Method for purifying potassium fluorotantalate crystals

Abstract

The application discloses a potassium fluorotantalate crystallization purification method, and relates to the technical field of tantalum hydrometallurgy and fluorotantalate crystallization purification. The method comprises the following steps: filtering a tantalum-containing fluorine acid solution, adding a potassium source and a tantalum-niobium separation type composite crystallization regulator, stirring and complexing, seed induction, controlled cooling crystallization, graded removal of the regulator, solid-liquid separation, and washing with a fluorine-containing potassium solution to obtain primary purified potassium fluorotantalate crystals, redissolving the primary purified potassium fluorotantalate crystals in a fluorine-containing acid solution, correcting the K / Ta molar ratio, repeatedly regulating and crystallizing, graded removal of the regulator, washing, and drying to obtain high-purity potassium fluorotantalate. The regulator can reduce the entrainment of niobium impurities and reduce the residual amount of the regulator itself, thereby improving the purity of the product and the Ta yield.

Description

Technical Field

[0001] This invention relates to the fields of tantalum hydrometallurgy and fluorotantalate crystallization and purification technology, specifically to a method for the crystallization and purification of potassium fluorotantalate. Background Technology

[0002] Tantalum and its compounds are widely used in electronic capacitors, sputtering targets, superhard materials, special alloys, and the preparation of high-purity tantalum oxide due to their high melting point, strong corrosion resistance, and excellent dielectric properties. Potassium fluorotantalate, as an important intermediate product in the hydrometallurgical process of tantalum, has its purity and impurity control levels directly affecting the quality of subsequent tantalum metal powder, tantalum oxide, and other high-purity tantalum compound products.

[0003] In the wet processing of tantalum-containing minerals, tantalum typically enters the tantalum-containing fluorine acid solution as a fluorine complex. Because niobium and tantalum are similar in chemical properties, ionic radius, and fluorine complexation behavior, the tantalum-containing fluorine acid solution often contains a certain amount of niobium impurities. During the crystallization of potassium fluorotantalate, niobium-fluorine complexes easily enter the potassium fluorotantalate crystals through mother liquor entrainment, crystal surface adsorption, intergranular encapsulation, or co-deposition, leading to an increase in niobium content in the product and affecting the purity of potassium fluorotantalate and the quality of subsequent products.

[0004] Existing methods for purifying potassium fluorotantalate typically involve controlling acidity, adjusting the amount of potassium source added, cooling crystallization, recrystallization, or multiple washing to reduce impurity content. While these methods can improve product purity to some extent, they still have the following shortcomings: First, relying solely on cooling crystallization and washing is insufficient to effectively suppress niobium impurity entrainment during crystal growth; second, excessive washing or repeated recrystallization can easily increase tantalum loss, reducing Ta yield; third, crystal particle size distribution and crystal surface morphology are difficult to control stably, easily leading to the formation of fine crystals, agglomerated crystals, or crystal structures encapsulating the mother liquor; fourth, most existing crystallization control methods only adjust crystal size or crystallization rate, lacking a composite control system that simultaneously considers hydrofluoric acid resistance, niobium complexation inhibition, crystal interface control, and reduction of mother liquor entrainment.

[0005] Therefore, it is necessary to provide a new method for purifying potassium fluorotantalate by crystallizing. This method involves introducing a composite crystallization regulator with complexation and hydrofluoric acid interface regulation functions, which can be removed in stages after crystallization. This improves the crystal growth behavior of potassium fluorotantalate during crystallization, reduces niobium impurity entrainment and regulator residue, increases the purity of potassium fluorotantalate, and balances process stability and industrial feasibility. Summary of the Invention

[0006] The purpose of this invention is to address the problems of easy niobium impurity entrainment, difficulty in controlling crystal morphology, significant recrystallization losses, and insufficient product purity stability in the existing potassium fluorotantalate crystallization purification process, and to provide a potassium fluorotantalate crystallization purification method. This method reduces the entrainment of niobium impurities in potassium fluorotantalate crystals by adding a composite crystallization regulator to a tantalofluoric acid-containing crystallization system, and by controlling the K to Ta molar ratio, seed-induced crystallization, controlling the cooling rate, washing with KF and HF, and secondary regulation of the crystallization process, thereby improving the purity and batch stability of the obtained potassium fluorotantalate product.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for purifying potassium fluorotantalate by crystallization, comprising the following steps: S1. Filter the tantalum fluoride solution to remove insoluble matter, and obtain a purified tantalum fluoride solution to be crystallized. The purified tantalum fluoride solution to be crystallized has a Ta concentration of 100-140 g / L, a free HF mass fraction of 8-12%, and a Nb concentration of 0.5-1.5 g / L.

[0008] S2. Add a potassium source to the purified tantalum fluoride solution to be crystallized, so that the molar ratio of K to Ta in the system is (1.85-2.15):1. Then add a tantalum-niobium separation type composite crystallization regulator and stir and complex at 50-75℃ for 20-90 min to obtain a pre-regulated crystallization mother liquor.

[0009] S3. Add potassium fluorotantalate seed crystals to the pre-controlled crystallization mother liquor, and cool it to 15-30℃ at a cooling rate of 0.15-0.80℃ / min. Keep it at this temperature for 1-4 hours to obtain potassium fluorotantalate coarse crystal slurry.

[0010] S4. The potassium fluorotantalate crude crystal slurry is subjected to solid-liquid separation, and the crystals are washed with potassium fluoride washing solution to obtain potassium fluorotantalate crystals that have been purified once.

[0011] S5. The purified potassium fluorotantalate crystals are redissolved in a fluorine-containing acidic solution to obtain a redissolved tantalofluoric acid solution. The concentration of Ta, the mass fraction of free HF, and the molar ratio of K to Ta in the redissolved tantalofluoric acid solution are detected, and potassium source and / or HF are added to make the molar ratio of K to Ta (1.85-2.15):1 and the mass fraction of free HF 5-18%. Then, the crystallization regulation, step-by-step removal of regulator, solid-liquid separation and washing processes in steps S2-S4 are repeated, and high-purity potassium fluorotantalate is obtained after drying.

[0012] As a preferred technical solution of the present invention, the tantalum-niobium separation-type composite crystallization regulator is further prepared from the following raw materials in parts by weight: 20-35 parts of carboxylated porous carbon microspheres, 25-45 parts of polytetrafluoroethylene micro powder, 5-15 parts of perfluorosulfonic acid resin, 4-10 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, 6-14 parts of vinylphosphonic acid, 3-8 parts of acrylic acid, 2-6 parts of maleic acid, 1-4 parts of N-vinylpyrrolidone, 0.2-0.8 parts of N,N′-methylenebisacrylamide, 0.2-0.6 parts of ammonium persulfate, 0.5-2.0 parts of polyvinylpyrrolidone, 60-120 parts of ethanol, 30-80 parts of N-methylpyrrolidone, and 200-450 parts of deionized water.

[0013] As a preferred embodiment of the present invention, the potassium fluorotantalate product further comprises K2TaF7 mass fraction ≥ 99.50%, Nb mass fraction ≤ 0.05%, and moisture mass fraction ≤ 0.20%.

[0014] As a preferred technical solution of the present invention, the potassium source is one or more of potassium fluoride, potassium hydroxide, and potassium carbonate; when the potassium source is potassium hydroxide, HF is detected and added simultaneously during the addition process to maintain the mass fraction of free HF in the system at 5-18%.

[0015] As a preferred technical solution of the present invention, the amount of the composite crystallization regulator added, on a dry basis, is 1.5-3.0% of the mass of Ta element in the tantalum fluoride purification solution to be crystallized.

[0016] As a preferred technical solution of the present invention, the potassium fluorotantalate seed crystal is K2TaF7 seed crystal with a D50 of 5-30μm.

[0017] As a preferred embodiment of the present invention, the amount of potassium fluorotantalate seed crystals added is 0.2-2.0% of the theoretical mass of K2TaF7.

[0018] As a preferred technical solution of the present invention, the theoretically generated K2TaF7 mass is calculated based on the assumption that all Ta elements in the tantalum fluoride purification solution to be crystallized are converted into K2TaF7.

[0019] As a preferred embodiment of the present invention, the potassium fluoride washing solution contains 2.0-4.0% KF and 1.0-2.5% HF by mass, and the washing temperature is 10-30°C. 60-100 parts by mass of potassium fluorotantalate wet crystals are used in the potassium fluoride washing solution.

[0020] As a preferred technical solution of the present invention, the fluorinated acidic solution is an aqueous solution of hydrofluoric acid with an HF mass fraction of 4-12%. For every 100 parts by mass of potassium fluorotantalate crystals purified once, 180-450 parts by mass of the fluorinated acidic solution are used. The redissolution temperature is 55-85℃ and the redissolution time is 20-90 min.

[0021] As a preferred technical solution of the present invention, in step S4, the solid-liquid separation is carried out by centrifugal separation or vacuum filtration; when centrifugal separation is carried out, the centrifugal speed is 1200-3000 rpm and the centrifugation time is 5-20 min; when vacuum filtration is carried out, the vacuum degree is -0.04 MPa to -0.09 MPa and the filtration time is 5-30 min.

[0022] As a preferred technical solution of the present invention, further, in step S5 the drying temperature is 80-100℃, the drying time is 6-10h, the drying atmosphere is nitrogen, and the moisture content of the high-purity potassium fluorotantalate obtained after drying is determined by Karl Fischer method and is ≤0.20%.

[0023] As a preferred embodiment of the present invention, the method for preparing the carboxylated porous carbon microspheres further includes the following steps:

[0024] A1. Mix glucose, polyvinylpyrrolidone and deionized water at a mass ratio of 1:(0.05-0.20):(8-15) and stir at 25-35℃ and 500-1000rpm for 20-40min to obtain a carbon source solution.

[0025] A2. The carbon source solution is transferred to a closed reaction vessel and hydrothermally reacted at 180-200℃ for 6-12 hours. After cooling to 25-35℃, solid-liquid separation is performed, and the solution is washed 3-5 times with deionized water and dried at 60-80℃ for 8-12 hours to obtain the carbon microsphere precursor.

[0026] A3. Mix the carbon microsphere precursor with potassium hydroxide at a mass ratio of 1:(1.5-3.0) and grind for 10-30 min. Under a nitrogen atmosphere, heat to 700-800℃ at a heating rate of 3-8℃ / min and keep warm for 1-3 h. After cooling, wash with 5-10% hydrochloric acid solution until the pH of the washing solution is 6.0-7.0. Then wash with deionized water 2-4 times and dry at 70-90℃ for 6-12 h to obtain porous carbon microspheres.

[0027] A4. The porous carbon microspheres are added to a nitric acid solution with a mass fraction of 10-30%, and the solid-liquid mass ratio of the porous carbon microspheres to the nitric acid solution is 1:(10-25). The mixture is oxidized at 60-80℃ and 300-700rpm for 2-6 hours to form carboxyl active sites on the pore wall surface and the outer surface of the porous carbon microspheres. After solid-liquid separation, the mixture is washed with deionized water until the pH of the washing solution is 6.0-7.0. The mixture is then vacuum dried at 60-80℃ for 8-14 hours, pulverized by air jet and passed through an 800-1500 mesh sieve to obtain carboxylated porous carbon microspheres.

[0028] As a preferred embodiment of the present invention, the preparation method of the tantalum-niobium separation-type composite crystallization regulator further includes the following steps:

[0029] B1. Mix carboxylated porous carbon microspheres, polyvinylpyrrolidone, and deionized water at a solid-liquid mass ratio of 1:8-15, disperse at 25-35℃ and 800-1500rpm for 20-40min, then sonicate at 200-400W for 10-30min, and adjust the pH of the system to 2.0-3.5 with a 5-10% nitric acid solution to obtain a carbon-based pre-dispersion.

[0030] B2. Vinylphosphonic acid, acrylic acid, maleic acid, N-vinylpyrrolidone and N,N′-methylenebisacrylamide are added sequentially to the carbon-based pre-dispersion solution. The temperature is raised to 60-75℃ under nitrogen protection. Ammonium persulfate is prepared into an aqueous solution with a mass fraction of 2-5% and added dropwise to the system at a dropping rate of 0.3-1.0 mL / min. After the addition is complete, the reaction is carried out at 60-75℃ and 500-900 rpm for 3-6 hours to form a phosphonic acid-carboxylic acid-lactam synergistic complexing intermediate layer on the surface of the carboxylated porous carbon microspheres, thus obtaining a complexing layer modified carbon-based microparticle slurry.

[0031] B3. Add polytetrafluoroethylene micro powder to a mixture of ethanol and deionized water, wherein the mass ratio of ethanol to deionized water is 1:(1.5-3.0), and disperse at 30-45℃ and 1000-1800rpm for 30-60min to obtain a polytetrafluoroethylene pre-dispersion; add perfluorosulfonic acid resin and polyvinylidene fluoride-hexafluoropropylene copolymer to N-methylpyrrolidone, and dissolve or disperse at 50-65℃ and 600-1000rpm for 40-90min to obtain a fluorinated polymer coating solution.

[0032] B4. Add the polytetrafluoroethylene pre-dispersion liquid to the complexed layer modified carbon-based microparticle slurry and disperse it for 20-50 min at 35-50℃ and 800-1400 rpm. Then, add the fluorinated polymer coating liquid to the system dropwise at a rate of 0.5-2.0 mL / min. During the dropwise addition, control the pH of the system to 2.0-4.0. After the dropwise addition is completed, continue to keep warm and disperse for 1-3 h, so that polytetrafluoroethylene, perfluorosulfonic acid resin and polyvinylidene fluoride-hexafluoropropylene copolymer form a fluoride-resistant interface shell on the outside of the phosphonic acid-carboxylic acid-lactam synergistic complexing intermediate layer, and obtain a core-complexed layer-fluorinated interface shell composite slurry.

[0033] B5. The core-complex layer-fluorinated interface shell composite slurry is subjected to solid-liquid separation and washed 3-5 times with an ethanol-water washing solution with a pH of 2.0-3.5. The mass ratio of ethanol to water in the ethanol-water washing solution is 1:2-4. The pH of the ethanol-water washing solution is adjusted with a nitric acid solution with a mass fraction of 5-10%. Subsequently, it is vacuum dried at 45-65℃ for 8-16 hours, pulverized by air jet and passed through a 600-1200 mesh sieve to obtain a tantalum-niobium separation type composite crystallization regulator.

[0034] The tantalum-niobium separation-type composite crystallization regulator described in this invention uses carboxylated porous carbon microspheres as a high specific surface area carrier. The carboxyl active sites on the pore wall surface and outer surface provide interfacial adsorption and distribution regulation sites for tantalum-niobium fluoride complexes. Its surface phosphonic acid-carboxylic acid-lactam synergistic complexing intermediate layer can exert differentiated complexing and interfacial regulation effects on tantalum-niobium fluoride complexes in tantalum-fluoride crystallization systems, weakening the tendency of niobium fluoride complexes to adsorb, co-deposit, and intergranular encapsulation on the surface of potassium fluorotantalate crystals, thus retaining more niobium impurities in the mother liquor. The outer surface is composed of polytetrafluoroethylene, perfluorosulfonic acid resin, and polyvinylidene fluoride. The fluoride-resistant fluorination interface shell formed by the difluoroethylene-hexafluoropropylene copolymer can improve the structural and dispersion stability of the regulator in the HF-containing system, avoiding deactivation of the regulator or the introduction of new insoluble impurities. At the same time, the tantalum-niobium separation composite crystallization regulator, combined with the control of the K to Ta molar ratio, potassium fluorotantalate seed-induced crystallization and slow cooling process, can reduce disordered spontaneous nucleation, fine crystal formation, crystal defects and mother liquor entrainment, thereby reducing the probability of niobium impurities entering the interior or interstices of potassium fluorotantalate crystals, increasing the K2TaF7 mass fraction of high-purity potassium fluorotantalate and reducing the Nb mass fraction.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1. The carboxylated porous carbon microspheres in the composite crystallization regulator of the present invention provide a high specific surface area and surface carboxyl sites. The phosphonic acid-carboxylic acid-lactam synergistic complexing intermediate layer can regulate the distribution state of tantalum and niobium fluoride complexes near the crystallization interface. The outer hydrofluoric acid fluorination resistant interface shell can improve the stability of the regulator in the HF-containing system, thereby reducing the probability of niobium impurities entering the interior of potassium fluorotantalate crystals or intercrystalline gaps with the mother liquor.

[0037] 2. By controlling the molar ratio of K to Ta in the crystallization system to (1.85-2.15):1, the potassium fluorotantalate crystallization process is kept within a relatively stable potassium source supply and supersaturation range, avoiding incomplete crystallization due to insufficient potassium source, and also avoiding salting-out side effects, increased fine crystals, or increased impurity co-entrapment due to excessive potassium source.

[0038] 3. By adding potassium fluorotantalate seed crystals with a D50 of 5-30 μm and controlling the amount of seed crystals added, this invention is beneficial to inducing potassium fluorotantalate to grow in a directional manner on the surface of existing seed crystals, reducing disordered spontaneous nucleation, improving the uniformity of crystal size, reducing the proportion of fine crystals, and thus reducing the chance of adsorbing mother liquor and niobium impurities on the crystal surface.

[0039] 4. This invention controls the cooling rate to 0.15-0.80℃ / min and maintains the crystallization temperature at 15-30℃ for 1-4 hours, allowing potassium fluorotantalate crystals to grow gradually. This reduces crystal defects, intergranular inclusions, and mother liquor entrainment caused by rapid cooling, which is beneficial for improving crystal integrity and purification effect.

[0040] 5. The present invention uses a washing solution containing KF and HF to wash the crystals, which can remove the residual acidic mother liquor and soluble impurities on the crystal surface while maintaining the stability of potassium fluorotantalate crystals, reduce product loss during the washing process, and improve purification efficiency and Ta yield.

[0041] 6. This invention further reduces the content of niobium and metal impurities by combining primary crystallization and secondary controlled crystallization, resulting in potassium fluorotantalate product with higher K2TaF7 content, lower Nb content and lower moisture content, which is suitable for subsequent preparation of high-purity tantalum oxide, tantalum metal powder or other high-purity tantalum compounds. Attached Figure Description

[0042] Figure 1 This is a SEM image of the carboxylated porous carbon microspheres prepared in Example 1 of this invention.

[0043] Figure 2 This is an XPS characterization image of the carboxylated porous carbon microspheres prepared in Example 1 of this invention.

[0044] Figure 3The image shows the SEM morphology and SEM-EDS elemental distribution characteristics of the tantalum-niobium separation-type composite crystallization regulator prepared in Example 1 of this invention. Detailed Implementation

[0045] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Preparation Example 1

[0047] Preparation of tantalum-niobium separation-type composite crystallization regulator:

[0048] 1. Preparation of carboxylated porous carbon microspheres:

[0049] The glucose used in this preparation example is anhydrous glucose, polyvinylpyrrolidone is PVP K30, potassium hydroxide is flake or granular potassium hydroxide, the hydrochloric acid solution is prepared by 37% hydrochloric acid and deionized water, and the nitric acid solution is prepared by 65% ​​nitric acid and deionized water.

[0050] A1. Weigh 20.00 parts by weight of glucose, 2.00 parts by weight of polyvinylpyrrolidone and 240.00 parts by weight of deionized water, and stir at 30℃ and 800 rpm for 30 min to fully dissolve and disperse the glucose and polyvinylpyrrolidone to obtain a carbon source solution.

[0051] A2. The carbon source solution was transferred to a closed reaction vessel and hydrothermally reacted at 190°C for 9 hours. After the reaction was completed, the solution was cooled to 30°C, and solid-liquid separation was performed. The solution was washed four times with deionized water and then dried at 70°C for 10 hours to obtain the carbon microsphere precursor.

[0052] A3. Weigh 10.00 parts by mass of the carbon microsphere precursor and 22.00 parts by mass of potassium hydroxide, mix and grind for 20 min; place the ground mixture in a nitrogen atmosphere, heat to 750℃ at a heating rate of 5℃ / min, and keep warm for 2 h; after activation, cool to 30℃, wash with 8% hydrochloric acid solution until the pH of the washing solution is 6.5, wash 3 times with deionized water, and then dry at 80℃ for 9 h to obtain porous carbon microspheres.

[0053] A4. Weigh 10.00 parts by weight of the porous carbon microspheres and add them to 180.00 parts by weight of a 20% nitric acid solution. Oxidize the microspheres at 70°C and 500 rpm for 4 hours to form carboxyl active sites on the pore wall surface and outer surface of the porous carbon microspheres. After the oxidation treatment, perform solid-liquid separation, wash with deionized water until the pH of the washing solution is 6.5, vacuum dry at 70°C for 12 hours, and then pulverize and pass through a 1000-mesh sieve to obtain carboxylated porous carbon microspheres.

[0054] Depend on Figure 1 As shown in the figure, the particles are generally nearly spherical or near-spherical in shape, with a relatively rough surface. Numerous irregular pores and honeycomb-like depressions can be observed, indicating that the carbon microspheres formed a distinct porous surface and high external surface roughness after activation. There is some contact and slight aggregation between the particles, but most of the spherical outlines remain relatively intact, consistent with the typical morphology of porous carbon microspheres obtained after glucose hydrothermal spherization and KOH activation pore formation. This demonstrates that the carboxylated porous carbon microspheres possess a spherical porous framework and a rough pore wall structure, providing a morphological basis for subsequent surface carboxyl site loading and interfacial adsorption.

[0055] Depend on Figure 2 As shown, the C1s peaks in this spectrum can be divided into CC / C=C skeleton carbon peaks, CO peaks, C=O peaks, and OC=O peaks, indicating that oxygen-containing functional groups such as ether hydroxyl groups, carbonyl groups, and carboxyl groups have been introduced into the surface of the porous carbon microspheres in addition to the graphitized / amorphous carbon skeleton. The C=O / OC=O peaks and -OH / COC / -COOH peaks in the O1s spectrum confirm the presence of oxygen-containing functional groups on the surface after oxidation.

[0056] 2. Preparation of tantalum-niobium separation-type composite crystallization regulator:

[0057] 2.1 Raw material components by weight:

[0058] The tantalum-niobium separation-type composite crystallization regulator is prepared from the following raw materials in parts by weight: 28.00 parts carboxylated porous carbon microspheres, 35.00 parts polytetrafluoroethylene micro powder, 10.00 parts perfluorosulfonic acid resin, 7.00 parts polyvinylidene fluoride-hexafluoropropylene copolymer, 10.00 parts vinylphosphonic acid, 5.50 parts acrylic acid, 4.00 parts maleic acid, 2.50 parts N-vinylpyrrolidone, 0.50 parts N,N′-methylenebisacrylamide, 0.40 parts ammonium persulfate, 1.20 parts polyvinylpyrrolidone, 80.00 parts ethanol, 55.00 parts N-methylpyrrolidone, and 420.00 parts deionized water.

[0059] The polytetrafluoroethylene micro powder has a particle size distribution of D50 < 11.0 μm and D90 < 15.0 μm, and was purchased from Fuzhou Taipuda New Materials Co., Ltd.

[0060] The perfluorosulfonic acid resin is Nafion. TM The perfluorinated resin powder was purchased from the Merck Group in Darmstadt, Germany.

[0061] The polyvinylidene fluoride-hexafluoropropylene copolymer is a powdered polyvinylidene fluoride-hexafluoropropylene copolymer, KYNAR FLEX ® 2801-00 POWDER.

[0062] The acrylic acid contains 200 ppm MEHQ as an inhibitor, MFCD00004367, purchased from the Merck Group in Darmstadt, Germany.

[0063] The N-vinylpyrrolidone contains sodium hydroxide as an inhibitor (MFCD00003197) and was purchased from the Merck Group in Darmstadt, Germany.

[0064] The polyvinylpyrrolidone is polyvinylpyrrolidone K30, which was purchased from the Merck Group in Darmstadt, Germany.

[0065] 2.2 Preparation method:

[0066] B1. Weigh 28.00 parts by weight of carboxylated porous carbon microspheres, 1.20 parts by weight of polyvinylpyrrolidone and 240.00 parts by weight of deionized water, disperse them at 30℃ and 1200 rpm for 30 min, and then sonicate them at 300 W for 20 min; then adjust the pH of the system to 2.8 with 10% nitric acid solution to obtain carbon-based predispersant.

[0067] B2. Add 10.00 parts by weight of vinylphosphonic acid, 5.50 parts by weight of acrylic acid, 4.00 parts by weight of maleic acid, 2.50 parts by weight of N-vinylpyrrolidone, and 0.50 parts by weight of N,N′-methylenebisacrylamide sequentially to the carbon-based pre-dispersion solution, and heat to 68°C under nitrogen protection; dissolve 0.40 parts by weight of ammonium persulfate in 9.60 parts by weight of deionized water to prepare a 4% ammonium persulfate aqueous solution, and add it dropwise to the system at a rate of 0.6 mL / min; after the addition is complete, react at 68°C and 700 rpm for 4.5 h to form a phosphonic acid-carboxylic acid-lactam synergistic complexation intermediate layer on the surface of the carboxylated porous carbon microspheres, and obtain a complexation layer modified carbon-based microparticle slurry.

[0068] B3. Weigh 35.00 parts by weight of polytetrafluoroethylene (PTFE) micro powder and add it to a mixture of 80.00 parts by weight of ethanol and 170.40 parts by weight of deionized water, wherein the mass ratio of ethanol to deionized water is 1:2.13. Disperse the mixture at 40°C and 1500 rpm for 45 min to obtain a PTFE pre-dispersion. Separately weigh 10.00 parts by weight of perfluorosulfonic acid resin and 7.00 parts by weight of polyvinylidene fluoride-hexafluoropropylene copolymer and add them to 55.00 parts by weight of N-methylpyrrolidone. Dissolve or disperse the mixture at 60°C and 800 rpm for 60 min to obtain a fluorinated polymer coating solution.

[0069] B4. The polytetrafluoroethylene pre-dispersion liquid is added to the complex layer modified carbon-based microparticle slurry and dispersed at 45°C and 1100 rpm for 35 min. Then, the fluorinated polymer coating liquid is added dropwise to the system at a rate of 1.0 mL / min. During the dropwise addition, the pH of the system is controlled at 3.0 using an 8% potassium hydroxide solution and a 10% nitric acid solution. After the dropwise addition is completed, the system is kept at 45°C for 2 h to obtain a core-complex layer-fluorinated interface shell composite slurry.

[0070] B5. The core-complex layer-fluorinated interface shell composite slurry is subjected to solid-liquid separation and washed four times with an ethanol-water washing solution with a pH of 3.0, wherein the mass ratio of ethanol to water in the ethanol-water washing solution is 1:3; then it is vacuum dried at 55°C for 12 hours, and then pulverized by air jet and passed through an 800-mesh sieve to obtain a tantalum-niobium separation type composite crystallization regulator.

[0071] The ethanol-water washing solution with a pH of 3.0 was prepared by adjusting it with a 10% nitric acid solution. During pH measurement, the ethanol-water washing solution was mixed with deionized water at a mass ratio of 1:1 and the aqueous phase reading was measured.

[0072] like Figure 3 As shown, SEM reveals that the particles are generally nearly spherical or near-spherical microspheres with a rough surface exhibiting obvious undulations, pores, and irregular interfaces after coating. EDS elemental surface scanning shows that carbon (C) is continuously distributed in the main particle region, indicating the presence of a carbon-based microsphere framework. O (O) elements largely overlap with the particle surface and pore walls, corresponding to oxygen-containing functional groups in carboxyl, carboxylic, phosphonic, and sulfonic acid groups. F (F) elements are clearly distributed at the particle's outer edge and surface, consistent with the expected formation of a fluoride-resistant fluorination interface shell by polytetrafluoroethylene (PTFE) micropowder, perfluorosulfonic acid resin, and polyvinylidene fluoride-hexafluoropropylene copolymer. P (P) elements, although showing a weak signal, are dispersed, corresponding to the phosphonic acid structure introduced by vinylphosphonic acid. N (N) elements are weakly distributed, corresponding to N-vinylpyrrolidone, polyvinylpyrrolidone, and lactam structures. S (S) elements are distributed in low-intensity dots or at the edges, consistent with the characteristic of relatively low sulfonic acid group content in perfluorosulfonic acid resin but its presence in the fluorinated interface layer.

[0073] Comparative Preparation Example 1

[0074] The preparation of the tantalum-niobium separation type composite crystallization regulator is carried out by referring to the preparation method in Preparation Example 1, except that the carboxylated porous carbon microspheres are replaced with an equal mass of commercially available uncarboxylated porous carbon microspheres, wherein the commercially available uncarboxylated porous carbon microspheres are spherical porous carbon microspheres, and the rest is the same as in Preparation Example 1.

[0075] The commercially available uncarboxylated porous carbon microspheres were purchased from Suzhou Qingtan Nanomaterials Co., Ltd., with a diameter of 80-200 nm.

[0076] Comparative Preparation Example 2

[0077] The preparation of the tantalum-niobium separation type composite crystallization regulator was carried out by referring to the preparation method in Preparation Example 1, except that the vinylphosphonic acid was replaced with an equal mass of 2-acrylamide-2-methylpropanesulfonic acid, and the rest remained the same as in Preparation Example 1.

[0078] Comparative preparation example 3

[0079] The preparation of the tantalum-niobium separation type composite crystallization regulator was carried out by referring to the preparation method in Preparation Example 1, except that N-vinylpyrrolidone was replaced with an equal mass of acrylamide, and the rest remained the same as in Preparation Example 1.

[0080] Comparative preparation example 4

[0081] The preparation of the tantalum-niobium separation type composite crystallization regulator is the same as that in Preparation Example 1, except that maleic acid is replaced with an equal mass of acrylic acid, and the rest is the same as in Preparation Example 1.

[0082] Comparative preparation example 5

[0083] The preparation of the tantalum-niobium separation type composite crystallization regulator was carried out by referring to the preparation method in Preparation Example 1, except that N,N′-methylenebisacrylamide was replaced with an equal mass of ethylene glycol dimethacrylate, and the rest remained the same as in Preparation Example 1.

[0084] Comparative preparation example 6

[0085] The preparation of the tantalum-niobium separation type composite crystallization regulator was carried out by referring to the preparation method in Preparation Example 1, except that the polytetrafluoroethylene micro powder was replaced with an equal mass of commercially available polyethylene micro powder, and the rest remained the same as in Preparation Example 1.

[0086] Among them, commercially available polyethylene micro powder is MIPELON. TM Fine-particle ultra-high molecular weight polyethylene powder (UHMWPE powder).

[0087] Comparative preparation example 7

[0088] The preparation of the tantalum-niobium separation type composite crystallization regulator is the same as that in Preparation Example 1, except that the perfluorosulfonic acid resin is replaced with an equal mass of sodium polystyrene sulfonate, and the rest is the same as in Preparation Example 1.

[0089] Sodium polystyrene sulfonate was purchased from Merck Group Darmstadt, Germany, MFCD00084449, with an average value of Mw~1,000,000.

[0090] Comparative Preparation Example 8

[0091] The preparation of the tantalum-niobium separation type composite crystallization regulator is the same as that in Preparation Example 1, except that the polyvinylidene fluoride-hexafluoropropylene copolymer is replaced with an equal mass of polyvinylidene fluoride powder, and the rest is the same as in Preparation Example 1.

[0092] The polyvinylidene fluoride powder is KYNAR. ® HSV 900 POWDER. Example 1

[0093] A method for purifying potassium fluorotantalate by crystallization: In this embodiment, the tantalum-niobium separation-type composite crystallization regulator obtained in Preparation Example 1 was used for the crystallization and purification of potassium fluorotantalate.

[0094] The potassium fluoride used is anhydrous potassium fluoride.

[0095] The potassium fluorotantalate seed crystals used were K2TaF7 seed crystals with a D50 of 15μm.

[0096] The hydrofluoric acid aqueous solution used was prepared by mixing 48% hydrofluoric acid and deionized water.

[0097] Tantalum-containing fluorine solutions, hydrofluoric acid aqueous solutions, and potassium fluoride-containing washing solutions are all prepared and used under fluorine corrosion resistant conditions.

[0098] S1. Take 1.000 L of a solution containing tantalum fluoride, filter to remove insoluble matter, and obtain a purified tantalum fluoride solution to be crystallized. The purified tantalum fluoride solution to be crystallized has a Ta concentration of 120 g / L, a free HF mass fraction of 10%, and a Nb concentration of 1.20 g / L.

[0099] S2. The purified tantalum fluoride solution to be crystallized is heated to 65°C and stirred at 700 rpm. 77.10 g of potassium fluoride is added to the purified tantalum fluoride solution to make the molar ratio of K to Ta in the system 2.00:1. After the potassium fluoride is completely dissolved, 3.00 g of the tantalum-niobium separation composite crystallization regulator obtained in Preparation Example 1 is added. The amount of the tantalum-niobium separation composite crystallization regulator added is 2.50% of the mass of Ta in the purified tantalum fluoride solution to be crystallized on a dry basis. Then, the mixture is stirred and complexed at 65°C for 60 min to obtain the pre-regulated crystallization mother liquor.

[0100] S3. Add 2.60 g of potassium fluorotantalate seed crystals to the pre-controlled crystallization mother liquor. The amount of potassium fluorotantalate seed crystals added is 1.00% of the theoretically generated K2TaF7 mass. Then, cool the liquor to 25°C at a cooling rate of 0.35°C / min and maintain the temperature at 25°C for crystallization for 2 hours to obtain a coarse potassium fluorotantalate slurry. The theoretically generated K2TaF7 mass is calculated based on the assumption that all Ta elements in the purified tantalum fluoride solution to be crystallized are converted into K2TaF7.

[0101] S4. The potassium fluorotantalate crude crystal slurry is first filtered through a 30μm HF-resistant polypropylene filter to retain the potassium fluorotantalate crystals, while the tantalum-niobium separation composite crystallization regulator and niobium-containing mother liquor pass through the filter. The retained crystals are then centrifuged at 2000 rpm for 10 min. After centrifugation, the crystals are washed with a potassium fluoride washing solution containing 3.0% KF and 1.5% HF at 20°C. 80.00 parts by weight of the potassium fluorotantalate washing solution are used for every 100.00 parts by weight of wet potassium fluorotantalate crystals. After washing, a first-purified potassium fluorotantalate crystal is obtained.

[0102] S5. The purified potassium fluorotantalate crystals are redissolved in an 8% HF aqueous solution. For every 100.00 parts by mass of purified potassium fluorotantalate crystals, 300.00 parts by mass of the aqueous solution are used. The redissolution temperature is 70°C, and the redissolution time is 60 min, yielding a redissolved tantalate fluoroacid solution. The molar ratio of K to Ta in the redissolved tantalate fluoroacid solution is detected and adjusted to 2.00:1, and the free HF mass fraction is adjusted to 10%. Subsequently, the tantalum-niobium separation-type composite crystallization regulator obtained in Preparation Example 1 is added. The amount of the tantalum-niobium separation-type composite crystallization regulator added, on a dry basis, is 1.80% of the mass of Ta in the redissolved tantalate fluoroacid solution. The mixture was stirred and complexed at 65℃ for 50 min; then potassium fluorotantalate seed crystals with a D50 of 15 μm were added, the amount of potassium fluorotantalate seed crystals added being 0.80% of the theoretical mass of K2TaF7 produced; the mixture was cooled to 25℃ at a cooling rate of 0.30℃ / min and kept at 25℃ for 2 h to obtain a secondary crystallization slurry; the secondary crystallization slurry was first filtered through a 30 μm HF-resistant polypropylene filter screen for graded filtration, and then the retained crystals were centrifuged at 2000 rpm for 10 min, and washed with a potassium fluoride washing solution of the same composition and amount as in step S4; after washing, the crystals were dried at 90℃ under a nitrogen atmosphere for 8 h to obtain high-purity potassium fluorotantalate. Example 2

[0103] A method for purifying potassium fluorotantalate by crystallization, referring to the purification method of Example 1, except that 77.10g of potassium fluoride added in step S2 is replaced with 74.42g of potassium hydroxide, so that the molar ratio of K to Ta in the system is still 2.00:1; during the addition of potassium hydroxide, the mass fraction of free HF is detected, and 48% hydrofluoric acid is added to maintain the mass fraction of free HF at 10%; in step S5, when detecting and adjusting the molar ratio of K to Ta in the redissolved tantalofluoric acid solution, potassium hydroxide is used as the potassium source for adjustment, and 48% hydrofluoric acid is added simultaneously to maintain the mass fraction of free HF at 10%, and the rest is the same as in Example 1. Example 3

[0104] A method for purifying potassium fluorotantalate by crystallization, referring to the purification method of Example 1, except that the potassium fluorotantalate seed crystals with a D50 of 15 μm used in steps S3 and S5 are replaced with potassium fluorotantalate seed crystals with a D50 of 8 μm. The amount of potassium fluorotantalate seed crystals added is still 1.00% and 0.80% of the theoretical mass of K2TaF7, respectively, and the rest is the same as in Example 1. Example 4

[0105] A method for purifying potassium fluorotantalate by crystallization, referring to the purification method of Example 1, except that the cooling rate in step S3 is replaced from 0.35℃ / min to 0.60℃ / min, and the cooling rate for secondary crystallization in step S5 is replaced from 0.30℃ / min to 0.50℃ / min, while the rest remains the same as in Example 1.

[0106] Comparative Examples 1-8

[0107] A method for purifying potassium fluorotantalate by crystallization, referring to the purification method of Example 1, wherein the tantalum-niobium separation type composite crystallization regulator obtained in Preparation Example 1 is replaced sequentially with the tantalum-niobium separation type composite crystallization regulator obtained in Comparative Preparation Examples 1-8, and the rest is the same as in Example 1.

[0108] Comparative Example 9

[0109] A method for purifying potassium fluorotantalate by crystallization is provided, referring to the purification method of Example 1, except that the operation of adding the tantalum-niobium separation composite crystallization regulator obtained in Example 1 in steps S2 and S5 is cancelled, that is, the tantalum-niobium separation composite crystallization regulator is not added during the crystallization process, and the rest is the same as in Example 1.

[0110] Comparative Example 10

[0111] A method for purifying potassium fluorotantalate by crystallization, referring to the purification method of Example 1, except that the tantalum-niobium separation-type composite crystallization regulator obtained in Preparation Example 1 added in steps S2 and S5 is replaced with an equal mass of commercially available polytetrafluoroethylene (PTFE) micropowder. The commercially available PTFE micropowder is the same as that used in Preparation Example 1, and the rest is the same as in Example 1.

[0112] Comparative Example 11

[0113] A method for purifying potassium fluorotantalate by crystallization, referring to the purification method of Example 1, except that the molar ratio of K to Ta in the system in step S2 is replaced from 2.00:1 to 1.60:1, that is, the amount of potassium fluoride added is replaced from 77.10g to 61.65g; when detecting and adjusting the molar ratio of K to Ta in the redissolved tantalofluoric acid solution in step S5, the molar ratio of K to Ta is also controlled at 1.60:1, and the rest is the same as in Example 1.

[0114] Performance testing:

[0115] 1. Determination of K2TaF7 mass fraction: The tantalum content corresponding to tantalum in the sample was determined by gravimetric method, and then converted to the mass fraction of potassium fluorotantalate according to stoichiometry. The specific steps are as follows: Weigh 0.1000 g of the potassium fluorotantalate sample to be tested, accurate to 0.0001 g, and place it in a pre-weighed platinum crucible. Add 2.0 g of potassium pyrosulfate and heat in a muffle furnace to 850 °C until the melt is transparent. After cooling to room temperature, leach the melt with hydrochloric acid solution, which is prepared by diluting 2.0 mL of concentrated hydrochloric acid with deionized water to 100.0 mL. Transfer the leachate to a 250 mL beaker, add 1.0 g of quantitative filter paper pulp, and heat to boiling on an electric furnace. Under continuous stirring, add 12.0 mL of tannic acid solution with a concentration of 100 g / L, and continue boiling for 5.0 min.

[0116] After cooling to room temperature, the precipitate was filtered using double-layered medium-speed quantitative filter paper. It was first washed four times with hot tannic acid washing solution, then twice with deionized water. The tannic acid washing solution was prepared to a final volume of 100.0 mL with 0.5 g tannic acid, 1.0 mL concentrated hydrochloric acid, and deionized water. The precipitate, along with the filter paper, was transferred to a pre-weighed porcelain crucible, dried and ashed on an electric furnace, then ignited at 850 °C for 15.0 min in a muffle furnace. After cooling to room temperature, it was weighed. A blank test was performed following the same procedure. Each sample was measured in triplicate, and the average value was taken. The data are shown in Table 1.

[0117] Calculate the mass fraction of tantalum oxide according to formula (1): w Ta2O5 =(m1-m2-m b ) / m s ×100% Equation (1); In the formula: w Ta2O5 m1 represents the mass fraction of tantalum oxide, in %; m2 represents the total mass of the precipitate and crucible after ignition, in g; m3 represents the constant weight mass of the crucible, in g; m4 represents the mass of the crucible. b The mass of the residue after burning in the blank test is expressed in grams (g); m s The value represents the sample mass, expressed in grams (g).

[0118] Convert the mass fraction of tantalum oxide to the mass fraction of K2TaF7 according to formula (2): w K2TaF7 =w Ta2O5 ×(2M) K2TaF7 / M Ta2O5 Equation (2); In the formula: w K2TaF7 K2TaF7 mass fraction, in %; M K2TaF7 The molar mass of K₂TaF₇ is taken as 392.14 g / mol; M Ta2O5 The molar mass of Ta₂O₅ is 441.89 g / mol.

[0119] That is: w K2TaF7 =w Ta2O5 ×1.775.

[0120] 2. Determination of Niobium Mass Fraction: The Nb mass fraction in high-purity potassium fluorotantalate was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The specific steps are as follows: Weigh 1.0000 g of the potassium fluorotantalate sample to be tested, accurate to 0.0001 g, and place it in a polytetrafluoroethylene beaker. Add 5.0 mL of 48.0% hydrofluoric acid and 2.0 mL of 65.0% nitric acid, and heat in a 60℃ water bath for 30.0 min to dissolve. After the sample is completely dissolved, cool to room temperature, add 10.0 mL of 200 g / L tartaric acid solution, and dilute to 100.0 mL with deionized water to obtain the sample solution to be tested. The analysis was performed using an inductively coupled plasma atomic emission spectrometer equipped with a hydrofluoric acid-resistant sample introduction system, which includes an HF-resistant nebulizer, an HF-resistant nebulization chamber, and a corrosion-resistant sample introduction tubing. The instrument operating conditions were as follows: RF power 1150W, plasma gas flow rate 15.0 L / min, auxiliary gas flow rate 1.5 L / min, nebulizing gas flow rate 0.8 L / min, observation height 15.0 mm, and niobium analysis spectral wavelength 309.418 nm. A standard working curve was plotted using niobium standard solutions. To reduce the influence of the high-tantalum matrix on niobium determination, the concentrations of hydrofluoric acid, nitric acid, tartaric acid, and tantalum matrix in the standard working solutions were kept consistent with those in the sample solution. The mass fractions of the niobium standard working solutions were 0.00 mg / L, 0.10 mg / L, 0.50 mg / L, 1.00 mg / L, 5.00 mg / L, and 10.00 mg / L, respectively. A linear fit was performed with niobium mass fraction as the x-axis and emission intensity as the y-axis, and the correlation coefficient was not less than 0.9995.

[0121] The sample solution to be tested was introduced into an inductively coupled plasma atomic emission spectrometer for measurement. The niobium mass fraction was calculated based on the standard working curve, and the data are shown in Table 1.

[0122] w Nb =(ρ×V×f×10 -6 / m s Equation (3) is calculated as follows: (1) × 100% In the formula: w Nb Nb mass fraction, in %; ρ, niobium concentration obtained from the standard working curve, in mg / L; V, final volume, in mL; f, dilution factor before testing, taken as 1 for undiluted samples; m s The value represents the sample mass, expressed in grams (g).

[0123] 3. Ta yield determination: The Ta yield was determined using a combination of gravimetric and computational methods. The specific steps are as follows: Accurately measure the volume of the tantalum fluoride purification solution used in step S1, denoted as V0, and determine the Ta concentration in the tantalum fluoride purification solution, denoted as C. Ta Calculate the mass of Ta element added to the purification solution of tantalum fluoride to be crystallized according to formula (4): m Ta,料液 =C Ta×V0 (4); Where: m Ta,料液 The mass of Ta added to the purification solution of tantalum fluoride to be crystallized is expressed in grams; C Ta V0 represents the concentration of Ta in the purified tantalum fluoride solution to be crystallized, in g / L; V0 represents the volume of the purified tantalum fluoride solution to be crystallized, in L.

[0124] Since K2TaF7 seed crystals are added during the crystallization process, and these seed crystals contain Ta, the mass of Ta brought in by the seed crystals should be deducted to avoid an artificially high Ta yield. The theoretical mass fraction of Ta in K2TaF7 is calculated according to formula (6): α Ta / =M Ta / M K2TaF7 =0.4614 Equation (6); In the formula: α Ta M represents the theoretical mass fraction of Ta in K2TaF7. Ta For Ta, take 180.95 g / mol; M K2TaF7 The molar mass of K2TaF7 is 392.14 g / mol.

[0125] Accurately weigh the total mass of K2TaF7 seed crystals added in steps S3 and S5, and denot it as M. 晶种 The mass of Ta brought in by the seed crystal is calculated according to formula (7): m Ta,晶种 =M 晶种 ×α Ta Equation (7); Accurately weigh the mass of the high-purity potassium fluorotantalate product obtained after drying in step S5, and record it as M. 产品 The mass fraction of K2TaF7 in the high-purity potassium fluorotantalate product was measured according to Section 1 above and denoted as w. K2TaF7 Calculate the mass of Ta element corresponding to K2TaF7 in the product according to formula (8): m Ta,产品 =M 产品 ×w K2TaF7 / 100×α Ta Equation (8); Calculate the yield of Ta according to formula (9): η Ta =(m Ta,产品 -m Ta,晶种 ) / m Ta,料液 ×100% Equation (9); In the formula: η Ta Ta yield, in %; m Ta,产品 The mass of Ta element corresponding to K2TaF7 in high-purity potassium fluorotantalate product is expressed in grams; mTa,晶种 The mass of Ta introduced by the K2TaF7 seed crystal is expressed in g; m Ta,料液 The mass of Ta element added to the tantalum fluoride purification solution to be crystallized is in g, and the data is shown in Table 1.

[0126] Table 1. Performance test data of the examples and comparative examples

[0127] Table 1 shows that Example 1 used the tantalum-niobium separation composite crystallization regulator obtained in Example 1, combined with potassium fluorotantalate seed crystals with a K / Ta molar ratio of 2.00:1 and a D50 of 15 μm, and relatively slow cooling crystallization conditions. Carboxylated porous carbon microspheres provided carboxyl active sites, and the phosphonic acid-carboxylic acid-lactam synergistic complexing intermediate layer weakened the adsorption, co-deposition, and encapsulation of niobium-fluorine complexes at the crystal interface. The fluorine-resistant fluorinated interface shell maintained the stable dispersion of the regulator in the HF system. Therefore, the K2TaF7 mass fraction was the highest at 99.86%, the Nb mass fraction was the lowest at 0.018%, and the Ta yield was also the highest at 94.6%.

[0128] In Example 2, the potassium source was replaced with potassium hydroxide instead of potassium fluoride. Although the K / Ta molar ratio remained at 2.00:1, potassium hydroxide would change the local acidity, fluorine complexation balance and ionic environment, resulting in a slightly weaker control of the crystallization interface. Therefore, the mass fraction of K2TaF7 decreased to 99.78%, Nb increased to 0.024%, and the Ta yield was 93.8%.

[0129] In Example 3, the seed crystal D50 was adjusted from 15 μm to 8 μm. The seed crystal is finer and has a larger specific surface area, which increases the number of induced nucleation sites and makes it easier to form more fine crystals or surface adsorption sites. This leads to a slight increase in mother liquor entrainment and niobium adsorption. Therefore, the K2TaF7 yield is 99.74%, the Nb yield is 0.027%, and the Ta yield is 93.5%.

[0130] Example 4 increased the cooling rate, which made the supersaturation of the system grow faster, slightly reduced the integrity of crystal growth, and increased the risk of intergranular inclusion and defect entrainment. Therefore, K2TaF7 was further reduced to 99.69%, Nb increased to 0.032%, and Ta yield was 92.9%.

[0131] Comparative Example 1 replaced carboxylated porous carbon microspheres with uncarboxylated porous carbon microspheres. Due to the lack of carboxyl active sites on the pore wall surface and outer surface, the ability to regulate the interface distribution of tantalum-niobium-fluorine complex was significantly reduced, K2TaF7 decreased to 99.28%, Nb increased to 0.071%, and Ta yield decreased to 90.7%.

[0132] Comparative Example 2 replaced vinylphosphonic acid with 2-acrylamido-2-methylpropanesulfonic acid. After the phosphonic acid site was deleted, the differential complexing and interfacial repulsion of the niobium fluoride complex were weakened, with K2TaF7 yield of 99.35%, Nb yield of 0.064%, and Ta yield of 91.2%.

[0133] In Comparative Example 3, acrylamide was used to replace N-vinylpyrrolidone. The contribution of the lactam structure was insufficient, and the coordination synergy of the phosphonic acid-carboxylic acid-lactam synergistic complex intermediate was reduced. The yield of K2TaF7 was 99.40%, Nb was 0.059%, and Ta was 91.7%.

[0134] In Comparative Example 4, when maleic acid was replaced with acrylic acid, the spatial distribution of carboxyl groups and the synergistic effect of multiple carboxyl groups were weakened, but the carboxylic acid complexation function was still retained. Therefore, the decrease was relatively small, with K2TaF7 at 99.46%, Nb at 0.052%, and Ta yield at 92.1%.

[0135] Comparative Example 5 replaced N,N′-methylenebisacrylamide with ethylene glycol dimethacrylate, which altered the crosslinking structure and hydrophilic complexing network, resulting in a decrease in the stability of the complexing intermediate layer and the degree of exposure of functional groups. The yield of K2TaF7 was 99.31%, Nb was 0.067%, and Ta was 90.9%.

[0136] In Comparative Example 6, when polyethylene micropowder was used instead of polytetrafluoroethylene micropowder, the chemical stability and low surface energy shielding effect of the fluorinated interface shell were significantly weakened. The regulator was more prone to instability in the strong HF system, K2TaF7 decreased to 99.22%, Nb increased to 0.079%, and Ta yield was 89.8%.

[0137] Comparative Example 7 replaced perfluorosulfonic acid resin with sodium polystyrene sulfonate. Although it still contained sulfonic acid groups, it lacked the hydrofluoric acid resistance of the perfluoro skeleton. Furthermore, the sodium salt polymer may alter the local ionic environment, resulting in one of the worst shell stability, with K2TaF7 at 99.18%, Nb at 0.083%, and Ta yield at 89.4%.

[0138] Comparative Example 8 replaced polyvinylidene fluoride-hexafluoropropylene copolymer with polyvinylidene fluoride powder. The flexibility and dispersion of the fluorinated interface shell were reduced, but it still had certain fluorine-containing acid-resistant characteristics. Therefore, the performance decline was slightly smaller than that of Comparative Examples 6 and 7. The K2TaF7 yield was 99.42%, Nb yield was 0.056%, and Ta yield was 91.9%.

[0139] Comparative Example 9 eliminated the tantalum-niobium separation-type composite crystallization regulator, and the system relied solely on conventional crystallization, washing, and recrystallization. This failed to effectively suppress the surface adsorption, co-deposition, and mother liquor entrainment of niobium-fluorine complexes. Consequently, Nb yielded the highest at 0.118%, K2TaF7 yielded a decrease to 98.91%, and Ta yield was only 86.7%.

[0140] Comparative Example 10 used commercially available polytetrafluoroethylene micropowder to replace the composite crystallization regulator. It only had inert acid resistance and weak interfacial dispersion effect, and lacked carboxylated porous carbon microspheres and phosphonic acid-carboxylic acid-lactam synergistic complexation intermediate layer. Therefore, the K2TaF7 content was 99.05%, the Nb content was 0.101%, and the Ta yield was 87.9%.

[0141] Comparative Example 11 reduced the K / Ta molar ratio to 1.60:1. Insufficient potassium source led to incomplete crystallization of potassium fluorotantalate, increased Ta residue in the mother liquor, and reduced crystal growth stability. Although the Nb content was lower than that of Comparative Example 9, it was still significantly higher than that of the Example, at 0.093%. The K2TaF7 content was as low as 98.76%, and the Ta yield was as low as 82.8%, indicating that the control of the K / Ta molar ratio has a key impact on both purity and yield.

[0142] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for purifying potassium fluorotantalate by crystallization, characterized in that, The steps include the following: S1. Filter the tantalum fluoride solution to remove insoluble matter, and obtain the tantalum fluoride purified solution to be crystallized. The tantalum fluoride purified solution to be crystallized has a Ta concentration of 100-140 g / L, a free HF mass fraction of 8-12%, and a Nb concentration of 0.5-1.5 g / L. S2. Add a potassium source to the purified tantalum fluoride solution to be crystallized, so that the molar ratio of K to Ta in the system is (1.85-2.15):

1. Then add a tantalum-niobium separation type composite crystallization regulator and stir and complex at 50-75℃ for 20-90 min to obtain a pre-regulated crystallization mother liquor. S3. Add potassium fluorotantalate seed crystals to the pre-controlled crystallization mother liquor, and cool it to 15-30℃ at a cooling rate of 0.15-0.80℃ / min, and keep it at the temperature for crystallization for 1-4 hours to obtain potassium fluorotantalate coarse crystal slurry. S4. The potassium fluorotantalate crude crystal slurry is subjected to solid-liquid separation, and the crystals are washed with potassium fluoride washing solution to obtain potassium fluorotantalate crystals that have been purified once. S5. The purified potassium fluorotantalate crystals are redissolved in a fluorine-containing acidic solution to obtain a redissolved tantalofluoric acid solution. The concentration of Ta, the mass fraction of free HF, and the molar ratio of K to Ta in the redissolved tantalofluoric acid solution are detected, and potassium source and / or HF are added to make the molar ratio of K to Ta (1.85-2.15):1 and the mass fraction of free HF 5-18%. Then, the crystallization regulation, step-by-step removal of regulator, solid-liquid separation and washing processes in steps S2-S4 are repeated, and high-purity potassium fluorotantalate is obtained after drying. The tantalum-niobium separation-type composite crystallization regulator is prepared from the following raw materials in parts by weight: 20-35 parts carboxylated porous carbon microspheres, 25-45 parts polytetrafluoroethylene micro powder, 5-15 parts perfluorosulfonic acid resin, 4-10 parts polyvinylidene fluoride-hexafluoropropylene copolymer, 6-14 parts vinylphosphonic acid, 3-8 parts acrylic acid, 2-6 parts maleic acid, 1-4 parts N-vinylpyrrolidone, 0.2-0.8 parts N,N′-methylenebisacrylamide, 0.2-0.6 parts ammonium persulfate, 0.5-2.0 parts polyvinylpyrrolidone, 60-120 parts ethanol, 30-80 parts N-methylpyrrolidone, and 200-450 parts deionized water; The preparation method of the tantalum-niobium separation type composite crystallization regulator includes the following steps: B1. Mix carboxylated porous carbon microspheres, polyvinylpyrrolidone, and deionized water at a solid-liquid mass ratio of 1:8-15, disperse at 25-35℃ and 800-1500rpm for 20-40min, then sonicate at 200-400W for 10-30min, and adjust the pH of the system to 2.0-3.5 with a 5-10% nitric acid solution to obtain a carbon-based pre-dispersion. B2. Vinylphosphonic acid, acrylic acid, maleic acid, N-vinylpyrrolidone and N,N′-methylenebisacrylamide are added sequentially to the carbon-based pre-dispersion solution. The temperature is raised to 60-75℃ under nitrogen protection. Ammonium persulfate is prepared into an aqueous solution with a mass fraction of 2-5% and added dropwise to the system at a dropping rate of 0.3-1.0 mL / min. After the addition is completed, the reaction is carried out at 60-75℃ and 500-900 rpm for 3-6 h to form a phosphonic acid-carboxylic acid-lactam synergistic complexing intermediate layer on the surface of the carboxylated porous carbon microspheres, thereby obtaining a complexing layer modified carbon-based microparticle slurry. B3. Add polytetrafluoroethylene (PTFE) micro powder to a mixture of ethanol and deionized water, wherein the mass ratio of ethanol to deionized water is 1:(1.5-3.0), and disperse at 30-45℃ and 1000-1800 rpm for 30-60 min to obtain a PTFE pre-dispersion; add perfluorosulfonic acid resin and polyvinylidene fluoride-hexafluoropropylene copolymer to N-methylpyrrolidone, and dissolve or disperse at 50-65℃ and 600-1000 rpm for 40-90 min to obtain a fluorinated polymer coating solution; B4. Add the polytetrafluoroethylene pre-dispersion liquid to the complexed layer modified carbon-based microparticle slurry and disperse it at 35-50℃ and 800-1400rpm for 20-50min. Then, add the fluorinated polymer coating liquid dropwise to the system at a rate of 0.5-2.0mL / min. During the dropwise addition, control the pH of the system to 2.0-4.

0. After the dropwise addition is completed, continue to keep warm and disperse for 1-3h, so that polytetrafluoroethylene, perfluorosulfonic acid resin and polyvinylidene fluoride-hexafluoropropylene copolymer form a fluoride-resistant interface shell on the outside of the phosphonic acid-carboxylic acid-lactam synergistic complexing intermediate layer, and obtain a core-complexed layer-fluorinated interface shell composite slurry. B5. The core-complex layer-fluorinated interface shell composite slurry is subjected to solid-liquid separation and washed 3-5 times with an ethanol-water washing solution with a pH of 2.0-3.

5. The mass ratio of ethanol to water in the ethanol-water washing solution is 1:2-4. The pH of the ethanol-water washing solution is adjusted with a nitric acid solution with a mass fraction of 5-10%. Subsequently, it is vacuum dried at 45-65℃ for 8-16 hours, then pulverized by air jet and passed through a 600-1200 mesh sieve to obtain a tantalum-niobium separation type composite crystallization regulator. The potassium fluorotantalate product contains K2TaF7 mass fraction ≥ 99.50%, Nb mass fraction ≤ 0.05%, and moisture mass fraction ≤ 0.20%.

2. The method for purifying potassium fluorotantalate by crystallization according to claim 1, characterized in that, The potassium source is one or more of potassium fluoride, potassium hydroxide, and potassium carbonate; When the potassium source is potassium hydroxide, HF is detected and added simultaneously during the addition process to maintain the mass fraction of free HF in the system at 5-18%.

3. The method for purifying potassium fluorotantalate by crystallization according to claim 1, characterized in that, The amount of the composite crystallization regulator added, on a dry basis, is 1.5-3.0% of the mass of Ta element in the tantalum fluoride purification solution to be crystallized.

4. The method for purifying potassium fluorotantalate by crystallization according to claim 1, characterized in that, The potassium fluorotantalate seed crystal is a K2TaF7 seed crystal with a D50 of 5-30 μm; The amount of potassium fluorotantalate seed crystals added is 0.2-2.0% of the theoretically generated K2TaF7 mass; The theoretically generated K2TaF7 mass is calculated based on the assumption that all Ta elements in the tantalic acid purification solution to be crystallized are converted into K2TaF7.

5. The method for purifying potassium fluorotantalate by crystallization according to claim 1, characterized in that, The potassium fluoride washing solution contains 2.0-4.0% KF and 1.0-2.5% HF by mass, and the washing temperature is 10-30℃. 60-100 parts by mass of potassium fluorotantalate wet crystals are used in the potassium fluoride washing solution.

6. The method for purifying potassium fluorotantalate by crystallization according to claim 1, characterized in that, The fluorinated acidic solution is an aqueous solution of hydrofluoric acid with an HF mass fraction of 4-12%. For every 100 parts by mass of potassium fluorotantalate crystals purified once, 180-450 parts by mass of the fluorinated acidic solution are used. The redissolution temperature is 55-85℃ and the redissolution time is 20-90 min.

7. The method for purifying potassium fluorotantalate by crystallization according to claim 1, characterized in that, In step S4, solid-liquid separation is performed by centrifugation or vacuum filtration. When centrifugation is performed, the centrifugation speed is 1200-3000 rpm and the centrifugation time is 5-20 min. When vacuum filtration is performed, the vacuum degree is -0.04 MPa to -0.09 MPa and the filtration time is 5-30 min.

8. The method for purifying potassium fluorotantalate by crystallization according to claim 1, characterized in that, In step S5, the drying temperature is 80-100℃, the drying time is 6-10h, and the drying atmosphere is nitrogen. The moisture content of the high-purity potassium fluorotantalate obtained after drying is determined by Karl Fischer method and is ≤0.20%.

9. The method for purifying potassium fluorotantalate by crystallization according to claim 1, characterized in that, The preparation method of the carboxylated porous carbon microspheres includes the following steps: A1. Mix glucose, polyvinylpyrrolidone and deionized water at a mass ratio of 1:(0.05-0.20):(8-15) and stir at 25-35℃ and 500-1000rpm for 20-40min to obtain a carbon source solution. A2. The carbon source solution is transferred to a closed reaction vessel and hydrothermally reacted at 180-200℃ for 6-12 hours. After cooling to 25-35℃, solid-liquid separation is performed, and the solution is washed 3-5 times with deionized water and dried at 60-80℃ for 8-12 hours to obtain the carbon microsphere precursor. A3. The carbon microsphere precursor and potassium hydroxide are mixed and ground at a mass ratio of 1:(1.5-3.0) for 10-30 min. The mixture is heated to 700-800℃ at a heating rate of 3-8℃ / min under a nitrogen atmosphere and kept at this temperature for 1-3 h. After cooling, the mixture is washed with a 5-10% hydrochloric acid solution until the pH of the washing solution is 6.0-7.

0. The mixture is then washed with deionized water 2-4 times and dried at 70-90℃ for 6-12 h to obtain porous carbon microspheres. A4. The porous carbon microspheres are added to a nitric acid solution with a mass fraction of 10-30%, and the solid-liquid mass ratio of the porous carbon microspheres to the nitric acid solution is 1:(10-25). The mixture is oxidized at 60-80℃ and 300-700rpm for 2-6 hours to form carboxyl active sites on the pore wall surface and the outer surface of the porous carbon microspheres. After solid-liquid separation, the mixture is washed with deionized water until the pH of the washing solution is 6.0-7.

0. The mixture is then vacuum dried at 60-80℃ for 8-14 hours, pulverized by air jet and passed through an 800-1500 mesh sieve to obtain carboxylated porous carbon microspheres.

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