Preparation method of al-si composite adsorbent and application of al-si composite adsorbent in deep fluorine removal of acidic fluorine-containing wastewater

Abstract

A preparation method of Al-Si composite adsorbent and application thereof in deep fluorine removal in acidic fluorine-containing wastewater, comprising the following steps: step 1) dissolving Al(NO3)3 9H2O in deionized water to prepare an acidic solution A; step 2) dissolving Na2SiO3 9H2O in deionized water to prepare an alkaline solution B; step 3) adding the A solution and the B solution into deionized water drop by drop, and controlling the pH stability of the system by adding NH4OH solution drop by drop; step 4) placing the system in a constant-temperature water bath to realize the densification of the gel network and the full formation of Al-Si bonds, and obtaining an Al-Si sol; step 5) removing Na + , NO3 ‑ , and other impurities by washing through centrifugation or siphon method, and obtaining an Al-Si hydrated gel slurry; step 6) vacuum drying the Al-Si hydrated gel slurry after low-temperature drying and freezing, and obtaining a precursor powder; and step 7) heat treating the precursor powder in an air atmosphere, and naturally cooling to obtain an Al-Si composite adsorbent. The Al-Si composite adsorbent can realize deep purification of fluorine ions under strong acidic conditions.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment materials technology, specifically to a method for preparing an Al-Si composite adsorbent and its application in the deep defluorination of acidic fluoride-containing wastewater. Background Technology

[0002] Currently, commonly used defluoridation methods include calcium-based precipitation, adsorption, and membrane separation. Calcium-based precipitation is widely used due to its low cost and simple operation, but its residual fluoride concentration remains as high as 20-50 mg / L after treatment, limited by solubility product (Ksp) and reaction kinetics, making it difficult to meet the deep purification requirements for drinking water and industrial emissions. While membrane separation offers good purification, its large equipment investment, high operating costs, and susceptibility to clogging limit its large-scale application. Adsorption, due to its high efficiency, controllable cost, and ease of operation, has become the mainstream technology for deep defluoridation. Commonly used adsorbents include activated alumina, zeolite, and metal oxide composite materials.

[0003] Activated alumina (such as γ-Al₂O₃) is a traditional fluoride removal adsorbent, but it has poor stability under strongly acidic conditions and a limited adsorption capacity (5-25 mg F). - The fluoride content is low (e.g.), and it is prone to dissolution, leading to a decrease in treatment efficiency. Existing Al-Si composite adsorbents are mostly prepared with a low Al / Si ratio, which makes them easily soluble in strongly acidic environments and unable to operate stably for long periods. While some high-performance adsorbents can reduce residual fluoride concentration, they suffer from complex preparation processes, high costs, poor oxidation resistance, and activity decay during storage, hindering their industrial application. Therefore, developing a deep fluoride removal material with strong acid resistance, high adsorption activity, good stability, and simple preparation is key to solving the problem of treating acidic fluoride-containing wastewater.

[0004] Chinese patent (CN202411986811.3) proposes a method for removing fluoride from fluoride-containing wastewater by adding a complexing agent (Ce(SO4)2). 4- ) 2- Ce(NO) 3- ) 4- The adsorption column after saturation adsorption is eluted with an eluent to remove solid CeF3- fluoride. Chinese patent (CN202511254738.5) proposes a method and agent for treating fluoride-containing wastewater, involving MOFs / organic nanocrystals / rare earth titanium dioxide composite materials. While some high-performance adsorbents can reduce residual fluoride concentration, they suffer from complex preparation processes, high costs, poor oxidation resistance, and activity decay during storage, hindering their industrial application. Therefore, developing a deep fluoride removal material with strong acid resistance, high adsorption activity, good stability, and simple preparation is key to solving the problem of treating acidic fluoride-containing wastewater. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing an Al-Si composite adsorbent and its application in the deep defluorination of acidic fluoride-containing wastewater. By optimizing the Si / Al ratio and preparation process, a stable Al-O-Si cross-linked structure is constructed, solving the problems of easy solubility and insufficient active sites of traditional adsorbents under strongly acidic conditions, thus combining excellent acid resistance and high-efficiency defluorination performance. The present invention provides the application of this adsorbent in the deep defluorination of acidic fluoride-containing wastewater, achieving deep purification of fluoride ions under strongly acidic conditions and meeting the emission requirements of different scenarios.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing an Al-Si mixed gel material includes the following steps: Step 1): Preparation of solution A: Al(NO3)3 Dissolve 9H2O in deionized water to prepare acidic solution A; Step 2): Preparation of solution B: Na2SiO3 Dissolve 9H2O in deionized water (gentle heating below 40℃ aids dissolution) to prepare alkaline solution B; Step 3): Co-precipitation into a gel: Solution A and solution B were added dropwise to deionized water, and the pH of the system was controlled to be stable by adding NH4OH solution dropwise. Step 4): Aging: The above system was placed in a constant temperature water bath and allowed to stand to achieve gel network densification and full formation of Al-Si bonds, thus obtaining Al-Si sol. Step 5): Washing: Na is removed by washing with centrifugation or siphon. + NO3 - The Al-Si hydrated gel slurry was obtained by removing impurities such as [unspecified substances]. Step 6): Drying: The Al-Si hydrated gel slurry was dried at low temperature and then vacuum dried to obtain the precursor powder. Step 7): Roasting: The precursor powder was kept at a constant temperature in air and then naturally cooled to obtain the Al-Si composite adsorbent.

[0007] In step 1), the pH of solution A is 2.5-3, and solution A is Al³. + An acidic solution with a concentration of 0.2~1M.

[0008] In step 2), the pH of solution B is 11-13, and solution B is Si. 4+An alkaline solution with a concentration of 0.2~1M is prepared, and the Al / Si molar ratio is controlled to be 0.6~2.0.

[0009] In step 3), under conditions of 25-40℃ and strong stirring, the dropping rate of liquid A and liquid B is kept consistent, and stirring is continued for 30-120 minutes after the addition is completed; to ensure uniform reaction of the system; the pH of the gelation in step 3) is controlled at 6.8±0.2. In step 4), the above system is placed in a constant temperature water bath at 60~80℃ and left to stand for 4~24 hours.

[0010] In step 5), the gel slurry is washed 2-3 times by centrifugation or siphon method. After washing, the solid content of the gel slurry is controlled to be 8-12wt% to avoid excessive solid content leading to excessive densification of the structure during subsequent drying and calcination.

[0011] In step 6), the Al-Si hydrated gel slurry is dried at a low temperature of 40-60℃ for 12-24 hours, frozen for 3-6 hours, and then vacuum dried for 24-48 hours.

[0012] In step 7), the precursor powder is heated to 300℃~900℃ in air at a rate of 5℃ / min and held at that temperature for 1-6 hours.

[0013] An Al-Si hybrid gel material is presented as near-spherical / ellipsoidal particles, which are partially fused together. The overall surface of the particles is relatively smooth and they appear in the form of aggregates, forming a porous stacked structure that provides abundant sites for the adsorption process. It contains a stable Al-O-Si cross-linked structure and a high density of Al-OH active sites, and is stable and insoluble under strongly acidic conditions of pH=2.

[0014] The Al-Si mixed gel material is used in the deep defluorination of acidic fluoride-containing wastewater as a defluorination material for the deep defluorination treatment of acidic fluoride-containing wastewater. Al-Si mixed gel material is added to fluoride-containing wastewater at a dosage of 0.3-0.5 g / 80 mL of wastewater and reacted at 25-40℃ for 30-120 min. The initial fluoride ion concentration of the fluoride-containing wastewater is 30-50 ppm, and the pH of the wastewater is 2-7. After treatment, the fluoride ion concentration is reduced to ≤1.5 mg / L or ≤5-10 mg / L.

[0015] The acidic fluoride-containing wastewater includes metallurgical industry effluent, industrial circulating fluid, or other acidic process fluoride-containing wastewater.

[0016] The beneficial effects of this invention are: 1. Significantly improved acid resistance: Through optimization of the Si / Al molar ratio of 0.6~2.0, high-temperature aging at 60~80℃ and gradient calcination at 300-900℃, the product forms a dense and stable Al-O-Si cross-linked structure, which remains stable and insoluble under strong acidic conditions of pH=2, thus solving the technical bottleneck of acidic dissolution of traditional low Si / Al ratio adsorbents. 2. High fluoride removal efficiency: The high density of Al-OH active sites on the material surface and inside ensures an adsorption capacity of 12-20 mg F. - / g, can deeply purify fluoride ion concentration from 30-50ppm to ≤1.5mg / L or ≤5-10mg / L, meeting the dual standards for drinking water and industrial discharge; 3. The preparation process is simple and controllable: all raw materials used are conventional chemical reagents, no complicated equipment is required, the reaction conditions are mild, and the drying method and calcination temperature can be adjusted according to actual needs, making it suitable for large-scale industrial production; 4. Excellent stability and safety: The product is not easily oxidized and deactivated during storage. The fluoride complex formed after defluorination has high stability and no risk of secondary release. Moreover, no toxic or harmful substances are generated during the preparation process, making it environmentally friendly. 5. Wide range of applications: It is suitable for the treatment of various acidic fluoride-containing wastewaters such as metallurgical discharge liquids, industrial circulating liquids, and chemical wastewaters. It is especially suitable for strongly acidic wastewater scenarios with a pH of around 2, making it highly practical. Attached Figure Description

[0017] Figure 1 This is a process flow diagram for preparing acid-resistant Al-Si composite materials.

[0018] Figure 2 The image shows the state of the Si / Al=1.0 product (calcined at 300℃) after soaking in a solution at pH=2 for 24 hours (compared to the product of Comparative Example 1).

[0019] Figure 3 This is a scanning electron microscope image of the product calcined at 900℃. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the embodiments.

[0021] Example 1: Preparation and properties of Al-Si=1 adsorbent (calcined at 300℃): Step 1. Preparation of solution A: Weigh 188g Al(NO3)3 Dissolve 9H₂O in 700mL of deionized water, stir until completely dissolved, and then bring the volume to 1L to obtain 0.5MAl³. + Soluble (pH 2.5); Step 2. Preparation of solution B: Weigh 142g Na2SiO3 9H₂O was dissolved in 500 mL of deionized water, and the solution was gently heated at 35 °C to aid dissolution. After cooling to room temperature, 0.5 MSi was obtained. 4+ The solution (pH 12) was prepared with an Al / Si molar ratio of 1.0. Step 3. Co-precipitation into a gel: Add solution A and solution B dropwise simultaneously (reaction temperature 25℃), while adding 25% NH4OH solution to control pH=7, reaction temperature 25℃; Step 4. Aging: Transfer the system to a constant temperature water bath and age it at 80°C for 12 hours to form a dense Al-Si hydrated gel. Step 5. Washing: Wash three times by centrifugation to remove impurity ions and obtain Al-Si hydrated gel slurry; Step 6. Drying: Freeze-drying was used, freezing the material at -40℃ for 4 hours, followed by vacuum drying to obtain a loose precursor powder (sample C). Step 7. Calcination: Take 10g of sample C1, put it into a tube furnace, raise the temperature to 300℃ at a heating rate of 5℃ / min, keep it at that temperature for 3h, and then cool it naturally to obtain the adsorbent (sample C1: Al@Si-1-freeze-dry-calcined at 300℃).

[0022] Performance testing: 0.3g of sample C1 was added to 80mL of simulated fluoride-containing wastewater with an initial concentration of 30ppm and pH=2, and the mixture was stirred and reacted at 25℃ for 30min. Test results showed: Fluoride removal performance: Fluoride ion removal rate ≥94%, adsorption capacity up to 7.52 mgF - / g, the fluoride ion concentration after treatment is ≤1.8mg / L, which meets the drinking water standard; Acid resistance: No dissolution or turbidity was observed after soaking in a pH=2 solution for 2 hours, indicating that the system is stable.

[0023] Example 2: Preparation and properties of Al-Si=1 adsorbent (calcined at 400℃): The preparation of solution A and solution B, co-precipitation into a gel, aging, washing, and drying steps are the same as in Example 1, to obtain precursor powder (sample C). Calcination: Take 10g of sample C and place it in a tube furnace. Heat the temperature to 400℃ at a rate of 5℃ / min and hold for 3 hours. After natural cooling, the adsorbent is obtained (sample C2: Al@Si-1-freeze-drying-calcination at 400℃).

[0024] Performance testing: Sample C20.3g was added to 80mL of simulated fluoride-containing wastewater with an initial concentration of 30ppm and pH=2, and the mixture was stirred at 25℃ for 30min. Test results showed: Fluoride removal performance: Fluoride ion removal rate ≥96%, adsorption capacity up to 7.68 mg F - / g, the fluoride ion concentration after treatment is ≤1.2mg / L, which meets the drinking water standard; Acid resistance: No dissolution was observed after soaking in a pH=2 solution for 4 hours, indicating structural stability; Example 3: Preparation and properties of Al-Si=1 adsorbent (calcination at 900℃): The preparation of solution A and solution B, co-precipitation into a gel, aging, washing, and drying steps are the same as in Example 2, to obtain precursor powder (sample C); Calcination: Take 10g of sample C, put it into a tube furnace, raise the temperature to 900℃ at a heating rate of 5℃ / min, hold for 3h, and then cool naturally to obtain the adsorbent (sample C3: Al@Si-1-freeze-dry-calcined at 900℃).

[0025] Performance testing: 0.3 g of sample C was added to 80 mL of simulated fluoride-containing wastewater with an initial concentration of 30 ppm and pH=2. The mixture was stirred and reacted at 25°C for 30 min. Test results showed: Fluoride removal performance: Fluoride ion removal rate ≥96%, adsorption capacity up to 7.68 mg F - / g, the fluoride ion concentration after treatment is ≤1.2mg / L, which meets the metallurgical discharge / circulating liquid standard; Acid resistance: It showed no dissolution or structural damage after soaking in a pH=2 solution for 8 hours, indicating the best acid resistance. Comparative Example 1: Preparation and performance of Al-Si=1 adsorbent (drying method comparison reference): Step 1. Preparation of solution A: Weigh 188g Al(NO3)3 Dissolve 9H₂O in 700mL of deionized water, stir until completely dissolved, and then bring the volume to 1L to obtain 0.5MAl³. + Solution (pH 2.5); Step 2. Preparation of solution B: Weigh 71g of Na2SiO3 9H₂O was dissolved in 500 mL of deionized water, and the solution was gently heated at 35 °C to aid dissolution. After cooling to room temperature, 0.25 MSi was obtained. 4+ Solution (pH 12), control Al / Si molar ratio = 1; Step 3. Co-precipitation into a gel: Add 200mL of deionized water to a 2L beaker, turn on strong stirring, and add solution A and solution B dropwise simultaneously (reaction temperature 25℃). At the same time, add 25% NH4OH solution dropwise to control pH=6.8±0.2. After the addition is complete, continue stirring for 30min. Step 4. Aging: Transfer the system to a constant temperature water bath and age at 80°C for 12 hours to form Al-Si hydrated gel; Step 5. Washing: Wash three times by centrifugation, each time at 3000 rpm for 10 minutes, to remove Na. + NO3- Impurities were removed to obtain Al-Si hydrated gel slurry; Step 6. Drying: Place the samples in a 105℃ oven and dry for 12 hours to obtain precursor powders (samples A, B, and C). Step 7. Calcination: Take 10g of samples A and B respectively, place them in a tube furnace, and heat them to 300℃, 400℃, and 900℃ respectively at a heating rate of 5℃ / min. Hold each temperature for 3 hours, and after natural cooling, obtain two adsorbents: Sample A1: Al@Si - 1-105℃ drying - 300℃ calcination Sample B1: Al@Si - 105℃ drying - 400℃ calcination Sample C1: Al@Si - 1-105℃ drying - 900℃ calcination Performance testing: 0.3g of each of the three samples was added to 80mL of simulated fluoride-containing wastewater with an initial concentration of 30ppm and pH=2, and the mixture was stirred and reacted at 25℃ for 30min. The test results showed: The defluorination efficiency ranking was: Sample B1 (oven drying + calcination at 400℃) > Sample C1 (oven drying + calcination at 300℃) > Sample A1 (oven drying + calcination at 900℃). Sample B1 had a removal rate of only 60% and an adsorption capacity of 4.8 mg F. - / g; Comparative Example 1 illustrates that drying in a 105℃ oven has a negative impact on the material. The material particles become harder, leading to severe agglomeration. The originally loose islands collapse, shrink, and undergo dehydration and condensation on the surface, resulting in a reduction of adsorption sites.

[0026] Comparative Example 2: Preparation and performance of Al-Si=0.5 adsorbent (acid resistance comparison reference): Step 1. Preparation of solution A: Weigh 188g Al(NO3)3 Dissolve 9H₂O in 700mL of deionized water, stir until completely dissolved, and then bring the volume to 1L to obtain 0.5MAl³. + Solution (pH 2.5); Step 2. Preparation of solution B: Weigh 71g of Na2SiO3 9H₂O was dissolved in 500 mL of deionized water, and the solution was gently heated at 35 °C to aid dissolution. After cooling to room temperature, 0.25 MSi was obtained. 4+ The solution (pH 12) was prepared with an Al / Si molar ratio of 0.5. Step 3. Co-precipitation into a gel: Add 200mL of deionized water to a 2L beaker, turn on strong stirring, and add solution A and solution B dropwise simultaneously (reaction temperature 25℃). At the same time, add 25% NH4OH solution dropwise to control pH=6.8±0.2. After the addition is complete, continue stirring for 30min. Step 4. Aging: Transfer the system to a constant temperature water bath and age at 80°C for 12 hours to form Al-Si hydrated gel; Step 5. Washing: Wash three times by centrifugation, each time at 3000 rpm for 10 minutes, to remove Na. + NO3 - Impurities were removed to obtain Al-Si hydrated gel slurry; Step 6. Drying: Using freeze drying, a loose precursor powder (sample D) and a precursor powder (sample E) are obtained. Step 7. Calcination: Take 10g each of samples D and E, place them in a tube furnace, and heat to 300℃ and 400℃ respectively at a heating rate of 5℃ / min, hold each temperature for 3 hours, and then allow to cool naturally to obtain two adsorbents: Sample D1: Al@Si-0.5-freeze-dried-calcined at 300℃ Sample E1: Al@Si-0.5-freeze-dried-calcined at 400℃ Performance testing: 0.3g of each of the two samples was added to 80mL of simulated fluoride-containing wastewater with an initial concentration of 30ppm and pH=2, and the mixture was stirred and reacted at 25℃ for 30min. The test results showed: The defluorination efficiency ranking was: Sample E1 (calcined at 400℃ + freeze-dried) > Sample D1 (calcined at 300℃ + freeze-dried), with Sample E2 having a removal rate of 62% and an adsorption capacity of 4.96 mg F. - / g; Acid resistance: Both samples showed significant dissolution after being soaked in a solution with pH=2, resulting in turbidity and low removal rate.

[0027] Comparative example 1 illustrates that different Al-Si ratios affect the acid resistance of materials. If the Si content is too low, the Al sites in the gel material to be formed will be exposed, leading to the dissolution and consumption of the material.

[0028] This invention provides a method for preparing an acid-resistant Al-Si composite adsorbent, the specific technical points of which are as follows: 1. Raw material selection and ratio optimization: using Al(NO3)3 9H2O is the aluminum source, Na2SiO3 Using 9H2O as the silicon source and controlling the Si / Al molar ratio, a stable Al-O-Si cross-linked structure is formed through the synergistic effect of silicon and aluminum elements, solving the problem of acidic dissolution of low-proportion products; using 25-28% NH4OH solution as a pH adjuster ensures that the pH of the system is stable and controllable during the gelation process.

[0029] 2. Control of key process parameters: 1) Gel formation stage: Control the reaction temperature at 25-40℃, pH at 6.8-7.2 (preferably 6.8±0.2), and the Al-Si ratio at 0.6-2. These conditions are conducive to the formation and stability of Al-OH and Al-O-Si bonds. Add solution A and solution B simultaneously to ensure reaction uniformity and avoid product agglomeration caused by excessively high local concentrations. 2) Aging stage: Aging is carried out in a constant temperature water bath at 60~80℃ for 12~24h. Compared with traditional low temperature short-time aging, it can strengthen the densification of gel network and cross-linking of Al-O-Si bonds, and improve the structural stability of the material. 3) Drying stage: Freeze-drying can be used to prepare high-performance precursors to meet the needs of different production conditions; 4) Calcination stage: Calcination temperature of 300~900℃ is used, and the material is heated at a heating rate of 5℃ / min and held for 1-6h (preferably 2h) to further promote Al-O-Si bond condensation, expose more high-density Al-OH active sites, and improve the mechanical strength and acid resistance of the material.

[0030] 3. Product structure design: The final Al-Si composite adsorbent has an Al-O-Si cross-linked structure as its framework, with a large number of Al-OH active sites distributed on its surface and inside. This ensures structural stability under strong acid conditions and achieves efficient fluoride removal through the specific binding of active sites with fluoride ions.

[0031] like Figure 1 The Al-Si hydrated gel sample, as shown in the aging stage, consists of two parts: the upper layer, primarily composed of deionized water as the main solvent, and the inner layer containing unreacted soluble ions (NO3). - The lower layer is an Al-Si hydrated gel aggregate, which is a structure formed by the dehydration condensation of a large number of sodium aluminum hydroxide and silica sol particles. The particles are interconnected by Al-O-Si bonds and hydroxyl hydrogen bonds.

[0032] like Figure 2 The diagram shows the dissolution phenomenon of Al@Si-0.5-freeze-dried-300℃ calcined material. The material dissolves at pH=2, which is manifested by the pH of the solution rising and the solution becoming turbid. The reaction is irreversible, indicating that the material has poor acid resistance.

[0033] like Figure 3 The SEM image of the Al@Si-1-freeze-dried-900℃ calcined material shown shows that the particle morphology and size are relatively uniform, mainly distributed between 0.2 and 1 μm. The particle surface is smooth and has a slight melting feel, which is a typical feature of high-temperature calcination at 900℃. However, the particles exist in the form of soft agglomerates, without serious hard agglomeration, thanks to the protection of the porous structure of the material by freeze-drying.

Claims

1. A method for preparing an Al-Si mixed gel material, characterized in that, Includes the following steps: Step 1): Add Al(NO3)3 Dissolve 9H2O in deionized water to prepare acidic solution A; Step 2): Na2SiO3 Dissolve 9H2O in deionized water to prepare alkaline solution B; Step 3): Add solution A and solution B dropwise to deionized water, and control the pH of the system to be stable by adding NH4OH solution dropwise; Step 4): The above system was placed in a constant temperature water bath and allowed to stand to achieve gel network densification and full formation of Al-Si bonds, thus obtaining Al-Si sol; Step 5): Wash the Al-Si hydrated gel slurry by centrifugation or siphon method; Step 6): The Al-Si hydrated gel slurry is dried at low temperature and then vacuum dried to obtain the precursor powder; Step 7): The precursor powder is kept at a constant temperature in air and then naturally cooled to obtain the Al-Si composite adsorbent.

2. The method for preparing an Al-Si mixed gel material according to claim 1, characterized in that, In step 1), the pH of solution A is 2.5-3, and solution A is Al³. + An acidic solution with a concentration of 0.2~1M.

3. The method for preparing an Al-Si mixed gel material according to claim 1, characterized in that, In step 2), the pH of solution B is 11-13, and solution B is Si. 4+ An alkaline solution with a concentration of 0.2~1M.

4. The method for preparing an Al-Si mixed gel material according to claim 1, characterized in that, In step 3), under strong stirring conditions at 25-40℃, the dropping rate of liquid A and liquid B is kept consistent, and stirring is continued for 30-120 minutes after the addition is completed; to ensure uniform reaction of the system; the pH of the gelation in step 3) is controlled at 6.8±0.2; and the Al / Si molar ratio is controlled at 0.6-2.

0.

5. The method for preparing an Al-Si mixed gel material according to claim 1, characterized in that, In step 4), the above system is placed in a constant temperature water bath at 60~80℃ and left to stand for 4~24 hours.

6. The method for preparing an Al-Si mixed gel material according to claim 1, characterized in that, In step 5), the gel slurry is washed 2-3 times by centrifugation or siphon method. After washing, the solid content of the gel slurry is controlled to be 8-12wt% to avoid excessive solid content leading to excessive densification of the structure during subsequent drying and calcination.

7. The method for preparing an Al-Si mixed gel material according to claim 1, characterized in that, In step 6), the Al-Si hydrated gel slurry is dried at a low temperature of 40-60℃ for 12-24 hours, frozen for 3-6 hours, and then vacuum dried for 24-48 hours.

8. The method for preparing an Al-Si mixed gel material according to claim 1, characterized in that, In step 7), the precursor powder is heated to 300℃~900℃ in air at a rate of 5℃ / min and held at that temperature for 1-6 hours.

9. An Al-Si mixed gel material prepared by the method according to any one of claims 1-8, characterized in that, The hybrid gel material presents as near-spherical / ellipsoidal particles, some of which are fused together. The overall surface of the particles is relatively smooth, and they appear in the form of aggregates, forming a porous stacked structure that provides abundant sites for the adsorption process. It contains a stable Al-O-Si cross-linked structure and a high density of Al-OH active sites, and is stable and insoluble under strongly acidic conditions with pH=2.

10. The application of the Al-Si mixed gel material prepared by the method according to any one of claims 1-8 in the deep defluorination of acidic fluoride-containing wastewater, characterized in that, Al-Si mixed gel material is added to fluoride-containing wastewater at a dosage of 0.3-0.5 g / 80 mL of wastewater and reacted at 25-40℃ for 30-120 min. The initial fluoride ion concentration of the fluoride-containing wastewater is 30-50 ppm, and the pH of the wastewater is 2-7. After treatment, the fluoride ion concentration is reduced to ≤1.5 mg / L or ≤5-10 mg / L.

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