Continuous crystallization method of aluminum fluoride

Abstract

The invention provides a continuous crystallization method of aluminum fluoride, in the continuous crystallization method, a multistage continuous crystallization kettle is adopted, the yield of an obtained crystal product is improved, the particle size is increased, the filtering performance is improved, the fluidity of the obtained product is ensured, and the continuous crystallization method is suitable for industrial production. Therefore, the content of impurities entrained by products is reduced. According to the invention, an existing aluminum fluoride batch-type reaction crystallization technology and a continuous crystallization equipment technology are creatively combined and transformed into an aluminum fluoride continuous reaction crystallization process technology, so that the aluminum fluoride crystallization efficiency and the production capacity are improved, the product performance is improved, and the energy consumption is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of crystallization technology and relates to a continuous crystallization method of aluminum fluoride. Background Art

[0002] Aluminum fluoride (AlF3), CAS number 7784-18-1. Aluminum fluoride is an inorganic substance, colorless or white crystals, almost insoluble in water, relatively stable in nature, and can be hydrolyzed when heated. It is mainly used as a metal smelting agent to smelt aluminum. In addition, aluminum fluoride is also widely used in the market of glass manufacturing, abrasives and grinding tools, and fluorinating agents.

[0003] Crystallization is one of the most effective methods to produce pure solids. During crystallization, the solute in the solution is separated due to the difference in solubility between it and the impurities. The crystallization process also directly affects the crystal form and purity of the product. At present, the traditional crystallization technology of aluminum fluoride adopts the common wet process, and then crystallizes at a constant temperature to obtain a hydrated aluminum fluoride product, which is then dried and dehydrated to obtain the finished aluminum fluoride product.

[0004] At present, the main crystallization process of aluminum fluoride is constant temperature crystallization. This process generally adopts an intermittent method, that is, a one-time rapid feeding. However, in the actual operation process, there are mainly the following problems: (1) Production efficiency: the process conditions are not stable and the crystal sedimentation is serious, resulting in poor filtration performance of the reaction crystallization process and low final product yield; (2) Scaling: the outlet of the crystallization device is seriously blocked and the labor intensity is high; (3) Crystallization time: the residence time is short and the control of the crystallization endpoint is unstable.

[0005] Based on the above technical status, the inventors believe that it is imperative to develop a reasonable and scientific continuous reaction crystallization technology suitable for aluminum fluoride based on the existing industrial crystallization production equipment, and to seek a continuous reaction crystallization technology for aluminum fluoride with low impurity content, large particle size, low energy consumption, high production efficiency, stable product quality, simple process and low production cost. Summary of the invention

[0006] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a continuous reaction crystallization process for aluminum fluoride, which realizes continuous crystallization, improves the yield of crystal products, increases particle size, improves filtration performance, and reduces crystallization process time and scaling. The washing method in the crystallization process is reduced to reduce the solvent residue of the product, while ensuring the fluidity of the final aluminum fluoride product and reducing impurities entrained in the product.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] One of the purposes of the present invention is to provide a continuous reaction crystallization process of aluminum fluoride, the continuous crystallization process comprising the following steps:

[0010] (1) adding aluminum hydroxide solid to a fluosilicic acid solution at a temperature of 85 to 95° C. under stirring, controlling the aluminum hydroxide solid to be in excess of 3 to 5 wt %, and reacting for 15 to 20 minutes to intercept the byproduct silicon dioxide, and the intercepted feed liquid enters the first stage crystallization kettle, wherein during the temperature rise and fall process, the liquid level change is maintained within 10% above or below the equilibrium liquid level;

[0011] (2) controlling the temperature of the first-stage crystallization kettle to be 90-95° C., adding aluminum fluoride seed crystals under stirring conditions so that the seed crystals are evenly dispersed in the first-stage crystallization kettle, and when the volume of the slurry reaches more than 80% of the volume of the first-stage crystallization kettle, the slurry is discharged from the first-stage crystallization kettle and enters the second-stage crystallization kettle;

[0012] (3) controlling the temperature of the second-stage crystallization kettle to 90-95° C., under stirring conditions, allowing the generated aluminum fluoride crystals to grow stably, and the slurry is discharged from the second-stage crystallization kettle and enters the solid-liquid separation system, wherein during the stable growth of the crystals, the liquid level change is maintained within 10% above or below the equilibrium liquid level;

[0013] (4) In the solid-liquid separation system, the separated solid is discharged from the solid-liquid separation system and the mother liquid is recycled.

[0014] Preferably, the stirring rate in step (1) is 200-350 rpm, for example, 200 rpm, 220 rpm, 250 rpm, 270 rpm, 300 rpm, 320 rpm, 350 rpm, etc.

[0015] Preferably, the concentration of the fluorosilicic acid solution in step (1) is 10-20wt%, for example, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, etc.

[0016] Preferably, the interception method in step (1) is filtration;

[0017] Preferably, in the intercepted liquid of step (1), the content of fluorosilicic acid impurities is 0.5-1wt% (e.g., 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%), the content of the maximum single impurity is 2-3wt% (e.g., 2wt%, 2.2wt%, 2.5wt%, 2.8wt%, 3wt%, etc.), and the content of total impurities is 8-9wt% (e.g., 8wt%, 8.2wt%, 8.5wt%, 8.7wt%, 9wt%, etc.);

[0018] Preferably, the added volume of the retained liquid in step (1) is 50-70% (e.g., 50%, 55%, 60%, 65%, 70%, etc.) of the volume of the first-stage crystallization kettle.

[0019] Preferably, the average particle size of the seed crystals in step (2) is 0.10-0.15 mm (e.g., 0.1 mm, 0.11 mm, 0.12 mm, 0.13 mm, 0.14 mm, 0.15 mm, etc.);

[0020] Preferably, the uniform dispersion time in step (2) is 2-4 h (e.g., 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc.);

[0021] Preferably, the stirring rate in step (2) is 100-200 rpm (e.g., 100 rpm, 120 rpm, 150 rpm, 180 rpm, 200 rpm, etc.).

[0022] Preferably, when the amount of the retained liquid added is 15-20 g / L (e.g., 15 g / mL, 16 g / mL, 17 g / mL, 18 g / mL, 19 g / mL, 20 g / mL, etc.), the amount of the seed added in step (2) is 2-6 g / L (e.g., 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, etc.).

[0023] Preferably, the stirring rate in step (3) is 100-150 rpm (e.g., 100 rpm, 110 rpm, 120 rpm, 130 rpm, 140 rpm, 150 rpm, etc.);

[0024] Preferably, the stable growth time of the crystal in step (3) is 2-4 h (e.g., 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc.).

[0025] Preferably, the mother liquor in step (4) is separated by evaporation and then circulated in the first-stage crystallization kettle to perform a multi-stage continuous crystallization process together with the continuously replenished aluminum fluoride crystallization mother liquor;

[0026] Preferably, the solid-liquid separation in step (4) is performed by vacuum filtration;

[0027] Preferably, the step (4) further comprises washing and drying the solid obtained after solid-liquid separation in sequence.

[0028] Preferably, the preparation method further comprises post-processing the solid obtained by solid-liquid separation;

[0029] Preferably, the post-treatment comprises: adding a saturated aqueous solution of aluminum fluoride to the solid obtained after solid-liquid separation for soaking and washing;

[0030] Preferably, based on the addition amount of 60 g of the dry solid obtained after solid-liquid separation, the addition amount of the saturated aluminum fluoride saturated aqueous solution is 45-60 g (eg, 45 g, 50 g, 55 g, 60 g, etc.).

[0031] The second object of the present invention is to provide a continuous crystallization process as described in the first object to obtain aluminum fluoride.

[0032] Preferably, the aluminum fluoride product yield is greater than 70%, and the bulk density is greater than 0.8 g / cm 3 .

[0033] Preferably, the average particle size of the aluminum fluoride is 0.10-0.15 mm.

[0034] The third object of the present invention is to provide an application of aluminum fluoride as described in the second object in metal smelting.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The method of the invention provides a process for continuously and stably producing aluminum fluoride crystals with high production efficiency, low impurity content, large particle size and easy filtration, and is not prone to scaling during the preparation process.

[0037] The method of the present invention clarifies the reaction time, constant temperature time, final crystallization temperature, seed addition amount, particle size and weight in the reaction and constant temperature crystallization, and improves the bulk density of the product to be greater than 0.8 g / cm 3 .

[0038] The method of the invention clarifies the post-processing method of the crystal product, so that the yield of aluminum fluoride after washing is greater than 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a scanning electron microscope image of the aluminum fluoride crystal product obtained by continuous crystallization in Example 1.

[0040] Figure 2 It is a continuous process flow chart constructed in Example 1.

[0041] Figure 3 This is the morphology of the aluminum fluoride crystal product obtained by continuous crystallization in Example 1.

[0042] Figure 4 This is the morphology of the aluminum fluoride crystal product produced by the conventional intermittent crystallization process in comparative example 1. DETAILED DESCRIPTION

[0043] It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those generally understood by those of ordinary skill in the art to which the present invention belongs. The technical scheme of the present invention is further illustrated below by specific embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0044] Example 1

[0045] This embodiment provides a continuous reaction crystallization process of aluminum fluoride, such as Figure 2 As shown, the following steps are included:

[0046] (1) Under the action of a stirring rate of 300 rpm, a fluosilicic acid raw material liquid with a concentration of 15 wt% and a volume of 50% of the volume of the first-stage crystallization kettle is introduced into a neutralization reaction tank, heated to 85° C. and kept warm for 20 min, and aluminum hydroxide solid powder is added to the reaction tank. After reacting for 15 min, the reaction liquid is discharged from the reaction tank and enters the first-stage crystallization kettle. During the heating and cooling process, the liquid level change is maintained within 10% above and below the equilibrium liquid level;

[0047] (2) controlling the temperature of the first-stage crystallization kettle to 90° C., adding aluminum fluoride seed crystals with a particle size of 0.01-0.15 mm (the amount of seed crystals added is 6 g, based on the amount of 20 g added per liter of aluminum fluoride crystallization mother liquor) at a stirring rate of 150 rpm, so that the seed crystals are uniformly dispersed in the first-stage crystallization kettle for 2 h, and when the volume of the slurry reaches more than 80% of the volume of the second-stage crystallization kettle, the slurry is discharged from the first-stage crystallization kettle and enters the second-stage crystallization kettle;

[0048] (3) controlling the temperature of the second-stage crystallization kettle to 90° C. and stirring at a rate of 100 rpm to allow aluminum fluoride crystals to grow stably for 4 hours, and the slurry is discharged from the second-stage crystallization kettle and enters the solid-liquid separation system, wherein during the stable growth of the crystals, the liquid level change is maintained within 10% above or below the equilibrium liquid level;

[0049] (4) In the centrifugal system, the separated solid is discharged from the centrifugal system and added with saturated aluminum fluoride crystallization mother liquor for washing (the amount of the dry solid added after centrifugal separation is 60 g, and the amount of the saturated aluminum fluoride saturated aqueous solution added is 50 g). After evaporation and separation, it enters the first-stage crystallization kettle for circulation, and performs a multi-stage continuous crystallization process together with the continuously replenished aluminum fluoride mother liquor.

[0050] The product obtained in Example 1 was tested and analyzed as follows:

[0051] (1) Particle size test (test equipment: Malvern Laser Particle Sizer Mastersizer 3000): Figure 1 The scanning electron microscope image of the product was obtained for this example. Figure 1 It can be seen that the average particle size of the product is 0.12 mm;

[0052] (2) Bulk density calculation (test equipment: measuring cylinder): Place the solid product without obvious agglomeration naturally in the measuring cylinder, and divide the total mass by the total volume to obtain the bulk density of the product, which is 0.852 g / cm 3 ;

[0053] (3) Yield analysis: According to

[0054]

[0055] The actual yield was calculated by the formula, and it can be known that the final yield of the product in this example is as high as 83%.

[0056] In the preparation method of the present application, the overall process takes 6.5 hours, and scaling problems will not occur during the preparation process.

[0057] Example 2

[0058] This embodiment provides a continuous crystallization process of aluminum fluoride, comprising the following steps:

[0059] (1) Under the action of a stirring rate of 250 rpm, a fluorosilicic acid raw material liquid with a concentration of 15 wt% and a volume of 50% of the volume of the first-stage crystallization kettle is introduced into a neutralization reaction tank, heated to 95° C. and kept warm for 30 min, and aluminum hydroxide solid powder is added to the reaction tank. After reacting for 15 min, the reaction liquid is discharged from the reaction tank and enters the first-stage crystallization kettle. During the heating and cooling process, the liquid level change is maintained within 10% above and below the equilibrium liquid level;

[0060] (2) Controlling the temperature of the first-stage crystallization kettle to 95° C., adding aluminum fluoride seed crystals with a particle size of 0.01-0.15 mm (the amount of seed crystals added is 5 g, based on the amount of 20 g added per liter of aluminum fluoride crystallization mother liquor) at a stirring rate of 150 rpm, so that the seed crystals are uniformly dispersed in the second-stage crystallization kettle for 3 h. When the volume of the slurry reaches more than 80% of the volume of the second-stage crystallization kettle, the slurry is discharged from the first-stage crystallization kettle and enters the second-stage crystallization kettle;

[0061] (3) controlling the temperature of the second-stage crystallization kettle to 95° C. and stirring at a rate of 150 rpm to allow aluminum fluoride crystals to grow stably for 4 hours, and the slurry is discharged from the second-stage crystallization kettle and enters the solid-liquid separation system, wherein during the stable growth of the crystals, the liquid level change is maintained within 10% above or below the equilibrium liquid level;

[0062] (4) In the centrifugal system, the separated solid is discharged from the centrifugal system and added with saturated aluminum fluoride crystallization mother liquor for washing (the amount of the dry solid added after centrifugal separation is 60 g, and the amount of the saturated aluminum fluoride saturated aqueous solution added is 50 g). After evaporation and separation, it enters the first-stage crystallization kettle for circulation, and performs a multi-stage continuous crystallization process together with the continuously replenished aluminum fluoride crystallization mother liquor.

[0063] The product obtained in this example was tested using the same test method as in Example 1. It was found that the average particle size of the product was 0.12 mm and the bulk density of the product was 0.890 g / cm 3 The final yield of the product can reach 80%.

[0064] In the preparation method of the present application, the overall process takes 7.8 hours, and scaling problems will not occur during the preparation process.

[0065] Example 3

[0066] This embodiment provides a continuous reaction crystallization process of aluminum fluoride, comprising the following steps:

[0067] (1) Under the action of a stirring rate of 350 rpm, a fluosilicic acid raw material liquid with a concentration of 15 wt% and a volume of 50% of the volume of the first-stage crystallization kettle is introduced into a neutralization reaction tank, heated to 95° C. and kept warm for 40 min, and aluminum hydroxide solid powder is added to the reaction tank. After reacting for 15 min, the reaction liquid is discharged from the reaction tank and enters the first-stage crystallization kettle. During the heating and cooling process, the liquid level change is maintained within 10% above and below the equilibrium liquid level;

[0068] (2) Controlling the temperature of the first-stage crystallization kettle to 95° C., adding aluminum fluoride seeds with a particle size of 0.01-0.15 mm (20 g per liter of aluminum fluoride crystallization mother liquor, and 2 g of seeds) at a stirring rate of 150 rpm, so that the seeds are evenly dispersed in the second-stage crystallization kettle for 4 h, and when the volume of the slurry reaches more than 80% of the volume of the second-stage crystallization kettle, the slurry is discharged from the first-stage crystallization kettle and enters the second-stage crystallization kettle;

[0069] (3) controlling the temperature of the second-stage crystallization kettle to 95° C. and stirring at a rate of 100 rpm to allow aluminum fluoride crystals to grow stably for 4 hours, and the slurry is discharged from the second-stage crystallization kettle and enters the solid-liquid separation system, wherein during the stable growth of the crystals, the liquid level change is maintained within 10% above or below the equilibrium liquid level;

[0070] (4) In the centrifugal system, the separated solid is discharged from the centrifugal system and added with saturated aluminum fluoride crystallization mother liquor for washing (the amount of the dry solid added after centrifugal separation is 60 g, and the amount of the saturated aluminum fluoride saturated aqueous solution added is 50 g). After evaporation and separation, it enters the first-stage crystallization kettle for circulation, and performs a multi-stage continuous crystallization process together with the continuously replenished aluminum fluoride mother liquor.

[0071] The product obtained in this example was tested using the same test method as in Example 1. It was found that the average particle size of the product was 0.15 mm and the bulk density of the product was 0.924 g / cm 3 , the final yield of the product can reach 88%.

[0072] In the preparation method of the present application, the overall process takes 9 hours, and scaling problems will not occur during the preparation process.

[0073] Comparative Example 1

[0074] One-step constant temperature reaction crystallization is adopted, which is a conventional batch process without adding seed crystals.

[0075] Fluorosilicic acid with a concentration of 15wt% is introduced into the first-stage crystallization kettle at a temperature of 70-90°C. The crystallization kettle is filled with high-temperature water and kept warm for 1 hour. Then, aluminum hydroxide solid powder is added into it at a stoichiometric ratio to react. The filtered aluminum fluoride crystallization mother liquor is placed in another crystallization kettle. The crystal temperature is guaranteed to grow for 5 hours at 90°C. The product after belt filtration is then washed twice and calcined in two stages to obtain the final product. The scaling phenomenon inside the mother liquor is serious. Including the labor intensity, the entire process time is about 12 hours, which is a long time. The final crystal product has a small particle size, a high impurity content, a low production efficiency, uneven product particles, and a low bulk density of about 0.629g / cm 3 , the final yield of the product is only 12%.

[0076] The particle size, bulk density and yield of the aluminum fluoride products in Example 1 and Comparative Example 1 are shown in the table below.

[0077] Table 1 Comparison of aluminum fluoride crystallization processes

[0078]

[0079] Figure 3 This is the morphology of the aluminum fluoride crystal product obtained by continuous crystallization in Example 1. Figure 4 The morphology of the aluminum fluoride crystal product obtained by conventional intermittent crystallization process in Comparative Example 1 is shown in FIG. Figure 3 and Figure 4By comparison, it can be seen that the average particle size of aluminum fluoride crystals produced by the traditional intermittent crystallization process is reduced by 50%, and explosive nucleation occurs, and product scaling and wall adhesion occur, and the final yield is reduced to 12%.

[0080] Comparative Example 2

[0081] A two-step crystallization method is adopted, with a neutralization tank and a first-stage crystallization kettle, but no second-stage crystallization kettle, to simulate a single-stage continuous reaction crystallization process.

[0082] (1) Under the action of a stirring rate of 300 rpm, a fluosilicic acid raw material liquid with a concentration of 15 wt% and a volume of 50% of the volume of the first-stage crystallization kettle is introduced into a neutralization reaction tank, heated to 85° C. and kept warm for 20 min, and aluminum hydroxide solid powder is added to the reaction tank. After reacting for 15 min, the reaction liquid is discharged from the reaction tank and enters the first-stage crystallization kettle. During the heating and cooling process, the liquid level change is maintained within 10% above and below the equilibrium liquid level;

[0083] (2) The temperature of the first-stage crystallization kettle was controlled at 90°C. Under the stirring rate of 150 rpm, aluminum fluoride seeds with a particle size of 0.01-0.15 mm were added (the amount added was 20 g per liter of aluminum fluoride crystallization mother liquor, and the amount of seed added was 6 g), so that the seeds were evenly dispersed in the first-stage crystallization kettle for 4 h, and the volume of the slurry reached more than 80% of the volume of the second-stage crystallization kettle.

[0084] (4) In the centrifugal system, the separated solid is discharged from the centrifugal system and added with saturated aluminum fluoride crystallization mother liquor for washing (the amount of the dry solid added after centrifugal separation is 60 g, and the amount of the saturated aluminum fluoride saturated aqueous solution added is 50 g). After evaporation and separation, it enters the first-stage crystallization kettle for circulation, and performs a multi-stage continuous crystallization process together with the continuously replenished aluminum fluoride crystallization mother liquor.

[0085] The product obtained in this comparative example was tested using the same test method as in Example 1. It was found that the average particle size of the product was 0.11 mm and the bulk density of the product was 0.713 g / cm 3 , the final yield of the product was 60%.

[0086] In the preparation method of the present application, the overall process takes 11.5 hours, and the problem of explosive nucleation occurs during the preparation process.

[0087] By comparing Comparative Example 2 with Example 1, it can be seen that the stable growth time of crystals without the second-stage crystallization kettle is reduced, and after adding the seed crystal, the supersaturation cannot be used for crystal growth, explosive nucleation occurs, the average particle size is reduced to 0.67 mm, and the yield is reduced to 60%.

[0088] Comparative Example 3

[0089] A two-step crystallization method is adopted, with a neutralization tank and a second-stage crystallization kettle, but without a first-stage crystallization kettle, to simulate a single-stage continuous reaction crystallization process.

[0090] (1) Under the action of a stirring rate of 300 rpm, a fluosilicic acid raw material liquid with a concentration of 15 wt% and a volume of 50% of the volume of the first-stage crystallization kettle is introduced into a neutralization reaction tank, heated to 85° C. and kept warm for 20 min, and aluminum hydroxide solid powder is added to the reaction tank. After reacting for 15 min, the reaction liquid is discharged from the reaction tank and enters the first-stage crystallization kettle. During the heating and cooling process, the liquid level change is maintained within 10% above and below the equilibrium liquid level;

[0091] (2) controlling the temperature of the second-stage crystallization kettle to 90° C. and stirring at a rate of 100 rpm to allow aluminum fluoride crystals to grow stably for 4 hours, and the slurry is discharged from the second-stage crystallization kettle and enters the solid-liquid separation system, wherein during the stable growth of the crystals, the liquid level change is maintained within 10% above or below the equilibrium liquid level;

[0092] (4) In the centrifugal system, the separated solid is discharged from the centrifugal system and added with saturated aluminum fluoride crystallization mother liquor for washing (the amount of the dry solid added after centrifugal separation is 60 g, and the amount of the saturated aluminum fluoride saturated aqueous solution added is 50 g). After evaporation and separation, it enters the first-stage crystallization kettle for circulation, and performs a multi-stage continuous crystallization process together with the continuously replenished aluminum fluoride mother liquor.

[0093] The product obtained in this comparative example was tested using the same test method as in Example 1. It was found that the average particle size of the product was 0.082 mm and the bulk density of the product was 0.750 g / cm 3 , the final yield of the product was 30%.

[0094] In the preparation method of the present application, the overall process takes 4.5 hours, and scaling problems occur during the preparation process.

[0095] By comparing Comparative Example 3 with Example 1, it can be seen that there is no first-stage crystallization kettle, there is no seed addition process, and the total crystallization time is shortened, scaling occurs in the crystallization kettle, the particle size of the crystal product is uneven, and the product bulk density is reduced, resulting in the final yield of the product being reduced to 30%.

[0096] Comparative Example 4

[0097] The only difference from Example 1 is that 0.042-0.084 mm aluminum fluoride seed crystals obtained by recrystallization are added, and the rest of the preparation method is the same as that of Example 1.

[0098] The product obtained in this comparative example was tested using the same test method as in Example 1. It can be seen that the average particle size of the product is in the range of 0.070-0.090 mm, and the bulk density of the product is 0.789 g / cm 3 , the final yield of the product was 80.03%.

[0099] In the preparation method of the present application, the overall process takes 6.5 hours, and no problems of explosive nucleation and scaling occur during the preparation process.

[0100] By comparing Comparative Example 4 with Example 1, it can be seen that after adding the 0.042-0.084 mm aluminum fluoride seed crystals obtained by recrystallization, the product crystals did not show scaling phenomenon, and finally a product with a particle size of 0.070-0.090 mm was obtained, the particle size was reduced, and the yield did not change much to 80.03%.

[0101] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A continuous crystallization method of aluminum fluoride, characterized in that: The continuous crystallization method of aluminum fluoride comprises the following steps: (1) Under stirring, aluminum hydroxide solid is added to the fluosilicic acid solution at a temperature of 85-95°C, and the excess of aluminum hydroxide solid is controlled to be 3-5wt%. After reacting for 15-20 minutes, the by-product silicon dioxide is intercepted, and the intercepted feed liquid enters the first-stage crystallization kettle. During the temperature rise and fall process, the liquid level change is maintained within 10% above and below the equilibrium liquid level; (2) Controlling the temperature of the first-stage crystallization kettle to 90-95°C, adding aluminum fluoride seed crystals under stirring conditions so that the seed crystals are evenly dispersed in the first-stage crystallization kettle, and when the volume of the slurry reaches more than 80% of the volume of the first-stage crystallization kettle, the slurry is discharged from the first-stage crystallization kettle and enters the second-stage crystallization kettle; (3) controlling the temperature of the second-stage crystallization kettle to 90-95°C, and allowing the generated aluminum fluoride crystals to grow stably under stirring conditions, and the slurry is discharged from the second-stage crystallization kettle and enters the solid-liquid separation system, wherein during the stable growth of the crystals, the liquid level change is maintained within 10% above or below the equilibrium liquid level; (4) In the solid-liquid separation system, the separated solids are discharged from the solid-liquid separation system and the mother liquor is recycled.

2. The continuous crystallization method of aluminum fluoride according to claim 1, characterized in that: The stirring rate in step (1) is 200-350 rpm; The concentration of the fluorosilicic acid solution in step (1) is 10-20wt%.

3. The continuous crystallization method of aluminum fluoride according to claim 1, characterized in that: The interception method in step (1) is filtration; In the intercepted liquid of step (1), the content of fluorosilicic acid impurities is 0.5-1wt%, the content of the maximum single impurity is 2-3wt%, and the content of total impurities is 8-9wt%; The added volume of the intercepted liquid in step (1) is 50-70% of the volume of the first-stage crystallization kettle.

4. The continuous crystallization method of aluminum fluoride according to claim 1, characterized in that: The average particle size of the aluminum fluoride seed crystals in step (2) is 0.01-0.15 mm; The uniform dispersion time in step (2) is 2-4 hours; The stirring rate in step (2) is 100-200 rpm; When the amount of the retained liquid added is 15-20 g / L, the amount of the seed added in step (2) is 2-6 g / L.

5. The continuous crystallization method of aluminum fluoride according to claim 1, characterized in that: The stirring rate in step (3) is 100-150 rpm; The stable growth time of the crystal in step (3) is 2-4 h.

6. The continuous crystallization method of aluminum fluoride according to claim 1, characterized in that: The mother liquor in step (4) is separated by evaporation and then circulated in the first-stage crystallization kettle to undergo a multi-stage continuous crystallization process together with the continuously replenished aluminum fluoride crystallization mother liquor; The solid-liquid separation method in step (4) is vacuum filtration.

7. The continuous crystallization method of aluminum fluoride according to claim 6, characterized in that: The preparation method further comprises post-processing the solid obtained by solid-liquid separation; The post-treatment comprises: adding a saturated aqueous solution of aluminum fluoride to the solid obtained after solid-liquid separation for soaking and washing; Based on the addition amount of 60 g of the dry solid obtained after solid-liquid separation, the addition amount of the saturated aluminum fluoride saturated aqueous solution is 45-60 g.

8. Aluminum fluoride product is obtained by crystallizing the aluminum fluoride continuous crystallization method according to any one of claims 1 to 7.

9. The aluminum fluoride crystal according to claim 8, characterized in that: The aluminum fluoride product yield is greater than 70%, and the product bulk density is greater than 0.8 g / cm 3 ; The average particle size of the aluminum fluoride is 100-150 μm.

10. Use of the aluminum fluoride according to claim 8 in smelting non-ferrous metals.

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