JPH0739637B2 - Anode for zinc and cadmium electrolysis - Google Patents

Description

TECHNICAL FIELD The present invention relates to an anode for zinc and cadmium electrolysis in which lead is hardly eluted and the recovered zinc and cadmium are high in quality, and corrosion resistance and electrolysis efficiency are excellent.

[Prior Art and Problems] Conventionally, lead alloy anodes have been generally used in zinc electrolytic smelting, and one example thereof is Pb-Ag (Ag; 0.2
~ 2%), lead alloy anodes of Pb-Ag-alkaline earth metals and the like are known. The anode is usually manufactured by a casting method in which a lead alloy is poured into a stationary mold.
However, since the anode manufactured by the above-mentioned stationary casting method is open pouring, outside air is engulfed, and small holes, that is, plow holes are easily generated inside the anode, and voltage loss increases due to such casting defects, and There is a problem that a short circuit is apt to occur at the time of energization in the defective portion, which causes a significant decrease in current efficiency. Further, lead is eluted from the defective portion into the electrolytic solution, leading to an increase in the lead quality of the cathode zinc and a deterioration in quality.

In zinc electrolysis, a lead oxide film is formed on the surface of the lead anode so that lead does not elute in the electrolytic solution, but if blowholes exist, the oxide film is sufficiently formed at the structural defect portion. However, there is also a problem that lead is eluted into the electrolytic solution and the quality of the cathode zinc deteriorates.

However, the cross-sectional width of the lead alloy anode produced by conventional stationary casting is
Blown holes of 0.3 to 2 mmφ in 620 mm average about 1
There are about 0-18.

Further, the anode used for electrolytic smelting of zinc is thinner than that of copper smelting, and the presence of the above-mentioned blow holes has a greater influence than in the case of copper smelting.

The current density of copper smelting is usually 150 to 220 A / m ² , but it is usually 300 to 600 A / m ² in zinc electrolysis, so the current density flowing in one anode is 2-3 times that of copper smelting. Next to
The influence is great.

Further, in zinc electrolysis, a hole is formed in the center of the anode in order to maintain good circulation of the electrolytic solution inside the electrolytic cell, and a hole for attaching a spacer is also formed. Therefore, when the blowhole exists inside the anode, this portion is exposed to the outside and is easily corroded, impairing the corrosion resistance, and lead elutes to deteriorate the quality of the cathode zinc. Normally, such a perforated anode is not used in copper electrolytic smelting, and it is necessary to eliminate blowholes more than copper smelting in zinc electrolytic smelting.

The above problem is also found in the electrolysis of cadmium. A lead alloy plate is also used as an insoluble anode in cadmium electrolysis, and an anode with few blowholes is required in order to improve the quality of recovered cadmium and the current efficiency.

[Means for Solving Problems] The present inventors have found that the blowholes existing inside the lead alloy anode have a great influence on the electrolytic recovery of zinc and cadmium, and on the other hand, they were obtained by continuous casting. It was noted that the anode had almost no blowholes, and the conventional problems were solved by using the lead alloy anode manufactured by the continuous casting.

[Constitution of the Invention] According to the present invention, a lead alloy hot water is obtained by continuously drawing a lead alloy hot water from a mold in a strip shape, and then cutting it into an anode shape, which has a porosity of 1.0% or less. An anode for zinc and cadmium electrolysis is provided.

Further, as a preferred embodiment thereof, there is provided an anode in which the lead alloy hot water is continuously drawn from the mold at the same time or after the drawing, and then rolled and cut into an anode shape.
Provided is an anode obtained by continuously drawing a lead alloy hot water from a mold in a strip shape in a non-oxidizing gas atmosphere, and then cutting it into an anode shape.

The lead alloy anode used in the present invention is manufactured by cutting a strip-shaped lead alloy obtained by continuously drawing a lead alloy hot water from a mold into an anode shape.

As a preferred continuous casting apparatus for producing the above anode,
It may be of the usual type in which the melt is poured from a tundish into a mold. The lead alloy that has passed through the mold and solidified is pressed by a pinch roll, further narrowed down by a leveler, and then cut into an anode shape. In continuous casting, when pouring molten metal from a tundish into a mold, the amount of outside air entrapped is extremely small and blowholes are reliably prevented. Incidentally, the porosity of the anode by the conventional stationary casting method is about 1.4 to 4.2%, whereas the porosity of the anode according to the present invention is 1.0% or less, and the porosity is significantly reduced. There is.

During the continuous casting, it is preferable that the lead alloy is passed through the mold under a non-oxidizing gas atmosphere such as nitrogen and argon. This can prevent oxidation of the alloy. Further, the anode manufactured by the continuous casting method has an advantage that the plate pressure is more uniform than that of the conventional stationary casting method.

Next, when the lead alloy is drawn from the mold, the plate thickness should be 5-30
Adjust to about mm. The anode used in zinc electrolytic smelting has a plate thickness smaller than that of a copper smelting anode (usually 10 mm or more) and is about 5 to 7 mm due to the size of the electrolytic cell. In order to obtain the above plate thickness, during continuous casting, the strip-shaped lead alloy drawn from the mold may be hot rolled as it is, or the strip-shaped alloy previously drawn from the mold may be heated and then rolled. Good. The rolled alloy strip is too smooth and serves as a protective film on the anode surface.
Since PbO ₂ and MnO ₂ are easily peeled off, it is advisable to form fine flaws on the surface by brushing after rolling to enhance the adhesiveness of the coating film.

The lead alloy anode can also be used for cadmium electrolysis.

[Examples and Comparative Examples] Example 1 (comparison of porosity) Anode of the present invention (Pb-1% Ag, plate width: 62.0 cm, length: 101c)
m, plate thickness: 7 mm) was horizontally cut into 11 equal parts, and the porosity of each cut piece was measured. On the other hand, a conventional stationary anode (Pb-1% Ag, plate width: 62.0 cm, length: 101 cm, plate thickness: 7 mm) that had been conventionally used was similarly cut and the porosity was measured. The results are shown in Table 1.

Example 2 (Production of Pb-1% Ag Anode) Pb was dissolved in a melting pot having a capacity of 5 tons, and the melt was heated at 320 to 340 ° C.
After adding 10Kg of Ag per 1000Kg of Pb to dissolve at 410-430 ℃
The temperature was raised to 0 to obtain a Pb-Ag alloy. The melt is passed through the mold from the tundish, the solidified Pb alloy is continuously drawn out by the first pinch roll and the second pinch roll, and the thickness is adjusted to 7 mm from above and below by the leveler, and 1010 mm in length and 620 mm in width by shirring. 25 pieces of anode plates were manufactured by cutting into the shape of the anode. The inside of the mold was of a hermetic type, and was sealed with Ar gas to prevent the oxidation of the melt. The composition of the obtained anode was Ag: 0.98% by weight, and the balance was Pb. The 25 anodes and 24 Al cathode plates were suspended in a zinc electrolytic cell to electrolytically recover zinc at a current density of 500 A / m ² .

Similarly, electrolytic recovery of zinc was carried out under the above-mentioned electrolysis conditions by using a conventional stationary casting anode. The results are shown in Table 2.

[Advantages of the Invention] Since the anode of the present invention has extremely few blow holes, there is almost no possibility of degrading the quality of cathode zinc due to elution of lead, and the quality of recovered zinc is improved. The plate pressure is more uniform than the stationary casting method. As a result, the surface distance between the anode and the cathode becomes constant, a local bias in the current density is prevented, and there is almost no short circuit between the anodes, thus improving the current efficiency.

Further, the anode used in the present invention has better corrosion resistance than the conventional one even when forming a perforated anode, and maintenance of the anode and the like can be greatly reduced as compared with the conventional electrolytic recovery.

Further, the anode used in the present invention has a uniform structure,
Zinc electrolysis using an anode having a thinner plate thickness than the copper electrolysis anode is more effective in preventing uneven current density. The effect of blowholes is greater in the zinc electrolysis anode than in the case of copper electrolysis, but this problem can be solved and the zinc electrolysis operation can be efficiently performed by using the anode produced by the continuous casting.

Also, when used as an anode for cadmium electrolysis, the quality of recovered cadmium is high because less lead is eluted, and the current density is uniform, the current efficiency is improved, and the corrosion resistance is also excellent.

Claims (3)

[Claims] 1. A lead alloy anode obtained by continuously drawing a lead alloy hot water from a mold in a strip shape and then cutting it into an anode shape, the anode having a porosity of 1.0% or less for zinc and cadmium electrolysis. . 2. The anode according to claim 1, wherein the lead alloy hot water is continuously drawn from the mold at the same time as or after being drawn, and then rolled to be cut into an anode shape. 3. The anode according to claim 1, which is obtained by continuously withdrawing a lead alloy hot water from a mold in a strip shape in a non-oxidizing gas atmosphere and then cutting it into an anode shape.