A method for producing aluminum fluoride using cryolite

Abstract

This invention discloses a method for preparing aluminum fluoride using cryolite. Using synthetic cryolite as raw material, a composite desodiuming agent is used in conjunction with granulation to ensure uniform mixing of the materials. By employing segmented temperature control and multi-stage countercurrent washing, the reaction conversion rate is increased to over 97.5%, and the desodiuming efficiency reaches 99.2%. The method innovatively uses reducing organic acids to deeply desulfate the crude aluminum fluoride, resulting in a product with sulfate residue ≤0.05% and sodium content ≤0.07%, meeting the requirements of the national standard GB / T 4292-2017 Aluminum Fluoride (AF-1).

Description

Technical Field

[0001] This invention relates to the field of fluorochemical materials preparation technology, and in particular to a method for preparing aluminum fluoride using cryolite. Background Technology

[0002] Aluminum fluoride is an important flux in the aluminum electrolysis industry and a key raw material in fields such as electronic materials and high-end ceramics. Its purity directly affects product performance.

[0003] Currently, the process of preparing aluminum fluoride from cryolite generally faces two major technical bottlenecks: First, incomplete sodium removal. Existing technologies mostly use aluminum sulfate as a single sodium removal agent, which is limited by reaction kinetics and has a low replacement efficiency between aluminum ions and sodium ions in the cryolite lattice. Second, excessive sulfate residue. The sodium sulfate generated in the sodium removal reaction is easily encapsulated within the aluminum fluoride lattice. The sulfur content of aluminum fluoride products prepared by traditional water washing processes is often greater than 1%, which cannot meet the quality requirements of the national standard GB / T4292-2017 Aluminum Fluoride (AF-1). Summary of the Invention

[0004] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a method for preparing aluminum fluoride using cryolite, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing aluminum fluoride using cryolite, wherein the method comprises the following steps: S1. Mix cryolite, composite sodium removal agent, and binder to form spherical particles with a diameter of 4mm. S2. Add the spherical particles described in S1 to a muffle furnace for segmented temperature-controlled calcination: pre-reaction at 300-400℃ for 30-60 min, main reaction at 500-550℃ for 60-120 min, and enhanced reaction at 650-750℃ for 30-60 min. S3. The calcined product obtained in S2 is pulverized and passed through a 200-mesh sieve with a sieve passing rate of ≥98%. The fine powder is leached with water to remove sodium, filtered, and washed to obtain crude aluminum fluoride. S4. Add the crude aluminum fluoride obtained in S3 to hot water at 60-95℃ at a solid-liquid ratio of 1:8-10 for slurrying, add reducing organic acid to deeply remove sulfate, filter and wash to obtain aluminum fluoride filter cake. S5. The washed filter cake is fed into a continuous pyrolysis furnace for roasting to remove organic matter, thereby obtaining aluminum fluoride product.

[0006] Preferably, the cryolite in S1 is synthetic cryolite with a purity ≥98.5%; the composite desodiuming agent is an aluminum source and persulfate complex, wherein the aluminum source is anhydrous aluminum sulfate or aluminum sulfate octadecahydrate, more preferably aluminum sulfate octadecahydrate, and the persulfate is sodium persulfate or ammonium persulfate, more preferably sodium persulfate, to reduce the introduction of other cations; the mixing mass ratio of the cryolite to the composite desodiuming agent is 1:1.7-2.0; the mass ratio of the aluminum source to the persulfate in the composite desodiuming agent is 1:0.15-0.35; the binder is deionized water, and the amount added is 5% of the total mass of the raw materials and the composite desodiuming agent; the spherical particles in S1 have a diameter of 4mm and a compressive strength ≥4N after drying.

[0007] Preferably, the segmented temperature-controlled calcination in S2 involves heating to 300-350℃ at a heating rate of 5℃ / min for a pre-reaction of 30-60 min, followed by heating to 500-550℃ for a main reaction of 60-120 min after the pre-reaction, and then heating to 650-750℃ for an enhancement reaction of 30-60 min after the main reaction.

[0008] Preferably, the solid-liquid ratio for sodium removal by water immersion in step S3 is 1:8-12, more preferably 1:10; the sodium removal by water immersion in step S3 involves two or more stages of countercurrent washing, and the reaction temperature for sodium removal by water immersion is 50-65°C, more preferably 55°C.

[0009] Preferably, the solid-liquid ratio of water addition during slurry processing in S4 is 1:8-12, more preferably 1:10; the deep desulfurization reaction temperature in S4 is 60-95℃, more preferably 80-85℃; the reducing organic acid in S4 is one or more of oxalic acid, citric acid, and ascorbic acid, more preferably oxalic acid; the amount of reducing organic acid added in S4 is 2-10% of the mass of crude aluminum fluoride, more preferably 3-5%.

[0010] Preferably, in step S5, the aluminum fluoride filter cake is pyrolyzed at a temperature ≥300°C, more preferably 350°C, to remove residual organic matter from the aluminum fluoride.

[0011] Compared with the prior art, the beneficial effects of the present invention are: (1) The composite desodiuming agent is used in conjunction with the granular raw material design, and the process of segmented temperature control and multi-stage washing is combined to make the material uniformly mixed, the reaction conversion rate reaches more than 97.5%, and the desodiuming efficiency reaches 99.2%.

[0012] (2) Deep desulfate removal is carried out using reducing organic acids. The product has a sulfate residue of ≤0.05% and a sodium content of ≤0.07%, which meets the requirements of the national standard GB / T 4292-2017 aluminum fluoride (AF-1). Attached Figure Description

[0013] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0014] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0015] Example 1: 100g of synthetic cryolite (98.5% purity) was mixed with 185g of composite desodiumning agent (160g of aluminum sulfate octadecylhydrate + 25g of sodium persulfate) and 14g of deionized water to form spherical particles with a diameter of 4mm. After drying, the compressive strength was 4.2N. Spherical particles were added to a muffle furnace and pre-reacted at 350°C at 5°C / min for 60 min, reacted at 550°C at 5°C / min for 90 min, and enhanced reaction at 700°C at 5°C / min for 60 min. The sintered product was pulverized and added to deionized water at 50-60℃ at a solid-liquid ratio of 1:10. The mixture was stirred and reacted for 60 minutes. After filtration and washing, crude aluminum fluoride was obtained with a sodium content of 0.94% and a sulfate content of 0.58%. Add crude aluminum fluoride to deionized water at 80-85℃ at a solid-liquid ratio of 1:10, add 5% (by dry weight) of oxalic acid to crude aluminum fluoride, stir and react for 90 minutes, filter, and wash to obtain aluminum fluoride filter cake. The aluminum fluoride filter cake was dried and then pyrolyzed at 350℃ for 2 hours to obtain the product aluminum fluoride, sodium 0.05%, and sulfate 0.025%.

[0016] Example 2: 100g of synthetic cryolite (98.5% purity) was mixed with 201.6g of composite desodiumning agent (168g of aluminum sulfate octadecylhydrate + 33.6g of sodium persulfate) and 14g of deionized water to form spherical particles with a diameter of 4.2N after drying. Spherical particles were added to a muffle furnace and pre-reacted at 350°C at 5°C / min for 60 min, reacted at 550°C at 5°C / min for 90 min, and enhanced reaction at 700°C at 5°C / min for 60 min. The sintered product was pulverized and then added to deionized water at 50-60℃ at a solid-liquid ratio of 1:10. The mixture was stirred and reacted for 60 minutes, filtered, and washed to obtain crude aluminum fluoride with a sodium content of 1.01% and a sulfate content of 0.64%. Add crude aluminum fluoride to deionized water at 80-85℃ at a solid-liquid ratio of 1:10, add 5% (by dry weight) of oxalic acid to crude aluminum fluoride, stir and react for 90 minutes, filter, and wash to obtain aluminum fluoride filter cake. The aluminum fluoride filter cake was dried and then pyrolyzed at 350℃ for 2 hours to obtain the product aluminum fluoride, sodium 0.06%, and sulfate 0.03%.

[0017] Example 3: 100g of synthetic cryolite (98.5% purity) was mixed with 170g of composite desodiumning agent (160g of aluminum sulfate octadecylhydrate + 20g of ammonium persulfate) and 14g of deionized water to form spherical particles with a diameter of 4mm. After drying, the compressive strength was 4.2N. Spherical particles were added to a muffle furnace and pre-reacted at 350°C at 5°C / min for 60 min, reacted at 550°C at 5°C / min for 90 min, and enhanced reaction at 700°C at 5°C / min for 60 min. The sintered product was pulverized and then added to deionized water at 50-60℃ at a solid-liquid ratio of 1:10. The mixture was stirred and reacted for 60 minutes, filtered, and washed to obtain crude aluminum fluoride with a sodium content of 0.88% and a sulfate content of 0.52%. Add crude aluminum fluoride to deionized water at 80-85℃ at a solid-liquid ratio of 1:10, add 5% (by dry weight) of oxalic acid to crude aluminum fluoride, stir and react for 90 min, filter, wash, and obtain aluminum fluoride filter cake. The aluminum fluoride filter cake was dried and then pyrolyzed at 350℃ for 2 hours to obtain the product aluminum fluoride, sodium 0.09%, and sulfate 0.055%.

[0018] Example 4: The difference from Example 1 is that the reducing organic acid is ascorbic acid, and the other reaction conditions are the same, to obtain crude aluminum fluoride with a sodium content of 0.92% and a sulfate content of 0.56%; after deep desulfation and pyrolysis, the product aluminum fluoride with a sodium content of 0.14% and a sulfate content of 0.10% is obtained.

[0019] Example 5: The difference from Example 1 is that the reducing organic acid is citric acid, while the other reaction conditions are the same, to obtain crude aluminum fluoride with a sodium content of 0.99% and a sulfate content of 0.57%; after deep desulfation and pyrolysis, the product aluminum fluoride with a sodium content of 0.13% and a sulfate content of 0.09% is obtained.

[0020] Comparative Example 1: The difference from Example 1 is that only aluminum sulfate octadecahydrate, a single aluminum source, is used as the desodiuming agent, while other reaction conditions remain unchanged, to obtain crude aluminum fluoride with a sodium content of 2.78% and sulfate content of 0.98%; after deep desulfation and pyrolysis, the product aluminum fluoride with a sodium content of 0.89% and sulfate content of 0.68% is obtained.

[0021] Comparative Example 2: The difference from Example 1 is that oxalic acid was not used for deep desulfate removal, while other reaction conditions remained unchanged, to obtain crude aluminum fluoride with a sodium content of 1.14% and a sulfate content of 0.82%; after washing with hot water, it was pyrolyzed to obtain the product aluminum fluoride with a sodium content of 1.05% and a sulfate content of 0.65%.

[0022] Table 1 Statistical data of the embodiments

[0023] As shown in Table 1, Examples 1-3 used different persulfate composite desodiuming agents, and by adjusting the ratio of the desodiuming agents, the conversion of aluminum fluoride and deep removal of sulfate were achieved. Examples 4-5 used citric acid and ascorbic acid for deep desulfurization, but the desulfurization efficiency was slightly lower than that of Examples 1-3. Therefore, oxalic acid is preferred among the various desulfurization reagents provided by this invention. In Comparative Example 1, a single aluminum source was used as the desodiuming agent, and the sodium and sulfur contents of the crude aluminum fluoride were relatively high. Even after deep desulfurization with oxalic acid, the product still could not meet the usage requirements. This shows that the reaction conversion rate is low when using a single aluminum source. Using the composite desodiuming agent provided by this invention can effectively improve the conversion rate of the desodiuming reaction. In Comparative Example 2, only hot water was used to wash the crude aluminum fluoride. The sodium and sulfate contents of the obtained product were not significantly reduced compared to the crude aluminum fluoride. Therefore, using reducing organic acids for deep desulfurization can significantly improve the desulfurization efficiency.

[0024] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing aluminum fluoride using cryolite, characterized in that: The method for preparing aluminum fluoride using cryolite includes the following steps: S1. Mix cryolite, composite sodium removal agent, and binder to form spherical particles with a diameter of 4mm. S2. Add the spherical particles described in S1 to a muffle furnace for segmented temperature-controlled calcination: pre-reaction at 300-400℃ for 30-60 min, main reaction at 500-550℃ for 60-120 min, and enhanced reaction at 650-750℃ for 30-60 min. S3. The calcined product obtained in S2 is pulverized and passed through a 200-mesh sieve with a sieve passing rate of ≥98%. The fine powder is leached with water to remove sodium, filtered, and washed to obtain crude aluminum fluoride. S4. Add the crude aluminum fluoride obtained in S3 to hot water at 60-95℃ at a solid-liquid ratio of 1:8-10 for slurrying, add reducing organic acid to deeply remove sulfate, filter and wash to obtain aluminum fluoride filter cake. S5. The washed filter cake is fed into a continuous pyrolysis furnace for roasting to remove organic matter, thereby obtaining aluminum fluoride product.

2. The method for preparing aluminum fluoride using cryolite according to claim 1, characterized in that: The cryolite in S1 is synthetic cryolite with a purity ≥98.5%; the composite desodiuming agent is an aluminum source and persulfate complex, the aluminum source being either anhydrous aluminum sulfate or aluminum sulfate octadecahydrate, and the persulfate being either sodium persulfate or ammonium persulfate or one or more; the mixing mass ratio of the cryolite to the composite desodiuming agent is 1:1.7-2.0; the mass ratio of the aluminum source to the persulfate in the composite desodiuming agent is 1:0.15-0.35; the binder is deionized water, and the amount added is 5% of the total mass of the raw materials and the composite desodiuming agent; the spherical particles in S1 have a diameter of 4mm and a compressive strength ≥4N after drying.

3. The method for preparing aluminum fluoride using cryolite according to claim 2, characterized in that: The segmented temperature-controlled calcination described in S2 involves heating to 300-350℃ at a heating rate of 5℃ / min for a pre-reaction of 30-60 min, followed by heating to 500-550℃ for a main reaction of 60-120 min, and then heating to 650-750℃ for an enhancement reaction of 30-60 min.

4. The method for preparing aluminum fluoride using cryolite according to claim 3, characterized in that: The solid-liquid ratio for sodium removal by water immersion in S3 is 1:8-12. The sodium removal by water immersion in S3 undergoes two or more stages of countercurrent washing. The reaction temperature for sodium removal by water immersion is 50-65℃.

5. The method for preparing aluminum fluoride using cryolite according to claim 4, characterized in that: The solid-liquid ratio for water slurrying in S4 is 1:8-12; the deep desulfurization reaction temperature in S4 is 60-95℃; the reducing organic acid in S4 is one or more of oxalic acid, citric acid, and ascorbic acid; and the amount of reducing organic acid added in S4 is 2-10% of the mass of crude aluminum fluoride.

6. The method for preparing aluminum fluoride using cryolite according to claim 5, characterized in that: S5 describes pyrolyzing the aluminum fluoride filter cake at a temperature ≥300℃ to remove residual organic matter from the aluminum fluoride.

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