JPH0689470B2 - Fabrication of oxygen evolution anode consisting of film-forming metal substrate and catalytic oxide coating containing ruthenium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates generally to catalytic oxygen-evolving anodes, and specifically to an acidic electrolyte comprising an anode substrate of a film-forming metal and a ruthenium-containing catalytic oxide. The present invention relates to a method for producing an oxygen-evolving anode having good dimensional stability, which can be applied to a method such as electrolytic extraction of metal from aluminum.

BACKGROUND OF THE TECHNOLOGY Oxygen-evolving anodes are exposed to the significantly more severe oxidizing and corrosive effects of oxygen and corrosive electrolytes generated at the anode. Therefore, in order to industrially apply the oxygen-evolving anode, it is necessary to secure its stable operation as an industrially usable anode and have a sufficiently long industrial service life to make the anode cost economically appropriate. To be able to do so, it must be adequately protected against oxygen generated at the anode.

Electrolytic cells for electrowinning of metal are generally operated at low current densities in order to even out the electrolytic deposition of metal on the cathode surface. Therefore, a very large anode area is required. Moreover, the value of the metal product obtained on the cathode is relatively low relative to the electrode area, so the cost of the anode is particularly limited and if this is economically feasible for electrowinning. There are restrictions to be tightened.

In the past, lead or lead alloy anodes were widely used for electrowinning of metals from sulfate solutions, but this has a high oxygen overvoltage and serious loss of anode material and contaminating metal products obtained at the cathode. There were restrictions. Although the lead-silver alloy anode lowers the oxygen overvoltage to some extent and improves the current efficiency, it still has the above-mentioned restrictions as a whole. Known titanium anodes coated with manganese dioxide or lead dioxide on the outside have high oxygen overvoltage, are unsuitable from the viewpoint of energy economy, and lack long-term service life, and therefore are not suitable for industrial use as oxygen generating anodes. However, it is not appropriate to replace the conventional lead anode, especially when it is widely used.

It has been proposed to coat the titanium anode with a protective interlayer consisting of a platinum group metal, but this too is insufficient to obtain a suitable service life for many industrial uses of the oxygen-evolving anode. is there.

Titanium anodes with good dimensional stability have also been proposed, which have a catalytic oxide which produces oxygen at a lowered potential in order to significantly reduce energy consumption and at the same time protect the substrate from anodization. However, most of the proposed oxygen-evolving anodes are relatively expensive, or their industrial long-term service life is limited, or both of these two reasons combine to make them industrially applicable over a wide range. It is a major obstacle to use.

The main problem in this respect is on the one hand the violent attack of oxygen under extremely harsh operating conditions of the oxygen-evolving anode, and on the other hand its extremely severe economic constraint when using this catalytic anode. In particular, it is important to maintain a high level of long-term catalytic activity and to secure a sufficiently low oxygen potential for a sufficiently long time so that the total cost of the energy consumption can be appropriate due to the total energy saving that can be accommodated during the lifetime of use. It will be difficult.

Since it is difficult for a single substance to meet these requirements for an oxygen generating anode by itself, different anode materials must be appropriately combined in order to meet these requirements as much as possible. It is clear that the selection of a suitable anode material is important for this purpose, and a wide range of materials have been proposed for that purpose. However, the combination of dissimilar anode materials for the production of combined operational anode structures suitable for use as oxygen generating anodes is severely limited.

Titanium forms a stable surface oxide film anodically, and since it has the ability to effectively protect the underlying metal titanium from corrosion, it is a film-forming metal that exhibits remarkable corrosion resistance. Is electrically insulating.

That is, an anode having good dimensional stability generally comprises a titanium base material provided with a catalyst coating capable of operating the anode at a low potential and at the same time protecting the underlying titanium from oxidation. On the other hand, all the electrolyte-exposed parts of the titanium substrate are rapidly passivated by partially forming a stable insulating anodic surface oxide film on the exposed parts. Effectively protected.

It is permanently coated with a catalyst coating and electrically connected to the titanium substrate in order to obtain an anode structure that can be used in operation, and it itself has suitable conductivity, catalytic activity and stability. It must be able to ensure satisfactory and stable anode long-term industrial operation. For this purpose, a suitable anode coating material must be selected and the anode substrate coated in a suitable manner.

It is known that ruthenium exhibits excellent catalytic activity for generating oxygen, but lacks adequate stability and tends to form volatile RuO ₄ under conditions of oxygen generation. Therefore, in order for ruthenium to effectively carry out long-term catalytic oxygen evolution at low potentials, it must be coated and stabilized in a suitable manner. This is a particularly limited technical problem that is the basis of the present invention. The first person to succeed with ruthenium was H. Beer,
He makes a chlorinated anode of good dimensional stability with a mixed oxide coating of the type described in more detail in Example 1 of US Pat. No. 3,632,498. It combines the high stability of rutile TiO ₂ with the excellent electrocatalytic properties of RuO ₂ for chlorine evolution. The mixed oxides simultaneously also increase the oxygen potential, thereby increasing the selectivity of the coating to produce chlorine rather than oxygen. These significant advantages, especially the high stability of such anodes, explain the reason for their remarkable success in the chlorine industry throughout the world over the years. However, anodes with such mixed oxide coatings of TiO ₂ —RuO ₂ appear unsuitable for many applications for oxygen evolution anodes.

To develop an industrially usable catalytic anode for one given application purpose, the industrial performance of the anode depends on the choice of the anode material, its manufacturing method and conditions, the industrial application and operation of the anode. It is a complicated problem because it depends on a number of factors such as conditions that are complicatedly entangled and interrelated.

The large number of patents reflects, in one aspect, great interest and effort in the development of catalytic anodes, while in the other, only a very small number of embodiments have large-scale industrial implementations. It is also noteworthy that it is only described. Considering the complexity of the problem and the interrelated factors, the surprising contradiction that only a very small number of such anodes have been put into practice despite the proposal of innumerable anodes Due to the complexity of this problem and the factors which are not different, every attempt to develop an anode which is fully able to meet the extremely rigorous technical and economic requirements It's a difficult and unpredictable project.

The state of the art for film-forming metal anodes with a catalytic oxide coating consisting of a noble metal oxide and manganese oxide is described in US Pat. No. 4,052,271. Example 8 of this patent specification is a titanium anode having a coating of iridium oxide and manganese oxide. This anode is said to be suitable for the production of peroxide compounds and is believed to have a relatively high oxygen potential for this purpose.
For this reason, it seems unsuitable for many industrial applications as an oxygen evolution anode.

U.S. Pat.No. 4,289,591 attaches a catalytic cathode and a catalytic oxygen generating anode to opposite surfaces of a solid polyelectrolyte ion transport membrane, respectively, and a catalyst comprising ruthenium oxide and manganese oxide is provided on the anode. The present invention relates to a method of generating oxygen. The catalyst was produced by a modification of the Adams method, mixing ruthenium and manganese salts, adding excess sodium nitrate,
The mixture consists of melting at 500 ° C. for 3 hours, washing and drying the residue to give ruthenium manganese oxide powder, which is then bonded to said solid polyelectrolyte ion transport membrane. The modified Adams process described above is useful in producing a finely divided catalyst powder consisting of a solid solution of ruthenium oxide and a small amount of manganese oxide and bonding it to the solid polymer electrolyte membrane. However, such composite membrane / electrode structures are unsuitable for methods that do not provide membrane separation between the anode and cathode, such as electrolytic methods such as electrowinning of zinc or copper.

The production of a perfect anode structure that can be used in operations with a catalytic oxide coating in combination with a film-forming metal substrate is extremely problematic and is suitable for industrial practice even with very slight variations in production conditions. It is well known in the industry that the performance of the anode is greatly affected.

It is also known that catalytic anodes containing ruthenium as oxygen generating anodes cause a significant increase in oxygen potential during operation. This fact is the main obstacle to the effective use of the excellent electrocatalytic properties of ruthenium in the oxygen-evolving anode and the main problem underlying the present invention.

DISCLOSURE OF THE INVENTION The main object of the present invention is to easily and economically produce a dimensionally stable oxygen generating anode comprising a film-forming metal anode substrate having a catalytic oxide coating containing ruthenium. .

Another object of the present invention is to provide a method for producing a dimensional stable anode, which is the most efficient application of ruthenium in order to maintain a reduced potential, a significant energy saving, and a long service life as an oxygen generating anode. That is.

Yet another object of the present invention is to produce an anode having good dimensional stability, especially an anode used as an oxygen generating anode in a method for electrowinning metals from an oxygen electrolyte. The present invention provides a manufacturing method as claimed in such a manner as to meet the above objects as much as possible.

It has been empirically established that the oxygen-evolving anode according to the present invention must contain a minimum proportion of manganese in order to ensure a suitable anode life under oxygen-evolving conditions. In this regard, the composition of the coating composition is RuO ₂ and MnO ₂ in order to maintain a low and practically constant oxygen evolution potential and to maintain a long anode life under oxygen evolution conditions. It is also established that a molar ratio of 1: 1 to 1: 9, preferably 1: 2 to 1: 4 must be selected. Further, the proportion of manganese in the oxide coating does not significantly increase the oxygen potential even if it is considerably increased within the above range, while the anode life under oxygen generating conditions is such that the proportion of manganese in the oxide coating within the above range. When increasing towards the upper limit of, it becomes significantly longer. It has also been determined that the number of oxide layers used according to the present invention also has a significant effect on anode life. The number of oxide layers depends on the coating composition selected in each case from 6 to 35 layers, preferably from about 10 to about 10 layers.
You have to choose in the range of 20 layers. The amount of ruthenium deposited is 4 to 2 per square meter of the anode substrate surface area.
It is in the range of 0, preferably about 6 to about 12 g. The choice of this amount should be determined in each case depending on the composition of the coating produced according to the invention.

That is, a stable oxide coating with a high manganese content is 4 to
It has been established that a relatively low ruthenium loading of 10 to 20 layers at 8 g / m ² is advantageously produced in the composition according to the invention. On the contrary, in the composition according to the present invention, the minimum oxide content of manganese corresponding to a molar ratio of 1: 1 corresponds to a ruthenium loading of 8 to 20 g / m ² in order to have a suitable anode life. The number of layers should be relatively large, 10 to 20 or more.

The ruthenium and manganese compounds contained in the coating solution applied according to the present invention ensure a uniform and ultrafine mixture of ruthenium and manganese over the entire surface of the oxide coating obtained by changing by heating. It must dissolve completely in order to do so. The present invention can be successful with the use of ruthenium chloride and manganese nitrate or manganese oxalate.

The application of the coating solution according to the invention can be successful if a water-soluble solvent or an organic solvent is used, especially ethanol or butanol.

Concentrated hydrochloric acid corresponding to about 4 to 15% by weight of the coating solution may be added to the solution, which also gives good coating.

Since the ruthenium and manganese compounds used in the production of the oxide coatings according to the invention have very different thermal decomposition temperatures, the temperatures chosen specifically so that they change simultaneously to ensure a good and homogeneous oxide coating. Must be heat treated.

Experiments have established that a heat treatment temperature of approximately 400 ° C. is necessary to ensure a good coating according to the invention. On the other hand, it has been found that a good coating cannot be obtained at a remarkably high temperature of 420 ° C or higher or a remarkably low temperature of 380 ° C or lower.

The following examples illustrate various modes of practicing the present invention.

Example 1 A titanium anode having a catalytic Ru—Mn oxide coating having a composition corresponding to a molar ratio of RuO ₂ and MnO ₂ of 50:50 was prepared by the following method.

A uniform coating solution containing ruthenium chloride and manganese nitrate in water at a molar ratio of 1: 1 was prepared with the following composition (% by weight).

Buddha RuCl ₃ aq (40% Ru) 10.5% Mn (NO 3) 2 · 4H 2 O 10.5% HCl (10N) 4.7% H 2 O 74.3% titanium specimen (100 × 20 × 1mm) sandblasting and 30 minutes Etching pretreatment was carried out in 15% HCl.

The coating liquid was continuously applied in 10 layers with a brush on the pretreated titanium test piece. Apply each layer of the applied solution at 100 ° C for 5
Air dry for 10 minutes, and dry the resulting layer in flowing air at 400 ° C for 10 minutes.
Was heat treated in. As a result, the metal salts were thermally decomposed and converted into oxides.

In this way, the oxide coating formed into 10 layers having a molar composition corresponding to the RuO ₂ / MnO ₂ molar ratio of 50:50 has a specific amount or deposition equivalent to 8 g / m ² on the unit surface area of the titanium base material. It contained an amount of ruthenium. In this way, one anode (S46) having a coating formed in 10 layers with a total ruthenium loading of 8 g / m ² was used in H ₂ SO ₄ 150 g / l as an oxygen evolution anode of 7500 A / m ² . An accelerated life test was performed by operating at a current density. On the other hand, the operating voltage of the anode was monitored until the anode broke down and a sudden voltage rise occurred. The life of this anode (S46) in the accelerated test was 90 hours.

Another anode (S28) was prepared by the same method except that manganese oxalate was used instead of manganese nitrate. This anode (S
28) shows an accelerated life test result of 85 hours at a current density of 7500 A / m ^2.
It was the end of his life.

Example 2 A titanium anode having a catalytic Ru-Mn-Co oxide coating was prepared under the same conditions as described in Example 1. However, the ruthenium chloride, manganese nitrate and cobalt nitrate solutions dissolved in water had the following composition (% by weight).

RuCl ₃ aq (40% Ru) 10% Mn (NO 3) implement _{2 · 4H 2 O 10% Co} (NO 3) 2 · 6H 2 O 2.6% HCl (10N) 12% H 2 O 65.4% titanium specimens Pretreatment was performed in the same manner as in Example 1, and the coating solution was applied to 10 layers to give a total ruthenium coating amount of 8 g.
/ m ² then RuO ₂ , MnO ₂ , and cobalt oxide in a molar ratio of 45:
An overall composition oxide coating corresponding to 45:10 was formed.

The coated anode (S37-I) thus prepared was tested as an oxygen generating anode in 150 g / l H ₂ SO ₄ at a current density of 500 A / m ^{2 and} the initial oxygen voltage was found to be the standard hydrogen electrode. It was 1.50 V, and after 20 months it was still operated at an oxygen voltage of 1.70 V against a standard hydrogen electrode. Similar anode (S37−
I) was subjected to the accelerated life test described in Example 1
It showed a life of 90 rh at a current density of 7500 A / m ² . The composition of this anode and the coating liquid (% by weight) is RuCl ₃ · water solution (40% R
u) 10%, Mn (NO 3) 2 · 4H 2 O 8.8%, Co (NO 3) 2 · 6H 2 O1.2
%, HCl (10N) 12.2%, H ₂ O 67.8%, another anode (S37-II) was prepared. The coated anode obtained from this coating solution had a ruthenium coverage of 8 g / m ² , RuO
_It had an oxide coating with an overall composition corresponding to a molar ratio of 50: 45: 5 of ₂ , MnO ₂ and cobalt oxide. When one of these anodes was operated at a current density of 500 A / m ² in 150 g / l H ₂ SO ₄ , the initial oxygen voltage was
It broke after 13 months at a current density of 500 A / m ² at 1.60 V.
A similar anode (S37-II) operated at 7500 A / m ² in 150 g / l H ₂ SO ₄ and exhibited a life of 40 rh accelerated life test.

Example 3 A titanium anode having a catalytic Ru-Mn oxide coating containing dispersed anatase-type TiO ₂ powder having a particle size of 1 micron or less was prepared by the following method in the same manner as described in Example 1. did.

The coating solution used in this case contained ruthenium chloride and mannan nitrate in n-butyl alcohol at a Ru / Mn molar ratio of 50:
Anatase type that dissolves at 50 and is evenly dispersed throughout the solution
The composition (% by weight) of TiO ₂ powder was as follows.

RuCl ₃ · aq · (40% Ru) 12.6% Mn (NO ₃ ) ₂ · 4H ₂ O 12.2% Dispersed anatase type TiO ₂ powder 3.9% Butyl alcohol 71.3% The composition was changed to oxide under the stated conditions and the ruthenium loading was 15 g / m ² and the total composition was Ru.
O _2, MnO ₂ and TiO ₂ molar ratio of 1: 1: to form a catalytic Ru-Mn oxide coating containing a uniformly dispersed anatase TiO ₂ powder was applied to the corresponding 7 Tier 1.

One of the anodes (S141) thus coated in 7 layers with a total ruthenium loading of 15 g / m ² was subjected to the accelerated life test as described in Example 1 and was run at 7500 A / m in 150 g / l H ₂ SO _4. 175hr ² of current density
Showed the life of.

Another anode (S141) made by exactly the same method was used at 150g / l H ₂ SO
_When tested as an oxygen-evolving anode operating at a current density of 500 A / m ^{2 in} ₄ , the initial oxygen voltage was 1.
At 53V, it was still running at 1.63V against a standard hydrogen electrode after 23 months. The same coating solution was applied in 8 layers, dried and pyrolyzed as described in Example 1 to give a total ruthenium coverage of 8 g / m ^2.
A second set of anodes (S142) was prepared so as to form an oxide coating with an overall composition corresponding to a RuO ₂ to MnO ₂ molar ratio of 1: 1.

One of this second set of anodes (S142) was tested in 150 g / l H ₂ SO ₄ at a current density of 500 A / m ² and under these test conditions after 7000 hr (292 days) standard hydrogen The electrodes were operated at an oxygen voltage of 1.57V.

Another one of this second set of anodes (S142) is 150g / l H ₂ SO ₄
79 hours for an accelerated life test at a current density of 7500 A / m ² in
Showed the life of.

The amount of ruthenium deposited was 8 g / m ² , and the overall composition was RuO ₂ , Mn.
Two different coating solutions were used in the same manner to form oxide coatings with molar ratios of O ₂ and TiO ₂ (powder) of 1: 1: 3 and 2: 2: 1 respectively, and another anode was used. Created.

The anode (S143) having a coating composition having a composition in which the molar ratio of RuO ₂ : MnO ₂ : TiO ₂ (powder) was 1: 1: 3 had a current density of 7500 A / m ² in 150 g / lH ₂ SO _4. The accelerated life test of the product showed a life of 68 hours. RuO ₂ : MnO ₂ : TiO ₂ (powder) with a coating equivalent to a molar ratio of 2: 2: 1, another anode (S144) has a life of 80 hours in an accelerated life test at a current density of 7500 A / m ^2. Indicated.

Example 4 A titanium anode with a catalytic Ru-Mn oxide coating containing dispersed metallic titanium powder having a particle size of 20 to 40 microns was prepared as follows.

The coating solution used in this case was one in which ruthenium chloride and manganese nitrate were dissolved in water at a molar ratio of 1: 1 and further metal titanium powder was uniformly dispersed and contained throughout the solution, and the following overall composition ( % By weight).

RuCl ₃ · Aqueous solution (40% Ru) 10.3% Mn (NO ₃ ) ₂ · 4H ₂ O 10.1% Dispersed Ti powder 2% HCl (10N) 4.6% H ₂ O 73% Conducted by applying this solution to 7 layers It was converted to oxide by the method described in Example 1, and the total ruthenium deposit was 8.4 g / m in 7 layers.
² , RuO ₂ : MnO ₂ : Ti (powder) was made to form an oxide coating containing uniformly dispersed titanium powder with an overall composition corresponding to a molar ratio of 38:38:24.

The anode (S48) thus coated with 7 layers and having a ruthenium coating amount of 8.4 g / m ² was subjected to the accelerated life test described in Example 1, and was 150 g / l at a current density of 7500 A / m ^2.
Of H ₂ SO ₄ was 134 hr.

That is, when the ruthenium loading is 8.4 g / m ² , the molar ratio of RuO ₂ : MnO ₂ is
The stability of the anode against oxygen evolution is improved by adding the titanium powder dispersed in the anodic oxide coating with a composition corresponding to 1: 1. This improved situation is that the anode (S48) has a life of 137 hours by the accelerated life test obtained at a current density of 7500 A / m ² and almost the same ruthenium loading of 8 g / m ² as RuO ₂ : MnO _2. The anode of Example 1 (S4 with a molar 1: 1 ratio of ₂ being the same (but not containing dispersed Ti)) coating composition.
This is evident from the significantly longer life obtained for 6) compared to 90 hours.

This anode (S48), which has a life of 137 hours in the accelerated test, has the same ruthenium compound coverage of 8 g / m ² and a RuO ₂ : MnO ₂ molar ratio of 1: 1 (however, it contains dispersed anatase-type TiO ₂₎ . In comparison with the anodes (S142), (S143) and (S144) of Example 3 having an accelerated test life of 70 to 80 hours, the similar improvement by adding the dispersed titanium powder is recognized.

The reason for this significant improvement in the stability of the anode by the addition of dispersed titanium powder cannot be explained exactly, but is probably the favorable effect of the dispersed titanium powder on the Ru-Mn oxide coated surface, or the dispersed titanium powder and Ru-
It is believed that favorable chemical interactions with the Mn oxide during its formation, or both, are obtained in combination.

Example 5 A titanium anode having a catalytic Ru-Mn oxide coating with an overall composition corresponding to a RuO ₂ to MnO ₂ molar ratio of 30:70 was prepared by the following method.

A coating solution of ruthenium chloride and manganese nitrate dissolved in 1-butyl alcohol at a molar ratio of 30:70 was prepared with the following composition (% by weight).

RuCl ₃ aq (40% Ru) 11.1% Mn (NO 3) 2 · 4H 2 O 25.8% butanol 63.1% titanium specimen (100 × 20 × 1mm) sandblasting,
It was pretreated by treatment in 1,1,1-trichloroethane for 10 minutes and etching in oxalic acid at 80 ° C. for 6 hours.

The coating solution was sequentially coated on the titanium test piece after pretreatment with a brush in 20 layers, and each coating layer was air-dried at 120 ° C for 10 minutes and further heat-treated at 400 ° C for 10 minutes in a stream of air. Was thermally decomposed into an oxide. The resulting oxide coating consisted of 20 layers with a composition of RuO ₂ : MnO ₂ of 30:70 and a ruthenium deposit of 8 g / m ² .

The anode (B ₂ ) thus prepared having a coating of 20 layers with a ruthenium loading of 8 g / m ² was 750 in 150 g / l H ₂ SO _4.
The accelerated life test at a current density of 0 A / m ² showed a life of 176 hr.

The same coating solution was applied to 13 layers, and the ruthenium coating amount was
Another anode (B ₁ ) that was the same except that it was made to be 6 g / m ² was subjected to an accelerated life test at a current density of 7500 A / m ^2.
It showed a life of 142 hours.

Also, the same coating solution was applied to 30 layers and the ruthenium coating amount was 12
Another anode (B ₄ ) which was the same except that it was made to have a g / m ² had a life of 137 hr as a result of an accelerated life test at a current density of 7500 A / m ² in 150 g / lH ₂ SO _4. Indicated.

It created an average particle diameter of 40 microns dispersed beta-MnO ₂ catalytic powder containing Ru- oxides manner similar to that described in Example 1 a comparative titanium anode (Q42) having a coating. However, the coated Ru oxide layer was 5 layers, the total amount of ruthenium deposited was 8 g / m ² , and it contained dispersed MnO ₂ powder corresponding to the same overall coating composition as the above-mentioned anodes B1, B2 and B4. That is, having an overall coating composition of 30% RuO ₂ and 70% MnO _{2 (} applied as a dispersed preformed powder in this comparative anode). The coating solution used in this case was composed of dissolved ruthenium chloride and dispersed MnO ₂ powder and had the composition shown in the following weight%.

RuCl ₃ aqueous solution (40% Ru) 12.7% β-MnO ₂ powder dispersed (average particle size 40 micron) 10.0% HCl (10N) 5.3% n-butyl alcohol 72% This solution was applied to 5 layers to give Example 1. A ruthenium oxide coating containing dispersed β-MnO ₂ powder was prepared which was converted to an oxide by the method described and formed in 5 layers with a total ruthenium loading of 8 g / m ² .

In this way, the comparative anode (Q42) having a composition equivalent to 30% of RuO _{2 and} 70% of MnO ₂ (powder) and having a coating formed in 5 layers with a ruthenium deposit of 8 g / m ² was 7500 A / m ² The life of the accelerated life test was 60 hr at the current density of. That is, this comparative anode (Q42) with a coating of the same overall composition as B ₂ but containing preformed and dispersed MnO ₂ powder was 7500 A / m ²
Although the life of the accelerated life test was 60 hr at the current density of, the same composition of ruthenium (8 g / m ² ) and the same overall composition, but Ru-Mn oxide was formed in situ on the anode. The anode has a life of 17500 according to the accelerated life test at 7500 A / m ² .
At 6 hours, the life was about three times longer.

Further, this ruthenium deposit is 8 g / m ² , and the molar ratio of RuO ₂ and MnO ₂ is 3
Anode (B2) with a Ru-Mn oxide coating having an overall composition equivalent to 0:70 shows a life of 176 hr by accelerated life test
Has the same ruthenium loading of 8 g / m ² but RuO ₂ and M
or the molar ratio of nO ₂ 1: Overall composition that is equivalent to 1 of the first embodiment the ratio of ruthenium to be applied in the method according to the invention has a Ru-Mn oxide coating is the minimum limit anode (S46 ) And (S48) are about twice as long as the life of 85 to 90 hours.

It is of particular significance to produce Ru-Mn oxide coatings based on the method of the present invention by applying a large proportion of manganese oxide formed in situ with a small amount of ruthenium oxide according to this comparative result. I understand.

Example 6 A titanium anode comprising a catalytic Ru-Mn oxide coating having a composition corresponding to a molar ratio of RuO ₂ and MnO ₂ of 14:86 was prepared as follows. A coating solution containing ruthenium chloride and manganese nitrate dissolved in 1-butyl alcohol was prepared with the following composition (% by weight).

RuCl ₃ aq (40% Ru) 8.3% Mn (NO 3) 2 · 4H 2 O 48.1% butanol 43.6% titanium specimen (100 × 20 × 1mm) were sandblasted 10 minutes 1,1,1-trichloroethane, It was pretreated by etching in oxalic acid at 80 ° C for 6 hours. The above coating solution was sequentially coated on a pretreated titanium test piece with a brush in 22 layers, and each coating layer was air-dried at 120 ° C. for 10 minutes, and the resulting dried layer was heat-treated at 400 ° C. for 10 minutes in an air stream. As a result, the metal salts were thermally decomposed and converted into oxides. The oxide coating applied to 22 layers in this way has a ruthenium coverage of 8 g / m 2.
^{In 2} , the total composition was equivalent to RuO ₂ : MnO ₂ 14:86.
In this way, the anode (E1) having a coating formed in 22 layers with a ruthenium loading of 8 g / m ² had an accelerated life of 200 hr at a current density of 7500 A / m ² in 150 g / l of H ₂ SO _4. .

Another anode (E2), which was made into 16 layers at the ruthenium loading of 6 g / m ² using the same solution, had a life of 182 hours as measured by an accelerated life test at 7500 A / m ² . Another anode (E3) was formed into 28 layers with a total ruthenium deposition amount of 10 g / m ² , and the life of the accelerated life test was 160 hours.

Another anode (E4) prepared by applying this solution to 33 layers to give a ruthenium coating amount of 12 g / m ² had an accelerated life test life of 193 hours.

As can be seen from the results of the accelerated life test described above, the anode having a high MnO ₂ / RuO ₂ molar ratio of 86:14 (about 6: 1) has a ruthenium deposit of 6 to 8 g / m ² . In the case of anodes (E1) and (E2) with a Ru-Mn oxide coating applied to 16 to 22 layers, the life is as shown in the accelerated life test results above.
It took 182 to 200 hours. On the contrary, there are more coating layers (28-33 layers), and the amount of ruthenium deposited is greater (10 ~
In the case of 12 g / m ² ) anodes (E3) and (E4), no significant improvement was observed as compared with the anodes (E1) and (E2), which had a smaller number of coating layers and a lower ruthenium deposit.

Similarly, the other anodes formed in 18 layers with a ruthenium loading of 8 g / m ² each showed the following accelerated life test life in sulfuric acid when tested by the same test method but at a lower current density.

Anode (4A): 520hr with current density of 3750A / m ² Anode (3A): 1760hr with current density of 1875A / m ² 〃 (2A): 8160hr with current density of 940A / m ² These accelerated life tests generate oxygen. It will be necessary to note that the tests are carried out at current densities which are considerably higher than the current densities normally required for many industrial uses of the anode. The accelerated life test result measured in the present invention has a normal operation when the anode current density is low, for example, an electrolytic density of 200 A / m ² as typified by an electrolytic extraction method of copper from a sulfuric acid electrolyte. Is a value corresponding to a considerably long service life.

Example 7 A titanium anode comprising a catalytic Ru—Mn oxide coating having a composition in which the molar ratio of RuO ₂ to MnO ₂ was 1: 4 was prepared by the following method.

A coating solution composed of ruthenium chloride and manganese nitrate dissolved in 1-butyl alcohol in a molar ratio of 1: 4 was prepared with the following composition (% by weight).

RuCl ₃ aq (40% Ru) 9.5% Mn (NO 3) was ₂ · 4H ₂ O 36.8% butanol 53.7% The coating solution was successively applied and dried was changed to an oxide coating in said conditions.

Thus, one anode (C2) having a catalytic Ru-Mn oxide coating applied to a composition corresponding to a molar ratio of ruthenium loading of 8 g / m ² RuO ₂ : MnO ₂ of 20:80 was 150 g. An accelerated life test at a current density of 7500 A / m ² in H ₂ SO ₄ / l showed a life of 175 hr. The coating solution produced by the same method had 16 coating layers and the ruthenium total coating amount was 12 g / m ² and the same solution was coated, and another anode (C1) was subjected to the accelerated life test at the current density of 7500 A / m ^2.
It showed a life of 135 hours.

Furthermore, another anode (C3) having the same solution prepared by applying the same solution to 21 layers and having a total ruthenium deposit of 12 g / m ² was subjected to an accelerated life test at a current density of 7500 A / m ² , resulting in a life of 187 hr. showed that.

Produced in yet another similar method and applying the same solution to 30 layers,
The anode (C4) with a total ruthenium deposit of 12 g / m ² showed a life of 126 hours as a result of the accelerated life test at a current density of 7500 A / m ² .

As can be seen from the results of the accelerated life test described above, MnO ₂ / RuO ₂
An anode having a high molar ratio of 4: 1 and a Ru-Mn oxide coating of 20 to 21 layers and a ruthenium coverage of 8 to 10 g /
175 to 187 hours for m ² anodes (C2) and (C3)
Contrary to this, when the ruthenium coating amount is 12g / m ² and the coating layer is 16 to 30 anodes (C4) and (C1), the result of accelerated life test Is 12
The result of accelerated life test is 175 to 1 in 6 to 137 hours.
The lifespan of the 87 hr anodes (C2) and (C3) is about 40% longer and no improvement over (C4) and (C5) is observed.

Based on the above test results, the anode (C4) having a ruthenium coating amount of 12 g / m ² and 30 coating layers has a longer life according to the accelerated life test.
It can also be seen that there is no significant improvement over 126 hours, compared to the fact that the anode (C1) coated with 16 layers with the same composition and the same ruthenium deposit has a life of 135 hours. . That is, even if the number of coating layers is increased from 16 layers to 30 layers, such stability of the anode does not increase.

Example 8 A titanium anode having an oxide coating containing various amounts of ruthenium and / or manganese was prepared and tested in the following manner.

Titanium test pieces (100 × 20 × 1 mm) were pretreated by sandblasting for 10 minutes in 1,1,1-trichloroethane and in oxalic acid at 80 ° C. for 6 hours. Ruthenium oxide coating (100% RuO ₂ )
A comparative anode (Ru100) having a was prepared by the following method.

(A) A pretreated titanium test piece is coated with a coating solution having the following composition (weight) in 9 layers with a brush.

(RuCl ₃ aqueous solution (40% Ru) 0.8 g; ethanol 2.4 g; HCl (10
N) 0.25 ml) (b) Each layer coated with the solution is air-dried at 120 ° C. for 15 minutes, and (c) each dried layer is heat-treated at 400 ° C. for 10 minutes in an air stream. As a result, the metal salts are thermally decomposed and converted into oxides.

This ruthenium oxide coating 9 layers ruthenium coating amount of 8g / m ² for comparison was used Ru100 as an oxygen generating anode 150g / l
Was tested in H ₂ SO ₄ at a current density of 500 A / m ² and showed an oxygen voltage of 1.50 V against a standard hydrogen electrode of 7500 A / m ²
The accelerated life test at a current density of 3.5 hours gave a life of 3.5 hours.

Similarly, it has a composition corresponding to a RuO ₂ : MnO ₂ molar ratio of 9: 1.
Ru-Mn oxide 0.926GRuCl ₃ aqueous electrode Ru90 having a coating (40% Ru), Mn ( NO 3) 2 · 4H 2 O0.103g, ethanol 5.5
A coating solution having a weight composition of 0.25 ml of HCl (10N) was applied to 9 layers in this case, and each layer was dried and heat treated in the same manner as described in steps (b) and (c) above.

RuO ₂ / MnO ₂ thus prepared has 90 layers of 90:10, and the ruthenium amount of the anode Ru90 is 8.1 g / m ^{2 and} the anode Ru90 is 150 g / l of H ₂ S.
When tested in a similar manner in O ₄ , it showed an oxygen voltage of 1.53 V against a standard hydrogen electrode at a current density of 500 A / m ^{2, and at} a current density of 7500 A / m ² the life by the accelerated life test was 9.8 hr. Atsuta

Similarly, RuO ₂ : MnO ₂ has a composition corresponding to 80:20 mol.
RuCl ₃ aq anode M5 with ru-Mn oxide coating (40% R
_{u) 0.721g, Mn (NO 3} ) 2 · 4H 2 O0.180g, ethanol 5.9 g, HC
In this case, a coating solution having a weight composition of l (10N) of 0.25 ml was applied to 7 layers, and each layer was dried and heat treated in the same manner as described in steps (b) and (c) above.

RuO ₂ / MnO with a ruthenium deposit of 8 g / m ² thus prepared
Anode M5 made so that ₂ has 80/20 7 coating layers
Was also tested in 150 g / l H ₂ SO ₄ and showed an oxygen voltage of 1.53 V against a standard hydrogen electrode at a current density of 500 A / m ² , and an accelerated life test at a current density of 7500 A / m ^2. The life was 10 hours.

Ru-M with a composition corresponding to a molar ratio of RuO ₂ / MnO ₂ of 50:50
An anode M8 with an n-oxide coating was made in the same way,
For此RuCl ₃ aq (40% Ru) 0.684g, Mn (NO 3) 2 · 4H
After coating 8 layers with a coating solution having a weight composition of 0.680 g of ₂ O, 3.6 g of ethanol, 0.25 ml of HCl (10N), each layer is dried as described in steps (b) and (c) above,
Heat treated.

The anode M8 thus prepared was coated with eight layers of ruthenium with a coating amount of 8 g / m ² and a RuO ₂ / MnO ₂ coating of 50:50.
A similar test was conducted in g / l H ₂ SO ₄ to give 500 A / m.
^At a current density of ² , an oxygen voltage of 1.56 V was shown with respect to the standard hydrogen electrode, and at a current density of 7500 A / m ² , the life by the accelerated life test was 55 hours.

An anode M4 having a Ru-Mn oxide coating having a composition corresponding to a RuO ₂ / MnO ₂ molar ratio of 30:70 was similarly prepared, but in this case, RuCl ₃ · water solution (40% Ru) 1.074 g _{, Mn (NO 3) 2 ·} 4H 2 O
A coating solution having a weight composition of 2.419 g, ethanol 3.6 g, and HCl (10 N) 0.25 ml was applied to 7 layers, and each layer was dried and heat-treated in the same manner as the method described in steps (b) and (c) above. . In this way, the anode M4 having a ruthenium deposit of 8 g / m ² and a RuO ₂ / MnO ₂ molar ratio of 30:70 formed in 7 layers
Was also tested in 150 g / l H ₂ SO ₄ and showed an oxygen voltage of 1.55 V against a standard hydrogen electrode at a current density of 500 A / m ² , and an accelerated life test at a current density of 7500 A / m ^2. The life was 115 hours.

An anode M13 having a Ru-Mn oxide coating with a composition corresponding to a molar ratio of RuO ₂ / MnO ₂ of 14:86 was prepared in the same manner. In this case, an aqueous RuCl ₃ solution (40% Ru) 0.537 g, Mn _{(NO 3) 2 · 4H 2} O
A coating solution having a weight composition of 3.127 g, ethanol 2.835 g, and HCl (10 N) 0.25 ml was applied to 11 layers, and each layer was dried and heat-treated in the same manner as in the above-described steps (b) and (c). The amount of ruthenium deposited in this way was 8 g / m ²
An anode M13 with a RuO ₂ / MnO ₂ coating of 14:86 formed in 11 layers was also tested in 150 g / l H ₂ SO ₄ at a current density of 500 A / m ² for a standard hydrogen electrode. It showed an oxygen voltage of 1.57 V and a life of 200 hours as measured by an accelerated life test at a current density of 7500 A / m ² .

Another anode Mn10 with manganese oxide (MnO ₂ ) coating
0 was made in the same way, but in this case Mn (NO ₃ ) ₂・ 4H ₂ O
A solution having a weight composition of 1.12 g and ethanol 10 g was applied to 11 layers and then dried in the same manner as in the above step (b).
Each dried layer was heat-treated for 10 minutes in an air stream at ℃ (this condition is considered to be suitable for the formation of MnO ₂ coating by thermal decomposition). The total oxide coverage of the resulting oxide coating (100% MnO ₂ ) was 26 g / m ² (ie the same as M13).

Thus, an anode Mn100 having an MnO ₂ coating formed in 11 layers with an Mn loading of 26 g / m ² was similarly tested in 150 g / l H ₂ SO ₄ and at a current density of 500 A / cm ² . It showed an oxygen voltage of about 3 V against the standard hydrogen electrode, and immediately broke in the accelerated life test at a current density of 7500 A / cm ² .

Anode M8, M4 having a Ru-Mn oxide coating prepared by the method of the present invention from the above test results as described above, and
M13 does not show a significant increase in oxygen voltage and at the same time the ratio of ruthenium in the coating composition is changed from RuO ₂ to MnO ₂ molar ratio of 1: 1 to
It is shown that decreasing within the range of the present invention corresponding to 1: 9 prolongs the anode life several times under oxygen generating conditions.

It should be further noted that both the anode M4 and the anode (B2) described in Example 5 had the same coating composition corresponding to a RuO ₂ / MnO ₂ molar ratio of 30/70 and the same ruthenium loading of 8 g. An anode made according to the present invention having / m ² , wherein M4 is 7
It has been applied to a layer and has a life of 115 hours as measured by an accelerated life test, whereas the anode (B2) has 20 layers of the same coating and has a life of 176 hours as a result of an accelerated life test. It has a long life. That is, RuO ₂ / MnO ₂ is 30/7
If the number of layers of such an anode having a coating composition corresponding to 0 and a ruthenium coverage of 8 g / m ² is increased from 7 to 20, the life in the accelerated life test increases from 115 hr to 176 hr. The life of the lower anode is significantly extended. The anode M13 and the anode (E1) described in Example 6 are R
An anode made according to the invention with the same coating composition of uO ₂ / MnO ₂ corresponding to a molar ratio of 14:86 and the same ruthenium loading of 8 g / m ² , but with 11 layers of M13 Formed by the accelerated life test was 200 hours, while the anode (E1) had 22 layers of the same coating and the accelerated life test also had a life of 200 hours. That is, RuO ₂ / MnO ₂ is 14:86
In the case of such an anode having a coating composition corresponding to the molar ratio of, both have a significant improvement in the lifetime of the anode under the condition of oxygen generation, as can be seen from the fact that the lifetime of the accelerated life test is 200 hours. I couldn't do it.

INDUSTRIAL APPLICABILITY The present invention is applied to the production of an anode having good dimensional stability, which can be industrially applied as a catalytic oxygen generating anode whose constraint on the cost of the anode is a fundamental requirement. The anode produced according to the present invention is particularly used for electrowinning metals such as copper and zinc from sulfate electrolytes.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C25C 7/02 306 7047-4K 307 7047-4K

Claims (6)

[Claims] 1. A continuous layer of a coating solution containing a ruthenium dioxide and a manganese compound in a concentration corresponding to a predetermined molar ratio of ruthenium dioxide to manganese dioxide selected from the molar ratio range of 1: 1 to 1: 9. B) applying each layer of the coating solution applied in step a) to obtain an almost dry layer consisting of a uniform mixture of the ruthenium compound and the manganese compound in the predetermined ratios; c) ) The dry product layer is added in an oxidizing atmosphere at about 400 ° C for 5 to 15
Heat treatment for 4 minutes to transform the compound into a uniform oxide layer; d) repeating steps a), b) and c) to 4 g / m ²
To 20 g / m ² corresponding to the ruthenium loading selected from the range of the oxide layer so as to gradually form a catalytic oxide coating containing a predetermined amount of ruthenium per unit surface area of the anode substrate. Forming a metal oxide anode substrate with a catalytic oxide coating containing ruthenium, characterized in that a selected number of 6 to 35 oxide layers are sequentially and successively formed. A method for producing a dimensionally stable oxygen generating anode. 2. A first substrate according to claim 1, wherein the anode substrate is mainly made of titanium or a titanium alloy.
The method described in the section. 3. An anode for electrowinning a metal from an acidic electrolyte containing manganese as an impurity, characterized in that the molar ratio is selected from the range of ruthenium 1 / manganese 1 to ruthenium 1 / manganese 3. A method according to claim 1 for manufacturing. 4. A process according to claim 1 wherein the coating solution contains concentrated hydrochloric acid in an amount corresponding to about 4 to 15% by weight of the solution. 5. The method according to claim 1, wherein the coating contains ethanol or butanol as an organic solvent. 6. For titanium powders with a particle size of less than 40 microns, said catalytic coating containing an amount of titanium-containing powder selected in an amount corresponding to a titanium loading of at most 10 g / m ² . The method according to claim 1, wherein the method is uniformly dispersed in the coating solution.