Integrated reaction process for preparing potassium fluoborate through efficient conversion of fluosilicic acid

Abstract

The invention discloses an integrated reaction process for preparing potassium fluoborate through efficient conversion of fluosilicic acid, and relates to the technical field of inorganic fluorine chemical industry, and the potassium fluoborate is prepared through the technologies of complexing metal impurities through EDTA disodium, catalyzing condensation reaction through Fe-TiO2, carrying out K2CO3 / nano gamma-Al2O3 composite desilicication, deeply removing sodium through ion exchange and carrying out mother liquor closed-loop circulation. The problems of serious sodium pollution, low reaction efficiency and resource waste in the traditional process are solved. The composite desiliconization agent improves the desiliconization rate to 96%, the reaction time is shortened by 40% through nanometer catalysis, the mother liquor recycling rate is 80%, and the silicon slag is converted into high-added-value nanometer white carbon black. The product purity is greater than or equal to 99.5%, the sodium residue is less than or equal to 0.003%, and the method is suitable for industrial production of electronic-grade potassium fluoborate.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic fluorochemical industry, and more specifically to an integrated reaction process for efficiently preparing potassium fluoroborate by converting fluorosilicic acid. Background Art

[0002] Potassium fluoroborate is an important raw material in the metallurgy and electronics fields. The traditional process has the following defects: 1. Severe sodium pollution: The existing technology usually uses NaCl for desilication, resulting in sodium residue in the product > 0.05%. Multiple water washes are required, generating high-salt wastewater. 2. Low reaction efficiency: The condensation reaction time between fluorosilicic acid and boric acid is long (≥180 minutes), and the lack of a catalyst leads to a conversion rate of less than 90%. 3. Resource waste: By-product silica slag (SiO2) is landfilled as solid waste, and the mother liquor is directly discharged, causing fluorine pollution.

[0003] The present invention aims to achieve the green preparation of high-purity KBF4 through a composite desilication agent, nano-catalysis, and closed-loop recycling technology.

[0004] Therefore, it is necessary to propose an integrated reaction process for efficiently preparing potassium fluoroborate by converting fluorosilicic acid to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems raised in the background art.

[0006] The present invention specifically adopts the following technical solutions to achieve the above purpose: An integrated reaction process for efficiently preparing potassium fluoroborate by converting fluorosilicic acid, comprising the following steps: a) Mix 20 - 35 parts by mass of boric acid, 0.5 - 1.2 parts by mass of disodium EDTA with 200 parts by mass of water, and heat to 80 - 85 °C for dissolution; b) Add 77.6 - 135.9 parts by mass of 40 wt% fluorosilicic acid to the solution in step a), and react at 75 - 80 °C for 90 - 120 minutes under the protection of 0.1 wt% nano-TiO2 catalyst and nitrogen; c) Add 4.5 - 7.8 parts by mass of a composite desilication agent to the reaction solution in step b), stir at 50 °C for 20 minutes for desilication, and then filter to obtain silica slag and a filtrate; d) The filtrate in step c) is de-sodiumed by an ion exchange resin, add 8.04 - 14.07 parts by mass of 20 wt% KCl solution, crystallize at 50 °C for 90 minutes to obtain potassium fluoroborate, and part of the mother liquor is returned to the crystallization step for reuse; e) The silica slag in step c) is pickled and spray-dried to obtain nano-silica white carbon black.

[0007] Further, the nano-TiO₂ catalyst is Fe-doped, with a particle size of 20-50 nm and an addition amount of 0.05-0.15% of the total mass of the reaction system.

[0008] Further, the particle size of γ-Al₂O₃ in the composite desiliconizing agent is 10-20 nm, and the mass ratio of K₂CO₃ to γ-Al₂O₃ is 4:1-5:1.

[0009] Further, 80% of the mother liquor in step d) is returned to the crystallization step for recycling, and the remaining 20% of the mother liquor is electrolyzed to recover the by-product CaF₂.

[0010] Further, in step e), the inlet temperature of spray drying is 170-190 °C, the outlet temperature is 70-90 °C, and the particle size of the obtained white carbon black is ≤50 nm.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the present invention, the desiliconization rate is increased from 85% to 96% by the composite desiliconizing agent. The purity of the prepared KBF₄ is ≥99.5%, the sodium residue is ≤0.003%, and it is green and environmentally friendly.

[0012] 2. In the present invention, the condensation reaction time is shortened by 40% through the catalysis of nano-TiO₂. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is the reaction flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the protection scope of the present invention.

[0015] Please refer to Figure 1 , an integrated reaction process for efficiently preparing potassium fluoroborate from fluosilicic acid.

[0016] 1. Raw material pretreatment Add 20 - 35 parts by mass of boric acid (purity ≥ 99.5%) and 200 parts by mass of deionized water into an enamel reactor with a jacket. Start the stirrer (rotation speed 200 - 300 rpm) and slowly heat up to 80 - 85 °C. Then add 0.5 - 1.2 parts by mass of disodium EDTA (analytical grade) and continuously stir until the solution becomes completely transparent (about 30 - 40 minutes). Monitor the pH value of the solution through an online pH meter and control it within the range of 2.5 - 3.0. If the pH value is too high, dilute sulfuric acid (5% concentration) can be added dropwise for adjustment. After dissolution, remove the undissolved impurities through a plate and frame filter (pore size 0.5 μm) to obtain a clear boric acid - EDTA mixed solution.

[0017] 2. Catalytic condensation reaction Transfer the solution obtained in step 1 to a high - pressure reactor (made of Hastelloy C276). Slowly add 77.6 - 135.9 parts by mass of 40 wt% fluosilicic acid (industrial grade) at a rate of 1 - 2 mL / min through a constant - pressure dropping funnel. Meanwhile, add a Fe - doped nano - TiO₂ catalyst with a mass ratio of 0.1 wt% (particle size 20 - 50 nm, specific surface area ≥ 120 m² / g) to the reaction system. The catalyst needs to be pre - activated in a nitrogen atmosphere for 30 minutes. During the reaction, introduce high - purity nitrogen (flow rate 0.5 L / min), maintain the pressure at 0.2 - 0.3 MPa, and the temperature at 75 - 80 °C (temperature control accuracy ±0.5 °C). The reaction time is 90 - 120 minutes. During this period, monitor the change in the intensity of the characteristic peak of the Si - F bond (1100 cm -1 ) through online infrared spectroscopy (IR) to ensure that the conversion rate of fluosilicic acid is ≥ 95%.

[0018] 3. Composite desilication and solid - liquid separation After the reaction is completed, cool the system to 50 °C and add 4.5 - 7.8 parts by mass of a composite desilication agent (mass ratio of K₂CO₃ to γ - Al₂O₃ is 4:1 - 5:1, particle size of γ - Al₂O₃ is 10 - 20 nm). The composite desilication agent needs to be pre - calcined at 400 °C for 2 hours to remove surface hydroxyl groups. Start a high - speed shear disperser (rotation speed 1000 - 1500 rpm) and continuously stir for 20 minutes to allow the desilication agent to fully contact with silicic acid. Then perform solid - liquid separation using a plate and frame filter press (filter cloth made of polypropylene, pore size 1 μm). Wash the filter cake (silica residue) 3 times with deionized water (water - material ratio 2:1 each time), and the filtrate (silica solution) enters the next process. The SiO₂ content in the silica residue is ≥ 98%, and the residual silicon concentration in the silica solution is ≤ 50 ppm.

[0019] 4. Ion exchange for sodium removal The filtrate obtained in Step 3 is passed through a series-connected 001×7 strongly acidic cation exchange resin column (resin packing height 1.5 m, column diameter ratio 3:1), and the flow rate is controlled at 10 - 15 BV / h. The resin needs to be regenerated with 5% HCl in advance and washed with deionized water until neutral. The sodium ion concentration in the exchanged solution is detected by inductively coupled plasma optical emission spectrometry (ICP-OES) to ensure ≤0.005% (i.e., ≤50 ppm). If the sodium residue exceeds the standard, secondary exchange or resin replacement is required.

[0020] 5. Crystallization and mother liquor recycling Add 8.04 - 14.07 parts by mass of 20wt% KCl solution (preheated to 50°C) to the solution after sodium removal, and use the programmed cooling crystallization method: the initial temperature of 50°C is maintained for 30 minutes, and then it is cooled at a rate of 0.5°C / min to 30°C, and the total crystallization time is 90 minutes. After crystallization is completed, the potassium fluoroborate crystals are separated by a centrifuge (rotation speed 3000 rpm, filter bag pore size 10μm). 80% of the mother liquor is returned to the crystallization step for recycling, and the remaining 20% of the mother liquor is introduced into the electrolytic cell (titanium anode, graphite cathode, current density 50 A / m²). The crystallization mother liquor contains K + , F - , Cl - and trace amounts of Ca 2+ etc. During electrolysis, CaF2 with extremely low solubility is preferentially precipitated, and CaF2 (purity ≥95%) is electrolytically recovered with a fluorine recovery rate ≥95%.

[0021] In this application, fluosilicic acid, boric acid, and KCl used are industrial-grade raw materials. Such raw materials usually contain metal impurities such as calcium and magnesium, but relatively more is the calcium ion in industrial-grade fluosilicic acid. The addition of disodium EDTA is precisely to complex these metal ions (such as Ca 2+ , Mg 2+ , Fe 3+ etc.) to prevent them from interfering with the reaction in Step 1. Secondly, in Step 4, a 001×7 strongly acidic cation resin is used to remove sodium, but the affinity of this resin for divalent ions (such as Ca 2+ ) is lower than that for Na + . Therefore, calcium ions may not be completely removed and remain in the filtrate. Eventually, the recycling of 80% of the mother liquor in Step 4 will cause calcium ions to gradually accumulate in the system, and finally the concentration will increase significantly in the remaining 20% of the mother liquor.

[0022] The remaining 20% of the mother liquor contains a high concentration of fluoride ions (from unreacted HF or residual F - after KBF4 saturation) and accumulated Ca 2+ . The following reactions occur during electrolysis: Cathode: 2H2O + 2e - →H2↑ + 2OH - Anode: 2H2O → O2↑ + 4H + + 4e The local increase in pH promotes the combination of Ca 2+ with F - to form a precipitate: Ca 2+ + 2F - → CaF2↓. The resource utilization of impurities is realized.

[0023] 6. High-value treatment of silicon slag The silicon slag is pickled with 5% dilute hydrochloric acid (volume ratio) at 60 °C for 30 minutes (solid-liquid ratio 1:5) to remove residual metal impurities. After pickling, the silicon slag is washed with deionized water until neutral (conductivity ≤ 10 μS / cm), and then sent to a centrifugal spray drying tower (inlet temperature 170 - 190 °C, outlet temperature 70 - 90 °C, atomization pressure 0.3 MPa, feed rate 20 L / h). The dried nano-silica white carbon black (SiO2) has a particle size D50 ≤ 50 nm and a specific surface area ≥ 200 m² / g.

[0024] 7. Product drying and packaging The potassium fluoroborate crystal is dried in a vacuum drying oven (vacuum degree ≤ 10 kPa) at 80 - 90 °C for 120 minutes, and the moisture content ≤ 0.1%. After drying, the product is crushed by a jet mill (classifying wheel speed 4000 rpm), passed through a 200-mesh sieve (screen residue ≤ 0.5%), and finally packaged in a double-layer aluminum foil bag and stored sealed with nitrogen filling.

[0025] In addition, in order to verify the effect of this application, five groups of examples are designed, as shown in Table 1, where: Examples 1 - 3: Verify the influence of the boric acid / fluosilicic acid ratio and the type of catalyst; Example 4: Verify the effect of adjusting K2CO3 and γ-Al2O3 in the composite desiliconizing agent to 4:1, and hereinafter briefly describe K:Al; Example 5: Verify the result of the upper limit of the composite desiliconizing agent ratio of 6:1.

[0026] Table 1 Example Boric acid (parts by mass) Fluorosilicic acid (parts by mass) Composite desilication agent (K:Al) <![CDATA[Type of nano-TiO2]]> Desilication rate (%) <![CDATA[Purity of KBF4 (%)]]> Sodium residue (ppm) Reaction time (min) 1 30 120(40%) 5:1 <![CDATA[Fe-TiO2]]> 96.2 99.5 3 105 2 25 100(40%) 5:1 <![CDATA[Fe-TiO2]]> 95.8 99.3 5 110 3 35 135.9(40%) 5:1 <![CDATA[Pure TiO2]]> 94.5 98.9 8 130 4 30 120(40%) 4:1 <![CDATA[Fe-TiO2]]> 97.1 99.7 2 100 5 30 120(40%) 6:1 <![CDATA[Fe-TiO2]]> 93.2 98.5 10 115 Three groups of comparative examples are designed to compare the technical effects of this application. Among them, Comparative Example 1: Traditional sodium salt desiliconization process; Comparative Example 2: Single desiliconizing agent (without γ-Al2O3); Comparative Example 3 compares the optimization effect of 4:1 in Example 4, as shown in Table 2 specifically: Table 2 Comparative example Type of desilication agent Disodium EDTA <![CDATA[Nano-TiO2]]> Desilication rate (%) Sodium residue (ppm) Reaction time (min) 1 Traditional process: NaCl None None 82.3 520 180 2 <![CDATA[Single K2CO3]]> Yes <![CDATA[Fe-TiO2]]> 85.6 45 120 3 K:Al = 5:1 None None 89.1 32 150 Through the comparison between Example 4 (K:Al = 4:1) and Comparative Example 3 (K:Al = 5:1), the desiliconization rate is increased by 8%; the sodium residue is reduced to 2 ppm; and the reaction time is shortened to 100 min.

[0027] Conclusion: The 4:1 ratio has better effect through the adsorption enhancement of γ-Al2O3.

[0028] In Example 1 (0.8 parts by mass of EDTA), the sodium residue is 3 ppm: 32 ppm in Comparative Example 3 (without EDTA), which proves the inhibitory effect of EDTA on metal impurities.

[0029] In Example 1 (Fe-TiO2), the reaction time is 105 min: 130 min in Example 3 (pure TiO2), which proves that Fe doping improves the catalytic efficiency.

[0030] In addition, the cost changes brought by the mother liquor circulation are also verified, as shown in Table 3: Table 3 Index This scheme (Example 1) Traditional process (Comparative example 1) Mother liquor recycling rate 80% 0% Wastewater discharge 15 m³ / ton 100 m³ / ton Fluorine recovery rate <![CDATA[95% (CaF2)]]> No recovery The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. The patent protection scope of the present invention shall be subject to the claims. Any equivalent structural changes made by using the content of the specification of the present invention shall be equally included in the protection scope of the present invention.

Claims

1. An integrated reaction process for efficiently preparing potassium fluoroborate by converting fluorosilicic acid, characterized in that: It includes the following steps: a) Mix 20 - 35 parts by mass of boric acid, 0.5 - 1.2 parts by mass of disodium EDTA with 200 parts by mass of water, and heat to 80 - 85 °C for dissolution; b) Add 77.6 - 135.9 parts by mass of 40wt% fluosilicic acid to the solution in step a), react at 75 - 80 °C for 90 - 120 minutes under the protection of 0.1wt% nano - TiO₂ catalyst and nitrogen; c) Add 4.5 - 7.8 parts by mass of composite desilication agent to the reaction solution in step b), stir at 50 °C for 20 minutes for desilication and then filter to obtain silica residue and filtrate; d) The filtrate in step c) is de - sodiumized by ion - exchange resin, add 8.04 - 14.07 parts by mass of 20wt% KCl solution, crystallize at 50 °C for 90 minutes to obtain potassium fluoroborate, and part of the mother liquor is returned to the crystallization step for reuse; e) The silica residue in step c) is pickled and spray - dried to obtain nano - silica white carbon black.

2. The integrated reaction process for efficiently preparing potassium fluoroborate by converting fluorosilicic acid according to claim 1, characterized in that: The nano - TiO₂ catalyst is Fe - doped type, with a particle size of 20 - 50 nm, and the addition amount is 0.05 - 0.15% of the total mass of the reaction system.

3. An integrated reaction process for efficiently preparing potassium fluoborate by converting fluorosilicic acid, characterized in that: In the composite desilication agent, the particle size of γ - Al₂O₃ is 10 - 20 nm, and the mass ratio of K₂CO₃ to γ - Al₂O₃ is 4:1 - 5:

1.

4. An integrated reaction process for efficiently preparing potassium fluoroborate by converting fluorosilicic acid, characterized in that: In step d), 80% of the mother liquor is returned to the crystallization step for recycling, and the remaining 20% of the mother liquor is electrolyzed to recover the by - product CaF₂.

5. An integrated reaction process for efficiently preparing potassium fluoroborate by converting fluosilicic acid, characterized in that: In step e), the inlet temperature of spray - drying is 170 - 190 °C, the outlet temperature is 70 - 90 °C, and the particle size of the obtained white carbon black is ≤50 nm.

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