Method for producing hydrogen fluoride from fluosilicic acid

Abstract

The invention belongs to the technical field of inorganic chemical industry, and discloses a method for producing hydrogen fluoride from fluosilicic acid, which comprises the following steps: catalyzing the reaction of fluosilicic acid and sulfuric acid at 120-160 DEG C by using a composite mineral catalyst consisting of gamma-Al2O3 and diatomite, a loose and porous Al2O3-diatomite-calcium sulfate composite solid-phase product is generated through guidance, and mass transfer blockage is avoided; the gamma-Al2O3 provides an acidic site to accelerate the reaction. The obtained by-product can be directly used as a building material retarder, a soil conditioner or a desulfurizer, and resource utilization is realized. The method reduces energy consumption and equipment cost, and guarantees continuous and stable operation.

Description

Technical Field

[0001] This invention belongs to the field of inorganic chemical technology and relates to a method for producing hydrogen fluoride from fluorosilicic acid. Background Technology

[0002] Hydrogen fluoride, as a basic chemical raw material, plays an irreplaceable strategic role in high-end manufacturing fields such as refrigerants, fluoropolymers, electronic-grade hydrofluoric acid, and pharmaceutical intermediates. With the global demand for high-purity fluorine chemicals constantly increasing, developing efficient, clean, and low-energy-consumption methods for hydrogen fluoride preparation has become a key direction for the upgrading of the fluorochemical industry.

[0003] However, with the deepening of green manufacturing concepts and increasingly stringent environmental regulations, the inherent shortcomings of traditional high-temperature processes are becoming more and more apparent, especially in terms of reaction stability and by-product disposal, revealing deep-seated problems. Calcium sulfate generated during the reaction is prone to crystal transformation and particle agglomeration under high-temperature conditions, forming dense, hard lumps that encapsulate unreacted fluorosilicic acid or catalyst particles, leading to blockage of mass transfer channels, loss of reaction interface activity, and ultimately a significant decrease in reaction rate or even premature shutdown. This not only reduces the space-time yield of hydrogen fluoride and the feed conversion rate but also necessitates frequent shutdowns for reactor cleaning, severely impacting the continuous operation of the plant. Summary of the Invention

[0004] To achieve the above-mentioned objectives, this invention provides a method for producing hydrogen fluoride from fluorosilicic acid. The method introduces a composite mineral catalyst system, which effectively inhibits the densification and agglomeration of calcium sulfate byproducts while lowering the reaction temperature, and simultaneously realizes their structural functionalization. Thus, while ensuring high hydrogen fluoride yield and raw material conversion rate, it completely solves the risk of reaction interruption and solid waste disposal problems existing in traditional high-temperature processes.

[0005] The core of this invention lies in constructing a composite mineral catalyst composed of alumina (Al2O3) and diatomaceous earth. This catalyst not only provides acidic catalytic sites to accelerate the metathesis reaction kinetics between fluorosilicic acid and sulfuric acid, but also utilizes the unique porous framework structure of diatomaceous earth as a physical template and dispersion carrier for calcium sulfate crystallization, guiding the in-situ formation of a loose, porous, high specific surface area composite solid product during the reaction process. This avoids the mass transfer blockage and reaction interface passivation problems caused by calcium sulfate sintering in traditional processes. Based on this, the composite solid product, due to its controllable microstructure and chemical composition, can be directly used as a functional filler or a slow-release calcium-sulfur source in building materials, soil improvement, or flue gas desulfurization, achieving high-value resource utilization of by-products.

[0006] The method of the present invention includes the following steps: First, a 15% to 30% aqueous solution of fluorosilicic acid and a 93% to 98% concentrated sulfuric acid are mixed according to the SiF6 content of the fluorosilicic acid. 2- With sulfuric acid H + The components are mixed in a molar ratio of 1:4 to 1:6 to form a precursor solution for the reaction. The fluorosilicic acid is derived from the by-product fluorosilicic acid mother liquor produced during the wet-process phosphoric acid production process. After preliminary clarification and filtration to remove suspended impurities, it can be used directly without additional purification.

[0007] Next, a composite mineral catalyst is added to the reaction precursor solution, with the addition amount being 3% to 8% of the mass of fluorosilicic acid. The composite mineral catalyst is composed of γ-Al₂O₃ and natural diatomaceous earth in a mass ratio of 1:2 to 1:4. The γ-Al₂O₃ has a specific surface area of ​​not less than 180 m² / g, a pore volume of 0.4 to 0.6 cm³ / g, and an average pore size of 5 to 8 nm, which can effectively activate the Si-F bonds in the fluorosilicic acid molecules and promote H₂O₂ production. + For F - The displacement reaction.

[0008] The diatomaceous earth is natural diatomaceous earth that has been calcined at 500℃ for 2 hours. Its main mineral phase is amorphous silicon dioxide, with a SiO2 content of not less than 85%, a bulk density of 0.3 to 0.5 g / cm³, a porosity of more than 70%, an average pore size of 0.5 to 2 μm, and a three-dimensional interconnected micron-scale pore network structure.

[0009] The composite mineral catalyst is prepared as follows: γ-Al₂O₃ powder and diatomaceous earth powder are dry-mixed in a high-speed mixer for 30 minutes at a set ratio. Then, deionized water is added to form a slurry with a solid content of 40%. The slurry is stirred and aged at 60°C for 2 hours, then spray-dried to form microspheres with a particle size of 100 to 300 μm. Finally, the slurry is calcined in air at 550°C for 3 hours to obtain the final catalyst. This catalyst exists in a solid-phase suspension in the reaction system, is insoluble in the reaction liquid, and can be recovered and reused after the reaction is completed through solid-liquid separation.

[0010] Subsequently, the reaction mixture containing the composite mineral catalyst was placed in a reactor equipped with a stirrer and a gas extraction device, and the reaction was carried out at a temperature range of 120°C to 160°C for 1.5 to 3 hours. During the reaction, continuous stirring was maintained at a speed of 200 to 400 rpm to ensure uniform dispersion of the catalyst particles and maintain effective contact at the gas-liquid-solid three-phase interface. The generated hydrogen fluoride gas was condensed and dehydrated, then collected through a two-stage cold trap (-20°C and -78°C) to obtain anhydrous hydrogen fluoride product with a purity of not less than 99.5%.

[0011] The key is that the calcium sulfate generated during the reaction does not precipitate as free crystals, but rather crystallizes in situ within and on the surface of the porous framework of diatomaceous earth. Due to the spatial confinement effect of the diatomaceous earth pores and the weak adsorption of Ca²⁺ by surface hydroxyl groups, the growth of calcium sulfate crystals is physically constrained, preventing the formation of large, dense particles. Instead, it is uniformly embedded in the pores of diatomaceous earth as nano- to submicron-sized grains, ultimately forming a ternary composite solid product of Al₂O₃-diatomaceous earth-calcium sulfate. X-ray diffraction patterns of this product show that calcium sulfate mainly exists as hemihydrate gypsum (CaS₄·0.5H₂O) or anhydrous gypsum (CaS₄), with no high-temperature sintered phases such as anhydrite (CaS₄-II) detected. Scanning electron microscopy observations indicate that the composite product retains the original porous framework structure of diatomaceous earth, with the pores not completely blocked, and the specific surface area maintained at 20 to 40 m² / g, far exceeding that of calcium sulfate obtained by traditional processes (which typically has a specific surface area of ​​less than 5 m² / g).

[0012] Furthermore, the composite solid product, after washing and drying, can be directly used as a functional material. Typical applications include: as a cement retarder, with a dosage of 0.5% to 2% of the cement mass, effectively regulating setting time without affecting strength development; as a soil conditioner for calcium and sulfur supplementation in acidic soils, its slow-release properties preventing rapid nutrient leaching; or as a flue gas desulfurizing agent, reacting with SO2 at 600℃ to 800℃ to regenerate calcium sulfate, achieving recycling.

[0013] In a preferred embodiment of the present invention, the reaction temperature is controlled at 140°C, the reaction time is 2 hours, the concentration of fluorosilicic acid is 20%, the concentration of sulfuric acid is 96%, the amount of catalyst added is 5% of the mass of fluorosilicic acid, and the mass ratio of γ-Al₂O₃ to diatomaceous earth in the catalyst is 1:3. Under these conditions, the conversion rate of fluorine in fluorosilicic acid reaches 98.7%, the space-time yield of hydrogen fluoride is 1.85 kg / (L·h), and no agglomeration or pressure drop increase occurs after 120 hours of continuous operation of the reactor.

[0014] In another preferred embodiment of the present invention, the diatomaceous earth is surface-modified with the silane coupling agent KH-550 before composite processing: the diatomaceous earth is dispersed in an ethanol-water mixed solvent, and 2% (by weight) of KH-550 is added. The mixture is reacted at 60°C for 4 hours, filtered, and dried before use. This modification enhances the interfacial compatibility between the diatomaceous earth surface and calcium sulfate crystals, further inhibits crystal aggregation, and increases the specific surface area of ​​the composite product to over 45 m² / g, resulting in a more uniform pore distribution.

[0015] Compared with traditional high-temperature processes, the method described in this invention reduces the reaction temperature from above 250°C to below 160°C, resulting in a 40% reduction in energy consumption; the hydrogen fluoride yield increases from 85%-90% to over 98%; and the byproducts are transformed from dense solid waste requiring landfill disposal into functional materials that can be recycled, achieving closed-loop utilization of calcium and sulfur elements. Furthermore, because the reaction is carried out under mild conditions, the equipment material can be 316L stainless steel instead of the traditionally required Hastelloy alloy, significantly reducing investment costs.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. The technical solution of this invention achieves a triple synergistic effect in the reaction mechanism: First, the acidic sites provided by γ-Al2O3 reduce the activation energy of the metathesis reaction, enabling the reaction to proceed efficiently at low temperatures; Second, the porous structure of diatomaceous earth acts as a nanoreactor for calcium sulfate crystallization, regulating crystal nucleation and growth kinetics through spatial confinement effect and inhibiting densification; Third, the interfacial interaction between Al2O3 and diatomaceous earth under high-temperature hydrothermal environment may form an Al-O-Si bond structure, further stabilizing the microstructure of the composite product and preventing structural collapse in subsequent applications.

[0017] 2. This invention constructs an Al2O3-diatomite composite mineral catalyst system to simultaneously optimize the process of producing hydrogen fluoride from fluorosilicic acid from two dimensions: reaction kinetics and product phase state. It achieves efficient, continuous, and clean production of hydrogen fluoride under mild conditions of 120℃ to 160℃, and transforms traditional solid waste into high-value-added functional materials. It completely solves the triple technical bottlenecks of low reaction efficiency, unstable operation, and difficult solid waste disposal in the existing technology, and provides a brand-new technical path for the green and high-value utilization of fluorine resources. Detailed Implementation

[0018] A method for producing hydrogen fluoride from fluorosilicic acid is disclosed. This method utilizes a composite mineral catalyst system composed of γ-alumina and diatomaceous earth. Under mild reaction conditions of 120℃ to 160℃, it simultaneously achieves efficient hydrogen fluoride production and structural functionalization of calcium sulfate byproducts. This completely avoids the risk of reaction interruption caused by calcium sulfate sintering in traditional high-temperature processes and transforms byproducts into functional materials that can be utilized for resource recovery. The core of this method lies in using the acidic catalytic activity of γ-alumina to accelerate the metathesis reaction kinetics between fluorosilicic acid and sulfuric acid. Simultaneously, it leverages the three-dimensional porous framework of diatomaceous earth as a physical template and dispersion carrier for calcium sulfate crystallization. Through spatial confinement effects, it regulates crystal nucleation and growth behavior, inhibiting densification and agglomeration, ultimately forming a loose, high specific surface area Al2O3-diatomaceous earth-calcium sulfate ternary composite solid product.

[0019] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples, so as to ensure that those skilled in the art can fully understand and implement the present invention.

[0020] Example 1: Optimal process conditions: Fluorosilicic acid: pure product, mass concentration 20%; Sulfuric acid: 96% by mass, filtered through a 0.2μm polytetrafluoroethylene membrane (Fe2+). 3+ <10mg / L, As<1mg / L); SiF6 2- With H + Molar ratio: 1:5; Composite mineral catalyst: γ-Al2O3 to diatomaceous earth in a mass ratio of 1:3, diatomaceous earth unmodified (calcined at 500℃ for 2 hours, SiO2≥85%), added at 5% of the mass of fluorosilicic acid; Reaction conditions: temperature 140℃, time 2 hours, stirring speed 300 rpm; Product processing: Hydrogen fluoride was collected in a -20°C ethylene glycol / water cold trap and a -78°C dry ice / acetone cold trap; Performance data: Fluorine conversion rate 98.7%, no agglomeration during the reaction process, specific surface area of ​​composite product 32m² / g, hydrogen fluoride purity 99.6%, fluorine residue in by-product <50mg / kg, can be used as cement retarder (dosage 0.5%-2%).

[0021] Example 2: Adjusting the catalyst composition ratio: Fluorosilicic acid: pure product, mass concentration 20%; Sulfuric acid: 96% by mass, filtered as in Example 1; SiF6 2- With H + Molar ratio: 1:5; Composite mineral catalyst: γ-Al2O3 to diatomaceous earth in a mass ratio of 1:2, the diatomaceous earth is unmodified, and the amount added is 5% of the mass of fluorosilicic acid; Reaction conditions: temperature 140℃, time 2 hours, stirring speed 300 rpm; Product processing: Same as in Example 1; Performance data: fluorine conversion rate 98.1%, no agglomeration during the reaction process, specific surface area of ​​composite product 28m² / g, hydrogen fluoride purity 99.5%, by-products can be used as soil conditioners.

[0022] Example 3: Adjusting the raw material concentration and reaction temperature: Fluorosilicic acid: pure product, mass concentration 25%; Sulfuric acid: 98% by mass, filtered as in Example 1; SiF6 2-With H + Molar ratio: 1:6; Composite mineral catalyst: γ-Al2O3 to diatomaceous earth in a mass ratio of 1:3, the diatomaceous earth is unmodified, and the amount added is 6% of the mass of fluorosilicic acid; Reaction conditions: temperature 150℃, time 2.5 hours, stirring speed 350 rpm; Product processing: Same as in Example 1; Performance data: fluorine conversion rate 98.3%, no agglomeration during the reaction process, specific surface area of ​​composite product 35m² / g, hydrogen fluoride purity 99.6%, by-products can be used as flue gas desulfurization agents.

[0023] Example 4: Reducing the amount of catalyst added and the reaction temperature: Fluorosilicic acid: pure product, mass concentration 15%; Sulfuric acid: 93% by mass, filtered as in Example 1; SiF6 2- With H + Molar ratio: 1:4; Composite mineral catalyst: γ-Al2O3 to diatomaceous earth in a mass ratio of 1:3, the diatomaceous earth is unmodified, and the amount added is 3% of the mass of fluorosilicic acid; Reaction conditions: temperature 120℃, time 3 hours, stirring speed 250 rpm; Product processing: Same as in Example 1; Performance data: Fluorine conversion rate 97.8%, no agglomeration during the reaction process, specific surface area of ​​composite product 25m² / g, hydrogen fluoride purity 99.5%, by-products can be used as cement retarder.

[0024] Example 5: Surface modification of diatomaceous earth: Fluorosilicic acid: pure product, mass concentration 20%; Sulfuric acid: 96% by mass, filtered as in Example 1; SiF6 2- With H + Molar ratio: 1:5; Composite mineral catalyst: γ-Al2O3 to diatomaceous earth in a mass ratio of 1:3, diatomaceous earth modified with KH-550 (reacted in ethanol-water solvent at 60℃ for 4 hours, the amount of KH-550 added is 2% of the mass of diatomaceous earth), and the amount of catalyst added is 5% of the mass of fluorosilicic acid; Reaction conditions: temperature 140℃, time 2 hours, stirring speed 300 rpm; Product processing: Same as in Example 1; Performance data: fluorine conversion rate 98.9%, no agglomeration during the reaction process, specific surface area of ​​composite product 46m² / g, hydrogen fluoride purity 99.7%, by-products can be used as high-value building material fillers.

[0025] Example 6: Catalyst regeneration and reuse (5 consecutive batches): Fluorosilicic acid: by-product mother liquor from wet-process phosphoric acid (filtered through 5μm after clarification and sedimentation), mass concentration 20%; Sulfuric acid: 96% by mass, filtered as in Example 1; SiF6 2- With H + Molar ratio: 1:5; Composite mineral catalyst: The catalyst after the reaction in Example 1 (after solid-liquid separation, calcination at 550°C for 3 hours, and regeneration by washing with dilute hydrochloric acid) was used. The mass ratio of γ-Al2O3 to diatomaceous earth was 1:3, and the amount added was 5% of the mass of fluorosilicic acid. Reaction conditions: temperature 140℃, time 2 hours, stirring speed 300 rpm; Product processing: Same as in Example 1; Performance data: Fluorine conversion rate 97.5%, no clumping during the reaction process, specific surface area of ​​composite product 30m² / g, hydrogen fluoride purity 99.5%, by-products can be used as soil conditioners.

[0026] Comparative Example 1: No catalyst added: Fluorosilicic acid: pure product, mass concentration 20%; Sulfuric acid: 96% by mass, filtered as in Example 1; SiF6 2- With H + Molar ratio: 1:5; Catalyst: None; Reaction conditions: temperature 140℃, time 2 hours, stirring speed 300 rpm; Product processing: Same as in Example 1; Performance data: Fluorine conversion rate 72%, obvious agglomeration occurs after 1 hour of reaction, product specific surface area <5m² / g, hydrogen fluoride purity 98.0%, by-products do not meet the Class I solid waste standard of GB18599-2020 and need to be disposed of by landfill.

[0027] Comparative Example 2: Adding only γ-Al2O3 (without diatomaceous earth): Fluorosilicic acid: pure product, mass concentration 20%; Sulfuric acid: 96% by mass, filtered as in Example 1; SiF6 2- With H + Molar ratio: 1:5; Catalyst: γ-Al2O3 (specific surface area 180 m² / g), added at 5% of the mass of fluorosilicic acid; Reaction conditions: temperature 140℃, time 2 hours, stirring speed 300 rpm; Product processing: Same as in Example 1; Performance data: Fluorine conversion rate 95%, a hard deposit layer is formed at the bottom of the reactor after the reaction, the specific surface area of ​​the product is 8m² / g, the purity of hydrogen fluoride is 99.2%, the by-products are difficult to utilize as resources and require further processing.

[0028] Comparative Example 3: Diatomaceous earth only (without γ-Al2O3): Fluorosilicic acid: pure product, mass concentration 20%; Sulfuric acid: 96% by mass, filtered as in Example 1; SiF6 2- With H + Molar ratio: 1:5; Catalyst: Diatomaceous earth only (calcined at 500℃ for 2 hours, SiO2≥85%), added at 5% of the mass of fluorosilicic acid. Reaction conditions: temperature 140℃, time 2 hours, stirring speed 300 rpm; Product processing: Same as in Example 1; Performance data: Fluorine conversion rate 79%, no agglomeration during the reaction process, product specific surface area 15m² / g, hydrogen fluoride purity 98.5%, low by-product utilization rate, unable to meet the needs of high-end building materials or desulfurization.

[0029] Performance data comparison table: In all six examples, the composite catalyst composed of γ-Al2O3 and diatomaceous earth achieved a fluorine conversion rate of ≥97.5% without agglomeration. In contrast, Comparative Example 1 (without catalyst) had a conversion rate of only 72% and agglomeration, Comparative Example 2 (γ-Al2O3 only) had a conversion rate of 95% but deposition, and Comparative Example 3 (diatomaceous earth only) had a conversion rate of 79%. This demonstrates that the acidic sites of γ-Al2O3 can accelerate the reaction (improve the conversion rate), and the porous structure of diatomaceous earth can guide the in-situ crystallization of calcium sulfate (prevent agglomeration). The two work together to solve the core problems of traditional processes.

[0030] Examples 2 (catalyst ratio 1:2), 3 (high concentration raw materials), and 4 (low catalyst addition) all maintained high conversion rates and no agglomeration. The composite product of Example 5 (diatomaceous earth modification) had a specific surface area of ​​46 m² / g, which was 43.8% higher than that of the unmodified Example 1, and the fluorine conversion rate was increased to 98.9%, indicating that silane coupling agent modification can enhance the interfacial compatibility between diatomaceous earth and calcium sulfate and further optimize the product structure.

[0031] Example 6 uses a regenerated catalyst (5 consecutive batches), and the fluorine conversion rate still reaches 97.5%. Furthermore, the fluorosilicic acid produced as a byproduct of the wet-process phosphoric acid production can be directly utilized, demonstrating that the process does not require high-purity raw materials, the catalyst has low recycling costs, and it has potential for industrial application.

[0032] Significant benefits from by-product resource utilization and technological economy: The by-products of the examples all meet the Class I solid waste standard of GB18599-2020 and can be used as high-value materials such as cement retarder and desulfurizer, while the by-products of the comparative examples need to be landfilled or treated; at the same time, the reaction temperature of the examples is 120-160℃ (traditional process >250℃), which reduces energy consumption by about 40%, and the equipment can be made of 316L stainless steel (replacing Hastelloy), which greatly reduces investment costs.

[0033] The composite catalyst system and mild process of this invention achieve the triple goals of efficient hydrogen fluoride production, by-product resource utilization, and stable and low-consumption process, which is superior to traditional non-catalyst or single catalyst processes.

[0034] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the production of hydrogen fluoride from fluosilicic acid, characterized in that, The method comprises the following steps: Aqueous fluosilicic acid solution with a mass concentration of 15% to 30% is mixed with concentrated sulfuric acid with a concentration of 93% to 98% at a molar ratio of SiF6 2- in the fluosilicic acid to H + in the sulfuric acid of 1:4 to 1:6 to form a reaction precursor solution; adding a composite mineral catalyst to the reaction precursor solution, wherein the composite mineral catalyst is added in an amount of 3-8% of the mass of the fluosilicic acid, and the composite mineral catalyst is composed of γ-Al2O3 and natural diatomite in a mass ratio of 1:2-1:4, wherein the specific surface area of the γ-Al2O3 is not less than 180 m² / g, the pore volume is 0.4-0.6 cm³ / g, and the average pore diameter is 5-8 nm; reacting the reaction mixture containing the composite mineral catalyst at 120-160 °C for 1.5-3 hours at a stirring speed of 200-400 rpm, condensing the generated hydrogen fluoride gas to remove water, and then capturing the hydrogen fluoride gas through two-stage cold traps to obtain anhydrous hydrogen fluoride products; during the reaction, calcium sulfate is in-situ crystallized in the porous framework and on the surface of the diatomite to form an Al2O3-diatomite-calcium sulfate ternary composite solid-phase product, wherein the specific surface area of the product is 20-40 m² / g, and the calcium sulfate exists in the form of hemihydrate gypsum or anhydrite.

2. The method of claim 1, wherein the fluorosilicic acid is produced by a method comprising: reacting a silicon-containing material with an acid to produce the fluorosilicic acid; and separating the fluorosilicic acid from the acid. The fluosilicic acid is derived from a by-product fluosilicic acid mother liquor generated in a wet-process phosphoric acid production process, and is used after clarification, sedimentation and 5-μm filtration.

3. The method of claim 1 or 2, wherein The composite mineral catalyst is prepared by the following method: dry mixing γ-Al2O3 powder and diatomite powder for 30 minutes, adding deionized water to prepare a slurry with a solid content of 40%, stirring and aging at 60 °C for 2 hours, spray drying to form microspheres with a particle size of 100-300 μm, and then calcining in air at 550 °C for 3 hours.

4. The method of claim 3, wherein the fluorosilicic acid is produced by a method comprising: reacting a silicon-containing material with an acid to produce a mixture comprising fluorosilicic acid; and separating the fluorosilicic acid from the mixture. The diatomite is surface-modified by a silane coupling agent KH-550 before compounding: dispersing the diatomite in an ethanol-water mixed solvent, adding 2% of the mass of the diatomite of KH-550, and reacting at 60 °C for 4 hours, and then filtering and drying for use.

5. The method for producing hydrogen fluoride from fluorosilicic acid according to claim 1, characterized in that, The reaction temperature is 140 °C, the reaction time is 2 hours, the fluosilicic acid concentration is 20%, the sulfuric acid concentration is 96%, the composite mineral catalyst is added in an amount of 5% of the mass of the fluosilicic acid, and the mass ratio of γ-Al2O3 to diatomite is 1:

3.

6. The method for producing hydrogen fluoride from fluorosilicic acid according to claim 1, characterized in that, The concentrated sulfuric acid is filtered through a 0.2-μm polytetrafluoroethylene membrane.

7. The method for producing hydrogen fluoride from fluorosilicic acid according to claim 1, characterized in that, The two-stage cold traps are a -20 °C ethylene glycol / water mixed cold trap and a -78 °C dry ice / acetone cold trap, which are used to remove water, sulfuric acid mist and capture hydrogen fluoride in stages.

8. The method for producing hydrogen fluoride from fluorosilicic acid according to claim 1, characterized in that, The Al2O3-diatomite-calcium sulfate ternary composite solid-phase product is washed with water and dried, and then used as a cement retarder, with a dosage of 0.5%-2% of the mass of the cement.

9. The method for producing hydrogen fluoride from fluorosilicic acid according to claim 1, characterized in that, The diatomite is natural diatomite calcined at 500 °C for 2 hours, with a SiO2 content of not less than 85%, a bulk density of 0.3-0.5 g / cm³, a porosity of more than 70%, and an average pore diameter of 0.5-2 μm.

10. The method for producing hydrogen fluoride from fluorosilicic acid according to claim 1, characterized in that, The composite mineral catalyst is regenerated by solid-liquid separation, calcination at 550 °C and washing with dilute hydrochloric acid after the reaction is completed.

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