from 400 C to 550 C.
[0026] The invention according to the eighth aspect is the anode
for electrowinning according to any one of the first to seventh
aspects, wherein a metal extracted by electrowinning is any one
of copper, zinc, nickel, cobalt, platinum, gold, silver, indium,
lead, ruthenium, rhodium, palladium, and iridium.
This arrangement provides the following effect in addition
to those obtained in any one of the first to seventh aspects.
(1) Since oxygen is produced at a lower potential, the electrolytic
voltage in electrowinning may be lowered so as to reduce the electric
power consumption rate of a metal. Thus, the anode is available
as an anode for electrowinning of various types of metals, thus
enabling outstanding general-purpose use.
[0027] The method for electrowinning according to the ninth
aspect of the present invention is a method for electrowinning in
CA 02831273 2013-11-18
_
the sulfuric acid based electrolytic solution, wherein a desired
metal is extracted using the anode for electrowinning according
to any one of the first to eighth aspects.
This arrangement provides the following effect.
(1) In the method for electrowinning in the sulfuric acid based
electrolytic solution, the potential of the anode for electrowinning
and the electrolytic voltage are reduced, and thus the electric
power consumption rate for electrowinning may be reduced.
Furthermore, the initial cost and the maintenance cost for the anode
for electrowinning are also reduced, thus reducing the cost of the
entire electrowinning process.
[0028] The invention according to the tenth aspect is the method
for electrowinning according to the ninth aspect, wherein a metal
extracted by electrowinning is any one of copper, zinc, nickel,
cobalt, platinum, gold, silver, indium, lead, ruthenium, rhodium,
palladium, and iridium.
(1) The electrolytic voltage is reduced and the reduced electrolytic
voltage is maintained even when the electrowinning is continued.
Thus, the electric power consumption rate for electrowinning a target
metal is reduced, andno degradation in the service life and durability
of the anode for electrowinning is caused by the effects of a side
reaction, so that the target metal may be extracted by electrowinning
with stability for a long period of time. This allows electrowinning
to be performed with outstanding efficiency and stability.
Advantageous Effects of Invention
[0029] The present invention provides the effects listed below.
1) In the electrowinning of a metal in a sulfuric acid based
electrolytic solution, the potential at which oxygen is produced
on the anode for electrowinning may be lowered when compared with
21
CA 02831273 2013-11-18
. '
a conventional one. Thus, irrespective of the type of the metal
_
to be extracted, the electrolytic voltage for the electrowinning
may be reduced, thereby significantly reducing the electric power
consumption rate.
2) Furthermore, since the potential at which oxygen is produced
on the anode for electrowinning may be lowered when compared with
a conventional one, various side reactions that would otherwise
possibly occur on the anode for electrowinning may be restrained.
Thus, in long-term electrowinning, the electrolytic voltage may
be prevented from being increased.
3) In addition to the aforementioned effects, the present invention
provides the effect to eliminate or alleviate the need for removing
oxide, oxyhydroxide, and other compounds which would be otherwise
deposited or accumulated by a side reaction on the anode for
electrowinning. Thus, damage to the anode for electrowinning which
wouldbe causedby such work is restrained, thus providing an elongated
service life to the anode for electrowinning.
4) In addition to the aforementioned effects, the present invention
provides the effect to eliminate or reduce the need for removing
oxide, oxyhydroxide, and other compounds which would be otherwise
deposited or accumulated by a side reaction on the anode for
electrowinning. Thus, maintenance or replacement of the anode for
electrowinning may be restrained or alleviated in electrowinning.
Furthermore, such removal work restrains the necessity of suspending
the electrowinning, thereby enabling electrowinning to be performed
continuously with an improved stability.
5) In addition to the aforementioned effects, the present invention
provides the effect in which the deposits would never restrict the
effective surface area of the anode for electrowinning, or the area
22
CA 02831273 2013-11-18
µ
_ -
of the anode available for electrowinning may be prevented from
_
being unevenly formed, since the deposits on the anode for
electrowinning are restrained. It is thus possible to prevent a
metal from being unevenly deposited on the cathode and an unsmooth
metal from being produced thereon, thereby restraining the
difficulty of reproducing the metal or degradation in the quality
of the metal to be extracted.
6) Furthermore, since metal is not grown unevenly on the cathode
for the aforementioned reasons, the metal grown on the cathode may
be prevented from reaching and short-circuiting the anode for
electrowinning. It is thus possible to prevent unavailability of
electrowinning. Furthermore, since the uneven growth and dendritic
growth of a metal on the cathode are restrained, the inter-electrode
distance between the anode for electrowinning and the cathode may
be reduced, and an increase in the electrolytic voltage to be caused
by an ohmic loss in the electrolytic solution may be restrained.
7) Furthermore, since various problems that would be otherwise caused
by deposits resulting from a side reaction on the anode for
electrowinning are resolved as described above, it is possible to
continuously perform electrowinning with stability and reduce
maintenance and management work in electrowinning, allowing the
product management of the extracted metal to be performed with ease.
Furthermore, the cost of the anode for electrowinning for a long-term
electrowinning may be reduced.
8) Furthermore, according to the present invention, when compared
with a conventional coated titanium electrode with a catalytic layer
containing iridium oxide, use of ruthenium oxide alleviates the
cost of the catalytic layer; and a reduced thermal decomposition
temperature reduces the cost of the step of forming the catalytic
23
CA 02831273 2013-11-18
t
layer as well.
9) In addition to the aforementioned effects, the present invention
provides the effect to reduce the manufacturing cost of the entire
electrowinning in the electrowinning of various metals in a sulfuric
acid based electrolytic solution.
Brief Description of Drawings
[0030] Fig. 1 is a graph of an X-ray diffraction image obtained
from the anodes for electrowinning according to Example 1, Example
2, and Comparative Example 1.
Description of Examples
[0031] Hereinafter, the present invention will be described
in more detail in accordance with the Examples and Comparative
Examples; however, the present invention is not limited to the
following Examples. For example, the present invention is also
applicable to electrowinning of other metals than zinc, copper,
and cobalt.
[0032] [Electrowinning of zinc]
Example 1
[0033] A commercially available titanium plate (5 cm in length,
1 cm in width, 1 mm in thickness) was immersed and etched in a 10%
oxalic acid solution at 90 C for 60 minutes and then washed and
dried. Next, prepared was an application liquid which was obtained
by adding ruthenium trichloride trihydrate (RuC13 =3H20) and tantalum
pentachloride (TaC15) to a butanol (n-C4H9OH) solution containing
6 vol% concentrated hydrochloric acid so that the molar ratio between
ruthenium and tantalum is 30:70 and the total of rutheniumand tantalum
is 50 g/L in terms of metal. This application liquid was applied
to the titanium plate dried as mentioned above, dried at 120 C for
10minutes, and then thermally decomposed for 20minutes in an electric
24
CA 02831273 2013-11-18
furnace that was held at 260 C. This series of application, drying,
and thermal decomposition was repeated five times in total in order
to prepare an anode for electrowinning according to Example 1, the
anode having a catalytic layer formed on the titanium plate that
was a conductive substrate.
[0034] An X-ray diffraction analysis of the structure of the
anode for electrowinning according to Example 1 shows that as shown
in Fig. 1, the diffraction peak equivalent to Ru02 was not observed
in the X-ray diffraction image, and the diffraction peak equivalent
to Ta205 was not observed, either. Note that the diffraction peak
of Ti was observed; however, this was caused by the titanium plate.
That is, the anode for electrowinning according to Example 1 had
the catalytic layer containing amorphous ruthenium oxide and
amorphous tantalum oxide formed on the titanium plate.
[0035] Prepared was an electrolytic solution of a 0.80 mol/L
of ZnSO4 and 2.0 mol/L of sulfuric acid, and a zinc plate (2 cm x
2 cm) was immersed as the cathode in this electrolytic solution.
Furthermore, the anode for electrowinning according to Example 1
above was buried in a polytetrafluoroethylene holder, and then,
with the electrode area in contact with the electrolytic solution
restricted to 1 cm2, was disposed in the same electrolytic solution
so as to be opposed to the aforementioned cathode with a predetermined
inter-electrode distance. Then, the inter-terminal voltage
(electrolytic voltage) was measured between the anode for
electrowinning and the cathode while performing electrowinning of
zinc by flowing, between the anode for electrowinning and the cathode,
an electrolysis current at a current density of either 10 mA/cm2
or 50 mA/cm2 with respect to the electrode area of the anode for
electrowinning. Note that the electrolytic solution was at 40 C.
CA 02831273 2013-11-18
Example 2
[0036] An anode for electrowinning according to Example 2 was
manufactured by the same method as that of Example 1 except that
the catalytic layer was formed at a thermal decomposition temperature
of not 260 C but 280 C. An X-ray diffraction analysis of the
structure of the anode for electrowinning according to Example 2
shows that as shown in Fig. 1, the diffraction peak equivalent to
Ru02 was not observed, and the diffraction peak equivalent to Ta205
was not observed, either. Note that the diffraction peak of Ti was
observed; however, this was caused by the titanium plate. That is,
the anode for electrowinning according to Example 2 had the catalytic
layer containing amorphous ruthenium oxide and amorphous tantalum
oxide formed on the titanium plate.
[0037] Prepared was an electrolytic solution of a 0.80 mol/L
of ZnSO4 and 2.0 mol/L of sulfuric acid, and a zinc plate (2 cm x
2 cm) was immersed as the cathode in this electrolytic solution.
Furthermore, the anode for electrowinning according to Example 2
above was buried in a polytetrafluoroethylene holder, and then,
with the electrode area in contact with the electrolytic solution
restricted to 1 cm2, was disposed in the same electrolytic solution
so as to be opposed to the aforementioned cathode with a predetermined
inter-electrode distance. Then, the inter-terminal voltage
(electrolytic voltage) was measured between the anode for
electrowinning and the cathode while performing electrowinning of
zinc by flowing, between the anode for electrowinning and the cathode,
an electrolysis current at a current density of either 10 mA/cm2
or 50 mA/cm2 with respect to the electrode area of the anode for
electrowinning. Note that the electrolytic solution was at 40 C.
[0038] (Comparative Example 1)
26
CA 02831273 2013-11-18
An anode for electrowinning according to Comparative Example
1 was manufactured by the same method as that of Example 1 except
that the catalytic layer was formed at a thermal decomposition
temperature of not 260 C but 360 C. An X-ray diffraction analysis
of the structure of the anode for electrowinning according to
Comparative Example 1 shows that as shown in Fig. 1, the diffraction
peak equivalent to Ru02 was observed, but the diffraction peak
equivalent to Ta205 was not observed. Note that the diffraction
peak of Ti was observed; however, this was caused by the titanium
plate. That is, the anode for electrowinning according to
Comparative Example 1 had the catalytic layer containing crystalline
ruthenium oxide and amorphous tantalum oxide formed thereon.
[0039] Prepared was an electrolytic solution of a 0.80 mol/L
of ZnSO4 and 2.0 mol/L of sulfuric acid, and a zinc plate (2 cm x
2 cm) was immersed as the cathode in this electrolytic solution.
Furthermore, the anode for electrowinning according to Comparative
Example 1 above was buried in a polytetrafluoroethylene holder,
and then, with the electrode area in contact with the electrolytic
solution restricted to 1 cm2, was disposed in the same electrolytic
solution so as to be opposed to the aforementioned cathode with
a predetermined inter-electrode distance. Then, the inter-terminal
voltage (electrolytic voltage) was measured between the anode for
electrowinning and the cathode while performing electrowinning of
zinc by flowing, between the anode for electrowinning and the cathode,
an electrolysis current at a current density of either 10 mA/cm2
or 50 mA/cm2 with respect to the electrode area of the anode for
electrowinning. Note that the electrolytic solution was at 40 C.
[0040] (Comparative Example 2)
A commercially available titanium plate (5 cm in length, 1
27
CA 02831273 2013-11-18
cm in width, 1 mm in thickness) was immersed and etched in a 10%
oxalic acid solution at 90 C for 60 minutes and then washed and
dried. Next, prepared was an application liquid which was obtained
by adding hexachloroiridic acid hexahydrate (H2IrC16.6H20) and
tantalum chloride (TaC15) to a butanol (n-C4H9OH) solution containing
6 vol% concentrated hydrochloric acid so that the molar ratio between
iridium and tantalum was 80:20 and the total of iridium and tantalum
was 70 g/L in terms of metal. This application liquid was applied
to the titanium plate dried as mentioned above, dried at 120 C for
minutes, and then thermally decomposed for 20 minutes in the
electric furnace that was held at 360 C. This series of application,
drying, and thermal decomposition was repeated five times in total
in order to prepare an anode for electrowinning according to
Comparative Example 2, the anode having a catalytic layer formed
on the titanium plate that was a conductive substrate.
[0041] An X-ray diffraction analysis of the structure of the
anode for electrowinning according to Comparative Example 2 shows
that, in the X-ray diffraction image, the diffraction peak equivalent
to 1r02 was not observed, and the diffraction peak equivalent to
Ta205 was not observed, either. That is, the anode for electrowinning
according to Comparative Example 2 had the catalytic layer containing
amorphous iridium oxide and amorphous tantalum oxide formed on the
titanium plate.
[0042] Prepared was an electrolytic solution of a 0.80 mol/L
of ZnSO4 and 2.0 mol/L of sulfuric acid, and a zinc plate (2 cm x
2 cm) was immersed as the cathode in this electrolytic solution.
Furthermore, the anode for electrowinning according to Comparative
Example 2 above was buried in a polytetrafluoroethylene holder,
and then, with the electrode area in contact with the electrolytic
28
CA 02831273 2013-11-18
=
solution restricted to 1 cm2, was disposed in the same electrolytic
solution so as to be opposed to the aforementioned cathode with
a predetermined inter-electrode distance. Then, the inter-terminal
voltage (electrolytic voltage) was measured between the anode for
electrowinning and the cathode while performing electrowinning of
zinc by flowing, between the anode for electrowinning and the cathode,
an electrolysis current at a current density of either 10 mA/cm2
or 50 mA/cm2 with respect to the electrode area of the anode for
electrowinning. Note that the electrolytic solution was at 40 C.
[0043] The inter-terminal voltages for electrowinning using
the anode for electrowinning according to Example 1, Example 2,
Comparative Example 1 and Comparative Example 2 above are as shown
in Table 1 to Table 4.
[0044] [Table 1]
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 1
Example 1
Example 1 - Example 1
mA/cm2 2.28 V 2.45 V 0.17 V
50 mA/cm2 2.41 V 2.60 V 0.19 V
[0045] [Table 2]
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 2
Example 1
Example 2 - Example 1
10 mA/cm2 2.28 V 2.34 V 0.06 V
50 mA/cm2 2.41 V 2.46 V 0.05 V
[0046] [Table 3]
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 1
Example 2
Example 1 - Example 2
10 mA/cm2 2.30 V 2.45 V 0.15 V
50 mA/cm2 2.40 V 2.60 V 0.20 V
[0047] [Table 4]
29
CA 02831273 2013-11-18
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 2
Example 2
Example 2 - Example 2
mA/cm2 2.30 V 2.34 V 0.04 V
50 mA/cm2 2.40 V 2.46 V 0.06 V
[0048] As shown in Table 1, in the electrowinning of zinc, when
the anode for electrowinning according to Example 1 was used in
which the catalytic layer containing amorphous ruthenium oxide and
amorphous tantalum oxide was formed by thermal decomposition at
260 C, the electrolytic voltage was lower by 0.17 V to 0.19 V when
compared with the case where the anode for electrowinning according
to Comparative Example 1 was used in which the catalytic layer
containing crystalline ruthenium oxide and amorphous tantalum oxide
was formed by thermal decomposition at 360 C. Furthermore, as shown
in Table 2, when the anode for electrowinning according to Example
1 was used, the electrolytic voltage was lower by 0.05 V to 0.06
V when compared with the case where the anode for electrowinning
according to Comparative Example 2 was used in which the catalytic
layer containing amorphous iridium oxide and amorphous tantalum
oxide was formed. That is, when the anode for electrowinning (Example
1) was used in which the catalytic layer containing amorphous
ruthenium oxide and amorphous tantalum oxide was formed, the
electrolytic voltage was significantly reduced when compared with
the case where the anode for electrowinning (Comparative Example
1) was used in which the catalytic layer containing crystalline
ruthenium oxide and amorphous tantalum oxide was formed.
Furthermore, the electrolytic voltage was further reduced when
compared with the case where the anode for electrowinning
(Comparative Example 2) was used in which the catalytic layer
containing amorphous iridium oxide and amorphous tantalum oxide
CA 02831273 2013-11-18
was formed.
[0049] Furthermore, as shown in Table 3, in the electrowinning
of zinc, when the anode for electrowinning according to Example
2 was used in which the catalytic layer containing amorphous ruthenium
oxide and amorphous tantalum oxide was formed by thermal
decomposition at 280 C, the electrolytic voltage was lower by 0.15
V to 0.20 V when compared with the case where the anode for
electrowinning according to Comparative Example 1 was used in which
the catalytic layer containing crystalline ruthenium oxide and
amorphous tantalum oxide was formed by thermal decomposition at
360 C. Furthermore, as shown in Table 4, when the anode for
electrowinning according to Example 2 was used, the electrolytic
voltage was lower by 0.04 V to 0.06 V when compared with the case
where the anode for electrowinning according to Comparative Example
2 was used in which the catalytic layer containing amorphous iridium
oxide and amorphous tantalum oxide was formed. That is, when the
anode for electrowinning (Example 2) was used in which the catalytic
layer containing amorphous ruthenium oxide and amorphous tantalum
oxide was formed, the electrolytic voltage was significantly reduced
when compared with the case where the anode for electrowinning
(Comparative Example 1) was used in which the catalytic layer
containing crystalline ruthenium oxide and amorphous tantalum oxide
was formed. Furthermore, the electrolytic voltage was further
reduced when compared with the case where the anode for electrowinning
(Comparative Example 2) was used in which the catalytic layer
containing amorphous iridium oxide and amorphous tantalum oxide
was formed.
[0050] [Electrowinning of copper]
Example 3
31
CA 02831273 2013-11-18
[0051] The electrolytic solution of Example 1 was replaced with
an electrolytic solution of 0.60 mol/L of CuSO4 and 0.90 mol/L of
sulfuric acid, and with other conditions kept the same as those
of Example 1, the inter-terminal voltage (electrolytic voltage)
was measured between the anode for electrowinning and the cathode
while performing electrowinning of copper.
Example 4
[0052] The electrolytic solution of Example 2 was replaced with
an electrolytic solution of 0.60 mol/L of CuSO4 and 0.90 mol/L of
sulfuric acid, and with other conditions kept the same as those
of Example 2, the inter-terminal voltage (electrolytic voltage)
was measured between the anode for electrowinning and the cathode
while performing electrowinning of copper.
[0053] (Comparative Example 3)
The electrolytic solution of Comparative Example 1 was replaced
with an electrolytic solution of 0.60 mol/L of CuSO4 and 0.90 mol/L
of sulfuric acid, and with other conditions kept the same as those
of Comparative Example 1, the inter-terminal voltage (electrolytic
voltage) was measured between the anode for electrowinning and the
cathode while performing electrowinning of copper.
[0054] (Comparative Example 4)
The electrolytic solution of Comparative Example 2 was replaced
with an electrolytic solution of 0.60 mol/L of CuSO4 and 0.90 mol/L
of sulfuric acid, and with other conditions kept the same as those
of Comparative Example 2, the inter-terminal voltage (electrolytic
voltage) was measured between the anode for electrowinning and the
cathode while performing electrowinning of copper.
[0055] The inter-terminal voltages for electrowinning using
the anode for electrowinning according to Example 3, Example 4,
32
CA 02831273 2013-11-18
Comparative Example 3 and Comparative Example 4 above are as shown
in Table 5 to Table 8.
[0056] [Table 5]
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 3
Example 3
Example 3 - Example 3
mA/cm2 1.17 V 1.28 V 0.11 V
50 mA/cm2 1.30 V 1.46 V 0.16 V
[0057] [Table 6]
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 4
Example 3
Example 4 - Example 3
10 mA/cm2 1.17 V 1.22 V 0.05 V
50 mA/cm2 1.30 V 1.37 V 0.07 V
[0058]
33
CA 02831273 2013-11-18
[Table 7]
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 3
Example 4
Example 3 - Example 4
mA/cm2 1.18 V 1.28 V 0.10 V
50 mA/cm2 1.30 V 1.46 V 0.16 V
[0059] [Table 8]
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 4
Example 4
Example 4 - Example 4
10 mA/cm2 1.18 V 1.22 V 0.04 V
50 mA/cm2 1.30 V 1.37 V 0.07 V
[0060] As shown in Table 5, in the electrowinning of copper,
when the anode for electrowinning according to Example 3 was used
in which the catalytic layer containing amorphous ruthenium oxide
and amorphous tantalum oxide was formed by thermal decomposition
at 260 C, the electrolytic voltage was lower by 0.11 V to 0.16 V
when compared with the case where the anode for electrowinning
according to Comparative Example 3 was used in which the catalytic
layer containing crystalline ruthenium oxide and amorphous tantalum
oxide was formed by thermal decomposition at 360 C. Furthermore,
as shown in Table 6, when the anode for electrowinning according
to Example 3 was used, the electrolytic voltage was lower by 0.05
V to 0.07 V when compared with the case where the anode for
electrowinning according to Comparative Example 4 was used in which
the catalytic layer containing amorphous iridium oxide and amorphous
tantalumoxide was formed. That is, when the anode for electrowinning
(Example 3 ) was used in which the catalytic layer containing amorphous
ruthenium oxide and amorphous tantalum oxide was formed, the
electrolytic voltage was significantly reduced when compared with
the case where the anode for electrowinning (Comparative Example
34
CA 02831273 2013-11-18
3) was used in which the catalytic layer containing crystalline
ruthenium oxide and amorphous tantalum oxide was formed.
Furthermore, the electrolytic voltage was further reduced when
compared with the case where the anode for electrowinning
(Comparative Example 4) was used in which the catalytic layer
containing amorphous iridium oxide and amorphous tantalum oxide
was formed.
[0061]
Furthermore, as shown in Table 7, in the electrowinning
of copper, when the anode for electrowinning according to Example
4 was used in which the catalytic layer containing amorphous ruthenium
oxide and amorphous tantalum oxide was formed by thermal
decomposition at 280 C, the electrolytic voltage was lower by 0.10
V to 0.16 V when compared with the case where the anode for
electrowinning according to Comparative Example 3 was used in which
the catalytic layer containing crystalline ruthenium oxide and
amorphous tantalum oxide was formed by thermal decomposition at
360 C. Furthermore, as shown in Table 8, when the anode for
electrowinning according to Example 4 was used, the electrolytic
voltage was lower by 0.04 V to 0.07 V when compared with the case
where the anode for electrowinning according to Comparative Example
4 was used in which the catalytic layer containing amorphous iridium
oxide and amorphous tantalum oxide was formed. That is, when the
anode for electrowinning (Example 4) was used in which the catalytic
layer containing amorphous ruthenium oxide and amorphous tantalum
oxide was formed, the electrolytic voltage was significantly reduced
when compared with the case where the anode for electrowinning
(Comparative Example 3) was used in which the catalytic layer
containing crystalline ruthenium oxide and amorphous tantalum oxide
was formed. Furthermore, the electrolytic voltage was further
CA 02831273 2013-11-18
reduced when compared with the case where the anode for electrowinning
_
(Comparative Example 4) was used in which the catalytic layer
containing amorphous iridium oxide and amorphous tantalum oxide
was formed.
[0062] [Electrowinning of cobalt]
Example 5
[0063] The electrolytic solution of Example 1 was replaced with
an electrolytic solution of 0.30 mol/L of CoSO4 and 2.0x10mol/L
of sulfuric acid, and with the conditions kept the same as those
of Example 1 except for a current density of 10 mA/cm2, the
inter-terminal voltage (electrolytic voltage) was measured between
the anode for electrowinning and the cathode while performing
electrowinning of cobalt.
Example 6
[0064] The electrolytic solution of Example 2 was replaced with
an electrolytic solution of 0.30 mol/L of CoSO4 and 2.0x10 mol/L
of sulfuric acid, and with the conditions kept the same as those
of Example 2 except for a current density of 10 mA/cm2, the
inter-terminal voltage (electrolytic voltage) was measured between
the anode for electrowinning and the cathode while performing
electrowinning of cobalt.
[0065] (Comparative Example 5)
The electrolytic solution of Comparative Example 1 was replaced
with an electrolytic solution of 0.30 mol/L of C0SO4 and 2.0x10-3
mol/L of sulfuric acid, and with the conditions kept the same as
those of Comparative Example 1 except for a current density of 10
mA/cm2, the inter-terminal voltage (electrolytic voltage) was
measured between the anode for electrowinning and the cathode while
performing electrowinning of cobalt.
36
CA 02831273 2013-11-18
[0066] (Comparative Example 6)
The electrolytic solution of Comparative Example 2 was replaced
with an electrolytic solution of 0.30 mol/L of CoSO4 and 2.0x10-3
mol/L of sulfuric acid, and with the conditions kept the same as
those of Comparative Example 2 except for a current density of 10
mA/cm2, the inter-terminal voltage (electrolytic voltage) was
measured between the anode for electrowinning and the cathode while
performing electrowinning of cobalt.
[0067] The inter-terminal voltages for electrowinning using
the anode for electrowinning according to Example 5, Example 6,
Comparative Example 5 and Comparative Example 6 above are as shown
in Table 9 to Table 12.
[0068] [Table 9]
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 5
Example 5
Example 5 - Example 5
mA/cm2 1.89 V 1.94 V 0.05 V
[0069] [Table 10]
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 6
Example 5
Example 6 - Example 5
10 mA/cm2 1.89 V 1.91 V 0.02 V
[0070]
37
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[Table 11]
Difference in
Electrolytic voltage electrolytic voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 5
Example 6
Example 5 - Example 6
mA/cm2 1.82 V 1.94 V 0.12 V
[0071] [Table 12]
Difference in electrolytic
Electrolytic voltage voltage
Current
(Degree of improvement)
density
Comparative Comparative Example 6
Example 6
Example 6 - Example 6
10 mA/cm2 1.82 V 1.91 V 0.09 V
[0072] As shown in Table 9, in the electrowinning of cobalt,
when the anode for electrowinning according to Example 5 was used
in which the catalytic layer containing amorphous ruthenium oxide
and amorphous tantalum oxide was formed by thermal decomposition
at 260 C, the electrolytic voltage was lower by 0.05 V when compared
with the case where the anode for electrowinning according to
Comparative Example 5 was used in which the catalytic layer containing
crystalline ruthenium oxide and amorphous tantalum oxide was formed
by thermal decomposition at 360 C. Furthermore, as shown in Table
10, when the anode for electrowinning according to Example 5 was
used, the electrolytic voltage was lower by 0.02 V when compared
with the case where the anode for electrowinning according to
Comparative Example 6 was used in which the catalytic layer containing
amorphous iridium oxide and amorphous tantalum oxide was formed.
That is, when the anode for electrowinning (Example 5) was used
in which the catalytic layer containing amorphous ruthenium oxide
and amorphous tantalum oxide was formed, the electrolytic voltage
was reduced when compared with the case where the anode for
electrowinning (Comparative Example 5) was used in which the
catalytic layer containing crystalline ruthenium oxide and amorphous
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tantalum oxide was formed. Furthermore, the electrolytic voltage
was further reduced when compared with the case where the anode
for electrowinning (Comparative Example 6) was used in which the
catalytic layer containing amorphous iridium oxide and amorphous
tantalum oxide was formed.
[0073]
Furthermore, as shown in Table 11, in the electrowinning
of cobalt, when the anode for electrowinning according to Example
6 was used in which the catalytic layer containing amorphous ruthenium
oxide and amorphous tantalum oxide was formed by thermal
decomposition at 280 C, the electrolytic voltage was lower by 0.12
V when compared with the case where the anode for electrowinning
according to Comparative Example 5 was used in which the catalytic
layer containing crystalline ruthenium oxide and amorphous tantalum
oxide was formed by thermal decomposition at 360 C. Furthermore,
as shown in Table 12, when the anode for electrowinning according
to Example 6 was used, the electrolytic voltage was lower by 0.09
V when compared with the case where the anode for electrowinning
according to Comparative Example 6 was used in which the catalytic
layer containing amorphous iridium oxide and amorphous tantalum
oxide was formed. That is, when the anode for electrowinning (Example
6) was used in which the catalytic layer containing amorphous
ruthenium oxide and amorphous tantalum oxide was formed, the
electrolytic voltage was reduced when compared with the case where
the anode for electrowinning (Comparative Example 5) was used in
which the catalytic layer containing crystalline ruthenium oxide
and amorphous tantalum oxide was formed. Furthermore, the
electrolytic voltage was further reduced when compared with the
case where the anode for electrowinning (Comparative Example 6)
was used in which the catalytic layer containing amorphous iridium
39
CA 02831273 2013-11-18
oxide and amorphous tantalum oxide was formed.
