Purification and recovery method of sodium fluorosilicate waste liquid

Abstract

The present invention relates to the technical field of sodium fluorosilicate preparation, and in particular to a method for purifying and recovering sodium fluorosilicate waste liquid, comprising the following steps: S1, adding HF solution to sodium fluorosilicate waste liquid, stirring the reaction at 50-80°C for 10-40min, cooling to room temperature and standing for 30-60min, filtering and removing impurities to obtain filtrate; S2, slowly adding sodium carbonate particles to the filtrate until the reaction has no bubble overflow, and then adding saturated sodium carbonate solution to the pH value of the filtrate is 8-9. A high-purity nanometer-scale sodium fluorosilicate product is obtained by the technical solution of the present invention, and the main content of sodium fluorosilicate is as high as 99.7%, which can be used as a cosolvent and additive, and is also suitable for use as a raw material in high-demand fields such as the electronics industry to produce downstream products; in addition, the filtrate obtained by the process is recycled and reused, effectively improving the yield of fluorine, and can better save energy, reduce production costs, and save energy and protect the environment.

Description

Technical Field

[0001] The invention relates to the technical field of sodium fluorosilicate preparation, and in particular to a method for purifying and recovering sodium fluorosilicate waste liquid. Background Art

[0002] Phosphate ore generally contains 2.5%-3.5% fluorine. When phosphate ore reacts with sulfuric acid to produce phosphoric acid, these fluorides are almost all released and converted into other forms. According to the analysis of phosphoric acid extraction experiments and actual production results, about 70%-80% of the fluorine in phosphate ore enters dilute phosphoric acid, about 15%-20% enters phosphogypsum, and about 3%-17% enters tail gas in the form of gas phase. Direct discharge will cause serious harm to the environment. The annual output of fluorosilicic acid, a byproduct of phosphate fertilizer, is huge. Therefore, as one of the main sources of fluorine resources, the utilization research of fluorosilicic acid, a byproduct of phosphoric acid, has important social, economic, and environmental significance. Most of the existing technologies further process fluorosilicic acid into fluorosilicates.

[0003] Sodium fluorosilicate is the most widely used fluorosilicate in the construction and building materials industries. It is mainly used as an enamel solvent, glass opacifier, acid-resistant cement and acid-resistant concrete coagulant and wood preservative. It is used in the pesticide industry to make insecticides. It is used as a preservative in the wood industry and a moisture absorbent for acid-resistant cement. It is used as an opacifier for glass and enamel; a coagulant in natural latex products, an additive in electroplating zinc, nickel, and iron ternary plating, and a plastic filler. In addition, it is also used in the fluoridation of pharmaceuticals and drinking water, and in the manufacture of sodium fluoride for artificial cryolite.

[0004] The existing sodium fluorosilicate production mainly comes from phosphorus chemical enterprises. The fluorosilicic acid produced by the tail gas absorption of the wet phosphoric acid production line reacts with sodium salt, and then is filtered, washed and dried to obtain the sodium fluorosilicate product. However, the fluorosilicic acid produced by the tail gas absorption of the wet phosphoric acid production line often contains impurities such as calcium salt, aluminum salt and silicon dioxide. The sodium fluorosilicate product obtained by this process has low purity and large particles, which greatly limits the scope of application. The effect of using it as a co-solvent and additive is not ideal, and it cannot be used as a reagent-grade raw material to prepare downstream high-purity products. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for purifying and recovering sodium fluorosilicate waste liquid to solve the problems of low purity and large particles of sodium fluorosilicate products in the prior art.

[0006] Based on the above purpose, the present invention provides a method for purifying and recovering sodium fluorosilicate waste liquid, comprising the following steps:

[0007] S1. Add HF solution to sodium fluorosilicate waste liquid, stir and react at 50-80°C for 10-40min, cool to room temperature and let stand for 30-60min, filter and remove impurities to obtain filtrate;

[0008] S2. Slowly add sodium carbonate particles to the filtrate until no bubbles overflow from the reaction, and then add saturated sodium carbonate solution until the pH value of the filtrate reaches 8-9.

[0009] Preferably, after step S2, the filtrate is placed in a crystallization tank, a nucleating agent with a particle size of 10-100 μm is placed in the crystallization tank for crystallization, the mixture is stirred at a speed of 40-100 r / min, a solid product is obtained by filtering, the solid product is washed with ethanol and dried to obtain nano sodium fluorosilicate particles.

[0010] Preferably, HF solution is added to the sodium fluorosilicate waste liquid to make the pH value of the sodium fluorosilicate waste liquid be 4-6, and the mass fraction of the HF solution be 10-50%.

[0011] Preferably, the crystallization process is as follows: stirring at room temperature for 5-20 min, cooling to 10-15°C at a rate of 0.2-1.5°C / min, maintaining for 10-30 min, and finally cooling to 0.5-5°C at a rate of 1-3°C / min, maintaining for 10-20 min.

[0012] Preferably, the nucleating agent is a silicone oil-modified molecular sieve, which is prepared by a microwave hydrothermal method.

[0013] Preferably, the specific process of the silicone oil modified molecular sieve using microwave hydrothermal method is as follows:

[0014] Silicone oil and silane coupling agent are dissolved in a mixture of dimethyl ether and acetone, the pH value of the solution is adjusted to 6-7, molecular sieves are added, and the reaction is carried out at a temperature of 80-120° C. and a pressure of 1-10 MPa for 5-20 minutes, and the silicone oil modified molecular sieve is obtained by ethanol filtering and drying.

[0015] Preferably, the mass ratio of the silicone oil, silane coupling agent and molecular sieve is 1: (0.8-1): (5-30); the volume ratio of dimethyl ether and acetone is 1: 0.2-10; the silicone oil and silane coupling agent are dissolved in a mixture of dimethyl ether and acetone, and the mass concentration of the silicone oil and the silane coupling agent is 20-60wt%.

[0016] Preferably, the particle size of the silicone oil modified molecular sieve is 10-100 μm.

[0017] Preferably, after step S2, a saturated sodium carbonate solution is continuously added at 60-90° C. until no precipitation is generated, and sodium fluoride crystals are obtained by centrifugation, which are then washed with ethanol and dried.

[0018] Preferably, the sodium fluorosilicate waste liquid comes from a by-product of wet-process phosphoric acid.

[0019] Beneficial effects of the present invention:

[0020] HF solution is added to the sodium fluorosilicate waste liquid produced as a byproduct of wet-process phosphoric acid. Sodium fluorosilicate dissolves in the HF solution. The SiO 2 The calcium salt reacts with HF to produce CaF precipitate, and the aluminum salt reacts to produce aluminum fluoride precipitate. At the same time, the aluminum salt reacts to produce a small amount of Na 3 AlF 6 After the reaction is completed, the temperature is lowered and allowed to stand. The difference in solubility between sodium fluorosilicate and sodium fluorosilicate is used to make trace amounts of Na 3 AlF 6 and other impurities crystallize and precipitate. After filtering, remove the precipitate generated by the reaction of sodium fluorosilicate with HF solution and other particulate impurities that do not participate in the reaction. Finally, add saturated sodium carbonate, CO 3 2- With H in solution + The reaction produces carbon dioxide and water, Na + With SiF6 - Sodium fluorosilicate is formed by ionic bonding, thereby improving the purity of sodium fluorosilicate, and the main content of sodium fluorosilicate is as high as 99.7%. The high-purity nano-scale sodium fluorosilicate product obtained by the technical solution of the present invention can be used as a co-solvent and additive, and is also suitable for the production of downstream products such as sodium fluoride and silicon dioxide as raw materials in high-demand fields such as the electronics industry; in addition, the filtrate obtained by the process is recycled and reused, which effectively improves the yield of fluorine, can better save energy, reduce production costs, and save energy and protect the environment. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0022] Embodiment 1:

[0023] The specific process of preparing silicone oil modified molecular sieve by microwave hydrothermal method is as follows:

[0024] Silicone oil and silane coupling agent are dissolved in dimethyl ether, and the pH value of the solution is adjusted to 7 with dilute hydrochloric acid, and then molecular sieve is added, the mass ratio of silicone oil, silane coupling agent and molecular sieve is 1:1:30, and the volume ratio of dimethyl ether and acetone is 1:10; the silicone oil and silane coupling agent are dissolved in a mixed solution of dimethyl ether and acetone, the mass concentration of silicone oil and silane coupling agent is 60wt%, and the reaction is carried out at a temperature of 120°C and a pressure of 1MPa for 20min, and after filtering, it is washed with ethanol for 3 times, and then washed with deionized water for 2 times, and dried in a vacuum box to obtain the silicone oil modified molecular sieve, and the particle size of the silicone oil modified molecular sieve is 10-100µm.

[0025] Embodiment 2:

[0026] The specific process of preparing silicone oil modified molecular sieve by microwave hydrothermal method is as follows:

[0027] Silicone oil and silane coupling agent are dissolved in dimethyl ether, and the pH value of the solution is adjusted to 6 with dilute hydrochloric acid, and then molecular sieve is added, the mass ratio of silicone oil, silane coupling agent and molecular sieve is 1:0.8:5, and the volume ratio of dimethyl ether and acetone is 1:0.2; the silicone oil and silane coupling agent are dissolved in a mixed solution of dimethyl ether and acetone, the mass concentration of silicone oil and silane coupling agent is 20wt%, and the reaction is carried out at a temperature of 80°C and a pressure of 10MPa for 5min, and after filtering, it is washed with ethanol for 3 times, and then washed with deionized water for 2 times, and dried in a vacuum box to obtain the silicone oil modified molecular sieve, and the particle size of the silicone oil modified molecular sieve is 10-100µm.

[0028] Embodiment 3:

[0029] The specific process of preparing silicone oil modified molecular sieve by microwave hydrothermal method is as follows:

[0030] Silicone oil and silane coupling agent are dissolved in dimethyl ether, and the pH value of the solution is adjusted to 6 with dilute hydrochloric acid, and then molecular sieve is added, the mass ratio of silicone oil, silane coupling agent and molecular sieve is 1:0.9:17, and the volume ratio of dimethyl ether and acetone is 1:5.1; the silicone oil and silane coupling agent are dissolved in a mixed solution of dimethyl ether and acetone, the mass concentration of silicone oil and silane coupling agent is 40wt%, and the reaction is carried out at a temperature of 100°C and a pressure of 5MPa for 12min, and after filtering, it is washed with ethanol for 3 times, and then washed with deionized water for 2 times, and dried in a vacuum box to obtain the silicone oil modified molecular sieve, and the particle size of the silicone oil modified molecular sieve is 10-100µm.

[0031] In Examples 1-3, based on the porous characteristics of the molecular sieve, under acidic and high temperature conditions, the siloxy functional group of the silane coupling agent dissolves in a mixed solvent of dimethyl ether and acetone to undergo a hydrolysis reaction to generate a Si-OH bond, and the Si-OH bond forms a chemical bond Si-O-Si with the hydroxyl group on the surface of the molecular sieve, thereby modifying the molecular sieve so that its surface contains abundant silicon-oxygen bonds and Si-OH bonds, and condensation reactions occur between the Si-OH bonds to generate oligomers containing -OH, and the oligomers containing -OH further cross-link with the silicon oxygen bonds in the silicone oil to form new Si-O-Si, and form a three-dimensional network structure coated on the surface of the molecular sieve, and the silicone oil modified molecular sieve surface obtained thereby has abundant Si-O-Si bonds. The Si-O-Si bonds on the surface of the silicone oil modified molecular sieve serve as heterogeneous nucleation sites for sodium fluorosilicate, which can reduce the energy barrier for nucleation, effectively promote the formation and growth of crystals, make the nucleation of sodium fluorosilicate more uniform, and the abundant nucleation sites suppress the particle size of the crystal nucleus to a certain extent. The silicone oil modified molecular sieve is synthesized in one step by the above method, and the reaction of the silane coupling agent with the hydroxyl groups on the surface of the molecular sieve, the condensation reaction between Si-OH bonds, and the cross-linking reaction of the oligomer containing -OH with the silicone oil are carried out simultaneously, and the reaction efficiency is high.

[0032] Embodiment 4:

[0033] A method for purifying and recovering sodium fluorosilicate waste liquid produced as a by-product of wet-process phosphoric acid comprises the following steps:

[0034] S1. Add HF solution to sodium fluorosilicate waste liquid to make the pH value of the sodium fluorosilicate waste liquid be 6, the mass fraction of HF solution is 50%, stir and react at 80°C for 10min, cool to room temperature and stand for 60min, filter and remove impurities to obtain a filtrate;

[0035] S2, slowly add sodium carbonate particles to the filtrate until no bubbles overflow from the reaction, and then add saturated sodium carbonate solution until the pH value of the filtrate is 9;

[0036] S3, placing the filtrate in a crystallization tank, placing a nucleating agent with a particle size of 10-100 μm into the crystallization tank for crystallization, stirring at a speed of 100 r / min, stirring at room temperature for 5 min, then cooling to 15°C at a rate of 0.2°C / min, holding for 10 min, and finally cooling to 0.5°C at a rate of 3°C / min, holding for 20 min, filtering to obtain a solid product, washing the solid product with ethanol and drying;

[0037] S4. Screening the solid product after drying in step S3 to separate the nano-sodium fluorosilicate particles and the nucleating agent, and recycling the nucleating agent. The nucleating agent used is obtained by the method of Example 3.

[0038] Embodiment 5:

[0039] A method for purifying and recovering sodium fluorosilicate waste liquid produced as a by-product of wet-process phosphoric acid comprises the following steps:

[0040] S1. Add HF solution to sodium fluorosilicate waste liquid to make the pH value of the sodium fluorosilicate waste liquid be 4, the mass fraction of HF solution be 10%, stir and react at 50°C for 40min, cool to room temperature and stand for 30min, filter and remove impurities to obtain a filtrate;

[0041] S2, slowly add sodium carbonate particles to the filtrate until no bubbles overflow from the reaction, and then add saturated sodium carbonate solution until the pH value of the filtrate reaches 8;

[0042] S3, placing the filtrate in a crystallization tank, placing a nucleating agent with a particle size of 10-100 μm into the crystallization tank for crystallization, stirring at a speed of 40 r / min, stirring at room temperature for 20 min, then cooling to 10°C at a rate of 1.5°C / min, keeping for 30 min, and finally cooling to 5°C at a rate of 1°C / min, keeping for 10 min, filtering to obtain a solid product, washing the solid product with ethanol and drying;

[0043] S4. Screening the solid product dried in step S3 to separate the nano-sodium fluorosilicate particles and the nucleating agent, and recycling the nucleating agent. The nucleating agent used is obtained by the method of Example 3.

[0044] Embodiment 6:

[0045] A method for purifying and recovering sodium fluorosilicate waste liquid produced as a by-product of wet-process phosphoric acid comprises the following steps:

[0046] S1. Add HF solution to sodium fluorosilicate waste liquid to make the pH value of the sodium fluorosilicate waste liquid be 5, the mass fraction of HF solution be 30%, stir and react at 65°C for 25min, cool to room temperature and stand for 45min, filter and remove impurities to obtain a filtrate;

[0047] S2, slowly add sodium carbonate particles to the filtrate until no bubbles overflow from the reaction, and then add saturated sodium carbonate solution until the pH value of the filtrate is 9;

[0048] S3, placing the filtrate in a crystallization tank, placing a nucleating agent with a particle size of 10-100 μm into the crystallization tank for crystallization, stirring at a speed of 70 r / min, stirring at room temperature for 15 min, then cooling to 12°C at a rate of 0.8°C / min, holding for 20 min, and finally cooling to 2.6°C at a rate of 2°C / min, holding for 15 min, filtering to obtain a solid product, washing the solid product with ethanol and drying;

[0049] S4. Screening the solid product dried in step S3 to separate the nano-sodium fluorosilicate particles and the nucleating agent, and recycling the nucleating agent. The nucleating agent used is obtained by the method of Example 3.

[0050] Embodiment 7:

[0051] A method for purifying and recovering sodium fluorosilicate waste liquid produced as a by-product of wet-process phosphoric acid is the same as the process of Example 6, except that the nucleating agent used is obtained by the method of Example 1.

[0052] Embodiment 8:

[0053] A method for purifying and recovering sodium fluorosilicate waste liquid produced as a by-product of wet-process phosphoric acid is the same as the process of Example 6, except that the nucleating agent used is obtained by the method of Example 2.

[0054] In Example 1-8, HF solution is added to the sodium fluorosilicate waste liquid produced as a byproduct of wet-process phosphoric acid, and the sodium fluorosilicate is dissolved in the HF solution. SiO 2 The calcium salt reacts with HF to produce CaF precipitate, and the aluminum salt reacts to produce aluminum fluoride precipitate. At the same time, the aluminum salt reacts to produce a small amount of Na 3 AlF 6 After the reaction is completed, the temperature is lowered and allowed to stand. The difference in solubility between sodium fluorosilicate and sodium fluorosilicate is used to make trace amounts of Na 3 AlF 6 and other impurities crystallize and precipitate. After filtering, remove the precipitate generated by the reaction of sodium fluorosilicate with HF solution and other particulate impurities that do not participate in the reaction. Finally, add saturated sodium carbonate, CO 3 2- With H in solution + The reaction produces carbon dioxide and water, Na + With SiF6 - It is combined into sodium fluorosilicate through ionic bonds, thereby improving the purity of sodium fluorosilicate.

[0055] The high-purity sodium fluorosilicate solution is subjected to a crystallization reaction, which is conducive to uniform nucleation. The crystallization process is divided into two stages: nucleation and grain growth. Under the action of the nucleating agent, stirring at room temperature for 5-20 minutes effectively reduces the energy barrier of nucleation and promotes the formation of a large number of nuclei on the surface of the nucleating agent; then gradually cools down to 10-15°C for nucleation growth, accelerating the growth rate of the nucleus. At the same time, due to the large number of nucleus centers, the upper limit of the crystal size is suppressed. When most of the sodium fluorosilicate is crystallized, the temperature is further lowered to promote the crystallization rate and the precipitation amount of sodium fluorosilicate. The use of gradient cooling crystallization can both promote crystallization and inhibit excessive grain size.

[0056] When sodium fluorosilicate crystals are precipitated and filtered, the filtrate contains fluoride ions and is recycled again. Hydrofluoric acid and an appropriate amount of silicon dioxide are added to convert it into SiF6 - , effectively improving the recovery rate of fluoride ions, the method is environmentally friendly and pollution-free.

[0057] Embodiment 9:

[0058] A method for purifying and recovering sodium fluorosilicate waste liquid produced as a by-product of wet-process phosphoric acid comprises the following steps:

[0059] S1. Add HF solution to sodium fluorosilicate waste liquid to make the pH value of the sodium fluorosilicate waste liquid be 5, the mass fraction of HF solution be 30%, stir and react at 65°C for 25min, cool to room temperature and stand for 45min, filter and remove impurities to obtain a filtrate;

[0060] S2. Slowly add sodium carbonate particles to the filtrate until no bubbles overflow from the reaction, and then add saturated sodium carbonate solution until the pH value of the filtrate reaches 8-9;

[0061] S3, adding saturated sodium carbonate solution to the filtrate from step S2 at 60-90° C. until no precipitation is generated, centrifuging to obtain sodium fluoride crystals, washing with ethanol and then drying; the waste liquid obtained by centrifugation is used for the next cycle.

[0062] Example 9 After obtaining a high-purity sodium fluorosilicate solution, continue to add excess saturated sodium carbonate, and the sodium carbonate reacts with the sodium fluorosilicate to generate high-purity sodium fluoride. The filtrate obtained after the reaction contains fluoride ions and is recycled again. Hydrofluoric acid and an appropriate amount of silicon dioxide are added to convert it into SiF6 - , effectively improving the recovery rate of fluoride ions, the method is environmentally friendly and pollution-free.

[0063] Comparative Example 1:

[0064] The method for purifying and recovering the sodium fluorosilicate waste liquid produced as a by-product of wet-process phosphoric acid in Comparative Example 1 is the same as the process in Example 6, except that no nucleating agent is used.

[0065] Comparative Example 2:

[0066] The method for purifying and recovering the sodium fluorosilicate waste liquid produced as a by-product of wet-process phosphoric acid in Comparative Example 2 is the same as that in Example 6, except that the crystallization process is carried out at room temperature.

[0067] The sodium fluorosilicate waste liquid used in Example 1-9 and Comparative Example 1-2 comes from the same batch of waste liquid and has the same composition. The content of sodium fluorosilicate in the waste residue obtained after evaporation, crystallization and drying of the waste liquid is 92%.

[0068] Test example:

[0069] The main content of sodium fluorosilicate in the sodium fluorosilicate crystals obtained after treatment in Examples 4 to 6 of the present invention is 99.6%, 99.5% and 99.7%, respectively. It can be seen that the method of the present invention can remove impurities in the by-product sodium fluorosilicate waste liquid, effectively purify sodium fluorosilicate, and obtain a reagent-grade product.

[0070] After testing, the particle size results of sodium fluorosilicate obtained in Examples 6-8 and Comparative Examples 1-2 are shown in Table 1.

[0071] Table 1 Sodium fluorosilicate particle size

[0072]

[0073] It can be seen from the data in Table 1 that compared with Comparative Examples 1-2, the particle size of the sodium fluorosilicate obtained in Examples 6-8 is mainly nanometer-scale, and the size is relatively uniform. Among them, the particle size in Example 6 is mainly distributed between 0.500-0.250µm. It can be seen that the addition of nucleating agent and the synergistic effect of crystallization conditions effectively suppress the particle size of the crystal and promote the uniform distribution of particle size. The present application scheme can obtain a high-purity nanometer-scale sodium fluorosilicate product, which can be used as a cosolvent and additive, and is also suitable for use in high-demand fields such as the electronics industry as raw materials to produce downstream products, such as sodium fluoride and silicon dioxide. In addition, the filtrate obtained by the process is recycled and reused, which effectively improves the yield of fluorine, can better save energy, reduce production costs, and save energy and protect the environment.

[0074] The purity of the sodium fluoride crystals obtained in Example 9 reached 99.999%.

[0075] In summary, the technical solution of the present invention has the following beneficial effects:

[0076] (1) HF solution is added to the sodium fluorosilicate waste liquid produced as a by-product of wet-process phosphoric acid. Sodium fluorosilicate dissolves in the HF solution. The SiO2 that may be contained in the waste liquid 2 The calcium salt reacts with HF to produce CaF precipitate, and the aluminum salt reacts to produce aluminum fluoride precipitate. At the same time, the aluminum salt reacts to produce a small amount of Na 3 AlF 6 After the reaction is completed, the temperature is lowered and allowed to stand. The difference in solubility between sodium fluorosilicate and sodium fluorosilicate is used to make trace amounts of Na 3 AlF 6 and other impurities crystallize and precipitate. After filtering, remove the precipitate generated by the reaction of sodium fluorosilicate with HF solution and other particulate impurities that do not participate in the reaction. Finally, add saturated sodium carbonate, CO 3 2- With H in solution + The reaction produces carbon dioxide and water, Na + With SiF6 - It is combined into sodium fluorosilicate through ionic bonds, thereby improving the purity of sodium fluorosilicate, and the main content of sodium fluorosilicate is as high as 99.7%.

[0077] (2) Based on the porous characteristics of the molecular sieve, the silane coupling agent forms abundant Si-O-Si and -OH oligomers on the surface of the molecular sieve. The oligomers containing -OH further undergo cross-linking reaction with the silicon-oxygen bonds in the silicone oil to form new Si-O-Si, and form a three-dimensional network structure coated on the surface of the molecular sieve. The surface of the silicone oil-modified molecular sieve thus obtained has abundant Si-O-Si bonds. The Si-O-Si bonds on the surface of the silicone oil-modified molecular sieve serve as heterogeneous nucleation sites for sodium fluorosilicate, which can reduce the energy barrier for nucleation, effectively promote the formation and growth of crystals, and make the nucleation of sodium fluorosilicate more uniform. The abundant nucleation sites inhibit the particle size of the crystal nucleus to a certain extent. The silicone oil-modified molecular sieve is synthesized in one step by the above method. The reaction of the silane coupling agent with the hydroxyl groups on the surface of the molecular sieve, the condensation reaction between the Si-OH bonds, and the cross-linking reaction of the oligomers containing -OH with the silicone oil proceed simultaneously, and the reaction efficiency is high.

[0078] (3) Gradient cooling crystallization can both promote crystallization and inhibit the excessive size of grains. The addition of nucleating agents and the synergistic effect of crystallization conditions effectively inhibit the particle size of the crystals and promote uniform distribution of particle size. The obtained sodium fluorosilicate particles are nano-sized, mainly distributed between 0.500-0.250µm.

[0079] (4) The high-purity nano-scale sodium fluorosilicate product can be used as a co-solvent and additive, and is also suitable for use as a raw material in the production of downstream products such as sodium fluoride and silicon dioxide in high-demand fields such as the electronics industry. In addition, the filtrate obtained by this process can be recycled and reused, which effectively improves the yield of fluorine, can better save energy, reduce production costs, and save energy and protect the environment.

[0080] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0081] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for purifying and recovering sodium fluorosilicate waste liquid, characterized in that: The following steps are involved: S1, adding HF solution to sodium fluorosilicate waste liquid, stirring and reacting at 50-80°C for 10-40min, cooling to room temperature and standing for 30-60min, filtering and removing impurities to obtain a filtrate; the sodium fluorosilicate waste liquid is a by-product of wet-process phosphoric acid; S2. Slowly add sodium carbonate particles to the filtrate until no bubbles overflow from the reaction, and then add saturated sodium carbonate solution until the pH value of the filtrate reaches 8-9; After step S2, the filtrate is placed in a crystallization tank, a nucleating agent with a particle size of 10-100 μm is added to the crystallization tank for crystallization, the mixture is stirred at a speed of 40-100 r / min, a solid product is obtained by filtering, and the solid product is washed with ethanol and dried to obtain nano sodium fluorosilicate particles.

2. The method according to claim 1, characterized in that HF solution is added to the sodium fluorosilicate waste liquid to make the pH value of the sodium fluorosilicate waste liquid be 4-6, and the mass fraction of the HF solution be 10-50%.

3. The method according to claim 1, characterized in that The crystallization process is specifically as follows: stirring at room temperature for 5-20 minutes, cooling to 10-15°C at a rate of 0.2-1.5°C / min, maintaining for 10-30 minutes, and finally cooling to 0.5-5°C at a rate of 1-3°C / min, maintaining for 10-20 minutes.

4. The method according to claim 1, characterized in that: The nucleating agent is a silicone oil modified molecular sieve, which is prepared by a microwave hydrothermal method.

5. The method according to claim 4, characterized in that The specific process of the silicone oil modified molecular sieve using microwave hydrothermal method is as follows: Silicone oil and silane coupling agent are dissolved in a mixture of dimethyl ether and acetone, the pH value of the solution is adjusted to 6-7, molecular sieves are added, the reaction is carried out at a temperature of 80-120° C. and a pressure of 1-10 MPa for 5-20 minutes, and the silicone oil modified molecular sieve is obtained by ethanol filtration and drying.

6. The method according to claim 5, characterized in that The mass ratio of the silicone oil, silane coupling agent and molecular sieve is 1: (0.8-1): (5-30); the volume ratio of dimethyl ether and acetone is 1: 0.2-10; the silicone oil and silane coupling agent are dissolved in a mixed solution of dimethyl ether and acetone, and the mass concentration of the silicone oil and the silane coupling agent is 20-60wt%.

7. The method according to claim 4, characterized in that The particle size of the silicone oil modified molecular sieve is 10-100 μm.

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