A method for recycling aluminum fluoride waste

Abstract

This invention discloses a method for recycling aluminum fluoride waste, belonging to the field of fluoride salt resource recycling technology. Addressing the problems of poor selectivity, high acid consumption, and low recovery rate in existing technologies for aluminum fluoride waste, this invention provides a selective separation method based on the principle that cryolite dissolves in aluminum salt solution while aluminum fluoride remains insoluble. The method includes: mixing aluminum fluoride waste with an aluminum salt solution, and conducting a selective dissolution reaction under specific temperature, pH, and liquid-solid ratio conditions, allowing cryolite and alumina to dissolve into the solution phase while aluminum fluoride remains insoluble; obtaining aluminum fluoride product and leachate through solid-liquid separation; the leachate can be further precipitated by adding fluoride salts to recover the cryolite product. This invention's method is simple, highly efficient, and produces high-purity products, achieving effective separation and resource utilization of the two valuable components in aluminum fluoride waste.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, and in particular to a method for recycling aluminum fluoride waste. Background Technology

[0002] Aluminum fluoride (AlF3) and cryolite (Na3AlF6) are important fluoride salt raw materials in the electrolytic aluminum industry. In the production process of aluminum fluoride by cryolite-aluminum sulfate roasting, a certain amount of sintering waste is generated. This waste contains aluminum fluoride, cryolite, and alumina, and cannot be directly used as raw materials for the electrolytic aluminum industry.

[0003] Currently, the main methods for recycling aluminum fluoride waste include acid leaching and alkaline leaching. Although acid leaching or alkaline leaching can achieve a certain degree of separation, they suffer from problems such as poor selectivity, high acid consumption, and low recovery rate. 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 recycling aluminum fluoride waste, 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 recycling aluminum fluoride waste, comprising the following steps: S1. Add aluminum fluoride waste to aluminum salt solution and carry out selective dissolution reaction under stirring conditions, so that cryolite and alumina dissolve while aluminum fluoride remains insoluble. S2. The reaction system of step S1 is subjected to solid-liquid separation to obtain aluminum fluoride filter cake and leachate; S3. Wash the aluminum fluoride filter cake from step S2 once with dilute acid slurry, then wash it once with clean water slurry. After drying the filter cake, the aluminum fluoride product is obtained. S4. Add fluoride salt to the leachate obtained in step S2, control the fluoride-aluminum ratio to 6:(1-1.2), and stir to crystallize cryolite. S5. The reaction system of S4 is subjected to solid-liquid separation, and after washing and drying, cryolite product is obtained.

[0006] Preferably, the aluminum fluoride waste has an aluminum fluoride mass fraction of 85-95%, a cryolite mass fraction of 2-15%, and an alumina mass fraction of 0.5-5%.

[0007] Preferably, the aluminum salt solution is one or more of aluminum sulfate solution, aluminum chloride solution, and aluminum nitrate solution, and the concentration of the aluminum salt solution is 0.1-1.5 mol / L.

[0008] Preferably, the temperature of the selective dissolution reaction is 60-90°C, and the reaction time is 0.5-4 hours.

[0009] Preferably, the pH value of the selective dissolution reaction is 1.0-3.0.

[0010] Preferably, the liquid-solid mass ratio of the aluminum salt solution to the mixture is (3:1)-(5:1).

[0011] Preferably, the solid-liquid separation is performed using at least one of filtration and centrifugal separation.

[0012] Preferably, the fluoride salt is one or more of sodium fluoride, potassium fluoride, or ammonium fluoride.

[0013] Preferably, the fluorine-aluminum ratio is 6:(1-1.2).

[0014] Preferably, the method further includes washing and drying the separated aluminum fluoride solid, and washing and drying the recovered cryolite product.

[0015] The technical principle of this invention lies in the following: cryolite (Na3AlF6) and alumina (Al2O3) can undergo a dissolution reaction in aluminum salt solutions to generate soluble aluminum fluoride complexes, while aluminum fluoride (AlF3) is almost insoluble under the same conditions. By adding fluoride to the aluminum fluoride complex solution to adjust the fluoride-aluminum ratio, cryolite can be recovered. The reaction mechanism can be expressed as follows: Na3AlF6 + Al3+ → soluble aluminum fluoride complex By controlling the concentration, temperature, pH, and other conditions of the aluminum salt solution, the selective dissolution of cryolite can be achieved, while aluminum fluoride remains insoluble, thus enabling the effective separation of the two.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. High separation efficiency: For aluminum fluoride waste with a cryolite content of 2-15%, the significant difference in solubility between cryolite and aluminum fluoride in aluminum salt solutions enables highly efficient selective separation. The cryolite dissolution rate can reach over 98%, the aluminum fluoride recovery rate can reach over 98%, and the product purity is high.

[0017] 2. Simple process: It only requires steps such as dissolution, separation, crystallization, washing and drying. The operation is simple and does not require complicated equipment or high temperature and high pressure conditions, making it easy to implement in industrial applications.

[0018] 3. Low cost: The aluminum salt solution used can be recycled or reused, resulting in low reagent consumption and low operating costs.

[0019] 4. Environmentally friendly: The separated solution can be recycled or treated harmlessly, meeting green and environmental protection requirements.

[0020] 5. High product value: The separated aluminum fluoride and cryolite products have high purity and can be directly used in electrolytic aluminum production or other industrial applications, realizing the high-value utilization of waste resources. Attached Figure Description

[0021] 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

[0022] 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.

[0023] Example 1 100g of aluminum fluoride waste (14.21% cryolite, 1.68% alumina, and 84.11% aluminum fluoride) was added to 300mL of 0.608 mol / L aluminum chloride solution. The pH was adjusted to 2.0 with hydrochloric acid, and the mixture was stirred at 70℃ for 2 hours. After the reaction was complete, the mixture was filtered while hot to obtain solid aluminum fluoride and filtrate. The solid aluminum fluoride was washed once with 2% dilute hydrochloric acid and twice with deionized water, and dried at 120℃ to obtain 83.6g of aluminum fluoride product with a purity of 98.5%. 38.5g of sodium fluoride was added to the filtrate, and the mixture was stirred for 30 minutes. Cryolite precipitate was precipitated, and after filtration, washing, and drying, 45.77g of cryolite product with a purity of 97.2% was obtained.

[0024] Example 2 100g of aluminum fluoride waste (5.45% cryolite, 0.58% alumina, and 93.97% aluminum fluoride) was added to 300mL of 0.23mol / L aluminum chloride solution. The pH was adjusted to 2.0 with hydrochloric acid, and the mixture was stirred at 80℃ for 2 hours. After the reaction was complete, the mixture was filtered while hot to obtain solid aluminum fluoride and filtrate. The solid aluminum fluoride was washed once with 2% dilute hydrochloric acid and twice with deionized water, then dried at 120℃ to obtain 93.4g of aluminum fluoride product with a purity of 98.1%. 17.5g of sodium fluoride was added to the filtrate, and the mixture was stirred for 30 minutes. Cryolite precipitate was precipitated, and after filtration, washing, and drying, 19.9g of cryolite product with a purity of 96.8% was obtained.

[0025] Example 3 100g of aluminum fluoride waste (5.45% cryolite, 0.58% alumina, and 93.97% aluminum fluoride) was added to 300mL of 0.23mol / L aluminum nitrate solution. The pH was adjusted to 2.0 with dilute nitric acid, and the mixture was stirred at 70℃ for 2 hours. After the reaction was complete, the mixture was filtered while hot to obtain solid aluminum fluoride and filtrate. The solid aluminum fluoride was washed once with 2% dilute nitric acid and twice with deionized water, then dried at 120℃ to obtain 92.6g of aluminum fluoride product with a purity of 98.2%. 17.5g of sodium fluoride precipitant was added to the filtrate, and cryolite was precipitated by stirring. After filtration, washing, and drying, 19.2g of cryolite product with a purity of 97.5% was obtained.

[0026] Example 4 100g of aluminum fluoride waste (5.45% cryolite, 0.58% alumina, and 93.97% aluminum fluoride) was added to 300mL of 0.115mol / L aluminum sulfate solution. The pH was adjusted to 2.0 with dilute sulfuric acid, and the mixture was stirred at 80℃ for 2 hours. After the reaction was complete, the mixture was filtered while hot to obtain solid aluminum fluoride and filtrate. The solid aluminum fluoride was washed once with 2% sulfuric acid and twice with deionized water, and dried at 105℃ to obtain 94.1g of aluminum fluoride product with a purity of 98.2%. 17.5g of sodium fluoride precipitant was added to the filtrate, and the cryolite was precipitated by stirring. After filtration, washing, and drying, 19.45g of cryolite product with a purity of 97.2% was obtained.

[0027] 100g of aluminum fluoride waste (14.21% cryolite, 1.68% alumina, and 84.11% aluminum fluoride) was treated using a traditional acid leaching method with a 10% hydrochloric acid solution. After acid leaching and separation, 93.5g of aluminum fluoride product (89.8% purity) was obtained. The cryolite dissolution rate was only 45.74%, and the separation effect was significantly lower than that of the method of this invention.

[0028] 100g of aluminum fluoride waste (14.21% cryolite, 1.68% alumina, and 84.11% aluminum fluoride) was treated using a traditional acid leaching method. After acid leaching and separation with a 20% hydrochloric acid solution, 90.7g of aluminum fluoride product (92.73% purity) was obtained. The cryolite dissolution rate was only 65.4%, indicating a significantly low separation efficiency.

[0029] The method of the present invention has been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for recycling aluminum fluoride waste, characterized in that, Includes the following steps: S1. Add aluminum fluoride waste to aluminum salt solution and carry out selective dissolution reaction under stirring conditions, so that cryolite and alumina dissolve while aluminum fluoride remains insoluble. S2. The reaction system of step S1 is subjected to solid-liquid separation to obtain aluminum fluoride filter cake and leachate; S3. Wash the aluminum fluoride filter cake from step S2 once with dilute acid slurry, then wash it once with clean water slurry. After drying the filter cake, the aluminum fluoride product is obtained. S4. Add fluoride salt to the leachate obtained in step S2, control the fluoride-aluminum ratio to 6:(1-1.2), and stir to crystallize cryolite. S5. The reaction system of S4 is subjected to solid-liquid separation, and after washing and drying, cryolite product is obtained.

2. The method for recycling aluminum fluoride waste according to claim 1, characterized in that, The aluminum fluoride waste has an aluminum fluoride mass fraction of 85-95%, a cryolite mass fraction of 2-15%, and an alumina mass fraction of 0.5-5%.

3. The method for recycling aluminum fluoride waste according to claim 2, characterized in that, The aluminum salt solution is one or more of aluminum sulfate solution, aluminum chloride solution, and aluminum nitrate solution, and the concentration of the aluminum salt solution is 0.1-1.5 mol / L.

4. The method for recycling aluminum fluoride waste according to claim 3, characterized in that, The selective dissolution reaction is carried out at a temperature of 60-90℃ for a reaction time of 0.5-4 hours.

5. The method for recycling aluminum fluoride waste according to claim 4, characterized in that, The pH value of the selective dissolution reaction is 1.0-3.

0.

6. The method for recycling aluminum fluoride waste according to claim 5, characterized in that, The liquid-solid mass ratio of the aluminum salt solution to the mixture is (3:1)-(5:1).

7. The method for recycling aluminum fluoride waste according to claim 6, characterized in that, The solid-liquid separation is performed using at least one of filtration and centrifugal separation.

8. The method for recycling aluminum fluoride waste according to claim 7, characterized in that, The fluoride salt is one or more of sodium fluoride, potassium fluoride, or ammonium fluoride.

9. The method for recycling aluminum fluoride waste according to claim 8, characterized in that, The fluorine-aluminum ratio is 6:(1-1.2).

10. The method for recycling aluminum fluoride waste according to claim 9, characterized in that, The method also includes washing and drying the separated aluminum fluoride solid, and washing and drying the recovered cryolite product.

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