Preparation method of cobalt sulfate electrolyte for ultra-high purity cobalt

Abstract

The application relates to a preparation method of a cobalt sulfate electrolyte for ultrahigh-purity cobalt, which adopts at least one chelating resin and at least one ion exchange resin to deeply remove impurities from cobalt sulfate stock solution, the content of Fe, Ni and Cu in the prepared cobalt sulfate electrolyte can be controlled to be less than 0.005 mg / L, and the electrolyte meets the preparation requirements of an ultrahigh-purity cobalt plate for integrated circuits.

Description

Technical Field

[0001] This invention relates to the fields of electrochemical technology and separation and purification technology, specifically to a method for preparing cobalt sulfate electrolyte for ultra-high purity cobalt. Background Technology

[0002] High-purity metals play a crucial role in the field of integrated circuits. In particular, my country has an urgent need for high-purity cobalt materials with a purity of 5N or higher. High-purity cobalt sputtering targets for integrated circuits are key contact layer materials for chips. Cobalt silicide gates based on self-aligned strained silicon technology can improve carrier mobility in the channel, reduce device impedance and power consumption, and enhance drive current, frequency response, and operating speed, making them a key material in large-scale integrated circuits with feature sizes above 90nm. With the development of semiconductor technology, the purity requirements for high-purity cobalt sputtering targets used in deep nanometer integrated circuit fabrication have become increasingly stringent, especially regarding the most harmful key impurities in large-scale integrated circuits such as Ni, Fe, and Cu. The limits for these impurity elements in the domestic and international integrated circuit industries have been reduced to below ppm. Therefore, the main challenge in preparing ultra-high-purity cobalt lies in overcoming the impurity removal technology for key impurities such as Ni, Fe, and Cu.

[0003] In the industry, the preparation methods for high-purity cobalt mainly include the preparation, purification, and electrolysis of cobalt solutions. Solution purification is primarily used to remove metallic impurities, such as Fe, Ni, and Cu, which are difficult to separate using electrochemical processes. However, because these impurities have extremely similar deposition potentials to cobalt at very low concentrations, the purification effect using electrolysis is poor. The resulting electrolytes often contain Ni and Fe concentrations greater than 0.5 mg / L. In practical applications, such electrolytes are unsuitable for preparing ultra-high-purity cobalt plates. Therefore, the preparation technology of electrolytes for ultra-high-purity cobalt still requires further exploration. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and provide a method for preparing cobalt sulfate electrolyte for ultra-high purity cobalt. This method uses at least one chelating resin and at least one ion exchange resin to deeply remove impurities from the cobalt sulfate stock solution. The content of Fe, Ni and Cu in the prepared cobalt sulfate electrolyte can be controlled at less than 0.005 mg / L. This electrolyte meets the preparation requirements of ultra-high purity cobalt plates for integrated circuits.

[0005] To achieve the above objectives, the present invention provides the following technical solution.

[0006] A method for preparing a cobalt sulfate electrolyte for ultra-high purity cobalt includes the following steps:

[0007] The raw cobalt plate was electrolytically dissolved using sulfuric acid solution as the electrolyte to obtain cobalt sulfate stock solution;

[0008] The cobalt sulfate stock solution is subjected to deep impurity removal using at least one chelating resin and at least one ion exchange resin to obtain a cobalt sulfate electrolyte.

[0009] The electrolytic dissolution involves the following reactions: the cobalt plate at the anode loses electrons to generate cobalt ions, which enter the sulfuric acid solution; and hydrogen ions at the cathode gain electrons to generate hydrogen gas.

[0010] Anode reaction equation: Co - 2e - =Co 2+

[0011] Cathode reaction equation: H + +2e - =H2.

[0012] In some embodiments of the present invention, the electrolytic dissolution is carried out in an electrolytic cell.

[0013] In some embodiments of the present invention, ultrapure water and sulfuric acid are prepared into a sulfuric acid solution with an acidity of 2-7 mol / L. The acidity may be, for example, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L, or 7 mol / L.

[0014] In some embodiments of the present invention, the concentration of the prepared cobalt sulfate stock solution is 50-200 g / L, and the pH value is 1-3. The concentration can be, for example, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, or 200 g / L. The pH value can be, for example, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3.

[0015] In some embodiments of the present invention, a filter membrane is provided on the outer surface of the anode before the electrolytic dissolution begins to prevent insoluble impurities detached from the anode during the electrolytic dissolution process from entering the electrolyte. In some specific embodiments, a diaphragm bag with a filtering function can be fitted onto the outer surface of the anode to prevent insoluble impurities detached from the anode during the electrolytic dissolution process from entering the electrolyte.

[0016] In some embodiments of the present invention, the electrolytic dissolution includes: firstly, electrolytic dissolution is performed using a raw cobalt plate as the anode and a raw cobalt plate as the cathode; when the acidity of the sulfuric acid solution reaches 0.5-1 mol / L (for example, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1.0 mol / L), the cathode is replaced with a hydrogen evolution electrode, and electrolytic dissolution continues, wherein the hydrogen evolution electrode is a Pt electrode, a Pt / C electrode or a Ru / C electrode.

[0017] Before the acidity of the sulfuric acid electrolyte reaches 0.5-1 mol / L, hydrogen ions are easily discharged and evolved. Therefore, in the early stage of electrolytic dissolution, the cathode can be a raw material cobalt plate. However, after the acidity of the sulfuric acid electrolyte reaches 0.5-1 mol / L, hydrogen ions are difficult to discharge and evolve. Therefore, in the later stage of electrolytic dissolution, the raw material cobalt plate cathode can be replaced with a hydrogen evolution electrode. Utilizing the characteristic that the overpotential of hydrogen on the hydrogen evolution electrode is lower than its overpotential on the cobalt plate, the deposition of cobalt ions on the cathode can be suppressed, thereby increasing the concentration of the cobalt sulfate stock solution and significantly improving production efficiency and acid utilization. At the same time, the hydrogen evolution electrode also further reduces the hydrogen ion concentration in the cobalt sulfate stock solution, avoiding the adverse effects of excessively high hydrogen ion concentration on the resin, which would cause difficulties in subsequent resin purification processes. It also avoids the problem of excessively high electrolyte acidity leading to hydrogen evolution reaction corrosion of the cathode and low electrolysis efficiency in subsequent electrolysis processes.

[0018] In some embodiments of the present invention, the process parameters for electrolytic dissolution using a cobalt plate as the cathode include: cell voltage 1-2V (e.g., 1V, 1.1V, 1.2V, 1.3V, 1.4V, 1.5V, 1.6V, 1.7V, 1.8V, 1.9V, or 2V), electrode spacing 10-20cm (e.g., 10cm, 11cm, 12cm, 13cm, 14cm, 15cm, 16cm, 17cm, 18cm, 19cm, or 20cm), and current density 40-120A / m. 2 (e.g., 40A / m) 2 45A / m 2 50A / m 2 55A / m 2 60A / m 2 65A / m 2 70A / m 2 75A / m 2 80A / m 2 85A / m 2 90A / m 2 95A / m 2 100A / m 2 105A / m 2110A / m 2 115A / m 2 Or 120A / m 2 The process parameters for electrolytic dissolution using a hydrogen evolution electrode as the cathode include: cell voltage 0.5-1V (e.g., 0.5V, 0.6V, 0.7V, 0.8V, 0.9V, or 1V); electrode spacing 10-20cm (e.g., 10cm, 11cm, 12cm, 13cm, 14cm, 15cm, 16cm, 17cm, 18cm, 19cm, or 20cm); and current density 5-20A / m. 2 (e.g. 5A / m) 2 6A / m 2 7A / m 2 8A / m 2 9A / m 2 10A / m 2 11A / m 2 12A / m 2 13A / m 2 14A / m 2 15A / m 2 16A / m 2 17A / m 2 18A / m 2 19A / m 2 Or 20A / m 2 ).

[0019] In some embodiments of the present invention, before performing deep impurity removal, the preparation method further includes: filtering the cobalt sulfate stock solution for preliminary impurity removal to obtain a cobalt sulfate refined filtrate. Then, the refined cobalt sulfate filtrate is further purified using the resin to obtain a cobalt sulfate electrolyte.

[0020] Preferably, a filter medium is used for the preliminary impurity removal, and the pore size of the filter medium is not greater than 1 μm.

[0021] More preferably, the preliminary impurity removal includes: passing the cobalt sulfate stock solution through a filter containing the filter medium at a flow rate of 1-5 BV / h (e.g., 1 BV / h, 1.5 BV / h, 2 BV / h, 2.5 BV / h, 3 BV / h, 3.5 BV / h, 4 BV / h, 4.5 BV / h, or 5 BV / h) to obtain a cobalt sulfate refined filtrate. The preliminary impurity removal is precision filtration. The impurities filtered in this step mainly originate from trace amounts of insoluble impurities (such as high-potential impurity particles, cobalt hydroxide precipitate, etc.) that pass through the filter membrane (e.g., diaphragm bag) on ​​the outer surface of the anode during electrolytic dissolution and enter the electrolyte, as well as impurities (such as dust) mixed into the cobalt sulfate stock solution from the air. These impurities, when immersed in acidic solutions for a long time, pose a risk of chemical dissolution and the formation of soluble impurities. Precision filtration can effectively reduce the content of insoluble impurities. Furthermore, removing these impurities through precision filtration can also prevent them from entering the resin micropores and causing blockage, leading to difficulties in resin regeneration. This also alleviates the problem of "brittleness" in cobalt plates prepared by electrolytic purification caused by insoluble impurities entering the cobalt sulfate electrolyte.

[0022] In some embodiments of the present invention, the chelating resin is an aminophosphate resin, an aminocarboxylic acid resin, or an oxime resin. The ion exchange resin is an acrylic resin, an epoxy resin, or a phenolic resin. The resins include, but are not limited to, phenolic ion exchange resin 122, acrylic ion exchange resins CXO-18 and AP-9, oxime chelating resin S9100, aminophosphate chelating resin D402, and aminocarboxylic acid chelating resin S9301. The present invention uses one or more of aminophosphate resins, aminocarboxylic acid resins, and oxime resins in combination with one or more of acrylic resins and phenolic resins to specifically remove various key impurities such as Fe, Ni, and Cu from the solution.

[0023] In some embodiments of the present invention, the deep cleaning is performed in a dynamic cleaning or static cleaning manner.

[0024] In embodiments where no preliminary impurity removal is performed, the dynamic impurity removal includes: passing the cobalt sulfate stock solution through the at least one chelating resin and the at least one ion exchange resin at a flow rate of 1-4 BV / h (e.g., 1 BV / h, 1.5 BV / h, 2 BV / h, 2.5 BV / h, 3 BV / h, 3.5 BV / h, or 4 BV / h).

[0025] In an embodiment for preliminary impurity removal, the dynamic impurity removal includes: passing the cobalt sulfate filtrate through the at least one chelating resin and the at least one ion exchange resin at a flow rate of 1-4 BV / h (e.g., 1 BV / h, 1.5 BV / h, 2 BV / h, 2.5 BV / h, 3 BV / h, 3.5 BV / h, or 4 BV / h).

[0026] In embodiments where no preliminary impurity removal is performed, the static impurity removal includes: immersing the at least one chelating resin and the at least one ion exchange resin separately in the cobalt sulfate stock solution for 2-4 hours (e.g., 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours).

[0027] In an embodiment of preliminary impurity removal, the static impurity removal includes: immersing the at least one chelating resin and the at least one ion exchange resin separately in the cobalt sulfate filtrate for 2-4 hours (e.g., 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours).

[0028] In some specific embodiments, at least one chelating resin and at least one ion exchange resin are each separately packed into different resin columns. For example, when using two chelating resins and two ion exchange resins, these four resins can be separately packed into four resin columns, or they can be separately packed into, for example, five resin columns, with two columns containing the same type of resin. Then, the cobalt sulfate stock solution or the cobalt sulfate filtrate is flowed through these resin columns at a flow rate of 1-4 BV / h. Preferably, these resin columns can be used in series.

[0029] In other specific embodiments, at least one chelating resin and at least one ion exchange resin are each separately packed into different containers. For example, when using two chelating resins and two ion exchange resins, these four resins can be separately packed into four containers, or they can be separately packed into, for example, five containers, with two containers containing the same type of resin. The containers are different from the resin columns described above. The containers can be, for example, barrels, tanks, or kettles. Then, the cobalt sulfate stock solution or the cobalt sulfate filtrate is added to one of the containers containing resin, soaked for 2-4 hours, the solution is separated, and the resulting solution is added to another container containing resin, soaked for 2-4 hours, and then the solution is separated again, and so on, until all containers containing resin have been used.

[0030] The resins are used in an alternating or continuous sequence of chelating resins and ion exchange resins. For example, when using one chelating resin and one ion exchange resin, the chelating resin can be used first, followed by the ion exchange resin; or, the ion exchange resin can be used first, followed by the chelating resin. Similarly, when using two chelating resins and two ion exchange resins, the two chelating resins can be used first, followed by the two ion exchange resins; or, the two ion exchange resins can be used first, followed by the two chelating resins; or, one chelating resin can be used first, followed by one ion exchange resin, then another chelating resin, and finally another ion exchange resin; or, one chelating resin can be used first, followed by two ion exchange resins, and finally another chelating resin. The order of resin use in this invention can be adjusted as needed. The resins of this invention can be reused after regeneration. The resin regeneration method comprises: dynamically regenerating the resin with a hydrochloric acid solution of 2-7 wt% (e.g., 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, or 7 wt%) at a flow rate of 2-6 BV / h (e.g., 2 BV / h, 2.5 BV / h, 3 BV / h, 3.5 BV / h, 4 BV / h, 4.5 BV / h, 5 BV / h, 5.5 BV / h, or 6 BV / h). Regenerate for 0.5-1 h, then dynamically regenerate for 0.5-1 h with a 3-6 wt% (e.g., 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, or 6 wt%) sodium hydroxide solution at a flow rate of 2-6 BV / h (e.g., 2 BV / h, 2.5 BV / h, 3 BV / h, 3.5 BV / h, 4 BV / h, 4.5 BV / h, 5 BV / h, 5.5 BV / h, or 6 BV / h). Then wash the resin with ultrapure water to bring the pH to 7-9.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. This invention provides a method for preparing cobalt sulfate electrolyte for ultra-high purity cobalt. The method uses at least one chelating resin and at least one ion exchange resin to deeply remove impurities from the cobalt sulfate stock solution. The content of Fe, Ni and Cu in the prepared cobalt sulfate electrolyte can be controlled at less than 0.005 mg / L. This electrolyte meets the preparation requirements of ultra-high purity cobalt plates for integrated circuits.

[0033] 2. This invention uses precision filtration to initially remove impurities from the cobalt sulfate raw solution, reducing the content of impurities such as anode mud and cobalt hydroxide precipitate formed during electrolytic dissolution in the electrolyte. This effectively avoids problems such as impurities entering the resin micropores and causing blockage, leading to difficulties in resin regeneration. At the same time, it alleviates the problem of solid impurities entering the cobalt sulfate electrolyte and causing "brittleness" in the cobalt plates prepared by electrolytic purification. Detailed Implementation

[0034] In view of the shortcomings of the prior art, the inventor of this patent, through long-term research, has proposed the technical solution of this invention. The embodiments of this invention are described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of the embodiments of this invention. Other embodiments obtained by those skilled in the art based on the embodiments of this invention without making innovative improvements are all within the protection scope of this invention.

[0035] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are all conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or through existing methods; unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations; unless otherwise specified, the experimental methods are all conventional methods.

[0036] Example 1

[0037] An electrolyte solution with an acidity of 5 mol / L was prepared using ultrapure water and analytical grade sulfuric acid and introduced into an electrolytic cell. Four cleaned cobalt plates were placed alternately as cathodes and three as anodes in the cell. A diaphragm bag was fitted over the anodes, and the plate spacing was set to 15 cm. The power was turned on, and the cell voltage was maintained at 1.8V with a current density of 110 A / m². 2 During electrosolidation, the current density gradually decreased, and after 15 days of electrosolidation, the current density decreased to 57 A / m. 2 When the acidity of the sulfuric acid electrolyte reached 0.5 mol / L, the cathode was replaced with a Pt / C electrode. The cell voltage was maintained at 0.7 V, and the electrode spacing remained unchanged. Electrolysis continued for 5 days, with the current density decreasing from 19 A / m. 2 Gradually decrease to 10A / m 2A cobalt sulfate stock solution with a pH of 2.5 and a concentration of 137.5 g / L was prepared, with Fe, Ni, and Cu contents of 1.5 mg / L, 2.6 mg / L, and 0.8 mg / L, respectively. The cobalt sulfate stock solution was passed through a filter equipped with a 1 μm pore size filter element at a flow rate of 3 BV / h to obtain a refined cobalt sulfate filtrate. This refined cobalt sulfate filtrate was then passed sequentially through a resin column packed with 122, CXO-18, CXO-18, D402, and S9301 resins in series at a flow rate of 5 BV / h to prepare a cobalt sulfate electrolyte. The impurities were Fe < 0.005 mg / L, Ni < 0.005 mg / L, and Cu < 0.005 mg / L. To verify that the cobalt sulfate electrolyte met the production requirements of ultra-high purity cobalt, ultra-high purity cobalt plates were prepared by electrolysis. The GDMS (glow discharge mass spectrometry) analysis results are shown in Table 1.

[0038] Table 1. Impurity element analysis results of ultra-high purity cobalt plates

[0039] Element determination Measurement results / ppm Fe 0.21 Ni 0.05 Cu 0.1

[0040] Example 2

[0041] A sulfuric acid electrolyte with an acidity of 5.6 mol / L was prepared using ultrapure water and analytical grade sulfuric acid and introduced into the electrolytic cell. Four cleaned cobalt plates were placed alternately as cathodes and three as anodes in the electrolytic cell. A diaphragm bag was fitted over the anodes, and the plate spacing was set to 15 cm. The power was turned on, and the cell voltage was maintained at 1.5V with a current density of 95 A / m. 2 During electrosolidation, the current density gradually decreased, and after 17 days of electrosolidation, the current density decreased to 52 A / m. 2 When the acidity of the sulfuric acid electrolyte reaches 0.5 mol / L, the cathode is replaced with a Ru / C electrode, the cell voltage is 0.7 V, the electrode spacing remains unchanged, and electrolysis continues for 6 days, with the current density increasing from 18 A / m. 2 Gradually decrease to 12A / m 2 A final cobalt sulfate stock solution with a pH of 1.8 and a concentration of 145.2 g / L was prepared, with Fe, Ni, and Cu contents of 1.2 mg / L, 2.9 mg / L, and 0.7 mg / L, respectively. The cobalt sulfate stock solution was passed through a filter equipped with a 1 μm pore size filter element at a flow rate of 3 BV / h to obtain a refined cobalt sulfate filtrate. The obtained refined cobalt sulfate filtrate was then sequentially immersed in PP tanks containing S9100, AP-9, AP-9, D402, and S9301 resins using a static deep impurity removal method, with each resin being immersed for 3 hours. This yielded a cobalt sulfate electrolyte with impurities of Fe < 0.005 mg / L, Ni < 0.005 mg / L, and Cu < 0.005 mg / L. To verify that the cobalt sulfate electrolyte met the production requirements for ultra-high purity cobalt, ultra-high purity cobalt plates were prepared by electrolysis. The GDMS analysis results are shown in Table 2.

[0042] Table 2. Impurity element analysis results of ultra-high purity cobalt plates

[0043] Element determination Measurement results / ppm Fe 0.23 Ni 0.02 Cu 0.09

[0044] Example 3

[0045] The method described in Example 1 was followed, except that preliminary impurity removal was not performed; instead, the cobalt sulfate stock solution underwent dynamic deep impurity removal directly. The resulting cobalt sulfate electrolyte contained impurities of Fe < 0.005 mg / L, Ni = 0.012 mg / L, and Cu = 0.035 mg / L. The impurity element analysis results of the prepared ultra-high purity cobalt plate are shown in Table 3 below. The results indicate that, compared with Example 1, the lack of preliminary impurity removal leads to higher levels of Ni and Cu impurities in the cobalt sulfate electrolyte, further resulting in higher levels of Ni and Cu impurities in the electrolyzed ultra-high purity cobalt plate.

[0046] Table 3. Impurity element analysis results of ultra-high purity cobalt plates

[0047] Element determination Measurement results / ppm Fe 0.25 Ni 0.23 Cu 0.72

[0048] Example 4

[0049] The method described in Example 2 was followed, except that preliminary impurity removal was not performed; instead, the cobalt sulfate stock solution underwent direct static deep impurity removal. The resulting cobalt sulfate electrolyte contained impurities of Fe < 0.005 mg / L, Ni = 0.018 mg / L, and Cu = 0.031 mg / L. The impurity element analysis results of the prepared ultra-high purity cobalt plate are shown in Table 4 below. The results indicate that, compared with Example 2, the lack of preliminary impurity removal leads to higher levels of Ni and Cu impurities in the cobalt sulfate electrolyte, further resulting in higher levels of Ni and Cu impurities in the electrolyzed ultra-high purity cobalt plate.

[0050] Table 4. Impurity element analysis results of ultra-high purity cobalt plates

[0051] Element determination Measurement results / ppm Fe 0.18 Ni 0.32 Cu 0.66

[0052] Example 5

[0053] The method described in Example 1 was followed, except that after the acidity of the sulfuric acid electrolyte reached 0.5 mol / L, the cathode was not replaced, and electrolysis continued for 5 days to prepare a cobalt sulfate stock solution with a pH of 0.2 and a concentration of 132.8 g / L. The contents of Fe, Ni, and Cu were 1.6 mg / L, 2.8 mg / L, and 0.9 mg / L, respectively. Subsequent steps were the same as in Example 1. The impurities in the obtained cobalt sulfate electrolyte were Fe = 0.01 mg / L, Ni = 0.52 mg / L, and Cu = 0.04 mg / L. The impurity element analysis results of the prepared ultra-high purity cobalt plate are shown in Table 5 below. This example illustrates that under the same conditions as in Example 1, a hydrogen evolution electrode was not used, resulting in a lower pH and lower concentration of the prepared cobalt sulfate stock solution. In addition, the impurity content of the prepared cobalt sulfate electrolyte was higher, which further led to a higher content of Fe, Ni, and Cu in the ultra-high purity cobalt plate prepared by electrolysis.

[0054] Table 5. Impurity element analysis results of ultra-high purity cobalt plates

[0055] Element determination Measurement results / ppm Fe 0.5 Ni 2.4 Cu 0.87

[0056] Comparative Example 1

[0057] The method described in Example 1 was followed, except that only chelating resins D402, S9301, S9301, S9301, and D402 were used for deep impurity removal. The resulting cobalt sulfate electrolyte contained impurities of Fe < 0.005 mg / L, Ni = 0.011 mg / L, and Cu = 0.022 mg / L. The elemental analysis results of the prepared ultra-high purity cobalt plates are shown in Table 6 below. The results indicate that the Ni and Cu impurity content in the electrolyte prepared using only chelating resins for deep impurity removal does not reach a level below 0.005 mg / L. This further leads to higher Ni and Cu contents in the electrolyzed ultra-high purity cobalt plates.

[0058] Table 6. Impurity element analysis results of ultra-high purity cobalt plates

[0059] Element determination Measurement results / ppm Fe 0.25 Ni 0.26 Cu 0.91

[0060] Comparative Example 2

[0061] The method described in Example 1 was followed, except that only ion exchange resins 122, CXO-18, CXO-18, CXO-18, and 122 were used for deep impurity removal. The resulting cobalt sulfate electrolyte contained impurities of Fe = 1.1 mg / L, Ni = 0.02 mg / L, and Cu < 0.005 mg / L. Using only ion exchange resin resulted in poor Fe removal, and Ni levels did not reach below 0.005 mg / L. The elemental analysis results of the prepared ultra-high purity cobalt plates are shown in Table 7 below. The results indicate that the Fe and Ni impurity content in the electrolyte prepared using only ion exchange resin for deep impurity removal does not reach below 0.005 mg / L. This further leads to higher Fe and Ni content in the electrolyzed ultra-high purity cobalt plates.

[0062] Table 7. Impurity element analysis results of ultra-high purity cobalt plates

[0063]

[0064]

[0065] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a cobalt sulfate electrolyte for ultra-high purity cobalt, characterized by, The method comprises the following steps: Electrolytic dissolution of raw material cobalt plate in sulfuric acid solution to obtain a cobalt sulfate stock solution; The electrolytic dissolution comprises: firstly, electrolytic dissolution is carried out with raw cobalt plates as anodes and raw cobalt plates as cathodes; when the acidity of the sulfuric acid solution reaches 0.5-1 mol / L, the cathode is replaced by a hydrogen evolution electrode, and electrolytic dissolution is continued, wherein the hydrogen evolution electrode is a Pt electrode, a Pt / C electrode or a Ru / C electrode; the process parameters for electrolytic dissolution with raw cobalt plates as cathodes include: cell voltage 1-2 V, electrode spacing 10-20 cm, current density 40-120 A / m 2 ; the process parameters for electrolytic dissolution with a hydrogen evolution electrode as a cathode include: cell voltage 0.5-1 V; electrode spacing 10-20 cm, current density 5-20 A / m 2 ; Deep impurity removal of the cobalt sulfate stock solution by chelating resin and ion exchange resin to obtain a cobalt sulfate electrolyte; the content of Fe, Ni and Cu in the cobalt sulfate electrolyte is controlled to be less than 0.005 mg / L.

2. The production method according to claim 1, characterized by, The chelating resin is amine-based phosphoric acid resin, amine-based carboxylic acid resin or oxime resin; the ion exchange resin is acrylic resin or phenolic resin.

3. The production method according to claim 1 or 2, characterized by, Before deep impurity removal, the preparation method further comprises: preliminary impurity removal of the cobalt sulfate stock solution by filtration to obtain a cobalt sulfate fine filtrate.

4. The production method according to claim 3, characterized by, The filtration is performed by using a filter medium, and the pore size of the filter medium is not greater than 1 μm; The filtration method comprises: passing the above-mentioned cobalt sulfate stock solution through a filter containing the filter medium at a flow rate of 1-5 BV / h to obtain the cobalt sulfate fine filtrate.

5. The production method according to claim 1 or 2, characterized by, The deep impurity removal is performed in a dynamic or static manner.

6. The preparation method according to claim 5, characterized in that, The dynamic impurity removal comprises: passing the cobalt sulfate stock solution through at least one chelating resin and at least one ion exchange resin at a flow rate of 1-4 BV / h to obtain the cobalt sulfate electrolyte; The static impurity removal comprises: separately immersing at least one chelating resin and at least one ion exchange resin in the cobalt sulfate stock solution for 2-4 hours.

7. The production method according to claim 1 or 2, characterized by, The filter membrane is arranged on the outer surface of the anode before the electrolytic dissolution of the raw material cobalt plate starts, so as to inhibit the insoluble impurities falling off from the anode from entering the electrolyte during the electrolytic dissolution.

8. The production method according to claim 1 or 2, characterized by, The concentration of the cobalt sulfate stock solution is 50-200 g / L, and the pH value is 1-3.

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