Method for preparing sodium fluorosilicate by step-by-step temperature control precipitation of wet-process phosphoric acid

Abstract

The application discloses a method for preparing sodium fluorosilicate by wet phosphoric acid step-by-step temperature control precipitation. The method comprises the following steps: adding a sodium sulfate solution at a constant speed under the condition that the temperature is 50-70 DEG C, cooling to room temperature after the reaction is completed, continuously adding a certain amount of a sodium sulfate solution and a crystal regulator at a constant speed, aging after a period of reaction, and then carrying out solid-liquid separation; washing the filter cake by using the sodium sulfate solution, and drying to obtain a sodium fluorosilicate product, and recycling the washing water to the precipitation reaction. The method can effectively reduce the phosphorus loss and improve the product purity by controlling the adding speed of the sodium sulfate solution, step-by-step adding and the mode of adding again after cooling after the reaction. The method can improve the particle size of the sodium fluorosilicate by using a compounded crystal regulator. The method can significantly improve the fluorine resource yield by using the sodium sulfate solution as a washing liquid, further optimize the filtering effect, and recycle the washing liquid to the precipitation section, so that the massive discharge of the washing wastewater is avoided.

Description

Technical Field

[0001] This invention relates to the field of phosphorus chemical fluorine resource recovery and utilization technology, and in particular to a method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process. Background Technology

[0002] In the wet-process phosphoric acid production process, approximately 80% of the fluorine in phosphate rock enters the phosphoric acid solution, primarily in the form of fluorosilicic acid (H₂SiF₆). If used directly in the production of compound fertilizers without defluorination, the fluorine will enter the soil along with the fertilizer, causing environmental pollution and resource waste. Therefore, recovering fluorine resources from wet-process phosphoric acid has significant environmental and economic value. Currently, using sodium sulfate as a defluorinating agent to recover sodium fluorosilicate from wet-process phosphoric acid is a common method in the industry. In existing phosphate chemical technologies, a typical method for producing sodium fluorosilicate uses fluorosilicic acid, a byproduct of wet-process phosphoric acid, as a raw material. For the technology of preparing sodium fluorosilicate by precipitation of dilute phosphoric acid, fluorine impurities in phosphoric acid are removed by adding a defluorinating agent. However, the byproduct sodium fluorosilicate usually has low purity and high phosphorus content, and the purity of the defluorinated product is not considered during the defluorination process.

[0003] Techniques for producing sodium fluorosilicate using the wet phosphoric acid precipitation method include, for example, CN108147383B, which discloses a wet phosphoric acid defluorination method. In this method, wet phosphoric acid and a defluorinating agent are added to a defluorination reaction tank. After the slurry is cooled, a portion is returned to the reaction tank. The remaining slurry undergoes liquid-solid separation and microfiltration to obtain defluorinated phosphoric acid. The thick slurry is filtered and washed to obtain sodium fluorosilicate semi-finished product. This method improves crystallization conditions through slurry recycling, but the purity of the sodium fluorosilicate semi-finished product is less than 87%, and the P2O5 content is higher than 0.3%, indicating that product purity needs further improvement. CN102730657A discloses a wet phosphoric acid defluorination and purification method. One separation method involves centrifuging the defluorinated slurry, then heating the solids with water and feeding them into a belt filter for filtration and countercurrent washing. This can increase the phosphorus yield from 95% to over 99%. However, the washing method generates a large amount of wastewater, and the sodium fluorosilicate (P2O5) content in the product is higher than 10%, resulting in low purity. CN105776221A discloses a method for recovering fluorine resources in phosphate fertilizer production. This method involves adding active silicon to a fluorinated phosphoric acid solution to convert all the fluorine into fluorosilicic acid. In the presence of seed crystals, sodium phosphate is used to precipitate fluorosilicates. This method introduces seed crystals to enhance crystallization, but the precipitant is sodium phosphate, which is expensive and not very practical. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process. This method regulates the crystallization process of sodium fluorosilicate through stepwise feeding, segmented temperature control, and feeding rate control, thereby reducing the phosphorus entrainment in sodium fluorosilicate and improving purity and yield. Simultaneously, a crystal regulator is added during the secondary precipitation process to promote crystal growth and facilitate filtration. Furthermore, sodium sulfate solution is used instead of water for filter cake washing, and the washing liquid is reused in the precipitation section, avoiding the generation of large amounts of washing wastewater and improving the yield of sodium fluorosilicate.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: (1) Preheat the wet phosphoric acid dilute acid, and add the first part of sodium sulfate solution to the dilute phosphoric acid at a controlled feeding rate under stirring conditions. After the feeding is completed, keep the temperature constant and continue stirring the reaction. (2) Cool the obtained slurry, add the remaining second part of sodium sulfate solution, react for a period of time, and then age it; (3) The aged slurry is filtered to separate the defluorinated phosphoric acid mother liquor and sodium fluorosilicate filter cake; (4) The obtained sodium fluorosilicate filter cake was washed with sodium sulfate solution and dried to obtain sodium fluorosilicate product; (5) The washing liquid is reused in the precipitation reaction section, and the defluorinated dilute acid is returned to the phosphoric acid system.

[0006] Furthermore, in step (1), the wet-process phosphoric acid P2O5 mass concentration is 25-26%, the F mass concentration is 1.1-1.3%, the sodium sulfate solution mass fraction used in the process is 15-20%, and the sodium sulfate solution temperature is 50-60℃.

[0007] The preheating temperature of phosphoric acid in step (1) is 50-70℃; the temperature after cooling in step (2) is 25℃-30℃; the stirring speed in steps (1) and (2) is 100-200 rpm.

[0008] Preferably, the total amount of sodium sulfate used is calculated based on a molar ratio of fluorosilicic acid to sodium sulfate in dilute phosphoric acid of 1:1.05 to 1:1.1. Fluorine in dilute acid solutions exists in complex forms and cannot be completely precipitated and removed as sodium fluorosilicate; therefore, the molar amount of sodium sulfate should not be too high.

[0009] Preferably, the feeding rate in steps (1) and (2) is 2 mL / min.

[0010] Preferably, the sodium sulfate feeding time in step (1) is 20-40 minutes, and the sodium sulfate feeding time in step (2) is 5-20 minutes.

[0011] Preferably, the mass ratio of the first portion of sodium sulfate to the second portion of sodium sulfate is 3:1.

[0012] Preferably, the reaction time after adding materials in step (1) is 30-60 minutes, the reaction time in step (2) is 20-40 minutes, and the aging time is 1-4 hours.

[0013] Preferably, in step (2), after adding the remaining second portion of sodium sulfate solution, a crystal regulator is added. The crystal regulator is a complex of sodium tartrate and polyglycerol-10 laurate, with a mass ratio of sodium tartrate to polyglycerol-10 laurate of (5~20):1, used to increase the size of sodium fluorosilicate crystal particles generated by secondary precipitation. Sodium tartrate selectively adsorbs onto the surface of sodium fluorosilicate crystals, regulating the relative growth rate of different crystal faces. Polyglycerol-10 laurate regulates mass transfer at the crystal interface and inhibits secondary nucleation through interfacial adsorption and steric hindrance. The two work synergistically to promote the directional growth and maturation of sodium fluorosilicate crystals, thereby obtaining sodium fluorosilicate crystals with larger particle size and easier solid-liquid separation.

[0014] Furthermore, in the crystal regulator, the mass ratio of sodium tartrate to polyglycerol-10 laurate is 10:1.

[0015] Furthermore, the total amount of the crystal regulator added is 50~200 mg / L based on the slurry, preferably 100 mg / L.

[0016] Furthermore, the crystal regulator is added after the secondary precipitation of sodium sulfate solution has been completed.

[0017] In step (4), the amount of washing liquid used is 0.5-2.0 times the wet weight of the filter cake.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The step-by-step feeding method is adopted, and the material is added at a uniform speed. A small amount of seed crystals are formed first, and the remaining part is added after cooling. The amount of sodium fluorosilicate entrained is low.

[0019] (2) Nucleation occurs in the high-temperature section and growth occurs in the low-temperature section, resulting in large crystal particles, complete crystal form, and high product purity.

[0020] (3) Add crystal regulator to control the growth of sodium fluorosilicate crystals in a directional manner, making them easy to filter.

[0021] (4) Sodium sulfate solution is used instead of pure water to wash the filter cake, which inhibits the dissolution of sodium fluorosilicate and results in a high yield of sodium fluorosilicate.

[0022] (5) The washing liquid is reused to realize material circulation and there is no process wastewater discharge. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the stepwise temperature-controlled precipitation of phosphoric acid to prepare sodium fluorosilicate according to the present invention.

[0024] Figure 2 The XRD pattern of the prepared sodium fluorosilicate product is shown.

[0025] Figure 3 Sodium fluorosilicate was prepared. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments. The present invention will be described in further detail, but is not limited to these embodiments.

[0027] Example 1 A method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process includes the following steps: (1) Prepare a 10% composite crystal regulator with a sodium tartrate to polyglycerol-10 laurate ratio of 10:1.

[0028] (2) Take 1000g of wet-process phosphoric acid with a P2O5 mass fraction of 25.65% and a F mass fraction of 1.15%, preheat it to 50℃, and add the first part of sodium sulfate solution (mass fraction 15%, temperature 50℃) to the dilute phosphoric acid at a feeding rate of 2mL / min under stirring at 100rpm. The feeding time is 33min. After the feeding is completed, keep the temperature at 50℃ and continue stirring for 30min. (3) Cool the obtained slurry to 25°C, add the remaining second part of sodium sulfate solution (with the same specifications as the first part of sodium sulfate solution), the feeding rate is 2 mL / min, and the feeding time is 11 min; (4) After the sodium sulfate feed is completed, add 100 mg / L of composite crystal regulator based on the slurry.

[0029] (5) After the addition of materials is complete, react for 20 minutes, then age for 1 hour; (6) The aged slurry is filtered to separate the defluorinated phosphoric acid mother liquor and sodium fluorosilicate filter cake; (7) The sodium fluorosilicate filter cake was washed with sodium sulfate solution of the above specifications. The amount of washing solution was 0.5 times the wet weight of the filter cake. The washed sodium fluorosilicate filter cake was dried to obtain sodium fluorosilicate product. (8) The washing solution is reused in the precipitation reaction section of step (1).

[0030] The total amount of sodium sulfate used was calculated based on a molar ratio of fluorosilicic acid to sodium sulfate in dilute phosphoric acid of 1:1.05, and the mass ratio of the first part of sodium sulfate to the second part of sodium sulfate was 3:1. Testing revealed that the obtained sodium fluorosilicate product had a purity of 99.27%, a defluorination rate of 88.55%, a phosphorus loss of 0.68%, a yield of 79.23%, and a particle size of 38.11 μm.

[0031] Example 2 A method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process includes the following steps: (1) Prepare a 10% composite crystal regulator with a sodium tartrate to polyglycerol-10 laurate ratio of 5:1.

[0032] (2) Take 1000g of wet-process phosphoric acid with a P2O5 mass fraction of 26.00% and a F mass fraction of 1.24%, preheat it to 60℃, and add the first part of sodium sulfate solution (mass fraction 18%, temperature 55℃) to the dilute phosphoric acid at a feeding rate of 2mL / min under stirring at 150 rpm. The feeding time is 20min. After the feeding is completed, keep the temperature at 60℃ and continue stirring for 45 minutes. (3) Cool the obtained slurry to 25°C, add the remaining second part of sodium sulfate solution (with the same specifications as the first part of sodium sulfate solution), the feeding rate is 2 mL / min, and the feeding time is 20 min.

[0033] (4) After the sodium sulfate feed is completed, add 50 mg / L of compound crystal regulator based on the slurry.

[0034] (5) After the addition of materials is complete, react for 30 minutes, then age for 2.5 hours; (6) The aged slurry is filtered to separate the defluorinated phosphoric acid mother liquor and sodium fluorosilicate filter cake; (7) The sodium fluorosilicate filter cake was washed with sodium sulfate solution of the above specifications. The amount of washing solution was 1.5 times the wet weight of the filter cake. The washed sodium fluorosilicate filter cake was dried to obtain sodium fluorosilicate product. (8) The washing solution is reused in the precipitation reaction section of step (1).

[0035] The total amount of sodium sulfate used was calculated based on a molar ratio of fluorosilicic acid to sodium sulfate in dilute phosphoric acid of 1:1.08, and the mass ratio of sodium sulfate solution used in the two steps was 1:1. Testing revealed that the obtained sodium fluorosilicate product had a purity of 99.45%, a defluorination rate of 87.68%, a phosphorus loss of 0.46%, a yield of 80.81%, and a particle size of 38.26 μm.

[0036] Example 3 A method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process includes the following steps: (1) Prepare a 10% composite crystal regulator, with sodium tartrate and polyglycerol-10 laurate in a ratio of 20:1.

[0037] (2) Take 1000g of wet-process phosphoric acid with a P2O5 mass fraction of 25.65% and a F mass fraction of 1.15%, preheat it to 70℃, and add the first part of sodium sulfate solution (mass fraction of 20%, temperature of 60℃) to the dilute phosphoric acid at a feeding rate of 2 mL / min under the stirring condition of 200 rpm. The feeding time is 28min. After the feeding is completed, keep the temperature at 70℃ and continue to stir for 60 minutes. (3) Cool the obtained slurry to 30°C, add the remaining second part of sodium sulfate solution (with the same specifications as the first part of sodium sulfate solution), the feeding rate is 2 mL / min, and the feeding time is 7 min.

[0038] (4) After sodium sulfate is added, add 200 mg / L of compound crystal regulator based on the slurry.

[0039] (5) After the addition of materials is complete, react for 40 minutes, then age for 4 hours; (6) The aged slurry is filtered to separate the defluorinated phosphoric acid mother liquor and sodium fluorosilicate filter cake; (7) The sodium fluorosilicate filter cake was washed with sodium sulfate solution of the above specifications. The amount of washing solution was 2.0 times the wet weight of the filter cake. The washed sodium fluorosilicate filter cake was dried to obtain sodium fluorosilicate product. (8) The washing solution is reused in the precipitation reaction section of step (1).

[0040] The total amount of sodium sulfate used was calculated based on a molar ratio of fluorosilicic acid to sodium sulfate in dilute phosphoric acid of 1:1.1, and the mass ratio of the first part of sodium sulfate to the second part of sodium sulfate was 4:1. Testing revealed that the obtained sodium fluorosilicate product had a purity of 99.30%, a defluorination rate of 89.72%, a phosphorus loss of 0.37%, a yield of 80.12%, and a particle size of 35.28 μm. Example 4 Without adding a crystal regulator, the remaining steps were the same as in Example 1. The obtained sodium fluorosilicate product had a purity of 99.21%, a defluorination rate of 80.65%, a phosphorus loss of 0.77%, a yield of 71.84%, and a particle size of 21.69 μm. Comparative Example 1 Take 1000g of the same dilute phosphoric acid as in Example 1 and heat to 50℃. Quickly pour the entire 15% sodium sulfate solution into the reactor at once. Stir and react at 50℃ for 2 hours. Filter the mixture, wash the filter cake with water (same amount as in Example 1), and dry under the same conditions. The obtained sodium fluorosilicate product has a purity of 97.54%, a defluorination rate of 76.04%, a phosphorus loss of 2.07%, a yield of 70.22%, and a particle size of 30.58μm.

[0041] Comparative Example 2 Take 1000g of the same dilute phosphoric acid as in Example 1, and maintain the temperature at 25℃ (without preheating). Pour the entire 15% sodium sulfate solution into the reactor quickly and all at once. Stir and react at 25℃ for 2 hours, age for 1 hour, then filter. Wash the filter cake with pure water (the amount used is the same as in Example 1), and dry under the same conditions as in Example 1. The obtained sodium fluorosilicate product has a purity of 97.31%, a defluorination rate of 78.01%, a phosphorus loss of 2.14%, a yield of 72.17%, and a particle size of 27.43μm. Comparative Example 3 The crystal regulator was sodium hydrogen tartrate, and the mass concentration of the regulator was the same as in Example 1. All other steps were the same as in Example 1. The obtained sodium fluorosilicate product had a purity of 99.24%, a defluorination rate of 84.76%, a phosphorus loss of 0.56%, a yield of 75.68%, and a particle size of 32.47 μm.

[0042] Comparative Example 4 The crystal regulator was polyglycerol-10 laurate. The mass concentration of the regulator was the same as in Example 1. All other steps were the same as in Example 1. The obtained sodium fluorosilicate product had a purity of 98.74%, a defluorination rate of 82.93%, a phosphorus loss of 0.82%, a yield of 73.92%, and a particle size of 30.86 μm.

[0043] Comparative Example 5 A method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process is the same as that in Example 1, except that the temperature of the sodium sulfate solution used in steps (1) and (2) is changed to 20°C.

[0044] Comparative Example 6 The steps are the same as in Example 1, except that the temperature of the sodium sulfate solution used in steps (1) and (2) is changed to 80°C, and the other parameters are the same as in Example 1. Comparative Example 7 The steps are the same as in Example 1, except that in step (1), the preheating temperature of phosphoric acid is changed to 30°C, and the reaction is carried out at 30°C after the feed is added. All other parameters are the same as in Example 1. Comparative Example 8 The steps are the same as in Example 1, except that: in step (1), the preheating temperature of phosphoric acid is changed to 90°C, and after adding the material, the temperature is maintained at 90°C for stirring reaction (which is 50–70°C higher than the range defined in the claims). All other parameters are the same as in Example 1.

[0045] Comparative Example 9 The steps are the same as in Example 1, except that the temperature is changed to 45°C after cooling in step (2), and the other parameters are the same as in Example 1.

[0046] Comparative Example 10 The steps are the same as in Example 1, except that the temperature after cooling in step (2) is changed to 10°C, and the other parameters are the same as in Example 1. Yield: Assuming that all fluorine in the dilute acid exists in the form of fluorosilicic acid, Yield = (Actual mass of sodium fluorosilicate produced / Theoretically, mass of sodium fluorosilicate produced according to the following equation) * 100% H2SiF6+Na2SO4=Na2SiF6(s)+H2SO4; Sodium fluorosilicate purity / %: The mass fraction of sodium fluorosilicate in the sodium fluorosilicate product, % . P2O5 content in precipitate / %: Mass fraction of P2O5 in sodium fluorosilicate product, % Defluorination rate / %: (1 - mass of fluorine after filtration following dilute acid precipitation reaction / mass of fluorine before dilute acid reaction) * 100%; Particle size / μm: Average particle size of sodium fluorosilicate products; Phosphorus loss: (1 - mass of P2O5 after filtration following dilute acid precipitation reaction / mass of P2O5 before dilute acid reaction) * 100%.

[0047] Table 1 Comparison of results between the examples and comparative examples.

[0048] The yield, purity, and defluorination rate of Comparative Example 5 (20℃) and Comparative Example 6 (80℃) were significantly lower than those of Example 1, with increased phosphorus loss. This indicates that the temperature of the sodium sulfate solution needs to be matched with the temperature of the reaction system. Too low a temperature will cause localized rapid cooling and nucleation, while too high a temperature will cause localized overheating and deterioration of crystal morphology, both of which are detrimental to the high-purity and efficient precipitation of sodium fluorosilicate.

[0049] Comparative Example 7 (30℃) had a yield of 78.53%, a particle size of only 22.31 μm, and a phosphorus loss as high as 1.36%; Comparative Example 8 (90℃) had a low yield, low defluorination rate, and high phosphorus loss. This indicates that if the first-step temperature is too low, the crystals are too fine and the entrainment is severe, while if it is too high, the dissolution rate of sodium fluorosilicate increases, and the defluorination rate and yield decrease significantly. Both of these factors significantly worsen the product quality and recovery rate.

[0050] Comparative Example 9 (45℃) showed a decrease in yield and defluorination rate due to incomplete precipitation; Comparative Example 10 (10℃) showed a slight increase in yield, but the explosive nucleation resulted in grain refinement, increased phosphorus inclusions, decreased purity, and increased energy consumption. This indicates that 25-30℃ is the optimal cooling range that balances precipitation completeness and crystal quality. Table 2. Quality Inspection Results of Sodium Fluorosilicate Products

[0051] As can be seen from the examples and comparative examples, the present invention reduces the phosphorus entrainment of sodium fluorosilicate by stepwise temperature-controlled precipitation, thereby improving product purity and yield. The crystal regulator increases the product particle size, while avoiding the discharge of washing wastewater. This solves the problems of high sodium fluorosilicate phosphorus content, low yield, small particle size, and washing wastewater discharge in traditional methods. The obtained sodium fluorosilicate product has high purity and large particles, and can be used as a high-quality raw material for the production of anhydrous hydrogen fluoride.

Claims

1. A method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process, characterized in that: (1) Preheat the wet phosphoric acid dilute acid, and add the first part of sodium sulfate solution to the dilute phosphoric acid under stirring. After the addition is completed, keep the temperature constant and continue stirring the reaction. (2) Cool down the slurry obtained in step (1), add the remaining second part of sodium sulfate solution, react for a period of time, and then age it; (3) The aged slurry is filtered to separate the defluorinated phosphoric acid mother liquor and sodium fluorosilicate filter cake; (4) The obtained sodium fluorosilicate filter cake was washed with sodium sulfate solution and dried to obtain sodium fluorosilicate product; (5) The washing liquid is reused in the precipitation reaction section, and the defluorinated dilute acid is returned to the phosphoric acid system.

2. The method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process according to claim 1, characterized in that, In step (1), the wet-process phosphoric acid P2O5 mass fraction is 25-26%, the F mass fraction is 1.1-1.3%, the sodium sulfate solution mass fraction used in the process is 15-20%, and the sodium sulfate solution temperature is 50-60℃.

3. The method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process according to claim 1, characterized in that, In step (1), the preheating temperature of phosphoric acid is 50-70℃; in step (2), the temperature after cooling is 25℃-30℃.

4. The method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process according to claim 1, characterized in that, The stirring speed in steps (1) and (2) is 100-200 rpm.

5. The method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process according to claim 1, characterized in that, The total amount of sodium sulfate used is based on a molar ratio of fluorosilicic acid to sodium sulfate in dilute phosphoric acid of 1:(1.05-1.1).

6. The method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process according to claim 1, characterized in that, The sodium sulfate solution is added at a rate of 1-3 mL / min relative to each liter of dilute phosphoric acid in steps (1) and (2). The sodium sulfate addition time in step (1) is 10-40 minutes, and the sodium sulfate addition time in step (2) is 5-30 minutes.

7. The method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process according to claim 1, characterized in that, The mass ratio of sodium sulfate added in the first part to sodium sulfate in the second part is (1-4):

1.

8. The method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process according to claim 1, characterized in that, After adding the materials in step (1), the reaction time is 30-60 minutes. After adding the materials in step (2), the reaction time is 20-40 minutes. The aging time is 1-4 hours.

9. The method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process according to claim 1, characterized in that, In step (2), after adding the remaining second part of sodium sulfate solution, a crystal regulator is also added. The crystal regulator is a complex of sodium tartrate and polyglycerol-10 laurate. The mass ratio of sodium tartrate to polyglycerol-10 laurate is (5~20):

1. The total amount of crystal regulator added is 50~200 mg / L based on the slurry.

10. The method for preparing sodium fluorosilicate by stepwise temperature-controlled precipitation of phosphoric acid using a wet process according to claim 1, characterized in that, In step (4), the amount of sodium sulfate solution used for washing is 0.5-2.0 times the wet weight of the filter cake.

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