JP2019052329A - Electrorefining method of low-grade copper anode, and electrolytic solution used therefor - Google Patents

Abstract

To provide an electrolytic method capable of electrorefining a low-grade copper anode resulting from a secondary raw material such as a refining residue of a nonferrous metal and electric/electronic equipment waste, which has been difficult to refine by electrorefining to date, without causing its passivation for a long period of time, and an electrolytic solution used therefor.SOLUTION: The electrorefining method for a low grade copper electrode is characterized by employing a low grade copper anode made of a copper alloy that contains metal elements other than copper as impurities, arranging the low grade copper anode and a cathode to face each other in an electrolytic solution having high solubility with respect to a metal element that forms a chemical compound adhering to the anode, and carrying out electrolysis to recover copper on the surface of the cathode.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrolytic refining method for a low-grade copper anode and an electrolytic solution used therefor.

In the electrolytic refining of copper, a plurality of anodes made of about 99% crude copper containing impurity elements and a plurality of anodes made of pure copper, titanium or stainless steel are usually used using an electrolytic solution mainly composed of sulfuric acid and copper sulfate. The cathodes are alternately arranged facing each other, and a constant current having a current density of about 200 to 350 A / m ^{2 is} passed to elute copper ions from the anode and simultaneously deposit copper on the cathode.

  The impurity element in the crude copper is immobilized as a dissolved chemical species in the slime or the electrolyte and separated from the crude copper.

  In such an electrolytic refining method, when the concentration of the impurity element in the crude copper increases, there is a problem that the anode becomes passivated and it is difficult to continue electrolysis.

  For this reason, conventionally, in order to apply electrolytic smelting to the purification of crude copper, it was necessary to adjust the purity of the crude copper to 99% or more in the smelting process.

  On the other hand, for the treatment of non-ferrous smelting waste and E-Scrap, that is, electrical and electronic equipment waste, etc., recycling that uses copper smelting to produce about 80-90% crude copper by the smelting process and refine it There is a process, but due to problems such as passivation described above, it is necessary to apply an electrowinning process that consumes more energy than electrolytic refining, leading to increased copper refining costs.

  When casting about 80 to 90% of crude copper, which is generated in the recycling process, and using this to electrorefine as a low grade copper anode, a trace amount component in the anode forms a hardly soluble compound, and anode slime As a result of adhering to the anode surface and forming a porous slime layer, the diffusion of copper ions eluted from the anode is inhibited, and copper sulfate, a non-conductive compound, is deposited between the anode surface and the anode slime. Activation becomes an obstacle, and therefore a technique for suppressing such inactivation is required.

  Until now, various methods for preventing passivation of the anode surface have been studied in electrolytic refining of copper (see, for example, Patent Documents 1 and 2).

  In the copper high current density electrolysis method described in Patent Document 1, anodes and cathodes are alternately arranged facing each other in an electrolytic solution filled in an electrolytic cell, and copper is electrolyzed at a high current density while circulating the electrolytic solution. When refining, an anionic activator is added to the electrolyte and a flow rate is imparted. In this method, the flow rate is given to the electrolytic solution by strengthening the liquid circulation, forced stirring with an impeller or the like, or air bubbling, and the slime adhering to the anode surface is thereby peeled off, thereby preventing passivation. In addition, an anionic activator such as thiourea added to the electrolyte is adsorbed on the anode surface, and the slime becomes electronegative. It is said that the slime that has been electronegative in this way can be prevented from adhering to the cathode surface because it receives an electric repulsive force from the cathode as the cathode. In addition, it is said that slime adhesion to the anode surface and passivation of the cathode surface can be suppressed without filtering the electrolyte and increasing the size of the equipment.

  In the method of electrolytic refining of copper described in Patent Document 2, an electrolytic refining apparatus provided with a stirrer having an impeller structure between an anode and a cathode is used, and the stirrer performs electrolysis in an electrolytic cell. By stirring the liquid and applying a flow rate to the electrolyte within a range where the slime layer formed on the anode surface does not collapse, the diffusion of copper ions eluted from the anode is promoted to suppress passivation and at the same time, the slime cathode It is said that it can be prevented from adhering to.

JP 2003-183870 A JP 2017-48438 A

However, in the method of Patent Document 1, the electronegative slime receives an attractive force from the anode, which is the anode, and therefore requires a flow rate of 10 times or higher than that of the conventional method to strip the slime. It was difficult. In addition, in high current density electrolysis where the current density exceeds 350 A / m ² , if the amount of organic additives such as thiourea is high, the cathode overvoltage increases and the electrodeposition state tends to deteriorate. was there.

  The method of Patent Document 2 is superior to the method of Patent Document 1 in that the equipment introduction cost is small, but if the electrode plate has a large surface area, is the number of arrangements of the stirrer having an impeller structure increased? However, measures such as increasing the size of the stirring device within the range that can be disposed in the gap between the anode and the cathode are necessary, and there is a side that is not necessarily excellent in practicality.

  The present invention has been made in view of the circumstances as described above, and is low-grade copper derived from secondary raw materials such as non-ferrous smelting residues and electrical and electronic equipment waste, which has been difficult to perform by conventional electrolytic refining. It is an object of the present invention to provide an electrolytic method capable of electrolytic refining without deactivating the anode for a long time and an electrolytic solution used therefor.

  The inventors of the present invention have intensively studied to cope with the above-mentioned problems. As a result, by using a specific acid solution as an electrolytic solution, it is possible to reduce adhesion of slime to the anode surface and passivate the anode surface. Found to suppress. The present invention has been completed based on such knowledge.

  (1) The method for electrolytic refining of a low-grade copper anode according to the present invention uses a copper alloy containing a metal element other than copper as an impurity as a low-grade copper anode, and is large relative to a metal element that forms a compound attached to the anode. The low-grade copper anode and cathode are arranged face-to-face in an electrolyte having solubility and electrolyzed to recover copper on the cathode surface.

  (2) In the method for electrolytic refining of a low-grade copper anode according to the present invention, it is preferably considered that the electrolyte is a sulfamic acid-copper sulfamate solution or a silicofluoric acid-copper silicofluorate solution.

  (3) In the electrolytic refining method for a low-grade copper anode of the present invention, the metal elements other than copper are Ag, Au, Pt, Pd, Ni, Pb, As, Sb, Bi, Se, Te, Sn, Zn, and Fe. It is preferably considered that the metal element is at least one metal element selected from the group consisting of:

  (4) In the method for electrolytic refining of a low-grade copper anode according to the present invention, it is preferable that the low-grade copper anode is a copper alloy containing 1 mass to 30 mass% in total of metal elements other than the copper.

(5) in low-grade copper anode for electrolytic refining process of the present invention, the electrolysis can be performed at a current density of 100A ^{/ m 2} ~400A ^/ m 2 is preferably considered.

  (6) The electrolytic solution for electrolytic refining of a low-grade copper anode according to the present invention is characterized by containing a sulfamic acid-copper sulfamate solution or a silicic acid-copper silicate solution as a main component.

  According to the electrolytic refining method of the present invention and the electrolytic solution used therefor, a low-grade copper anode derived from secondary raw materials such as non-ferrous metal smelting residues and electrical and electronic equipment waste, which has been difficult to perform by conventional electrolytic refining, Electrolytic refining can be performed without being inactivated over time.

It is the graph which showed the relationship between the time required for passivation, and the voltage between terminals when electrolyzing a copper alloy containing 1 mass% of metal elements other than copper as impurities in the conventional sulfuric acid-copper sulfate aqueous solution and pure copper is there. The graph which showed the relationship between the time required for passivation, and the voltage between terminals when the copper alloy which contains 1 mass% of Sb, Pb, Ag, Au, Pd, or Pt as an impurity in the electrolyte solution of this invention was electrolyzed It is. It is the graph which showed the relationship between the time which the passivation state in the electrolytic refining of the 82% copper anode of Example 1, and the voltage between terminals. (A) is a photograph showing the stainless steel cathode after electrolysis of Example 1 and copper electrodeposited thereon. (B) is a photograph showing a dried and washed anode after electrolysis in Example 1. It is the graph which showed the relationship between the time which the passivation required in the electrolytic refining of the 80% copper anode of Example 2-1, and the voltage between terminals. (A) is a photograph showing a stainless steel cathode after electrolysis of Example 2-1 and copper electrodeposited thereon. (B) is a photograph showing a dried and washed anode after electrolysis in Example 2-1. It is the graph which showed the relationship between the time which the passivation required in the electrolytic refining of the 70% copper anode of Example 2-2, and the voltage between terminals. (A) is a photograph showing a stainless steel cathode after electrolysis of Example 2-2 and copper electrodeposited thereon. (B) is a photograph showing a dried and washed anode after electrolysis in Example 2-2. (A) is an SEM image of slime that had settled below the 82% copper anode of Example 1. (B) is an SEM image of slime floating on the electrolyte solution surface of Example 1. FIG. 9A is a graph showing the XRD pattern of slime.

  Hereinafter, the electrolytic refining method for a low-grade copper anode of the present invention and the electrolytic solution used therefor will be described in detail.

  In the present specification, the term “low-grade copper anode” means an anode using a copper alloy containing 1 mass to 30 mass% in total of metal elements other than copper as impurities.

  The method of electrolytic refining of a low-grade copper anode according to the present invention uses a copper alloy containing a metal element other than copper as an impurity as a low-grade copper anode, and has a high solubility for a metal element that forms a compound attached to the anode. A low-grade copper anode and a cathode are arranged face-to-face in an electrolytic solution, electrolyzed, and copper is recovered on the cathode surface.

  In the electrolytic refining method for a low-grade copper anode according to the present invention, it is preferably considered that the electrolytic solution is a sulfamic acid-copper sulfamate solution or a silicofluoric acid-copper silicate solution.

  Moreover, in the electrolytic refining method of the low grade copper anode of the present invention, the metal elements other than the copper are Ag, Au, Pt, Pd, Ni, Pb, As, Sb, Bi, Se, Te, Sn, Zn, and Fe. It is preferably considered that it is at least one metal element selected from the group.

Sulfamic acid is a chemical widely used in the plating field, cleaning agents, and the like, and is represented by a chemical formula in which one of hydroxyl OH of sulfuric acid is substituted with NH ₂ of amino group, and is also called amidosulfuric acid. . It is known that sulfamic acid has a high solubility in sulfamate derived from a metal that forms a compound that easily adheres to an anode such as Pb. Therefore, in the conventional electrolytic refining in sulfuric acid, it does not produce a compound of an impurity metal element such as lead sulfate PbSO ₄ contained in the slime generated by electrolysis, which easily adheres to the anode surface, and dissolves Pb etc. Thus, it is considered that slime sticking to the anode surface can be suppressed. However, so far, it has not been proposed to use an electrolyte containing sulfamic acid as a main component for electrolytic refining of a low-grade copper anode.

  Examples of the concentration of sulfamic acid in the electrolytic solution include a range of 60 to 120 g / L, preferably 80 to 100 g / L. Moreover, as a density | concentration of the copper sulfamate in electrolyte solution, the range of 40-100 g / L, for example, preferably 40-60 g / L is illustrated, for example.

In addition, silicic acid is also known to dissolve Pb and the like in the same manner as sulfamic acid, and it dissolves impurity metal element compounds such as PbSO _{4 in} the slime to suppress the adhesion of slime to the anode surface. I think it can be done. By using a specific electrolytic solution having a large solubility for the metal element that forms a compound that easily adheres to the anode, it is possible to suppress the passivation of the anode surface and perform continuous electrolytic refining. .

  In the electrolytic refining method for a low-grade copper anode according to the present invention, it is preferably considered that the low-grade copper anode is a copper alloy containing 1 mass to 30 mass% in total of metal elements other than copper. If the content is within the above range, purity of 99.99% or more from secondary raw materials such as non-ferrous metal smelting residue and electrical and electronic equipment waste, which could not be refined without the conventional electrowinning process The electrolytic copper can be obtained by electrolytic refining. In addition, in the normal electrowinning process, it is necessary to apply a current to the electrode and the electrolytic solution at a voltage of about 2 V. In the electrolytic refining, a current is applied to the raw material and the electrolytic solution at a voltage of about 0.2 to 0.4 V. Then, electrolytic copper can be obtained. That is, in the present invention, the power consumption can be reduced to about 1/10 to 1/5 at maximum by electrolytic refining a low-grade copper anode derived from secondary raw materials such as non-ferrous metal smelting residues and recycled products. Is possible.

  On the other hand, in the electrolytic refining method for a low-grade copper anode of the present invention, for example, a stainless steel thin plate or a pure copper thin plate (copper seed plate) is used as the cathode.

The low-grade copper anode for electrolytic refining process of the present invention, the electrolyte, it is preferred considered performed at a current density of ^{100A / m 2 ~400A / m 2} . In consideration of energy saving, and more preferably at a range of current density ^{200A / m 2 ~300A / m 2} . If the current density is within the above range, it is possible to obtain electrolytic copper having a good surface state while suppressing power consumption. On the other hand, if the current density exceeds 400 A / m ² , dendrite copper or a bump-like structure is formed, and slime or electrolyte solution that falls off from the anode is involved, leading to a decrease in purity of the cathode. Further, the obtained copper grows in the anode direction and is short-circuited to cause a decrease in current efficiency and an electrolytic failure, which is not preferable. Such current density control can be performed by a conventionally known current control technique.

  In addition, the electrolysis is preferably considered to be constant current electrolysis. In the present specification, the term “constant current” is not limited to supplying power at a constant current value from the start to the end of electrolytic scouring. Electrolysis is performed at a high current value, and electrolysis is also performed at a low current value during a relatively high time period such as daytime when the power usage fee is relatively high. On the other hand, current control that periodically fluctuates in a very short time of several seconds to several minutes is not included in the “constant current”.

In the method for electrolytic refining of a low-grade copper anode according to the present invention, it is considered that the temperature of the electrolytic solution during constant current electrolysis is in the range of 20 ° C to 80 ° C, more preferably 20 ° C to 40 ° C. When the liquid temperature is high, it is possible to suppress the generation of slime mainly composed of antimony such as Sb ₂ O _3, passivation due to the slime, and purity reduction due to the slime adhering to the cathode. In addition, the electrical conductivity of the electrolytic solution increases, and a reduction in cell voltage during electrolysis can be expected. On the other hand, when the electrolytic solution exceeds 80 ° C., sulfamic acid is easily decomposed and ammonium hydrogen sulfate may be generated. Therefore, there is a possibility that the effect of suppressing the adsorption of slime to the anode and the effect of suppressing the passivation of the anode surface by the specific electrolyte of the present invention may be reduced. If the liquid temperature of the electrolytic solution is within the above range, the effect of suppressing the adsorption of slime to the anode and the effect of suppressing the passivation of the anode surface by the electrolytic solution of the present invention are exhibited over a long period of time. Regarding the liquid temperature of the electrolytic solution, conventionally known heat-retaining / cooling means can be appropriately used.

  In the method for electrolytic refining of a low-grade copper anode according to the present invention, the electrolysis time can be determined by the above-described current density and the thickness of the target copper cathode. As a guideline, for example, the continuous energization time in electrolysis is 24 hours. This is preferably taken into account. More practically, it is considered that it is 50 hours or more, preferably 100 hours or more, more preferably 150 hours or more.

  In the method for electrolytic refining of a low-grade copper anode according to the present invention, the gray solid product deposited immediately under the anode is considered to be anode mud, that is, slime, and contains high concentrations of Au, Ag, and the like. Therefore, in the method for electrolytic refining of a low-grade copper anode according to the present invention, valuable metals that are noble than copper can be recovered as a secondary.

Note that valuable metals (Ag, Au, Pt, Pd, etc.) that do not elute into the electrolyte but are distributed to the slime can be separated and purified by a conventionally known method after being recovered after the completion of electrolysis. . Moreover, it has been confirmed that Pb and Ni accumulate in the electrolytic solution, and Pb can be recovered by adding sulfuric acid. Furthermore, Ni can be recovered by crystallization or the like after separating copper ions as Cu ₂ S by supplying S ² -ions such as thioacetamide or H ₂ S to the electrolytic solution.

  The electrolytic solution for electrolytic refining of a low-grade copper anode of the present invention is mainly composed of a sulfamic acid-copper sulfamate solution or a silicofluoric acid-copper silicate solution.

  In the electrolytic solution for electrolytic refining of a low grade copper anode, it is preferable to add an additive. As additives, known additives such as glue, polymer compounds, chloride ions, thiourea, etc., which are known to improve the electrodeposition form of copper, and other than copper contained as impurities in the anode It is preferably considered that it is a complex-forming agent with other metal elements. Examples of the complexing agent such as the latter include at least one selected from the group consisting of tartaric acid, acetic acid and citric acid. These additives can be used alone or in combination of two or more. In particular, when the additive is tartaric acid, it is thought that it forms a complex with Pb and Sn as impurities to increase the solubility of slime, and is excellent in terms of treatment of waste liquid after electrolytic refining, detoxification, etc. Yes.

  Examples of the additive amount of the additive and complexing agent include 10 g / L or less, preferably 5 g / L or less. When the addition amount is within the above range, the impurity metal element and the additive form a complex and dissolve in the electrolytic solution, so that the effect of suppressing passivation on the anode surface can be improved. On the other hand, when the added amount is, for example, 100 g / L, copper sulfate is likely to be precipitated due to a decrease in the solubility of copper, and on the contrary, passivation of the anode surface may be promoted.

  Although an Example is shown below, the electrolytic refining method of this invention and the electrolyte solution used for it are not limited at all by these Examples.

<1. Electrolytic test of copper alloy containing 1 mass% of only one type of metal elements other than copper>
Commercially available high-purity metal reagents other than copper, copper (I) oxide (Cu ₂ O) used for oxygen concentration adjustment, and pure copper wire for wiring are weighed to the desired composition, and an alumina tamman tube (SSA with an inner diameter of 20 mm) -H, manufactured by Nikkato Co., Ltd.) and then set in a siliconite heating element vertical electric furnace. Next, a flow rate of 200 cm ³ / min. Then, argon gas was introduced to replace the inside of the furnace with argon, and the temperature was raised to 1200 ° C. and held for 2 hours. After the holding, the Tamman tube was taken out from the furnace and cooled with air while blowing argon gas. After cooling, the rod-shaped copper alloy was taken out from the Tamman tube, cut in the diameter direction of the Tamman tube, and used as a low-grade copper anode. In addition, the copper anode was produced using pure copper as a reference example, and it used for the electrolytic test with the following procedures.
<2. Electrolysis test>
Above 1. After cutting the various copper alloys obtained in step 1 in the diameter direction of the Tamman tube so that the thickness is about 10 mm, soldering PVC coated copper wire on one side, non-conductive resin (Epofix, Marumoto Struers Co., Ltd.) Cold resin was buried in Tokyo (made by company). Next, this is surfaced with emery paper # 220 to # 2000 using a rotary polishing machine (Doctor Wrap ML-182, manufactured by Marto, Inc., Tokyo), and alumina particles having a particle size of 0.3 mm are used as abrasives. A low grade copper anode was fabricated by buffing. Further, SUS304 stainless steel having a diameter of 20 mm and a thickness of 1 mm was subjected to copper wire attachment, resin embedding, and polishing in the same procedure to produce a stainless steel cathode.

  The electrolytic solution was prepared by dissolving a commercially available high purity reagent in distilled water. Here, the sulfamic acid-sulfamic acid copper-based solution was prepared according to the following formula by dissolving basic copper carbonate in the sulfamic acid solution.

4H ₃ NSO ₃ aq. + CuCO ₃ · Cu (OH) ₂ (s)
→ 2Cu (H ₂ NSO ₃ ) ₂ aq. + 3H ₂ O + CO ₂ (g) (1)
The following two types of electrolytic solutions were prepared and tested.
(I) H ₂ SO ₄ concentration 160 g L ⁻¹ , Cu (II) concentration 40 g L ⁻¹ sulfuric acid-copper sulfate solution (ii) H ₃ NSO ₃ concentration 100 g L ⁻¹ , Cu (II) concentration 40 g L ⁻¹ The sulfamic acid-copper sulfamate-based solution of the present invention was subjected to constant current electrolysis by the two-electrode method using the electrolytic solution prepared as described above, the produced low-grade copper anode and the stainless steel cathode. The current density was 300 A / m ² and continued for a maximum of 24 hours or until the electrolysis voltage increased significantly. In addition, in the sulfuric acid-copper sulfate solution of the electrolytic solution (i), the liquid temperature was adjusted and kept so that the temperature of the electrolytic solution was within the range of 40 ° C. ± 2 ° C. In the sulfamic acid-copper sulfamate solution of the electrolytic solution (ii), the liquid temperature was adjusted and kept so that the temperature of the electrolytic solution was within a range of 25 ° C. ± 2 ° C.

  FIG. 1 and Table 1 show the passivation time of the anode surface when electrolysis was performed using a low-grade copper anode or pure copper as an anode in a sulfuric acid-copper sulfate solution.

  In the pure copper anode, the voltage between the terminals started to increase greatly after 22.9 hours from the start of electrolysis, and this was designated as the passivation time of pure copper. It was confirmed that the passivation time was shortened in the low grade copper anode containing 1 mass% of Sb, Ag, Au, Pt, Pd or Se as impurities as compared with pure copper. In particular, in the case of a low-grade copper anode containing 1 mass% of Pb as an impurity, it was confirmed that the voltage between terminals (Terminal voltage) rose to about 2 V after 3.3 hours from the start of electrolysis, and remained almost constant. It was done. In this case, it is considered that the following reaction proceeds on the surface of the low-grade copper anode.

(I) Pb + SO ₄ ²⁻ → PbSO ₄ + 2e ⁻ (2)
(Ii) PbSO ₄ + 2H ₂ O → PbO ₂ + H ₂ SO ₄ + 2H ⁺ + 2e ⁻ (3)
(Iii) 2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻ (4)
As a result of Pb being exposed on the surface (electrode surface) of the low-grade copper anode due to the progress of copper dissolution, the chemical reaction occurring at the low-grade copper anode was switched from the dissolution of copper to the generation of oxygen due to these series of reactions. Conceivable.

On the other hand, when a low-grade copper anode was electrolyzed using a sulfamic acid-copper sulfamate solution, as shown in FIG. 2, none of the copper alloys was passivated within a range of 24 hours. Therefore, it was confirmed that the sulfamic acid-copper sulfamate solution has a great effect on suppression of passivation.
<3. Preparation and electrolysis of low-grade copper anodes containing various metal elements as impurities>
Based on the charge composition of the low grade copper anode shown in Table 2, In the same manner, a low-grade copper anode was produced.

Example 1
A copper alloy containing a metal element other than 17.04 mass% copper, which is a total of Ag2.09 mass%, Pb5.02 mass%, Ni4.08 mass%, and Sb5.85 mass%, and 1.04 mass% O as impurities. This was used as a low grade copper anode (82% copper anode).

1. Using the low-grade copper anode thus obtained, The electrolytic test was conducted in the same manner as above. The current density was 300 A / m ² and continued for a maximum of 168 hours.

(Example 2-1)
As an impurity, Ag of 4.12 mass%, Au of 0.21 mass%, Pb of 4.09 mass%, Ni of 4.02 mass%, As of 1.43 mass%, Sb of 4.00 mass%, Bi of 1.46 mass%, and Se of 1.02 mass% of 20.35 mass% A copper alloy containing a metal element other than copper was prepared, and an electrolytic test was conducted in the same manner as in Example 1 except that this was used as a low-grade copper anode (80% copper anode).

(Example 2-2)
As an impurity, 29.90 mass% of Ag 5.94 mass%, Au 0.31 mass%, Pb 5.95 mass%, Ni 5.99 mass%, As 2.10 mass%, Sb 6.03 mass%, Bi 2.09 mass%, and Se 1.49 mass%. A copper alloy containing a metal element other than copper was prepared, which was used as a low-grade copper anode (70% copper anode), and the electrolytic solution obtained by filtering the electrolytic solution after 80% copper anode electrolysis in Example 2-1 was used as the electrolytic solution. The electrolytic test was conducted in the same manner as in Example 1 except that it was reused.

1. Using the thus obtained low-grade copper anode of Examples 1-2, The electrolytic test was conducted in the same manner as above. The current density was 300 A / m ² and continued for a maximum of 168 hours.

  In the 82% copper anode of Example 1, as shown in FIG. 3, the voltage between terminals showed a value of about 0.6 V immediately after the start of electrolysis, and then gradually increased to about 0.9 V. The value of such inter-terminal voltage is smaller than the inter-terminal voltage (about 2.0 to 2.3 V) in electrowinning, but the inter-terminal voltage in electrolytic refining using a conventional sulfuric acid-copper sulfate solution as an electrolytic solution ( About 0.3V).

  Moreover, although the voltage between terminals rose intermittently to about 2V, it has confirmed that it was immediately reversed in about 15 minutes. Moreover, generation | occurrence | production of gas has been confirmed, while the voltage between terminals is rising to about 2V. Such a voltage increase and depolarization is considered to be a phenomenon caused by decomposition of sulfamic acid, generation of slime containing Pb, and slime detachment from the anode surface shown in the following reaction formula.

H ₃ NSO ₃ + H ₂ O → NH ₃ + H ₂ SO ₄ (5)
Pb ²⁺ + H ₂ SO ₄ → PbSO ₄ + 2H ⁺ (6)
When PbSO ₄ is generated on the anode surface by the equation (6), the anode reaction changes as in equations (3) and (4), and the oxygen generation reaction proceeds. At this time, it is considered that when the slime is dropped due to the generation of oxygen from the gap between the slime containing Pb, copper is exposed again, and the anode reaction returns to the dissolution of copper and is reversed.

  Further, as shown in FIG. 4 (A), it was confirmed that electrolytic copper having a good electrodeposition was recovered at the cathode after electrolysis. On the other hand, as shown in FIG. 4B, it was confirmed that the 82% copper anode dissolved copper and the anode volume was greatly reduced. In addition, slime was observed under the anode and on the surface of the electrolyte during electrolysis.

  The 80% copper anode of Example 2-1 did not passivate the anode as shown in FIG. Compared with Example 1, the frequency at which the inter-terminal voltage increased was low, but a plurality of peaks indicating an increase in the inter-terminal voltage were superimposed, and a broad peak was confirmed. Further, the cathode after electrolysis had a shape almost equivalent to that shown in FIG.

  In the 70% copper anode of Example 2-2, the anode was not passivated as shown in FIG. Compared with Example 1, the frequency at which the inter-terminal voltage increased was higher, and a plurality of peaks indicating an increase in the inter-terminal voltage were superimposed, and a broad peak was confirmed. Moreover, in the cathode after electrolysis, as shown in FIG. 8 (A), the electrodeposition form at the lower part of the cathode was unsatisfactory because there were many irregularities and voids existed. During electrolysis, not only under the anode and the surface of the electrolyte, but also slime drifting in the electrolyte was confirmed.

The electrolytic failure in Example 2-2 is considered to be a phenomenon caused by the repeated use of the electrolytic solution. That is, it is considered that as a result of exceeding the limit amount that can be immobilized as dissolved chemical species in the electrolytic solution, the excessive amount becomes slime and adheres to the cathode, thereby causing electrolysis failure.
<4. Impurity concentration measurement and current efficiency in electrodeposited copper cathodes>
After electrolysis of the low-grade copper anodes of Examples 1-2, the copper electrodeposited on the stainless steel cathode was peeled off, about half of which was dissolved in about 50 ml of 4-fold diluted nitric acid, and then 100 ml using a volumetric flask. The concentration of the impurity element in the solution obtained by appropriately diluting the solution was determined by using inductively coupled plasma emission spectroscopy (ICP-OES) (iCAP7400, manufactured by Thermo Scientific, Yokohama), and the electrodeposited copper was determined. The impurity concentration inside was measured. Further, the extent to which metal elements other than copper as impurities in the low-grade copper anode were dissolved in the electrolytic solution was also measured by ICP-OES analysis.

Further, the current efficiency was calculated from the energization current value I, the energization time t, the weight W of copper deposited on the cathode, the Faraday constant F, and the atomic weight M _{Cu of} copper by the following formula.

100 · W / [{(I · t) / (2F)} · M _Cu ] (7)
The results are shown in Table 3.

  In Table 3, nd means that the impurity element was below the limit of quantification in the copper concentration obtained from the ICP-OES analysis of the solution of the cathode and its diluted solution, and specifically indicates less than 1 ppm. .

  As shown in Table 3, when the concentration of metal elements as impurities in copper deposited on the cathode after electrolysis was analyzed by ICP-OES, each metal element of Ag, Pb, Ni and Sb was analyzed in Example 1. Since all were below the limit of quantification, it was considered that 99.99 mass% or more of electrodeposited copper was obtained. The current efficiency obtained from the weight of the cathode electrodeposited at this time was 100.4%. From these results, it has been clarified that the sulfamic acid-copper sulfamate solution is a very promising electrolyte system capable of electrolytically refining a low-grade copper anode.

  In addition, although it is prescribed | regulated that the Ag density | concentration in the copper cathode after electrolytic refining is less than 25 ppm by international standards, in the electrolytic refining method of the low grade copper anode of this invention, the measurement result with Ag concentration of 1 ppm or less is shown. Obtained. Therefore, it was confirmed that high-purity electrolytic copper with very few impurities can be obtained.

  Moreover, about Example 2-1, Ag12ppm, Sb13ppm, Bi13ppm was confirmed from the cathode as impurities of significant concentration among impurities added to the anode, and other elements were below the limit of quantification. Therefore, it can be said that copper having a purity of 99.99% or more was obtained also in this case.

On the other hand, in Example 2-2, the concentrations of metal elements other than copper as impurities were 27 ppm Ag, 29 ppm As, and 30 ppm Sb, respectively, and the impurity concentration compared to Examples 1 and 2-1. Was big. In Example 2-2, since the form of electrodeposition was poor, it is considered that there is a high possibility that the electrolyte solution and the slime in the electrolyte solution were involved.
<5. Measurement of impurity concentration in electrolytic solution after electrolysis>
Regarding the electrolytic solution after electrolysis, 4. In the same manner as above, the concentration of metal elements other than copper as impurities was measured using the ICP-OES method. The results are shown in Table 4.

  As shown in Table 4, in Example 1, the concentrations of metal elements other than copper as impurities were an Ag concentration of 0.247 ppm, a Pb concentration of 613 ppm, an Ni concentration of 606 ppm, and an Sb concentration of 56.9 ppm, respectively. It was suggested that most of Ni was dissolved in the electrolyte. On the other hand, Ag, which is a noble metal than copper, has a very low concentration in the electrolytic solution, and is considered to be mostly distributed in the slime. In addition, Sb was partially dissolved in the electrolytic solution, but most of the Sb is considered to form a hardly soluble compound and distributed in the slime.

In Example 2-1, in addition to the metal elements Ag, Pb, Ni, and Sb added as impurities in the anode in Example 1, Au, As, and Bi were added to the anode. In this case, the tendency for Pb, Ni, As, and Bi to increase in the electrolytic solution after electrolysis was observed. Therefore, it is considered that these elements are immobilized as dissolved chemical species in the electrolytic solution. On the other hand, Sb had a lower concentration than that of Example 1. This is presumably because it reacted with As ions dissolved from the anode to produce hardly soluble SbAsO ₄ or the like.
<6. Slime component analysis>
After electrolytic refining, the slime that settled below the 82% copper anode of Example 1 and the slime that floated on the surface of the electrolytic solution were collected together with the electrolytic solution, filtered, washed, and then electron microscope SEM-EDS. (JSM-6510A, JEOL) Tissue observation and simple component analysis, and phase identification using an X-ray diffractometer (Ultima IV / 285PDS, Rigaku) were performed.

  As shown in FIG. 9A, as a result of observation by SEM, in the slime that had settled below the 82% copper anode, a large number of bumps were confirmed on the surface. On the other hand, as shown in FIG. 9 (B), it was confirmed that the slime floating on the surface of the electrolyte had few surface bulges and each slime mass was relatively small.

From the results of FIG. 10, it was confirmed that the slime that had settled below the 82% copper anode was a mixture of Ag, NiO, and Ab ₂ O ₃ and was rich in noble metals. On the other hand, the slime floating on the surface of the electrolytic solution is considered to be composed of Sb ₂ O ₃ and PbSO ₄ . Therefore, it is considered that the noble metal can be recovered by recovering the slime settled as the anode mud and dissolving it in an appropriate solvent.

  From the slime recovered in Examples 2-1 to 2-2, bismuth arsenate and antimony arsenate could be confirmed in addition to the compounds of impurity metal elements other than copper found in Example 1.

Claims (6)

Using a copper alloy containing a metal element other than copper as an impurity as a low-grade copper anode,
The low-grade copper anode and the cathode are face-to-face arranged in an electrolytic solution having a large solubility with respect to a metal element forming a compound adhering to the anode, and electrolysis is performed to collect copper on the cathode surface. A method for electrolytic refining of low-grade copper anodes.   2. The method of electrolytic refining a low-grade copper anode according to claim 1, wherein the electrolytic solution is a sulfamic acid-copper sulfamate solution or a silicofluoric acid-copper silicate solution.   The metal element other than copper is at least one metal element selected from the group consisting of Ag, Au, Pt, Pd, Ni, Pb, As, Sb, Bi, Se, Te, Sn, Zn, and Fe. The method for electrolytic refining of a low-grade copper anode according to claim 1 or 2.   4. The low-grade copper anode according to claim 1, wherein the low-grade copper anode is a copper alloy containing 1 mass to 30 mass% in total of metal elements other than the copper. 5. Electrolytic refining method. The electrolytic current density 100A ^/ m 2 ~400A ^/ low-grade copper anode for electrolytic refining method according to any one of claims 1 to 4 ^{and m} and performing at ^2.   An electrolytic solution for electrolytic refining of a low-grade copper anode, characterized by comprising a sulfamic acid-copper sulfamate solution or a silicofluoric acid-copper silicate solution as a main component.