JPH09217190A - Energization method in electrolytic refining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the degradation in current efficiency and improve an electrodeposited surface state by setting specified pause time at the time of changing over a forward direction to backward direction. SOLUTION: The pause time in changeover of forward and backward energization in electrolytic refining of metal is 30 to 100 seconds and the changeover of current directions is executed at a ratio of once every 15 minutes to 1 hour, by which the occurrence of an anode passive state is prevented and the degradation in the current efficiency is minimized. The degradation in the current efficiency occurs in the instantaneous shorting by the reversing of the current in the electrified layer of the cathode surface, in addition to the dissolution of the cathode. Then, the electrodeposition progresses even during the discharge time and the degradation in the current efficiency is effectively prevented if the current direction is reversed after the electrified layer is discharged with the pause of the specified time. The reason thereof conceivably lies in that the required metallic ion concn. is restored by natural convection and diffusion while the electrified layer is not annihilated right after the service interruption.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention can be utilized for operations such as electrolytic refining of copper and nickel, electrolytic extraction, and the like, which use a high current density.

[0002]

2. Description of the Related Art In electrolytic refining of copper or the like, a high current density operation is performed in order to improve productivity. In electrolysis with high current density, particles may be generated on the cathode side and passivated on the anode side. For this reason, the direction of the current of the anode and the cathode is periodically, that is, the positive electrode of electricity is connected to the anode side and the negative electrode of electricity is connected to the cathode side to conduct electricity (hereinafter, referred to as positive direction), or to the anode side. An industrial method is an energization method (hereinafter referred to as PR energization) in which an electric negative electrode is connected and an electric positive electrode is connected to a cathode side to energize (hereinafter, reverse direction) to reduce polarization on an electrode surface. Has been used for.

However, there is a problem that the appearance of PR-conducting electrolytic copper is deteriorated as compared with that of unidirectionally-conducting electrolytic copper. Further, in PR energization, in general, re-melting of the electrodeposited surface is repeated in a short cycle of about several minutes or less, so that there is a problem that the actual current efficiency becomes low.

It has been attempted to extend the current reversal time or increase the amount of current for reversal in order to prevent the deterioration of the appearance, but remelting is not always performed uniformly, and the current efficiency is further improved. It was not effective because it decreased.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to improve the surface of electrodeposition and effectively utilize electric power during PR energization.

[0006]

In order to solve the above-mentioned problems, the present invention provides a certain pause time when switching the energization from the forward direction to the reverse direction. This constant dwell time is associated with the disappearance of the charged layer in the electrolyte. Further, in the present invention, switching of energization is performed in a long cycle to minimize a decrease in current efficiency. The method of the present invention is called PPR energization, as opposed to conventional PR energization.

According to the energization method of the present invention, in the electrolytic refining of a metal in which an electric current is applied while periodically reversing the electric current, an electric current is applied in the reverse direction after a power failure for a certain period of time in which the charged layer is present after the application of the positive direction. Is characterized by.

The certain period of time is preferably 30 seconds or more and less than 100 seconds. Also, switching the current direction is 15 minutes to 1
By performing the operation once a time, it is possible to prevent the occurrence of anode passivation and suppress the decrease in current efficiency to the minimum. Further, the metal is copper or nickel,
It is selected from gold, silver, lead and zinc.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In PPR energization used in high current density electrolysis, energization in the forward and reverse directions is periodically repeated as in the conventional PR energization. In PPR energization for the purpose of preventing anode passivation, switching in the forward and reverse directions is the same as the conventional PR.
It has been found that the switching can be sufficiently prevented by switching once every 15 minutes to 1 hour, which is a cycle longer than a few minutes of energization. If passivation can be prevented, it is more efficient and economical to reduce the switching frequency.

Further, in the conventional PR method, there is a problem that the current efficiency is lowered because part of the electrodeposition on the cathode is dissolved. However, the decrease in current efficiency is caused not only by the dissolution of the cathode but also on the surface of the cathode. It is considered that this is also due to the fact that the charging layer such as the double layer is short-circuited instantaneously due to the reversal of the current. To prevent this, if the charging layer is discharged and then the current direction is reversed as in PPR energization, it is considered that electrodeposition proceeds even during the discharge time, which is effective in preventing a decrease in current efficiency.

The discharge time on the electrode surface can be easily known by the change in the cell voltage after the power failure of the electrolytic cell. As a result of measuring the discharge time under various current densities, it was found that the discharge was completed within about 30 seconds. That is, it is considered that the current efficiency can be prevented from being lowered by providing a power failure time of at least 30 seconds after the current is applied in the positive direction and completely discharging the power. The margin time in this regard is 100 seconds, so that a further power outage reduces production efficiency.

It has also been found that the electric copper surface is effectively improved when the reverse current is zero during PPR energization, that is, when a temporary power failure is performed. It has been known for a long time to improve the appearance by applying a PR current, but it has been found that the improvement of the appearance is difficult unless reverse electrolysis is performed for a long time.

In copper electrolysis, the copper concentration on the cathode surface is close to 0 during energization, but this tendency is accelerated especially at high current densities. When the copper concentration on the cathode surface becomes 0, smooth electrodeposition cannot be obtained, but by reversing the current direction, the cathode surface can be dissolved and the copper concentration near the surface can be recovered.

However, as in the case of PPR energization, even if a power failure occurs without reversing the current, the liquid concentration on the electrode surface during energization and the diffusion from the electrolytic solution to the electrode surface restores the copper concentration on the cathode surface to a considerable extent. can do. Therefore, it is conceivable that the copper concentration on the electrode surface will be further increased by recovering the copper concentration by natural convection and diffusion due to the liquid flow and reversing the current after the disappearance for about 30 seconds after the power failure, where the charged layer does not disappear. To be In PPR energization, the natural convection and diffusion phenomena are effectively used in the power failure operation, so that the copper concentration on the cathode surface can be increased more economically than in the conventional PR energization electrolysis.

As described above, the current efficiency is improved and the electrodeposition surface is improved by the energization method in which the current is switched by the long cycle and the temporary power failure is carried out for about 30 seconds to completely discharge at the time of switching from the forward direction to the reverse direction. The improvement of the condition can be effectively realized.

[0016]

【Example】

[Example 1] Purified anode (size: length 1030 x width 10)
50 pieces x thickness 38 mm, weight 360 kg 26 sheets and copper cathode (size length 1050 x width 1070 x thickness 0.7 m)
m, weight about 7 kg) 25 sheets electrolyzer (size length 300
0 × width 1260 × depth 1390 mm). Copper 5
An electrolytic solution having a composition of 0 g / l and sulfuric acid 190 g / l and having a liquid temperature of 60 ° C. was circulated at 20 liters per minute. The cathode current density was 350 A / m ^{2 in} both the forward and reverse directions.

Three battery tanks were prepared and used as tank A, tank B, and tank C. The effective current efficiency was defined by the following formula (Equation 1).

[0018]

## EQU1 ## E = (TP × IP-TR × IR) / (TP + T
R) × 100 E; Effective current efficiency (%) TP; Forward direction time TR; Reverse direction time IP; Forward direction current IR; Reverse direction current

This effective current efficiency directly affects the electric power consumption rate and becomes an index of economic efficiency.

In tank A, electricity was applied in the forward direction for 200 seconds and then electricity was applied in the reverse direction for 10 seconds. The effective current efficiency of tank A was 90.5%.

In tank B, a reversing time of 30 seconds was set every 29.5 minutes in the positive direction of the energization method. The effective current efficiency of tank B is 9
It was 6.2%.

The tank C was turned off every 29 minutes and 10 seconds for 30 seconds and then reversed for 20 seconds. Effective current efficiency of tank C is 97.7.
%.

Power was supplied for 240 hours, and it was checked every day during the power supply whether or not a short circuit occurred. After the completion of energization, the appearance of electrolytic copper was visually evaluated on a 90-point scale. As shown in the results in Table 1, it was confirmed that the operation performance of the long-period energization of the tank C, which had a power failure at the time of switching, was excellent.

[0024]

[Table 1] [Effect of energization method on operating results] Energization method Appearance Short-circuit rate Current efficiency Effective current efficiency (points) (%) (%) (%) A Short cycle PR 59 3.81 86.8 90.5 B long period PR 67 6.83 93.0 96.2 C long period PPR 72 1.43 94.3 97.7

[Embodiment 2] Although Embodiment 1 is of copper electrolysis, when the same PPR electrolysis was applied to nickel metal electrolysis, gold electrolysis, and lead electrolysis, similar effects were obtained.

[0026]

EFFECTS OF THE INVENTION Since the present invention is configured as described above, it is possible to prevent the deterioration of current efficiency and improve the appearance in the operation at high current density, and improve the productivity and quality.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C25C 1/20 C25C 1/20

Claims (4)

[Claims] 1. In electrolytic refining of a metal, in which an electric current is periodically applied while reversing the electric current, the electric current is applied in the reverse direction after a power failure for a period of time until the charge layer disappears after applying the electric current in the positive direction. How to energize. 2. The energization method according to claim 1, wherein the constant time is 30 seconds or more and less than 100 seconds. 3. The switching of the current direction is performed once every 15 minutes to 1 hour to prevent the occurrence of anode passivation and to minimize the decrease in current efficiency. The energization method according to Item 1. 4. The metal is copper or nickel, gold, silver, lead,
The energization method according to claim 1, which is zinc.