JP5213828B2 - Method for electrolytic purification of copper - Google Patents

Description

  The present invention relates to a copper electrolytic purification method, and more particularly, to a copper electrolytic purification method that can be used as a countermeasure during a power failure.

  A process called a permanent cathode (PC) method is known as an electrolytic purification process for converting crude copper into purified copper. The PC method is a method in which a metal plate is used as a cathode, and the copper electrodeposited by electrolysis on the surface of the cathode is peeled off to make a product. Compared with the conventional method, the PC method has higher productivity and high quality copper. In recent years, it has been used in various electrolytic refining factories.

  In an electrolytic refining factory, there may be a simultaneous power outage for about 8-12 hours about once a year for substation equipment. There may be a power outage due to conductor work, piping work, electrolytic cell maintenance, etc. However, in an electrolytic refining factory using the PC method, if energization is stopped for a long time, a problem of lamination occurs. “Lamination” is divided into two layers, when the electrodeposited copper is mechanically peeled from the cathode, between the electrodeposited copper layer deposited before the power failure and the re-electrodeposited copper layer deposited after the power failure. It refers to a phenomenon in which cracks generated at the lower end of the electrodeposited copper layer are difficult to propagate to the re-electrodeposited copper layer.

  When the crack of the electrodeposited copper layer does not progress smoothly, it is necessary to repeatedly apply a load called “flapping” by the PC stripper to cause the crack to be forcibly generated. In ordinary electrolytic purification, the electrodeposited copper can be completely removed by performing flapping once.

  However, when a power outage for a long time occurs during electrolytic refining, it is necessary to repeat the flapping operation many times due to the above-described problems. Therefore, the working time is prolonged and the copper production efficiency is lowered. Since the cathode electrode plate may need to be replaced due to poor stripping of electrodeposited copper, the working time may be further prolonged. The poor stripping of the electrodeposited copper is considered to be one of the causes that the electrodeposited copper is exposed to the electrolytic solution for a long period of time and a thin film is deposited on the electrodeposited copper. For this reason, it is necessary to take some measures against thin film adhesion in order to suppress electrodeposition copper stripping failure.

  In Japanese Patent Application Laid-Open No. 2008-248273, at the time of a planned power outage at an electrolytic refining plant, the current applied to the electrolytic cell is gently dropped, and then the power is restored to the power outage at a low current until the power outage is restored. A method for inhibiting thin film formation is disclosed.

JP 2008-248273 A

  In view of the above-described problems, the present invention provides another method for suppressing poor peeling of electrodeposited copper. Providing another method as a countermeasure for suppressing the peeling defect of electrodeposited copper is useful because it increases the options and makes it possible to take more preferable countermeasures according to individual circumstances of those skilled in the art.

  In order to solve the above-mentioned problems, the present inventor has intensively studied and removed a thin film adhering to the surface of the electrodeposited copper by passing a current in a direction opposite to that during normal operation between the electrodes for a certain period after the power failure. It has been found that when the normal operation is resumed afterwards, it is possible to suppress the stripping failure of the electrodeposited copper.

The present invention completed on the basis of the above knowledge is, in one aspect, a method of performing copper electrolytic purification by immersing the first electrode and the second electrode made of crude copper in an electrolytic cell containing an electrolytic solution, a) flowing a first current between the first electrode and the second electrode with the first electrode as a cathode and the second electrode as an anode, and depositing an electrodeposited copper layer on the surface of the first electrode; ) A step of stopping the supply of the first current; and (c) after the lapse of a predetermined time after the stop, a second current having the first electrode as an anode and the second electrode as a cathode is between the first electrode and the second electrode. Removing the copper compound layer containing copper chloride formed on the electrodeposited copper layer by holding the electrodeposited copper immersed in the electrolyte after stopping , and (d) a copper compound After removal of the layer, a third current is generated with the first electrode as the cathode and the second electrode as the anode. It flowed between the electrode and a second electrode, an electrolytic purification process for copper and a step of electrodepositing re electrostatic Chakudoso the surface of the electrostatic Chakudoso.

  In one embodiment, the copper electrolytic purification method according to the present invention further includes a step of causing a liquid flow to the electrode surface of the first electrode between at least the step (b) and the step (d).

  In one embodiment, the copper electrolytic purification method according to the present invention further includes a step of circulating an electrolytic solution between at least step (b) and step (d).

  In one embodiment, the copper electrolytic purification method according to the present invention has a current density smaller than the second current between the step (b) and the step (c), the first electrode as an anode, and the second electrode as an anode. The method further includes a step of flowing a fourth current serving as a cathode between the first electrode and the second electrode.

In one embodiment of the copper electrolytic purification method according to the present invention, the current density of the second current is 100 to 350 A / m ² .

  According to the present invention, it is possible to effectively remove the copper compound layer adhering to the surface of the electrodeposited copper that is exposed to the electrodeposition liquid for a long time during a power outage, and therefore, it is possible to prevent the replacement time from being extended due to poor peeling of the electrodeposited copper. . In addition, since the number of electrode replacements due to poor stripping of electrodeposited copper is reduced, there is no need to reduce production and the production efficiency of copper products is improved. Since the obtained copper product does not generate fragmentary protrusions or the like due to the influence of a power failure, the appearance of the product is improved. Further, since troubles and breakdowns of the stripping machine are reduced, repair costs can be reduced and productivity can be improved.

It is the schematic explaining an example of the electrolytic purification system for enforcing the electrolytic purification method of copper which concerns on embodiment of this invention. It is a schematic diagram showing the lamination | stacking state of the electrodeposition copper layer electrodeposited on a cathode electrode plate, and a re-electrodeposition copper layer. It is a flowchart explaining the electrolytic purification method of copper which concerns on embodiment of this invention.

  Next, embodiments of the present invention will be described with reference to the drawings. The following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is the following in terms of the structure and arrangement of components. It is not something specific.

-Electrolytic purification system-
The electrolytic purification system shown in FIG. 1 includes an electrolytic cell 1, a rectifier 2, a circulation tank 3, a head tank 4, and a control device 5. An electrolytic solution 11 is accommodated in the electrolytic cell 1. As the electrolyte solution 11, for example, a sulfuric acid electrolyte solution having a copper concentration of 50 to 60 g / L and a chlorine concentration of 50 to 60 mg / L can be used. A first electrode 13 made of stainless steel, aluminum, or the like and a second electrode 12 made of crude copper are immersed in the electrolytic solution 11. As the second electrode 12, for example, crude copper having 99.2 to 99.6% copper grade and containing Ni, Bi or the like as impurities can be used. Masking with resin (edge strip protector) is performed on the side surface of the first electrode 13. As shown in FIG. 2, a V-shaped groove 14 is formed at the bottom of the first electrode 13.

  The rectifier 2 supplies power to the first electrode 13 and the second electrode 12 immersed in the electrolytic cell 1. The circulation tank 3 may be provided with, for example, a sensor for controlling the physical state (temperature, concentration, etc.) of the electrolytic solution 11 in the electrolytic tank 1. Moreover, a pump (not shown) for circulating the electrolytic solution 11 through the electrolytic cell 1, the circulation tank 3, and the head tank 4 may be provided as necessary.

  The control device 5 controls the operation state of the electrolytic cell 1, the rectifier 2, the circulation tank 3, and the head tank 4. For example, the control device 5 determines the value of the current density supplied to the electrolytic cell 1 according to the operation status of the electrolytic purification system shown in FIG. 1, the timing of supplying current to the second electrode 12 and the first electrode 13, the energization period, etc. To control.

  Although not shown, in the copper electrolytic purification system according to the embodiment, an auxiliary power source (auxiliary rectifier) may be further provided. With the auxiliary power supply (auxiliary rectifier), it is possible to cause a weak current to flow in the electrolytic cell 1 during a power failure, or to cause a liquid flow to the electrode surface of the first electrode 13 in the electrolytic cell 1.

-Copper electrolytic purification method-
The copper electrolytic purification method according to the embodiment of the present invention will be described with reference to the flowchart shown in FIG.

  In step S1, normal operation is performed. That is, after operating conditions are set by the control device 5, the first electrode 13 is used as a cathode (a positive charge flows from the solution toward the electrode), and the second electrode 12 is set as an anode (the electrode from the electrode toward the solution). A first current (ordinary current) that is assumed to be an electric charge flows between the first electrode 13 and the second electrode 12. Thereby, the electrodeposited copper layer 6 is deposited on the surface of the first electrode 13. At this time, the circulation tank 3 may be driven as necessary, the electrolyte solution 11 may be circulated at a predetermined circulation flow rate, and the electrolyte solution 11 may be replenished into the electrolyte tank 1 from the head tank 4.

The conditions of the electrolytic solution 11 during normal operation can be set to, for example, a liquid temperature of 60 to 65 ° C., a copper concentration of 50 to 60 g / L, and a chlorine concentration of 50 to 60 mg / L. The current density of the first current is about 250~325A / m ^2.

  In step S2 of FIG. 3, the supply of the first current is stopped due to a power failure or the like. By stopping the supply of the first current, the deposition of the electrodeposited copper layer 6 on the first electrode 13 stops. After the supply of the first current is stopped, a power failure countermeasure is taken in step S3. Details of step S3 will be described later.

In step S4, normal operation is resumed. That is, a third current is flown with the first electrode 13 as a cathode and the second electrode 12 as an anode. By resuming normal operation, a re-deposited copper layer 7 is deposited on the electrodeposited copper layer 6 shown in FIG. The current density of the third current may be a 250~325A / m ² approximately.

  In step S5, the electrodeposited copper layer 6 and the re-electrodeposited copper layer 7 formed on the first electrode 13 are peeled off using a PC peeling machine. First, in the flexing process of the PC stripper, an external force is applied to the first electrode 13, the electrodeposited copper layer 6, and the re-electrodeposited copper layer 7 shown in FIG. The electrodeposited copper layer 7 is bent to cause peeling at the interface 8 between the first electrode 13 and the electrodeposited copper layer 6. In the chiseling step, a wedge is driven into the interface 8 to separate the electrodeposited copper layer 6 and the re-electrodeposited copper layer 7. In the down-end process, the electrodeposited copper layer 6 and the re-deposited copper layer 7 are simultaneously grasped with a grip and opened horizontally with the bottom of the electrodeposited copper layer 6 as a fulcrum, thereby causing a crack in the electrodeposited portion in contact with the groove 14. .

  When the crack does not progress smoothly, the electrodeposited copper layer 6 and the re-electrodeposited copper layer 7 are opened horizontally, and the electrodeposited copper layer 6 and the re-electrodeposited copper layer 7 are brought closer to the first electrode 13 side. Repeat the flapping operation as one set multiple times. Thereby, the electrodeposited copper layer 6 and the re-electrodeposited copper layer 7 are completely cut off from the first electrode 13 to obtain a product.

-Details of power outage countermeasures-
Before explaining the details of step S3, first, the reaction in the electrolytic cell 1 before and after the power failure will be explained. As described above, the electrolytic refining of copper during normal operation (step S1) is usually performed at a current density of about 250 to 325 A / m ^2, but when a power failure occurs, the current density in the electrolytic cell 1 is increased all at once. The electrodeposited copper layer 6 (see FIG. 2) deposited on the first electrode 13 becomes zero and is exposed to the electrolytic solution 11 for a long time. Thereafter, normal operation is resumed, the current value is increased to a normal operation value at once, and after forming the re-electrodeposited copper layer 7, the cross-sectional structure of the electrodeposited copper laminated on the first electrode 13 is observed. A streak pattern is observed at the interface 9 between the layer 6 and the re-deposited copper layer 7. The longer the blackout time, the clearer the streak pattern was, and it was found that the crystal growth did not inherit the history before the blackout. This streak pattern is considered to be a copper compound layer mainly composed of copper chloride (CuCl (s)).

The formation mechanism of CuCl (s) is considered as follows. During normal operation (step S1), Cu is deposited on the first electrode 13 according to the following formulas (1) and (2).
Cu ²⁺ + e ⁻ → Cu ⁺ (1)
Cu ⁺ + e ⁻ → Cu (2)

In the process of the formula (1) and the formula (2), a part of the monovalent copper ion that easily forms a chloride complex forms a complex with the chloride ion contained in the electrolytic solution 11, and the formula (3) ) And formula (4) to be reduced to copper.
Cu ⁺ + Cl ⁻ → CuCl (aq) (3)
CuCl (aq) + e ⁻ → Cu + Cl ⁻ (4)

During a power failure, the generation of CuCl (s) proceeds according to the following formulas (5) and (6). Since Cu ²⁺ is contained in the electrolytic solution 11, Cu ⁺ is dissolved on the surface of the first electrode 13 according to the equation (5). At this time, if chloride ions are present in the vicinity of the electrode surface of the first electrode 13 in the electrolytic solution 11 at a predetermined concentration or more, CuCl (s) is generated. During a power outage, it is considered that CuCl (s) is sequentially generated on the surface of the electrolytic copper layer 6 by the Cu ⁺ ions and the Cl ⁻ ions generated in the formula (5).
Cu ⁰ + Cu ²⁺ → 2Cu ⁺ (5)
Cu ⁺ + Cl ⁻ → CuCl (s) (6)

  In the copper electrolytic purification method according to the embodiment, as a power failure countermeasure (step S3), after a predetermined time has elapsed after the power failure, a second current having the first electrode 13 as an anode and the second electrode 12 as a cathode. (Reverse current) is passed between the first electrode 13 and the second electrode 12. Thereby, CuCl (s) produced on the surface of the electrolytic copper layer 6 is electrolyzed and dissolved in the electrolytic solution 11 and removed from the surface of the electrodeposited copper layer 6.

The current density of the second current is preferably from 100~350A / m ^2, more preferably 200~250A / m ^2. For example, when the power outage period is 12 hours or more, the timing of supplying the second current is preferably several hours before the restart of operation, specifically, 3 to 8 hours or more before the restart of operation. Preferably, it is 3 to 5 hours before restarting operation.

  In order to confirm that CuCl (s) has been removed from the surface of the electrodeposited copper layer 6, sample evaluation may be performed using EPMA (electron beam microanalyzer) or the like.

  Furthermore, in step S3, it is preferable to further include a step of causing a liquid flow to the electrode surface of the first electrode 13. Examples of the method for causing the liquid flow include a method of stirring the electrolytic solution 11 in the electrolytic cell 1 or a method of circulating the electrolytic solution 11 through the circulation tank 3 and the head tank 4. The method is not particularly limited as long as the liquid flow occurs with respect to the electrode 13 of the electrode 13.

It is said that chloride ions in the electrolyte 11 are likely to be adsorbed specifically on the copper surface, and the effective concentration on the surface of the electrodeposited copper layer 6 (first electrode 13) during a power outage is somewhat higher. Is guessed. In contrast, by causing a liquid flow to the electrode surface of the first electrode 13, the chlorine content in the vicinity of the first electrode 13 is reduced, so that specific adsorption of chloride ions can be suppressed. In addition, since the Cu ⁺ ions generated by the reaction of the formula (5) can be dissipated into the electrolytic solution 11, the uneven distribution of the concentration around the first electrode 13 is relaxed, and the reaction of the formula (6) is performed. The precipitation of CuCl (s) shown can be suppressed.

  The step of causing the liquid flow may not always be performed during a power failure. For example, when a power outage continues for 8 to 12 hours or more, a certain effect can be obtained by causing the liquid flow to occur for about 1 to 5 hours after the start of the power outage, preferably about 2 to 3 hours after the start of the power outage. it can. Moreover, it is also preferable to carry out for about 1 to 5 hours before restarting operation. For example, a certain effect can be obtained by carrying out the operation for 2 to 3 hours before the restart of operation.

  For example, when the electrolytic solution 11 is circulated, the circulation flow rate is preferably about 20 to 60 L / min, more preferably about 35 to 45 L / min per tank. If the circulation flow rate is 20 L / min or less, the composition distribution of the electrolytic solution 11 in the electrolytic cell 1 may be uneven, which may adversely affect electrolytic copper. On the other hand, when the circulating flow rate is 60 L / min or more, there is a case where electrolytic copper is contaminated due to the starch at the bottom of the tank.

Further, in step S <b> 3, it is preferable that a weak current (= fourth current) having the first electrode 13 as an anode and the second electrode 12 as a cathode flows between the first electrode 13 and the second electrode 12. The current density of the fourth current is preferably 10 to 100 A / m ² , and more preferably 10 to 20 A / m ² . During the power failure, the fourth current may be supplied at any time after the power failure by using an auxiliary power source or the like before supplying the second current using the first electrode 13 as an anode and the second electrode 12 as a cathode. It may be done intermittently. It has also been confirmed that even when PR electrolysis is employed as the second current, the adsorption of chlorine can be reduced as compared with the case where no measures are taken during a power failure.

  In order to describe the present invention in more detail, examples will be given below, but the present invention is not limited to these examples.

Experiments were conducted based on the conditions shown in Table 1 as a countermeasure against power failure. As the electrolytic solution, a sulfuric acid electrolytic solution of Cu: 52 ± 2 g / L and H ₂ SO ₄ : 180 ± 5 g / L was used. SUS316L (first electrode 13) was used as the cathode, and crude copper (second electrode 12) was used as the anode. The current density (first current and third current) during normal operation was 320 A / m ² , the temperature of the electrolytic solution 11 was 65 ± 5 ° C., and the power failure time was 24 hours.

“Liquid circulation 1” in Table 1 indicates a case where the electrolytic solution is circulated at 42 L / min per electrolytic cell for 3 hours immediately after the start of the power failure. “Anode current (small)” indicates a case where a weak anode current (fourth current) having a current density of −10 A / m ² is supplied during a power failure. “Liquid circulation 2” indicates a case where the electrolytic solution is circulated at 42 L / min per electrolytic cell from 3 hours before resumption of normal operation. “Anode current (large)” indicates a case where an anode current (second current) having a current density of −263.3 A / m ² is passed from 3 hours before the start of re-energization to the time of the start of re-energization.

  Table 2 shows the change in the number of times of flapping based on each test condition shown in Table 1. The “flapping frequency” refers to the operation of opening the electrodeposited copper horizontally from the bottom of the electrodeposited copper as a fulcrum when the electrodeposited copper is peeled off (open state) and the electrodeposited copper opened in the horizontal direction again. The combination of the operation of returning to the closed state (closed state) was calculated as “once”. In Table 2, “N number (number of strips)” means the number of electrodeposited copper actually peeled from the cathode electrode plate, “Flap number (maximum value)” means the maximum number of flapping times, “Flap number (average value)” indicates an average value of the number of flappings.

  As shown in Table 2, the maximum value of the number of flappings was 5 in the conventional example (Test 1) in which power failure countermeasures were not taken during a power failure. On the other hand, in Test 3, the number of times of flapping is reduced to a maximum of about 2. Moreover, compared with the average value of the number of times of flapping in the conventional example being 3.83 times, in the case of Test 2, the number of times of flapping can be reduced to 2.20 times, resulting in poor stripping of electrodeposited copper. It can be seen that can be effectively reduced.

DESCRIPTION OF SYMBOLS 1 Electrolysis tank 2 Rectifier 3 Circulation tank 4 Head tank 5 Control apparatus 6 Electrodeposition copper layer 7 Re-deposition copper layer 8, 9 Interface 11 Electrolyte solution 12 2nd electrode 13 1st electrode 14 V-shaped groove | channel

Claims (5)

A method of performing copper electrolytic purification by immersing a first electrode and a second electrode made of crude copper in an electrolytic cell containing an electrolytic solution,
(A) A first current having the first electrode as a cathode and the second electrode as an anode is passed between the first electrode and the second electrode, and an electrodeposited copper layer is deposited on the surface of the first electrode A process of
(B) stopping the supply of the first current;
(C) After a predetermined time has elapsed after the stop, a second current having the first electrode as an anode and the second electrode as a cathode is caused to flow between the first electrode and the second electrode, and after the stop, Removing the copper compound layer containing copper chloride formed on the electrodeposited copper layer by holding the electrodeposited copper in an electrolyte solution ; and
(D) After the removal of the copper compound layer, a third current having the first electrode as a cathode and the second electrode as an anode is passed between the first electrode and the second electrode, and the electrodeposited copper layer A method of electrodepositing a re-electrodeposition copper layer on the surface of the copper.   The method for electrolytic purification of copper according to claim 1, further comprising a step of causing a liquid flow to the electrode surface of the first electrode at least between step (b) and step (d).   The method for electrolytic purification of copper according to claim 1, further comprising a step of circulating the electrolytic solution at least between step (b) and step (d).   Between the step (b) and the step (c), a current density is smaller than the second current, the fourth electrode having the first electrode as an anode and the second electrode as a cathode, the first electrode and The method for electrolytic purification of copper according to claim 1, further comprising a step of flowing between the second electrodes. 5. The method for electrolytic purification of copper according to claim 1, wherein the second current has a current density of 100 to 350 A / m ² .

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