Potassium fluosilicate cyclic regeneration and white carbon black co-production method

Abstract

The invention discloses a method for cyclic regeneration of potassium fluosilicate and co-production of white carbon black, and relates to the technical field of inorganic chemical industry, a closed-loop potassium element circulation system is established, potassium fluosilicate is used as a key intermediate, high-efficiency conversion of fluorine-silicon resources is realized, consumption of sylvite is remarkably reduced, and production cost is reduced. Therefore, the problems of one-way material flow, high production cost, difficulty in waste liquid treatment and the like in the traditional process are solved.

Description

Technical Field

[0001] This invention relates to the field of inorganic chemical technology, and more specifically to a method for the recycling and co-production of potassium fluorosilicate and silica. Background Technology

[0002] The rapid development of global industries such as phosphorus chemicals, aluminum electrolysis, and steel has generated a large amount of fluorine-containing byproducts, especially fluorosilicic acid (H2SiF6). Taking the production of wet-process phosphoric acid as an example, approximately 100 to 150 kilograms of fluorosilicic acid are generated for every ton of phosphoric acid produced (calculated as P2O5). If this fluorosilicic acid is discharged directly without treatment, it will cause serious environmental pollution, such as water acidification and soil fluoride contamination. It also means a waste of valuable fluorine and silicon resources. Therefore, how to efficiently, economically, and environmentally treat and utilize fluorosilicic acid has become a major technical challenge that urgently needs to be overcome in the current industrial sector.

[0003] Currently, the main technologies for utilizing fluorosilicic acid include the following approaches:

[0004] The traditional method for producing fluorosilicate products involves converting fluorosilicic acid into salts such as sodium fluorosilicate, potassium fluorosilicate, or magnesium fluorosilicate. Potassium fluorosilicate (H₂SiF₆) has a certain market demand due to its applications in wood preservation, ceramics manufacturing, and metallurgical fluxing. Its preparation typically involves reacting fluorosilicic acid with potassium chloride or potassium sulfate, followed by precipitation to obtain the product. However, this method merely converts fluorosilicic acid into another primary product, offering limited added value. More importantly, the acidic mother liquor (such as hydrochloric acid) generated during the reaction still requires further treatment, failing to fundamentally solve the waste disposal problem.

[0005] Ammonia process: This process typically involves reacting fluorosilicic acid with ammonia water to produce ammonium fluoride and silica (i.e., precipitate). This process is relatively simple and can simultaneously yield both fluorine and silicon products. However, its main drawbacks are: firstly, the resulting ammonium fluoride has a relatively low market value, and its production process is energy-intensive; secondly, the precipitate prepared by this method is easily coated with impurities and has an uneven particle size distribution, often making it difficult to meet the stringent performance requirements of high-end applications such as high-reinforcing rubber.

[0006] Direct alkaline hydrolysis process: This method involves the direct reaction of potassium hydroxide or sodium hydroxide with fluorosilicic acid to produce the corresponding fluorides and silica. Although this method can yield high-value potassium fluoride or sodium fluoride, its biggest drawback is the enormous consumption of alkali, which leads to a sharp increase in production costs, making the process economically unfeasible.

[0007] The process of co-producing hydrofluoric acid and precipitated silica through thermal decomposition involves first converting fluorosilicic acid into a potassium fluorosilicate intermediate, followed by thermal decomposition or reaction with concentrated sulfuric acid to generate gaseous silicon tetrafluoride (SiF4) and hydrogen fluoride (HF). The silicon tetrafluoride is then hydrolyzed to produce precipitated silica. For example, some patent documents mention that after fluorosilicic acid reacts with a soluble potassium salt (such as potassium sulfate) to form a potassium fluorosilicate precipitate, this precipitate is decomposed under the action of an ionic liquid or concentrated sulfuric acid, and the resulting silicon tetrafluoride is then hydrolyzed to obtain precipitated silica. The advantage of this type of process is that it can simultaneously obtain high-value hydrofluoric acid and precipitated silica.

[0008] However, while existing technology disclosures sometimes mention the possibility of recovering some materials (such as potassium sulfate), they generally fail to systematically describe a complete "recycling" closed-loop process centered on significantly reducing the consumption of key materials (especially potassium salts). Potassium salts, as a key reactant in this process, are a significant factor contributing to the high total cost due to their one-time input and potential loss during separation and purification.

[0009] Therefore, it is necessary to propose a method for the recycling and co-production of potassium fluorosilicate and silica to solve the above problems. Summary of the Invention

[0010] The purpose of this invention is to solve the problems mentioned in the background art.

[0011] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0012] A method for the recycling and co-production of potassium fluorosilicate and silica, comprising the following steps:

[0013] (a) Potassium fluorosilicate precipitate formation: The fluorosilicic acid raw material is mixed and reacted with the potassium sulfate solution recycled in step (e) in a precipitation reactor to generate potassium fluorosilicate precipitate and dilute sulfuric acid, and the potassium fluorosilicate precipitate is subjected to solid-liquid separation.

[0014] (b) Decomposition of potassium fluorosilicate: The potassium fluorosilicate obtained in step (a) is heated and reacted with concentrated sulfuric acid in a decomposition reactor to generate a gaseous product containing silicon tetrafluoride and hydrogen fluoride, as well as a solid or liquid material containing regenerated potassium sulfate.

[0015] (c) Preparation of silica by gas-phase hydrolysis of silicon tetrafluoride: The gaseous product generated in step (b) is passed into a gas-phase hydrolysis reactor and reacted with water vapor at high temperature to generate solid silica and gaseous hydrogen fluoride.

[0016] (d) Product separation and recovery: The reaction product of step (c) is subjected to gas-solid separation, the silica is collected, and the remaining hydrogen fluoride-containing gas is absorbed and purified to obtain hydrogen fluoride product.

[0017] (e) Recycling of potassium sulfate: The material containing regenerated potassium sulfate generated in step (b) is cooled, crystallized and purified, and then recycled back to step (a) as the potassium sulfate solution for reaction with new fluorosilicic acid raw material.

[0018] Furthermore, the fluorosilicic acid raw material described in step (a) has undergone pretreatment for phosphorus removal and / or arsenic removal before use.

[0019] Furthermore, the reaction temperature in step (a) is controlled at 20~60℃, and the molar ratio of potassium sulfate to fluorosilicic acid is 1.05~1.2:1.

[0020] Furthermore, ultrasound assistance is introduced into the precipitation reaction process in step (a), wherein the frequency of the ultrasound is 20~40kHz.

[0021] Furthermore, the decomposition reaction temperature in step (b) is controlled at 250~450℃, and the mass fraction of concentrated sulfuric acid used is not less than 98%.

[0022] Furthermore, the decomposition reaction in step (b) is carried out in an ionic liquid medium, wherein the ionic liquid is an imidazole or quaternary ammonium salt ionic liquid.

[0023] Furthermore, the temperature of the gas-phase hydrolysis reaction in step (c) is controlled at 1000~1400℃, and the molar ratio of water vapor to silicon tetrafluoride is greater than 10:1.

[0024] Furthermore, in step (c), the specific surface area of ​​the prepared silica is controlled to be between 100 and 300 m² by adjusting the residence time of the gaseous product in the high-temperature zone of the hydrolysis reactor. 2 Within the range of / g.

[0025] Furthermore, in step (e), the material containing recycled potassium sulfate is treated by multi-stage cooling crystallization or vacuum evaporation crystallization to improve the recovery rate of potassium sulfate.

[0026] Furthermore, the method also includes an impurity removal step: periodically introducing a portion of the circulating potassium sulfate solution from step (e) into a bypass purification unit to remove accumulated impurity ions through membrane separation or ion exchange technology before returning it to the circulation system.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. The core innovation of this invention lies in the construction of a closed-loop recycling system for potassium sulfate. Potassium salt is used as a reaction carrier rather than a consumable in the process, and its consumption is limited to a very small amount of physical loss, effectively reducing raw material costs, which constitute a major part of the cost in traditional processes.

[0029] 2. This invention successfully transforms the large amount of low-value, high-pollution byproduct fluorosilicic acid generated by industries such as phosphorus chemical industry into two high-value-added mainstream chemical products—high-quality silica and hydrofluoric acid—achieving atom-economic utilization of fluorine and silicon resources.

[0030] 3. This invention solves the pollution problem of fluorosilicic acid at its source. The closed-loop design minimizes the generation and discharge of waste liquid. Compared with the ammonia process, this method avoids the treatment of ammonia nitrogen wastewater. The entire process makes full use of materials and fully conforms to the development direction of circular economy and green chemical industry.

[0031] 4. This invention uses a gas-phase method to prepare silica. By controlling parameters such as hydrolysis temperature and residence time, the specific surface area, pore volume, and particle size distribution of the product can be flexibly adjusted, thereby producing high-strength silica products that meet the requirements of different high-end applications. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention proposes a closed-loop cyclic co-production method using potassium sulfate (K2SO4) as a circulating carrier and potassium fluorosilicate (K2SiF6) as a core intermediate. This method connects the generation and decomposition steps of potassium fluorosilicate in a series, allowing the potassium salt to be recycled as a "catalyst" carrier in the reaction, rather than a disposable consumable.

[0034] 1. Complete process flow

[0035] This method mainly includes the following five steps:

[0036] Step 1: Precipitation reaction of potassium fluorosilicate.

[0037] Crude fluorosilicic acid solutions from the phosphate fertilizer industry or other sources are treated to remove impurities such as phosphorus and arsenic before entering the reaction vessel. The pretreated fluorosilicic acid solution is then fed into a precipitation reaction vessel. Under set temperature and stirring conditions, it is thoroughly mixed and reacted with the mother liquor containing potassium sulfate, which is recycled from subsequent steps. The fluorosilicic acid undergoes a metathesis reaction with potassium sulfate, producing potassium fluorosilicate precipitate with low solubility and dilute sulfuric acid.

[0038] Core chemical reaction: H₂SiF₆ + K₂SO₄ (recycled) → K₂SiF₆↓ + H₂SO₄

[0039] After the reaction is complete, the resulting slurry is subjected to solid-liquid separation. A centrifuge or filter press is selected for the separation to obtain a wet potassium fluorosilicate solid filter cake and a filtrate containing dilute sulfuric acid.

[0040] To ensure the purity of potassium fluorosilicate, the filter cake needs to be washed to remove impurities adhering to its surface.

[0041] Depending on the water quality, some of the washing water can be reused to prepare circulating mother liquor, thereby reducing water consumption and material loss.

[0042] The separated dilute sulfuric acid can be purified or used directly in other industrial production, depending on its concentration and purity, thus achieving preliminary comprehensive utilization of resources.

[0043] Step 2: Decomposition reaction of potassium fluorosilicate

[0044] The purified potassium fluorosilicate solid obtained in step one is mixed with high-concentration sulfuric acid in a reactor specifically designed for hydrogen fluoride production and heated to react. Under the high temperature and strong dehydration effect of concentrated sulfuric acid, potassium fluorosilicate decomposes to produce gaseous silicon tetrafluoride (SiF4), gaseous hydrogen fluoride (HF), and solid or molten potassium sulfate.

[0045] Core chemical reaction: K₂SiF₆ + H₂SO₄ --> SiF₄↑ + 2HF↑ + K₂SO₄ (regeneration)

[0046] First, fluorine and silicon are separated in gaseous form (SiF4, HF) to facilitate subsequent conversion and utilization; second, potassium is converted into potassium sulfate to create conditions for subsequent recycling; finally, the generated hydrogen fluoride is itself a high-value-added product.

[0047] The mixture of silicon tetrafluoride and hydrogen fluoride produced in the reaction is sent to the next step for further processing after dust removal. The potassium sulfate at the bottom of the reactor is recycled and regenerated in step five after cooling.

[0048] Step 3: Vapor-phase hydrolysis of silicon tetrafluoride and preparation of silica.

[0049] The mixed gas of silicon tetrafluoride and hydrogen fluoride from step two is introduced into a gas-phase hydrolysis reactor. Under preset high-temperature conditions, the mixed gas comes into full contact with excess water vapor and reacts. Silicon tetrafluoride reacts with water vapor to produce solid silicon dioxide (i.e., white carbon black) and gaseous hydrogen fluoride.

[0050] Core chemical reaction: SiF4 + 2H2O --> SiO2↓ (white carbon black) + 4HF↑

[0051] The resulting silica is in the form of an extremely fine powder and needs to be collected through a multi-stage collection system including cyclone separators and bag filters. The collected crude silica needs to undergo a series of subsequent refining processes, including aging, washing, drying, pulverizing, and grading, to obtain a final product that meets the quality requirements of different application fields such as rubber reinforcing agents, silicone rubber fillers, and matting agents.

[0052] Step 4: Hydrogen fluoride absorption and purification

[0053] After gas-solid separation in step three, the remaining gas mainly consists of hydrogen fluoride and excess water vapor. The total amount of hydrogen fluoride includes the hydrogen fluoride generated in steps two and three. This mixed gas is then passed through a multi-stage falling film absorber or packed tower, where it is countercurrently absorbed using a circulating hydrofluoric acid solution. Finally, through processes such as condensation and distillation, high-purity hydrofluoric acid or anhydrous hydrogen fluoride products can be obtained.

[0054] This step enables the high-value recovery of fluorine resources. Compared with ammonium fluoride produced in the ammonia process, hydrofluoric acid has a wider market value and application range, and is a key basic raw material for the production of fluoropolymers, refrigerants, electronic-grade chemicals, and other products.

[0055] Step 5: Potassium sulfate recycling

[0056] The high-temperature potassium sulfate material discharged from the bottom of the reactor in step two is cooled and then precipitated through a crystallization process.

[0057] The potassium sulfate obtained from crystallization may contain small amounts of unreacted potassium fluorosilicate or other sulfate impurities. Therefore, purification is required through recrystallization or multi-stage washing to ensure that the recycled potassium sulfate has high purity, preventing impurities from accumulating in the system and affecting subsequent reaction efficiency and product quality.

[0058] The purified potassium sulfate is dissolved and prepared into a solution of a specific concentration. This solution is then pumped back to the precipitation reactor in step one as a circulating mother liquor for reaction with new fluorosilicic acid raw materials, thus starting a new cycle.

[0059] Through closed-loop design, potassium sulfate theoretically circulates only as a reaction carrier within the system, requiring only the replenishment of minimal losses due to physical degradation during separation and transfer. This minimizes potassium salt consumption, a major cost component of the original process, significantly improving the method's economic efficiency.

[0060] By organically combining the above five steps, a complete, closed-loop production system is formed, from the input of fluorosilicic acid waste to the output of silica and hydrofluoric acid products, while simultaneously achieving efficient recycling of potassium salts internally.

[0061] 2. Key process parameters and control points

[0062] Step 1: Precipitation reaction of potassium fluorosilicate

[0063] Fluorosilicic acid concentration: The concentration of raw material fluorosilicic acid is usually controlled within the range of 10% to 25% by mass. Too low a concentration will lead to a decrease in equipment volume utilization and an increase in energy consumption; too high a concentration may be detrimental to the reaction and material transportation due to increased solution viscosity.

[0064] Reaction temperature: The reaction temperature is generally controlled between 20 and 60℃. Lower temperatures favor the precipitation of potassium fluorosilicate because its solubility increases with increasing temperature, but at the same time, they slow down the reaction rate. Therefore, the optimal temperature needs to be selected by comprehensively considering both the precipitation rate and the reaction efficiency.

[0065] The K₂SO₄ / H₂SiF₆ molar ratio is typically slightly excess, with the molar ratio to fluorosilicic acid generally controlled at 1.05–1.2:1. This helps ensure complete precipitation of fluorosilicic acid and improves fluorine recovery.

[0066] Reaction pH: The initial pH is usually between 1 and 2, and the pH does not change much during the reaction. Real-time monitoring of the pH helps to determine the endpoint of the reaction.

[0067] Stirring speed and reaction time: Maintaining a moderate stirring speed (e.g., 100-300 rpm) helps promote mass transfer and avoids localized uneven concentration and precipitate encapsulation. The reaction time is generally 30-90 minutes, and the optimal aging time needs to be determined experimentally to obtain a crystal form that is easy to filter.

[0068] Step 2: Decomposition reaction of potassium fluorosilicate

[0069] Reaction temperature: Usually controlled between 250 and 450℃. Too low a temperature will lead to incomplete decomposition, while too high a temperature may exacerbate equipment corrosion and increase the occurrence of side reactions.

[0070] H2SO4 concentration and dosage: High-concentration sulfuric acid with a mass fraction of not less than 98% must be used. The amount of sulfuric acid used must be stoichiometric and slightly excessive to ensure the completeness of the reaction.

[0071] Reaction pressure: Operating under a slight negative pressure facilitates the timely removal of gaseous products (SiF4, HF), thereby promoting the reaction to proceed in the forward direction and ensuring the safety of production operations.

[0072] Catalyst / Reaction Medium: In some optimized processes, ionic liquids can be introduced as reaction media. Ionic liquids have advantages such as high thermal stability and low vapor pressure, which can significantly reduce reaction temperature, improve decomposition efficiency, and can be recycled, making them an important direction for technological improvement.

[0073] Step 3: Vapor-phase hydrolysis of silicon tetrafluoride

[0074] Hydrolysis temperature: High temperature is key to achieving gas-phase hydrolysis and producing high-quality silica. The hydrolysis temperature is generally controlled between 1000 and 1400℃. Temperature directly affects the primary particle size, specific surface area, and structural properties of silica.

[0075] H2O / SiF4 molar ratio: The water vapor needs to be much greater than the stoichiometric ratio, usually greater than 10:1, which not only ensures complete hydrolysis of silicon tetrafluoride, but also effectively controls the aggregation state of silica.

[0076] Gas flow rate and residence time: Controlling the residence time of reactants in the high-temperature zone regulates the particle size and particle size distribution of silica. If the residence time is too long, the particles are prone to sintering and growth; if the residence time is too short, the reaction may be incomplete.

[0077] Step 5: Potassium sulfate recycling

[0078] Crystallization temperature and rate: By controlling the cooling rate and the final temperature of the cooling crystallization process, potassium sulfate crystals with moderate particle size and easy separation can be obtained, thereby reducing potassium loss caused by mother liquor entrainment.

[0079] Purity control of circulating mother liquor: The concentration of impurity ions such as phosphorus, iron, and aluminum in the circulating mother liquor must be tested regularly. When impurities accumulate to a certain level, a portion of the mother liquor needs to be diverted for advanced bypass treatment, such as through ion exchange or membrane separation, or it can be discharged and replenished with fresh potassium sulfate to maintain the stability of the entire circulation system and product quality.

[0080] Potassium balance accounting: Establish a rigorous potassium material balance system to accurately measure the amount of potassium entering and leaving the system, as well as flowing between various units. This accounting allows for the timely detection of abnormal potassium loss points.

[0081] Example 1

[0082] This embodiment aims to demonstrate the basic process flow of the present invention, achieving efficient conversion of fluorosilicic acid and co-production of silica and hydrofluoric acid.

[0083] 1. Fluorosilicic acid pretreatment and precipitation:

[0084] The crude fluorosilicic acid solution from the wet-process phosphoric acid production line, with a mass fraction of approximately 18% and a pH of approximately 1.5, is first pre-precipitated by adding a small amount of lime milk and potassium dihydrogen phosphate to remove impurities such as phosphorus, iron, and aluminum. The pre-treated fluorosilicic acid solution is clear, with impurity content below 100 ppm.

[0085] The pretreated fluorosilicic acid solution was fed into the precipitation reactor at a flow rate of 1000 kg / h. Simultaneously, a potassium sulfate solution of approximately 20% concentration, which was refluxed in step five, was added at an appropriate flow rate to maintain the molar ratio of potassium sulfate to fluorosilicic acid at 1.1:1.

[0086] The reaction temperature was controlled at 45℃, the stirring speed at 150 rpm, and the reaction time at 60 minutes. The reaction produced potassium fluorosilicate precipitate and dilute sulfuric acid.

[0087] The slurry is subjected to solid-liquid separation using a plate and frame filter press to obtain a wet potassium fluorosilicate filter cake with a moisture content of approximately 25% and a dilute sulfuric acid filtrate. The filter cake is then subjected to two-stage countercurrent washing, with part of the wash water being reused to prepare the circulating mother liquor.

[0088] 2. Decomposition of potassium fluorosilicate:

[0089] The washed potassium fluorosilicate filter cake, on a dry basis, was fed into a dedicated high-temperature decomposition reactor at a flow rate of 200 kg / h. Simultaneously, concentrated sulfuric acid (98% by mass) was added, with its molar ratio to potassium fluorosilicate controlled at 2.5:1.

[0090] The reactor operates at 380℃, with the reaction pressure maintained at a slight negative pressure of -0.01MPa. Potassium fluorosilicate decomposes under the action of concentrated sulfuric acid, producing a mixed gas of SiF4 and HF, as well as molten potassium sulfate.

[0091] After preliminary dust removal by a cyclone separator, the mixed gas proceeds to the next step. Molten potassium sulfate is discharged from the bottom of the furnace and proceeds to step five.

[0092] 3. Preparation of silica by vapor-phase hydrolysis of silicon tetrafluoride:

[0093] The SiF4 and HF mixed gas from step two is introduced into the gas-phase hydrolysis reactor. Simultaneously, superheated steam is introduced, controlling the molar ratio of steam to SiF4 to be 15:1.

[0094] The internal temperature of the hydrolysis reactor is controlled at 1200℃. SiF4 reacts with water vapor to produce silica and HF.

[0095] The gas-solid mixture at the reactor outlet is rapidly cooled to below 300°C, and then the silica product is collected by a bag filter. The collected crude silica is then aged, washed, dried, pulverized, and classified to obtain the final silica product. This silica has a specific surface area of ​​approximately 180 m². 2 / g, with uniform particle size distribution.

[0096] 4. Hydrogen fluoride absorption and purification:

[0097] The HF-containing gas, after the silica has been separated by a bag filter, is sent to a multi-stage falling film absorption tower. HF is absorbed countercurrently using a circulating hydrofluoric acid solution to form a hydrofluoric acid solution with a mass fraction of approximately 30%.

[0098] The crude hydrofluoric acid solution was further purified by distillation to obtain anhydrous hydrogen fluoride product with a mass fraction of over 99.5%.

[0099] 5. Potassium sulfate recycling:

[0100] The molten potassium sulfate discharged in step two is cooled and crystallized to obtain crude potassium sulfate crystals.

[0101] Crude potassium sulfate crystals are purified by centrifugation, followed by hot water dissolution and recrystallization to obtain potassium sulfate crystals with a purity of over 99%.

[0102] The purified potassium sulfate is dissolved to prepare a 20% solution, which is then refluxed back to step one, thus achieving the recycling of potassium sulfate. During this recycling process, only about 1% of the potassium sulfate lost due to physical loss or the accumulation of a small amount of impurities needs to be replenished.

[0103] Example 2

[0104] This embodiment further optimizes the potassium recycling efficiency and improves the performance of silica based on Embodiment 1.

[0105] 1. Fluorosilicic acid pretreatment and precipitation:

[0106] Similar to Example 1, but the mother liquor (dilute sulfuric acid) after potassium fluorosilicate precipitation is partially concentrated by passing it through a nanofiltration membrane before entering the dilute sulfuric acid treatment unit to recover trace amounts of dissolved potassium salt and improve the potassium recovery rate.

[0107] The potassium fluorosilicate filter cake is washed using a three-stage countercurrent process, with precise control over the amount of washing water used in each stage to ensure that the residual potassium content in the filter cake is less than 0.1%.

[0108] 2. Decomposition of potassium fluorosilicate:

[0109] Similar to Example 1, the decomposition temperature was precisely controlled at 390°C to obtain a more stable SiF4 and HF gas production rate.

[0110] The waste heat generated by the decomposition furnace is preheated by a heat exchanger and then used to heat the steam entering step three, achieving cascaded energy utilization and expected to save about 10% of fuel consumption.

[0111] 3. Preparation of silica by vapor-phase hydrolysis of silicon tetrafluoride:

[0112] The internal temperature of the hydrolysis reactor was raised to 1350℃, and the molar ratio of water vapor to SiF4 was 20:1.

[0113] By adjusting the reactor structure and gas flow rate, the residence time of the gaseous products in the high-temperature zone was controlled to 1.5 seconds.

[0114] The collected silica products, after refining, have a specific surface area of ​​250m². 2 / g, with larger pore volume, suitable for high-end reinforcement applications.

[0115] 4. Hydrogen fluoride absorption and purification:

[0116] Same as Example 1, but the absorption tower uses a more efficient packed tower and the temperature of the absorbent is strictly controlled to ensure that the HF absorption efficiency reaches more than 99.8%.

[0117] 5. Potassium sulfate recycling:

[0118] Potassium sulfate crystallization mother liquor is further recovered by evaporation crystallization, increasing the total recovery rate of recycled potassium salt from 99% in Example 1 to over 99.5%.

[0119] Approximately 5% of the circulating potassium sulfate solution is drawn off for bypass treatment every 30 days. This portion of the solution is passed through an ion exchange resin to remove accumulated polyvalent ion impurities such as calcium, magnesium, and aluminum. The purified solution is then returned to the circulation system.

[0120] Example 3

[0121] This embodiment focuses on using advanced technologies to further reduce energy consumption and pursue products with higher purity.

[0122] 1. Fluorosilicic acid pretreatment and precipitation:

[0123] Same as Example 1, but with the introduction of ultrasonic assistance during the precipitation reaction. The ultrasonic frequency was 30 kHz and the ultrasonic power was 500 W. Under the action of ultrasound, the reaction time was shortened to 40 minutes, the potassium fluorosilicate precipitate crystals were more uniform, the filtration performance was better, and the precipitation rate was increased by 2%.

[0124] The washed filter cake is dehydrated by a high-efficiency filter press, reducing the moisture content to 20%, which reduces the energy consumption of subsequent decomposition steps.

[0125] 2. Decomposition of potassium fluorosilicate:

[0126] The washed potassium fluorosilicate filter cake is fed into a decomposition reactor containing an ionic liquid as the medium. The ionic liquid used is an imidazole-based ionic liquid, such as 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM][HSO4]).

[0127] The reaction temperature was significantly reduced to 220℃. In ionic liquid media, potassium fluorosilicate can be efficiently decomposed to generate SiF4 and HF.

[0128] Potassium sulfate, a byproduct of decomposition, is separated from the ionic liquid in solid form. The ionic liquid is then recovered through filtration and distillation for recycling. Compared to concentrated sulfuric acid decomposition, this method reduces energy consumption by approximately 30% and significantly reduces equipment corrosion.

[0129] 3. Preparation of silica by vapor-phase hydrolysis of silicon tetrafluoride:

[0130] The hydrolysis temperature was controlled at 1100℃, and the molar ratio of water vapor to SiF4 was 12:1.

[0131] By precisely controlling the residence time of the gas in the hydrolysis zone, ultrafine silica with an average particle size of 10 nm and a specific surface area of ​​up to 300 m² was prepared. 2 / g.

[0132] After silica collection, an online surface modification unit is introduced. A silane coupling agent (e.g., bis-(γ-triethoxysilylpropyl)-dipropylene tetrasulfide, grade Si-69) is sprayed onto the silica powder at a ratio of 2% by mass for in-situ surface modification. The modified silica exhibits better compatibility with the rubber matrix and superior reinforcing effect.

[0133] 4. Hydrogen fluoride absorption and purification:

[0134] The absorption tower uses a new type of high-efficiency packing material and utilizes multi-stage cooling technology to increase the HF absorption efficiency to over 99.9%.

[0135] The refining process employs a multi-tower distillation system to ensure that the final anhydrous hydrogen fluoride product has a purity of 99.99%, meeting the requirements for electronic applications.

[0136] 5. Potassium sulfate recycling:

[0137] The potassium sulfate crystallization mother liquor is treated with a combination of membrane concentration technology and evaporation crystallization to further improve the recovery rate of potassium sulfate, with a total potassium recovery rate of up to 99.8%.

[0138] The circulating potassium sulfate solution is periodically extracted for deep purification. Chelating resin adsorption and ion exchange treatment are used to remove trace heavy metal ions and organic impurities, ensuring the purity of the circulating potassium sulfate and preventing the accumulation of impurities from affecting product quality.

[0139] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the content of the present invention's specification shall also be included within the scope of protection of the present invention.

Claims

1. A method for the recycling and co-production of potassium fluorosilicate and silica, characterized in that, The method includes the following steps: (a) Potassium fluorosilicate precipitate formation: The fluorosilicic acid raw material is mixed and reacted with the potassium sulfate solution recycled in step (e) in a precipitation reactor to generate potassium fluorosilicate precipitate and dilute sulfuric acid, and the potassium fluorosilicate precipitate is subjected to solid-liquid separation. (b) Decomposition of potassium fluorosilicate: The potassium fluorosilicate obtained in step (a) is heated and reacted with concentrated sulfuric acid in a decomposition reactor to generate a gaseous product containing silicon tetrafluoride and hydrogen fluoride, as well as a solid or liquid material containing regenerated potassium sulfate. (c) Preparation of silica by gas-phase hydrolysis of silicon tetrafluoride: The gaseous product generated in step (b) is passed into a gas-phase hydrolysis reactor and reacted with water vapor at high temperature to generate solid silica and gaseous hydrogen fluoride. (d) Product separation and recovery: The reaction product of step (c) is subjected to gas-solid separation, the silica is collected, and the remaining hydrogen fluoride-containing gas is absorbed and purified to obtain hydrogen fluoride product. (e) Recycling of potassium sulfate: The material containing regenerated potassium sulfate generated in step (b) is cooled, crystallized and purified, and then recycled back to step (a) as the potassium sulfate solution for reaction with new fluorosilicic acid raw material; In step (e), the material containing recycled potassium sulfate is treated by multi-stage cooling crystallization or vacuum evaporation crystallization to improve the recovery rate of potassium sulfate. The method also includes an impurity removal step: periodically introducing a portion of the circulating potassium sulfate solution from step (e) into a bypass purification unit to remove accumulated impurity ions by membrane separation or ion exchange technology before returning it to the circulation system.

2. The method for the recycling and co-production of potassium fluorosilicate and silica according to claim 1, characterized in that, The fluorosilicic acid raw material described in step (a) has undergone pretreatment for phosphorus removal and / or arsenic removal before use.

3. The method for the recycling and co-production of potassium fluorosilicate and silica according to claim 1, characterized in that, The reaction temperature in step (a) is controlled at 20~60℃, and the molar ratio of potassium sulfate to fluorosilicic acid is 1.05~1.2:

1.

4. The method for the recycling and co-production of potassium fluorosilicate and silica according to claim 1 or 3, characterized in that, Ultrasonic assistance was introduced during the precipitation reaction in step (a), and the frequency of the ultrasonic waves was 20~40kHz.

5. The method for the recycling and co-production of potassium fluorosilicate and silica according to claim 1, characterized in that, The decomposition reaction temperature in step (b) is controlled at 250~450℃, and the mass fraction of concentrated sulfuric acid used is not less than 98%.

6. The method for the recycling and co-production of potassium fluorosilicate and silica according to claim 1 or 5, characterized in that, The decomposition reaction in step (b) is carried out in an ionic liquid medium, wherein the ionic liquid is an imidazole or quaternary ammonium salt ionic liquid.

7. The method for the recycling and co-production of potassium fluorosilicate and silica according to claim 1, characterized in that, The temperature of the gas-phase hydrolysis reaction in step (c) is controlled at 1000~1400℃, and the molar ratio of water vapor to silicon tetrafluoride is greater than 10:

1.

8. The method for the recycling and co-production of potassium fluorosilicate and silica according to claim 1, characterized in that, In step (c), the specific surface area of ​​the prepared silica is controlled to be between 100 and 300 m² by adjusting the residence time of the gaseous product in the high-temperature zone of the hydrolysis reactor. 2 Within the range of / g.