Method for removing phosphorus and silicon from sodium tungstate solution

Abstract

The invention belongs to the technical field of wet metallurgy of tungsten, and particularly relates to a method for removing phosphorus and silicon from a sodium tungstate solution, which comprises the following steps: adjusting the pH value of the sodium tungstate solution containing phosphorus and silicon to 9-10 at the temperature of 25-60 DEG C, adding an aluminum salt saturated solution, stirring to obtain a mixed solution, and standing at the temperature of 25-60 DEG C; the ratio of the mass of aluminum in the aluminum salt saturated solution to the total mass of silicon and phosphorus in the sodium tungstate solution is (1.1-1.8): 2; the pH value of the mixed solution is adjusted to 13-14, the temperature is 80-90 DEG C, calcium salt is added, stirring and standing are conducted, then filtering is conducted, a sodium tungstate purified solution is obtained, and the mass ratio of the calcium salt calculated by CaO to the aluminum salt calculated by Al2O3 is 1: (1-2). According to the technical scheme, it is found that when the aluminum salt and the calcium salt are jointly used, the adding sequence influences the phosphorus and silicon removal effect, and a method for deeply removing phosphorus and silicon by adding the aluminum salt and then adding the calcium salt is developed; the optimal phosphorus and silicon removal effect is determined by adjusting the adding time, the adding amount and the reaction conditions of the aluminum salt and the calcium salt; through the synergistic effect of aluminum, calcium and silicon, the problem that single aluminum salt precipitation is difficult to filter is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrometallurgy of tungsten, specifically to a method for removing phosphorus and silicon from a sodium tungstate solution. BACKGROUND

[0002] Sodium tungstate is an important chemical raw material, widely used in hard alloy, electronic industry, catalyst and other fields. However, in the production process of sodium tungstate, the existence of impurities will seriously affect its purity and performance.

[0003] Currently, calcium salt is commonly used for phosphorus removal in industrialization, and its dosage may reach 30-80 times of the theoretical dosage according to the different types of calcium salt. Moreover, the phosphorus removal effect of sodium tungstate is also affected by silicon. In the presence of phosphorus and silicon impurities, the use of a single impurity removal reagent not only has poor effect, but also greatly increases the dosage of calcium salt. The patent with publication number CN112853123A mentions that sodium aluminate and magnesium oxide can be used to remove silicon. Sodium aluminate and magnesium oxide will not introduce new impurities by reacting with other impurities, and sodium aluminate can also act as a flocculating agent, making the generated silicic acid and magnesium silicate flocculate together, thereby increasing the particle size of the generated insoluble substances and improving the silicon removal effect. However, although the aluminum salt has good silicon removal effect, the aluminum salt precipitate also has the problem of difficult filtration.

[0004] In summary, the existing technology can remove phosphorus and silicon to some extent, but still has some problems and deficiencies. First, the method of using aluminum salt or calcium salt alone cannot remove phosphorus and silicon simultaneously, and additional treatment steps are needed to improve the removal efficiency. Second, these methods often require high chemical dosage, increasing the treatment cost. In addition, the method of using aluminum salt or calcium salt alone has certain limitations in practical application, and it is difficult to meet the removal needs under different conditions. Therefore, it is of great practical significance and application value to develop a new method for removing phosphorus and silicon by combining aluminum salt and calcium salt. SUMMARY

[0005] To solve the above problems, the application provides a method for removing phosphorus and silicon from a sodium tungstate solution. This method changes the morphology of the precipitate by pre-flocculation with aluminum salt, and simultaneously utilizes the high precipitation capacity of calcium salt for phosphorus and the synergistic effect between aluminum, calcium and silicon, thereby solving the problem of difficult filtration of single aluminum salt precipitation and achieving simultaneous deep removal of phosphorus and silicon.

[0006] The method for removing phosphorus and silicon from a sodium tungstate solution provided by the application comprises the following steps: S1. Obtain a sodium tungstate solution containing phosphorus and silicon, adjust the pH of the sodium tungstate solution to 9-10, control the temperature to 25-60℃, add a saturated aluminum salt solution to the sodium tungstate solution, and perform a first stirring to obtain a mixed solution. The ratio of the mass of aluminum in the saturated aluminum salt solution to the total mass of silicon and phosphorus in the sodium tungstate solution is (1.1-1.8):2. S2. Adjust the pH of the mixed solution to 13-14, control the temperature to 80-90℃, add calcium salt to the mixed solution, stir for the second time, let it stand, and then filter to obtain sodium tungstate purified solution and filter residue. The mass ratio of the calcium salt (calculated as CaO) to the aluminum salt (calculated as Al2O3) is 1:(1-2).

[0007] Under alkaline conditions, adding aluminum salts to sodium tungstate solution allows the aluminum salts to hydrolyze and form positively charged, highly adsorbent and flocculating aluminum hydroxyl polymers and amorphous Al(OH)3 polymers. These polymers preferentially bind to or capture silicate and some phosphate ions, forming fine-particle flocs that provide nuclei for subsequent co-precipitation with calcium salts. Adding a saturated aluminum salt solution to the alkaline sodium tungstate solution ensures rapid supersaturation of the aluminum salt under alkaline conditions, promoting rapid polymer formation and enhancing its ability to capture silicon and phosphorus. While adding a non-saturated aluminum salt solution to the alkaline sodium tungstate solution can have some effect due to pH increase, it cannot guarantee that the aluminum salt will remain saturated in the system. Furthermore, if the pH of the sodium tungstate solution is too high, Al(OH)4 will immediately form upon the addition of aluminum salt. - Dissolution eliminates the flocculation effect. Therefore, in step S1, the pH of the sodium tungstate solution is adjusted to the range of 9-10 to ensure good flocculation by the aluminum salt. Temperature also affects the solubility of aluminum salt; therefore, controlling the temperature between 25-60℃ weakens its impact on solubility. The pH of the mixed solution is then adjusted to 13-14, and the temperature is controlled at 80-90℃ before adding calcium salt. Under high alkalinity and high temperature conditions, the calcium salt preferentially reacts with phosphorus and silicon bound in the flocs to form a stable precipitate mainly composed of calcium silicate phosphate (Ca-Si-P complex), achieving deep phosphorus removal. Excess calcium salt also reacts with residual aluminum and silicon to form insoluble calcium aluminosilicate, achieving deep silicon removal without binding with tungstate and causing tungsten loss. Furthermore, calcium aluminosilicate and calcium silicate phosphate particles are coarser than ordinary aluminum salt precipitates, with greater porosity between crystals, making them easier to filter. Simple filtration then simultaneously removes phosphorus and silicon, solving the problem of difficult filtration of ordinary aluminum salt precipitates.

[0008] If aluminum salt solution and calcium salt are added simultaneously, the calcium salt will have already reacted almost completely before the aluminum salt's capture and adsorption effect can be fully realized. Therefore, adding them simultaneously can only achieve the effect of removing silicon. Similarly, adding calcium salt first cannot simultaneously solve the problem of excessive phosphorus and silicon. On the other hand, adding aluminum salt alone to remove phosphorus and silicon easily forms colloids under alkaline conditions, resulting in limited efficiency. Adding calcium salt alone easily reacts with tungstate ions to form calcium tungstate precipitate under strongly alkaline conditions, causing tungsten loss. The "aluminum-calcium synergy" cleverly avoids the shortcomings of each: aluminum first "locks in" impurities, and calcium then "strengthens" the precipitate and promotes separation. The two complement each other, forming a purification effect of "1+1>2". This technical solution also has advantages in alkaline solutions such as sodium molybdate.

[0009] Furthermore, the concentration of the sodium tungstate solution, calculated as WO3, is 50~200g / L, and the phosphorus content and silicon content in the sodium tungstate solution are ≤1g / L and ≤1g / L, respectively.

[0010] Furthermore, the aluminum salt includes aluminum sulfate, and the calcium salt includes calcium carbonate.

[0011] Furthermore, in step S1, the first stirring rate is 200~400 r / min, and the time is 1~2 h.

[0012] Furthermore, in step S2, sodium hydroxide is used to adjust the pH of the mixed solution to 13-14.

[0013] Furthermore, in step S2, the second stirring rate is 200~400 r / min, and the time is 1~2 h.

[0014] Furthermore, in step S2, the settling time is 1 to 2 hours.

[0015] Furthermore, in step S2, a Buchner funnel with an outer diameter of 200 mm, an inner diameter of 190 mm, and a volume of 5 L, and double-ring filter paper with a diameter of 18 cm are used for filtration, and the filtration time for each liter of sodium tungstate purified solution is ≤2 min.

[0016] Furthermore, the filter residue includes calcium silicate phosphate and calcium aluminosilicate.

[0017] Furthermore, the phosphorus content and silicon content in the sodium tungstate purification solution are ≤0.05g / L and ≤0.05g / L, respectively.

[0018] This application proposes a method for removing phosphorus and silicon from sodium tungstate solution, which yields the following beneficial effects: it innovatively discovers that the order of addition of aluminum and calcium salts affects the phosphorus and silicon removal efficiency, and develops a method for deep phosphorus and silicon removal by adding aluminum salt first and then calcium salt; the optimal phosphorus and silicon removal efficiency is determined by adjusting the timing, amount, and reaction conditions of adding aluminum and calcium salts; and the problem of difficult precipitation and filtration of single aluminum salts is solved through the synergistic effect between aluminum, calcium, and silicon. Detailed Implementation

[0019] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0020] This application discloses a method for removing phosphorus and silicon from a sodium tungstate solution, comprising the following steps: S1. Obtain a sodium tungstate solution containing phosphorus and silicon. Adjust the pH of the sodium tungstate solution to 9-10 and control the temperature to 25-60℃. Add a saturated aluminum sulfate solution to the sodium tungstate solution and stir the reaction at a rate of 200-400 r / min for 1-2 h to obtain a mixed solution. The ratio of the mass of aluminum in the saturated aluminum sulfate solution to the total mass of silicon and phosphorus in the sodium tungstate solution is (1.1-1.8):2. Specifically, the pH of the sodium tungstate solution can be adjusted to any one or a combination of 9, 9.2, 9.4, 9.6, 9.8, and 10; the temperature can be controlled to any one or a combination of 25℃, 35℃, 45℃, 55℃, and 60℃; the stirring speed can be any one or a combination of 200 r / min, 250 r / min, 300 r / min, 350 r / min, and 400 r / min; and the ratio of the mass of aluminum in the saturated aluminum sulfate solution to the total mass of silicon and phosphorus in the sodium tungstate solution can be any one or a combination of 1.1:2, 1.2:2, 1.3:2, 1.4:2, 1.5:2, 1.6:2, 1.7:2, and 1.8:2.

[0021] S2. Adjust the pH of the mixed solution to 13-14, control the temperature to 80-90℃, add calcium carbonate to the mixed solution, stir the reaction at a rate of 200-400 r / min for 1-2 h, let it stand for 1-2 h, and then filter to obtain sodium tungstate purified solution and filter residue. The mass ratio of calcium carbonate (calculated as CaO) to aluminum sulfate (calculated as Al2O3) is 1:(1-2). Specifically, the pH of the mixed solution can be adjusted to any one or any two of 13, 13.2, 13.4, 13.6, 13.8, and 14; the temperature can be controlled to any one or any two of 80℃, 82℃, 84℃, 86℃, 88℃, and 90℃; the stirring speed can be any one or any two of 200r / min, 250r / min, 300r / min, 350r / min, and 400r / min; and the mass ratio of calcium carbonate (CaO) to aluminum sulfate (Al2O3) can be any one or any two of 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, and 1:2.

[0022] Preferably, the concentration of the sodium tungstate solution, calculated as WO3, is 50~200 g / L, and the phosphorus content and silicon content in the sodium tungstate solution are ≤1 g / L and ≤1 g / L, respectively.

[0023] Preferably, in step S2, sodium hydroxide is used to adjust the pH of the mixed solution to 13-14.

[0024] Preferably, in step S2, a Buchner funnel with an outer diameter of 200 mm, an inner diameter of 190 mm, and a volume of 5 L, and double-ring filter paper with a diameter of 18 cm are used to filter the mixed solution after the reaction with calcium salt, and the filtration time for each liter of sodium tungstate purified solution is ≤2 min.

[0025] Preferably, the filter residue includes calcium silicate phosphate and calcium aluminosilicate.

[0026] Preferably, the phosphorus content and silicon content in the sodium tungstate purification solution are ≤0.05g / L and ≤0.05g / L, respectively.

[0027] The technical solution of this application will be further described below with reference to specific embodiments. In all the following embodiments and comparative examples, the sodium tungstate solution containing phosphorus and silicon impurities has a phosphorus content of 1 g / L and a silicon content of 1 g / L. The concentration of the sodium tungstate solution as WO3 is 150 g / L. The saturated aluminum salt solution used is a saturated aluminum sulfate solution prepared at 20°C, wherein the mass fraction of Al is 57.08 g / L. The calcium salt used is calcium carbonate. During filtration, a Buchner funnel with an outer diameter of 200 mm, an inner diameter of 190 mm, and a volume of 5 L, and double-ring filter paper with a diameter of 18 cm are used.

[0028] Example 1 The pH of a sodium tungstate solution containing phosphorus and silicon impurities was adjusted to 9, and the temperature was set to 25°C. A saturated aluminum sulfate solution was added to the sodium tungstate solution, with the volume of the saturated aluminum sulfate solution being 2% of the volume of the sodium tungstate solution. The mixture was stirred at 200 r / min for 1 h to obtain a mixed solution. The pH of the mixed solution was adjusted to 14, and the temperature was set to 80°C. Calcium carbonate was added to the mixed solution, with the mass ratio of calcium carbonate (CaO) to aluminum sulfate (Al2O3) being 1:1. The mixture was stirred at 200 r / min for 1 h, and after standing for 1 h, it was filtered to obtain a purified sodium tungstate solution and filter residue. The filtration time for each liter of purified sodium tungstate solution was ≤2 min. The sodium tungstate purified solution obtained in this embodiment was tested, and the phosphorus content was <0.05 g / L and the silicon content was <0.05 g / L.

[0029] Example 2 The pH of a sodium tungstate solution containing phosphorus and silicon impurities was adjusted to 10, and the temperature was set to 60°C. A saturated aluminum sulfate solution was added to the sodium tungstate solution, with the volume of the saturated aluminum sulfate solution being 3% of the volume of the sodium tungstate solution. The mixture was stirred at 400 r / min for 2 h to obtain a mixed solution. The pH of the mixed solution was adjusted to 13, and the temperature was set to 90°C. Calcium carbonate was added to the mixed solution, with the mass ratio of calcium carbonate (CaO) to aluminum sulfate (Al2O3) being 1:1. The mixture was stirred at 400 r / min for 2 h, and after standing for 2 h, it was filtered to obtain a purified sodium tungstate solution and filter residue. The filtration time for each liter of purified sodium tungstate solution was ≤2 min. The sodium tungstate purified solution obtained in this embodiment was tested, and the phosphorus content was <0.05 g / L and the silicon content was <0.05 g / L.

[0030] Example 3 The pH of a sodium tungstate solution containing phosphorus and silicon impurities was adjusted to 10, and the temperature was set to 60°C. A saturated aluminum sulfate solution was added to the sodium tungstate solution, with the volume of the saturated aluminum sulfate solution being 3% of the volume of the sodium tungstate solution. The mixture was stirred at 400 r / min for 2 h to obtain a mixed solution. The pH of the mixed solution was adjusted to 13, and the temperature was set to 90°C. Calcium carbonate was added to the mixed solution, with the mass ratio of calcium carbonate (CaO) to aluminum sulfate (Al2O3) being 1:2. The mixture was stirred at 400 r / min for 2 h, and after standing for 2 h, it was filtered to obtain a purified sodium tungstate solution and filter residue. The filtration time for each liter of purified sodium tungstate solution was ≤2 min. The sodium tungstate purified solution obtained in this embodiment was tested, and the phosphorus content was <0.05 g / L and the silicon content was <0.05 g / L.

[0031] Example 4 The pH of a sodium tungstate solution containing phosphorus and silicon impurities was adjusted to 9.5 and the temperature to 40℃. A saturated aluminum sulfate solution was added to the sodium tungstate solution, with the volume of the saturated aluminum sulfate solution being 2.5% of the volume of the sodium tungstate solution. The mixture was stirred at 300 r / min for 1.5 h to obtain a mixed solution. The pH of the mixed solution was adjusted to 13.5 and the temperature to 85℃. Calcium carbonate was added to the mixed solution, with the mass ratio of calcium carbonate (CaO) to aluminum sulfate (Al2O3) being 1:1.5. The mixture was stirred at 300 r / min for 1.5 h and allowed to stand for 1.5 h before filtration to obtain purified sodium tungstate solution and filter residue. The filtration time for each liter of purified sodium tungstate solution was ≤2 min. The sodium tungstate purified solution obtained in this embodiment was tested, and the phosphorus content was <0.05 g / L and the silicon content was <0.05 g / L.

[0032] Comparative Example 1 The only difference between this comparative example and Example 1 is that: first, the pH of the sodium tungstate solution was adjusted to 14 and the temperature to 80°C, and calcium carbonate was added; then, the pH was adjusted to 9 and the temperature to 25°C, and a saturated aluminum sulfate solution was added. The filtration time for each liter of sodium tungstate purified solution is ≥3h; The sodium tungstate purification solution obtained in this comparative example was tested, and the phosphorus content was <0.05 g / L and the silicon content was 0.57 g / L.

[0033] Comparative Example 2 The only difference between this comparative example and Example 1 is that the pH of the sodium tungstate solution was adjusted to 9, the temperature was set to 25°C, and a saturated aluminum sulfate solution and calcium carbonate were added. The mixture was then stirred at a rate of 200 r / min for 1 h, allowed to stand for 1 h, and then filtered. The filtration time for each liter of sodium tungstate purified solution is ≤2 min; The sodium tungstate purified solution obtained in this comparative example was tested, and the phosphorus content was 0.64 g / L and the silicon content was <0.05 g / L.

[0034] Comparative Example 3 The only difference between this comparative example and Example 1 is that the mass ratio of calcium carbonate (calculated as CaO) to aluminum sulfate (calculated as Al2O3) is 1:3. The filtration time for each liter of sodium tungstate purified solution is ≥5 min; The sodium tungstate purification solution obtained in this comparative example was tested, and the phosphorus content was <0.05 g / L and the silicon content was 0.14 g / L.

[0035] Comparative Example 4 The only difference between this comparative example and Example 1 is that the volume of the added saturated aluminum sulfate solution is 1% of the volume of the sodium tungstate solution, and the ratio of the mass of added calcium carbonate (calculated as CaO) to the mass of aluminum sulfate (calculated as Al2O3) is 2:1. The filtration time for each liter of sodium tungstate purified solution is ≥5 min; The sodium tungstate purification solution obtained in this comparative example was tested, and the phosphorus content was <0.05 g / L and the silicon content was 0.71 g / L.

[0036] Comparative Example 5 The only difference between this comparative example and Example 1 is that calcium carbonate is not added, and the mixed solution obtained after reacting with saturated aluminum sulfate solution is allowed to stand for 1 hour and then filtered. The filtration time for each liter of sodium tungstate purified solution is ≥3 hours; The sodium tungstate purification solution obtained in this comparative example was tested, and the phosphorus content was 0.97 g / L and the silicon content was 0.28 g / L.

[0037] Comparative Example 6 The only difference between this comparative example and Example 1 is that: instead of adding a saturated aluminum sulfate solution, the pH of the sodium tungstate solution was directly adjusted to 14, the temperature was set to 80°C, calcium carbonate was added, and then the mixture was stirred, allowed to stand, and filtered. The filtration time for each liter of sodium tungstate purified solution is ≥5 min; The sodium tungstate purified solution obtained in this comparative example was tested, and the phosphorus content was 0.29 g / L and the silicon content was 0.99 g / L.

[0038] Comparative Example 7 The only difference between this comparative example and Example 1 is that ferric hydroxide is used instead of calcium carbonate, and the mass ratio of ferric hydroxide (Fe2O3) to aluminum sulfate (Al2O3) is 1:1. The filtration time for each liter of sodium tungstate purified solution is ≥8 min; The sodium tungstate purification solution obtained in this comparative example was tested, and the phosphorus content was 0.96 g / L and the silicon content was 0.23 g / L.

[0039] Comparative Example 8 The only difference between this comparative example and Example 1 is that the pH of the mixed solution was adjusted to 10 before adding calcium carbonate. The filtration time for each liter of sodium tungstate purified solution is ≥7 min; The sodium tungstate purified solution obtained in this comparative example was tested, and the phosphorus content was 0.44 g / L and the silicon content was <0.05 g / L.

[0040] Comparative Example 9 The only difference between this comparative example and Example 1 is that the pH of the mixed solution was adjusted to 13 before adding the saturated aluminum sulfate solution. The filtration time for each liter of sodium tungstate purified solution is ≥7 min; The sodium tungstate purification solution obtained in this comparative example was tested, and the phosphorus content was <0.05 g / L and the silicon content was 0.55 g / L.

[0041] Comparative Example 10 The only difference between this comparative example and Example 1 is that the temperature of the mixed solution was adjusted to 80°C before adding the saturated aluminum sulfate solution. The filtration time for each liter of sodium tungstate purified solution is ≥7 min; The sodium tungstate purification solution obtained in this comparative example was tested, and the phosphorus content was 0.35 g / L and the silicon content was <0.05 g / L.

[0042] Comparative Example 11 The only difference between this comparative example and Example 1 is that the temperature of the mixed solution was adjusted to 40°C before adding calcium carbonate. The filtration time for each liter of sodium tungstate purified solution is ≥7 min; The sodium tungstate purification solution obtained in this comparative example was tested, and the phosphorus content was <0.05 g / L and the silicon content was 0.38 g / L.

[0043] Comparative Example 12 The only difference between this comparative example and Example 3 is that the added aluminum sulfate is an unsaturated solution; The filtration time for each liter of sodium tungstate purified solution is ≤2 min; The sodium tungstate purification solution obtained in this comparative example was tested, and the phosphorus content was 0.43 g / L and the silicon content was 0.50 g / L.

[0044] This application proposes a method for removing phosphorus and silicon from sodium tungstate solution, which yields the following beneficial effects: it innovatively discovers that the order of addition of aluminum and calcium salts affects the phosphorus and silicon removal efficiency, and develops a method for deep phosphorus and silicon removal by adding aluminum salt first and then calcium salt; the optimal phosphorus and silicon removal efficiency is determined by adjusting the timing, amount, and reaction conditions of adding aluminum and calcium salts; and the problem of difficult precipitation and filtration of single aluminum salts is solved through the synergistic effect between aluminum, calcium, and silicon.

[0045] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for removing phosphorus and silicon from sodium tungstate solution, characterized in that, Includes the following steps: S1. Obtain a sodium tungstate solution containing phosphorus and silicon, adjust the pH of the sodium tungstate solution to 9-10, control the temperature to 25-60℃, add a saturated aluminum salt solution to the sodium tungstate solution, and perform a first stirring to obtain a mixed solution. The ratio of the mass of aluminum in the saturated aluminum salt solution to the total mass of silicon and phosphorus in the sodium tungstate solution is (1.1-1.8):

2. S2. Adjust the pH of the mixed solution to 13-14, control the temperature to 80-90℃, add calcium salt to the mixed solution, stir for the second time, let it stand, and then filter to obtain sodium tungstate purified solution and filter residue. The mass ratio of the calcium salt (calculated as CaO) to the aluminum salt (calculated as Al2O3) is 1:(1-2).

2. The method for removing phosphorus and silicon from sodium tungstate solution according to claim 1, characterized in that, The sodium tungstate solution has a concentration of 50~200 g / L (calculated as WO3), and the phosphorus content and silicon content in the sodium tungstate solution are ≤1 g / L and ≤1 g / L, respectively.

3. The method for removing phosphorus and silicon from sodium tungstate solution according to claim 1, characterized in that, The aluminum salt includes aluminum sulfate, and the calcium salt includes calcium carbonate.

4. The method for removing phosphorus and silicon from sodium tungstate solution according to claim 1, characterized in that, In step S1, the first stirring rate is 200~400 r / min, and the time is 1~2 h.

5. The method for removing phosphorus and silicon from sodium tungstate solution according to claim 1, characterized in that, In step S2, sodium hydroxide is used to adjust the pH of the mixed solution to 13-14.

6. The method for removing phosphorus and silicon from sodium tungstate solution according to claim 1, characterized in that, In step S2, the second stirring rate is 200~400 r / min, and the time is 1~2 h.

7. The method for removing phosphorus and silicon from sodium tungstate solution according to claim 1, characterized in that, In step S2, the settling time is 1 to 2 hours.

8. The method for removing phosphorus and silicon from sodium tungstate solution according to claim 1, characterized in that, In step S2, a Buchner funnel with an outer diameter of 200 mm, an inner diameter of 190 mm, and a volume of 5 L, and double-ring filter paper with a diameter of 18 cm are used for filtration. The filtration time for each liter of sodium tungstate purified solution is ≤2 min.

9. The method for removing phosphorus and silicon from sodium tungstate solution according to claim 1, characterized in that, The filter residue includes calcium silicate phosphate and calcium aluminosilicate.

10. The method for removing phosphorus and silicon from sodium tungstate solution according to claim 1, characterized in that, The sodium tungstate purification solution contains ≤0.05g / L phosphorus and ≤0.05g / L silicon.