An integrated reaction process for efficiently converting fluorosilicic acid into potassium fluoroborate

Abstract

The present invention discloses an integrated reaction process for efficiently converting fluorosilicic acid to prepare potassium fluoroborate, which relates to the field of inorganic fluorine chemical technology. The process solves the problems of severe sodium pollution, low reaction efficiency, and waste of resources in traditional processes by using disodium EDTA to complex metal impurities, Fe-TiO2 catalytic condensation reaction, K2CO3 / nano-γ-Al2O3 composite desiliconization, ion exchange deep sodium removal, and mother liquor closed-loop circulation technology. The composite desiliconizer increases the desiliconization rate to 96%, nanocatalysis shortens the reaction time by 40%, the mother liquor recycling rate reaches 80%, and silicon slag is converted into high-value-added nano-silica. The product of the present invention has a purity of ≥99.5% and a sodium residue of ≤0.003%, and is suitable for the industrial production of electronic-grade potassium fluoroborate.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic fluorine chemical industry, and more particularly to an integrated reaction process for efficiently converting fluorosilicic acid into potassium fluoroborate. Background Art

[0002] Potassium fluoroborate is an important raw material in the fields of metallurgy and electronics. The traditional process has the following defects:

[0003] 1. Serious sodium pollution: Existing technologies usually use NaCl for desiliconization, resulting in a sodium residue of >0.05% in the product, requiring multiple water washings and producing high-salt wastewater;

[0004] 2. Low reaction efficiency: The condensation reaction time of fluorosilicic acid and boric acid is long (≥180 minutes), and the lack of catalyst results in a conversion rate of less than 90%;

[0005] 3. Waste of resources: By-product silicon slag (SiO2) is landfilled as solid waste, and the mother liquor is directly discharged, causing fluorine pollution.

[0006] The present invention aims to achieve green preparation of high-purity KBF4 through composite desiliconizing agent, nanocatalysis and closed-loop circulation technology.

[0007] Therefore, it is necessary to propose an integrated reaction process for efficiently converting fluorosilicic acid to prepare potassium fluoroborate to solve the above problems. Summary of the Invention

[0008] The purpose of the present invention is to solve the problems raised in the background technology.

[0009] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0010] An integrated reaction process for efficiently converting fluorosilicic acid into potassium fluoroborate comprises the following steps:

[0011] a) Mix 20-35 parts by mass of boric acid, 0.5-1.2 parts by mass of disodium EDTA, and 200 parts by mass of water, and heat to 80-85°C to dissolve;

[0012] b) adding 77.6-135.9 parts by mass of 40 wt% fluorosilicic acid to the solution of step a), and reacting at 75-80° C. for 90-120 minutes in the presence of 0.1 wt% nano-TiO2 catalyst and nitrogen protection;

[0013] c) adding 4.5-7.8 parts by weight of a composite desiliconizing agent to the reaction solution of step b), stirring at 50° C. for 20 minutes for desiliconization, and then filtering to obtain silicon slag and a filtrate;

[0014] d) The filtrate from step c) is subjected to ion exchange resin to remove sodium, 8.04-14.07 parts by mass of 20 wt% KCl solution is added, and crystallized at 50° C. for 90 minutes to obtain potassium fluoroborate, and the mother liquor is returned to the crystallization step for reuse;

[0015] e) In step c), the silicon slag is pickled and spray-dried to obtain nano-silica.

[0016] Furthermore, the nano-TiO2 catalyst is Fe-doped, has a particle size of 20-50 nm, and is added in an amount of 0.05-0.15% of the total mass of the reaction system.

[0017] Furthermore, 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.

[0018] Furthermore, 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 CaF2 by-product.

[0019] Furthermore, in step e), the inlet temperature of the spray drying is 170-190° C., the outlet temperature is 70-90° C., and the obtained silica particle size is ≤50 nm.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention increases the desiliconization rate from 85% to 96% through a composite desiliconizing agent. The purity of the prepared KBF4 is ≥99.5%, and the sodium residue is ≤0.003%, which is green and environmentally friendly.

[0022] 2. The present invention shortens the condensation reaction time by 40% through nano-TiO2 catalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a reaction flow chart of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] See also Figure 1 , an integrated reaction process for efficiently converting fluorosilicic acid to produce potassium fluoroborate.

[0026] 1. Raw material pretreatment

[0027] Add 20-35 parts by weight of boric acid (purity ≥99.5%) and 200 parts by weight of deionized water to a jacketed enameled reactor. Start the stirrer (200-300 rpm) and slowly raise the temperature to 80-85°C. Then, add 0.5-1.2 parts by weight of disodium EDTA (analytical grade) and continue stirring until the solution becomes completely transparent (approximately 30-40 minutes). Monitor the pH of the solution with an online pH meter and maintain it within the range of 2.5-3.0. If the pH is high, adjust it by adding dilute sulfuric acid (5% concentration). After dissolution is complete, remove undissolved impurities through a plate-and-frame filter (pore size 0.5 μm) to obtain a clear boric acid-EDTA mixture.

[0028] 2. Catalytic condensation reaction

[0029] The solution obtained in step 1 was transferred to an autoclave (made of Hastelloy C276). 77.6-135.9 parts by mass of 40 wt% fluorosilicic acid (industrial grade) was slowly added via a constant pressure dropping funnel at a rate of 1-2 mL / min. Simultaneously, 0.1 wt% of Fe-doped nano-TiO2 catalyst (particle size 20-50 nm, specific surface area ≥120 m² / g) was added to the reaction system. The catalyst was pre-activated under a nitrogen atmosphere for 30 minutes. During the reaction, high-purity nitrogen was introduced (flow rate 0.5 L / min), maintaining a pressure of 0.2-0.3 MPa and a temperature of 75-80°C (temperature control accuracy ±0.5°C). The reaction lasted 90-120 minutes, during which time the characteristic peak of the Si-F bond (1100 cm-1) was monitored by online infrared spectroscopy (IR). -1 ) intensity changes to ensure that the conversion rate of fluorosilicic acid is ≥95%.

[0030] 3. Composite desiliconization and solid-liquid separation

[0031] After the reaction, the system is cooled to 50°C and 4.5-7.8 parts by weight of a composite desiliconizing agent (K₂CO₃:γ-Al₂O₃ mass ratio of 4:1-5:1, γ-Al₂O₃ particle size 10-20 nm) is added. The composite desiliconizing agent must be pre-calcined at 400°C for 2 hours to remove surface hydroxyl groups. A high-speed shear disperser (1000-1500 rpm) is operated and stirred continuously for 20 minutes to ensure full contact between the desiliconizing agent and the silicic acid. A plate-and-frame filter press (polypropylene filter cloth, 1 μm pore size) is then used for solid-liquid separation. The filter cake (silicon slag) is washed three times with deionized water (2:1 water-to-material ratio each time), and the filtrate (silicon liquid) is transferred to the next process. The SiO₂ content in the silicon slag is ≥98%, and the residual silicon concentration in the silicon liquid is ≤50 ppm.

[0032] 4. Ion exchange to remove sodium

[0033] Pass the filtrate from step 3 through a series of 001×7 strongly acidic cation exchange resin columns (resin packing height 1.5 m, column diameter ratio 3:1) at a flow rate of 10-15 BV / h. The resin should be regenerated with 5% HCl and washed with deionized water until neutral. The sodium ion concentration of the exchanged solution should be monitored by inductively coupled plasma optical emission spectroscopy (ICP-OES) to ensure it is ≤0.005% (i.e., ≤50 ppm). If residual sodium exceeds the standard, perform a second exchange or replace the resin.

[0034] 5. Crystallization and mother liquor circulation

[0035] To the sodium-removed solution, 8.04-14.07 parts by weight of a 20wt% KCl solution (preheated to 50°C) was added. A programmed cooling crystallization method was used: the initial temperature was maintained at 50°C for 30 minutes, followed by a cooling rate of 0.5°C / min to 30°C for a total of 90 minutes. After crystallization, the potassium fluoroborate crystals were separated using a centrifuge (3000 rpm, filter bag pore size 10μm). 80% of the mother liquor was recycled to the crystallization step, and the remaining 20% ​​was introduced into an electrolytic cell (titanium anode, graphite cathode, current density 50 A / m²). The crystallization mother liquor contained K. + 、F - 、Cl - and trace amounts of Ca 2+ During electrolysis, CaF2 with extremely low solubility is preferentially precipitated, and CaF2 (purity ≥95%) is recovered by electrolysis, with a fluorine recovery rate ≥95%.

[0036] The fluorosilicic acid, boric acid and KCl used in this application are industrial grade raw materials. Such raw materials usually contain metal impurities such as calcium and magnesium, but the calcium ion in the industrial grade fluorosilicic acid is the most abundant. The addition of disodium EDTA is to complex these metal ions (such as Ca 2+ Mg 2+ 、Fe 3+ etc.), to prevent it from interfering with the reaction in step 1. Secondly, step 4 uses 001×7 strong acid cation resin to remove sodium, but this resin is sensitive to divalent ions (such as Ca 2+ ) has a lower affinity than Na + Therefore, calcium ions may not be completely removed and remain in the filtrate. Ultimately, the recycling of 80% of the mother liquor in step 4 will cause calcium ions to gradually accumulate in the system, and eventually the concentration in the remaining 20% ​​of the mother liquor will increase significantly.

[0037] The remaining 20% ​​of the mother liquor contains high concentrations of fluoride ions (from incompletely converted HF or residual F after KBF4 saturation). - ) and accumulated Ca 2+ The following reactions occur during electrolysis:

[0038] Cathode: 2H2O+2e- →H2↑+2OH -

[0039] Anode: 2H2O→O2↑+4H + +4e

[0040] Local pH increase promotes Ca 2+ With F - Binding precipitate: Ca 2+ +2F - →CaF2↓. Realizes the resource utilization of impurities.

[0041] 6. Silicon slag high value treatment

[0042] The silicon slag was pickled with 5% dilute hydrochloric acid (volume ratio) at 60°C for 30 minutes (solid-to-liquid ratio 1:5) to remove residual metallic impurities. After pickling, the slag was washed with deionized water until neutral (conductivity ≤ 10 μS / cm) and then fed into a centrifugal spray dryer (inlet temperature 170-190°C, outlet temperature 70-90°C, atomization pressure 0.3 MPa, feed rate 20 L / h). The dried nano-silica (SiO2) particle size D50 ≤ 50 nm and the specific surface area ≥ 200 m² / g were obtained.

[0043] 7. Product drying and packaging

[0044] Potassium fluoroborate crystals were dried in a vacuum drying oven (vacuum ≤ 10 kPa) at 80-90°C for 120 minutes to a moisture content of ≤ 0.1%. The dried product was pulverized in a jet mill (classifying impeller speed 4000 rpm), passed through a 200-mesh sieve (residue ≤ 0.5%), and finally packaged in double-layer aluminum foil bags and sealed with nitrogen for storage.

[0045] In addition, in order to verify the effect of this application, five groups of examples are designed, as shown in Table 1, where:

[0046] Example 1-3: Verification of the influence of the boric acid / fluorosilicic acid ratio and catalyst type;

[0047] Example 4: Verify the effect of adjusting the ratio of K2CO3 to γ-Al2O3 in the composite desiliconizer to 4:1, and briefly describe K:Al in the following;

[0048] Example 5: Verification of the results of the upper limit of the composite desiliconizing agent ratio of 6:1.

[0049] Table 1

[0050] Example Boric acid (parts by mass) Fluorosilicic acid (parts by mass) Composite desiliconizer (K:Al) <![CDATA[Type of nano-TiO2]]> Desiliconization 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

[0051] Three comparative examples were designed to compare the technical effects of the present application, wherein comparative example 1: conventional sodium salt desiliconization process; comparative example 2: single desiliconization agent (without γ-Al2O3); comparative example 3: 4:1 optimization effect of comparative example 4, as shown in Table 2:

[0052] Table 2

[0053] Comparative Example Desiliconizing agent type Disodium EDTA <![CDATA[Nano-TiO2]]> Desiliconization rate (%) Sodium residue (ppm) Reaction time (min) 1 Traditional process: NaCl none none 82.3 520 180 2 <![CDATA[Single K2CO3]]> have <![CDATA[Fe-TiO2]]> 85.6 45 120 3 K:Al=5:1 none none 89.1 32 150

[0054] By comparing Example 4 (K:Al=4:1) with 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.

[0055] Conclusion: The 4:1 ratio has better effect through the adsorption enhancement of γ-Al2O3.

[0056] The residual sodium in Example 1 (0.8 parts by mass of EDTA) was 3 ppm, while that in Comparative Example 3 (no EDTA) was 32 ppm, demonstrating the inhibitory effect of EDTA on metal impurities.

[0057] The reaction time of Example 1 (Fe-TiO2) is 105 min; that of Example 3 (pure TiO2) is 130 min, which proves that Fe doping improves the catalytic efficiency.

[0058] In addition, the cost changes brought about by mother liquor recycling are also verified, as shown in Table 3:

[0059] Table 3

[0060] index This solution (Example 1) Traditional process (Comparative Example 1) Mother liquor recycling rate 80% 0% Wastewater discharge 15m³ / ton 100m³ / ton Fluorine recovery rate <![CDATA[95%(CaF2)]]> No recycling

[0061] The above are only 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 based on the claims. Any equivalent structural changes made using the contents of the description of the present invention shall also be included in the scope of protection of the present invention.

Claims

1. An integrated reaction process for efficiently converting fluorosilicic acid into potassium fluoroborate, characterized by: The following steps are involved: a) Mix 20-35 parts by mass of boric acid, 0.5-1.2 parts by mass of disodium EDTA, and 200 parts by mass of water, and heat to 80-85°C to dissolve; b) adding 77.6-135.9 parts by mass of 40 wt% fluorosilicic acid to the solution of step a), and adding 0.1 wt% of a nano-TiO2 catalyst based on the total mass of the reaction system to the reaction system, wherein the nano-TiO2 catalyst is Fe-doped, and reacting at 75-80° C. for 90-120 minutes under nitrogen protection; c) adding 4.5-7.8 parts by mass of a composite desiliconizing agent to the reaction solution of step b), wherein the composite desiliconizing agent comprises K2CO3 and γ-Al2O3 in a mass ratio of 4:1-5:1, stirring at 50°C for 20 minutes to desiliconize, and then filtering to obtain silicon slag and filtrate; d) The filtrate from step c) is subjected to ion exchange resin to remove sodium, and 8.04-14.07 parts by weight of a 20 wt% KCl solution is added and crystallized at 50° C. for 90 minutes to obtain potassium fluoroborate. The mother liquor is returned to the crystallization step for reuse; e) In step c), the silicon slag is pickled and spray-dried to obtain nano-silica.

2. The integrated reaction process for efficiently converting hydrofluorosilicic acid into potassium fluoroborate according to claim 1, characterized in that: The particle size of the nano-TiO2 catalyst is 20-50nm.

3. The integrated reaction process for efficiently converting hydrofluorosilicic acid into potassium fluoroborate according to claim 1, characterized in that: The particle size of γ-Al2O3 in the composite desiliconizing agent is 10-20 nm.

4. The integrated reaction process for efficiently converting hydrofluorosilicic acid into potassium fluoroborate according to claim 1, 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 CaF2 by-product.

5. The integrated reaction process for efficiently converting hydrofluorosilicic acid into potassium fluoroborate according to claim 1, characterized in that: In the step e), the inlet temperature of the spray drying is 170-190° C., the outlet temperature is 70-90° C., and the obtained white carbon black particle size is ≤50 nm.

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