Preparation method of cryolite

Abstract

The invention discloses a cryolite preparation method, which comprises: mixing an inorganic aluminum salt and an organic acid sodium salt, and dissolving in deionized water to form a clear solution A; adding a fluorination reagent into the deionized water, and stirring and dissolving to obtain a fluorination solution B; adding the fluorinated solution B into the clarified solution A, and adjusting the pH value to obtain a mixed solution; transferring the mixed solution into a reaction kettle for hydrothermal reaction; and after the hydrothermal reaction, naturally cooling the reaction liquid to room temperature, carrying out reduced pressure suction filtration to obtain a precipitate, washing the precipitate, carrying out centrifugal separation, and drying to obtain the cryolite. The cryolite synthesis method is simple, operation conditions are easy to control, the structure and morphology of cryolite are easy to control, cryolite microspheres with novel structures can be synthesized, and the size, wall thickness and the like of the microspheres can be regulated and controlled.

Description

Technical Field

[0001] The invention relates to the field of preparation of inorganic compounds, in particular to a method for preparing cryolite. Background Art

[0002] More than 90% of artificial cryolite is used as flux for aluminum electrolysis. It is also used in enamel opacifier, welding flux, casting deoxidizer, pesticide insecticide, chain olefin composite catalyst, rubber, wear-resistant filler for grinding wheels, glass sunscreen and cosmetic additives.

[0003] Traditional artificial cryolite is produced by wet methods, the main methods include hydrofluoric acid method (dry and wet method), fluosilicic acid method, carbonation method, aluminum industry recycling method, etc. The cryolite obtained by these methods has a larger particle size (the particle size is generally around 15μm), and the microstructure is a regular octahedron or disordered polyhedron or irregular grain agglomeration. The apparent particle size of cryolite sold on the market is generally 1 to 10mm. At present, there is little consideration on how to produce cryolite products with new structures such as smaller particle size, high dispersion, and regular structure, which limits the application of cryolite in other aspects. In the fields of chain olefin complexes, pesticides, insecticides, and cosmetics additives, fine-grained cryolite is required, and existing products can no longer meet the requirements.

[0004] Chinese patent CN108975369A discloses a production process of pure cryolite without wastewater discharge, including the following steps: 1) pulping; 2) reaction; 3) centrifugal separation; 4) purification; 5) precipitation; 6) alkalization; 7) wastewater treatment. Although this process can produce pure cryolite, the preparation process is long and still needs to be operated under alkaline conditions, which consumes a large amount of alkali and is costly. If cryolite with a high molecular weight ratio can be synthesized under acidic conditions, it will not only open up a new path for the preparation of cryolite, but also can widely use waste liquid containing aluminum and fluorine-containing waste acid to prepare cryolite.

[0005] Chinese patent CN101264918A discloses a method for producing ultrafine cryolite, which uses Bayer process concentrate, caustic soda and hydrofluoric acid as raw materials to produce cryolite. Although the particle size can be controlled at 1 to 5 μm, the particle morphology is irregular and exists in the form of polyhedral grains of various sizes. In addition, the product purity is not high and contains some impurities such as AlF3, silicon oxide, and iron oxide. Summary of the invention

[0006] The present invention aims to overcome the above-mentioned problems existing in the cryolite preparation method in the prior art and provides a method for preparing cryolite. Through the hydrothermal reaction of inorganic aluminum salt, organic acid sodium salt and fluorination reagent and controlling the pH of the reaction solution, the morphology, particle size and wall thickness of cryolite can be effectively controlled. The method has the characteristics of simple process, easy control, small particle size, novel structure and low production cost.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing cryolite comprises the following steps: (1) dissolving an inorganic aluminum salt and an organic acid sodium salt in deionized water to form a clear solution A; (2) adding a fluorination agent into deionized water, stirring and dissolving to obtain a fluorination liquid B; (3) adding fluorinated liquid B to the clear solution A and adjusting the pH to obtain a mixed solution; (4) transferring the mixed solution to a reactor for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution is naturally cooled to room temperature, and a precipitate is obtained by filtration under reduced pressure. The precipitate is washed, centrifuged, and then dried to obtain cryolite.

[0008] The present invention adopts a hydrothermal synthesis method to prepare cryolite, which does not require stirring, is easy to operate and control, and has mild reaction conditions. In addition, the present invention can regulate the structure of cryolite by adjusting the organic acid sodium salt, the fluoridation agent and the pH value of the mixed solution: the organic acid sodium salt, as a morphology regulator, can regulate the growth rate of each crystal face, control the wall thickness, size and surface of the cryolite product, and play an important role in the morphology of the cryolite; the fluoridation agent can effectively adjust the crystal phase composition and structural morphology of the cryolite; and regulating the pH value can regulate the morphology and structure of the cryolite. At the same time, the present invention can also obtain cryolite products of different sizes, wall thicknesses and dispersities by adjusting parameters such as material molar ratio, pH value, reaction temperature, reaction time, etc. The cryolite product prepared by the method of the present invention has a unique structure, high purity, no agglomeration (good dispersibility), and uniform particle size (good regularity), and can be used in the fields of chain olefin complexes, pesticides, insecticides, and cosmetic additives, which can meet market demand and have good economic and social benefits.

[0009] Preferably, in step (1), the molar ratio of the inorganic aluminum salt to the organic acid sodium salt is 1:2 to 1:10.

[0010] Preferably, the inorganic aluminum salt is one of Al(NO3)3·9H2O, Al2(SO4)3·18H2O, and Al2(SiO3)3·4H2O.

[0011] Preferably, the organic acid sodium salt is one or two of sodium edetate, sodium acetate, sodium citrate, sodium benzoate, sodium malate and sodium gluconate.

[0012] Preferably, the fluorination agent in step (2) is one or two of NaBF4, HF, NaF, and NH4F.

[0013] Preferably, in the mixed solution of step (3), the molar ratio of aluminum ions to fluoride ions in the inorganic aluminum salt and the fluoriding agent is 1:0.5 to 1:4.

[0014] Preferably, in step (3), the pH value of the mixed solution is adjusted to 1-6 or 7-12 with an inorganic acid or base.

[0015] Preferably, the inorganic acid is one of nitric acid, sulfuric acid and hydrochloric acid; the alkali is one of ammonia water, sodium hydroxide and sodium ethoxide.

[0016] Preferably, the hydrothermal reaction temperature in step (4) is 100-200° C., and the reaction time is 12-24 h.

[0017] Preferably, the drying temperature in step (5) is 90 to 110° C., and the drying time is 12 to 24 hours.

[0018] Therefore, the present invention has the following beneficial effects: (1) The hydrothermal synthesis method is carried out in a kettle reaction, which does not require stirring, is easy to operate and control, and has mild reaction conditions; and cryolite products of different sizes, wall thicknesses, and dispersities can be obtained by adjusting parameters such as material type, dosage, pH value, reaction temperature, and reaction time; (2) The morphology and structure of cryolite can be controlled by adjusting the organic sodium salt, fluorination agent and pH value; (3) The method of the present invention is simple and has good effects, and has opened up a new way for the synthesis of ice crystals. The cryolite produced has a unique structure, high purity, no agglomeration, and uniform particle size; (4) The cryolite product produced by the method of the present invention can be used in the fields of olefin complexes, pesticides, insecticides and cosmetic additives, etc., can meet market demand, and has good economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the X-ray diffraction pattern of cryolite obtained in Example 1 of the present invention (standard PDF card comparison).

[0020] Figure 2 1 is a SEM image of cryolite obtained in Examples 2, 3, 4 and 7 of the present invention; Among them, (a) Example 3; (b) Example 2; (c) Example 4; (d) Example 7. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0022] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art.

[0023] Overall embodiment: A method for preparing cryolite comprises the following steps: (1) dissolving an inorganic aluminum salt and an organic acid sodium salt in deionized water to form a clear solution A; (2) adding a fluorination agent into deionized water, stirring and dissolving to obtain a fluorination liquid B; (3) adding fluorinated liquid B to the clear solution A and adjusting the pH to obtain a mixed solution; (4) transferring the mixed solution to a reactor for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution is naturally cooled to room temperature, and a precipitate is obtained by filtration under reduced pressure. The precipitate is washed, centrifuged, and then dried to obtain cryolite.

[0024] As a specific implementation manner, in step (1), the molar ratio of the inorganic aluminum salt to the organic acid sodium salt is 1:2 to 1:10.

[0025] As a specific implementation, the inorganic aluminum salt is one of Al(NO3)3·9H2O, Al2(SO4)3·18H2O, and Al2(SiO3)3·4H2O.

[0026] As a specific implementation, the organic acid sodium salt is one or two of sodium edetate, sodium acetate, sodium citrate, sodium benzoate, sodium malate, and sodium gluconate.

[0027] As a specific embodiment, the fluorination reagent in step (2) is one or two of NaBF4, HF, NaF, and NH4F.

[0028] As a specific implementation, in the mixed solution of step (3), the molar ratio of aluminum ions to fluoride ions in the inorganic aluminum salt and the fluoridation reagent is 1:0.5 to 1:4.

[0029] As a specific implementation, in step (3), the pH value of the mixed solution is adjusted to 1-6 or 7-12 with an inorganic acid or base.

[0030] As a specific implementation, the inorganic acid is one of nitric acid, sulfuric acid, and hydrochloric acid; the alkali is one of ammonia water, sodium hydroxide, and sodium ethoxide.

[0031] As a specific implementation, the hydrothermal reaction temperature in step (4) is 100-200° C., and the time is 12-24 hours.

[0032] As a specific implementation, the drying temperature in step (5) is 90 to 110° C., and the drying time is 12 to 24 hours.

[0033] Embodiment 1: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium citrate were weighed in a molar ratio of 1:2 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 1 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 180 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and the precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The cryolite was dried at 100°C for 12 h and was obtained as sample 1. Its X-ray diffraction pattern (standard PDF card reference) is shown in the figure. Figure 1 as shown in .

[0034] Embodiment 2: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium citrate were weighed in a molar ratio of 1:2 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 3 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 180 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and the precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The cryolite was obtained by drying at 100°C for 12 h, which was recorded as sample 2. Its SEM image is shown in FIG. Figure 1 As shown in (b), the morphology is solid microspheres.

[0035] Embodiment 3: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium citrate were weighed in a molar ratio of 1:2.5 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated liquid B to the clear solution A, and add ammonia water to adjust the pH value to 10 (measured with a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 180 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and the precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The cryolite was obtained by drying at 100°C for 12 h, which was recorded as sample 3. Its SEM image is shown in FIG. Figure 1 As shown in (a), the morphology is an irregular polyhedron.

[0036] Embodiment 4: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium ethylenediaminetetraacetate were weighed in a molar ratio of 1:4 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 3 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 180 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and the precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The cryolite was obtained by drying at 100°C for 12 h, which was recorded as sample 4. Its SEM image is shown in FIG. Figure 1 As shown in (c), the morphology is hollow microspheres.

[0037] Embodiment 5: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium ethylenediaminetetraacetate were weighed in a molar ratio of 1:5 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 3 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 180 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and a precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The precipitate was dried at 100°C for 12 h to obtain cryolite, which was recorded as sample 5.

[0038] Embodiment 6: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium ethylenediaminetetraacetate were weighed in a molar ratio of 1:8 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 3 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 180 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and a precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The precipitate was dried at 100°C for 12 h to obtain cryolite, which was recorded as sample 6.

[0039] Embodiment 7: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium citrate were weighed in a molar ratio of 1:5 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:1 and dissolving it in deionized water to form fluorinated liquid B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 3 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 180 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and the precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The cryolite was dried at 100°C for 12 h to obtain sample 7. Its SEM image is shown in FIG. Figure 1 As shown in (d), the morphology is bayberry-like microspheres.

[0040] Embodiment 8: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium ethylenediaminetetraacetate were weighed in a molar ratio of 1:5 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:4 and dissolving it in deionized water to form fluorinated liquid B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 3 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 180 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and a precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The precipitate was dried at 100°C for 12 h to obtain cryolite, which was recorded as sample 8.

[0041] Embodiment 9: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium citrate were weighed in a molar ratio of 1:5 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 3 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 100 °C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and a precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The precipitate was dried at 100°C for 12 h to obtain cryolite, which was recorded as sample 9.

[0042] Embodiment 10: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium citrate were weighed in a molar ratio of 1:5 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 3 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 140 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and a precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The precipitate was dried at 100°C for 12 h to obtain cryolite, which was recorded as sample 10.

[0043] Embodiment 11: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium citrate were weighed in a molar ratio of 1:5 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 3 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 200 °C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and a precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The precipitate was dried at 100°C for 12 h to obtain cryolite, which was recorded as sample 11.

[0044] Comparative Example 1: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium nitrate were weighed in a molar ratio of 1:5 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated solution B to the clear solution A, and add concentrated HNO3 to adjust the pH value to 3 (measured using a pH meter) to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 180 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and a precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The precipitate was dried at 100°C for 12 h to obtain cryolite, which was recorded as sample 12.

[0045] Comparative Example 2: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium ethylenediaminetetraacetate were weighed in a molar ratio of 1:5 and dissolved in deionized water to form a clear solution A; (2) After vigorous stirring for 30 min, add concentrated HNO3 to the clear solution A to adjust the pH value to 3 (measured using a pH meter); (3) After continuing to stir for 30 min, the clear solution A was transferred to a Teflon bottle in a stainless steel autoclave, sealed, and maintained at 180 °C for 24 h for hydrothermal reaction; (4) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and a precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The precipitate was dried at 100°C for 12 h to obtain cryolite, which was recorded as sample 13.

[0046] Comparative Example 3: A method for preparing cryolite comprises the following steps: (1) Al(NO3)3·9H2O and sodium ethylenediaminetetraacetate were weighed in a molar ratio of 1:5 and dissolved in deionized water to form a clear solution A; (2) weighing NaBF4 at an Al / F molar ratio of 1:2 and dissolving it in deionized water to form fluoride solution B; (3) After vigorous stirring for 30 min, slowly add fluorinated liquid B dropwise to the clear solution A to obtain a mixed solution; (4) After continuing to stir for 30 min, the mixture was transferred to a Teflon bottle in a stainless steel high-pressure reactor, sealed, and maintained at 180 ° C for 24 h for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution was naturally cooled to room temperature, and a precipitate was obtained by vacuum filtration. The precipitate was washed with deionized water and ethanol in sequence, and finally centrifuged and precipitated. The precipitate was dried at 100°C for 12 h to obtain cryolite, which was recorded as sample 14.

[0047] The size, morphology, purity and dispersibility of the cryolite obtained in the above examples and comparative examples were tested, and the results are shown in Table 1.

[0048] Table 1: Cryolite morphology and performance test results.

[0049] As can be seen from Table 1, in the process of synthesizing cryolite by hydrothermal method of the present invention, the morphology, size, wall thickness, dispersity, regularity and crystal phase of cryolite can be adjusted by adjusting different pH values, the amount of organic sodium salt and the amount of NaBF4 (Al / F molar ratio). In the acidic environment range of pH values ​​1 and 3, cryolite with solid microsphere morphology is mainly generated; while in the alkaline environment of pH=10, irregular polyhedral crystal particles are mainly generated. Organic sodium salt has an important influence on the structural morphology of cryolite. Organic sodium salt mainly plays a role in the structural assembly of cryolite microcrystals. In comparative example 1, since no organic sodium salt is added, irregular polyhedral cryolite is generated. In Examples 4-6, the addition of different amounts of organic sodium salt has a greater influence on the wall thickness and microsphere diameter of the hollow microspheres. The amount of NaBF4 (Al / F molar ratio) also has a significant effect on the cryolite sample. In comparative example 2, no fluorination agent (NaBF4) was added, and the result showed that no cryolite NaAlF6 was generated. When the amount of NaBF4 (Al / F molar ratio) was 1:1, the generated cryolite existed in the shape of bayberry balls, and the particle size was 3.5 μm. The method for synthesizing cryolite by this method is simple, the operating conditions are easy to control, the structural morphology of cryolite is easy to control, and cryolite microspheres with novel structures can be synthesized, and the size and wall thickness of the microspheres can be adjusted.

Claims

1. A method for preparing cryolite, comprising: Follow these steps: (1) dissolving an inorganic aluminum salt and an organic acid sodium salt in deionized water to form a clear solution A; (2) adding a fluorination agent into deionized water, stirring and dissolving to obtain a fluorination liquid B; (3) Adding fluorinated solution B to clear solution A and adjusting the pH to obtain a mixed solution; (4) transferring the mixed solution to a reactor for hydrothermal reaction; (5) After the hydrothermal reaction, the reaction solution is naturally cooled to room temperature, and the precipitate is obtained by filtration under reduced pressure. The precipitate is washed, centrifuged and dried to obtain cryolite.

2. The method for preparing cryolite according to claim 1, characterized in that: In step (1), the molar ratio of the inorganic aluminum salt to the organic acid sodium salt is 1:2 to 1:

10.

3. The method for preparing cryolite according to claim 1 or 2, characterized in that: The inorganic aluminum salt is one of Al(NO3)3·9H2O, Al2(SO4)3·18H2O and Al2(SiO3)3·4H2O.

4. The method for preparing cryolite according to claim 1 or 2, characterized in that: The organic acid sodium salt is one or two of sodium ethylenediaminetetraacetate, sodium acetate, sodium citrate, sodium benzoate, sodium malate and sodium gluconate.

5. The method for preparing cryolite according to claim 1, characterized in that: The fluorination reagent in step (2) is one or two of NaBF4, HF, NaF, and NH4F.

6. The method for preparing cryolite according to claim 1, characterized in that: In the mixed solution of step (3), the molar ratio of aluminum ions to fluoride ions in the inorganic aluminum salt and the fluoridation reagent is 1:0.5 to 1:

4.

7. The method for preparing cryolite according to claim 1 or 6, characterized in that: In step (3), the pH value of the mixed solution is adjusted to 1-6 or 7-12 with an inorganic acid or base.

8. The method for preparing cryolite according to claim 7, characterized in that: The inorganic acid is one of nitric acid, sulfuric acid and hydrochloric acid; the alkali is one of ammonia water, sodium hydroxide and sodium ethoxide.

9. The method for preparing cryolite according to claim 1, characterized in that: The hydrothermal reaction temperature in step (4) is 100-200°C and the time is 12-24h.

10. The method for preparing cryolite according to claim 1, characterized in that: The drying temperature in step (5) is 90-110°C and the drying time is 12-24 hours.

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