Preparation method of high-purity sodium fluoride and product thereof

Abstract

The spherical sodium fluoride seed crystal is prepared under the action of the crystallization aid; in the preparation process of the sodium fluoride, the sodium fluoride can be uniformly crystallized and grown on the surface of the spherical seed crystal, and adhesion of silicon dioxide and sodium fluosilicate particles on the seed crystal is hindered, so that the phenomenon that the sodium fluoride is coated with silicon dioxide and sodium fluosilicate is avoided, the content of impurity silicon in a sodium fluoride product is reduced, and the purity of the sodium fluoride is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation and purification of sodium fluoride, and particularly relates to a preparation method of high-purity sodium fluoride and its product. Background Art

[0002] As the main raw material for sodium batteries, lithium batteries, and optical glass, high-purity sodium fluoride can be used to prepare the cathode material of sodium batteries, sodium hexafluorophosphate electrolyte, additives for the cathode material of lithium batteries, and coating materials, and is widely used in sodium-ion power batteries, sodium-ion energy storage batteries, lithium metal batteries, and flat glass. With the gradual development of the new energy industry and the gradual maturity of products and markets, the future market demand is huge.

[0003] Sodium fluoride can be prepared by the method of neutralizing electronic-grade hydrofluoric acid with sodium carbonate or sodium hydroxide. However, this method has high raw material costs, large equipment investment, weak product market competitiveness, and violent reactions, and strong corrosion to equipment. After the equipment is corroded, impurities in the equipment materials migrate into the sodium fluoride product, resulting in high impurity content in the product and making it difficult to meet the quality requirements of high-purity sodium fluoride.

[0004] Sodium fluoride can be prepared by the method of reacting sodium fluorosilicate with sodium carbonate. Although this method has low raw material costs, due to the presence of silicon dioxide and solid sodium fluorosilicate in the reaction system, there is a coating phenomenon between sodium fluoride and silicon dioxide and sodium fluorosilicate, resulting in a decrease in the purity of sodium fluoride and an increase in the content of silicon impurities, affecting the product quality.

[0005] CN 117361574 A discloses a preparation method of high-purity sodium fluoride. First, a mixed alkali is reacted with hydrofluoric acid to obtain a crude sodium fluoride product, and then the crude sodium fluoride product is purified by a recrystallization method to reduce the total amount of metal cations in the crude product to obtain a primary purified sodium fluoride; then the primary purified sodium fluoride is dissolved, and the sodium fluoride is further purified by an ion exchange resin to obtain high-purity sodium fluoride. However, this method has a long process, high energy consumption, resulting in high production costs and low economic benefits after multiple dissolutions, crystallizations, and purifications. At the same time, a large amount of fluorine-containing wastewater will be generated during the multiple dissolutions, crystallizations, and purifications, polluting the environment. Summary of the Invention

[0006] In order to solve the above technical problems, in the first aspect of the present invention, a preparation method of high-purity sodium fluoride is provided, including the following steps: Step S1, preparation of crystallization liquid: Add a crystallization aid to water, stir and dissolve to obtain a crystallization liquid; Step S2, preparation of crystal seeds: Add sodium fluorosilicate and sodium carbonate to the crystallization liquid obtained in step S1 in sequence, stir and react, and then filter the reaction slurry through a vibrating screen. The material on the screen is the sodium fluoride crystal seeds; Step S3, preparation of the seed bottom liquid: Add the sodium fluoride seeds obtained in Step S2 to water, stir and mix evenly to obtain the seed bottom liquid; Step S4, preparation of the sodium fluoride slurry: Add the sodium fluorosilicate slurry and the sodium carbonate solution to the seed bottom liquid obtained in Step S3 simultaneously, adjust the final pH to 7.0 - 8.5, and stir and react for 1 h to obtain the sodium fluoride slurry; Step S5, sedimentation and separation: Put the sodium fluoride slurry obtained in Step S4 into a washing machine for sedimentation and separation, and then obtain high-purity sodium fluoride products after washing, centrifuging, and drying.

[0007] As a preferred solution, the crystallization aid in Step S1 is one or more of ammonium bicarbonate, ammonium carbonate, and carbamide.

[0008] As a preferred solution, the crystallization aid is ammonium bicarbonate.

[0009] As a preferred solution, the crystallization aid is ammonium carbamate.

[0010] As a preferred solution, the mass ratio of ammonium bicarbonate to ammonium carbamate in the crystallization aid is 1:1.

[0011] As a preferred solution, the mass ratio of ammonium carbonate to ammonium carbamate in the crystallization aid is 1:1.

[0012] As a preferred solution, the mass ratio of the crystallization liquid: sodium fluorosilicate: sodium carbonate in Step S2 is 100:19:22.

[0013] As a preferred solution, the mesh number of the vibrating screen in Step S2 is 100 - 150 meshes.

[0014] As a preferred solution, the reaction time in Step S2 is 2 h, and the reaction temperature is 30°C - 35°C.

[0015] As a preferred solution, the reaction temperature in Step S4 is 70°C - 90°C.

[0016] As a preferred solution, the mass ratio of the sodium fluorosilicate slurry to the seed bottom liquid in Step S4 is 3:1.

[0017] As a preferred solution, the mass ratio of the sodium fluorosilicate slurry to the sodium carbonate solution in Step S4 is (0.7 - 0.75):1.

[0018] The main chemical reaction formula of the technical solution of the present invention is: Na2SiF6 + 2Na2CO3 → 6NaF + SiO2↓ + 2CO2↑.

[0019] In the second aspect of the present invention, a high-purity sodium fluoride is provided, and the high-purity sodium fluoride is made by the aforementioned preparation method.

[0020] Through the above technical solutions, the present invention has the following technical effects: (1) By utilizing the effect of the crystallization aid, spherical sodium fluoride seeds are prepared; during the preparation of sodium fluoride, sodium fluoride can uniformly crystallize and grow on the surface of the spherical seeds, hindering the attachment of silicon dioxide and sodium fluorosilicate particles to the seeds, thereby avoiding the coating phenomenon of sodium fluoride with silicon dioxide and sodium fluorosilicate, reducing the impurity silicon content in the sodium fluoride product, and improving the purity of sodium fluoride.

[0021] (2) Using sodium fluorosilicate and sodium carbonate as raw materials effectively reduces the raw material cost, production cost, and improves the product competitiveness. Description of the Drawings

[0022] Figure 1 It is a process flow chart of high-purity sodium fluoride. Detailed Embodiments

[0023] The present invention will be further described below in conjunction with embodiments. Unless otherwise specified, the percentages in the present invention are all mass percentages.

[0024] Embodiment 1 High-purity sodium fluoride is prepared through the following steps: Step S1, preparation of crystallization solution: Add 40 g of crystallization aid to 960 g of water, stir and dissolve completely to obtain 1000 g of crystallization solution with a mass fraction of 4%; the crystallization aid is ammonium bicarbonate; Step S2, preparation of seeds: Add 190 g of sodium fluorosilicate and 220 g of sodium carbonate to the crystallization solution obtained in step S1 in sequence, stir and react for 2 h, the reaction temperature is 30°C - 35°C, and then filter the reaction slurry through a 100-mesh vibrating screen. The material on the screen is the sodium fluoride seeds; Step S3, preparation of seed bottom solution: Add 200 g of the sodium fluoride seeds obtained in step S2 to 300 g of water, stir and mix evenly to obtain a seed bottom solution with a mass fraction of 40%; Step S4, preparation of sodium fluoride slurry: Add 1500 g of sodium fluorosilicate slurry with a mass fraction of 30% and 2143 g of sodium carbonate solution with a mass fraction of 25% to the seed bottom solution obtained in step S3 at the same time, control the reaction temperature at 70°C, adjust the end point pH to 8.5, stir and react for 1 h to obtain a sodium fluoride slurry; Step S5, sedimentation separation: Put the sodium fluoride slurry obtained in step S4 into a washing machine for sedimentation separation, and then obtain high-purity sodium fluoride products after washing, centrifuging, and drying.

[0025] Embodiment 2 High-purity sodium fluoride is prepared through the following steps: Step S1, preparation of crystallization solution: Add 40 g of crystallization aid to 960 g of water, stir until dissolved completely to obtain a crystallization solution with a mass fraction of 4%; the mass ratio of ammonium bicarbonate to ammonium carbamate in the crystallization aid is 1:1; Step S2, preparation of seed crystals: Add 190 g of sodium fluorosilicate and 220 g of sodium carbonate to the crystallization solution obtained in Step S1 in sequence, stir and react for 2 h, with the reaction temperature being 30°C to 35°C, and then filter the reacted slurry through a 120-mesh vibrating screen, and the material on the screen is the sodium fluoride seed crystals; Step S3, preparation of seed crystal bottom liquid: Add 200 g of the sodium fluoride seed crystals obtained in Step S2 to 300 g of water, stir and mix evenly to obtain a seed crystal bottom liquid with a mass fraction of 40%; Step S4, preparation of sodium fluoride slurry: Add 1500 g of a sodium fluorosilicate slurry with a mass fraction of 30% and 2083 g of a sodium carbonate solution with a mass fraction of 25% to the seed crystal bottom liquid obtained in Step S3 simultaneously, control the reaction temperature at 80°C, adjust the end point pH to 8.0, stir and react for 1 h to obtain a sodium fluoride slurry; Step S5, sedimentation and separation: Put the sodium fluoride slurry obtained in Step S4 into a washing machine for sedimentation and separation, and then obtain high-purity sodium fluoride products after washing, centrifuging and drying.

[0026] Example 3 High-purity sodium fluoride is prepared through the following steps: Step S1, preparation of crystallization solution: Add 40 g of crystallization aid to 960 g of water, stir until dissolved completely to obtain a crystallization solution with a mass fraction of 4%; the mass ratio of ammonium carbonate to ammonium carbamate in the crystallization aid is 1:1; Step S2, preparation of seed crystals: Add 190 g of sodium fluorosilicate and 220 g of sodium carbonate to the crystallization solution obtained in Step S1 in sequence, stir and react for 2 h, with the reaction temperature being 30°C to 35°C, and then filter the reacted slurry through a 120-mesh vibrating screen, and the material on the screen is the sodium fluoride seed crystals; Step S3, preparation of seed crystal bottom liquid: Add 200 g of the sodium fluoride seed crystals obtained in Step S2 to 300 g of water, stir and mix evenly to obtain a seed crystal bottom liquid with a mass fraction of 40%; Step S4, preparation of sodium fluoride slurry: Add 1500 g of a sodium fluorosilicate slurry with a mass fraction of 30% and 2083 g of a sodium carbonate solution with a mass fraction of 25% to the seed crystal bottom liquid obtained in Step S3 simultaneously, control the reaction temperature at 85°C, adjust the end point pH to 8.0, stir and react for 1 h to obtain a sodium fluoride slurry; Step S5, sedimentation and separation: Put the sodium fluoride slurry obtained in Step S4 into a washing machine for sedimentation and separation, and then obtain high-purity sodium fluoride products after washing, centrifuging and drying.

[0027] Example 4 High-purity sodium fluoride is prepared through the following steps: Step S1, preparation of crystallization solution: Add 40 g of crystallization aid to 960 g of water, stir until dissolved completely to obtain a crystallization solution with a mass fraction of 4%; the crystallization aid is ammonium carbonate; Step S2, preparation of crystal seeds: Add 190 g of sodium fluorosilicate and 220 g of sodium carbonate to the crystallization solution obtained in Step S1 in sequence, stir and react for 2 h, with the reaction temperature being 30°C to 35°C, and then filter the reaction slurry through a 150-mesh vibrating screen. The material on the screen is the sodium fluoride crystal seeds; Step S3, preparation of crystal seed bottom solution: Add 200 g of the sodium fluoride crystal seeds obtained in Step S2 to 300 g of water, stir and mix evenly to obtain a crystal seed bottom solution with a mass fraction of 40%; Step S4, preparation of sodium fluoride slurry: Add 1500 g of a sodium fluorosilicate slurry with a mass fraction of 30% and 2000 g of a sodium carbonate solution with a mass fraction of 25% to the crystal seed bottom solution obtained in Step S3 simultaneously, control the reaction temperature at 90°C, adjust the end-point pH to 7.0, stir and react for 1 h to obtain a sodium fluoride slurry; Step S5, sedimentation and separation: Put the sodium fluoride slurry obtained in Step S4 into a washing machine for sedimentation and separation, and then obtain high-purity sodium fluoride products after washing, centrifuging and drying.

[0028] The quality of the high-purity sodium fluoride products obtained in each example is shown in Table 1. The purity of the obtained high-purity sodium fluoride products reaches over 99.5%, the silicon content is less than 0.05%, the moisture content is less than 0.1%, and the content of each metal impurity is less than 100 mg / kg, which can meet the quality standards of high-purity sodium fluoride.

[0029] Table 1 Analysis results of the high-purity sodium fluoride products produced by the present invention The specific embodiments described above are only further detailed descriptions of the purpose, technical solutions and beneficial effects of the present invention, and are not limitations on the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing high-purity sodium fluoride and its product, characterized in that, It includes the following steps: Step S1, crystallization solution preparation: Add a crystallization aid to water, stir and dissolve to obtain a crystallization solution; Step S2, seed crystal preparation: Sequentially add sodium fluorosilicate and sodium carbonate to the crystallization solution obtained in Step S1, stir and react, and then filter the reaction slurry through a vibrating screen. The material on the screen is the sodium fluoride seed crystal; Step S3, seed crystal bottom solution preparation: Add the sodium fluoride seed crystal obtained in Step S2 to water, stir and mix evenly to obtain a seed crystal bottom solution; Step S4, sodium fluoride slurry preparation: Add a sodium fluorosilicate slurry and a sodium carbonate solution to the seed crystal bottom solution obtained in Step S3 at the same time, adjust the end point pH to 7.0 - 8.5, stir and react for 1 h to obtain a sodium fluoride slurry; Step S5, sedimentation separation: Put the sodium fluoride slurry obtained in Step S4 into a washing machine for sedimentation separation, and then obtain high-purity sodium fluoride products after washing, centrifuging and drying.

2. The preparation method according to claim 1, wherein The crystallization aid is ammonium bicarbonate.

3. The preparation method according to claim 1, characterized in that, The crystallization aid is ammonium carbamate.

4. The preparation method according to claim 1, wherein The mass ratio of ammonium bicarbonate to ammonium carbamate in the crystallization aid is 1:

1.

5. The preparation method according to claim 1, wherein, The mass ratio of ammonium carbonate to ammonium carbamate in the crystallization aid is 1:

1.

6. The preparation method according to claim 2, characterized in that, The reaction time in Step S2 is 2 h, and the reaction temperature is 30°C - 35°C.

7. The preparation method according to claim 6, characterized in that, The reaction temperature in Step S4 is 70°C - 90°C.

8. A high-purity sodium fluoride, characterized in that, The high-purity sodium fluoride is made by the preparation method described in Claim 1.

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