JP2020084297A - Cathode plate for electrolysis and electrolytic refining method using the same - Google Patents

Abstract

To provide a cathode plate for electrolysis capable of making a seed plate group having nearly the same thickness in a plurality of mother boards charged into an electrolytic bath.SOLUTION: A cathode plate 1 for electrolysis comprises a stainless steel flat plate part 10 having an approximately rectangular shape and immersed into an electrolytic solution in an electrolytic bath, and a pair of copper cross beams 20 holding a rectangular protrusion protruding upward from front and rear surfaces in at least both ends of an upper edge part of the flat plate part. A total average value of a plurality of average values obtained by calculating an average value of surface roughness (Ra) of both contact surfaces of the flat plate part 10 and the cross beam 20 about all cathode plates for electrolysis cathode plate for electrolysis charged into one electrolytic bath is less than or equal to 5.0 μm, and the standard deviation is less than or equal to 2.5 μm.SELECTED DRAWING: Figure 1

Description

The present invention relates to a cathode plate used in electrolytic refining of non-ferrous metals and an electrolytic refining method using the same, and more specifically, a flat plate made of stainless steel used as a mother plate in a seed plate electrolysis of copper electrolytic refining and The present invention relates to a cathode plate composed of a copper cross beam and an electrolytic refining method using the same.

In electrolytic refining of non-ferrous metals such as copper, multiple insoluble anodes or target metal anodes as anode plates and multiple seed plates of target metals as cathode plates are alternately placed in an electrolytic cell filled with an electrolytic solution. It is carried out by charging and electrolyzing them by applying a direct current to them. For the latter plurality of seed plates, the same electrolysis as above is performed using a mother plate such as stainless steel as a cathode plate, and when the target metal is thinly electrodeposited on the mother plate, the thin electrodeposit is stripped from the mother plate. It is made by that. The mother plate used in the electrolysis (seed plate electrolysis) for producing this seed plate is, for example, as disclosed in Patent Document 1, a substantially rectangular flat plate portion made of stainless steel having a predetermined thickness, and the flat plate. It is composed of a pair of rectangular rod-shaped copper cross beams which hold the upper edge of the copper plate to hang it in the electrolytic cell and supply power to the flat plate portion.

By the way, the seed plate peeled off from the above mother plate suffers from electrodeposition strain and strain at the time of peeling. The seed plate is usually peeled off and then stacked and stored in a pallet, but the storage on the pallet rarely corrects the distortion and flattens it. When a seed plate in such a distorted state is loaded into an electrolytic cell and electrolyzed, a locally narrow portion occurs in the surface distance between the seed plate and the anode plate as a cathode plate. , It causes a short circuit in that part. As a result, the current efficiency is reduced and the production amount of electrolytic copper is reduced. Therefore, the distortion of the seed plate is corrected before charging it into the electrolytic cell. For general correction of the strain of the seed plate, a method using a strain correcting device such as a molding machine or a press equipped with a roller is known. For example, Patent Document 2 discloses a technique of using a seed plate strain removing device that is a combination of a movable reduction roll and a fixed roll.

On the other hand, in order to efficiently carry out electrolytic refining, it is desirable to uniformly supply power to a plurality of mother plates loaded in the electrolytic cell. However, since the mother plate is reused after the seed plate is peeled off, deterioration such as deformation and corrosion may occur during repeated use, resulting in non-uniform current distribution to the plurality of mother plates. In particular, in the case of the structure in which the pair of copper cross beams described above is bolted to the flat plate part, the mother plate is impacted when the mother plate is taken out of the electrolytic cell and moved, for example, when the seed plate is peeled off. Mechanical force such as vibration or vibration is applied, the bolt gradually loosens and the mist of the electrolytic solution enters the gap between the copper cross beam and the flat plate part, and corrosion progresses in that part and corrosion products are generated. There was something to generate.

As a result, the contact resistance at the contact surfaces of the copper cross beam and the flat plate portion may increase, and the current distribution may become uneven. As a method for preventing the contact resistance between the copper cross beam and the flat plate portion from increasing, for example, Patent Document 3 proposes a technique of welding the copper cross beam and the flat plate portion. Further, Patent Document 4 proposes a technique of interposing a gold foil between the copper cross beam and the flat plate portion.

JP, 2011-32564, A JP, 9-165693, A JP-A-1-319695 JP, 7-70783, A

The strain reduction method using the strain correction device described in Patent Document 1 may not be able to satisfactorily correct the strain if the thickness varies among the seed plates. For example, when correcting the distortion of the seed plate using a roller, an excessively thick seed plate may increase the distortion rather than increasing the effectiveness of the roller, or an abnormality may occur due to overload of equipment. .. On the contrary, if the seed plate was too thin, the correction by the roller was not effective, and in this case, the distortion might be rather large. In order to suppress the problems that occur in such a strain correcting device, it is desirable to prepare a seed plate group having the same thickness so that the thickness does not vary between the seed plates and introduce them into the strain correcting device.

In order to produce a seed plate group having the same thickness, it is preferable to make the distribution of the current supplied to the plurality of mother plates loaded in the electrolytic cell uniform. That is, by uniformizing the current distribution, the copper electrodeposition amounts formed on the plurality of mother plates are less likely to vary, and thus it becomes possible to manufacture a seed plate group having the same thickness. On the contrary, if the current supplied to a plurality of mother plates varies, the thickness of the seed plate will vary.For example, in the case of an excessively thin seed plate, it will be difficult to peel it off from the mother plate, increasing the load on the operator. However, the ratio of defective seed plates is increased.

In the above case, since the current distribution can be made uniform by applying the techniques of Patent Documents 3 and 4 described above, it is possible to manufacture the seed plate group having the same thickness. However, when the copper cross beam and the flat plate portion are welded by the method disclosed in Patent Document 3, the work-hardened copper cross beam may be annealed by heat and the strength may be reduced. In addition, intergranular corrosion cracking may occur in the flat plate made of stainless steel. Furthermore, since the copper cross beam and the flat plate portion are welded to each other, even if either the flat plate portion made of stainless steel or the copper cross beam is deteriorated by long-term use, they can be easily separated from each other. It cannot be repaired. On the other hand, when the copper cross beam and the gold foil are brought into contact with each other by the method disclosed in Patent Document 4, diffusion occurs between the gold foil and the copper of the copper cross beam with the passage of time, and the gold foil is finally formed. As a result, the current distribution may be non-uniform due to an increase in contact resistance at the contact surface between the copper cross beam and the flat plate portion.

The present invention has been made in view of such circumstances, by making the current distribution to a plurality of electrolysis cathode plates as a mother plate loaded in the electrolytic cell uniform, a seed plate group having substantially the same thickness It is an object of the present invention to provide a cathode plate for electrolysis which can be manufactured and an electrolytic refining method using the same.

The inventors of the present invention examined the current value flowing through each mother plate in the electrolytic cell during electrolysis during the production of the seed plate and the respective resistance values that determine the current flowing through the mother plate. We obtained the knowledge that the variation in the contact resistance between the beam and the flat plate sandwiched between them is the main cause of the non-uniformity of the current distribution across multiple mother plates. The inventors have found that the variation of 1 is caused by the surface roughness of both contact surfaces of the copper cross beam and the flat plate portion, and completed the present invention.

That is, the cathode plate for electrolysis according to the present invention has a substantially rectangular flat plate portion made of stainless steel that is immersed in the electrolytic solution in the electrolytic cell, and a rectangular protrusion that protrudes upward at least at both ends of its upper edge portion. A cathode plate for electrolysis comprising a pair of copper cross beams sandwiched from the back surface, wherein the average value of the surface roughness (Ra) of both abutting surfaces of the flat plate portion and the cross beam is defined as one electrolytic cell. It is characterized in that a total average value of a plurality of average values obtained by calculating for all of the electrolysis cathode plates charged in (1) is 5.0 μm or less and a standard deviation is 2.5 μm or less.

According to the present invention, the current distribution can be made uniform for a plurality of mother plates charged in the electrolytic cell, so that the generation ratio of defective seed plates is reduced and a seed plate group having substantially the same thickness is manufactured. be able to. By introducing this seed plate into the strain correction device, it becomes possible to stably manufacture a cathode with a small strain, and it is possible to increase the current efficiency during copper electrolytic refining, so that the productivity can be increased.

It is an exploded perspective view of a specific example of the cathode plate for electrolysis concerning the present invention.

Hereinafter, an embodiment of a cathode plate for electrolysis according to the present invention will be described with reference to FIG. The cathode plate 1 of this specific example of the present invention is a mother plate used during seed plate electrolysis of copper electrolytic refining, and includes a flat plate portion 10 made of stainless steel having a substantially rectangular shape and an upper edge portion of the flat plate portion 10. It is composed of a pair of square rod-shaped copper cross beams 20 which are sandwiched from the front and back surfaces. More specifically, the flat plate portion 10 is formed so that its length in the width direction is slightly narrower than the inner width of the electrolytic cell into which it is inserted, and its front and back surfaces have a predetermined surface roughness. The polishing process is performed.

Since the flat plate portion 10 is almost entirely immersed in the electrolytic solution except for the projections described later, it is formed of a material having excellent corrosion resistance against corrosion and deformation by the electrolytic solution. For example, SUS316L is preferably used. ing. The flat plate portion 10 has a substantially L-shape that covers a region from the uppermost portion to the lowermost portion of one side edge portion thereof and a substantially half region of the lower edge portion on the one side edge portion side. The bent insulating material 11 having a U-shaped cross section is attached. With this insulating material 11, the electrodeposited copper that has been electrodeposited on both sides during electrolysis of the seed plate can be easily peeled off.

In addition, the flat plate portion 10 is provided with substantially rectangular protrusions 12 projecting upward at three locations, that is, the center portion of the upper edge portion and both end portions thereof. The connection with the cross beam 20 is made. As a result, electric power is supplied to the flat plate portion 10 via the cross beam 20. The shape of the cathode plate 1 is not limited to that shown in FIG. 1. For example, there is a case where the substantially rectangular protrusion does not exist in the central portion and only two end portions are provided.

Each of the above-mentioned three protrusions 12 is provided with a through hole 13 for inserting the bolt 30. A through hole 21 is also provided at a position corresponding to the through hole 13 of the protrusion 12 in the pair of cross beams 20, and the protrusion 12 of the flat plate portion 10 is covered by the pair of cross beams 20. The flat plate portion 10 and the cross beam 20 are fixed to each other by inserting the bolt 30 into the through hole 13 of the protrusion 12 and the through hole 21 of the cross beam 20 and screwing it with the nut 31. be able to.

Since the pair of cross beams 20 is longer than the width of the flat plate portion 10, both end portions of the pair of cross beams 20 can be placed on the upper edges of the opposite wall portions of the electrolytic cell. The part 10 can be immersed in the electrolytic solution in a state of being hung from the pair of cross beams 20. A power feeding plate called a bus bar is placed on the opposite wall portions of the electrolytic cell, and the end portions of the pair of cross beams 20 are brought into contact with the power feeding plate, so that the power feeding plate and the pair of power feeding plates are connected from the power source. Power is supplied to the flat plate portion 10 via the cross beam 20 of FIG. As a result, copper as the target metal can be electrodeposited on the front and back surfaces of the flat plate portion 10.

When this electrodeposit reaches a predetermined thickness, the cathode plate 1 is pulled out of the electrolytic cell, and the electrodeposit is stripped from the flat plate portion 10 using the insulating material 11 described above. This gives a seed plate. The cathode plate 1 after the seed plate is peeled off can be reused as a mother plate. However, when the electrolytic solution enters the gap between the pair of cross beams 20 and the protrusion 12 of the flat plate portion 10, these abutting portions are corroded. The rate of progress of this corrosion causes a difference when the surface roughness of the contact surfaces of the pair of cross beams 20 and the protrusions 12 of the flat plate portion 10 varies between the cathode plates 1, resulting in contact. Differences in resistance also occur between the cathode plates 1, and the current distribution to the plurality of cathode plates 1 becomes uneven.

In order to prevent the occurrence of such a non-uniform current distribution, in the embodiment of the present invention, the average surface roughness (Ra) of the contact surfaces of the pair of cross beams 20 and the protrusions 12 is averaged. The total average value of a plurality of average values obtained by calculating the values for all the cathode plates 1 loaded in one electrolytic cell is 5.0 μm or less, and the standard deviation is 2.5 μm or less. As a result, it is possible to make the current distribution uniform with respect to the plurality of cathode plates 1 as mother plates loaded in the electrolytic cell, so that the generation ratio of defective seed plates can be reduced and seed plate groups having substantially the same thickness can be obtained. It can be made. On the contrary, when the total average value of the above surface roughness (Ra) exceeds 5.0 μm or the standard deviation exceeds 2.5 μm, the influence of the variation of the contact resistance of the corresponding contact surface becomes too large. The current distribution for all cathode plates 1 becomes non-uniform.

Specifically, when the total number of cathode plates loaded in one electrolytic cell is, for example, 50, the contact surface of the pair of cross beams 20 of the i-th cathode plate from one end of the electrolytic cell is any portion of the surface roughness of the inner (Ra) to Ra ₁ (i), the i-th any site on the surface roughness of the contact surface of the projection 12 of the cathode plate (Ra) Ra ₂ ( i), the arithmetic mean value x(i) can be expressed by the following equation 1.
[Formula 1]
x(i)=(Ra ₁ (i)+Ra ₂ (i))/2

Therefore, a plurality of average values (that is, x(1), x(2),...) Obtained by calculating the above x(i) for all the cathode plates 1 loaded in one electrolytic cell The total average value X and standard deviation Y of x, x(50) can be calculated by the following equations 2 and 3, respectively. Therefore, the total average value X in the following formula 2 may be set to 5.0 μm or less, and the standard deviation Y in the following formula 3 may be set to 2.5 μm or less.
[Formula 2]
X=(x(1)+x(2)+...+x(50))/50
[Formula 3]
Y = [((x (1 ) -X) 2 + (x (2) -X) 2 + ··· + (x (50) -X) 2) / 50] 1/2

In the embodiment of the present invention, the surface roughness (Ra) of both contact surfaces of the pair of cross beams 20 and the projections 12 is further increased in each of all the cathode plates 1 loaded in the one electrolytic cell. It is preferable that the average value obtained by the above equation 1) is 2.5 μm or more and 7.5 μm or less. When the average value of the surface roughness (Ra) is larger than 7.5 μm, the electrolytic solution easily enters the gap between the contact surfaces. On the other hand, it is not preferable to make it smaller than 2.5 μm because it takes too much time and effort.

When the surface roughness (Ra) of the contact surfaces of the pair of cross beams 20 and the protrusions 12 of the flat plate portion 10 does not satisfy the above requirements, the contact surfaces may be polished. .. As this polishing method, a polishing method using a general surface grinder or a traveling wheel polishing machine can be used. Further, in order to prevent the mist of the electrolytic solution from entering the gap between the pair of cross beams 20 and the protrusion 12 of the flat plate portion 10, the pair of cross beams 20 and the protrusion 12 are covered. It is preferable to provide a cover or caulk the entrance of the gap.

Next, a method for producing a copper electrolytic refining seed plate using the above-described electrolysis cathode plate of one embodiment of the present invention will be described. As described above, first, a pair of cross beams made of copper and a flat plate portion made of stainless steel are prepared, and their contact surfaces are polished, and then a release agent is applied to the electrodeposition surface of the flat plate portion and dried. Then, the pair of cross beams and the flat plate portion are fixed with bolts and nuts to assemble the mother plate. By placing both ends of the pair of cross beams on the opposite wall portions of the electrolytic cell, a flat plate portion as a cathode suspended under the electrolytic cell can be inserted through the pair of cross beams. Power is supplied. Further, anodes made of blister copper are inserted into the positions facing the electrodeposited surfaces on the front and back sides of the flat plate portion to supply electric power.

In this way, by energizing the cathode of the mother plate composed of the pair of cross beams and the flat plate portion and the anode of the blunt copper, copper is electrodeposited on the front and back electrodeposited surfaces of the mother plate. A copper sulfate solution is used as the electrolytic solution, and an additive is added if necessary. The electrolysis conditions may be appropriately selected depending on the electrolyzer and process. The seed plate formed on the electrodeposition surface of the mother plate has a thickness of about 0.6 mm. After completion of this electrodeposition, the peeling device peels the seed plate from the electrodeposited surface of the mother plate. The seed plate having tears and wrinkles that occur when it is peeled off is detected in the inspection process and treated as a defective product.

[Reference example]
A flat plate made of stainless steel having a width of 1070 mm, a length of 1050 mm, and a thickness of 3 mm, which is integrally formed with projections of 35 mm in length and 200 mm in width at the center and both ends of the upper edge of the electrodeposition portion, and the protrusions. A pair of copper cross beams (length 1460 mm, width 35 mm, thickness 10 mm) for sandwiching the parts from the front and back surfaces were prepared. Before sandwiching the above-mentioned protrusions with a cross beam, the arithmetic average roughness (Ra) of each contact surface where these contact each other was determined in accordance with JIS B0601-2001. A stylus roughness measuring instrument (SJ-201) manufactured by Mitutoyo Corporation was used to create a roughness curve for obtaining the arithmetic average roughness (Ra). After the projection is sandwiched by a pair of cross beams, a total of 6 through holes each having an inner diameter of 10 mm provided in the projection and corresponding cross-beam threaded through holes are provided. The long screw bolt was inserted and fixed.

50 mother plates and 51 anodes assembled in this way are arranged in an alternating manner in an electrolytic cell and have a composition of Cu concentration of 45 to 47 g/L and H ₂ SO ₄ concentration of 180 to 190 g/L. A seed plate made of electrolytic copper was manufactured by being filled with an electrolytic solution and conducting current for 22 hours under the conditions of the parallel method with an electrolytic temperature of 60° C. and a cathode current density of 250 A/m ² . During the energization, a vinyl sheet was put on the electrolytic cell to keep the heat and prevent evaporation. Four hours or more after starting this electrolysis, the cathode current in the cross beam was measured using a clamp meter (keysight U1213A) manufactured by Keysight Technology, Inc.

Further, the contact resistance between the flat plate portion and the cross beam was determined from the cathode current and the voltage drop measured using the same clamp meter as above. After stopping the energization, all 50 mother plates were pulled up from the electrolytic cell to peel off the seed plate. In order to evaluate the variation in the electrodeposition amount of these 50 mother plates, the mass of the two seed plates peeled from each of the 50 mother plates was measured. Based on the arithmetic mean and standard deviation of the seed plate unit weight, which is the total mass of the two seed plates produced per one of the mother plates, the variation in the electrodeposition amount of the 50 mother plates was evaluated.

[Example]
Next, with respect to each of the 50 mother plates used in the above-mentioned reference example, after the contact surfaces of the protrusions and the cross beams were both sanded with #400 sandpaper, the cross beams and the protrusions were polished. The surface roughness of both abutting surfaces with the section was measured in the same manner as in the above reference example. Then, after reassembling these to form a mother plate, they were charged into the electrolytic cell and electrolyzed in the same manner as in the above-mentioned reference example, and the cathode current and each contact resistance value were measured. After electrolysis, the seed plate unit weight of the seed plate peeled off from each mother plate was measured. The contact between the cross beam and the projections of the 50 mother plates obtained by the above-mentioned formulas 1 to 3 was used to find the variations in the cathode current and the seed plate unit weight of the 50 mother plates in the above-mentioned examples and reference examples. The total average value X and the standard deviation Y of the surface roughness (Ra) of the surface are shown in Table 1 below.

From the results of Table 1 above, in the example, the contact surfaces of the cross beam of the mother plate and the protrusions of the flat plate portion were flattened by polishing, so that variations in surface roughness, contact resistance, and cathode current compared to the reference example. It can be seen that the dispersion of the seed plate unit weight of the seed plate peeled off from each mother plate is also reduced as compared with the reference example. Therefore, it can be seen that even with a stainless cathode that is repeatedly used, a seed plate group having the same thickness can be produced from one electrolytic cell by polishing the contact surface between the cross beam and the protrusion of the flat plate portion.

DESCRIPTION OF SYMBOLS 1 Cathode plate 10 Flat plate part 11 Insulating material 12 Projection part 13 Through hole 20 A pair of cross beams 21 Through hole 30 Bolt 31 Nut

Claims (4)

A substantially rectangular flat plate made of stainless steel, which is immersed in the electrolytic solution in the electrolytic cell, and a pair of copper cross beams that sandwich upwardly protruding rectangular projections from the front and back surfaces at least at both ends of the upper edge of the flat plate. And a mean value of surface roughness (Ra) of both abutting surfaces of the flat plate portion and the cross beam for all electrolysis cathode plates loaded in one electrolysis cell. A cathode plate for electrolysis, wherein a total average value of a plurality of calculated average values is 5.0 μm or less and a standard deviation is 2.5 μm or less. The cathode plate for electrolysis according to claim 1, wherein a cover is provided on the contact surface between the flat plate portion and the pair of cross beams to prevent the electrolytic solution from entering. All of the electrolysis cathode plates loaded in the one electrolysis cell have an arithmetic mean value of surface roughness (Ra) of the contact surfaces of the flat plate portion and the pair of cross beams of 2.5 μm. The cathode plate for electrolysis according to 1 or 2, wherein the thickness is 7.5 μm or less. An electrorefining method comprising: producing a seed plate by using the electrolysis cathode plate according to any one of claims 1 to 3 as a mother plate.

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