Preparation method of aluminum fluoride crystal

Abstract

The invention provides a preparation method of an aluminum fluoride crystal, the method optimizes a neutralization reaction, improves the filtering performance of silicon dioxide and reduces the loss of mother liquor, a constant-temperature crystallization method of adding a seed crystal is adopted in the crystallization process, and by optimizing the crystallization temperature, the seed crystal addition amount and the seed crystal particle size, the crystallization yield is improved. The problem that aluminum fluoride crystals scale on the wall of a crystallizer in the process at the present stage is solved, ellipsoidal aluminum fluoride particles with the uniform particle size and the particle size larger than 100 microns are obtained, the aluminum fluoride crystallization process technology is improved, the production capacity of the aluminum fluoride crystals is improved, the product performance is improved, and energy consumption is reduced.

Description

Technical Field

[0001] The invention belongs to the field of particle engineering and relates to a method for preparing aluminum fluoride crystals, in particular to a method for preparing large-particle aluminum fluoride crystals with high yield. Background Art

[0002] In modern industrial production, aluminum fluoride (AlF3) as an important inorganic compound has broad application prospects. Especially in the aluminum electrolysis industry, aluminum fluoride can effectively reduce the melting point of cryolite, thereby significantly improving the efficiency and economy of the aluminum electrolysis process. In addition, high-purity aluminum fluoride also has important applications in ceramics, glass, catalysts and other high-tech fields.

[0003] In the process of phosphate fertilizer production, fluorosilicic acid (H2SiF6) is generated in large quantities as a by-product. If fluorosilicic acid is not handled properly, it will pollute the environment, but it is also a fluorine-containing resource with high utilization value. Therefore, converting fluorosilicic acid into high value-added products, such as high-purity aluminum fluoride, can not only solve environmental problems but also create economic benefits. Aluminum hydroxide (Al(OH)3), as one of the raw materials for the production of aluminum fluoride, has a wide source and a mature preparation process. The preparation of high-purity aluminum fluoride by the reaction of aluminum hydroxide and fluorosilicic acid not only has a relatively simple process, but also can make full use of existing chemical raw materials, reducing production costs and environmental burdens.

[0004] Compared with the traditional wet process (using concentrated sulfuric acid and fluorite as raw materials), the hydrofluorosilicic acid process for producing aluminum fluoride has the characteristics of low production cost and good product quality. However, in the actual production process, the aluminum fluoride product particles are small and the particle size distribution is uneven, which leads to serious scaling of the reactor, large product losses in the washing and filtration stages, low aluminum fluoride single-pass recovery rate, and low production efficiency.

[0005] In view of the above problems, it is very necessary to provide a large-particle aluminum fluoride crystal with high yield. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing large-particle aluminum fluoride crystals with high yield, so as to solve the problems of small product particles and uneven particle size distribution in the current process of producing aluminum fluoride by hydrofluorosilicic acid, which leads to serious scaling of the reactor, large product loss in the washing and filtration stages, and low single-pass recovery rate of aluminum fluoride.

[0007] The process for producing aluminum fluoride by a hydrofluorosilicic acid process disclosed in the present invention is as follows: adding aluminum hydroxide (Al(OH)3) solid powder into preheated hydrofluorosilicic acid (H2SiF6) at one time for neutralization reaction, then filtering the silicon dioxide waste solid, conveying the filtered mother liquor to a crystallization tank for crystallization, filtering to obtain a crude crystal product of aluminum fluoride trihydrate (AlF3·3H2O). The obtained aluminum fluoride trihydrate is dried and roasted to obtain an anhydrous aluminum fluoride product.

[0008] One of the objects of the present invention is to provide a high-yield aluminum fluoride production process, the process comprising the following steps:

[0009] The present invention adopts the following technical solution:

[0010] (1) adding aluminum hydroxide powder to a fluosilicic acid solution at a temperature of 60-100° C. (e.g., 60° C., 65° C., 70° C., 75° C., 80° C., 85° C., 90° C., 95° C., 100° C., etc.) under stirring, reacting, and separating the solid and the liquid to obtain a filtrate;

[0011] (2) Under stirring conditions, adding aluminum fluoride trihydrate seed crystals to the filtrate, and crystallizing at a constant temperature of 80-100° C. (e.g., 80° C., 85° C., 90° C., 95° C., 100° C., etc.) for 2-6 h (e.g., 2 h, 3 h, 4 h, 5 h, 6 h, etc.) to obtain aluminum fluoride crystals.

[0012] Preferably, the reaction in step (1) is as follows:

[0013] H2SiF6l+2AlOH3s→SiO2↓+2AlF3+4H2O.

[0014] Preferably, the stirring rate in step (1) is 100-800 rpm (e.g., 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, etc.);

[0015] Preferably, the stirring rate in step (2) is 100-800 rpm (e.g., 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, etc.).

[0016] Preferably, based on 1 g of aluminum hydroxide powder, the amount of fluorosilicic acid added is 1.5-1.8 g (eg, 1.5 g, 1.6 g, 1.7 g, 1.8 g, etc.).

[0017] Preferably, the reaction time of step (1) is 10-30 min (e.g., 10 min, 15 min, 20 min, 25 min, 30 min, etc.).

[0018] Preferably, based on the added volume of the filtrate being 1 L, the added amount of the aluminum fluoride trihydrate seed crystals in step (2) is 5-30 g (e.g., 5 g, 10 g, 15 g, 20 g, 25 g, 30 g, etc.);

[0019] Preferably, the average particle size of the aluminum fluoride trihydrate seed crystals in step (2) is 0.02-0.5 mm (e.g., 0.02 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, etc.).

[0020] Preferably, the step (2) further comprises: solid-liquid separation and drying of the mixture obtained after isothermal crystallization;

[0021] The drying includes drying at room temperature first and then drying at 500-700°C (e.g., 500°C, 520°C, 550°C, 580°C, 600°C, 620°C, 650°C, 670°C, 700°C, etc.).

[0022] As a preferred technical solution of the present invention, the preparation method of aluminum fluoride crystals is as follows Figure 1 As shown, the following steps are included:

[0023] (1) The neutralization reaction between aluminum hydroxide solid powder and fluorosilicic acid includes:

[0024] After the fluorosilicic acid solution is preheated in the reactor, aluminum hydroxide powder is added at one time, stirred thoroughly to make it evenly mixed, and filtered after the reaction.

[0025] The neutralization reaction occurring in the reactor is as follows:

[0026] H2SiF6(1)+2Al(OH)3(s)→SiO2↓+2AlF3+4H2O

[0027] (2) The crystallization of aluminum fluoride trihydrate includes:

[0028] The filtered silicon dioxide (SiO2) is washed with water and then crystallized together with the mother liquor in a crystallizer. The crystallization process is constant temperature stirring crystallization.

[0029] (3) The preparation of aluminum fluoride comprises:

[0030] The solid product obtained by filtration is first dried to reduce the moisture content of the product to 25-15%, and then calcined at a high temperature of 500-700° C. to finally obtain an anhydrous aluminum fluoride crystal product (water content <2.5%).

[0031] Preferably, the fluorosilicic acid solution is obtained by absorbing fluorine-containing waste gas (SiF4) in phosphate fertilizer production through water, wherein the fluorosilicic acid concentration is 10-20%wt.

[0032] Preferably, in step (1), the fluorosilicic acid solution is preheated to 60-100° C. in a reaction kettle, and then aluminum hydroxide powder is added at one time.

[0033] The second object of the present invention is to provide a preparation method as described in the first object to prepare aluminum fluoride crystals.

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

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

[0036] The method of the invention provides a process for producing aluminum-rich crystals with high production efficiency, large particle size and easy filtration.

[0037] The method of the invention clarifies the feed ratio, reaction time, reaction temperature in the neutralization reaction, the temperature, time, seed addition amount, and seed particle size in the crystallization process, and the final single-pass yield of aluminum fluoride is greater than 80%, the aluminum fluoride particle size is greater than 100 μm, and the product purity is greater than 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a process flow chart for preparing aluminum fluoride crystals.

[0039] Figure 2 This is the silicon dioxide obtained by suction filtration after the neutralization reaction in Comparative Example 1.

[0040] Figure 3 These are the aluminum fluoride trihydrate crystals remaining on the crystallizer wall at the end of crystallization in Comparative Example 1.

[0041] Figure 4 This is the crystal morphology of aluminum fluoride obtained in Comparative Example 1.

[0042] Figure 5 This is the crystal morphology of aluminum fluoride obtained in Example 1.

[0043] Figure 6 This is the crystal morphology of aluminum fluoride obtained in Example 2. DETAILED DESCRIPTION

[0044] 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.

[0045] Example 1

[0046] (1) Fluorosilicic acid solution was preheated to 95°C in a reactor, and the materials were added in a stoichiometric ratio, i.e., a mass ratio of 1:1.6 (aluminum hydroxide: fluosilicic acid). The reaction lasted for 30 minutes and then filtered. The silica particles after filtration were of moderate size, the filtration time was 5 minutes, the filtration performance was good, and the mother liquor was clear.

[0047] (2) Before crystallization begins, 15 g / L (mass of seed crystals / volume of mother liquor) of aluminum fluoride trihydrate seed crystals are added to the mother liquor, and crystallization is carried out at a constant temperature of 90°C for 4 hours. At the end of crystallization, there is no formation of aluminum fluoride trihydrate crystals on the wall of the crystallizer, and the aluminum fluoride content in the mother liquor is 72 g / L. Figure 5 As shown, it is an ellipsoidal aggregate with a particle size greater than 100 μm and a bulk density of 0.843 g / cm 3 The maximum angle formed by the free slope of the powder accumulation layer and the horizontal plane is 39°. The friction of the particle layer is small, which meets the production fluidity. The single-pass yield is 77.18%, and the calculation method is:

[0048]

[0049] The effect of the amount of seed added in step (2) on the single-pass yield of aluminum fluoride was investigated.

[0050]

[0051] The effect of crystallization time in step (2) on the single-pass yield of aluminum fluoride was investigated.

[0052]

[0053]

[0054] The effect of crystallization temperature in step 2 on the single-pass yield of aluminum fluoride was investigated.

[0055]

[0056] The effect of seed crystal size on the single-pass yield of aluminum fluoride in step 2 was investigated.

[0057]

[0058] Example 2

[0059] (1) Fluorosilicic acid solution was preheated to 80°C in a reactor, and the materials were added in a stoichiometric ratio, i.e., a mass ratio of 1:1.5 (aluminum hydroxide: fluosilicic acid). The reaction lasted for 10 minutes and then filtered. The silica particles after filtration were of moderate size, the filtration time was 5 minutes, the filtration performance was good, and the mother liquor was clear.

[0060] (2) Before crystallization begins, 20 g / L (mass of seed crystals / volume of mother liquor) of aluminum fluoride trihydrate seed crystals with a particle size of 0.02-0.40 mm are added to the mother liquor, and the crystallization is carried out at a constant temperature of 80°C for 5 hours. At the end of crystallization, there is no wall formation of aluminum fluoride trihydrate crystals on the wall of the crystallizer, and the aluminum fluoride content in the mother liquor is 52 g / L. Figure 6 As shown, it is an ellipsoidal aggregate with a particle size greater than 100 μm and a bulk density of 0.920 g / cm 3 The maximum angle formed by the free slope of the powder accumulation layer and the horizontal plane is 35°, the friction of the particle layer is small, which meets the production fluidity, and the single-pass yield is 82.31%.

[0061] Example 3

[0062] (1) Fluorosilicic acid solution was preheated to 100°C in a reactor, and the materials were added in a stoichiometric ratio, i.e., a mass ratio of 1:1.8 (aluminum hydroxide: fluosilicic acid). The reaction lasted for 30 minutes and then filtered. The silica particles after filtration were of moderate size, the filtration time was 10 minutes, the filtration performance was good, and the mother liquor was clear.

[0063] (2) Before crystallization begins, 30 g / L (mass of seed crystals / volume of mother liquor) of aluminum fluoride trihydrate seed crystals with a particle size of 0.02-0.40 mm are added to the mother liquor, and the crystallization is carried out at a constant temperature of 100°C for 3 hours. At the end of crystallization, there is no wall formation of aluminum fluoride trihydrate crystals on the wall of the crystallizer, and the aluminum fluoride content in the mother liquor is 52 g / L. After drying and calcining, the aluminum fluoride particles are as follows Figure 5 As shown, it is an ellipsoidal aggregate with a particle size greater than 100 μm and a bulk density of 0.968 g / cm 3 The maximum angle formed by the free slope of the powder accumulation layer and the horizontal plane is 32°, the friction of the particle layer is small, which meets the production fluidity, and the single-pass yield is 84.72%.

[0064] Comparative Example 1

[0065] This embodiment provides a method for crystallizing aluminum fluoride, comprising the following steps:

[0066] (1) Preheat the hydrofluorosilicic acid solution to 75°C in a reactor, add aluminum hydroxide to hydrofluorosilicic acid at a mass ratio of 1:1.05-1:1.1, react for 30 minutes, and then filter. Figure 2 As shown, the silica particles after filtration are relatively fine and become muddy after filtration for 30 minutes, indicating poor filtration performance.

[0067] (2) The mother liquor obtained by filtration is crystallized at 90°C for 4 hours. Figure 3 As shown in Figure 2, at the end of crystallization, aluminum fluoride trihydrate crystals were severely condensed on the wall of the crystallizer, and the aluminum fluoride content in the mother liquor was 192 g / L. Figure 4 As shown, it is a single long rod-shaped crystal with a particle size of less than 50 μm and a bulk density of 0.629 g / cm 3 The maximum angle formed by the free slope of the powder accumulation layer and the horizontal plane is 45°. The particle layer has large friction, poor fluidity, and difficult production and transportation. The one-way yield is 12%.

[0068] Comparative Example 2

[0069] (1) Fluorosilicic acid solution was preheated to 95°C in a reactor, and the materials were added in a stoichiometric ratio, i.e., a mass ratio of 1:1.6 (aluminum hydroxide: fluosilicic acid). The reaction lasted for 30 minutes and then filtered. The silica particles after filtration were of moderate size, the filtration time was 5 minutes, the filtration performance was good, and the mother liquor was clear.

[0070] (2) During the crystallization process, aluminum fluoride trihydrate seeds were not added to the mother liquor. The crystallization was carried out at 90°C for 4 hours. At the end of the crystallization, aluminum fluoride trihydrate crystals had a small amount of wall formation on the wall of the crystallizer. The aluminum fluoride content in the mother liquor was 113 g / L. Figure 4 Similar to the ellipsoidal aggregates, the particle size is less than 100 μm, and the bulk density is 0.713 g / cm 3 The maximum angle formed by the free slope of the powder accumulation layer and the horizontal plane is 42°. The friction of the particle layer is large, the fluidity is poor, the production and transportation are more difficult, and the one-way yield is 20.39%.

[0071] 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 method for preparing aluminum fluoride crystals, characterized in that: The preparation method comprises the following steps: (1) adding aluminum hydroxide powder to a fluosilicic acid solution at a temperature of 60-100° C. under stirring, reacting, and separating the solid from the liquid to obtain a filtrate; (2) Add aluminum fluoride trihydrate seed crystals to the filtrate under stirring conditions and crystallize at a constant temperature of 80-100°C for 2-6 hours to obtain aluminum fluoride crystals.

2. The method for preparing aluminum fluoride crystals according to claim 1, characterized in that: The reaction described in step (1) is as follows.

3. The method for preparing aluminum fluoride crystals according to claim 1, characterized in that: The stirring rate in step (1) is 100-800 rpm; The stirring rate in step (2) is 100-800 rpm.

4. The method for preparing aluminum fluoride crystals according to claim 1, characterized in that: Based on the addition amount of aluminum hydroxide powder being 1 g, the addition amount of fluorosilicic acid is 1.5-1.8 g.

5. The method for preparing aluminum fluoride crystals according to claim 1, characterized in that: The reaction time of step (1) is 10-30 min.

6. The method for preparing aluminum fluoride crystals according to claim 1, characterized in that: Based on the added volume of the filtrate being 1 L, the added amount of the aluminum fluoride trihydrate seed crystals in step (2) is 5-30 g; The average particle size of the aluminum fluoride trihydrate seed crystals in step (2) is 0.02-0.5 mm.

7. The method for preparing aluminum fluoride crystals according to claim 1, characterized in that: The step (2) further comprises: performing solid-liquid separation and drying on the mixture obtained after the isothermal crystallization; The drying includes drying at room temperature first and then drying at 500-700°C.

8. Aluminum fluoride crystals are prepared according to the method for preparing aluminum fluoride crystals according to any one of claims 1 to 7.

9. The aluminum fluoride crystal according to claim 8, characterized in that: The aluminum fluoride crystals are ellipsoidal aggregates with an average particle size greater than 100 μm.

10. Use of the aluminum fluoride crystals according to claim 8 in the aluminum electrolysis industry.

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