A method for separating fluorosilicic acid and hydrofluoric acid using anion exchange membranes

Abstract

This invention discloses a method for separating fluorosilicic acid and hydrofluoric acid using an anion exchange membrane, comprising the following steps: adding a flocculant to a fluorosilicic acid-hydrofluoric acid mixture, aging it, then adding a desulfurizing agent to carry out a desulfurization reaction to obtain a mixed solution, adding the mixed solution to the feed side of an anion exchange membrane for membrane separation, and obtaining a hydrofluoric acid solution with a mass concentration of 2-30% on the clear water side after separation. This invention uses a flocculant to rapidly settle solids such as sodium fluorosilicate and potassium fluorosilicate in the fluorosilicic acid-hydrofluoric acid mixture, uses a desulfurizing agent to remove sulfuric acid, and then uses an anion exchange membrane to effectively separate fluorosilicic acid and hydrofluoric acid in the fluorosilicic acid-hydrofluoric acid mixed solution. The hydrofluoric acid separated by membrane separation has high purity and high output value, increases the utilization rate of by-product hydrofluoric acid, and reduces costs.

Description

Technical Field

[0001] This invention relates to the field of chemical production, and specifically to a method for separating fluorosilicic acid-hydrofluoric acid using anion exchange membranes. Background Technology

[0002] In the production of hydrogen fluoride using the fluorite process and the etching of glass with hydrofluoric acid, a large amount of fluorosilicic acid-fluorosilicic acid mixture is generated. The concentrations of fluorosilicic acid and hydrofluoric acid are typically 5-40%, mixed with a small amount of sulfuric acid, generally at a concentration of 1-2%, and accompanied by solids such as sodium fluorosilicate and potassium fluorosilicate that are difficult to precipitate. Due to the similar properties of fluorosilicic acid and hydrofluoric acid, it is difficult to find a method to separate this mixture into fluorosilicic acid and hydrofluoric acid without undergoing a chemical change. Generally, the fluorosilicic acid-hydrofluoric acid solution is used to process fluoride salts or neutralized with lime to remove acidity, turning it into calcium fluoride (calcium fluorosilicate) for storage.

[0003] With the development of novel organic membrane materials and their application technologies, their superiority in liquid and gas phase separation is increasing, and their application range is becoming wider. Membrane separation typically features high separation efficiency, low energy consumption, and low cost. Among them, anion exchange membranes, with their unique pore channels and charge distribution, exhibit high selectivity for anion permeability.

[0004] Existing technologies present the problem that fluorosilicic acid and hydrofluoric acid are difficult to separate directly in fluorosilicic acid-hydrofluoric acid solutions. Summary of the Invention

[0005] This invention addresses the problem of the difficulty in directly separating fluorosilicic acid and hydrofluoric acid in fluorosilicic acid-hydrofluoric acid solutions, and aims to provide a method for separating fluorosilicic acid and hydrofluoric acid using an anion exchange membrane.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for separating fluorosilicic acid-hydrofluoric acid using an anion exchange membrane includes the following steps:

[0008] A flocculant is added to a fluorosilicic acid-hydrofluoric acid mixture, which is then aged. A desulfurizing agent is added, and a desulfurization reaction is carried out to obtain a mixed solution. The mixed solution is then added to the feed side of an anion exchange membrane for membrane separation. After separation, a hydrofluoric acid solution with a mass concentration of 2-30% is obtained on the water side.

[0009] Furthermore, in the fluorosilicic acid-hydrofluoric acid mixed solution, the mass concentration of fluorosilicic acid is 5-30%, the mass concentration of hydrofluoric acid is 5-50%, and the mass concentration of sulfuric acid is 1-2%.

[0010] Furthermore, the flocculant is polyacrylamide.

[0011] Furthermore, the amount of flocculant added is 0.1-0.5‰ of the mass of the fluorosilicic acid-hydrofluoric acid mixture.

[0012] Furthermore, the desulfurization temperature is 30-70℃, and the time is 2-4 hours.

[0013] Furthermore, the desulfurizing agent is calcium carbonate, calcium hydroxide, barium carbonate, or barium hydroxide.

[0014] Furthermore, the amount of desulfurizing agent used is 1.02-1.05 times the amount of sulfuric acid in the fluorosilicic acid-hydrofluoric acid mixture.

[0015] Furthermore, the preparation method of the anion exchange membrane is as follows: the anion membrane material is dissolved in an organic solvent, and after complete dissolution, it is ultrasonically degassed and allowed to stand to obtain a casting solution; the base membrane is fully impregnated in the organic solvent, and then the base membrane is transferred to the casting solution for full impregnation; the impregnated base membrane is fixed on a polytetrafluoroethylene plate, and then the base membrane is coated by scraping, and then placed in an oven to dry to obtain an anion exchange membrane.

[0016] Furthermore, the thickness of the anion exchange membrane is 120–200 μm.

[0017] Furthermore, the anion exchange membrane material is a cyclic ammonium type phenolphthalein polyarylether sulfone membrane material.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention provides a novel method for separating fluorosilicic acid and hydrofluoric acid from a fluorosilicic acid-hydrofluoric acid mixed solution. The method involves using a flocculant to rapidly settle solids such as sodium fluorosilicate and potassium fluorosilicate in the mixture, removing sulfuric acid using a desulfurizing agent, and then effectively separating the fluorosilicic acid and hydrofluoric acid from the mixed solution using an anion exchange membrane. The hydrofluoric acid separated by the membrane has high purity and high production value, increasing the utilization rate of by-product hydrofluoric acid, reducing costs, and providing an efficient separation method for hydrofluoric acid production tailings and hydrofluoric acid glass etching solutions. It also effectively protects my country's fluorite resources.

[0020] Furthermore, the anion exchange membrane material in this invention is a cyclic ammonium-type phenolphthalein polyarylethersulfone membrane material. By selecting the quaternary ammonium salt functional groups, the pore size can be effectively adjusted, thereby achieving different diffusion properties for different anions and realizing anion separation. This membrane material also has the characteristics of acid resistance, alkali resistance, and high temperature resistance, exhibiting high stability. This invention fabricates the membrane material into a membrane cell module for direct and effective separation of fluorosilicic acid and hydrofluoric acid, offering great flexibility in production and facilitating the efficient utilization of this fluorosilicic acid-hydrofluoric acid mixed solution. Attached Figure Description

[0021] Figure 1This is a flowchart of the method of the present invention. Detailed Implementation

[0022] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0023] See Figure 1 The present invention provides a method for separating fluorosilicic acid-hydrofluoric acid using an anion exchange membrane, comprising the following steps:

[0024] (a) A flocculant is added to the fluorosilicic acid-hydrofluoric acid mixture used in the fluorite process for etching glass with hydrogen fluoride and hydrofluoric acid, and aging is carried out to allow solids such as sodium fluorosilicate and potassium fluorosilicate to settle rapidly; wherein, in the fluorosilicic acid-hydrofluoric acid mixture, the mass concentration of fluorosilicic acid is 5-30%, the mass concentration of hydrofluoric acid is 5-50%, and the mass concentration of sulfuric acid is 1-2%. The preferred flocculant is polyacrylamide, and the amount of flocculant added is 0.1-0.5‰ of the mass of the fluorosilicic acid-hydrofluoric acid mixture.

[0025] (b) Add the fluorosilicic acid-hydrofluoric acid mixed solution to the desulfurizing agent to remove sulfuric acid from the mixed solution; wherein the desulfurization temperature is 30-70℃ and the time is 2-4h, and the desulfurizing agent is preferably calcium carbonate, calcium hydroxide, barium carbonate or barium hydroxide.

[0026] (c) Add the mixture obtained in step (b) to the feed side of the anion exchange membrane for membrane separation;

[0027] (d) The fluorosilicic acid remaining on the raw material side after separation is used for the production of fluoride salts, and a hydrofluoric acid solution with a mass concentration of 2-30% is obtained on the water side.

[0028] The anion exchange membrane is prepared as follows: the anion membrane material is dissolved in an organic solvent, and after complete dissolution, it is ultrasonically degassed for 5-30 minutes and allowed to stand for 1-2 hours to obtain a casting solution; the base membrane is fully impregnated in the organic solvent, and then the base membrane is transferred to the casting solution for full impregnation; the impregnated base membrane is fixed on a polytetrafluoroethylene plate, and then the base membrane is coated by scraping, and then placed in an oven to dry for 5-7 hours to obtain an anion exchange membrane with a thickness of 120-200 μm.

[0029] The base film is preferably at least one of PVDF film, PTFE film, PP film, nylon mesh and PP mesh, wherein the pore size of PVDF film, PTFE film and PP film is 0.22μm to 30μm, and the mesh number of nylon mesh and PP mesh is 100 to 400 mesh.

[0030] The viscosity of the casting solution at 25°C is 10000–20000 mPa·s;

[0031] The purity of the anion exchange membrane material is >95%, and the molecular weight is 50,000 to 150,000, preferably around 70,000 to 140,000.

[0032] The mass ratio of the anion exchange membrane material to the organic solvent is 1:1 to 9;

[0033] The organic solvent is preferably dimethyl sulfoxide, 2-pyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide.

[0034] The preferred anion exchange membrane is a cyclic ammonium phenolphthalein polyarylether sulfone membrane material. This cyclic ammonium phenolphthalein polyarylether sulfone membrane material is prepared through the following process: Under nitrogen protection, cyclic ammonium phenolphthalein, 4,4-difluorodiphenyl sulfone, biphenyl phenol, a basic compound, DMSO, and toluene are added to a reaction flask and refluxed at 140°C for 8 hours. After reflux, toluene and water are removed by azeotropic distillation. The reaction is then carried out at 180°C for 12 hours to obtain a viscous polymerization solution. After cooling to room temperature, DMSO is added for dilution, the solid is filtered off, and the solution is poured into water at 70°C to obtain the polymer product. The polymer product is then vacuum-dried at 120°C for 20–28 hours to obtain a PES-PPH-Pi polymer. The PES-PPH-Pi polymer is dissolved in DMSO, and iodomethane (twice the molar amount of amino groups in the PES-PPH-Pi polymer) is added. The mixture is stirred at room temperature for 6–8 hours, then precipitated in ethanol to obtain the polymer. After filtration, the polymer is vacuum-dried at 80°C for 24 hours to obtain the anion exchange membrane material.

[0035] The cyclic ammonium phenolphthalein structure is shown in formula (1):

[0036]

[0037] In formula (1), the R group is a nitrogen-containing heterocycle, preferably piperidinyl, tetrahydropyrroleyl or morpholinyl;

[0038] The alkaline compound is preferably sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, magnesium hydroxide, barium carbonate, or barium hydroxide.

[0039] The following are specific examples.

[0040] Example 1

[0041] Preparation of membrane material: A 500 mL three-necked flask was purged with nitrogen and fitted with a condenser and a water separator. 11.7 mmol piperidinium cycloammonium phenolphthalein (PPH-Pi), 14.6 mmol 4,4-difluorodiphenyl sulfone, 2.9 mmol biphenyl hydroquinone, 43.8 mmol K₂CO₃, 46 mL DMSO, and 6 mL toluene were added. The mixture was refluxed at 140 °C for 8 h. After reflux, the toluene and water were removed by azeotropic distillation. The mixture was then reacted at 180 °C for 12 h to obtain a viscous polymerization solution. After cooling to room temperature, 100 mL of [the solution] was added... The solid was filtered off by diluting the product with DMSO and then poured into water at 70°C to obtain the polymer product. The polymer was then vacuum dried at 120°C for 20 hours and then dissolved in DMSO. Iodomethane with twice the molar amount of amino groups in the polymer was added. The mixture was stirred at room temperature for 6 hours, and the polymer was precipitated in ethanol. After filtration, the polymer was vacuum dried at 80°C for 24 hours to obtain the cyclic ammonium phenolphthalein polyarylene ether sulfone membrane, i.e., the iodinated membrane material PES-PPH-Pi, with a molecular weight of approximately 70,000.

[0042] Preparation of the anion exchange membrane: 2g of iodinated membrane material PES-PPH-Pi with a piperidinyl R group was dissolved in 8g of DMSO and stirred for 3 hours until completely dissolved. The solution was then ultrasonically degassed for 10 minutes and allowed to stand for 1 hour to obtain the casting solution. A 0.22μm PP base membrane was thoroughly immersed in the DMSO solution to remove air bubbles. The 0.22μm PP base membrane was then immersed in the prepared casting solution. The immersed 0.22μm PP base membrane was laid flat on a polytetrafluoroethylene (PTFE) plate and rolled with a roller to ensure a tight bond between the base membrane and the casting solution, eliminating air bubbles. The PTFE plate was transferred to a 70℃ oven and dried for 7 hours to obtain an anion exchange membrane (150μm thick). The anion exchange membrane was repeatedly rinsed in deionized water and then immersed in deionized water for later use.

[0043] Separation: Polyacrylamide (0.5‰ of the mass of the fluorosilicic acid-hydrofluoric acid mixture) was added to a fluorosilicic acid-hydrofluoric acid mixture obtained by glass etching (fluorosilicic acid mass content 15%, hydrofluoric acid mass content 2%, sulfuric acid mass content 2%, and total mass content of insoluble substances such as sodium fluorosilicate and potassium fluorosilicate 1%). After aging for 6 hours, the mixture was filtered to obtain a clear fluorosilicic acid-hydrofluoric acid mixture. Calcium carbonate (1.02 times the mass of sulfuric acid) was then added to this mixture, and the mixture was reacted at 30°C for 2 hours. After precipitation and filtration, a desulfurized fluorosilicic acid-hydrofluoric acid mixture solution was obtained. This solution was then added to the feed side of the anion exchange membrane, and water was added to the product side of the membrane tank for automatic diffusion. After 5 hours, hydrofluoric acid with a mass concentration of 20% was obtained on the water side, while the feed side yielded a fluorosilicic acid solution.

[0044] The separation efficiency of hydrofluoric acid is 98.3%, and the mass content of fluorosilicic acid is less than 0.05%, meeting the requirements of Class I industrial hydrofluoric acid in GB 7744-2008.

[0045] Example 2

[0046] Preparation of membrane material: A 500 mL three-necked flask was purged with nitrogen and fitted with a condenser and a water separator. 12.1 mmol of morpholinocycloammonium phenolphthalein (PPH-Mor), 14.6 mmol of 4,4-difluorodiphenyl sulfone, 3.1 mmol of biphenyl phenol, 88 mmol of potassium hydroxide, 46 mL of DMSO, and 6 mL of toluene were added. The mixture was refluxed at 140 °C for 6 h. After reflux, the toluene and water were removed by azeotropic distillation. The mixture was then reacted at 180 °C for 12 h to obtain a viscous polymerization solution. After cooling to room temperature, 120 mL of DMSO was added for dilution, the solid was filtered off, and the solution was poured into water at 70 °C to obtain the polymer product. The polymer was vacuum dried at 120 °C for 28 h, then dissolved in DMSO. Iodomethane with a molar amount twice that of the amino group in the polymer was added. The mixture was stirred at room temperature for 8 h, precipitated in ethanol, filtered, and vacuum dried at 80 °C for 24 h to obtain the iodinated membrane material PES-PPH-Mor, with a molecular weight of approximately 85,000.

[0047] Preparation of the anion exchange membrane: PES-PPH-Mor (3g), a membrane material with a morpholino group (R group), was dissolved in 10g of 2-pyrrolidone. The mixture was stirred for 5 hours until completely dissolved, followed by ultrasonic degassing for 20 minutes and standing for 2 hours to obtain the casting solution. A 0.22μm PVDF base membrane was thoroughly immersed in the 2-pyrrolidone solution to remove air bubbles. Then, the 0.22μm PVDF base membrane was immersed in the prepared casting solution. The immersed 0.22μm PVDF base membrane was laid flat on a polytetrafluoroethylene (PTFE) plate and rolled with a roller to ensure a tight bond between the base membrane and the casting solution, eliminating air bubbles. The PTFE plate was transferred to a 70℃ oven and dried for 7 hours to obtain an anion exchange membrane (120μm thick). The anion exchange membrane was repeatedly rinsed in deionized water and then immersed in deionized water for later use.

[0048] Separation: Polyacrylamide (0.5‰ of the mass of the fluorosilicic acid-hydrofluoric acid mixture) was added to a fluorosilicic acid-hydrofluoric acid mixture obtained from glass etching (10% fluorosilicic acid, 35% hydrofluoric acid, 2% sulfuric acid, and 1% total mass of insoluble substances such as sodium fluorosilicate and potassium fluorosilicate). After aging for 6 hours, the mixture was filtered to obtain a clear fluorosilicic acid-hydrofluoric acid solution. Calcium carbonate (1.02 times the mass of sulfuric acid) was then added to this solution, and the mixture was reacted at 30°C for 3 hours. After precipitation and filtration, a desulfurized fluorosilicic acid-hydrofluoric acid solution was obtained. This solution was then added to the feed side of an anion exchange membrane, and water was added to the product side of the membrane. Automatic diffusion was performed. After 10 hours, hydrofluoric acid with a mass concentration of 34% was obtained on the water side, while the feed side yielded a fluorosilicic acid solution.

[0049] The separation efficiency of hydrofluoric acid is 96%, and the mass content of fluorosilicic acid is less than 0.05%, which meets the requirements of Class I industrial hydrofluoric acid in GB 7744-2008.

[0050] Example 3

[0051] Preparation of membrane material: A 500 mL three-necked flask was purged with nitrogen and fitted with a condenser and a water separator. 11.5 mmol tetrahydropyrrolidone cycloammonium phenolphthalein (PPH-Py), 14.6 mmol 4,4-difluorodiphenyl sulfone, 3.3 mmol biphenyl phenol, 88 mmol sodium hydroxide, 46 mL DMSO, and 6 mL toluene were added. The mixture was refluxed at 140 °C for 7 h. After reflux, the toluene and water were removed by azeotropic distillation. The mixture was then reacted at 180 °C for 12 h to obtain a viscous polymerization solution. After cooling to room temperature, 115 mL DMSO was added for dilution, the solid was filtered off, and the solution was poured into water at 70 °C to obtain the polymer product. The polymer was vacuum dried at 120 °C for 28 h, then dissolved in DMSO. Iodomethane with a molar amount twice that of the amino group in the polymer was added. The mixture was stirred at room temperature for 8 h, precipitated in ethanol, filtered, and vacuum dried at 80 °C for 24 h to obtain the iodinated membrane material PES-PPH-Py, with a molecular weight of approximately 140,000.

[0052] Preparation of the anion exchange membrane: 5g of PES-PPH-Py membrane material with a tetrahydropyrrole group (R group) was dissolved in 20g of DMSO and stirred for 3 hours until completely dissolved. The solution was then ultrasonically degassed for 30 minutes and allowed to stand for 2 hours to obtain the casting solution. A 0.22μm PP base membrane was thoroughly immersed in the DMSO solution to remove air bubbles. The 0.22μm PP base membrane was then immersed in the prepared casting solution. The immersed 0.22μm PP base membrane was laid flat on a polytetrafluoroethylene (PTFE) plate and rolled with a roller to ensure a tight bond between the base membrane and the casting solution, eliminating air bubbles. The PTFE plate was transferred to a 70℃ oven and dried for 5 hours to obtain an anion exchange membrane (200μm thick). The anion exchange membrane was repeatedly rinsed in deionized water and then immersed in deionized water for later use.

[0053] Separation: Polyacrylamide (0.5‰ of the mass of the fluorosilicic acid-hydrofluoric acid mixture) was added to a fluorosilicic acid-hydrofluoric acid mixture obtained from glass etching (5% fluorosilicic acid, 30% hydrofluoric acid, 2% sulfuric acid, and 1% total mass of insoluble substances such as sodium fluorosilicate and potassium fluorosilicate). After aging for 6 hours, the mixture was filtered to obtain a clear fluorosilicic acid-hydrofluoric acid mixture. Calcium carbonate (1.02 times the mass of sulfuric acid) was then added to this mixture, and the mixture was reacted at 30°C for 2 hours. After precipitation and filtration, a desulfurized fluorosilicic acid-hydrofluoric acid mixture solution was obtained. This solution was then added to the feed side of an anion exchange membrane, and water was added to the product side of the membrane. Automatic diffusion was performed. After 10 hours, hydrofluoric acid with a mass concentration of 29% was obtained on the water side, while the fluorosilicic acid solution remained on the feed side.

[0054] The separation efficiency of hydrofluoric acid is 97.3%, and the mass content of fluorosilicic acid is less than 0.05%, meeting the requirements of Class I industrial hydrofluoric acid in GB 7744-2008.

[0055] This invention can increase a company's profit by 5,000 yuan for every ton of hydrofluoric acid (100% concentration) recovered, thus effectively reducing the production cost of manufacturing companies.

[0056] Example 4

[0057] Preparation of membrane material: Same as in Example 1;

[0058] Preparation of the anion exchange membrane: 1 g of iodinated membrane material PES-PPH-Pi with a piperidinyl R group was dissolved in 9 g of DMSO and stirred for 3 h until completely dissolved. The solution was then ultrasonically degassed for 5 min and allowed to stand for 1.5 h to obtain the casting solution. A 30 μm PTFE membrane was thoroughly immersed in the DMSO solution to remove air bubbles from the base membrane. The PTFE membrane was then immersed in the prepared casting solution. The immersed PTFE membrane was laid flat on a polytetrafluoroethylene (PTFE) plate and rolled with a roller to ensure a tight bond between the base membrane and the casting solution, eliminating air bubbles. The PTFE plate was transferred to a 70 °C oven and dried for 7 h to obtain the anion exchange membrane. The anion exchange membrane was repeatedly rinsed in deionized water and then immersed in deionized water for later use.

[0059] Separation: Polyacrylamide (0.1‰ of the mass of the fluorosilicic acid-hydrofluoric acid mixture) was added to a fluorosilicic acid-hydrofluoric acid mixture obtained by glass etching (30% fluorosilicic acid, 50% hydrofluoric acid, 1% sulfuric acid, and 1% total mass of insoluble substances such as sodium fluorosilicate and potassium fluorosilicate). After aging for 6 hours, the mixture was filtered to obtain a clear fluorosilicic acid-hydrofluoric acid mixture. Barium hydroxide (1.05 times the mass of sulfuric acid) was then added to this mixture, and the mixture was reacted at 70°C for 2 hours. After precipitation and filtration, a desulfurized fluorosilicic acid-hydrofluoric acid mixture solution was obtained. This solution was then added to the feed side of an anion exchange membrane, and water was added to the product side of the membrane cell for automatic diffusion. After 6 hours, hydrofluoric acid was obtained on the water side, and the fluorosilicic acid solution remained on the feed side.

[0060] Example 5

[0061] Preparation of membrane material: Same as in Example 1;

[0062] Preparation of the anion exchange membrane: 1 g of iodinated membrane material PES-PPH-Pi with a piperidinyl R group was dissolved in 9 g of DMSO and stirred for 3 h until completely dissolved. The solution was then ultrasonically degassed for 5 min and allowed to stand for 1.5 h to obtain the casting solution. A 30 μm PTFE membrane was thoroughly immersed in the DMSO solution to remove air bubbles from the base membrane. The PTFE membrane was then immersed in the prepared casting solution. The immersed PTFE membrane was laid flat on a polytetrafluoroethylene (PTFE) plate and rolled with a roller to ensure a tight bond between the base membrane and the casting solution, eliminating air bubbles. The PTFE plate was transferred to a 70 °C oven and dried for 7 h to obtain the anion exchange membrane. The anion exchange membrane was repeatedly rinsed in deionized water and then immersed in deionized water for later use.

[0063] Separation: Polyacrylamide (0.3‰ of the mass of the fluorosilicic acid-hydrofluoric acid mixture) was added to a fluorosilicic acid-hydrofluoric acid mixture obtained by glass etching (20% fluorosilicic acid, 5% hydrofluoric acid, 1.5% sulfuric acid, and 1% total mass of insoluble substances such as sodium fluorosilicate and potassium fluorosilicate). After aging for 6 hours, the mixture was filtered to obtain a clear fluorosilicic acid-hydrofluoric acid solution. Barium carbonate (1.03 times the mass of sulfuric acid) was then added to this solution. After reacting at 50°C for 3 hours, precipitation and filtration were performed to obtain a desulfurized fluorosilicic acid-hydrofluoric acid solution. This solution was then added to the feed side of an anion exchange membrane, while water was added to the product side of the membrane. Automatic diffusion was performed, and after 7 hours, hydrofluoric acid was obtained on the water side, while the fluorosilicic acid solution remained on the feed side.

[0064] Example 6

[0065] Preparation of membrane material: Same as in Example 1;

[0066] Preparation of the anion exchange membrane: 1 g of iodinated membrane material PES-PPH-Pi with a piperidinyl R group was dissolved in 9 g of DMSO and stirred for 3 h until completely dissolved. The solution was then ultrasonically degassed for 5 min and allowed to stand for 1.5 h to obtain the casting solution. A 30 μm PTFE membrane was thoroughly immersed in the DMSO solution to remove air bubbles from the base membrane. The PTFE membrane was then immersed in the prepared casting solution. The immersed PTFE membrane was laid flat on a polytetrafluoroethylene (PTFE) plate and rolled with a roller to ensure a tight bond between the base membrane and the casting solution, eliminating air bubbles. The PTFE plate was transferred to a 70 °C oven and dried for 7 h to obtain the anion exchange membrane. The anion exchange membrane was repeatedly rinsed in deionized water and then immersed in deionized water for later use.

[0067] Separation: Polyacrylamide (0.4‰ of the mass of the fluorosilicic acid-hydrofluoric acid mixture) was added to a fluorosilicic acid-hydrofluoric acid mixture obtained by glass etching (fluorosilicic acid content 25%, hydrofluoric acid content 15%, sulfuric acid content 2%, and total mass of insoluble substances such as sodium fluorosilicate and potassium fluorosilicate 1%). After aging for 6 hours, the mixture was filtered to obtain a clear fluorosilicic acid-hydrofluoric acid mixture. Calcium hydroxide (1.02 times the mass of sulfuric acid) was then added to this mixture, and the mixture was reacted at 40°C for 4 hours. After precipitation and filtration, a desulfurized fluorosilicic acid-hydrofluoric acid mixture solution was obtained. This solution was then added to the feed side of an anion exchange membrane, and water was added to the product side of the membrane cell for automatic diffusion. After 8 hours, hydrofluoric acid was obtained on the water side, and the fluorosilicic acid solution remained on the feed side.

[0068] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0069] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for separating fluorosilicic acid-hydrofluoric acid using an anion exchange membrane, characterized in that, Includes the following steps: A flocculant is added to a fluorosilicic acid-hydrofluoric acid mixture, and the mixture is aged. Then a desulfurizing agent is added, and a desulfurization reaction is carried out to obtain a mixed solution. The mixed solution is added to the raw material side of an anion exchange membrane for membrane separation. After separation, a hydrofluoric acid solution with a mass concentration of 2-30% is obtained on the clear water side. The amount of flocculant added is 0.1-0.5‰ of the mass of the fluorosilicic acid-hydrofluoric acid mixture; The desulfurization temperature is 30-70℃, and the time is 2-4 hours; The amount of desulfurizing agent used is 1.02-1.05 times the amount of sulfuric acid in the fluorosilicic acid-hydrofluoric acid mixture; The desulfurizing agent is calcium carbonate or calcium hydroxide; The anion exchange membrane is a cyclic ammonium phenolphthalein polyarylether sulfone membrane material. The cyclic ammonium phenolphthalein polyarylether sulfone membrane material is prepared through the following process: Under nitrogen protection, cyclic ammonium phenolphthalein, 4,4-difluorodiphenyl sulfone, biphenyl phenol, a basic compound, DMSO, and toluene are added to a reaction flask and refluxed at 140°C for 8 hours. After the reaction, toluene and water are removed by azeotropic distillation. Then, the reaction is carried out at 180°C for 12 hours to obtain a viscous polymerization solution. After cooling to room temperature, DMSO is added for dilution, the solid is filtered off, and the solution is poured into water at 70°C to obtain a polymer product. The polymer product is vacuum dried at 120°C for 20–28 hours to obtain a PES-PPH-Pi polymer. The PES-PPH-Pi polymer is dissolved in DMSO, and iodomethane with twice the molar amount of amino groups in the PES-PPH-Pi polymer is added. The mixture is stirred at room temperature for 6–8 hours, and then precipitated in ethanol to obtain the polymer. After filtration, the polymer is vacuum dried at 80°C for 24 hours to obtain the anion exchange membrane material. The cyclic ammonium phenolphthalein structure is shown in formula (1): （1） In formula (1), the R group is a nitrogen-containing heterocycle, which is piperidinyl, tetrahydropyrroleyl or morpholinyl; In a fluorosilicic acid-hydrofluoric acid mixed solution, the mass concentration of fluorosilicic acid is 5-30%, the mass concentration of hydrofluoric acid is 5-50%, and the mass concentration of sulfuric acid is 1-2%. The flocculant is polyacrylamide.

2. The method for separating fluorosilicic acid-hydrofluoric acid using an anion exchange membrane according to claim 1, characterized in that, The preparation method of anion exchange membrane is as follows: dissolve the anion membrane material in an organic solvent, degas it by ultrasonication after complete dissolution, let it stand, and obtain the casting solution; fully impregnate the base membrane in the organic solvent, and then transfer the base membrane to the casting solution for full impregnation; The impregnated base film is fixed on a polytetrafluoroethylene plate, then the base film is coated with a scraper, and then placed in an oven to dry, thus obtaining an anion exchange membrane.

3. The method for separating fluorosilicic acid-hydrofluoric acid using an anion exchange membrane according to claim 1, characterized in that, The thickness of the anion exchange membrane is 120–200 μm.

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