A method for preparing micronized aluminum hydroxide using polycrystalline seed composites

Abstract

This application provides a method for preparing micronized aluminum hydroxide using a multi-seed composite process, belonging to the field of aluminum hydroxide preparation. The method includes: adding micronized aluminum hydroxide seed crystals and boehmite seed crystals to a supersaturated sodium aluminate solution with a set caustic ratio and a set Al2O3 concentration to carry out a decomposition reaction, obtaining a mixed slurry; performing solid-liquid separation on the mixed slurry to obtain a filter cake; and washing and drying the filter cake to obtain micronized aluminum hydroxide. This application, by simultaneously adding micronized aluminum hydroxide seed crystals and boehmite seed crystals to a sodium aluminate solution, utilizes the differences in crystal form and reactivity between the different seed crystals to inhibit crystal agglomeration, preparing a micronized aluminum hydroxide product with uniform particle size, good dispersibility, and no large particles. The particle size D50 of the micronized aluminum hydroxide is 1.5μm~2.5μm, the D90 is 3.5μm~4.0μm, and the content of particles larger than 10μm is ≤0.1%.

Description

Technical Field

[0001] This application relates to the field of aluminum hydroxide preparation technology, and in particular to a method for preparing micronized aluminum hydroxide using a multi-crystal composite. Background Technology

[0002] Micronized aluminum hydroxide is an important inorganic functional material with advantages such as high whiteness, low oil absorption, excellent flame retardancy, and good heat resistance. It is widely used in cables, insulators, flame-retardant fillers, catalyst carriers, ceramic materials, toothpaste abrasives, paper fillers, and high-grade coatings. With the rapid development of industries such as polymer materials, electronics, and rail transportation, the demand for micronized aluminum hydroxide is increasing, especially for products with concentrated particle size distribution, good dispersibility, and no agglomeration.

[0003] The main industrial methods for preparing micronized aluminum hydroxide include seed decomposition, carbon fractionation, and sol-gel methods. Among these, seed decomposition involves adding seed crystals to a supersaturated sodium aluminate solution. By controlling process parameters such as decomposition temperature, time, and sodium aluminate concentration, aluminate ions in the sodium aluminate solution precipitate as aluminum hydroxide. This method has advantages such as mature technology, low cost, and suitability for large-scale production. However, traditional seed decomposition methods typically add only a single seed crystal (such as micronized aluminum hydroxide seed crystals) for decomposition. During the decomposition process, aluminate ions continuously precipitate on the seed crystal surface, and the aluminum hydroxide grains gradually grow. Because the single seed crystal has the same crystal form, the growth rate of the grains in different directions is relatively small, easily leading to agglomeration and overlap between grains, forming large-sized hard agglomerates. This agglomeration not only affects the dispersibility of micronized aluminum hydroxide but also leads to a wider particle size distribution and a large number of large particles, thereby reducing the product's application performance. To address these issues, researchers have attempted methods such as adding dispersants, controlling supersaturation during decomposition, and using ultrasound-assisted decomposition. However, these methods suffer from drawbacks including complex processes, high costs, and the potential introduction of impurities. Therefore, overcoming the shortcomings of existing single-crystal decomposition methods for preparing micronized aluminum hydroxide, such as easy crystal agglomeration, wide particle size distribution, and high content of large particles, is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] This application provides a method for preparing micronized aluminum hydroxide using a multi-species composite method, which overcomes the technical problems of easy grain agglomeration, wide particle size distribution, and high content of large particles in the preparation of micronized aluminum hydroxide by single-species fractional decomposition in the prior art.

[0005] This application provides a method for preparing micronized aluminum hydroxide using a multi-seed composite process, the method comprising: Micronized aluminum hydroxide seed crystals and pseudoboehmite seed crystals are added to a supersaturated sodium aluminate solution with a set caustic ratio and a set Al2O3 concentration to carry out a decomposition reaction and obtain a mixed slurry; the mass ratio of the micronized aluminum hydroxide seed crystals to the pseudoboehmite seed crystals is (1~2):1. The mixture slurry is subjected to solid-liquid separation to obtain filter cake; The filter cake is washed and dried to obtain micronized aluminum hydroxide.

[0006] Optionally, the set caustic ratio is 1.05 to 1.75.

[0007] Optionally, the Al2O3 concentration is set to 120 g / L to 160 g / L.

[0008] Optionally, the particle size D50 of the micronized aluminum hydroxide seed crystals is 1 μm to 3 μm.

[0009] Optionally, the particle size D50 of the pseudo-boehmite seed crystals is 1μm to 3μm.

[0010] Optionally, the mass concentration of the micronized aluminum hydroxide in the slurry of the micronized aluminum hydroxide seed crystals is 80 g / L to 120 g / L; The mass concentration of boehmite in the slurry of the boehmite seed crystals is 80 g / L to 120 g / L. The total added volume of the slurry of the micronized aluminum hydroxide seed crystals and the slurry of the pseudoboehmite seed crystals is 1% to 3% of the volume of the supersaturated sodium aluminate solution.

[0011] Optionally, the mass ratio of the micronized aluminum hydroxide seed crystals to the pseudoboehmite seed crystals is 1:1 or 2:1.

[0012] Optionally, the decomposition reaction includes the following parameters: decomposition temperature of 60℃~80℃, decomposition time of 24h~48h, and stirring speed of 100rpm~300rpm.

[0013] Optionally, the drying temperature is 100℃~120℃, and the drying time is 12h~24h.

[0014] Optionally, the micronized aluminum hydroxide meets the following properties: particle size D50 is 1.5μm to 2.5μm, D90 is 3.5μm to 4.0μm, and the content of particles with a particle size greater than 10μm is ≤0.1%.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing micronized aluminum hydroxide using a multi-seed composite method. Micronized aluminum hydroxide seed crystals and boehmite seed crystals are simultaneously added to a supersaturated sodium aluminate solution with a set caustic ratio and a set Al₂O₃ concentration, and the mass ratio of micronized aluminum hydroxide seed crystals to boehmite seed crystals is controlled at (1~2):1. Since micronized aluminum hydroxide seed crystals and boehmite seed crystals are two different crystal types with different crystal structures and surface properties, the aluminate ions exhibit different crystallization growth directions and morphologies on the surfaces of different seed crystals during the decomposition reaction. This makes it difficult for aluminum hydroxide grains grown with different seed crystals as nuclei to overlap and agglomerate, thereby effectively suppressing grain agglomeration. Meanwhile, the reactivity of boehmite seed crystals is higher than that of micronized aluminum hydroxide seed crystals, with an earlier decomposition peak, while the decomposition peak of micronized aluminum hydroxide seed crystals is later. This results in staggered precipitation: boehmite seed crystals induce aluminum hydroxide precipitation first in the early stages of decomposition, while micronized aluminum hydroxide seed crystals enter their decomposition peak after a period of time. At this point, the concentration of aluminate ions in the solution has decreased, thus inhibiting the continued growth of aluminum hydroxide grains previously grown using boehmite seed crystals as nuclei, preventing excessive grain growth and the formation of large particles. Through the synergistic effect of these two seed crystals, this application, after solid-liquid separation, washing, and drying following the decomposition reaction, ultimately obtains a micronized aluminum hydroxide product with uniform particle size, good dispersibility, and no large particles, thereby solving the technical problems of grain agglomeration, wide product particle size distribution, and high content of large particles in the prior art. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is an SEM surface image of the micronized aluminum hydroxide provided in Example 1 of this application; Figure 2 This is a particle size distribution map of micronized aluminum hydroxide provided in Example 1 of this application; Figure 3 This is an SEM surface image of the micronized aluminum hydroxide provided in Example 2 of this application; Figure 4 This is the particle size distribution map of micronized aluminum hydroxide provided in Example 2 of this application; Figure 5SEM surface image of micronized aluminum hydroxide provided in Comparative Example 1 of this application; Figure 6 The particle size distribution spectrum of micronized aluminum hydroxide provided in Comparative Example 1 of this application; Figure 7 This is a SEM surface image of micronized aluminum hydroxide provided in Comparative Example 2 of this application; Figure 8 The particle size distribution map of micronized aluminum hydroxide provided in Comparative Example 2 of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0021] This application, based on extensive experimental research, has discovered that simultaneously adding two or more different crystal seed types (e.g., micronized aluminum hydroxide seed and boehmite seed) to a sodium aluminate solution can effectively inhibit the agglomeration of micronized aluminum hydroxide grains. The basic principle is that different crystal seed types have different crystal structures and surface properties. During decomposition, the crystallization growth direction and morphology of aluminate ions differ on the surfaces of different seed types. Therefore, aluminum hydroxide grains grown using different seed types as nuclei are less prone to overlapping and agglomeration. Furthermore, different seed types have different reactivity, and their decomposition peak occurs at different times. The highly reactive boehmite seed decomposes rapidly in the initial stage of decomposition, inducing aluminum hydroxide precipitation. After a period of decomposition, the micronized aluminum hydroxide seed enters its decomposition peak. At this time, the concentration of aluminate ions in the solution decreases, and the growth of the micronized aluminum hydroxide nuclei inhibits the continued growth of aluminum hydroxide grains previously grown using boehmite seed nuclei, thereby further inhibiting agglomeration and the formation of large particles.

[0022] Based on the above findings, this application provides a method for preparing micronized aluminum hydroxide using a multi-seed composite process, the method comprising: S1. Add micronized aluminum hydroxide seed crystals and pseudoboehmite seed crystals to a supersaturated sodium aluminate solution with a set caustic ratio and a set Al2O3 concentration to carry out a decomposition reaction and obtain a mixed slurry; the mass ratio of micronized aluminum hydroxide seed crystals to pseudoboehmite seed crystals is (1~2):1. S2. The mixed slurry is subjected to solid-liquid separation to obtain filter cake; S3. Wash and dry the filter cake to obtain micronized aluminum hydroxide.

[0023] It should be noted that step S1 is the core reaction stage of the entire method. First, by controlling the caustic ratio of the sodium aluminate solution and the Al2O3 concentration, a mother liquor environment with suitable supersaturation and controllable decomposition kinetics is constructed, providing thermodynamic conditions for the uniform precipitation of aluminum hydroxide crystals. Second, micronized aluminum hydroxide seed crystals and boehmite seed crystals are simultaneously added to this supersaturated solution, with their mass ratio controlled at (1~2):1 (i.e., micronized aluminum hydroxide seed crystals are the majority). This composite seed addition method utilizes the differences in crystal structure and surface characteristics between the two types of seed crystals: boehmite seed crystals have high activity and an early decomposition peak, enabling them to induce the precipitation of aluminate ions on their surface first; while micronized aluminum hydroxide seed crystals have relatively low activity and a late decomposition peak, playing a dominant role in the later stages of decomposition. This staggered crystallization mechanism effectively avoids the overlapping and agglomeration caused by the synchronous growth of grains in all directions during the decomposition of a single seed crystal. Meanwhile, the design with a higher proportion of micronized aluminum hydroxide seed crystals (1-2 times) ensures that the main crystal form of the product remains micronized aluminum hydroxide, and suppresses the problem of increased product particle size caused by an excessively high proportion of boehmite (e.g., 1:2). Finally, this step generates a mixed slurry containing aluminum hydroxide crystals through a decomposition reaction.

[0024] Step S2 achieves solid-liquid separation, separating the generated micronized aluminum hydroxide solid particles from the sodium aluminate mother liquor. After the decomposition reaction, the slurry contains not only the target product, micronized aluminum hydroxide, but also a large amount of unreacted sodium aluminate, by-product sodium carbonate, and dissolved impurity ions. Through solid-liquid separation (such as filtration or centrifugation), the mother liquor can be efficiently recovered (it can be adjusted and recycled to prepare a new supersaturated sodium aluminate solution), while also providing filter cake for subsequent washing. This step is crucial for ensuring product purity and process economy, preventing impurities from remaining on or inside the product during the drying stage.

[0025] Step S3 comprises two operations: washing and drying. Washing aims to further remove sodium aluminate, sodium hydroxide, and other soluble impurities adhering to the filter cake surface, preventing these impurities from forming clumps or affecting the product's whiteness, oil absorption, and other application properties after drying. Washing typically uses deionized water or hot water until the washing solution is neutral or undetectable alkalinity. The drying process (e.g., drying at 100–120°C) removes free moisture from the filter cake, dispersing the sodium hydroxide particles and maintaining their original morphology. Excessive drying temperature or time may lead to hard agglomeration or crystal transformation of the particles; however, the mild drying conditions employed in this method, combined with the agglomeration-inhibiting decomposition process in S1, ultimately yield a well-dispersed, non-agglomerated micronized aluminum hydroxide product. Furthermore, the dried product can be further pulverized and sieved as needed to meet the particle size distribution requirements of different applications.

[0026] In some implementations, the caustic ratio is set to 1.05 to 1.75.

[0027] In some implementations, the Al2O3 concentration is set to 120 g / L to 160 g / L.

[0028] By controlling the caustic ratio of the supersaturated sodium aluminate solution to 1.05–1.75 and the Al₂O₃ concentration to 120–160 g / L, a mother liquor system with suitable decomposition kinetics can be constructed. Within this range, the solution has a moderate degree of supersaturation, ensuring sufficient driving force for the precipitation of aluminate ions on the seed crystal surface while avoiding explosive nucleation caused by excessive supersaturation. This provides a stable liquid phase environment for uniform and controllable crystal growth in subsequent multi-seed composite decomposition. For example, the caustic ratio can be set to 1.05, 1.35, 1.38, 1.41, 1.44, 1.47, 1.50, 1.53, 1.55, 1.75, etc., and the Al₂O₃ concentration can be set to 120 g / L, 125 g / L, 130 g / L, 135 g / L, 140 g / L, 145 g / L, 150 g / L, 160 g / L, etc.

[0029] In some embodiments, the particle size D50 of the micronized aluminum hydroxide seed crystals is 1 μm to 3 μm.

[0030] In some embodiments, the particle size D50 of the pseudo-boehmite seed crystals is 1 μm to 3 μm.

[0031] The particle size D50 of both micronized aluminum hydroxide seed crystals and pseudoboehmite seed crystals is 1μm to 3μm. Seed crystals within this size range have a large specific surface area, providing ample crystal growth sites. Simultaneously, this matches the final particle size of the target product (D50 1.5–2.5μm), facilitating the epitaxial growth of newly generated aluminum hydroxide on the seed crystal surface during decomposition, rather than generating new crystal nuclei, thus ensuring uniform and controllable product particle size. For example, the particle size D50 of micronized aluminum hydroxide seed crystals can be 1μm, 1.3μm, 1.6μm, 1.9μm, 2.2μm, 2.5μm, 2.8μm, 3μm, etc. The particle size D50 of pseudoboehmite seed crystals can be 1μm, 1.3μm, 1.6μm, 1.9μm, 2.2μm, 2.5μm, 2.8μm, 3μm, etc.

[0032] In some embodiments, the mass concentration of the micronized aluminum hydroxide in the micronized aluminum hydroxide seed slurry is 80 g / L to 120 g / L; The mass concentration of boehmite in the boehmite seed slurry is 80 g / L to 120 g / L. The total added volume of the slurry of the micronized aluminum hydroxide seed crystals and the slurry of the pseudoboehmite seed crystals is 1% to 3% of the volume of the supersaturated sodium aluminate solution.

[0033] The total volume of the micronized aluminum hydroxide seed slurry and the pseudoboehmite seed slurry added is limited to 1% to 3% of the volume of the supersaturated sodium aluminate solution. This addition amount provides a sufficient crystallization interface for the decomposition reaction, ensuring efficient precipitation of aluminate ions; at the same time, it avoids the rapid depletion of solution supersaturation and the resulting fine particle size due to excessive seed crystals, allowing the decomposition process to proceed smoothly and facilitating the acquisition of micronized aluminum hydroxide products with concentrated particle size and good dispersibility. For example, the total volume of the micronized aluminum hydroxide seed slurry and the pseudoboehmite seed slurry added is 1%, 1.25%, 1.5%, 1.75%, 2%, 2.25%, 2.5%, 3%, etc., of the supersaturated sodium aluminate solution volume.

[0034] In some embodiments, the mass ratio of micronized aluminum hydroxide seed crystals to pseudoboehmite seed crystals is 1:1 or 2:1.

[0035] The mass ratio of micronized aluminum hydroxide seed crystals to boehmite seed crystals is 1:1 or 2:1. When a 2:1 ratio is used, the micronized aluminum hydroxide seed crystals constitute the majority, ensuring the consistency of the main crystal form of the product. Simultaneously, a small amount of highly active boehmite seed crystals induces precipitation in the early stages of decomposition, creating a staggered effect with the later decomposition peak of the micronized aluminum hydroxide seed crystals, effectively inhibiting grain agglomeration and excessive growth. When a 1:1 ratio is used, the synergistic effect of the two seed crystals is more balanced, also yielding a product with a narrow particle size distribution and no large particles.

[0036] In some embodiments, the decomposition reaction includes the following parameters: decomposition temperature of 60°C to 80°C, decomposition time of 24h to 48h, and stirring speed of 100rpm to 300rpm.

[0037] The decomposition temperature is controlled between 60℃ and 80℃, which ensures a moderate decomposition reaction rate while inhibiting excessively rapid grain growth at high temperatures or an increase in fine grains at low temperatures. The decomposition time is 24h to 48h, providing sufficient time for aluminate ions to fully precipitate and uniformly grow on the seed crystal surface, ensuring that the decomposition rate meets industrial requirements. The stirring speed is 100rpm to 300rpm, which allows the two types of seed crystals to be uniformly dispersed in the sodium aluminate solution, avoiding seed crystal sedimentation, promoting mass transfer of solute to the seed crystal surface, and preventing adhesion and agglomeration between grains. For example, the decomposition temperature can be 60℃, 63℃, 66℃, 69℃, 72℃, 75℃, 78℃, 80℃, etc. The decomposition time can be 24h, 27h, 30h, 33h, 36h, 39h, 42h, 48h, etc. The stirring speed can be 100rpm, 130rpm, 160rpm, 190rpm, 220rpm, 250rpm, 280rpm, 300rpm, etc.

[0038] In some embodiments, the drying temperature is 100°C to 120°C, and the drying time is 12 hours to 24 hours.

[0039] The drying temperature is controlled at 100℃~120℃, and the drying time is 12h~24h. This effectively removes moisture from the filter cake while avoiding particle agglomeration or crystal transformation caused by excessively high temperature or time, thus maintaining the product's dispersibility and morphological integrity, and obtaining free-flowing micronized aluminum hydroxide product. For example, the drying temperature can be 100℃, 103℃, 106℃, 109℃, 112℃, 115℃, 118℃, 120℃, etc., and the drying time can be 12h, 14h, 16h, 18h, 20h, 22h, 23h, 24h, etc.

[0040] In some embodiments, the micronized aluminum hydroxide meets the following properties: particle size D50 is 1.5μm to 2.5μm, D90 is 3.5μm to 4.0μm, and the content of particles with a particle size greater than 10μm is ≤0.1%.

[0041] This application utilizes the differences in crystal form and reactivity between different seed crystals to simultaneously add micronized aluminum hydroxide seed crystals and pseudoboehmite seed crystals to a sodium aluminate solution, thereby inhibiting crystal agglomeration and preparing a micronized aluminum hydroxide product with uniform particle size, good dispersibility, and no large particles. For example, the particle size D50 of the micronized aluminum hydroxide can be 1.5μm, 1.7μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, 2.4μm, 2.5μm, etc. The D90 can be 3.5μm, 3.6μm, 3.7μm, 3.8μm, 4.0μm, etc. The content of particles larger than 10μm can be 0%, 0.02%, 0.04%, 0.05%, 0.06%, 0.07%, 0.09%, 0.1%, etc.

[0042] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0043] Example 1: Decomposition of 1:1 composite of micronized aluminum hydroxide and pseudoboehmite seed crystals This embodiment provides a method for preparing micronized aluminum hydroxide using a multi-seed composite process, the method comprising the following steps: Preparation of supersaturated sodium aluminate solution: Add industrial aluminum hydroxide and sodium hydroxide to deionized water, heat to 100℃ to dissolve, and obtain supersaturated sodium aluminate solution after clarification and filtration. Adjust the caustic ratio αk of the solution to 1.45 and the Al2O3 concentration to 140 g / L.

[0044] Seed preparation: Weigh the required amounts of micronized aluminum hydroxide powder and boehmite powder separately, add appropriate amounts of deionized water (or distilled water) to each, disperse evenly under stirring, and then bring each to the target volume to achieve a mass concentration of 100 g / L for both micronized aluminum hydroxide and boehmite, thus obtaining the corresponding seed slurry. Weigh the micronized aluminum hydroxide seed slurry (D50=2.0μm) and the boehmite seed slurry (D50=2.0μm) separately, with a mass ratio of 1:1. The total volume of the two seed slurries added is 2% of the volume of the supersaturated sodium aluminate solution. Add the mixed seed crystals to the sodium aluminate solution, control the decomposition temperature at 70℃, and the decomposition time at 36h, continuously stirring at a stirring speed of 200 rpm during the decomposition process.

[0045] Post-processing: After decomposition, the obtained slurry is filtered and washed, the filter cake is dried at 110℃ for 18 hours, and then pulverized and sieved to obtain micronized aluminum hydroxide product.

[0046] Example 2: Decomposition of micronized aluminum hydroxide and pseudoboehmite seed crystals in a 2:1 composite ratio This embodiment is based on the disclosure in Embodiment 1, with the following modifications: Seed preparation: Weigh out micronized aluminum hydroxide seed slurry (D50=2.0μm, mass concentration 100g / L) and boehmite seed slurry (D50=2.0μm, mass concentration 100g / L), respectively, with a mass ratio of 2:1. The total volume of the two seed crystals added is 2% of the volume of the sodium aluminate solution.

[0047] Comparative Example 1: Decomposition of a single micronized aluminum hydroxide seed crystal This comparative example is modified from the one disclosed in Example 1 as follows: Weigh out a small amount of aluminum hydroxide seed slurry (D50=2.0μm, mass concentration of 100g / L) and add it to a saturated sodium aluminate solution. The volume of the seed slurry added is 2% of the volume of the sodium aluminate solution.

[0048] Comparative Example 2: Decomposition of 1:2 composite of micronized aluminum hydroxide and pseudoboehmite seed crystals This comparative example is modified from the one disclosed in Example 1 as follows: Seed preparation: Weigh out micronized aluminum hydroxide seed slurry (D50=2.0μm, mass concentration 100g / L) and boehmite seed slurry (D50=2.0μm, mass concentration 100g / L) separately, with a mass ratio of 1:2. The total volume of the two seed slurries added is 2% of the volume of the sodium aluminate solution.

[0049] The surface morphology and particle size distribution of the micronized aluminum hydroxide samples obtained in Examples 1, 2, 1, and 2 were measured, and the results are as follows: Figures 1 to 8 As shown in Table 1, the surface morphology was observed using a Sigma 300 scanning electron microscope (SEM); the particle size distribution of the samples was analyzed using a Malvern particle size analyzer.

[0050] Table 1. Particle size distribution of the micronized aluminum hydroxide samples from the examples and comparative examples.

[0051] Figure 1 The surface morphology of the product obtained when the mass ratio of micronized aluminum hydroxide seed crystals to pseudoboehmite seed crystals is 1:1 is shown. As can be seen from the figures, compared to the product obtained from single-seed decomposition, the micronized aluminum hydroxide produced by bi-seed decomposition exhibits reduced agglomeration and smaller particle size. Figure 2 As shown in Table 1, the D50 (2.02 μm) of the micronized aluminum hydroxide sample in Example 1 is significantly lower than that of the micronized aluminum hydroxide sample in Comparative Example 1, and the D90 is reduced to one-fifth of that of the micronized aluminum hydroxide sample in Comparative Example 1. The particle size distribution is relatively concentrated, and no large particle peaks are observed.

[0052] Figure 3 The surface morphology of the product prepared with a mass ratio of micronized aluminum hydroxide seed crystals to pseudoboehmite seed crystals of 2:1 is shown. More micronized aluminum hydroxide seed crystals reduce the decomposition kinetics of the system, resulting in a more stable decomposition. As can be seen from the figures, the agglomerated particles are further reduced, and the particle size is further decreased. Figure 4 As shown in Table 1, the micronized aluminum hydroxide sample of Example 2 also did not show large particle peaks, exhibiting better dispersibility.

[0053] Figure 5 The surface morphology of the decomposition product of a single micronized aluminum hydroxide seed crystal is shown. It can be seen that in the micronized aluminum hydroxide sample of Comparative Example 1, severe agglomeration occurs between aluminum hydroxide grains, forming a large number of large agglomerates. This surface morphology results in a high specific surface area, leading to high oil absorption, which has an adverse effect on the use of downstream products. Figure 6 Table 1 shows the particle size distribution of the micronized aluminum hydroxide sample in Comparative Example 1. The micronized aluminum hydroxide sample has a wide particle size distribution range, with D50 = 2.3 μm. It can be clearly seen that there are still some large particles in the particle size range above 20 μm.

[0054] Figure 7 The surface morphology of the product prepared with a mass ratio of micronized aluminum hydroxide seed crystals to pseudoboehmite seed crystals of 1:2 is shown. Pseudoboehmite seed crystals are more reactive, and more pseudoboehmite seed crystals accelerate the reaction of the system. Although no agglomerated particles are produced, larger single crystals are generated. Figure 8 Table 1 shows that the D50 of the micronized aluminum hydroxide sample in Comparative Example 2 is close to 3 μm, which does not meet the product requirements.

[0055] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: (1) This application uses two different crystal types of seeds, namely micronized aluminum hydroxide seed and pseudoboehmite seed, to simultaneously add the seeds. By utilizing the differences in the crystal growth direction and growth morphology of the different seed types, the agglomeration phenomenon between aluminum hydroxide grains is effectively suppressed. The micronized aluminum hydroxide prepared has good dispersibility and no obvious agglomerates.

[0056] (2) This application utilizes the characteristics of high activity and early decomposition peak of boehmite seed crystals and relatively low activity and late decomposition peak of micronized aluminum hydroxide seed crystals to achieve “staggered” precipitation in the decomposition process, suppress excessive growth of crystals, and produce a narrow particle size distribution with no large particles.

[0057] (3) The method of this application is simple, requires no dispersant or additional equipment, is low in cost, and is easy to industrialize.

[0058] (4) Compared with the decomposition of single micronized aluminum hydroxide seed crystals, the micronized aluminum hydroxide product prepared in this application has a more uniform particle size, with a particle size D50 of 1.5μm to 2.5μm, a D90 of 3.5μm to 4.0μm, and a particle content of ≤0.1% with a particle size greater than 10μm.

[0059] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing micronized aluminum hydroxide using a multi-seed composite process, characterized in that, The method includes: Micronized aluminum hydroxide seed crystals and pseudoboehmite seed crystals are added to a supersaturated sodium aluminate solution with a set caustic ratio and a set Al2O3 concentration to carry out a decomposition reaction and obtain a mixed slurry; the mass ratio of the micronized aluminum hydroxide seed crystals to the pseudoboehmite seed crystals is (1~2):

1. The mixture slurry is subjected to solid-liquid separation to obtain filter cake; The filter cake is washed and dried to obtain micronized aluminum hydroxide.

2. The method according to claim 1, characterized in that, The set caustic ratio is 1.05 to 1.

75.

3. The method according to claim 1, characterized in that, The Al2O3 concentration was set to be 120 g / L to 160 g / L.

4. The method according to claim 1, characterized in that, The particle size D50 of the micronized aluminum hydroxide seed crystals is 1μm to 3μm.

5. The method according to claim 1, characterized in that, The particle size D50 of the pseudo-boehmite seed crystals is 1μm to 3μm.

6. The method according to claim 1, characterized in that, The mass concentration of aluminum hydroxide in the slurry of the aluminum hydroxide seed crystals is 80 g / L to 120 g / L. The mass concentration of boehmite in the slurry of the boehmite seed crystals is 80 g / L to 120 g / L. The total added volume of the slurry of the micronized aluminum hydroxide seed crystals and the slurry of the pseudoboehmite seed crystals is 1% to 3% of the volume of the supersaturated sodium aluminate solution.

7. The method according to claim 1, characterized in that, The mass ratio of the micronized aluminum hydroxide seed crystals to the pseudoboehmite seed crystals is 1:1 or 2:

1.

8. The method according to claim 1, characterized in that, The decomposition reaction includes the following parameters: decomposition temperature of 60℃~80℃, decomposition time of 24h~48h, and stirring speed of 100rpm~300rpm.

9. The method according to claim 1, characterized in that, The drying temperature is 100℃~120℃, and the drying time is 12h~24h.

10. The method according to claim 1, characterized in that, The micronized aluminum hydroxide meets the following properties: particle size D50 is 1.5μm~2.5μm, D90 is 3.5μm~4.0μm, and the content of particles with a particle size greater than 10μm is ≤0.1%.

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