A method for preparing high-purity potassium fluoroborate using by-product fluorosilicic acid

Abstract

This invention discloses a method for preparing high-purity potassium fluoroborate using by-product fluorosilicic acid, belonging to the field of fine chemical technology. It aims to solve the problems of incomplete removal of silicon impurities, limited product purity, and high raw material costs and environmental pressures associated with traditional fluorosilicic acid methods for potassium fluoroborate preparation. This invention uses by-product fluorosilicic acid as raw material and achieves green and efficient preparation of high-purity potassium fluoroborate by introducing a multi-stage targeted silicon removal and purification control strategy. The process includes raw material pretreatment and compatibility, primary reaction and initial silicon removal, secondary reaction and deep silicon removal, and tertiary reaction and directional crystallization. This methodological innovation, combined with the discovery of key parameters, enables a product purity of up to 99.7%, with the key impurity silica content below 0.02%, and a product yield as high as 96.2%. This invention not only significantly improves product purity and realizes high-value utilization of by-product resources and reduces production costs, but also has the advantages of being green, environmentally friendly, and highly safe.

Description

Technical Field

[0001] This invention relates to the field of fine chemical technology, and more specifically to a method for preparing high-purity potassium fluoroborate using by-product fluorosilicic acid. Background Technology

[0002] Potassium fluoroborate (KBF4) is an important inorganic salt widely used in electroplating, metal smelting, abrasive industry, flame retardants, fluxing agents, and organic synthesis. Its main preparation methods can be divided into two categories: the hydrofluoric acid method and the fluorosilicic acid method.

[0003] The hydrofluoric acid process typically uses hydrofluoric acid (HF) and boric acid (H3BO3) as raw materials. First, they react to produce fluoroboric acid (KBF4), which then reacts with potassium hydroxide (KOH) or potassium chloride (KCl) to produce potassium fluoroborate. The product prepared by this method usually has high purity, meeting the needs of high-end applications. However, hydrofluoric acid is a highly toxic and corrosive chemical, and its production, transportation, and use pose extremely high safety risks and stringent environmental requirements, resulting in high raw material costs, complex operation, and high equipment investment. Furthermore, the hydrofluoric acid process is not a sustainable green production route, and its industrial applications are subject to numerous limitations.

[0004] The fluorosilicic acid method utilizes fluorosilicic acid (H₂SiF₆), a byproduct of phosphate fertilizer production, as a fluorine-containing raw material. It reacts with boric acid to produce fluoroboric acid, which is then reacted with potassium salts to prepare potassium fluoroborate. Compared to the hydrofluoric acid method, the fluorosilicic acid method has significant cost advantages and enables the comprehensive utilization of byproducts from the phosphate chemical industry, aligning with the development concepts of green and circular economies. However, fluorosilicic acid contains a large amount of silicon impurities. These silicon impurities generate various forms of silicides (such as silicic acid, fluorosilicates, and silicon dioxide) during the reaction. These silicides are easily entrained in the product, severely affecting the purity of potassium fluoroborate.

[0005] Traditional fluorosilicic acid methods face numerous challenges in silicon removal. For example, some methods attempt to precipitate silicon by controlling reaction temperature, acidity, or adding flocculants, but the results are often unsatisfactory. A common traditional one-step method involves reacting fluorosilicic acid with boric acid, then directly adding potassium chloride for crystallization, followed by a single filtration. While this method is simple, the final product typically has a high silica content due to the ineffective removal of silicon impurities, resulting in a purity that rarely exceeds 99%, usually hovering around 97%. This is because, under a single reaction environment, silicon impurities cannot be completely separated from the solution. Some silicon exists in colloidal or fine particle form, which is difficult to remove completely by conventional filtration methods; others may exist as soluble fluorosilicates, directly entering subsequent crystallization steps and ultimately contaminating the product. This method often leads to low product purity and persistently high silica impurity content, failing to meet the purity requirements of high-end applications.

[0006] Other attempts at improvement include removing silica by simply adjusting the pH after the reaction of fluorosilicic acid and boric acid. For example, neutralizing the solution to pH=7. The principle is to convert silica that failed to precipitate under acidic conditions into silicic acid precipitate in a near-neutral environment. However, this simple neutralization strategy also has significant limitations. When the pH reaches neutral, although some silica gel will precipitate, it may simultaneously trigger the hydrolysis of fluoroborate, generating boric acid and fluorides, thereby reducing the yield of fluoroborate. More importantly, the neutralization process may cause some of the already formed fine silica gel particles to redissolve or form ultrafine particles that are difficult to filter, thus failing to achieve thorough deep silica removal. Therefore, even with some pH adjustment, the product purity can only reach about 98%, and the impurity silica content is still difficult to control at a very low level. This indicates that relying solely on traditional, simple silica removal methods is insufficient to fundamentally solve the problem of low product purity in the fluorosilicic acid method.

[0007] Furthermore, existing fluorosilicic acid methods also have drawbacks in the crystallization process. Common crystallization methods may result in uneven crystal size, severe mother liquor entrainment, increased washing load, and reduced product yield and purity. Achieving directional crystal growth and efficient separation is also crucial for improving product quality and economic benefits.

[0008] In summary, while the fluorosilicic acid method offers resource and cost advantages, its core bottleneck lies in the complete removal of impurity silicon and the improvement of product purity. Existing technologies lack refined and multi-layered control over silicon removal strategies, making it difficult to achieve high levels of product purity and limiting its application in high-end fields.

[0009] Therefore, it is necessary to propose a method for preparing high-purity potassium fluoroborate using by-product fluorosilicic acid 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 preparing high-purity potassium fluoroborate using by-product fluorosilicic acid includes the following steps:

[0013] (1) Raw material pretreatment: The by-product fluorosilicic acid solution is aged at 50-60℃ for 2-4 hours, and then pre-filtered to obtain a refined fluorosilicic acid solution;

[0014] (2) Primary reaction and primary desiliconization: The purified fluorosilicic acid solution obtained in step (1) is slowly added to the hot boric acid solution at a molar ratio of H2SiF6 to H3BO3 of 2.08~2.15:1 and the reaction is carried out with vigorous stirring at a temperature of 78-82℃; then the solution is filtered while hot using a filter with a pore size of 1-3μm to obtain the filtrate.

[0015] (3) Secondary reaction and deep desiliconization: Add ammonia water slowly to the filtrate obtained in step (2) while stirring continuously at a temperature of 65-70℃, and control the pH value of the solution within a narrow range of 5.0-5.5; after the addition is completed, keep it warm and age; then use a precision filter with a pore size of 0.22-0.45μm for precision filtration to obtain a high-purity ammonium fluoroborate solution;

[0016] (4) Tertiary reaction and directional crystallization: Potassium chloride solution is reacted according to K... + [BF4] in NH4BF4 - The molar ratio is 1.03~1.08:1. The solution is slowly added to the high-purity ammonium fluoroborate solution obtained in step (3) using the reverse addition method. The solution is then cooled to 10-15℃ at a rate of ≤5℃ / hour at a temperature of 30-35℃ and kept warm for aging. The solution is then filtered and rinsed with a pre-cooled ethanol-water mixture. Finally, the solution is dried at an absolute pressure of ≤5kPa and a temperature of 90℃ to obtain the high-purity potassium fluoroborate product.

[0017] Furthermore, in step (1), the mass concentration of the by-product fluorosilicic acid solution is 40%.

[0018] Furthermore, in step (2), the mass concentration of the hot boric acid solution is 25%, and the vigorous stirring reaction lasts for 3 hours.

[0019] Furthermore, in step (2), the filter is a sintered borosilicate filter.

[0020] Furthermore, in step (2), the stirring rate of the vigorous stirring is 300 rpm.

[0021] Furthermore, in step (3), the mass concentration of the ammonia water is 20%, and the heat preservation and aging time after the addition is completed is 1 hour.

[0022] Furthermore, in step (3), the precision filter is a polyvinylidene fluoride membrane.

[0023] Furthermore, in step (4), the mass concentration of the potassium chloride solution is 20%.

[0024] Furthermore, in step (4), the heat preservation and curing time is 2 hours.

[0025] Furthermore, in step (4), the volume ratio of the pre-cooled ethanol-water mixture is 1:4.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. This invention utilizes multi-stage targeted silicon removal and purification control to transform impurity silicon into different forms stepwise and efficiently remove it. First, in the fluorosilicic acid pretreatment stage, a portion of high-polymerization silica colloids is pre-precipitated through aging. Second, in the first-stage reaction, a strong acid environment and specific temperature conditions are used to induce the precipitation and efficient separation of most silicon as coarse-grained silica particles. Third, in the second-stage deep silicon removal, by controlling the solution pH within a narrow range of 5.0-5.5, the remaining trace amounts of soluble fluorosilicate ions are almost quantitatively transformed into extremely fine flocculent silica precipitates and precisely filtered out. This multi-stage, targeted silicon removal strategy results in a final product with a silica content far lower than traditional methods, reaching <0.02%, and a product purity as high as 99.7%, even exceeding the purity of products prepared by the expensive and dangerous hydrofluoric acid method.

[0028] 2. This invention uses fluorosilicic acid, a byproduct of phosphate fertilizer production, as the main fluorine-containing raw material, making full use of industrial waste and significantly reducing raw material costs. Simultaneously, the filter residue obtained from the first-stage silicon removal process is high-purity silicon dioxide, which can be used as a precursor for high-value-added products such as silica, achieving comprehensive resource utilization and high-value-added processing, further enhancing economic benefits, and aligning with the development direction of green chemistry.

[0029] 3. This invention couples the reaction process with the impurity removal target, employing a "divide and conquer" strategy by designing different chemical environments for different forms of silicon impurities. Particularly in the second-stage deep silicon removal, the final pH value of ammonia addition is controlled within a narrow range of 5.0-5.5. Experiments have shown that under these specific weakly acidic conditions, residual fluorosilicate ions can be almost quantitatively converted into silica gel precipitate, while the risk of ammonium fluoroborate hydrolysis is extremely low, effectively protecting the product. If the pH is conventionally increased to 7, it may lead to the hydrolysis of a small amount of fluoroborate and potentially the resolubilization of some silica gel.

[0030] 4. In the fourth crystallization step, this invention employs a "reverse addition" method and programmed temperature control, which effectively controls the nucleation and growth process of potassium fluoroborate crystals, producing crystals with uniform particle size, minimal mother liquor entrainment, and easy washing. Combined with subsequent rinsing and drying processes, the final product yield can reach 96.2%, significantly higher than traditional methods.

[0031] 5. Compared to the hydrofluoric acid method, this invention avoids the use of highly toxic and corrosive hydrofluoric acid, greatly reducing safety risks and environmental pressures during production. The entire process is rationally designed, generates minimal waste, and the byproducts have high-value utilization potential, aligning with the green manufacturing concept of sustainable development. 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] Example 1

[0034] This embodiment aims to illustrate in detail the complete process and effects of the method for preparing high-purity potassium fluoroborate using by-product fluorosilicic acid according to the present invention.

[0035] Step 1: Raw Material Pretreatment and Preparation. Take 2000 kg of a 40% (w / w) by-product fluorosilicic acid solution and place it in a corrosion-resistant reactor equipped with a stirring and heating device. Heat the fluorosilicic acid solution to 55°C and maintain stirring (approximately 80 rpm) at this temperature for 3 hours. During this aging process, some of the highly polymerized silica colloids in the solution gradually coagulate and precipitate. After aging, perform preliminary filtration of the solution using a plate and frame filter press to remove the pre-precipitated silica colloids, yielding approximately 1800 kg of refined fluorosilicic acid solution. The filtered silica colloids can be collected and processed separately. Simultaneously, prepare the following solutions:

[0036] Dissolve 250 kg of boric acid (H3BO3) in 750 kg of deionized water and heat to 85°C to prepare a 25% (w / w) hot boric acid solution. Mix 200 kg of ammonia water (NH3·H2O) with 800 kg of deionized water to prepare a 20% (w / w) ammonia solution. Dissolve 200 kg of potassium chloride (KCl) in 800 kg of deionized water to prepare a 20% (w / w) potassium chloride solution. Store all solutions in appropriate storage tanks for later use.

[0037] Step 2: Primary reaction and initial desilication, using an acidic environment to solidify silicon, transferring the prepared 25% boric acid hot solution (85℃) to a 10m... 3The solution was placed in a glass-lined reactor and kept at a constant temperature. Then, the purified fluorosilicic acid solution obtained in the first step was slowly added to the hot boric acid solution at a rate controlled at approximately 500 kg / hour. During this process, the molar ratio of H₂SiF₆ to H₃BO₃ was precisely controlled at 2.12:1. The temperature inside the reactor was maintained between 78-82°C during the addition process, and a powerful stirrer was activated at a speed of 300 rpm to ensure thorough mixing of the reactants and promote silicon precipitation.

[0038] After the addition is complete, the reaction continues at 80℃ and 300rpm for 3 hours. During this stage, the following reactions mainly occur: H₂SiF₆ + 4H₃BO₃ → 4HBF₄ + H₂SiF₃ + 3H₂O, and the polymerization and dehydration of silicic acid to form silica precipitate: H₂SiO₃ → SiO₂·nH₂O (precipitate). After the reaction is complete, the reaction mixture is filtered while hot at approximately 75℃ through a candle filter equipped with a sintered borosilicate filter with a pore size of 2μm. The filter residue is high-purity silica, which, after washing and drying, can be used as a precursor for silica. The filtrate, mainly containing fluoroboric acid and trace amounts of soluble silica impurities, is collected for subsequent steps.

[0039] Step 3: Secondary reaction and deep desiliconization. Residual silica is removed through chemical conversion. The filtrate from step 2 is transferred to another reactor equipped with a stirrer and pH electrode, maintaining the temperature at 68°C. A 20% (w / w) ammonia solution is slowly added dropwise at a rate controlled at approximately 20 kg / h. The pH of the solution is monitored in real-time, and the addition endpoint is controlled at pH 5.2. This specific weakly acidic environment is crucial for the complete conversion of residual fluorosilicate ions while minimizing the hydrolysis of fluoroboric acid. Under these pH conditions, the residual fluorosilicate ions react with the ammonia solution to form a very fine, flocculent silica gel precipitate: SiF6. 2- +2NH3·H2O→SiO2·nH2O (precipitate) +2NH4 + +6F - Simultaneously, fluoroboric acid is converted to ammonium fluoroborate: HBF4 + NH3·H2O → NH4BF4 + H2O. After the addition is complete, the mixture is aged at 68°C for 1 hour to allow the silica gel precipitate to fully form and grow, facilitating subsequent filtration. The mixture is then filtered through a precision filter equipped with a 0.3 μm pore size polyvinylidene fluoride (PVDF) membrane. This step ensures the purity of the final product, effectively removing all residual ultrafine silica gel particles from the solution to obtain a high-purity ammonium fluoroborate solution.

[0040] Step 4: Tertiary reaction and directional crystallization to control product formation. The high-purity ammonium fluoroborate solution obtained in Step 3 is transferred to a crystallization reactor. A 20% potassium chloride solution is slowly added to the ammonium fluoroborate solution using a reverse addition method, at a rate of approximately 15 kg / hour. K is controlled... + [BF4] in NH4BF4 - The molar ratio was 1.05:1. During the addition process, the solution temperature was maintained at 30-35℃. After the addition was complete, a cooling program was started, slowly lowering the solution temperature from 35℃ to 12℃ at a rate of 3℃ / hour. The solution was then aged at 12℃ for 2 hours to promote uniform growth and full precipitation of potassium fluoroborate crystals. The crystallization reaction was: NH4BF4 + KCl → KBF4 (precipitate) + NH4Cl. After aging, solid-liquid separation was performed using a centrifuge to obtain potassium fluoroborate crystals.

[0041] The crystals were rinsed with a pre-cooled ethanol-water mixture (volume ratio 1:4, pre-cooled to 5°C) to remove mother liquor and soluble impurities trapped on the crystal surface. The amount of rinsing solution used was approximately 10% of the crystal mass. Finally, the rinsed potassium fluoroborate crystals were transferred to a vacuum drying oven and vacuum dried at an absolute pressure ≤5 kPa and a temperature of 90°C until constant weight was obtained, yielding high-purity potassium fluoroborate product.

[0042] Product performance data: The potassium fluoroborate product prepared in this embodiment was tested and found to have a purity of 99.7%, a content of the key impurity silicon dioxide (SiO2) of less than 0.02%, and a product yield (based on boron) of 96.2%.

[0043] Example 2

[0044] This example aims to demonstrate the impact of minor adjustments to the core parameters within the range of the first and third steps on product performance.

[0045] Step 1: Raw Material Pretreatment and Preparation. Take 2000 kg of a 40% (w / w) by-product fluorosilicic acid solution and age it at 50°C for 2 hours. After preliminary filtration, a refined fluorosilicic acid solution is obtained. The preparation of other raw material solutions is the same as in Example 1.

[0046] Step 2: Primary reaction and initial silicon removal. The purified fluorosilicic acid solution is mixed with a hot boric acid solution, controlling the molar ratio of H₂SiF₆ to H₃BO₃ to be 2.08:1. The reaction is carried out at 78°C and 300 rpm for 3 hours. The mixture is then filtered while hot using a sintered borosilicate filter with a pore size of 1 μm. Other procedures are the same as in Example 1.

[0047] Step 3: Secondary reaction and deep desiliconization. The filtrate obtained in step 2 was slowly added dropwise with 20% ammonia solution at 65°C under stirring, maintaining the pH at 5.0. After the addition was complete, the solution was aged at this temperature for 1 hour. The solution was then precisely filtered using a 0.22μm polyvinylidene fluoride membrane to obtain a high-purity ammonium fluoroborate solution.

[0048] Step 4: Tertiary reaction and directional crystallization. Add 20% potassium chloride solution according to K... + [BF4] in NH4BF4 - The ammonium fluoroborate solution was added in a molar ratio of 1.03:1 using a reverse addition method. The solution was then cooled to 10°C at a rate of 5°C / hour at 30°C and maintained at this temperature for 2 hours. After filtration, the solution was rinsed with a pre-cooled ethanol-water mixture (volume ratio 1:4) and finally dried at 90°C under an absolute pressure ≤5 kPa.

[0049] Product performance data: The potassium fluoroborate product prepared in this embodiment was tested and found to have a purity of 99.6%, a silica content of less than 0.025%, and a yield of 95.8%.

[0050] Example 3

[0051] This embodiment aims to further verify the robustness of adjusting the core parameters within the range of the first and third steps.

[0052] Step 1: Raw Material Pretreatment and Preparation. Take 2000 kg of a 40% (w / w) by-product fluorosilicic acid solution and age it at 60°C for 4 hours. After preliminary filtration, a refined fluorosilicic acid solution is obtained. The preparation of other raw material solutions is the same as in Example 1.

[0053] Step 2: Primary reaction and initial silicon removal. The purified fluorosilicic acid solution is mixed with a hot boric acid solution, controlling the molar ratio of H₂SiF₆ to H₃BO₃ to be 2.15:1. The reaction is carried out at 82°C and 300 rpm for 3 hours. The mixture is then filtered while hot using a sintered borosilicate filter with a pore size of 3 μm. Other procedures are the same as in Example 1.

[0054] Step 3: Secondary reaction and deep desiliconization. The filtrate obtained in step 2 was slowly added dropwise with 20% ammonia solution at 70°C under stirring, maintaining the pH at 5.5. After the addition was complete, the solution was aged at this temperature for 1 hour. The solution was then precisely filtered using a 0.45μm polyvinylidene fluoride (PVDF) membrane to obtain a high-purity ammonium fluoroborate solution.

[0055] Step 4: Tertiary reaction and directional crystallization. Add 20% potassium chloride solution according to K... + [BF4] in NH4BF4 -The ammonium fluoroborate solution was added in a molar ratio of 1.08:1 using a reverse addition method. The solution was then cooled to 15°C at a rate of 2°C / hour from 35°C and maintained at this temperature for 2 hours. After filtration, the solution was rinsed with a pre-cooled ethanol-water mixture (volume ratio 1:4) and finally dried at 90°C under an absolute pressure ≤5 kPa.

[0056] Product performance data: The potassium fluoroborate product prepared in this embodiment was tested and found to have a purity of 99.65%, a silica content of less than 0.022%, and a product yield of 96.0%.

[0057] Comparative Experimental Data and Analysis

[0058] To fully demonstrate the significant effects and inventiveness of the method for preparing high-purity potassium fluoroborate using by-product fluorosilicic acid, we conducted the following comparative experiments and analyzed the results in detail.

[0059] Comparative Example 1: Traditional One-Step Method. This comparative example simulates a common existing process for preparing potassium fluoroborate using the fluorosilicic acid method. The specific operation is as follows:

[0060] A 40% (w / w) solution of by-product fluorosilicic acid was directly mixed with a 25% (w / w) hot boric acid solution (85°C), controlling the molar ratio of H₂SiF₆ to H₃BO₃ to be approximately 2.1:1, and the reaction was carried out at 80°C for 3 hours. After the reaction was completed, a 20% potassium chloride solution was directly added to K₂. + [BF4] in NH4BF4 - Crystallization was carried out at a molar ratio of 1.05:1 and cooled to crystallize at room temperature. The crystals were then filtered once, rinsed with cold water, and dried at 90°C.

[0061] Results Analysis: Testing revealed that the potassium fluoroborate product prepared in Comparative Example 1 had a purity of 97.5%, with a critical impurity content of silica as high as 0.45%. The product yield was 89.5%. This traditional one-step method, lacking an effective stepwise removal strategy for silica impurities, allows a large amount of silica impurities to directly enter the crystallization process, including unreacted fluorosilicic acid, colloidal silica, and fine silica particles, ultimately becoming entrained in the product and severely affecting its purity. Its byproduct is silica-containing slag, which has low value.

[0062] Comparative Example 2: Silicon Removal Method Without pH Control. This comparative example aims to verify the importance of pH control in the third step of this invention. The specific operation is as follows:

[0063] The first two steps are essentially the same as in Example 1, namely, fluorosilicic acid pretreatment, and the primary reaction and initial desiliconization. In the filtrate obtained after the second step of filtration, 20% ammonia solution is slowly added dropwise at 68°C with stirring, but the pH of the solution is adjusted to pH=7 (i.e., the conventional neutralization point) at the endpoint of the addition. After the addition is complete, the solution is aged at this temperature for 1 hour, and then precision filtered using a 0.3 μm polyvinylidene fluoride (PVDF) membrane. The subsequent third-stage reaction and directional crystallization steps are the same as in Example 1.

[0064] Results Analysis: The potassium fluoroborate product prepared in Comparative Example 2 had a purity of 98.9% and a silica content of 0.15%, a key impurity. The product yield was 93.8%. Compared to Example 1 of this invention, although the purity was improved, it still did not reach the superior level of this invention. This indicates that adjusting the pH to neutral (pH=7), while capable of precipitating some silica, is not the optimal choice. In a neutral environment, ammonium fluoroborate may undergo some hydrolysis, leading to the loss of fluoroborate ions, thus affecting product yield and purity. Simultaneously, some silica particles may become unstable again or form difficult-to-filter morphologies in a neutral environment, failing to achieve thorough deep silica removal. In this invention, the pH is controlled within a narrow weakly acidic range of 5.0-5.5 to achieve efficient silica removal and product protection. The byproduct is silica slag, which has low to medium value.

[0065] Comparative Example 3: Hydrofluoric Acid Method. This comparative example represents another major route for preparing high-purity potassium fluoroborate in the prior art. The specific operation is as follows: First, high-purity hydrofluoric acid is reacted with boric acid to produce fluoroboric acid. Then, the obtained fluoroboric acid is reacted with high-purity potassium hydroxide to produce potassium fluoroborate. After conventional steps such as crystallization, washing, and drying.

[0066] Results Analysis: Testing showed that the potassium fluoroborate product prepared in Comparative Example 3 had a purity of 99.5%, and the content of the key impurity, silica, was undetectable, meaning it was below the detection limit. The product yield was 92.0%. Although the hydrofluoric acid method can obtain high-purity products, its overall process cost is extremely high, mainly due to the expensive and highly toxic nature of hydrofluoric acid raw materials and the stringent requirements for equipment and operating environment. Example 1 of this invention, using inexpensive by-product raw materials, achieves a product purity of 99.7%, with the silica content below 0.02%, even surpassing the purity of products from the hydrofluoric acid method, and also boasts a higher yield, fully demonstrating the significant advancement and economic value of this invention. Furthermore, the hydrofluoric acid method produces no valuable by-products.

[0067] Table 1 Comparison of Effects between Examples and Comparative Examples

[0068] Features / Parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Product purity 99.7% 99.6% 99.65% 97.5% 98.9% 99.5% <![CDATA[SiO2 content]]> <0.02% <0.025% <0.022% 0.45% 0.15% Not detected Product yield 96.2% 95.8% 96.0% 89.5% 93.8% 92.0% by-products High-purity silica High-purity silica High-purity silica Silicon slag silicon slag No valuable byproducts Process safety Lower risk (compared to the HF method) Lower risk (compared to the HF method) Lower risk (compared to the HF method) Higher risk (traditional process) Lower risk (compared to the HF method) Extremely high risk (highly toxic HF) cost Low Low Low lower medium Extremely high

[0069] In summary, the comparative experiments clearly demonstrate that the process of this invention, using inexpensive by-product raw materials and employing an innovative multi-stage targeted silicon removal strategy, achieves a high level of product purity (99.7%) and a SiO2 content of <0.02%, surpassing even the expensive and dangerous hydrofluoric acid method. Furthermore, this invention significantly improves product yield and enables the high-value utilization of the by-product, silica.

[0070] 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 preparing high-purity potassium fluoroborate using by-product fluorosilicic acid, characterized in that, Includes the following steps: (1) Raw material pretreatment: The by-product fluorosilicic acid solution with a mass concentration of 40% is aged at 50-60℃ for 2-4 hours, and then pre-filtered to obtain a refined fluorosilicic acid solution; (2) Primary reaction and primary desiliconization: The refined fluorosilicic acid solution obtained in step (1) is slowly added to the hot boric acid solution at a molar ratio of H2SiF6 to H3BO3 of 2.08~2.15:

1. The reaction is carried out with strong stirring at a stirring rate of 300 rpm at a temperature of 78-82℃. Then, the solution is filtered while hot using a sintered borosilicate filter with a pore size of 1-3 μm to obtain the filtrate. (3) Secondary reaction and deep desiliconization: Add ammonia water slowly to the filtrate obtained in step (2) while stirring continuously at a temperature of 65-70℃, and control the pH value of the solution within a narrow range of 5.0-5.5; after the addition is completed, keep it warm and age; then use a polyvinylidene fluoride membrane precision filter with a pore size of 0.22-0.45μm for precision filtration to obtain a high-purity ammonium fluoroborate solution; (4) Tertiary reaction and directional crystallization: A 20% potassium chloride solution was prepared according to K... + [BF4] in NH4BF4 - The molar ratio of potassium fluoroborate is 1.03~1.08:

1. It is slowly added to the high-purity ammonium fluoroborate solution obtained in step (3) using the reverse addition method. The solution is cooled to 10-15℃ at a rate of ≤5℃ / hour at a temperature of 30-35℃ and kept warm for 2 hours. Then it is filtered and washed with a pre-cooled ethanol-water mixture with a volume ratio of 1:

4. Finally, it is dried at an absolute pressure of ≤5kPa and a temperature of 90℃ to obtain the high-purity potassium fluoroborate product. In step (3), the mass concentration of the ammonia water is 20%, and the heat preservation and aging time after the addition is 1 hour.

2. The method for preparing high-purity potassium fluoroborate using by-product fluorosilicic acid according to claim 1, characterized in that, In step (2), the mass concentration of the hot boric acid solution is 25%, and the vigorous stirring reaction lasts for 3 hours.