JP2013040368A - Operating method of lead electrorefining equipment - Google Patents

Abstract

Provided is a method for operating a lead electrolytic refining facility that can maintain the temperature of an electrolyte solution and prevent deterioration of the quality of electrodeposited lead even during a power failure.
A lead electrolytic purification comprising an electrolytic cell, an anode and a cathode inserted into the electrolytic cell, an electrolytic solution circulating device for circulating the electrolytic solution in the electrolytic cell, and a heater for heating the electrolytic solution. In the facility, the circulating flow rate of the electrolytic solution during a power outage is set to a flow rate at which the oxidation of the electrolytic solution is suppressed to the extent that impurities are not deposited on the cathode. Since the temperature of the electrolytic solution can be maintained, it is possible to prevent salt from depositing in the electrolytic solution circulation system and to prevent the electrolytic cell from being damaged. Oxygen entrainment in the electrolyte circulation system can be suppressed and oxidation of the electrolyte can be suppressed, and it is possible to prevent impurities from depositing on the cathode and degrading the quality of electrodeposited lead.
[Selection] Figure 1

Description

  The present invention relates to a method for operating a lead electrolytic purification facility. More specifically, the present invention relates to a method for operating a lead electrolytic purification facility during a power outage.

  In electrolytic purification, an anode and a cathode are inserted into an electrolytic tank filled with an electrolytic solution, and a current is applied between the anode and the cathode to deposit a target metal on the cathode. In order to obtain uniform and high-quality electrodeposition, the electrolyte is circulated in the electrolyte circulation system, and the electrolyte discharged from the electrolytic cell is freed of impurities in the liquid purification process and supplied to the electrolytic cell again. The

  For example, in the case of electrolytic purification of lead, the Betz method is generally used. The Betz method uses an electrolytic solution consisting of silicic acid and lead silicofluoride, and the crude lead with a purity of about 98% obtained by dry smelting is used as the anode, and the seed plate lead formed from pure lead as a plate is used as the cathode. . Crude lead constituting the anode contains impurities such as zinc, iron, arsenic, antimony, bismuth, copper, and silver in addition to lead.

  When electricity is applied between the anode and the cathode, lead elutes from the anode surface into the electrolyte and deposits on the cathode surface. At this time, impurities having a higher potential than lead, such as arsenic, antimony, bismuth, copper, silver, and the like contained in the anode remain as slime on the anode surface without being eluted. On the other hand, impurities having a lower potential than lead, such as zinc and iron, elute from the anode into the electrolyte but do not deposit on the cathode surface. Therefore, only lead is deposited on the cathode surface, and high purity electrodeposited lead can be obtained (see Non-Patent Document 1).

By the way, in an electrolytic refining facility, there is a case where the energization between the anode and the cathode is temporarily stopped or lowered (hereinafter referred to as a power failure) for the purpose of maintenance of the facility or adjustment of the production amount. At this time, the following two operational problems may occur.
(1) During energization, Joule heat is generated due to the electric resistance of the electrolyte existing between the anode and the cathode. Therefore, when a power failure occurs, the generation of Joule heat stops or decreases, and the temperature of the electrolyte decreases. When the temperature of the electrolytic solution is lowered for a long period of time, there is a problem that crystals of salt of the electrolytic solution component are deposited in the piping of the electrolytic solution circulation system, thereby obstructing the passage of the electrolytic solution.
(2) Moreover, when the temperature of electrolyte solution falls, the material which comprises an electrolytic cell will shrink. Therefore, when energization and power failure are repeated, heating and cooling of the electrolytic cell are repeated, and there is a problem that the electrolytic cell is damaged due to expansion and contraction.

  In order to avoid the above problem, even during a power failure, the temperature of the electrolyte is maintained by a heater provided in the electrolyte circulation system by circulating the electrolyte.

However, the electrolytic solution used for lead electrolytic purification has a feature that the electric resistance is higher than the electrolytic solution used for copper electrolytic purification. For this reason, there is a problem that the amount of heat generated by the electrolyte during energization is large, and in order to supplement this amount of heat generated by a heater, equipment costs are required.
Further, when all of the amount of heat generated during energization is supplemented by a heater, there is a problem that immediately after resuming energization, heat generated by energization is also added and the amount of heat in the electrolytic cell becomes excessive.

  Furthermore, in the case of lead electrolytic refining, the present inventor has a problem that bismuth and copper contained in the anode are easily eluted and deposited on the cathode surface when the power is interrupted for a long time while circulating the electrolyte. I found it. When bismuth or copper is deposited on the cathode surface, there is a problem that the quality of electrodeposited lead is lowered. In general, it is rare to cause a power outage for a long period of time in lead electrolytic refining, so it is considered that this problem has not been realized until now.

Edited by The Japan Institute of Metals, “Metal Smelting Engineering” The Japan Institute of Metals, issued July 1, 2006, p.138-139

  In view of the above circumstances, an object of the present invention is to provide a method for operating a lead electrolytic refining facility that can maintain the temperature of an electrolytic solution even during a power outage and prevent deterioration of the quality of electrodeposited lead.

A method for operating a lead electrolytic refining facility according to a first aspect of the present invention includes an electrolytic cell, an anode and a cathode inserted in the electrolytic cell, an electrolytic solution circulating device for circulating an electrolytic solution in the electrolytic cell, and the electrolytic solution circulating device. In a lead electrolytic refining facility comprising a heater for heating a circulating electrolyte solution, the circulating flow rate of the electrolyte solution during a power outage is smaller than the circulating flow rate during energization.
The operation method of the lead electrolytic purification equipment of the second invention is the first invention, wherein the circulating flow rate of the electrolytic solution during a power failure is set to a flow rate at which the oxidation of the electrolytic solution is suppressed to such an extent that impurities are not deposited on the cathode. It is characterized by.
The operation method of the lead electrolytic refining facility according to the third invention is characterized in that, in the second invention, the circulating flow rate of the electrolytic solution during a power outage is approximately half of the circulating flow rate during energization.

According to the first invention, since the temperature of the electrolytic solution can be maintained, it is possible to prevent the salt from being deposited in the electrolytic solution circulation system and to prevent the electrolytic cell from being damaged. In addition, since the circulating flow rate of the electrolyte during a power outage is made smaller than the circulating flow rate during energization, oxygen entrainment in the electrolyte circulation system is suppressed, and oxidation of the electrolyte can be suppressed. Therefore, it is possible to prevent the quality of the electrodeposited lead from deteriorating due to impurities being deposited on the cathode.
According to the second invention, it is possible to prevent impurities from precipitating on the cathode and degrading the quality of electrodeposited lead.
According to the third aspect of the invention, the circulation flow rate of the electrolytic solution during a power outage is made approximately half of the circulating flow rate during energization, so that oxygen entrainment in the electrolytic solution circulation system can be suppressed and oxidation of the electrolytic solution can be suppressed. Therefore, it is possible to prevent the quality of the electrodeposited lead from deteriorating due to impurities being deposited on the cathode.

It is the schematic of general lead electrolysis refinement | purification equipment. It is a graph which shows the measurement result of the current density in an Example, and the bismuth density | concentration of electrolyte solution. It is a graph which shows the measurement result of the current density and electrolyte solution temperature in an Example. It is a graph which shows the measurement result of the current density and the bismuth density | concentration of electrolyte solution in a comparative example. It is a graph which shows the measurement result of the current density and electrolyte solution temperature in a comparative example.

Next, an embodiment of the present invention will be described with reference to the drawings.
First, the structure of a general lead electrolytic purification facility will be described.
In FIG. 1, 1 is an electrolysis tank, 2 is a drainage tank, 3 is a pump, 4 is a heat exchanger, 5 is a liquid supply tank, and these form an electrolyte circulation system.

  A plurality of pairs of crude lead anodes and pure lead cathodes are inserted into the electrolytic cell 1 and filled with an electrolytic solution. The electrolytic solution is discharged from one end of the electrolytic tank 1 and supplied to the drained tank 2 by a drop. The drainage tank 2, the heat exchanger 4 and the liquid supply tank 5 are connected by a pipe, and a pump 3 is interposed in the pipe. By driving the pump 3, a predetermined flow rate of the electrolyte is supplied from the drainage tank 2 to the heat exchanger 4 or the liquid supply tank 5. The electrolytic solution supplied to the heat exchanger 4 is heated and supplied to the liquid supply tank 5. Then, the electrolytic solution discharged from the liquid supply tank 5 is supplied to the electrolytic tank 1 by a drop.

  Thus, the electrolytic solution circulates in the electrolytic solution circulation system, and the electrolytic solution discharged from the electrolytic cell 1 is heated and then supplied to the electrolytic cell 1 again. Further, impurities are removed while the electrolytic solution circulates in the electrolytic solution circulation system. Removal of impurities in the electrolyte includes, for example, extracting a part of the electrolyte from the electrolyte circulation system and cementing impurities such as bismuth and copper on the lead plate that have nobler potential than lead. It is carried out by precipitating impurities by the treatment.

Further, a power source is connected to the anode and the cathode inserted into the electrolytic cell 1, and electricity is passed between the anode and the cathode so that lead eluted from the anode is deposited on the cathode. In addition, the power supply between the anode and the cathode can be stopped or reduced (hereinafter referred to as a power failure) for equipment maintenance, production volume adjustment, and the like.
In the present specification, the term “power failure” is a concept including so-called safety energization that lowers the energization between the anode and the cathode in addition to the case where the energization between the anode and the cathode is completely stopped.

In addition, the drainage tank 2, the pump 3, the liquid supply tank 5, and the piping that connects them correspond to the electrolytic solution circulation device described in the claims. The heat exchanger 4 corresponds to the heater described in the claims.
The operation method of the lead electrolytic refining equipment according to the present invention is not limited to the lead electrolytic refining equipment having the above-described configuration, and the lead is provided with an electrolytic solution circulating device that circulates the electrolytic solution in the electrolytic bath and a heater that heats the electrolytic solution. As long as it is an electrolytic purification facility, it can be applied to a lead electrolytic purification facility having any configuration.

  The inventor of the present application has found that when the power is interrupted in a state where the electrolytic solution is circulated, impurities contained in the anode are deposited on the cathode surface because the electrolytic solution is oxidized.

More specifically, when the electrolytic solution is oxidized, the electrolytic solution acts as an oxidant on the surface of the anode, and impurities such as bismuth and copper contained in the anode are oxidized and eluted into the electrolytic solution. Impurities eluted in the electrolyte are considered to be reduced and deposited at the cathode.
The reason why impurities are not deposited on the cathode during energization is that the inside of the electrolyzer being energized is electrically reduced, so that the oxidized electrolyte is reduced and impurities are not eluted from the anode. it is conceivable that.

The oxidation of the electrolytic solution occurs when the electrolytic solution circulates in the electrolytic solution circulation system. Specifically, when the electrolytic solution is sucked by the pump 3, when the electrolytic solution is supplied from the electrolytic cell 1 to the drainage tank 2, oxygen is involved when the electrolytic solution is supplied from the liquid supply tank 5 to the electrolytic cell 1. Oxidized.
Here, since the supply from the electrolytic cell 1 to the drainage tank 2 and the supply from the liquid supply tank 5 to the electrolytic tank 1 are performed by natural flow using a drop, the more the circulating flow rate is, the more oxygen is involved. Become more oxidized.

  Therefore, if the circulating flow rate of the electrolyte during a power outage is less than the circulating flow rate during energization, less oxygen is entrained in the electrolyte circulation system, oxidation can be suppressed, and precipitation of impurities on the cathode can be suppressed. Conceivable. In other words, the circulating flow rate of the electrolytic solution during a power outage may be reduced to a flow rate at which the oxidation of the electrolytic solution is suppressed to such an extent that impurities are not deposited on the cathode.

  On the other hand, when the circulation of the electrolytic solution is stopped, the electrolytic solution cannot be heated by the heat exchanger 4, so the temperature of the electrolytic solution is lowered, salt is deposited in the piping of the electrolytic solution circulation system, and the expansion and contraction are repeated. There is a problem that the electrolytic cell is damaged.

  Therefore, it is necessary to circulate the electrolyte to some extent even during a power outage and heat the heat exchanger 4 to maintain the temperature. Note that the temperature of the electrolyte does not need to be maintained during energization, is a temperature at which salt crystals of the electrolyte component do not precipitate in the piping of the electrolyte circulation system, and expands due to repeated power outages and energization. It is sufficient that the temperature is such that the electrolytic cell may not be damaged due to shrinkage.

As described above, by adjusting the circulation flow rate of the electrolytic solution during a power failure, the oxygen entrainment in the electrolytic solution circulation system can be suppressed and the oxidation of the electrolytic solution can be suppressed. Therefore, it is possible to prevent the quality of the electrodeposited lead from deteriorating due to impurities being deposited on the cathode.
Moreover, since the temperature of electrolyte solution can be maintained with the heat exchanger 4, it can prevent that salt precipitates in an electrolyte solution circulation system, and can prevent that an electrolytic cell is damaged.

In addition, the measurement of the circulating flow rate of the electrolytic solution takes time required to fill up the electrolyte circulation system by interposing a weir type flow meter or receiving the electrolytic solution discharged from the electrolytic cell 1 in a container of a known capacity. A simple method such as measuring can be employed.
Further, the flow rate of the electrolytic solution discharged from the electrolytic cell 1 may be measured, or the flow rate of the electrolytic solution supplied to the electrolytic cell 1 may be measured. However, since the electrolytic solution is also oxidized by measuring the circulation flow rate, it is preferable to measure the flow rate of the electrolytic solution discharged from the electrolytic cell 1 because the oxidation of the supplied electrolytic solution in the electrolytic cell 1 can be suppressed. .

Next, examples will be described.
The following examples and comparative examples were carried out in the lead electrolytic purification equipment shown in FIG.
The electrolytic cell 1 was filled with an electrolytic solution by inserting a crude lead anode and a pure lead cathode. Here, the dimensions of the electrolytic cell 1 are 1,100 mm in width, 6,000 mm in length, 1,500 mm in depth, the dimensions of the anode are 740 mm wide, 920 mm long, 30 mm thick, the weight is about 270 kg, and the dimensions of the cathode are It is 740mm wide, 920mm long and 3mm thick. 54 anodes and 55 cathodes were alternately inserted into the electrolytic cell 1 at intervals of 110 mm. The electrolyte contains lead silicofluoride (PbSiF ₆ ) at a concentration of 110 g / L, free hydrosilicofluoric acid (H ₂ SiF ₆ ) at 110 g / L, and impurity bismuth at a concentration of 0.001 to 0.002 g / L. .

  The electrolytic solution is discharged from one end of the electrolytic cell 1 and supplied to the drainage tank 2 having a capacity of 3000 L by a drop. The electrolyte is supplied to the heat exchanger 4 and the supply tank 5 by the pump 3 connected to the drain tank 2, and the electrolyte supplied to the heat exchanger 4 is heated and supplied to the supply tank 5. . Then, the electrolytic solution discharged from the liquid supply tank 5 is supplied to the electrolytic tank 1 by a drop.

During energization, the heat exchanger 4 was adjusted so that the temperature of the electrolyte immediately after heating was 45 ° C., and the flow rate of the pump 3 was set to 30 L / min. Further, the current density was set to 185 A / m ² during energization.

(Example)
As shown in the graph of FIG. 2, after 190 hours in the energized state, the current density was set to 0 A / m ² and a power failure (hereinafter referred to as complete power failure) was caused. After a complete power failure for 120 hours, the current density was switched to 6.8 A / m ² for safe energization and then returned to the energized state. Note that one scale on the horizontal axis of the graph shown in FIG. 2 is 24 hours.
During complete power failure and safety energization, the flow rate of the pump 3 was set to 15 L / min, and the circulating flow rate of the electrolyte was half of the circulating flow rate during energization.

  During this period, the bismuth concentration and temperature of the electrolytic solution in the electrolytic cell 1 were measured. As a result, the graphs shown in FIGS. 2 and 3 were obtained. The bismuth concentration was determined by sampling the electrolytic solution and analyzing it using ICP emission spectral analysis.

From the graph shown in Fig. 2, the concentration of bismuth during complete power outage and safety energization is suppressed to approximately twice the concentration of bismuth during energization, and is 0.002 g / L or less, which does not cause a problem in the quality of electrodeposited lead. It was confirmed that.
Also, the cathode was lifted and washed, the electrodeposited lead was sampled, dissolved in nitric acid, and analyzed using ICP emission spectroscopy (Seiko Instruments Inc. SPS7800). As a result, the bismuth quality of electrodeposited lead was less than 10 ppm. It was confirmed that the copper quality was less than 5 ppm, which was the same as the quality of electrodeposited lead obtained by continuous energization.

  Further, from the graph shown in FIG. 3, it was confirmed that the electrolyte temperature during complete power failure and safety energization was maintained at about 45 ° C. without changing from the electrolyte temperature during energization. Therefore, it has been found that the salt of the electrolyte component does not precipitate in the piping of the electrolytic solution circulation system, and there is no possibility that the electrolytic solution is impeded. Further, it was found that the electrolytic cell 1 is not repeatedly heated and cooled, and the electrolytic cell 1 is not damaged by expansion and contraction.

(Comparative example)
As shown in the graph of FIG. 4, after 190 hours had passed in the energized state, the power was cut off for 120 hours through the safety energization. After that, the safety energization was performed again to restore the energized state. Note that one scale on the horizontal axis of the graph shown in FIG. 4 is 24 hours.
During complete power failure and safety energization, the flow rate of the pump 3 was set to 30 L / min, and the circulating flow rate of the electrolyte was the same as the circulating flow rate during energization.

  During this period, the bismuth concentration and temperature of the electrolytic solution in the electrolytic cell 1 were measured. As a result, the graphs shown in FIGS. 4 and 5 were obtained.

From the graph shown in FIG. 4, it was confirmed that the bismuth concentration during complete power failure and safety energization increased sharply as compared with the example, and increased to about 10 times the bismuth concentration during energization at the maximum.
Also, the cathode was lifted and cleaned, and the electrodeposited lead was sampled and dissolved in nitric acid, and analyzed using ICP emission spectroscopy (Seiko Instruments Inc. SPS7800). As a result, the bismuth quality of electrodeposited lead was 175 ppm. In other words, the copper quality was 25 ppm, which was confirmed to be higher than that of the example.

  Further, from the graph shown in FIG. 5, it is confirmed that the electrolyte temperature during the safety energization is lower than the electrolyte temperature during the energization, and the electrolyte temperature during the complete power failure is further lower than the electrolyte temperature during the safety energization. It was. For this reason, it has been found that there is a possibility that a salt crystal of the electrolyte component is deposited in the piping of the electrolytic solution circulation system, or the electrolytic cell 1 is damaged due to expansion and contraction.

DESCRIPTION OF SYMBOLS 1 Electrolysis tank 2 Drainage tank 3 Pump 4 Heat exchanger 5 Liquid supply tank

Claims (3)

An electrolytic cell, an anode and a cathode inserted in the electrolytic cell, an electrolytic solution circulating device for circulating the electrolytic solution in the electrolytic cell, and a heater for heating the electrolytic solution circulated by the electrolytic solution circulating device In lead electrolytic purification equipment,
A method for operating a lead electrolytic refining facility, characterized in that a circulating flow rate of the electrolyte during a power failure is less than a circulating flow rate during energization. 2. The method of operating a lead electrolytic refining facility according to claim 1, wherein a circulation flow rate of the electrolytic solution during a power failure is set to a flow rate at which oxidation of the electrolytic solution is suppressed to such an extent that impurities are not deposited on the cathode. The method for operating a lead electrolytic refining facility according to claim 2, wherein the circulating flow rate of the electrolyte during a power failure is approximately half of the circulating flow rate during energization.

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