Method for producing aluminum fluoride by recycling fluorine-containing and phosphorus-containing wastewater

Abstract

The present application belongs to the technical field of industrial wastewater resource utilization, and particularly relates to a method for producing aluminum fluoride from fluorine-containing and phosphorus-containing wastewater, which comprises the following steps: S1, calculating the theoretical amount of fluorine-containing and phosphorus-containing wastewater based on the phosphorus concentration of the wastewater through a fitting model; S2, preparing aluminum hydroxide into a slurry; S3, mixing the fluorine-containing and phosphorus-containing wastewater with the aluminum hydroxide slurry after preheating to obtain a reaction liquid; S4, reacting the reaction liquid under heating and stirring to obtain an aluminum fluoride turbid liquid; and S5, solid-liquid separating the turbid liquid to obtain aluminum fluoride trihydrate solids, and sequentially performing drying and calcination treatment to obtain an aluminum fluoride product. The present application can effectively inhibit the introduction of phosphorus impurities by precisely regulating the fluorine-aluminum ratio, and realize the direct preparation of high-purity aluminum fluoride from wastewater. According to the present application, the prepared aluminum fluoride product has a fluorine content higher than 61%, an aluminum content higher than 31.5%, and a phosphorus content lower than 300 ppm.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater resource utilization technology, and particularly relates to a method for producing aluminum fluoride from fluoride- and phosphorus-containing wastewater. Background Technology

[0002] With the rapid development of new energy industries such as electric vehicles, the market demand for lithium hexafluorophosphate, a core electrolyte material for lithium-ion batteries, has increased dramatically. The mainstream industrial processes for producing lithium hexafluorophosphate, such as dry and wet processes, inevitably generate fluoride- and phosphorus-containing wastewater. Direct discharge of this wastewater will cause serious and lasting harm to water bodies and the environment.

[0003] Currently, the main goal of wastewater treatment technologies for this type of wastewater is still to achieve harmless discharge standards. For example, public application CN115784539A proposes a lithium hexafluorophosphate wastewater treatment process, which reduces pollutants through acidification hydrolysis, phosphorus and fluoride removal, and lithium recovery; public application CN116573735A proposes a series treatment method and device for phosphorus removal, alkalization, fluoride removal, and deep fluoride removal. Overall, the core mechanism of these technologies relies on acid-base neutralization reactions to remove pollutants by generating phosphate and fluoride precipitates. These processes have significant shortcomings: the final products are mostly low-value-added mixed slag, which usually needs to be outsourced for solid waste treatment, resulting in significant resource waste. If aluminum fluoride is synthesized directly from this type of wastewater using conventional routes, there is usually a serious problem of excessive phosphorus content, making it difficult to meet product quality requirements. Currently, research on resource recovery and high-value utilization technologies for fluorine resources is still relatively weak, with the core bottleneck being the lack of economical, stable, and scalable high-value-added conversion processes. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies in treating fluoride and phosphorus-containing wastewater, such as low resource utilization and difficulty in achieving high-value conversion, and to provide a resource-based production method that can directly and efficiently convert fluoride resources in wastewater into high-purity, low-phosphorus aluminum fluoride products.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for the resource utilization of fluoride- and phosphorus-containing wastewater to produce aluminum fluoride includes the following steps: S1. Measure the phosphorus concentration in the fluoride- and phosphorus-containing wastewater. Calculate the theoretical dosage of the wastewater using the fitted model Y = 0.0484X + 1.97, where Y represents the excess of fluoride relative to the theoretical requirement, and X represents the phosphorus concentration in the wastewater, in g / L; R 2 Also known as goodness of fit, it represents the degree to which the independent variable X explains the dependent variable Y. R0 2The value of is between [0,1], and the closer it is to 1, the better the fit. It is only used to represent the fit effect and is not used in calculating wastewater usage. In the fitting model of this invention, R0... 2 =0.9939; S2. Prepare aluminum hydroxide slurry; S3. The theoretical amount of fluorine- and phosphorus-containing wastewater is preheated and mixed with aluminum hydroxide slurry to obtain a reaction solution. The reaction solution is reacted under heating and stirring conditions to obtain aluminum fluoride turbid liquid. S4. After solid-liquid separation of the turbid aluminum fluoride liquid, aluminum trihydrate solid is obtained. The aluminum trihydrate solid is then dried and calcined sequentially to obtain the aluminum fluoride product.

[0006] Furthermore, the fluorine- and phosphorus-containing wastewater in step S1 is a byproduct of lithium hexafluorophosphate production.

[0007] Furthermore, in step S2, the concentration of aluminum hydroxide slurry is 30-50%, preferably 50% (by mass).

[0008] Furthermore, in step S3, the preheating temperature of the fluoride- and phosphorus-containing wastewater is 50~100℃, preferably 50℃; the reaction temperature is 100~120℃, and the reaction time is 2~4h, preferably 120℃, and the reaction time is 3h.

[0009] Furthermore, in step S4, the drying temperature is 110-120℃, preferably 120℃, and the drying time is 2-4 hours, preferably 2 hours.

[0010] Furthermore, in step S4, the calcination temperature is 400-600℃, preferably 550℃, and the time is 2-4h, preferably 2h.

[0011] Furthermore, in step S4, the aluminum fluoride product has a fluorine content higher than 61%, an aluminum content higher than 31.5%, and a phosphorus content lower than 300 ppm.

[0012] The advantages of this invention are as follows: To achieve efficient recovery and high-value utilization of fluorine resources in fluorine- and phosphorus-containing wastewater during the production of lithium hexafluorophosphate, a quantitative model between phosphorus concentration in wastewater and key process parameters (fluorine dosage ratio) was established through systematic experiments. The core of controlling the phosphorus content of the product is to precisely adjust the fluorine dosage ratio according to the model, promoting the reaction of phosphorus and fluorine to generate PF5 or PF3 gas that escapes from the reaction system, reducing phosphorus co-precipitation, and thus reducing the phosphorus content in the product. Based on this model, the stoichiometric ratio of fluorine and aluminum is precisely controlled, effectively inhibiting the co-precipitation and physical entrainment of phosphorus impurities during the synthesis process. This allows the fluorine components in the wastewater to be directly converted into low-phosphorus, high-purity aluminum fluoride products that meet industrial standards, achieving a technological leap from pollution control to resource recycling. Attached Figure Description

[0013] Figure 1 This is a process flow diagram of the method for producing aluminum fluoride from fluoride- and phosphorus-containing wastewater according to the present invention. Detailed Implementation

[0014] Example 1 A method for the resource utilization of fluoride- and phosphorus-containing wastewater to produce aluminum fluoride is disclosed. The method involves using fluoride- and phosphorus-containing wastewater, a byproduct of lithium hexafluorophosphate production, with a phosphorus concentration of 32.84 g / L. This wastewater is used as raw material for resource utilization experiments. First, based on the phosphorus concentration in the wastewater (X = 32.84 g / L), a fitting model Y = 0.0484X + 1.97 is used, with R... 2 =0.9939, the fluorine addition ratio is calculated to be 3.57; aluminum hydroxide is prepared into a 50% slurry, which is slowly added to wastewater preheated to 50℃ under stirring to obtain an aluminum fluoride reaction solution; the aluminum fluoride reaction solution is continuously stirred at 100℃ for 3 hours to obtain an aluminum fluoride turbid liquid; the aluminum fluoride turbid liquid is separated into solid and liquid components to obtain aluminum trihydrate wet material; the aluminum trihydrate wet material is dried at 110℃ for 2 hours, and then calcined at 550℃ for 2 hours to finally obtain the aluminum fluoride product. Testing shows that the aluminum fluoride product contains 66.1% fluorine, 33.0% aluminum, and 117 ppm phosphorus.

[0015] Example 2 Except for adjusting the reaction temperature to 110℃, the raw materials, steps, and parameters were the same as in Example 1. The resulting aluminum fluoride product contained 65.2% fluorine, 33.5% aluminum, and 144 ppm phosphorus.

[0016] Example 3 Except for adjusting the reaction temperature to 120℃, the raw materials, steps, and parameters were the same as in Example 1. The resulting aluminum fluoride product had a fluorine content higher than 65.7%, an aluminum content higher than 33.0%, and a phosphorus content of 72.9 ppm.

[0017] Example 4 Fluorine- and phosphorus-containing wastewater, a byproduct of lithium hexafluorophosphate production, was tested and found to have a phosphorus concentration of 22.29 g / L. This wastewater was used as raw material for a resource utilization experiment. First, based on the phosphorus concentration in the wastewater (X = 22.29 g / L), a fitting model Y = 0.0484X + 1.97 was used, with R... 2=0.9939, the fluorine addition ratio is calculated to be 3.05; aluminum hydroxide is prepared into a 50% slurry, which is slowly added to wastewater preheated to 50℃ under stirring to obtain an aluminum fluoride reaction solution; the aluminum fluoride reaction solution is continuously stirred at 120℃ for 3 hours to obtain an aluminum fluoride turbid liquid; the aluminum fluoride turbid liquid is separated into solid and liquid components to obtain aluminum trihydrate wet material; the aluminum trihydrate wet material is dried at 110℃ for 2 hours, and then calcined at 550℃ for 2 hours to finally obtain the aluminum fluoride product. Testing shows that the aluminum fluoride contains 65.8% fluorine, 33.8% aluminum, and 206 ppm phosphorus, with a yield of 65.4%.

[0018] Example 5 Fluorine- and phosphorus-containing wastewater, a byproduct of lithium hexafluorophosphate production, was tested and found to have a phosphorus concentration of 17.7 g / L. This wastewater was used as raw material for a resource utilization experiment. First, based on the phosphorus concentration in the wastewater (X = 17.7 g / L), a fitting model Y = 0.0484X + 1.97 was established, with R... 2 =0.9939, the fluorine addition ratio is calculated to be 2.82; aluminum hydroxide is prepared into a 50% slurry, which is slowly added to wastewater preheated to 50℃ under stirring to obtain an aluminum fluoride reaction solution; the aluminum fluoride reaction solution is continuously stirred at 120℃ for 3 hours to obtain an aluminum fluoride turbid liquid; the aluminum fluoride turbid liquid is separated into solid and liquid components to obtain wet aluminum fluoride trihydrate; the wet aluminum fluoride trihydrate is dried at 110℃ for 2 hours, and then calcined at 550℃ for 2 hours to finally obtain the aluminum fluoride product. Testing shows that the aluminum fluoride contains 64.7% fluorine, 34.9% aluminum, and 289 ppm phosphorus.

[0019] Example 6 Fluorine- and phosphorus-containing wastewater, a byproduct of lithium hexafluorophosphate production, was tested and found to have a phosphorus concentration of 19.9 g / L. This wastewater was used as raw material for a resource utilization experiment. First, based on the phosphorus concentration in the wastewater (X = 19.9 g / L), a fitting model Y = 0.0484X + 1.97 was used, with R... 2 =0.9939, the fluorine addition ratio is calculated to be 2.93; aluminum hydroxide is prepared into a 50% slurry, which is slowly added to wastewater preheated to 50℃ under stirring to obtain an aluminum fluoride reaction solution; the aluminum fluoride reaction solution is continuously stirred at 120℃ for 3 hours to obtain an aluminum fluoride turbid liquid; the aluminum fluoride turbid liquid is separated into solid and liquid components to obtain aluminum trihydrate wet material; the aluminum trihydrate wet material is dried at 110℃ for 2 hours, and then calcined at 550℃ for 2 hours to finally obtain the aluminum fluoride product. Testing shows that the aluminum fluoride contains 61.6% fluorine, more than 32.4% aluminum, and 42.5 ppm phosphorus.

[0020] Comparative Example 1 Comparative Example 1 synthesized aluminum fluoride using a conventional route without model fitting. The fluorine addition factor was set to 2.23, and the remaining raw materials, steps, and parameters were the same as in Example 4. The resulting aluminum fluoride contained 65.2% fluorine, 33.6% aluminum, and 0.22% phosphorus.

[0021] Comparative Example 2 In Comparative Example 2, the wastewater dosage was not fitted using a model; the fluoride addition factor was directly set to 1.95. The remaining raw materials, steps, and parameters were the same as in Example 4. The resulting aluminum fluoride contained 66.8% fluoride, 32.7% aluminum, and 0.27% phosphorus.

Claims

1. A method for the resource utilization of fluoride- and phosphorus-containing wastewater to produce aluminum fluoride, characterized in that, Includes the following steps: S1. Measure the phosphorus concentration in fluoride- and phosphorus-containing wastewater and fit the model Y = 0.0484X + 1.97, R0 2 =0.9939 Calculate the theoretical amount of fluoride and phosphorus-containing wastewater, where Y represents the excess multiple of fluoride relative to the theoretical requirement, and X represents the phosphorus concentration in the fluoride and phosphorus-containing wastewater, with the unit being g / L; S2. Prepare aluminum hydroxide slurry; S3. The theoretical amount of fluorine- and phosphorus-containing wastewater is preheated and mixed with aluminum hydroxide slurry to obtain a reaction solution. The reaction solution is reacted under heating and stirring conditions to obtain aluminum fluoride turbid liquid. S4. After solid-liquid separation of the turbid aluminum fluoride liquid, aluminum trihydrate solid is obtained. The aluminum trihydrate solid is then dried and calcined sequentially to obtain the aluminum fluoride product.

2. The method as described in claim 1, characterized in that: The fluorine- and phosphorus-containing wastewater in step S1 is a byproduct of lithium hexafluorophosphate production.

3. The method as described in claim 1, characterized in that: In step S2, the concentration of aluminum hydroxide slurry is 30-50%.

4. The method as described in claim 1, characterized in that: In step S3, the preheating temperature of the fluoride- and phosphorus-containing wastewater is 50~100℃, the reaction temperature is 100~120℃, and the reaction time is 2~4h.

5. The method as described in claim 1, characterized in that: In step S4, the drying temperature is 110-120℃ and the drying time is 2-4 hours.

6. The method as described in claim 1, characterized in that: In step S4, the calcination temperature is 400-600℃ and the time is 2-4 hours.

7. The method as described in claim 1, characterized in that: In step S4, the aluminum fluoride product has a fluorine content higher than 61%, an aluminum content higher than 31.5%, and a phosphorus content lower than 300 ppm.

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