Method for preparing silica by-product from fluosilicic acid

Abstract

The application discloses a method for preparing white carbon black by-product of aluminum fluoride from fluosilicic acid, and belongs to the field of aluminum fluoride production, which comprises the following steps: (1) preparing white carbon black and aluminum fluoride supersaturated solution; (2) crystallizing the aluminum fluoride supersaturated solution; and (3) calcining monohydrate aluminum fluoride. The step (1) produces white carbon black meeting the national standard A, the step (2) controls the temperature and rotating speed in the reaction kettle, and adds crystal seeds in a corresponding proportion, so that large-particle monohydrate aluminum fluoride particles with large loose bulk density are obtained, the monohydrate aluminum fluoride is calcined, the purity of anhydrous aluminum fluoride is improved to more than 99%, the alumina impurity is reduced to less than 0.05%, the product quality is obviously improved, the problems of high equipment investment, large dust and complex process in the traditional dry method are effectively avoided, the production cost is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of aluminum fluoride production, and specifically to a method for preparing silica, a byproduct of aluminum fluoride production, from fluorosilicic acid. Background Technology

[0002] Anhydrous aluminum fluoride (AlF3) is an irreplaceable flux in the aluminum electrolysis industry. Its crystal form, purity, particle size, and loose packing density directly affect the current efficiency, energy consumption, and fluorine balance of the electrolytic cell. Currently, the industry commonly uses dry or wet processes: the dry process directly reacts hydrogen fluoride gas with aluminum hydroxide (or alumina) at high temperatures of 400–700℃ to prepare aluminum fluoride. Although the process is shorter, the reaction is highly exothermic, causing severe equipment corrosion; the resulting product has a wide particle size distribution, high impurity content, and a large amount of unreacted α-alumina residue, leading to increased fluoride consumption in the electrolytic cell. The wet process typically involves reacting an aluminum source with hydrofluoric acid in the liquid phase to generate aluminum fluoride trihydrate, followed by dehydration at temperatures above 600℃ to prepare anhydrous aluminum fluoride. This process improves product purity compared to the traditional dry process, but the dehydration temperature is high, the time is long, the material is prone to sintering and agglomeration, and the loose packing density is low; the wet process product has a low free fluorine content and generally does not require secondary treatment. Furthermore, existing technologies generally suffer from the following common problems: (1) Difficulty in controlling crystal form: In the existing technology, aluminum fluoride hydrate (especially aluminum fluoride trihydrate) is prone to hydrolysis reaction during high-temperature dehydration, which makes it difficult to improve the purity of the product. It is very easy to generate α-type or γ-type alumina, and a large amount of heat energy will be consumed during calcination.

[0003] (2) High impurity content: Impurities such as Na, Si, and Fe in the raw materials migrate and accumulate at high temperatures, making it difficult to meet the requirements of high-end electrolytic aluminum for AF-1 grade AlF3.

[0004] (3) Uneven particle size distribution: There is a lack of effective means to control crystal nuclei, the particle size of the product is wide, and dust loss is easy to occur in the electrolytic cell.

[0005] (4) High energy consumption: The dehydration temperature is generally higher than 600℃, and multiple crushing and screening are required, resulting in high overall energy consumption.

[0006] (5) Dust pollution: The low loose density of the product leads to serious dust pollution during material transfer.

[0007] Therefore, developing a new method to stably obtain high-purity, high-bulk-density α-type anhydrous aluminum fluoride under mild conditions and to achieve high-value recovery of by-products has become a pressing technical challenge for the fluorochemical and aluminum electrolysis industries. This study aims to overcome the shortcomings of existing technologies and provide an efficient, environmentally friendly, and low-cost aluminum fluoride production solution. Summary of the Invention

[0008] Existing technologies suffer from problems such as poor product quality, high production costs, significant environmental pollution, and difficulty in simultaneously meeting the requirements for high purity and low oxygen content. Therefore, to address these issues, this invention provides a method for preparing silica, a byproduct of aluminum fluoride production, from fluorosilicic acid.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing silica, a byproduct of aluminum fluoride, from fluorosilicic acid is as follows: (1) Dilute the fluorosilicic acid to 15~18wt%, and then preheat it to 75~85℃; (2) Add aluminum hydroxide to the fluorosilicic acid solution in step (1) according to the molar ratio of fluorosilicic acid to aluminum hydroxide 1.0:(1.9~2.0) to obtain a mixed solution; heat the mixed solution to 95~100℃ and stir evenly to obtain a mixed slurry; filter the mixed slurry while hot to obtain a silica filter cake and a supersaturated aluminum fluoride solution; the reaction equation is as follows: H2SiF6+ 2Al(OH)3= 2AlF3+ SiO2↓+4H2O (3) Wash the silica filter cake with deionized water and dry it to obtain silica powder. (4) Add AlF3•3H2O or AlF3•H2O seed crystals to the supersaturated aluminum fluoride solution, then transfer the supersaturated aluminum fluoride solution to a high-temperature and high-pressure reactor, raise the temperature to 120~130℃, keep the vapor pressure inside the container at 0.1~0.3MPa, control the reactor rotation speed at 100~200rpm, and crystallize for 5~6h; (5) Cool down to 20~30℃, filter the slurry, wash the filter cake with deionized water and dry it to obtain AlF3•H2O crystals; (6) The obtained AlF3•H2O crystals are initially calcined at 200~250℃ for 20~40min; the product after initial calcination is further heated to 550~600℃ and kept at that temperature for 1~2h; the obtained AlF3 solid is sieved to obtain aluminum fluoride product with a purity ≥99% that meets the national standard AF-1.

[0010] Furthermore, the aluminum hydroxide described in step (1) conforms to the AH-1 standard in GB / T 4294-2010.

[0011] Furthermore, in step (2), the concentration of the aluminum fluoride supersaturated solution is 150~200g / L, and the pH value is 1~2.

[0012] Furthermore, the drying temperature in step (3) is 60~80℃.

[0013] Furthermore, in step (3), the silica powder conforms to the Class A product standard of GB / T 20020-2025.

[0014] Furthermore, in step (4), the heating rate is 4~6℃ / min.

[0015] Furthermore, in step (4), the amount of seed crystals added is 5% to 25% of the theoretical aluminum fluoride production mass.

[0016] Furthermore, in step (5), drying refers to drying at 60~80℃ for 4~8 hours. Compared with existing technologies, this invention provides a method for preparing high-purity, large-particle anhydrous aluminum fluoride by utilizing the byproduct of the reaction between fluorosilicic acid and aluminum hydroxide, namely silica, and then inducing the crystallization of aluminum fluoride mother liquor through liquid-phase reaction-calcination process. This method offers the following advantages: 1. In the process of preparing aluminum fluoride mother liquor using fluorosilicic acid and aluminum hydroxide, the present invention produces silica that meets the national standard Class A.

[0017] 2. This invention uses fluorosilicic acid and aluminum hydroxide to prepare a supersaturated aluminum fluoride solution. By controlling the temperature and rotation speed of crystallization in the reaction vessel and adding an appropriate proportion of seed crystals, large-particle, high-density monohydrate aluminum fluoride particles are obtained. This effectively avoids the problems of high investment, large dust, and complex process of traditional dry process equipment, reduces production costs, and improves production efficiency. 3. This invention optimizes the crystallization process by adding 5-25% seed crystals to a supersaturated aluminum fluoride solution, thereby improving the quality and regularity of the crystals, solving the problem of insufficient crystal quality in the prior art, and ensuring the purity and performance of the final product. 4. The present invention uses a calcination process for aluminum fluoride monohydrate, which improves the purity of anhydrous aluminum fluoride to over 99%, and reduces alumina impurities to below 0.05%, thus significantly improving product quality. 5. The anhydrous aluminum fluoride prepared by this invention has good particle distribution uniformity and loose packing density, which greatly improves the flowability of the product, effectively solves the problem of poor product flowability in traditional methods, and improves the efficiency of subsequent processes. 6. By optimizing the crystallization and calcination processes, this invention reduces heat energy consumption during production, lowers production costs, and avoids the amorphous powder caused by direct dehydration of aluminum fluoride trihydrate, effectively reducing dust problems during subsequent use and improving the safety and controllability of the production process. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Example 1

[0020] A method for preparing silica, a byproduct of aluminum fluoride production from fluorosilicic acid, such as... Figure 1 As shown, it includes the following steps: Step 1: Prepare a supersaturated solution of silica and aluminum fluoride: Step 101: Dilute the fluorosilicic acid by-product of phosphate fertilizer with water to 15 wt%, and then preheat it to 80 ℃; Step 102: Weigh aluminum hydroxide conforming to the AH-1 grade in GB / T 4294-2010 according to the molar ratio of fluorosilicic acid to aluminum hydroxide of 1.0:1.9, and then add it to the preheated fluorosilicic acid solution in one go to obtain a mixed solution; Step 103: Heat the mixed solution to 95°C and stir for 30 minutes, controlling the stirring speed at 450 rpm, to obtain the mixed slurry solution.

[0021] Step 104: Filter the mixed slurry while hot to obtain white carbon black filter cake and aluminum fluoride supersaturated solution. The pH value of the aluminum fluoride supersaturated solution is 1-2. Step 105: Wash the silica filter cake with twice the mass of deionized water. Step 106: Dry the washed silica filter cake at 60℃ for 8 hours to obtain silica powder.

[0022] Step 2: Crystallization treatment of supersaturated aluminum fluoride solution: Step 201: Add AlF3·3H2O seed crystals (theoretically, 5% by mass of aluminum fluoride is generated, calculated based on the reaction equation H2SiF6 + 2Al(OH)3 = 2AlF3 + SiO2↓ + 4H2O and the amount of Al(OH)3 added) to a 150 g / L supersaturated aluminum fluoride solution. Then transfer the supersaturated aluminum fluoride solution to a high-temperature, high-pressure reactor, control the heating rate at 5 °C / min, raise the temperature to 120 °C, and maintain the pressure at the vapor pressure inside the container (0.13 MPa). Step 202: Control the reactor rotation speed to 180 rpm and crystallize for 5 hours; Step 203: Cool to 20-30℃ at a rate of 2℃ / min. Filter the slurry to obtain an AlF3·H2O filter cake, and wash the filter cake with twice the mass of deionized water. Step 204: Dry the washed AlF3·H2O filter cake at 60℃ for 8 hours to obtain AlF3·H2O crystals.

[0023] Step 3, Aluminum fluoride calcination treatment: Step 301: The obtained AlF3·H2O crystals are subjected to preliminary calcination at a temperature of 250℃ for 30 minutes. Step 302: Continue heating the pre-calcined product to 550℃ for 2 hours; Step 303: After passing the calcined AlF3 solid through an 80-mesh sieve, a product with a purity ≥99% and conforming to the national standard AF-1 is obtained. Example 2

[0024] A method for preparing silica, a byproduct of aluminum fluoride production from fluorosilicic acid, such as... Figure 1 As shown, it includes the following steps: Step 1: Prepare a supersaturated solution of silica and aluminum fluoride: Step 101: Dilute the fluorosilicic acid by-product of phosphate fertilizer with water to 15 wt%, and then preheat it to 80 ℃; Step 102: Weigh aluminum hydroxide conforming to the AH-1 grade in GB / T 4294-2010 according to the molar ratio of fluorosilicic acid to aluminum hydroxide of 1.0:1.99, and then add it to the preheated fluorosilicic acid solution in one go to obtain a mixed solution; Step 103: Heat the mixed solution to 95°C and stir for 30 minutes, controlling the stirring speed at 500 rpm to obtain the mixed slurry solution.

[0025] Step 104: Filter the mixed slurry while hot to obtain white carbon black filter cake and aluminum fluoride supersaturated solution. The pH value of the aluminum fluoride supersaturated solution is 1-2. Step 105: Wash the silica filter cake with twice the mass of deionized water. Step 106: Dry the washed silica filter cake at 60°C for 8 hours to obtain silica powder.

[0026] Step 2: Crystallization treatment of supersaturated aluminum fluoride solution: Step 201: Add theoretical aluminum fluoride to a 180 g / L supersaturated aluminum fluoride solution to generate AlF3·3H2O seed crystals at a mass of 25%. Then transfer the supersaturated aluminum fluoride solution to a high-temperature and high-pressure reactor, control the heating rate at 5 °C / min, raise the temperature to 123 °C, and maintain the pressure at the vapor pressure inside the container (0.2 MPa). Step 202: Control the reactor rotation speed to 200 rpm and crystallize for 5 hours; Step 203: Cool to 20-30℃ at a rate of 2℃ / min. Filter the slurry to obtain an AlF3·H2O filter cake, and wash the filter cake with twice the mass of deionized water. Step 204: Dry the washed AlF3·H2O filter cake at 60℃ for 8 hours to obtain AlF3·H2O crystals.

[0027] Step 3, Aluminum fluoride calcination treatment: Step 301: The obtained AlF3·H2O crystals are subjected to preliminary calcination at a temperature of 220℃ for 30 minutes. Step 302: Continue heating the pre-calcined product to 600℃ for 1 hour; Step 303: After passing the calcined AlF3 solid through an 80-mesh sieve, a product with a purity ≥99% and conforming to the national standard AF-1 is obtained. Example 3

[0028] A method for preparing silica, a byproduct of aluminum fluoride production from fluorosilicic acid, such as... Figure 1 As shown, it includes the following steps: Step 1: Prepare a supersaturated solution of silica and aluminum fluoride: Step 101: Dilute the fluorosilicic acid by-product of phosphate fertilizer with water to 18 wt%, and then preheat to 80 ℃; Step 102: Weigh aluminum hydroxide conforming to the AH-1 grade in GB / T 4294-2010 according to the molar ratio of fluorosilicic acid to aluminum hydroxide of 1.0:1.95, and then add it to the preheated fluorosilicic acid solution in one go to obtain a mixed solution; Step 103: Heat the mixed solution to 95°C and stir for 30 minutes, controlling the stirring speed at 450 rpm, to obtain the mixed slurry solution.

[0029] Step 104: While the mixture is still hot, filter it to obtain a white carbon black filter cake and a supersaturated aluminum fluoride solution. The pH value of the supersaturated aluminum fluoride solution is 1-2. Step 105: Wash the silica filter cake with twice the mass of deionized water. Step 106: Dry the silica filter cake at 60℃ for 8 hours to obtain silica powder.

[0030] Step 2: Crystallization treatment of supersaturated aluminum fluoride solution: Step 201: Add theoretical aluminum fluoride to a 200 g / L supersaturated aluminum fluoride solution to generate AlF3·3H2O seed crystals at a mass of 15%. Then transfer the supersaturated aluminum fluoride solution to a high-temperature and high-pressure reactor, control the heating rate at 5 °C / min, raise the temperature to 130 °C, and maintain the pressure at the vapor pressure inside the container (0.3 MPa). Step 202: Control the reactor rotation speed to 150 rpm and crystallize for 5 hours; Step 203: Cool to 20-30℃ at a rate of 2℃ / min. Filter the slurry to obtain an AlF3·H2O filter cake, and wash the filter cake with twice the mass of deionized water. Step 204: Dry the washed AlF3·H2O filter cake at 60℃ for 8 hours to obtain AlF3·H2O crystals.

[0031] Step 3, Aluminum fluoride calcination treatment: Step 301: The obtained AlF3·H2O crystals are subjected to preliminary calcination at a temperature of 250℃ for 30 minutes. Step 302: Continue heating the pre-calcined product to 600℃ for 1 hour; Step 303: After passing the calcined AlF3 solid through an 80-mesh sieve, a product with a purity ≥99% and conforming to the national standard AF-1 is obtained.

[0032] Table 1 shows the quality test results of the silica prepared in Examples 1 to 3.

[0033] Table 2 shows the quality test results of the aluminum fluoride prepared in Examples 1 to 3.

[0034] As shown in Table 1, the silica prepared in Examples 1 to 3 of this application all meet the Class A standard. As shown in Table 2, the aluminum fluoride obtained in Examples 1 to 3 of this application all meet the AF-1 standard.

[0035] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing silica, a byproduct of aluminum fluoride, from fluorosilicic acid, characterized in that, The process is as follows: (1) Dilute the fluorosilicic acid to 15~18wt%, and then preheat it to 75~85℃; (2) Add aluminum hydroxide to the fluorosilicic acid solution in step (1) according to the fluorosilicic acid:aluminum hydroxide molar ratio of 1.0:(1.9~2.0) to obtain a mixed solution; heat the mixed solution to 95~100℃ and stir evenly to obtain a mixed slurry; filter the mixed slurry while hot to obtain a white carbon black filter cake and an aluminum fluoride supersaturated solution; (3) The silica filter cake was washed with deionized water and dried to obtain silica powder. (4) Add AlF3·3H2O or AlF3·H2O seed crystals to the supersaturated aluminum fluoride solution, then transfer the supersaturated aluminum fluoride solution to a high-temperature and high-pressure reactor, raise the temperature to 120~130℃, keep the vapor pressure inside the container at 0.1~0.3MPa, control the reactor rotation speed at 100~200rpm, and crystallize for 5~6h; (5) Cool down to 20~30℃, filter the slurry, wash the filter cake with deionized water and dry it to obtain AlF3·H2O crystals; (6) The obtained AlF3·H2O crystals are initially calcined at 200~250℃ for 20~40min; the product after initial calcination is further heated to 550~600℃ and kept at that temperature for 1~2h; the obtained AlF3 solid is sieved to obtain aluminum fluoride product with a purity ≥99% that meets the national standard AF-1.

2. The method for preparing silica, a byproduct of aluminum fluoride, from fluorosilicic acid according to claim 1, is characterized in that, The aluminum hydroxide mentioned in step (1) conforms to the AH-1 standard in GB / T 4294-2010.

3. The method for preparing silica, a byproduct of aluminum fluoride, from fluorosilicic acid according to claim 1, is characterized in that... In step (2), the concentration of the supersaturated aluminum fluoride solution is 150~200g / L, and the pH value is 1~2.

4. The method for preparing aluminum fluoride by-product silica from fluorosilicic acid according to claim 1, characterized in that, In step (3), drying refers to drying at 60~80℃ for 6~8 hours.

5. The method for preparing silica, a byproduct of aluminum fluoride, from fluorosilicic acid according to claim 1, is characterized in that, In step (3), the silica powder conforms to the Class A product standard of GB / T 20020-2025.

6. The method for preparing silica, a byproduct of aluminum fluoride, from fluorosilicic acid according to claim 1, is characterized in that, In step (4), the heating rate is 4~6℃ / min.

7. The method for preparing silica, a byproduct of aluminum fluoride, from fluorosilicic acid according to claim 1, is characterized in that, In step (4), the amount of seed crystals added is 5% to 25% of the theoretical aluminum fluoride production mass.

8. The method for preparing silica, a byproduct of aluminum fluoride, from fluorosilicic acid according to claim 1, is characterized in that, In step (5), drying refers to drying at 60~80℃ for 4~8h with a cooling rate of 1~3℃ / min.

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