Method for efficiently removing silicon impurities in battery-grade nickel sulfate

Abstract

The invention provides a method for efficiently removing silicon impurities in battery-grade nickel sulfate, and belongs to the technical field of solution impurity removal. The method comprises the following steps: adjusting the pH value of a nickel sulfate solution to 3-5, adding sodium sulfide into the nickel sulfate solution, stirring at 60-80 DEG C, and filtering. According to the method, sodium sulfide is introduced as a precipitator, sodium sulfide can react with silicon impurities in the battery-grade nickel sulfate solution to generate insoluble precipitates to achieve the purpose of removing the impurities, and the precipitation reaction has a particularly remarkable removal effect on the silicon impurities under a proper pH value, and has relatively small influence on nickel. According to the method, the silicon impurities can be quickly converted into the precipitates, so that the process period is shortened, the requirement of batch production can be met, the practicability is high, the operation is simple, the cost is low, the silicon impurities in the battery-grade nickel sulfate can be efficiently and selectively removed, and the method has wide application value.

Description

Technical Field

[0001] The invention relates to the technical field of solution impurity removal, and in particular to a method for efficiently removing silicon impurities in battery-grade nickel sulfate. Background Art

[0002] Nickel metal is an important industrial raw material. It is widely used in many fields due to its excellent physical and chemical properties. For example, nickel is often used to make various high-performance alloys. These alloys have excellent corrosion resistance and high temperature resistance. They are widely used in high-end manufacturing industries such as aerospace and energy, especially the application of nickel in lithium-ion battery positive electrode materials. With the rapid development of the global lithium battery industry, the demand for high-purity battery-grade nickel sulfate has increased rapidly, and the purity requirements have become higher and higher. However, the excessive silicon impurity content in battery-grade nickel sulfate may lead to the instability of the electrode material structure, especially the deposition of silicates on the electrode surface, which will cause irreversible capacity loss and reduce the cycle life. In addition, silicon will react with lithium ions to form an irreversible solid electrolyte interface (SEI) film, which further aggravates the capacity decay. Moreover, the presence of silicon impurities will significantly affect the key properties of battery materials such as purity, conductivity, ion transport, and cycle stability, and bring hidden dangers in manufacturing process and safety.

[0003] In the face of the rapidly developing lithium battery industry, the removal of silicon impurities in battery-grade nickel sulfate is particularly important. At present, the existing silicon removal methods mainly include chemical precipitation, electrocoagulation, ion exchange, reverse osmosis and flotation. Chemical precipitation is a recognized and effective silicon removal method because of its simple operation and cheap and easy-to-obtain silicon removal agents. Depending on the added silicon removal agent, chemical precipitation can be divided into magnesium salt silicon removal, aluminum salt silicon removal, iron salt silicon removal and calcium salt silicon removal. However, the silicon removal efficiency of these methods is not high. To achieve the ideal silicon removal effect, it may be necessary to process a large amount of reagents and sedimentation sludge, which increases the processing cost and environmental burden, and may introduce new impurities such as iron, aluminum and chlorine. Therefore, it is urgent to develop a method for efficiently removing silicon impurities in battery-grade nickel sulfate. Summary of the invention

[0004] In view of the technical problems existing in the background technology, the present invention provides a method for efficiently removing silicon impurities in battery-grade nickel sulfate, aiming to solve the technical problem of low silicon removal efficiency in the existing nickel sulfate refining process.

[0005] In a first aspect, the present invention provides a method for efficiently removing silicon impurities in battery-grade nickel sulfate, comprising the following steps: adjusting the pH value of the nickel sulfate solution to 3-5, adding sodium sulfide to the nickel sulfate solution, stirring at 60-80°C and then filtering.

[0006] The present invention utilizes the ability of sodium sulfide to react with silicon impurities in a battery-grade nickel sulfate solution to generate insoluble precipitates to achieve the purpose of removing silicon. Under acidic conditions, silicon usually exists in the solution in the form of silicic acid or its polymers. Since silicic acid is a weak acid, its dissociation degree in the solution is low, but its solubility in an acidic medium is relatively high. After adding sodium sulfide, the dissociated S 2- Will react with Si in silicic acid 4+ The ions react to form insoluble silicon sulfide precipitation. The specific chemical reaction can be expressed as: Si 4+ +2S 2- →SiS2↓.

[0007] Preferably, the molar ratio of sulfur in the sodium sulfide to silicon in the nickel sulfate solution is 4-8.

[0008] More preferably, the molar ratio of sulfur in the sodium sulfide to silicon in the nickel sulfate solution is 6.

[0009] Excess ratio is a chemical engineering term, usually used to describe the excess of a reactant relative to another reactant in a chemical reaction. Specifically, it refers to the ratio between the amount of reactant actually put in and the amount of reactant theoretically required in a chemical reaction. The calculation formula of excess ratio can be expressed as: Excess ratio = (n 实际投入的反应物 -n 理论所需反应物 ) / n 理论所需反应物 .

[0010] In the present invention, the molar ratio of sulfur in the sodium sulfide to silicon in the nickel sulfate solution is converted into an excess ratio of sodium sulfide feed amount to silicon in the nickel sulfate solution, that is, the excess ratio is 1-3.

[0011] The dosage of sodium sulfide has a great influence on the removal rate. With the increase of dosage, the removal rate of silicon ions by sodium sulfide can be improved to a certain extent. However, excessive dosage of sodium sulfide may produce a salt effect, change the activity coefficient of the solution, thereby changing the dissociation degree or solubility, and reducing the precipitation rate.

[0012] Preferably, the pH value of the solution is adjusted to 4.5.

[0013] In the present invention, the pH of the solution can be adjusted to acidic by using conventional acidic reagents in the art, such as one or more combinations of hydrochloric acid, nitric acid, acetic acid and sulfuric acid. The pH value will affect the form and solubility of ions in the solution.

[0014] Preferably, the stirring speed is 30 to 50 rpm; for example, 30 rpm, 35 rpm, 40 rpm, 45 rpm or 50 rpm, etc., but is not limited to the listed values, and other values ​​not listed in the above numerical range are also applicable; more preferably, the stirring speed is 40 rpm. Stirring can increase the contact opportunity between the reactants, thereby increasing the reaction rate. Within a certain range, as the stirring speed increases, the reaction of sodium sulfide with silicon impurities in the nickel sulfate solution is more sufficient, which helps the precipitation of silicon impurities, but too fast a stirring speed may increase the turbulence of the solution, thereby slowing down the sedimentation rate of the precipitate, resulting in difficulty in filtering, and too slow a stirring speed may not be enough to fully mix the precipitate, affecting the precipitation effect.

[0015] In the present invention, the stirring temperature is 60-80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values, and other values ​​not listed in the above numerical range are also applicable. More preferably, the stirring temperature is 75°C. Controlling the temperature at 60-80°C can ensure the reaction efficiency and precipitation efficiency, while avoiding side reactions caused by excessively high temperature, and ensuring the effectiveness and economy of the silicon removal process.

[0016] Preferably, the stirring time is 2 to 10 hours; for example, 2 hours, 3 hours, 5 hours, 8 hours or 10 hours, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable; more preferably, the stirring time is 2 to 5 hours.

[0017] As the stirring time increases, the removal rate increases rapidly. When the stirring time exceeds 5 h, the large amount of precipitate generated inhibits the movement of ions, thus slowing down the reaction rate.

[0018] The present invention utilizes the ability of sodium sulfide to react with silicon impurities in a battery-grade nickel sulfate solution to generate insoluble precipitates to achieve the purpose of removing silicon. Under acidic conditions, silicon usually exists in the solution in the form of silicic acid or its polymers. Since silicic acid is a weak acid, its dissociation degree in the solution is low, but its solubility in an acidic medium is relatively high. After adding sodium sulfide, the dissociated S 2- Will react with Si in silicic acid 4+ The ions react to form insoluble silicon sulfide precipitation. The specific chemical reaction can be expressed as: Si 4+ +2S 2- →SiS2↓.

[0019] The solution also contains a large amount of nickel ions, and S 2- +Ni 2+ →NiS↓ reaction, resulting in nickel loss. Since the Ksp (solubility product constant) of SiS2 is much lower than the Ksp of NiS, in an environment where nickel ions and silicon ions coexist, S2- Will give priority to Si 4+ In addition, when multiple metal ions coexist, high charge density ions can preferentially bind to high electronegative ligands, while Si 4+ is an ion with high charge density, which has a strong affinity to S 2- This strong affinity to sulfur makes Si 4+ with Ni 2+ Under the coexistence conditions, Si 4+ Will give priority to S 2- Combined, a highly insoluble silicon sulfide SiS2 precipitate is formed.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for efficiently removing silicon impurities from battery-grade nickel sulfate. Sodium sulfide is introduced as a precipitant. Sodium sulfide can react with silicon impurities in a battery-grade nickel sulfate solution to generate an insoluble precipitate to achieve the purpose of removing impurities. Moreover, this precipitation reaction has a particularly significant effect on removing silicon impurities at an appropriate pH, while having little effect on nickel. (2) The chemical properties of the introduced sodium sulfide are stable. After addition, it does not require complex operation control and is easy to automate. It is suitable for large-scale application. It has a good removal effect on silicon impurities under different concentrations, temperatures and pH conditions. It has strong adaptability and can be flexibly applied to nickel sulfate solutions under different working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a rendering of the effect of the method for removing silicon impurities in battery-grade nickel sulfate described in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0023] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0024] Example 1 A method for efficiently removing silicon impurities from battery-grade nickel sulfate comprises the following steps: Take battery-grade nickel sulfate crystals and place them in pure water. Stir at 40 rpm. After the nickel sulfate is completely dissolved, take samples to detect the concentrations of nickel sulfate and silicon impurities. Then add sodium sulfide with an excess ratio of 2.0 (the ratio of the amount of sodium sulfide added to the amount theoretically required to remove silicon impurities) to the solution. Adjust the pH of the solution to 4.5 with hydrochloric acid. Stir at 75°C at 40 rpm for 2 h. After filtering, take samples to detect the nickel sulfate content and silicon content in the filtrate.

[0025] The nickel sulfate content measured after the nickel sulfate was completely dissolved before silicon removal was 84.14 g / L, and the silicon content was 74.7 mg / L.

[0026] The nickel sulfate content in the filtrate after silicon removal was 74.13 g / L, and the silicon content was 11.1 mg / L.

[0027] Figure 1 This is a rendering of the method for removing silicon impurities in battery-grade nickel sulfate described in Example 1 of the present invention. The silicon impurity removal rate is 85.14% and the nickel loss rate is 11.89%.

[0028] Example 2 The difference between this embodiment and embodiment 1 is that the stirring temperature is 60° C., and the remaining steps are the same as those in embodiment 1.

[0029] Example 3 The difference between this embodiment and embodiment 1 is that the stirring temperature is 80° C., and the other steps are the same as those in embodiment 1.

[0030] Example 4 The difference between this embodiment and embodiment 1 is that the stirring speed is 30 rpm, and the other steps are the same as those in embodiment 1.

[0031] Example 5 The difference between this embodiment and embodiment 1 is that the stirring speed is 50 rpm, and the other steps are the same as those in embodiment 1.

[0032] Example 6 The difference between this embodiment and embodiment 1 is that the pH of the solution is adjusted to 3, and the remaining steps are the same as those in embodiment 1.

[0033] Example 7 The difference between this embodiment and embodiment 1 is that the pH of the solution is adjusted to 5, and the remaining steps are the same as those in embodiment 1.

[0034] Example 8 The difference between this embodiment and embodiment 1 is that the excess ratio is 1, and the remaining steps are the same as those in embodiment 1.

[0035] Example 9 The difference between this embodiment and embodiment 1 is that the excess ratio is 3, and the remaining steps are the same as those in embodiment 1.

[0036] Example 10 The difference between this embodiment and embodiment 1 is that the heat preservation and stirring time is 5 hours, and the other steps are the same as those in embodiment 1.

[0037] Embodiment 11 The difference between this embodiment and embodiment 1 is that the heat preservation and stirring time is 10 hours, and the other steps are the same as those in embodiment 1.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that the stirring temperature is 50° C., and the remaining steps are the same as those in Example 1.

[0039] Comparative Example 2 The difference between this comparative example and Example 1 is that the stirring temperature is 90° C., and the remaining steps are the same as those in Example 1.

[0040] Comparative Example 3 The difference between this comparative example and Example 1 is that the stirring speed is 20 rpm, and the other steps are the same as those in Example 1.

[0041] Comparative Example 4 The difference between this comparative example and Example 1 is that the stirring speed is 60 rpm, and the other steps are the same as those in Example 1.

[0042] Comparative Example 5 The difference between this comparative example and Example 1 is that the pH of the solution is adjusted to 2.5, and the remaining steps are the same as those in Example 1.

[0043] Comparative Example 6 The difference between this comparative example and Example 1 is that the pH of the solution is adjusted to 5.5, and the remaining steps are the same as those in Example 1.

[0044] Comparative Example 7 The difference between this comparative example and Example 1 is that the excess ratio is 3.5, and the remaining steps are the same as those in Example 1.

[0045] Comparative Example 8 The difference between this comparative example and Example 1 is that the heat preservation and stirring time is 1 hour, and the other steps are the same as those in Example 1.

[0046] In the method for removing silicon impurities in battery-grade nickel sulfate described in Examples 1 to 11 and Comparative Examples 1 to 8, after the nickel sulfate is completely dissolved, samples are taken to measure the concentrations of nickel sulfate and silicon. After stirring and filtering, samples are taken to detect the concentrations of nickel sulfate and silicon in the filtrate, and the silicon impurity removal rate and nickel ion loss rate are calculated. The results are shown in Table 1.

[0047] Table 1 Silicon impurity removal rate and nickel ion loss rate of the methods described in Examples 1 to 11 and Comparative Examples 1 to 8

[0048] As shown in Table 1, the results of Examples 1 to 3 and Comparative Examples 1 to 2 show that the reaction temperature has a great influence on the precipitation rate of silicon. When the temperature is less than 75°C, the precipitation rate of silicon increases significantly with the increase of the reaction temperature. When the reaction temperature is 75°C, the precipitation rate reaches the maximum. If the reaction temperature is further increased, the precipitation rate decreases. The results of Example 1, Examples 4 to 5 and Comparative Examples 3 to 4 show that the removal rate increases with the increase of the stirring rate within the range of 20 to 40 rpm. The precipitation rate decreases within the range of 40 to 60 r / min. Too fast or too slow stirring speed may be unfavorable to the formation of precipitates and affect the precipitation effect. The results of Example 1, Examples 6-7 and Comparative Examples 5-6 show that the effect of solution pH on the precipitation effect is also significant. At too high a pH value, sodium sulfide may form sulfide precipitates with other metal ions in the solution, which will reduce the removal efficiency of silicon impurities; the results of Example 1, Examples 8-9 and Comparative Example 7 show that the amount of sodium sulfide added has a great influence on the removal rate. As the amount of addition increases, the removal rate of silicon ions by sodium sulfide can be improved to a certain extent, but excessive sodium sulfide addition may produce a salt effect, change the activity coefficient of the solution, thereby changing the dissociation degree or solubility, and reducing the precipitation rate; the results of Example 1, Examples 10-11 and Comparative Example 8 show that as the stirring time increases, the removal rate increases rapidly, and after the stirring time exceeds 5h, the large amount of precipitate generated inhibits the movement of ions, so the reaction rate slows down.

[0049] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for efficiently removing silicon impurities in battery-grade nickel sulfate, characterized in that: The method comprises the following steps: adjusting the pH value of the nickel sulfate solution to 3-5, adding sodium sulfide into the nickel sulfate solution, stirring at 60-80° C. and filtering.

2. A method for efficiently removing silicon impurities in battery-grade nickel sulfate according to claim 1, characterized in that: The molar ratio of sulfur element in the sodium sulfide to silicon element in the nickel sulfate solution is 4-8.

3. A method for efficiently removing silicon impurities in battery-grade nickel sulfate according to claim 2, characterized in that: The molar ratio of sulfur element in the sodium sulfide to silicon element in the nickel sulfate solution is 6.

4. The method for efficiently removing silicon impurities in battery-grade nickel sulfate according to claim 1, characterized in that: The pH value of the nickel sulfate solution was adjusted to 4.

5.

5. The method for efficiently removing silicon impurities in battery-grade nickel sulfate according to claim 1, characterized in that: The acidic reagent used to adjust the pH value of the nickel sulfate solution includes one or more of hydrochloric acid, nitric acid, acetic acid and sulfuric acid.

6. The method for efficiently removing silicon impurities in battery-grade nickel sulfate according to claim 1, characterized in that: The stirring speed is 30-50 rpm.

7. A method for efficiently removing silicon impurities in battery-grade nickel sulfate according to claim 6, characterized in that: The stirring speed is 40 rpm.

8. The method for efficiently removing silicon impurities in battery-grade nickel sulfate according to claim 1, characterized in that: The stirring temperature is 75°C.

9. The method for efficiently removing silicon impurities in battery-grade nickel sulfate according to claim 1, characterized in that: The stirring time is 2 to 10 hours.

10. The method for efficiently removing silicon impurities in battery-grade nickel sulfate according to claim 9, characterized in that: The stirring time is 2 to 5 hours.

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