JP5102670B2 - Method for producing lead alloy electrode having β-PbO2 coating - Google Patents

Description

  The present invention relates to the improvement of lead alloy electrodes for the purpose of improving the corrosion resistance of the surface of lead alloy electrodes in zinc electrowinning, saving power by reducing the electrolysis voltage, and improving product quality.

The lead alloy electrode used in the electrolytic extraction process of zinc smelting has corrosion resistance by forming an oxide film on its surface. There are alpha-PbO ₂ and beta-PbO ₂ in the form of lead dioxide, but usually, the major oxides generated on the anode surface is alpha-PbO _2.
When a lead oxide film having α-PbO ₂ as a main oxide is produced, the electrolysis voltage increases and the power consumption increases. In addition, there is a problem in that a film containing α-PbO ₂ as a main oxide falls off and the dropped film lowers the product purity.

Since it is known that the electrolysis voltage is reduced by adding Ca to the Pb—Ag alloy, an electrode of a Pb—Ag—Ca alloy was produced and an electrolysis test was performed. Electrolysis was performed at 500 A / m ² for 20 days. As a result, the electrolysis voltage of the Pb—Ag—Ca alloy was lower than that of the Pb—Ag alloy. Moreover, when the X-ray diffraction of the anode surface was performed after the completion of electrolysis, α-PbO ₂ was formed on the surface of the Pb—Ag alloy and β-PbO ₂ was formed on the surface of the Pb—Ag—Ca alloy. That is, it is easy to form a film having β-PbO ₂ as a main oxide on the surface by adding Ca. On the other hand, when there is too much addition amount of Ca, there exists a problem that a crack will increase in an oxide film. If there are many cracks, the adhesion of the oxide film will deteriorate, causing the oxide film to fall off. Although it may not be a problem for a short period, it can be said that an electrode to which Ca is added is not suitable for long-term electrolysis.

Since β-PbO ₂ has a denser structure than α-PbO _2, it is difficult to drop off. Moreover, since it is thought that it is hard to become a floating slime because the crystal grain is large, it is difficult to adversely affect the product purity. Therefore, by forming a film having β-PbO ₂ as a main oxide rather than α-PbO ₂ , the electrolysis voltage is lowered, so that reduction in power cost and improvement in product quality can be expected.

Although it is generally known that β-PbO ₂ is produced by an oxidation reaction from lead sulfate, the production takes time. Moreover, Mn is contained in the actual electrolytic process liquid. In the sulfuric acid solution containing Mn, there is a problem that an oxide film is not easily generated.
Further, the following document 1 discloses a technique for immersing lead oxide in the electrode surface, but the technique for generating β-PbO ₂ as described above on the electrode surface is limited. Since lead is exposed on the electrode surface, the α-PbO ₂ is produced. In addition, in this method, there is a manufacturing process for separately producing β-PbO ₂ powder and immersing it on the surface, which is expensive. Further improvement is required to prevent β-PbO ₂ from falling off the electrode.
Japanese Utility Model Publication No. 4-40769

The product of the oxide film to the alpha-PbO ₂ and the main oxide, the decrease in product quality due to dropping of the increase and the oxide film of the electrolytic voltage has been a problem, oxides of beta-PbO ₂ and the main oxide By preferentially generating the film, the purpose is to suppress the electrolysis voltage and prevent the film from falling off, thereby reducing the power cost and improving the product quality in operation.
In addition, there has been a demand for a simple technique for generating β-PbO ₂ on the electrode surface with little desorption and suppressing an increase in electrolytic voltage.

According to the present invention, an anode of a lead alloy electrode is disposed in an electrolytic solution, and β-PbO _{2 is} formed on the surface of the electrode by an operation of repeatedly energizing and interrupting current with a cathode disposed in the solution. It is an electrode manufacturing method which produces | generates a membrane | film | coat.
Until now, oxide generation on the electrode surface has been performed at a constant current. However, constant current electrolysis is performed by repeatedly conducting and shutting off (referring to non-energization at a current of 0 A and a voltage of 0 V). The production of β-PbO ₂ can be promoted more than when the product is produced.

It has become possible to promote the production of β-PbO ₂ by repeating energization and interruption. In addition, β-PbO ₂ has a lower electrolysis voltage than α-PbO _{2 and} can reduce power costs. Furthermore, beta-PbO ₂ because its structure is dense, hard to fall off from the electrode surface, quality of the products as compared to the alpha-PbO ₂ so less likely to float slime for even fall off large crystal grains It is considered high.

In the present invention, the lead alloy electrode may be a lead alloy electrode for zinc electrowinning, the lead alloy is a lead alloy containing silver, the cathode is an aluminum cathode, the electrolyte is a sulfuric acid solution, respectively. preferable.
Moreover, it is thought that this invention is applicable not only to a sulfuric acid solution but to the process liquid containing Mn. This time, when electrolysis was performed for 24 hours using an sulfuric acid solution containing Mn to repeatedly turn on and off, a β-PbO ₂ film could be formed.
In the above acid solution, a lead alloy electrode is used as an anode and an aluminum cathode is used as a cathode, and energization and shut-off operations are performed. The energization and interruption operations may be performed manually or current control may be performed by a program or the like.

[Common] A Pb-1% Ag alloy is produced in accordance with the method for producing a lead alloy electrode shown in FIG. That is, pure lead and pure silver are precisely weighed so that Ag is 1% by mass and melted (850 to 900 ° C.) using an electric furnace. The mold (10 mm × 10 mm × 100 mm mold) is preheated (about 300 ° C.) in advance. Allow to cool at room temperature after casting. The composition of the alloy is confirmed by ICP, and wiring and resin filling are carried out only for those with an Ag content of 1% by mass, and processed into the electrode shape shown in FIG. Next, after polishing the surface with water-resistant abrasive paper, etching is performed with a mixed solution of acetic acid: hydrogen peroxide solution = 3: 1 (volume ratio), and ultrasonic cleaning is performed with distilled water for 2 minutes to use as an anode electrode. Pure Al is used for the cathode, and it is made in the same shape as the anode.

An outline of the electrolysis apparatus is shown in FIG. That is, Pb-1.0 mass% Ag alloy is used for the anode, pure aluminum is used for the cathode, and the distance between the electrodes is 30 mm. The amount of the electrolyte is 500 ml and kept at 40 ° C. A galvanostat is used for the constant current power source, and the current density is 500 A / m ² .

[Example 1] Table 1 shows test conditions, and Table 2 shows various energization conditions and results. Electrolysis is performed for 24 hours under the energization conditions shown in Table 2 to form an oxide film on the anode surface. Thereafter, constant current electrolysis is performed for 1 week at a current density of 500 A / m ² using each anode on which an oxide film is formed, and the electrolysis voltage is measured. After the completion of electrolysis, the anode was taken out from the electrolyte solution, washed with distilled water and dried, and then subjected to X-ray diffraction on the anode surface, SEM observation, and mass measurement of the substance dropped into the electrolyte solution.

FIG. 4 shows SEM images of the anode surface on which oxide was generated by electrolysis for 24 hours under various energization conditions. Α-PbO ₂ was generated on the surface of the anode subjected to electrolysis at a constant current for 24 hours, and β-PbO ₂ was generated on the surface of the anode subjected to electrolysis that was repeatedly turned on and off. Using this electrode, constant current electrolysis was performed at a current density of 500 A / m ² for one week.

FIG. 5 shows the result of X-ray diffraction on the anode surface after constant-current electrolysis for one week, and FIG. 6 shows the result of SEM observation. That is, the main oxide on the surface of the anode subjected to constant-current electrolysis for one week using the anode in which α-PbO ₂ was generated is α-PbO ₂ , and the oxide is generated by an electrolytic method in which energization and interruption are repeated. The main oxide on the anode surface is β-PbO ₂ .

FIG. 7 shows the transition of the electrolysis voltage when performing constant-current electrolysis for one week. Electrolysis voltage tends to be lower in an anode in which oxide is generated by an electrolytic method in which energization and interruption are repeated than in an anode in which an oxide film is generated at a constant current for 24 hours. That is, the electrolysis voltage is lowered because the main oxide produced on the anode surface is β-PbO ₂ .

Regarding the measurement of the mass of the fallout in the electrolyte, the amount of fallout in the test in which the electrolysis was repeated for 24 hours to produce an oxide film and the constant current electrolysis for 1 week was 0.0027 g. Yes (when producing β-PbO ₂ ). On the other hand, after the oxide was generated at a constant current, the weight of the fallout under the condition of performing constant-current electrolysis for 1 week was 0.0179 g (when α-PbO _{2 was} generated). That is, it is clear that β-PbO ₂ is produced with a smaller amount of fallout. When the amount of fallen substances is large, the quality of the cathode is lowered, so that a film containing β-PbO ₂ as a main oxide is formed and the amount of fallen substances is reduced, thereby improving the cathode quality.

[Supplementary example 1]
Electrolysis for generating an oxide film on the electrode surface was performed for 24 hours under the conditions shown in Table 3. The test conditions are as shown in Table 4. After completion of electrolysis, the electrode was taken out from the electrolyte, washed with distilled water and dried, and then the anode surface was subjected to X-ray diffraction and SEM observation.

FIG. 8 shows an X-ray diffraction result of the anode surface subjected to electrolysis for 24 hours. That is, the anode surface is alpha-PbO ₂ which was electrolytically at 24 hours constant current without interrupting the energization of the current, the anode surface was carried out and blocking conduction of current is generated by β-PbO _2.
Further, β-PbO ₂ is generated even if the intervals between energization and interruption are not equal. However, if the current cut-off time is too long as in 1-11, PbSO ₄ is generated, so it is considered not good that the OFF (current cut-off) time is too long.
In this case, the electrolysis time is 24 hours. However, when current is applied and cut off, β-PbO ₂ is generated even in less than 24 hours.

FIG. 9 shows an SEM image of the anode surface after electrolysis. That is, α-PbO ₂ is a fine crystal while β-PbO ₂ is a crystal grain.
When performing electrolysis for producing an oxide film, the production of a film containing β-PbO ₂ as a main oxide on the anode surface can be promoted by performing an electrolysis method in which current is repeatedly turned on and off.
According to this supplementary example, it was found that changing the current application and interruption time affects the generation of the oxide film. However, the adjustment of this time may be considered according to the liquid characteristics, electrode area, composition, etc. .

[Supplementary example 2]
Mn was added to the sulfuric acid solution (Mn addition amount: 2 g / L), and electrolysis was performed for 24 hours to generate an oxide under the conditions shown in Tables 5 and 6.
FIG. 10 shows the result of X-ray diffraction of the anode surface on which oxide was generated by electrolysis for 24 hours. Although the oxide film formed by conducting the energization and interruption electrolysis methods was β-PbO ₂ , the oxide film was not thick. Therefore, it is considered that the metal Pb that is the base material of the anode has been identified.
FIG. 11 shows an SEM image of the anode surface on which oxide was generated by electrolysis for 24 hours. It was confirmed that MnO ₂ was present in addition to PbO ₂ (EDS). That is, it was confirmed that β-PbO ₂ was generated on the electrode surface even when Mn was present in the solution.

[Supplementary Example 3]
Mn was added to the sulfuric acid solution (Mn addition amount: 2 g / L), and electrolysis was performed for 24 hours to generate oxides under the energizing conditions shown in Tables 7 and 8. Thereafter, constant current electrolysis was performed at 500 A / m ² for 1 week using the anode in which the oxide was generated.
FIG. 12 shows the transition of the electrolysis voltage when electrolysis is performed at a constant current for 1 week. Similar to the sulfuric acid solution test, the electrolysis voltage was lower in the anode subjected to the current energization and interruption electrolysis than the anode subjected to the electrolysis of oxide generation at a constant current for 24 hours.
In FIG. 12, the place where the voltage is extremely lowered or increased is the electrolyte exchange point.

As shown in Example 1 and Supplementary Examples 1 to 3, it was possible to efficiently promote the production of β-PbO ₂ on the surface of the lead alloy electrode by repeating energization and interruption. β-PbO ₂ has a lower electrolysis voltage than α-PbO _{2 and} can reduce power costs. Furthermore, beta-PbO ₂ because its structure is dense, hard to fall off from the electrode surface, quality of the products as compared to the alpha-PbO ₂ so less likely to float slime for even fall off large crystal grains It is considered high.

Electrode production flow Electrode schematic Electrolyzer schematic SEM image of the anode surface after 24 hours of pre-electrolysis X-ray diffraction results of anode surface after constant electrolysis for 1 week after preliminary electrolysis SEM image of the anode surface after constant electrolysis for 1 week after preliminary electrolysis Electrolytic voltage transition diagram when conducting constant-current electrolysis for 1 week after preliminary electrolysis X-ray diffraction results of anode surface after 24 hours of pre-electrolysis SEM image of the anode surface after 24 hours of pre-electrolysis X-ray diffraction result of anode surface pre-electrolyzed using sulfuric acid solution with Mn added for 24 hours SEM image of anode surface subjected to 24 hours pre-electrolysis using Mn added sulfuric acid solution Electrolytic voltage transition diagram when conducting electrolysis for 1 week after performing electrolysis for 24 hours using sulfuric acid solution containing Mn

Claims (6)

An anode of a lead alloy electrode is disposed in an acid solution, and a β-PbO ₂ film is formed on the surface of the electrode by an operation of repeatedly energizing and interrupting current with a cathode disposed in the solution. Electrode manufacturing method.   The manufacturing method according to claim 1, wherein the lead alloy electrode is a lead alloy electrode for zinc electrowinning.   The manufacturing method according to claim 1, wherein the lead alloy is a lead alloy containing silver.   The manufacturing method according to claim 1, wherein the cathode is an aluminum cathode.   The manufacturing method according to claim 1, wherein the acid solution is a sulfuric acid solution.   The manufacturing method according to claim 1, wherein the acid solution is a sulfuric acid solution in which manganese is dissolved.