A method for preparing high-purity spherical aluminum hydroxide, high-purity spherical aluminum hydroxide, and a type of high-purity alumina microspheres.

Abstract

A method for preparing high-purity spherical aluminum hydroxide, high-purity spherical aluminum hydroxide, and a high-purity alumina microsphere, comprising the following steps: (1) adding sodium aluminate solution to aluminum hydroxide seed crystals, and introducing CO2 for carbonation neutralization decomposition to obtain aluminum hydroxide; (2) adding the obtained aluminum hydroxide seed crystals back into a new sodium aluminate solution for carbonation neutralization decomposition; (3) repeating step (2) 4 to 10 times for multiple cycles of carbonation neutralization decomposition, followed by separation and washing to obtain high-purity spherical aluminum hydroxide; wherein the particle size D of the aluminum hydroxide seed crystals is... 50 The particle size is 70–100 μm. This application involves multiple cycles of carbonation and neutralization decomposition, allowing the seed crystals to grow continuously, filling surface defects time and again until they become smooth, spherical aluminum hydroxide. The spherical aluminum hydroxide prepared in this application has a sphericity of 80–95%, a particle size of 90–150 μm, and a purity of 99.9%. High-purity spherical alumina products can be obtained through calcination.

Description

Technical Field

[0001] This application belongs to the field of multi-variety alumina technology, specifically relating to a method for preparing high-purity spherical aluminum hydroxide. Background Technology

[0002] Spherical alumina belongs to the fine chemical product family of alumina materials. It possesses excellent pressing and sintering properties, which can greatly improve the quality of ceramic products. Its regular morphology avoids scratches and is beneficial as a polishing and grinding material. In the petrochemical industry, ultrafine spherical alumina powder, used directly as a catalyst, can reduce wear, increase catalyst lifespan, and thus lower production costs. Spherical aluminum hydroxide can be calcined to obtain alumina. Currently, there are many methods for producing spherical aluminum hydroxide, mainly including: roll forming, extrusion forming, oil-ammonia column, hot oil column, sol-gel, and template agent methods.

[0003] CN110204316A provides a method for preparing high-purity alumina grinding microspheres. The main technical solution is as follows: High-purity alumina powder is ground and pulverized to obtain high-purity alumina nanoparticles with an average particle size of 100–500 nm; the high-purity alumina nanoparticles, organic monomers, and water are mixed uniformly to obtain an inorganic-organic mixture, wherein the mass ratio of high-purity alumina nanoparticles to organic monomers is 40:100–100:100, and the mass ratio of organic monomers to water is 10:100–30:100; 0.05–5% by mass of an initiator and 0.1–10% by mass of an organic monomer are added to the inorganic-organic mixture, and the mixture is stirred uniformly to carry out a bead-like polymerization reaction, obtaining a reaction solution containing microsphere precursors; the reaction solution containing microsphere precursors is separated, washed, and dried to obtain microsphere blanks; the microsphere blanks are then sieved, debinded at low temperature, sintered, and microspheres with poor sphericity or that are broken are removed to obtain high-purity alumina grinding microspheres.

[0004] CN101214984B discloses a method for preparing alumina microspheres, with the following specific steps: (1) placing the raw material in a crucible; (2) pyrolyzing the raw material in the crucible at 1150–1350 °C using a sintering furnace; (3) holding the pyrolysis at this temperature for 0.5–1.5 h; and (4) cooling the furnace to room temperature. Compared with the prior art, the advantages of this invention are that it utilizes the pyrolysis of polymer precursors to form alumina microspheres with perfect spherical structure, without the need for any protective atmosphere or catalyst. This method not only simplifies the equipment and process but also results in a short production cycle, high product purity, and excellent process controllability and repeatability. Single-crystal and polycrystalline alumina microspheres can be obtained by controlling the pyrolysis temperature, and the particle size of the microspheres can be adjusted by controlling the holding time.

[0005] CN108258231B discloses a method for preparing porous alumina microspheres. The main technical solution is as follows: Step 1, dissolve polyvinylpyrrolidone in anhydrous ethanol, stir ultrasonically for 20-40 min, and obtain a dispersed alcohol solution after cooling; Step 2, add aluminum ammonium carbonate and sodium chloride to the dispersed alcohol solution, stir evenly to form a homogeneous suspension; Step 3, place the suspension in a vacuum distillation reactor for vacuum distillation reaction for 20-50 min to obtain a viscous concentrate; Step 4, add the viscous concentrate to a mold and slowly heat until the ethanol is completely removed to obtain an alumina microsphere precursor; Step 5, place the alumina microsphere precursor in a muffle furnace and react under gradient pressure for 2-4 h, slowly depressurize and then perform gradient sintering reaction for 4-6 h, and obtain porous alumina microspheres after natural cooling; Step 6, place the porous alumina microspheres in deionized water and react ultrasonically for 3-4 h, remove and dry to obtain porous alumina microspheres.

[0006] CN114735734A discloses a method for producing readily soluble aluminum hydroxide using the Bayer process. The method disclosed in this invention uses carbon decomposition to prepare seed crystals, which are then added to Bayer process concentrate for seed decomposition to produce aluminum hydroxide product. The process conditions for carbon decomposition and seed decomposition are improved, reducing the single crystal particle size and increasing the seed crystal agglomeration particle size. This results in a final aluminum hydroxide product with a different crystal structure than aluminum hydroxide produced by the conventional Bayer process, producing readily soluble aluminum hydroxide with coarse particle size and high acid solubility. The aluminum hydroxide prepared using this method, after grading, yields D... 50 With a particle size of 90 μm or larger, and under conditions of 21% hydrochloric acid concentration, 95°C temperature, 15% aluminum hydroxide mass fraction, and a reaction time of 1 hour, the acid solubility is over 90%, significantly higher than the 55-65% acid solubility of conventional aluminum hydroxide. Furthermore, the method of this invention fully utilizes the aluminum in the aluminum hydroxide washing solution from the Bayer process, greatly reducing aluminum salt raw material consumption and lowering production costs.

[0007] CN101450811A discloses a method for extracting alumina from coal gangue. The main technical solution is as follows: Coal gangue is ground into powder and then passed through a fluidized bed furnace; iron is removed by calcination and magnetic separation. The iron-removed gangue is reacted with acid to obtain an alumina solution free of silicon impurities. The aluminum-containing solution is concentrated and crystallized, then calcined at low temperature to obtain crude alumina. The crude alumina is then reacted with uranium hydroxide to obtain uranium aluminate mother liquor. Iron and iron impurities are removed, aluminum hydroxide seed crystals are added to the mother liquor, and CO2 gas is introduced for seeding to obtain aluminum hydroxide precipitate. After calcination, metallurgical-grade alumina is obtained. This method extracts alumina directly by leaching with hydrochloric acid and sulfuric acid under normal pressure without using any additives.

[0008] CN1552925A discloses a processing method for industrial waste, which is waste from the aluminum and recycled aluminum smelting industry and the aluminum and aluminum alloy application industry. It contains: 60-90 parts by weight of Al2O3, 0-20 parts by weight of Al, 0-15 parts by weight of SiO2, and may also contain 0-15 parts by weight of impurities. The processing method includes the following steps in sequence: (1) Leaching: The raw material is leached at a leaching temperature of 70-220℃, a caustic alkali concentration of 100-220 g / L, and a leaching time of 0.2-8h to form a sodium aluminate solution; (2) Separation: The leached slurry is subjected to liquid-solid separation to obtain a sodium aluminate solution; (3) Decomposition: Aluminum hydroxide seed crystals are added to the sodium aluminate solution for seed decomposition or CO2 is introduced for carbonation decomposition to obtain aluminum hydroxide; (4) Calcination: The aluminum hydroxide is calcined at a temperature of 500-1500℃ to obtain aluminum oxide. These two patents describe a process for producing easily soluble aluminum hydroxide using carbon seeding. Carbonated aluminum hydroxide (which is more active) is added as a seed crystal to a sodium aluminate solution for seeding and decomposition to prepare aluminum hydroxide. The aluminum hydroxide is completely decomposed in one step to become the product, which is crumbly and easily acid-soluble. It is then used as a raw material for acid-soluble aluminum hydroxide. The aluminum hydroxide is then calcined to obtain alumina. The resulting metallurgical-grade alumina product has poor morphology and low quality, and does not meet the current applications in fields such as high thermal conductivity, grinding, and catalysis.

[0009] To solve the above problems, it is urgent to prepare an aluminum hydroxide with high sphericity and high purity, which can be obtained after calcination. Summary of the Invention

[0010] To address the aforementioned issues, this application proposes a method for preparing high-purity spherical aluminum hydroxide, wherein the sphericity of the spherical aluminum hydroxide is >90%, the particle size is 90–150 μm, and the purity is 99.9%, and the purity of the high-purity alumina microspheres is >99.99%, and the sphericity is >90%.

[0011] A method for preparing high-purity spherical aluminum hydroxide includes the following steps:

[0012] (1) Add sodium aluminate solution to aluminum hydroxide seed crystals, and then introduce CO2 to perform carbonation, neutralization and decomposition to obtain aluminum hydroxide;

[0013] (2) The obtained aluminum hydroxide was added back into a new sodium aluminate solution as a seed crystal to carry out carbonation, neutralization and decomposition;

[0014] (3) Repeat step (2) 4 to 10 times to perform multiple cycles of carbonation, neutralization and decomposition, separation and washing to obtain high-purity spherical aluminum hydroxide.

[0015] The particle size D of the aluminum hydroxide seed crystals 50 It is 70–100 μm.

[0016] Preferably, the aluminum hydroxide seed crystal is a high-purity aluminum hydroxide (99.9% purity) seed crystal, which is selected from aluminum hydroxide process high-purity aluminum hydroxide, modified Bayer process high-purity aluminum hydroxide, carbon fractionation process high-purity aluminum hydroxide, seed fractionation process high-purity aluminum hydroxide, and ammonium salt process high-purity aluminum hydroxide.

[0017] Preferably, the aluminum hydroxide seed crystals are selected from high-purity aluminum hydroxide produced by the modified Bayer process.

[0018] Preferably, the amount of aluminum hydroxide seed crystals added is 200–400 g / L.

[0019] Preferably, the carbonation neutralization decomposition temperature is 70–90°C, and the time is 1 hour.

[0020] Preferably, the Al2O3 content of sodium aluminate is 70–120 g / L.

[0021] Preferably, the sodium aluminate solution is prepared by: using high-purity sodium aluminate solid as raw material and high-purity water as solvent for slurry preparation, filtering the obtained sodium aluminate solution to remove insoluble matter, and obtaining sodium aluminate solution.

[0022] Preferably, the CO2 concentration is 30-40%.

[0023] Preferably, the method for adjusting the CO2 concentration is as follows: using purchased food-grade high-purity CO2 with a concentration of 100% and a purity of 99.99%, and diluting it with air purified by three levels to obtain a CO2 concentration of 30-40%.

[0024] Preferably, the obtained high-purity spherical aluminum hydroxide has a sphericity of 80-95%, a particle size of 90-150 μm, and a purity of 99.9%.

[0025] Preferably, the high-purity alumina microspheres have a purity >99.99% and a sphericity >90%;

[0026] Preferably, the high-purity alumina microspheres are prepared by: subjecting high-purity spherical aluminum hydroxide to hydrothermal treatment at 200°C for 2 hours, filtering and washing, drying, and calcining at 1200°C to obtain high-purity alumina microspheres. These high-purity alumina microspheres are used in fields such as high thermal conductivity, grinding, and catalysis.

[0027] This invention uses high-purity aluminum hydroxide as seed crystals, which are added to a sodium aluminate solution. CO2 is used as a decomposition and neutralization agent for carbonation and neutralization. By adjusting parameters such as the concentration of each component in the sodium aluminate solution, temperature, CO2 aeration rate, and time, the aluminum hydroxide precipitated from the sodium aluminate solution continues to grow on the surface of coarse-grained aluminum hydroxide crystals. With the aim of spheroidizing the aluminum hydroxide, through multiple cycles of carbonation, neutralization, and decomposition, the aluminum hydroxide grows while the particle morphology becomes increasingly spherical, ultimately yielding a high-purity spherical aluminum hydroxide product with a uniform crystal phase. After calcination, a high-purity spherical alumina product is obtained, mainly used in fields such as high thermal conductivity, grinding, and catalysis. This technology is simple, stable, and has significant market application value.

[0028] This application can bring the following beneficial effects:

[0029] 1. In this application, high-purity aluminum hydroxide seed crystals are added to sodium aluminate solution, and then CO2 is introduced to carry out multiple cycles of carbonation, neutralization and decomposition. This allows the high-purity aluminum hydroxide seed crystals to grow continuously under decomposition conditions, filling surface defects one by one until they grow into spherical aluminum hydroxide with a smooth surface.

[0030] 2. This application selects high-purity aluminum hydroxide seed crystals with a particle size D. 50 The size is 70-100 μm to ensure that the seed crystals do not decompose too quickly in the sodium aluminate solution, allowing them to grow smoothly into spherical shapes. If the aluminum hydroxide seed crystals are too fine, the seed crystal activity will be too high, making them easy to decompose in the sodium aluminate solution and slowing down their growth rate into spherical shapes.

[0031] 3. The spherical aluminum hydroxide prepared in this application can be calcined to produce high-purity spherical alumina products, which are mainly used in fields such as high thermal conductivity, grinding, and catalysis.

[0032] 4. The spherical aluminum hydroxide prepared in this application has a sphericity of 80-95%, a particle size of 90-150 μm, and a purity of 99.9%.

[0033] 5. The high-purity alumina microspheres prepared in this application have a purity >99.99% and a sphericity >90%;

[0034] 6. This application has the advantages of simple and stable process and low cost, and has great market promotion and application value. Attached Figure Description

[0035] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0036] Figure 1 SEM image of the spherical aluminum hydroxide obtained in Example 1;

[0037] Figure 2 SEM image of aluminum hydroxide obtained in Comparative Experiment 1 without seed crystals; Detailed Implementation

[0038] Example 1: (1) High-purity sodium aluminate solid (Al2O3 content 41%, Na2O content 30%, purity 99.9%) was slurried with high-purity water (resistance greater than 130,000 Ω) as solvent, and the Al2O3 concentration in the sodium aluminate solution was adjusted to 90 g / L. After filtration, sodium aluminate solution was obtained.

[0039] (2) Using food-grade high-purity CO2 (purity 99.99%) as raw material, and air after three-stage filtration as CO2 diluent, the mixture is mixed to obtain CO2 gas with a concentration of 35%.

[0040] (3) Add modified Bayer process aluminum hydroxide seed crystals to 1L of sodium aluminate solution at a concentration of 300g / L, with a particle size D 50 The sample had a particle size of 80 μm and a purity of 99.9%. It was subjected to carbonation neutralization and decomposition by introducing CO2 with a concentration of 35%. The stirring was started at 200 r / m, the decomposition temperature was 90℃, and the decomposition time was 1 h, to obtain aluminum hydroxide.

[0041] (4) The obtained aluminum hydroxide is added back as a seed crystal to a new sodium aluminate solution for carbonation, neutralization and decomposition;

[0042] (5) Repeat step (4) 6 times, separate and wash, to obtain high-purity spherical aluminum hydroxide with a particle size D. 50 It has a diameter of 148 μm and a sphericity of 92%.

[0043] Example 2: (1) High-purity sodium aluminate solid (Al2O3 content 41%, Na2O content 30%, purity 99.9%) was slurried with high-purity water (resistance greater than 130,000 Ω) as solvent, and the Al2O3 concentration of the sodium aluminate solution was adjusted to 90 g / L. After filtration, sodium aluminate solution was obtained.

[0044] (2) Using food-grade high-purity CO2 (purity 99.99%) as raw material, and air after three-stage filtration as CO2 diluent, the mixture is mixed to obtain CO2 gas with a concentration of 30%.

[0045] (3) High-purity aluminum hydroxide seed crystals obtained by the aluminum alkoxide method are added to 1L of sodium aluminate solution at a concentration of 300g / L, with a particle size D 50 The sample had a particle size of 70 μm and a purity of 99.9%. It was subjected to carbonation neutralization and decomposition by introducing CO2 with a concentration of 30%. The stirring was started at 200 r / m, the decomposition temperature was 90℃, and the decomposition time was 1 h, to obtain aluminum hydroxide.

[0046] (4) The obtained aluminum hydroxide is added back as a seed crystal to a new sodium aluminate solution for carbonation, neutralization and decomposition;

[0047] (5) Repeat step (4) 6 times, separate and wash, to obtain high-purity spherical aluminum hydroxide with a particle size D. 50 It has a diameter of 102 μm and a sphericity of 81%.

[0048] Example 3: (1) High-purity sodium aluminate solid (Al2O3 content 41%, Na2O content 30%, purity 99.9%) was slurried with high-purity water (resistance greater than 130,000 Ω) as solvent, and the Al2O3 concentration of the sodium aluminate solution was adjusted to 90 g / L. After filtration, sodium aluminate solution was obtained.

[0049] (2) Using food-grade high-purity CO2 (purity 99.99%) as raw material, and air after three-stage filtration as CO2 diluent, the mixture is mixed to obtain CO2 gas with a concentration of 40%.

[0050] (3) Add high-purity aluminum hydroxide seed crystals obtained by carbon fractionation to 1L of sodium aluminate solution at a concentration of 300g / L. The particle size D 50 The sample was 100 μm thick and 99.9% pure. It was then subjected to carbonation neutralization and decomposition by introducing 40% CO2. The stirring was started at 200 r / m, the decomposition temperature was 90℃, and the decomposition time was 1 h to obtain aluminum hydroxide.

[0051] (4) The obtained aluminum hydroxide is added back as a seed crystal to a new sodium aluminate solution for carbonation, neutralization and decomposition;

[0052] (5) Repeat step (4) 6 times, separate and wash, to obtain high-purity spherical aluminum hydroxide with a particle size D. 50 It has a diameter of 136 μm and a sphericity of 87%.

[0053] Example 4: Unlike Example 1, the particle size D of the modified Bayer process aluminum hydroxide seed crystals in step (3) is different. 50 The particle size was 70 μm, and high-purity spherical aluminum hydroxide was finally obtained, with a particle size D. 50 It has a diameter of 97 μm and a sphericity of 89%.

[0054] Example 5: Unlike Example 1, the particle size D of the modified Bayer process aluminum hydroxide seed crystals in step (3) is different. 50 The particle size was 100 μm, and high-purity spherical aluminum hydroxide was finally obtained, with a particle size D. 50 It has a diameter of 143 μm and a sphericity of 83%.

[0055] Example 6: Unlike Example 1, in step (3), modified Bayer process aluminum hydroxide seed crystals were added to 1L of sodium aluminate solution at a concentration of 200g / L, ultimately yielding high-purity spherical aluminum hydroxide with a particle size D.50 It has a diameter of 126 μm and a sphericity of 91%.

[0056] Example 7: Unlike Example 1, in step (3), modified Bayer process aluminum hydroxide seed crystals were added to 1L of sodium aluminate solution at a concentration of 400g / L, ultimately yielding high-purity spherical aluminum hydroxide with a particle size D. 50 It has a diameter of 114 μm and a sphericity of 82%.

[0057] Example 8: Unlike Example 1, the decomposition temperature in step (3) is 70°C, ultimately yielding high-purity spherical aluminum hydroxide with a particle size D. 50 It has a diameter of 133 μm and a sphericity of 79%.

[0058] Example 9: Unlike Example 1, the decomposition temperature in step (3) is 100℃, ultimately yielding high-purity spherical aluminum hydroxide with a particle size D. 50 It has a diameter of 125 μm and a sphericity of 90%.

[0059] Example 10: Unlike Example 1, the decomposition was repeated 4 times in step (5), ultimately yielding high-purity spherical aluminum hydroxide with a particle size D. 50 It has a diameter of 117 μm and a sphericity of 86%.

[0060] Example 11: Unlike Example 1, the decomposition was repeated 10 times in step (5), ultimately yielding high-purity spherical aluminum hydroxide with a particle size D. 50 It has a diameter of 137 μm and a sphericity of 90%.

[0061] Example 12: Unlike Example 1, in step (1), the concentration of Al2O3 in the sodium aluminate solution was adjusted to 70 g / L, ultimately yielding high-purity spherical aluminum hydroxide with a particle size D. 50 The particle size is 124 μm, and the sphericity is 89%. Example 13: Unlike Example 1, in step (1), the concentration of Al2O3 in the sodium aluminate solution was adjusted to 120 g / L, and high-purity spherical aluminum hydroxide was finally obtained, with a particle size D 50 The particle size was 129 μm and the sphericity was 85%. Example 14: The high-purity spherical aluminum hydroxide obtained in Example 1 was subjected to hydrothermal treatment at 200°C for 2 hours, filtered, washed, dried, and calcined at 1200°C to obtain high-purity alumina microspheres with a purity of 99.99% and a sphericity of 92%.

[0062] Comparative Example 1: (1) High-purity sodium aluminate solid (Al2O3 content 41%, Na2O content 30%, purity 99.9%) was slurried with high-purity water (resistance greater than 130,000 Ω) as solvent, and the Al2O3 concentration of the sodium aluminate solution was adjusted to 90 g / L. After filtration, sodium aluminate solution was obtained.

[0063] (2) Using food-grade high-purity CO2 (purity 99.99%) as raw material, and air after three-stage filtration as CO2 diluent, the mixture is mixed to obtain CO2 gas with a concentration of 35%.

[0064] (3) A 35% CO2 solution was passed into a sodium aluminate solution for carbonation neutralization and decomposition. The stirring was started at 200 r / m, the decomposition temperature was 90℃, and the decomposition time was 1 h to obtain aluminum hydroxide with a particle size D. 50 It has a diameter of 74 μm, is not a spherical crystal, and consists of columnar, divergent aluminum hydroxide particles (see...). Figure 2 The sphericity is 0%.

[0065] Comparative Example 2: Unlike Example 1, the particle size D of the modified Bayer process aluminum hydroxide seed crystals in step (3) is different. 50 The particle size was 20 μm, resulting in irregular aluminum hydroxide aggregates with a particle size D. 50 It has a diameter of 134 μm and a sphericity of 0%.

[0066] Comparative Example 3: (1) High-purity sodium aluminate solid (Al2O3 content 41%, Na2O content 30%, purity 99.9%) was slurried with high-purity water (resistance greater than 130,000 Ω) as solvent, and the Al2O3 concentration of the sodium aluminate solution was adjusted to 90 g / L. After filtration, sodium aluminate solution was obtained.

[0067] (2) Modified Bayer process aluminum hydroxide seed crystals were added to 1L of sodium aluminate solution at a concentration of 300g / L, with a particle size D. 50 With a particle size of 80 μm and a purity of 99.9%, aluminum hydroxide was decomposed by stirring at 200 rpm for 1 hour at a temperature of 90 °C. The particle size D was 80 μm. 50 It has a value of 41 μm and a sphericity of 0%.

[0068] In all embodiments and comparative examples, the sphericity was calculated as follows: the sphericity of the particles was tested and characterized using a scanning electron microscope (SEM) and IPP software; the particle size was measured using a Mastersizer 3000 laser particle size analyzer; and the purity was measured using an ICP purity analyzer.

[0069] Table 1. Particle size, sphericity, and purity of high-purity spherical aluminum hydroxide.

[0070]

[0071] Table 2. Impurity content of high-purity spherical alumina in Example 14

[0072]

[0073] Analysis of the data from Examples 1, 2, and 3 in Table 1 shows that modified Bayer process high-purity aluminum hydroxide seed material is the optimal choice. In the experiment, due to the different processes, modified Bayer process high-purity aluminum hydroxide, aluminum alkoxide process high-purity aluminum hydroxide, and carbon fractionation process high-purity aluminum hydroxide have different structures and morphologies. Modified Bayer process high-purity aluminum hydroxide particles have relatively smooth crystal morphology and good sphericity of cyclic decomposition particles. Aluminum alkoxide process high-purity aluminum hydroxide is loose and irregular, and the sphericity of cyclic decomposition particles is poor. Carbon fractionation process high-purity aluminum hydroxide particles have columnar growth and large surface defects, and the sphericity of particles after 6 cycles of decomposition is generally poor.

[0074] Analysis of the data from Examples 1, 4, and 5 in Table 1 shows that the optimal seed particle size is 80 μm. Under the same decomposition conditions, the seed particle size affects the sphericity of the decomposition product. Finer particle size results in higher decomposition activity and faster release of aluminum hydroxide, which is not conducive to perfecting the sphericity of the particles. Conversely, larger seed particle size results in lower decomposition activity and is not conducive to the uniform growth of spherical particles.

[0075] Analysis of the data from Examples 1, 6, and 7 in Table 1 shows that the optimal amount of seed crystals added is 300 g / L. Under the same decomposition conditions, the amount of seed crystals added affects the sphericity of the product. When the solid content of the seed crystals is low, the supersaturation of the decomposition is low, and the growth of spherical aluminum hydroxide is slow. When the solid content of the seed crystals is high, the decomposition is fast, but at the same time, under stirring conditions, the wear between particles causes the particle size to decrease.

[0076] Analysis of the data from Examples 1, 8, and 9 in Table 1 shows that the optimal decomposition temperature is 90℃. The decomposition temperature affects the sphericity of the product. If the temperature is too low, the decomposition rate is fast and the nucleation amount is large, which is not conducive to the growth of coarse spherical alumina particles. If the temperature is too high, the decomposition is slow and not conducive to particle growth.

[0077] Analysis of the data from Examples 1, 10, and 11 in Table 1 shows that the optimal number of cycles is 6. The number of decomposition cycles has a significant impact on the sphericity of the product. If the number of cycles is too low, the surface growth of aluminum hydroxide will be incomplete, resulting in poor sphericity. If the number of cycles is too high, the wear between aluminum hydroxide particles will be severe, which is not conducive to particle growth. At the same time, if the number of cycles is too high, the production cost will increase, resulting in poor economic efficiency.

[0078] Analysis of the data from Examples 1, 12, and 13 in Table 1 shows that the optimal Al2O3 content of sodium aluminate is 90 g / L. The supersaturation curve of the sodium aluminate solution indicates that both excessively high and excessively low Al2O3 concentrations in the sodium aluminate solution will increase the stability of the solution, which is not conducive to improving the decomposition rate and will affect the growth of spherical aluminum hydroxide particles.

[0079] Analysis of the data from Example 1 and Comparative Example 1 in Table 1 shows that the sphericity of aluminum hydroxide obtained by direct carbonation and neutralization without adding seed crystals is 0%. Carbonation and decomposition without adding seed crystals will cause a large number of explosive nucleation, rapid growth of granular particles, severe surface defects of particles, and no sphericity.

[0080] Analysis of the data from Example 1 and Comparative Example 2 in Table 1 shows that when the seed particle size is 20 μm, the sphericity of the obtained aluminum hydroxide is 0%. If the seed particle size is too fine and the activity is too high, it will trigger a large number of secondary nucleation, which is not conducive to particle growth. Small particles grow in a dispersed manner, resulting in poor particle sphericity.

[0081] like Figure 1 As shown in the SEM image of the spherical aluminum hydroxide obtained in Example 1, the aluminum hydroxide obtained in Example 1 has a very smooth and flat surface and a regular spherical shape. Under the conditions of Example 1, the decomposition rate, nucleation amount and seed particle growth requirements are well matched, satisfying the slow spherical growth of seed particles, and the particle size and morphology of the decomposition product are relatively good.

[0082] Analysis of the data from Example 14 in Table 2 shows that the impurity content of the obtained high-purity alumina microspheres is significantly reduced. The main impurity of the spherical aluminum hydroxide obtained in Example 1 is Na2O, which is caused by the decomposition process in the alkaline system. Na2O exists mainly in the form of attached alkali and intercrystalline alkali. The hydrothermal method can effectively remove Na2O through lattice rearrangement, while the spherical crystal morphology remains unchanged. This lays the foundation for the production of high-purity alumina. Then, high-purity spherical alumina products are obtained by calcination at 1200℃.

[0083] like Figure 2 As shown in the SEM image of aluminum hydroxide obtained in Comparative Example 1, the surface of aluminum hydroxide obtained in Comparative Example 1 is very uneven and is not a regular sphere, but rather columnar and divergent aluminum hydroxide particles.

[0084] Analysis of the data from Comparative Examples 1 and 3 shows that aluminum hydroxide obtained without CO2 introduction and without carbonation decomposition is a fine, irregular particle product. Because CO2 is not introduced for neutralization and decomposition, the decomposition reaction is slow and the amount of nucleation is small, which is not conducive to particle growth. At the same time, under rapid stirring at 200 r / m, the small particles formed by secondary nucleation will form a bimodal particle size distribution and have poor particle morphology.

[0085] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0086] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for producing high-purity spherical aluminum hydroxide, characterized by, The method comprises the following steps: (1) adding aluminum hydroxide seeds into a sodium aluminate solution, and performing carbonation neutralization and decomposition by passing in CO2 to obtain aluminum hydroxide; (2) adding the obtained aluminum hydroxide as seeds into a new sodium aluminate solution to perform carbonation neutralization and decomposition; (3) repeating step (2) for 4-10 times to perform multiple cycles of carbonation neutralization and decomposition, and separating and washing to obtain high-purity spherical aluminum hydroxide; The particle size D of the aluminum hydroxide seed crystals 50 The value is 70-100μm.

2. The production method according to claim 1, characterized by, The aluminum hydroxide seeds are high-purity aluminum hydroxide seeds with a purity of 99.9%, and the high-purity aluminum hydroxide seeds are selected from alcohol aluminum method high-purity aluminum hydroxide, modified Bayer method high-purity aluminum hydroxide, carbon fraction method high-purity aluminum hydroxide, seed fraction method high-purity aluminum hydroxide, and ammonium salt method high-purity aluminum hydroxide.

3. The preparation method according to claim 2, characterized in that, The aluminum hydroxide seeds are selected from modified Bayer method high-purity aluminum hydroxide.

4. The production method according to claim 3, characterized by, The addition amount of the aluminum hydroxide seeds is 200-400 g / L.

5. The preparation method according to claim 1, characterized in that, The carbonation neutralization and decomposition temperature is 70-100 ℃, and the time is 1 h.

6. The method of claim 1, wherein, The Al2O3 content of the sodium aluminate is 70-120 g / L.

7. The preparation method according to claim 1, characterized in that, The CO2 concentration is 30-40%.

8. The method of claim 1, wherein, The obtained high-purity spherical aluminum hydroxide has a sphericity of 80-95%, a particle size of 90-150 μm, and a purity of 99.9%.

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