Preparation method of 7N ultrahigh-purity copper

Abstract

The invention provides a preparation method of 7N ultrahigh-purity copper, which comprises the following steps: taking 4N copper as an anode, placing the anode in a diaphragm bag, taking a first titanium plate as a cathode, taking a copper nitrate solution as an electrolyte, and carrying out pre-electrolysis; and after the pre-electrolysis is finished, a second titanium plate serves as a cathode, electrolyte circulating electrolysis is conducted, the section of the second titanium plate is in a trapezoid shape, the long edge of the trapezoid is close to the bottom of the electrolytic bath, and the 7N ultra-high-purity copper is obtained after electrolysis is finished. According to the preparation method provided by the invention, the overall purity of the electrolytic copper product obtained at the cathode can reach 7N or above, the purity and the component uniformity of the ultra-high-purity copper product are improved, and the problems of non-uniform copper purity and low yield caused by the fact that the purity of copper close to the bottom of an electrolytic bath in an existing electrolysis method does not reach the standard are solved; the yield of ultra-high pure copper products is improved to 100%, the material utilization rate and the production capacity are improved, and the product cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of metal preparation, and specifically relates to a method for preparing 7N ultra-high purity copper. Background Art

[0002] With the continuous development of modern science and technology, the demand for high-purity metal materials is becoming more and more vigorous, especially in the semiconductor, optoelectronics and new energy industries. Among them, high-purity copper materials have excellent electrical properties, thermal conductivity and corrosion resistance, and are widely used.

[0003] 7N high-purity copper, that is, copper material with a purity of 99.99999%, plays an indispensable role in the manufacture of key devices such as semiconductor chips, flat-panel displays, and solar cells because of its excellent conductivity and stable physical properties. Especially in thin film deposition technology, it has become an important raw material for semiconductor targets, which can effectively improve the uniformity and adhesion of the film and ensure the accuracy and quality of the chip manufacturing process.

[0004] The traditional high-purity copper process usually adopts electrolysis, where the copper anode in the electrolytic cell dissolves impurities in the copper, so that the copper material is deposited on the cathode to obtain high-purity copper. However, in the actual production process, when a large-capacity PVC electrolytic cell is used for copper electrolysis, the long-term standing of the electrolyte will cause more impurities to accumulate at the bottom, especially high silver content, which will cause the purity of the copper deposited at the cathode to vary greatly in different areas. Usually, the copper purity of the upper layer of the electrolytic cell can reach 7N, but due to the accumulation of impurities at the bottom, the purity can only be maintained at 6N or even 5N, resulting in uneven copper purity. This uneven purity phenomenon directly affects the yield of 7N high-purity copper, which is usually only 66.7%, resulting in the final high-purity copper material in actual application. There are problems of material waste and excessive production costs, which not only reduces the profit of the product, but also makes the company face greater challenges in large-scale production.

[0005] CN115896870A and CN115449848A respectively disclose a method for preparing high-purity copper, which adopts a continuous refining electrolysis process, specifically, first electrolyzing 4N copper as a raw material to obtain 5N or 6N high-purity copper, and then electrolyzing the high-purity copper as a raw material again to obtain 7N copper. This method requires continuous electrolysis, which has high energy consumption and cost, and is not conducive to industrialized continuous production.

[0006] CN116479471A discloses a method for preparing ultra-high purity electrolytic copper, wherein tetrazole, an additive, is added to an electrolyte, and the additive reacts with impurities in the electrolyte to precipitate some impurities, thereby improving the purity of the electrolytic copper. This method requires the use of additives for reaction, and impurities are continuously generated during the continuous electrolysis process. The additives are continuously consumed, and continuous replenishment is required. Moreover, only certain impurities can be treated, which increases production costs and is not universal.

[0007] Therefore, based on the problems existing in the existing high-purity copper production process, the present invention provides a method for preparing 7N ultra-high purity copper. Summary of the invention

[0008] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing 7N ultra-high purity copper, the composition of the obtained ultra-high purity copper is uniform, the overall quality reaches above 7N, and the yield of ultra-high purity copper is improved.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for preparing 7N ultra-high purity copper, the preparation method comprising the following steps:

[0011] (1) using 4N copper as an anode, placing the anode in a diaphragm bag, using a first titanium plate as a cathode, and using a copper salt solution as an electrolyte to perform pre-electrolysis;

[0012] (2) After the pre-electrolysis is completed, the electrolyte circulation electrolysis is continued with 4N copper as the anode and the second titanium plate as the cathode. The cross-section of the second titanium plate is a trapezoid, and the long side of the trapezoid is close to the bottom of the electrolytic cell. After the electrolysis is completed, the 7N ultra-high purity copper is obtained on the second titanium plate.

[0013] The process of preparing high-purity copper by electrolysis uses 4N copper as the anode. During the electrolysis process, impurities in the copper anode will be deposited at the bottom of the electrolytic cell or form dissolved ions. After a long period of electrolysis, the electrolyte is left to stand, resulting in the accumulation of more impurities at the bottom, especially high silver content, which leads to large differences in the purity of the deposited copper in different areas, resulting in uneven copper purity. The copper purity near the top of the electrolytic cell can usually reach 7N, and the copper purity near the bottom of the electrolytic cell can only be maintained at 6N or even 5N, resulting in the yield of 7N ultra-high purity copper usually being only about 66.7%.

[0014] The preparation method provided by the present invention can prepare ultra-high purity copper products with a purity of 7N and uniform composition. First, in the pre-electrolysis process, it is helpful to remove some impurities and pollutants, improve the reaction efficiency of subsequent electrolysis, and place the anode in a diaphragm bag to isolate anode impurities. In the formal electrolysis process, a trapezoidal titanium plate is used as the cathode, so that the current density at the bottom of the cathode is lower than that at the top, thereby improving the uniformity of the composition of the ultra-high purity copper product, so that the overall purity of the electrolytic copper obtained at the cathode can reach 7N, and the finished product rate of the electrolytic copper is directly increased to 100%.

[0015] Preferably, the copper salt comprises copper nitrate.

[0016] Preferably, in the electrolyte, the concentration of copper salt is 60-100 g / L, for example, 60 g / L, 70 g / L, 80 g / L, 90 g / L or 100 g / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] Preferably, the preparation process of the electrolyte includes: obtaining a copper nitrate solution by reacting 4N copper and nitric acid, and filtering and purifying the copper nitrate solution to obtain the electrolyte.

[0018] Preferably, the filtration purification comprises using a filter membrane and a resin in sequence.

[0019] Preferably, the pore size of the filter membrane is 0.1 μm.

[0020] Preferably, the resin comprises CAG-47.

[0021] Preferably, the current density of the pre-electrolysis in step (1) is 100-200 A / m 2 , for example, it can be 100A / m 2 , 120A / m 2 , 140A / m 2 , 150A / m 2 、160A / m 2 、180A / m 2 or 200A / m 2 , but not limited to the listed values, other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the pre-electrolysis time in step (1) is 3-15 days, for example, 3 days, 5 days, 8 days, 10 days, 12 days or 15 days, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the temperature of the pre-electrolysis in step (1) is 20-40°C, for example, 20°C, 25°C, 30°C, 35°C or 40°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] Preferably, in step (1), the cross-section of the first titanium plate is square.

[0025] Preferably, the diaphragm bag and the anode are pretreated separately and independently before the pre-electrolysis in step (1).

[0026] Preferably, the pretreatment of the diaphragm bag comprises: soaking it in pure water and nitric acid solution in sequence.

[0027] Preferably, the concentration of the nitric acid solution is 8-12wt%, for example, 8wt%, 9wt%, 10wt%, 11wt% or 12wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the soaking time with pure water is 3-5 hours, for example, it can be 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0029] Preferably, the soaking time in the nitric acid solution is 3-5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the pretreatment of the anode includes: using a nitric acid solution to remove surface oxides and oil stains, and then rinsing with water.

[0031] Preferably, the concentration of the nitric acid solution is 8-12wt%, for example, 8wt%, 9wt%, 10wt%, 11wt% or 12wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, the electrolyte is allowed to stand before the electrolysis in step (2).

[0033] Preferably, the standing time is 20-30 hours, for example, 20 hours, 22 hours, 25 hours, 28 hours or 30 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] Preferably, in step (2), the ratio of the lengths of the long and short sides of the trapezoidal cross-section of the second titanium plate is (1.1-1.5):1, for example, it can be 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the average current density of the electrolysis in step (2) is 100-130A / m 2 , for example, it can be 100A / m 2 、105A / m 2 , 110A / m 2 , 115A / m 2 , 120A / m 2 , 125A / m 2 or 130A / m 2 , but not limited to the listed values, other unlisted values ​​within the numerical range are also applicable.

[0036] Preferably, the electrolyte circulation method in step (2) comprises: during the electrolysis process, the electrolyte is discharged from the bottom of the electrolytic cell and the electrolyte is replenished at the same time, and the discharge rate and the replenishment rate are the same.

[0037] Preferably, the rate of fluid infusion is 0.5-1.5 L / min, for example, it can be 0.5 L / min, 0.8 L / min, 1.0 L / min, 1.2 L / min or 1.5 L / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] As a preferred technical solution of the preparation method provided by the present invention, the preparation method comprises the following steps:

[0039] (1) 4N copper and nitric acid are used to prepare an electrolyte with a copper nitrate concentration of 60-100 g / L, 4N copper is used to remove surface oxides and oil stains with a nitric acid solution, and then rinsed with water to use as an anode, the anode diaphragm bag is soaked with pure water and nitric acid solution in turn, the anode is placed in the anode diaphragm bag, and a first titanium plate with a square cross-section is used as a cathode to perform pre-electrolysis, and the current density of the pre-electrolysis is 100-200 A / m 2 , the pre-electrolysis temperature is 20-40° C., and the pre-electrolysis time is 3-15 days;

[0040] (2) After the pre-electrolysis is completed, the electrolyte is allowed to stand for 20-30 hours. After the standing, 4N copper is used as the anode and the second titanium plate is used as the cathode. The cross-section of the second titanium plate is a trapezoid, and the long side of the trapezoid is close to the bottom of the electrolytic cell. The ratio of the long side to the short side of the trapezoid is (1.1-1.5):1. Electrolysis is performed, and the average current density of the electrolysis is 100-130A / m 2 During the electrolysis process, the electrolyte is discharged from the bottom of the electrolytic cell, and at the same time, the electrolyte is replenished at a rate of 0.5-1.5 L / min. The replenishment and discharge rates are the same. The discharged electrolyte is purified and then reused for the replenishment. When the electrolysis is completed, 7N ultra-high purity copper is obtained on the second titanium plate.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The preparation method provided by the present invention can obtain an electrolytic copper product at the cathode with an overall purity of more than 7N, thereby improving the purity and composition uniformity of the ultra-high purity copper product, solving the problem of uneven copper purity and low yield caused by the copper purity near the bottom of the electrolytic cell not meeting the standard in the existing electrolysis method, and increasing the yield of ultra-high purity copper products to 100%, thereby improving material utilization and production volume, and reducing product costs. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0044] Example 1

[0045] This embodiment provides a method for preparing 7N ultra-high purity copper, the preparation method comprising the following steps:

[0046] (1) preparing an electrolyte: reacting 4N copper with analytical pure nitric acid to obtain a copper nitrate solution, filtering the copper nitrate solution with a 0.1 μm filter, and then filtering it through a CAG-47 resin to obtain a copper nitrate electrolyte with a concentration of 80 g / L;

[0047] (2) Electrode and diaphragm bag pretreatment: 4N copper is used as the anode, and 10% nitric acid solution is used to remove the oxide scale and oil stains on the copper surface, and then rinsed with pure water. Prepare the first titanium plate and the second titanium plate. The shape of the first titanium plate is square, and the shape of the second titanium plate is trapezoidal. The ratio of the long side to the short side of the trapezoid is 1.2:1. Rinse the first titanium plate and the second titanium plate with pure water, soak the anode diaphragm bag with pure water, and then soak it in 10% nitric acid for 4 hours, and then rinse it with pure water;

[0048] (3) Pre-electrolysis: The anode is placed in the anode diaphragm bag, and placed in the electrolytic cell together with the first titanium plate and the electrolyte for electrolysis. The current density is controlled at 150 A / m2 , the temperature was controlled at 25°C, and the cycle was 5 days;

[0049] (4) Circulation electrolysis: After the pre-electrolysis, the electrolyte in the electrolytic cell was allowed to stand for 24 h, and then a second titanium plate was placed as a cathode, with the long side of the second titanium plate close to the bottom of the electrolytic cell and the short side away from the bottom of the electrolytic cell, for circulation electrolysis. The average current density of the electrolysis was 100 A / m 2 During the electrolysis process, the electrolyte is discharged from the bottom of the electrolytic cell. At the same time, the electrolyte is replenished above the electrolytic cell at a rate of 1L / min. The replenishment and discharge rates are kept the same to keep the electrolyte level stable. The discharged electrolyte is filtered and purified before being used for replenishment. The electrolysis is continued until the anode is exhausted. After the end, 7N ultra-high purity copper is obtained on the second titanium plate.

[0050] Example 2

[0051] This embodiment provides a method for preparing 7N ultra-high purity copper, the preparation method comprising the following steps:

[0052] (1) preparing an electrolyte: reacting 4N copper with analytical pure nitric acid to obtain a copper nitrate solution, filtering the copper nitrate solution with a 0.1 μm filter, and then filtering it through a CAG-47 resin to obtain a copper nitrate electrolyte with a concentration of 60 g / L;

[0053] (2) Pretreatment of electrodes and diaphragm bags: 4N copper is used as the anode, and 10% nitric acid solution is used to remove the oxide scale and oil stains on the copper surface, and then rinsed with pure water. Prepare the first titanium plate and the second titanium plate. The shape of the first titanium plate is square, and the shape of the second titanium plate is trapezoidal. The ratio of the long side to the short side of the trapezoid is 1.3:1. Rinse the first titanium plate and the second titanium plate with pure water, soak the anode diaphragm bag with pure water, and then soak it in 10% nitric acid for 4 hours, and then rinse it with pure water;

[0054] (3) Pre-electrolysis: The anode is placed in the anode diaphragm bag, and placed in the electrolytic cell together with the first titanium plate and the electrolyte for electrolysis. The current density is controlled at 130 A / m 2 , the temperature was controlled at 25°C, and the cycle was 8 days;

[0055] (4) Circulation electrolysis: After the pre-electrolysis, the electrolyte in the electrolytic cell was allowed to stand for 20 h, and then a second titanium plate was placed as a cathode. The second titanium plate was placed so that its long side was close to the bottom of the electrolytic cell and its short side was far from the bottom of the electrolytic cell. Circulation electrolysis was performed, and the average current density of the electrolysis was 110 A / m 2During the electrolysis process, the electrolyte is discharged from the bottom of the electrolytic cell. At the same time, the electrolyte is replenished above the electrolytic cell at a rate of 0.5L / min. The replenishment and discharge rates are kept the same to keep the electrolyte level stable. The discharged electrolyte is filtered and purified before being used for replenishment. The electrolysis is continued until the anode is exhausted. After the end, 7N ultra-high purity copper is obtained on the second titanium plate.

[0056] Example 3

[0057] This embodiment provides a method for preparing 7N ultra-high purity copper, the preparation method comprising the following steps:

[0058] (1) preparing an electrolyte: reacting 4N copper with analytical pure nitric acid to obtain a copper nitrate solution, filtering the copper nitrate solution with a 0.1 μm filter, and then filtering it with a CAG-47 resin to obtain a copper nitrate electrolyte with a concentration of 100 g / L;

[0059] (2) Electrode and diaphragm bag pretreatment: 4N copper is used as the anode, and 10% nitric acid solution is used to remove the oxide scale and oil stains on the copper surface, and then rinsed with pure water. Prepare the first titanium plate and the second titanium plate. The shape of the first titanium plate is square, and the shape of the second titanium plate is trapezoidal. The ratio of the long side to the short side of the trapezoid is 1.2:1. Rinse the first titanium plate and the second titanium plate with pure water, soak the anode diaphragm bag with pure water, and then soak it in 10% nitric acid for 4 hours, and then rinse it with pure water;

[0060] (3) Pre-electrolysis: The anode is placed in the anode diaphragm bag, and placed in the electrolytic cell together with the first titanium plate and the electrolyte for electrolysis. The current density is controlled to be 120A / m 2 , the temperature was controlled at 20°C, and the cycle was 12 days;

[0061] (4) Circulation electrolysis: After the pre-electrolysis, the electrolyte in the electrolytic cell was allowed to stand for 30 h, and then a second titanium plate was placed as a cathode. The second titanium plate was placed so that its long side was close to the bottom of the electrolytic cell and its short side was far from the bottom of the electrolytic cell. Circulation electrolysis was performed, and the average current density of the electrolysis was 120 A / m 2 During the electrolysis process, the electrolyte is discharged from the bottom of the electrolytic cell. At the same time, the electrolyte is replenished above the electrolytic cell at a rate of 0.8L / min. The replenishment and discharge rates are kept the same to keep the electrolyte level stable. The discharged electrolyte is filtered and purified before being used for replenishment. The electrolysis is continued until the anode is exhausted. After the end, 7N ultra-high purity copper is obtained on the second titanium plate.

[0062] Example 4

[0063] This embodiment provides a method for preparing 7N ultra-high purity copper. Compared with Example 1, the current density of the pre-electrolysis in step (3) is controlled to be 60 A / m 2, the rest are the same as in Example 1.

[0064] Example 5

[0065] This embodiment provides a method for preparing 7N ultra-high purity copper. Compared with Example 1, the average current density of electrolysis in step (4) is controlled to be 150 A / m 2 , the rest are the same as in Example 1.

[0066] Comparative Example 1

[0067] This comparative example provides a method for preparing 7N ultra-high purity copper. Compared with Example 1, step (3) pre-electrolysis is not performed, that is, the anode is placed in the anode diaphragm bag, and the second titanium plate is directly used for cyclic electrolysis. The rest is the same as Example 1.

[0068] Comparative Example 2

[0069] This comparative example provides a method for preparing 7N ultra-high purity copper. Compared with Example 1, in the cyclic electrolysis of step (4), a second titanium plate with a square cross-section is used, that is, the second titanium plate has the same size as the first titanium plate, and the rest is the same as Example 1.

[0070] Comparative Example 3

[0071] This comparative example provides a method for preparing 7N ultra-high purity copper. Compared with Example 1, during the electrolysis process of step (4), electrolyte circulation is not performed, that is, no electrolyte discharge or electrolyte replenishment is performed during the electrolysis process. The rest is the same as Example 1.

[0072] Comparative Example 4

[0073] This comparative example provides a method for preparing 7N ultra-high purity copper. Compared with Example 1, no anode diaphragm bag is used in the electrolysis process in step (3) and step (4), and the rest is the same as Example 1.

[0074] The 7N ultra-high purity copper plates prepared in the embodiments and comparative examples were sampled at the upper and lower ends and the middle position, and GDMS (glow discharge mass spectrometry) detection was performed. The sampling positions were recorded as site A, site B and site C in the same direction. The results are listed in Table 1.

[0075] Table 1

[0076] A site purity B site purity C site purity Example 1 7N 7N 7N Example 2 7N 7N 7N Example 3 7N 7N 7N Example 4 5N 5N 5N Example 5 6N 5N 5N Comparative Example 1 5N 5N 5N Comparative Example 2 7N 7N 6N Comparative Example 3 7N 6N 5N Comparative Example 4 5N 5N 5N

[0077] As can be seen from Table 1, the preparation method provided by the present invention can obtain ultra-high purity copper with uniform composition. The purity and component consistency of the copper product are improved through the anode diaphragm bag, pre-electrolysis, the second titanium plate and the electrolyte circulation.

[0078] In summary, the purity of the electrolytic copper product obtained at the cathode by the preparation method provided by the present invention can reach 7N or above as a whole, thereby improving the purity and composition uniformity of the ultra-high purity copper product, solving the problem of uneven copper purity and low yield caused by the copper purity near the bottom of the electrolytic cell in the existing electrolysis method not meeting the standard, and increasing the yield of ultra-high purity copper products to 100%, thereby improving material utilization and production volume, and reducing product costs.

[0079] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing 7N ultra-high purity copper, characterized in that: The preparation method comprises the following steps: (1) using 4N copper as an anode, placing the anode in a diaphragm bag, using a first titanium plate as a cathode, and using a copper salt solution as an electrolyte to perform pre-electrolysis; (2) After the pre-electrolysis is completed, the electrolyte circulation electrolysis is continued with 4N copper as the anode and the second titanium plate as the cathode. The cross-section of the second titanium plate is a trapezoid, and the long side of the trapezoid is close to the bottom of the electrolytic cell. After the electrolysis is completed, the 7N ultra-high purity copper is obtained on the second titanium plate.

2. The preparation method according to claim 1, characterized in that: The copper salt includes copper nitrate; Preferably, the concentration of copper salt in the electrolyte is 60-100 g / L.

3. The preparation method according to claim 1 or 2, characterized in that: The current density of the pre-electrolysis in step (1) is 100-200A / m 2 ; Preferably, the pre-electrolysis time in step (1) is 3-15 days.

4. The preparation method according to any one of claims 1 to 3, characterized in that The temperature of the pre-electrolysis in step (1) is 20-40°C.

5. The preparation method according to any one of claims 1 to 4, characterized in that: Step (1) The cross section of the first titanium plate is square.

6. The preparation method according to any one of claims 1 to 5, characterized in that: Before the pre-electrolysis in step (1), the diaphragm bag and the anode are pre-treated separately and independently; Preferably, the pretreatment of the diaphragm bag comprises: soaking it in pure water and nitric acid solution in sequence; Preferably, the pretreatment of the anode includes: using a nitric acid solution to remove surface oxides and oil stains, and then rinsing with water.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The electrolyte is allowed to stand before the electrolysis in step (2); Preferably, the standing time is 20-30 hours.

8. The preparation method according to any one of claims 1 to 7, characterized in that: Step (2) The ratio of the lengths of the long and short sides of the trapezoidal cross section of the second titanium plate is (1.1-1.5):1; Preferably, the average current density of the electrolysis in step (2) is 100-130A / m 2 .

9. The preparation method according to any one of claims 1 to 8, characterized in that: The method for circulating the electrolyte in step (2) comprises: during the electrolysis process, the electrolyte is discharged from the bottom of the electrolytic cell and the electrolyte is replenished at the same time, and the discharge rate and the replenishment rate are the same; Preferably, the rate of fluid replacement is 0.5-1.5 L / min.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The preparation method comprises the following steps: (1) 4N copper and nitric acid are used to prepare an electrolyte with a copper nitrate concentration of 60-100 g / L, 4N copper is used to remove surface oxides and oil stains with a nitric acid solution, and then rinsed with water to use as an anode, the anode diaphragm bag is soaked with pure water and nitric acid solution in turn, the anode is placed in the anode diaphragm bag, and a first titanium plate with a square cross-section is used as a cathode to perform pre-electrolysis, and the current density of the pre-electrolysis is 100-200 A / m 2 , the pre-electrolysis temperature is 20-40° C., and the pre-electrolysis time is 3-15 days; (2) After the pre-electrolysis is completed, the electrolyte is allowed to stand for 20-30 hours. After the standing, 4N copper is used as the anode and the second titanium plate is used as the cathode. The cross-section of the second titanium plate is a trapezoid, and the long side of the trapezoid is close to the bottom of the electrolytic cell. The ratio of the long side to the short side of the trapezoid is (1.1-1.5):

1. Electrolysis is performed, and the average current density of the electrolysis is 100-130A / m 2 During the electrolysis process, the electrolyte is discharged from the bottom of the electrolytic cell, and at the same time, the electrolyte is replenished at a rate of 0.5-1.5 L / min. The replenishment and discharge rates are the same. The discharged electrolyte is purified and then reused for the replenishment. When the electrolysis is completed, 7N ultra-high purity copper is obtained on the second titanium plate.