High-purity aluminum hydroxide, preparation method and application thereof

Abstract

The application relates to high-purity aluminum hydroxide and a preparation method and application thereof, the product has high purity and excellent acid solubility; the method is prepared by cooperation of regulation of refined sodium aluminate solution, high-purity aluminum hydroxide seed induction and other links, and meets the strict requirements of raw materials for synthesis of aluminum alkyl hypophosphite; wherein, the concentration of aluminum oxide in the refined sodium aluminate solution and the caustic ratio are limited, the adding mode of the refined sodium aluminate solution is strictly controlled, high alkalinity induced impurity eutectoid is avoided, suitable supersaturation is maintained, the seed separation process is stabilized, the particles with developed pores are formed, and the acid dissolution reaction activity is improved; the high-purity aluminum hydroxide seed is used as a nucleation center to prepare uniformized crystal nucleus, effectively guides the ordered growth of crystals, inhibits secondary nucleation and disordered agglomeration, and reduces the adsorption and inclusions of sodium ions on the crystal surface; based on the high-purity aluminum hydroxide, the obtained aluminum alkyl hypophosphite flame retardant can meet the strict requirements of high-end application scenarios on halogen-free flame retardants.

Description

Technical Field

[0001] This application relates to the field of aluminum hydroxide preparation technology, and in particular to a high-purity aluminum hydroxide, its preparation method, and its application. Background Technology

[0002] Alkyl aluminum hypophosphite is a novel, highly efficient phosphorus-based halogen-free flame retardant with outstanding advantages such as excellent thermal stability, high flame retardant efficiency, and low smoke emission. It has been widely used in the flame retardant modification of engineering plastics such as polypropylene (PP), polyethylene (PE), polyamide (PA), and polybutylene terephthalate (PBT), as well as general polymer materials. In the synthesis of this type of flame retardant, high-purity aluminum hydroxide is the key aluminum source. Its chemical purity, acid solubility, and microstructure directly determine the reaction conversion rate, product purity, thermal decomposition temperature, and final flame retardant performance, making it a core factor affecting product quality and production costs.

[0003] Currently, the industrial preparation of aluminum hydroxide for the synthesis of alkyl hypophosphite mainly employs carbon fractionation or conventional seed fractionation processes. However, these methods have some limitations: On the one hand, while some readily soluble aluminum hydroxides have their reactivity enhanced through specific seed crystals or carbonization, their impurity content is high (e.g., sodium, iron, silicon, calcium, magnesium, etc.), making it difficult to meet the purity requirements (≥99.9%) of high-end flame retardant materials. On the other hand, although some high-purity aluminum hydroxides can achieve high purity through deep purification, the use of continuous seed fractionation and other densification crystallization processes results in excessively high crystallinity, dense structure, and low porosity, leading to insufficient acid solubility in organic acid systems (typically only 92%~96%), incomplete reaction, and residual unreacted aluminum sources, affecting product uniformity and thermal stability. Furthermore, traditional industrial aluminum hydroxides generally suffer from wide particle size distribution, irregular crystal forms, and high impurity content, making it difficult to achieve complete conversion during neutralization reactions with alkyl hypophosphite. Residual impurities not only reduce product purity, but may also catalyze the thermo-oxidative degradation of polymers during processing or use, significantly reducing the thermal decomposition temperature of alkyl aluminum hypophosphite and weakening its flame retardant properties.

[0004] In view of this, it is necessary to design a high-purity aluminum hydroxide, its preparation method, and its application to solve the above problems. Summary of the Invention

[0005] This application provides a high-purity aluminum hydroxide, its preparation method, and its application, in order to solve the current technical problem of achieving both high purity and high acid solubility.

[0006] In a first aspect, this application provides a high-purity aluminum hydroxide, wherein the acid solubility of the high-purity aluminum hydroxide is ≥99.99%; the purity of the high-purity aluminum hydroxide is ≥99.96%; and the particle size of the high-purity aluminum hydroxide is 40μm~60μm. The impurity content in the high-purity aluminum hydroxide, by mass percentage, meets the following requirements: Ca < 3 ppm, Fe < 1 ppm, Si < 10 ppm, Mg < 1 ppm, Ga < 10 ppm, Na < 350 ppm.

[0007] Secondly, this application provides a method for preparing the above-mentioned high-purity aluminum hydroxide, comprising the following steps: A refined sodium aluminate solution is provided, wherein the concentration of alumina in the refined sodium aluminate solution is 80 g / L to 150 g / L, and the caustic ratio of the refined sodium aluminate solution is α. K The value is between 1.30 and 1.60. A second refined sodium aluminate solution is provided, wherein the concentration of alumina in the second refined sodium aluminate solution is 80 g / L to 150 g / L, and the caustic ratio of the second refined sodium aluminate solution is α. K The value is between 1.30 and 1.60. The refined sodium aluminate solution and high-purity aluminum hydroxide seed crystals are mixed and decomposed to obtain seed slurry; The refined sodium aluminate solution was added to the seed slurry to carry out a seed decomposition reaction, yielding aluminum hydroxide solid-liquid product; and... The aluminum hydroxide solid-liquid mixture is subjected to solid-liquid separation, washing, and drying in sequence to obtain the high-purity aluminum hydroxide.

[0008] In some embodiments, the purity of the high-purity aluminum hydroxide seed crystals is ≥99.9%; and / or, The high-purity aluminum hydroxide seed crystals have a particle size of 1.5 μm to 3.5 μm; and / or, The mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals is 100:(1~3).

[0009] In some embodiments, the reaction temperature of the decomposition reaction is 55°C to 70°C; and / or, The decomposition reaction takes 12 to 36 hours.

[0010] In some embodiments, the volume ratio of the refined sodium aluminate solution II to the seed slurry is (30~40):1; and / or, The reaction temperature for the seed decomposition reaction is 63℃~75℃; and / or, The reaction time for the seed decomposition reaction is 10 h to 20 h; and / or, The refined sodium aluminate solution II is added to the seed slurry in equal volumes multiple times within 15h to 20h, with a time interval of 3h to 5h between two consecutive additions of the refined sodium aluminate solution II to the seed slurry.

[0011] In some embodiments, the preparation method of the first refined sodium aluminate solution or the second refined sodium aluminate solution includes the following steps: Industrial aluminum hydroxide and alkaline solution are mixed and redissolved to obtain a redissolved sodium aluminate solution. The redissolved sodium aluminate solution is mixed with a purifying agent and then subjected to purification and filtration in sequence to obtain a first sodium aluminate solution. Adjust the concentration of the first sodium aluminate solution to obtain a second sodium aluminate solution; and, The second sodium aluminate solution is subjected to fine filtration to obtain either the first refined sodium aluminate solution or the second refined sodium aluminate solution.

[0012] In some embodiments, the alkaline solution comprises a sodium hydroxide solution; and / or, The remelting treatment temperature is 95℃~115℃; and / or, The caustic ratio α of the redissolved sodium aluminate solution K The value is 1.30~1.60.

[0013] In some embodiments, the purifying agent includes any one or more of aluminum hydroxide hydrate, polyaluminum chloride, activated alumina, and calcium hydroxide; and / or, The purification process is performed at a temperature of 50℃~65℃; and / or, The purification process takes 45 to 90 minutes; and / or, The solid-liquid ratio of the purifying agent to the redissolved sodium aluminate solution is (3g~7g):1L.

[0014] In some embodiments, the washing reagent includes any one or more of high-purity water and ultrapure water; The temperature of the washing reagent is 80℃~90℃; The mass ratio of the reagent to the high-purity aluminum hydroxide is (7~10):1.

[0015] Thirdly, this application provides an application of the above-mentioned high-purity aluminum hydroxide and / or the high-purity aluminum hydroxide obtained by the above preparation method, wherein the high-purity aluminum hydroxide can be used in the preparation of alkyl aluminum hypophosphite.

[0016] The technical solutions provided in this application have the following advantages compared with the prior art: 1. The high-purity aluminum hydroxide provided in this application has the advantages of high purity, excellent acid solubility and controllable particle size distribution. It successfully solves the key problem of "difficulty in synergistic effect between high purity and high acid solubility" in the prior art, and provides a high-quality raw material basis for the green, efficient and large-scale preparation of high-performance phosphorus flame retardants.

[0017] 2. The method for preparing high-purity aluminum hydroxide provided in this application, through the synergistic effect of multiple steps including deep purification of heavy solution, precise control of refined sodium aluminate solution, induction of high-purity aluminum hydroxide seed crystals, and optimization of agglomeration conditions, successfully prepares small-crystal agglomerated, easily soluble high-purity aluminum hydroxide, possessing both high purity and high acid solubility, fully meeting the stringent requirements for raw materials in the synthesis of alkyl aluminum hypophosphite. The obtained product has a purity ≥99.96%, a particle size of 40μm~60μm, and an acid solubility of 99.99% or higher. Specifically, the alumina concentration in the refined sodium aluminate solution is limited to 80g / L~150g / L, and the caustic ratio α... K By controlling the alkalinity between 1.30 and 1.60, both high alkalinity and impurity co-precipitation are avoided, while maintaining a suitable supersaturation level to ensure the stability of the seeding process. This results in loosely structured, porous particles, enhancing reactivity. Using high-purity aluminum hydroxide seed crystals as nucleation centers effectively guides orderly crystal growth, inhibits spontaneous nucleation and disordered aggregation, leading to more uniform crystallization and significantly reducing sodium ion adsorption and encapsulation on crystal faces, thus reducing Na2O residue at the source. In summary, this method overcomes the technical bottleneck of traditional high-purity aluminum hydroxide, which struggles to simultaneously achieve both high purity and high acid solubility. It provides a green, controllable, and scalable process for preparing easily soluble high-purity aluminum hydroxide, laying a crucial raw material foundation for the high-quality production of high-end phosphorus-based halogen-free flame retardants.

[0018] 3. The application of high-purity aluminum hydroxide provided in this application, based on its high purity, high acid solubility, and uniform particle size distribution, exhibits excellent reactivity and stoichiometric controllability during the reaction with alkyl hypophosphite. This significantly improves the reaction conversion rate and reduces the generation of unreacted aluminum sources and byproducts. The alkyl hypophosphite flame retardant prepared from this raw material has advantages such as high thermal decomposition temperature, white color, and good batch-to-batch consistency. It not only effectively ensures the stability of high-purity aluminum hydroxide during high-temperature processing but also significantly improves the flame retardant efficiency, mechanical property retention rate, and overall processing safety of end materials such as engineering plastics, fully meeting the stringent requirements of high-end application scenarios for halogen-free flame retardants. Attached Figure Description

[0019] 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.

[0020] 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.

[0021] Figure 1A flowchart of a method for preparing high-purity aluminum hydroxide according to this application is shown; Figure 2 The following are electron microscope images of the high-purity aluminum hydroxide prepared in Example 1 of this application at different magnifications; Figure 3 The figure shows the acid solubility test results of aluminum hydroxide obtained in Comparative Example 2 and high-purity aluminum hydroxide prepared in Example 1 of this application. Detailed Implementation

[0022] 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.

[0023] Various embodiments of this application may exist in the form of a range. It should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of this application. Therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in this application, it means including any referenced number (fraction or integer) within the indicated range. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this application can be purchased commercially or prepared by existing methods. In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. In addition, in this application, the terms "comprising," "including," etc., mean "including but not limited to." In this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any actual relationship or order between these entities or operations. In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this application, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or multiple.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0025] This application provides a high-purity aluminum hydroxide, wherein the acid solubility of the high-purity aluminum hydroxide is ≥99.99%; the purity of the high-purity aluminum hydroxide is ≥99.96%; and the particle size of the high-purity aluminum hydroxide is 40μm~60μm. The impurity content in the high-purity aluminum hydroxide, by mass percentage, meets the following requirements: Ca < 3 ppm, Fe < 1 ppm, Si < 10 ppm, Mg < 1 ppm, Ga < 10 ppm, Na < 350 ppm.

[0026] The high-purity aluminum hydroxide provided in this application combines high purity, excellent acid solubility, and controllable particle size distribution, successfully solving the key problem of "difficulty in synergistically achieving high purity and high acid solubility" in the prior art, and providing a high-quality raw material basis for the green, efficient, and large-scale preparation of high-performance phosphorus-based flame retardants.

[0027] like Figure 1 As shown, based on a general inventive concept, this application provides a method for preparing the above-mentioned high-purity aluminum hydroxide, comprising the following steps: Step 1: Provide a refined sodium aluminate solution; the refined sodium aluminate solution includes refined sodium aluminate solution one and refined sodium aluminate solution two; the concentration of alumina in the refined sodium aluminate solution is 80 g / L~150 g / L, and the caustic ratio α of the refined sodium aluminate solution is... K The value is between 1.30 and 1.60. Step 2: Mix the refined sodium aluminate solution and high-purity aluminum hydroxide seed crystals to carry out a decomposition reaction to obtain seed slurry; Step 3: Pump the seed slurry into the decomposition tank; then add the refined sodium aluminate solution II to the seed slurry to carry out the seed decomposition reaction, and obtain aluminum hydroxide solid-liquid product; Step 4: Separate the aluminum hydroxide solid and liquid mixture sequentially, wash and dry it to obtain the high-purity aluminum hydroxide.

[0028] The method for preparing high-purity aluminum hydroxide provided in this application embodiment involves synergistically controlling the composition of the refined sodium aluminate solution (alumina concentration of 80 g / L to 150 g / L, caustic ratio α). K By employing high-purity aluminum hydroxide seed crystals (1.30~1.60 g / L) and optimizing the seed decomposition process, a synergistic improvement in product purity, acid solubility, and controllable particle size was achieved. Specifically, the introduction of high-purity aluminum hydroxide seed crystals as nucleation centers effectively guides directional crystal growth, inhibits spontaneous nucleation and disordered aggregation, making the crystallization process more uniform and controllable. Simultaneously, it significantly reduces the adsorption and encapsulation of sodium ions and other impurities on the crystal surface, reducing Na2O residue from the source and ensuring product purity. A deeply purified refined sodium aluminate solution is used, combined with solid-liquid separation and thorough washing, to efficiently remove residual sodium ions and other soluble impurities from the mother liquor, ensuring that the Na content in the final product is below 350 ppm and the overall purity reaches ≥99.96%. The alumina concentration in the refined sodium aluminate solution is controlled at 80 g / L~150 g / L, and the caustic ratio α... KBy controlling the alkalinity between 1.30 and 1.60, both the co-precipitation of impurities caused by high alkalinity and sufficient supersaturation to support stable and continuous seed decomposition are avoided. This promotes the formation of loosely structured aluminum hydroxide particles with suitable porosity, significantly improving the product's reactivity. In summary, the obtained aluminum hydroxide exhibits a small-crystal agglomerate structure with a particle size concentrated between 40 μm and 60 μm. It has a moderate specific surface area and well-developed internal channels. Its acid solubility in phosphoric acid or organic acid systems reaches 99.99%, and the dissolved solution is clear and transparent, without turbidity or residue, fully meeting the high reactivity requirements of raw materials for the synthesis of alkyl aluminum hypophosphite. This preparation method overcomes the technical bottleneck of traditional high-purity aluminum hydroxide, which struggles to simultaneously achieve both high purity and high acid solubility in quality control. Thus, it provides a readily soluble high-purity aluminum hydroxide suitable for the production of high-end phosphorus-based flame retardants, along with its green, controllable, and scalable preparation method.

[0029] As an optional implementation, in this embodiment of the application, the purity of the high-purity aluminum hydroxide seed crystals is ≥99.9%; the particle size of the high-purity aluminum hydroxide seed crystals is 1.5μm~3.5μm.

[0030] Thus, by strictly controlling the particle size of high-purity aluminum hydroxide seeds within the range of 1.5μm to 3.5μm, the nucleation density and aggregation behavior of aluminum hydroxide crystals during subsequent seed decomposition can be effectively regulated: if the particle size of high-purity aluminum hydroxide seeds is less than 1.5μm, it is easy to cause excessive nucleation and increase the amount of fine powder in the product; if the particle size of high-purity aluminum hydroxide seeds is greater than 3.5μm, it will result in insufficient induction ability and difficulty in forming a uniform aggregation structure.

[0031] In this embodiment, the mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals is 100:(1~3).

[0032] Therefore, if the mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals is greater than 100:1, the insufficient quantity of high-purity aluminum hydroxide seed crystals will lead to insufficient activation energy required for decomposition, making it difficult for aluminum hydroxide to precipitate and resulting in a lack of crystal nuclei in the system. This will cause the resulting product to have larger particle size, increased alkali coating on individual particles, and consequently reduce product purity and acid solubility. If the mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals is less than 100:3, the excessive quantity of high-purity aluminum hydroxide seed crystals will cause the product to precipitate rapidly and disorderly. Rapid precipitation will lead to an increase in lattice alkali in the product, reducing purity and further affecting the acid solubility. Disordered precipitation will make it difficult to control the product morphology, thus affecting the stability of the acid solubility of batch products. Therefore, by controlling the mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals within the range of 100:(1~3), a balance can be effectively achieved, resulting in high-purity aluminum hydroxide with moderate particle size and high acid solubility.

[0033] As an optional implementation, in this embodiment of the application, the reaction temperature of the decomposition reaction is 55℃~70℃; the reaction time of the decomposition reaction is 12h~36h.

[0034] Thus, by rationally limiting the amount of high-purity aluminum hydroxide seed crystals added and synergistically controlling the temperature and time of the decomposition reaction, the induced nucleation efficiency and initial crystal growth rate of high-purity aluminum hydroxide seed crystals in refined sodium aluminate solution can be effectively regulated, thereby preparing a seed slurry with uniform grains, good dispersibility, and high surface activity. This highly active seed slurry provides a stable and efficient crystallization basis for subsequent seed decomposition reactions, which is conducive to achieving controllable particle size, loose structure, and low impurity content in the aluminum hydroxide product, thereby ensuring the high acid solubility and high purity of the final high-purity aluminum hydroxide.

[0035] As an optional implementation, in this embodiment of the application, the volume ratio of the refined sodium aluminate solution II to the seed slurry is (30~40):1.

[0036] In this embodiment of the application, the reaction temperature of the seed decomposition reaction is 63℃~75℃.

[0037] The reaction temperature of the decomposition reaction is higher than that of the decomposition reaction.

[0038] Thus, by setting the reaction temperature of the seed decomposition reaction to be higher than that of the seed slurry preparation stage, not only is the lattice reconstruction and crystal structure optimization of aluminum hydroxide crystal nuclei promoted, which is conducive to the formation of uniform and loose small crystal aggregates, but also the removal of sodium ions from the lattice is significantly accelerated, allowing them to migrate more fully into the mother liquor, thereby further reducing the residual amount of sodium oxide in the product and effectively improving the purity and acid solubility of the final high-purity aluminum hydroxide.

[0039] In the embodiments of this application, the reaction time of the seed decomposition reaction is 10h~20h (i.e., the time from when all the refined sodium aluminate solution has been added).

[0040] In this embodiment, the refined sodium aluminate solution II is added to the seed slurry in equal volumes multiple times over 15-20 hours. The refined sodium aluminate solution II is added to the seed slurry in 5-8 equal volumes.

[0041] Thus, by adding refined sodium aluminate solution in stages and multiple times, the process of the seed decomposition reaction can be effectively controlled, avoiding excessive local supersaturation caused by adding a large amount at once. This prevents problems such as violent reaction, uncontrolled crystal growth, or impurity inclusion, and is conducive to obtaining aluminum hydroxide products with uniform particle size, regular structure, and high purity.

[0042] In summary, by reasonably limiting the volume ratio of refined sodium aluminate solution II to seed slurry, the reaction temperature and time of the seed decomposition reaction, and the number of batches and the feeding interval of refined sodium aluminate solution II, the nucleation, growth and aggregation behavior of aluminum hydroxide can be effectively controlled, promoting the orderly aggregation of crystals in a uniform and loose small grain manner, while significantly reducing the inclusion and residue of impurities such as sodium during the crystal growth process, thereby stably preparing high-purity aluminum hydroxide products with both high purity and high acid solubility.

[0043] In this embodiment, the time interval between two consecutive additions of the refined sodium aluminate solution to the seed slurry is 3 to 5 hours.

[0044] Thus, by controlling the addition time interval of refined sodium aluminate solution II to 3h~5h, it can be ensured that the solution added each time fully participates in the reaction, while effectively avoiding reaction fluctuations caused by local supersaturation or sudden changes in concentration, thereby maintaining the stability and controllability of the crystallization process.

[0045] In the embodiments of this application, the seed decomposition reaction is carried out under stirring conditions, and the stirring rate is 20 r / min to 50 r / min.

[0046] As an optional implementation, in this embodiment of the application, the method for preparing the refined sodium aluminate solution includes the following steps: Industrial aluminum hydroxide and alkaline solution are mixed and redissolved to obtain a redissolved sodium aluminate solution. The redissolved sodium aluminate solution is mixed with a purifying agent and then subjected to purification and filtration in sequence to obtain a first sodium aluminate solution. Adjust the concentration of the first sodium aluminate solution to obtain a second sodium aluminate solution; and, The second sodium aluminate solution is subjected to fine filtration to obtain the refined sodium aluminate solution.

[0047] The concentration of alumina in the second sodium aluminate solution is the same as that in the refined sodium aluminate solution, both being 80 g / L to 150 g / L; the caustic ratio α of the second sodium aluminate solution... K The concentration is the same as that of the refined sodium aluminate solution, which is 1.30~1.60.

[0048] As an optional implementation, in this embodiment of the application, the alkaline solution includes a sodium hydroxide solution; The temperature for the remelting treatment is 95℃~115℃; The caustic ratio α of the redissolved sodium aluminate solution K The value is 1.30~1.60.

[0049] Thus, by limiting the temperature of the redissolution process and the caustic ratio of the redissolved sodium aluminate solution, it is possible to ensure that industrial aluminum hydroxide and alkaline solution are fully mixed and completely dissolved, thereby stably obtaining a redissolved sodium aluminate solution with the required concentration and composition.

[0050] As an optional implementation, in the embodiments of this application, the purifying agent includes any one or more of aluminum hydroxide hydrate, polyaluminum chloride, activated alumina, and calcium hydroxide (lime milk).

[0051] Thus, by limiting the type of purifying agent, impurities introduced during the preparation process can be efficiently adsorbed without adversely affecting the sodium aluminate solution system, thereby effectively ensuring the purification effect and purity of the refined sodium aluminate solution.

[0052] In this embodiment of the application, the temperature of the purification process is 50℃~65℃; The purification process takes 45 to 90 minutes. The solid-liquid ratio of the purifying agent to the redissolved sodium aluminate solution is (3g~7g):1L.

[0053] Thus, by limiting the temperature and time of the purification reaction and controlling the amount of purifying agent added, deep purification of sodium aluminate solution can be achieved. This effectively promotes the formation of insoluble precipitates of Ca, Fe, Si, Mg, Cr, Cd, V, Ti and other transition metal impurities in the solution, which are then efficiently separated and removed in the form of filter cake, thereby obtaining a high-purity refined sodium aluminate solution.

[0054] In this embodiment of the application, the fine filtration is performed using a precision filter to remove residual fine suspended particles in the solution.

[0055] In this embodiment of the application, the concentration of the first sodium aluminate solution is adjusted by adding any one or more of high-purity water and ultrapure water.

[0056] As an optional implementation, in this embodiment of the application, the washing reagent includes any one or more of high-purity water and ultrapure water; The temperature of the washing reagent is 80℃~90℃; The mass ratio of the reagent to the high-purity aluminum hydroxide is (7~10):1.

[0057] Thus, through the optimized washing conditions described above, soluble impurities such as sodium ions remaining on the surface and in the pores of aluminum hydroxide particles can be efficiently removed: high temperature and high purity water significantly improve the solubility and diffusion rate of sodium salts, while a sufficient liquid-to-solid ratio and multiple washes ensure that impurities are fully replaced and carried out of the system. This washing process effectively dissolves and leaches sodium ions adsorbed or entrained on the surface of aluminum hydroxide into the washing liquid, thereby significantly reducing the residual amount of sodium oxide and other alkali metal impurities in the final product, ensuring the production of high-purity aluminum hydroxide with high acid solubility.

[0058] Based on a general inventive concept, this application provides an application of the above-mentioned high-purity aluminum hydroxide, which can be used in the preparation of alkyl aluminum hypophosphite.

[0059] Thus, this high-purity aluminum hydroxide, due to its high purity, high acid solubility, and uniform particle size distribution, exhibits excellent reactivity and stoichiometric controllability during the reaction with alkyl hypophosphite, significantly improving the reaction conversion rate and reducing the formation of unreacted aluminum sources and byproducts. The resulting alkyl hypophosphite aluminum flame retardant possesses advantages such as high thermal decomposition temperature, pure white color, and good batch-to-batch consistency. It not only effectively ensures the stability of high-purity aluminum hydroxide during high-temperature processing but also significantly improves the flame retardant efficiency, mechanical property retention, and overall processing safety of end materials such as engineering plastics, fully meeting the stringent requirements of high-end applications for halogen-free flame retardants.

[0060] 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. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0061] Example 1 Example 1 provides a method for preparing high-purity aluminum hydroxide, comprising the following steps: Step 1: Provide a refined sodium aluminate solution; The refined sodium aluminate solution includes Refined Sodium Aluminate Solution I and Refined Sodium Aluminate Solution II; the concentration of alumina in the refined sodium aluminate solution is 100 g / L, and the caustic ratio of the refined sodium aluminate solution is α. K It is 1.35; Step 2: Place 5m 3 A refined sodium aluminate solution is mixed with high-purity aluminum hydroxide seed crystals and subjected to a decomposition reaction to obtain a seed slurry. The purity of the high-purity aluminum hydroxide seed crystals is ≥99.9%; the particle size of the high-purity aluminum hydroxide seed crystals is 2.5μm; the mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals is 100:1; the reaction temperature of the decomposition reaction is 60℃, and the reaction time of the decomposition reaction is 20h. Step 3: Pump the seed slurry into the decomposition tank; then add 150m... 3 A refined sodium aluminate solution was added to the seed slurry to carry out a seed decomposition reaction, yielding aluminum hydroxide solid-liquid product. The volume ratio of refined sodium aluminate solution II to seed slurry was 30:1; the reaction temperature for the seed decomposition reaction was 68℃; the reaction time for the seed decomposition reaction was 12 hours; refined sodium aluminate solution II was added to the seed slurry in 6 equal volumes over 15 hours, with each addition being 25 ml. 3 The time interval between two consecutive additions of refined sodium aluminate solution to the seed slurry was 3 hours; the seed decomposition reaction was carried out at a stirring rate of 20 r / min. Step 4: Separate the solid and liquid components of aluminum hydroxide sequentially, wash and dry them to obtain high-purity aluminum hydroxide; Solid-liquid separation is performed using a filter press; the mother liquor obtained from solid-liquid separation can be returned to the process to replace part of the alkali solution dissolution. The washing process uses high-purity water at 82℃; the mass ratio of the reagent to high-purity aluminum hydroxide is 9:1. The preparation method of refined sodium aluminate solution includes the following steps: Industrial aluminum hydroxide and sodium hydroxide solutions were mixed and reconstituted to obtain a reconstituted sodium aluminate solution; the reconstitution temperature was 98℃; the caustic ratio α of the reconstituted sodium aluminate solution was... KIt is 1.30; The sodium aluminate solution was mixed with a purifying agent and then purified and filtered sequentially to obtain the first sodium aluminate solution. The purifying agent included any one or more of aluminum hydroxide hydrate, polyaluminum chloride, activated alumina, and calcium hydroxide. The purification temperature was 60℃ and the purification time was 60 min. The solid-liquid ratio of the purifying agent to the sodium aluminate solution was 5 g: 1 L. Adjust the concentration of the first sodium aluminate solution to obtain a second sodium aluminate solution with a concentration of 100 g / L; The second sodium aluminate solution was finely filtered to obtain a refined sodium aluminate solution.

[0062] High-purity aluminum hydroxide was prepared by the above method. The acid solubility of the high-purity aluminum hydroxide was 99.99%, the purity was 99.96%, and the particle size was 40μm~60μm. The impurity content in the high-purity aluminum hydroxide met the following requirements by mass percentage: Ca<3ppm, Fe<1ppm, Si<10ppm, Mg<1ppm, Ga<10ppm, Na<350ppm. The specific indicators are shown in Table 1.

[0063] Furthermore, the high-purity aluminum hydroxide product prepared in this embodiment was analyzed by electron microscopy, and the results are as follows: Figure 2 As shown, the product is a small-crystal agglomerate with uniform particle size.

[0064] Example 2 Example 2 provides a method for preparing high-purity aluminum hydroxide, comprising the following steps: Step 1: Provide a refined sodium aluminate solution; The refined sodium aluminate solution includes Refined Sodium Aluminate Solution I and Refined Sodium Aluminate Solution II; the concentration of alumina in the refined sodium aluminate solution is 110 g / L, and the caustic ratio of the refined sodium aluminate solution is α. K It is 1.45; Step 2: Place 5m 3 A refined sodium aluminate solution is mixed with high-purity aluminum hydroxide seed crystals and subjected to a decomposition reaction to obtain a seed slurry. The purity of the high-purity aluminum hydroxide seed crystals is ≥99.9%; the particle size of the high-purity aluminum hydroxide seed crystals is 2.8μm; the mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals is 100:1.5; the reaction temperature of the decomposition reaction is 62℃, and the reaction time of the decomposition reaction is 22h. Step 3: Pump the seed slurry into the decomposition tank; then add 150m... 3 A refined sodium aluminate solution was added to the seed slurry to carry out a seed decomposition reaction, yielding aluminum hydroxide solid-liquid product. The volume ratio of refined sodium aluminate solution II to seed slurry was 30:1; the reaction temperature for the seed decomposition reaction was 70℃; the reaction time for the seed decomposition reaction was 16 hours; refined sodium aluminate solution II was added to the seed slurry in 6 equal volumes over 20 hours, with each addition being 25 ml. 3 The time interval between two consecutive additions of refined sodium aluminate solution to the seed slurry was 4 hours; the seed decomposition reaction was carried out at a stirring rate of 20 r / min. Step 4: Separate the solid and liquid components of aluminum hydroxide sequentially, wash and dry them to obtain high-purity aluminum hydroxide; Wash with 85℃ high-purity water; the mass ratio of reagent to high-purity aluminum hydroxide is 8:1. The preparation method of refined sodium aluminate solution includes the following steps: Industrial aluminum hydroxide and sodium hydroxide solutions were mixed and reconstituted to obtain a reconstituted sodium aluminate solution; the reconstitution temperature was 102℃; the caustic ratio α of the reconstituted sodium aluminate solution was... K It is 1.42; The sodium aluminate solution was mixed with a purifying agent and then purified and filtered sequentially to obtain the first sodium aluminate solution. The purifying agent included any one or more of aluminum hydroxide hydrate, polyaluminum chloride, activated alumina, and calcium hydroxide. The purification temperature was 57°C. The purification time was 70 min. The solid-liquid ratio of the purifying agent to the sodium aluminate solution was 6 g: 1 L. The concentration of the first sodium aluminate solution was adjusted to obtain a second sodium aluminate solution with a concentration of 110 g / L; The second sodium aluminate solution was finely filtered to obtain a refined sodium aluminate solution.

[0065] High-purity aluminum hydroxide was prepared by the above method, and the specific indicators are shown in Table 1.

[0066] Example 3 Example 3 provides a method for preparing high-purity aluminum hydroxide for alkyl aluminum hypophosphite, comprising the following steps: Step 1: Provide a refined sodium aluminate solution; The refined sodium aluminate solution includes Refined Sodium Aluminate Solution I and Refined Sodium Aluminate Solution II; the concentration of alumina in the refined sodium aluminate solution is 110 g / L, and the caustic ratio of the refined sodium aluminate solution is α. K It is 1.52; Step 2: Place 5m 3 A refined sodium aluminate solution is mixed with high-purity aluminum hydroxide seed crystals and subjected to a decomposition reaction to obtain a seed slurry. The purity of the high-purity aluminum hydroxide seed crystals is ≥99.9%; the particle size of the high-purity aluminum hydroxide seed crystals is 3μm; the mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals is 100:2; the reaction temperature of the decomposition reaction is 63℃, and the reaction time of the decomposition reaction is 24h. Step 3: Pump the seed slurry into the decomposition tank; then add 150m... 3 A refined sodium aluminate solution was added to the seed slurry to carry out a seed decomposition reaction, yielding aluminum hydroxide solid-liquid product. The volume ratio of refined sodium aluminate solution II to seed slurry was 30:1; the reaction temperature for the seed decomposition reaction was 68℃; the reaction time for the seed decomposition reaction was 18 hours; refined sodium aluminate solution II was added to the seed slurry in 6 equal volumes over 20 hours, with each addition being 25 ml. 3 The time interval between two consecutive additions of refined sodium aluminate solution to the seed slurry was 4 hours; the seed decomposition reaction was carried out at a stirring rate of 20 r / min. Step 4: Separate the solid and liquid components of aluminum hydroxide sequentially, wash and dry them to obtain high-purity aluminum hydroxide; Wash with 85℃ high-purity water; the mass ratio of reagent to high-purity aluminum hydroxide is 8:1. The preparation method of refined sodium aluminate solution includes the following steps: Industrial aluminum hydroxide and sodium hydroxide solutions were mixed and reconstituted to obtain a reconstituted sodium aluminate solution; the reconstitution temperature was 107℃; the caustic ratio α of the reconstituted sodium aluminate solution was... K It is 1.45; The sodium aluminate solution was mixed with a purifying agent and then purified and filtered sequentially to obtain the first sodium aluminate solution. The purifying agent included any one or more of aluminum hydroxide hydrate, polyaluminum chloride, activated alumina, and calcium hydroxide. The purification temperature was 62℃ and the purification time was 70 min. The solid-liquid ratio of the purifying agent to the sodium aluminate solution was 4 g: 1 L. The concentration of the first sodium aluminate solution was adjusted to obtain a second sodium aluminate solution with a concentration of 110 g / L; The second sodium aluminate solution was finely filtered to obtain a refined sodium aluminate solution.

[0067] High-purity aluminum hydroxide was prepared by the above method, and the specific indicators are shown in Table 1.

[0068] Example 4 Example 4 provides a method for preparing high-purity aluminum hydroxide for alkyl aluminum hypophosphite, comprising the following steps: Step 1: Provide a refined sodium aluminate solution; The refined sodium aluminate solution includes Refined Sodium Aluminate Solution I and Refined Sodium Aluminate Solution II; the concentration of alumina in the refined sodium aluminate solution is 120 g / L, and the caustic ratio of the refined sodium aluminate solution is α. K It is 1.53; Step 2: Place 5m 3 A refined sodium aluminate solution is mixed with high-purity aluminum hydroxide seed crystals and subjected to a decomposition reaction to obtain a seed slurry. The purity of the high-purity aluminum hydroxide seed crystals is ≥99.9%; the particle size of the high-purity aluminum hydroxide seed crystals is 3.2μm; the mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals is 100:2.5; the reaction temperature of the decomposition reaction is 64℃, and the reaction time of the decomposition reaction is 24h. Step 3: Pump the seed slurry into the decomposition tank; then add 150m... 3 A refined sodium aluminate solution was added to the seed slurry to carry out a seed decomposition reaction, yielding aluminum hydroxide solid-liquid product. The volume ratio of refined sodium aluminate solution II to seed slurry was 30:1; the reaction temperature for the seed decomposition reaction was 69℃; the reaction time for the seed decomposition reaction was 18 hours; refined sodium aluminate solution II was added to the seed slurry in 5 equal volumes over 20 hours, with each addition being 30 ml. 3 The time interval between two consecutive additions of refined sodium aluminate solution to the seed slurry was 5 hours; the seed decomposition reaction was carried out at a stirring rate of 20 r / min. Step 4: Separate the solid and liquid components of aluminum hydroxide sequentially, wash and dry them to obtain high-purity aluminum hydroxide; The washing process uses high-purity water at 87℃; the mass ratio of the reagent to high-purity aluminum hydroxide is 7:1. The preparation method of refined sodium aluminate solution includes the following steps: Industrial aluminum hydroxide and sodium hydroxide solutions were mixed and reconstituted to obtain a reconstituted sodium aluminate solution; the reconstitution temperature was 105℃; the caustic ratio α of the reconstituted sodium aluminate solution was... K It is 1.44; The sodium aluminate solution was mixed with a purifying agent and then purified and filtered sequentially to obtain the first sodium aluminate solution. The purifying agent included any one or more of aluminum hydroxide hydrate, polyaluminum chloride, activated alumina, and calcium hydroxide. The purification temperature was 58℃ and the purification time was 55 min. The solid-liquid ratio of the purifying agent to the sodium aluminate solution was 3 g: 1 L. Adjust the concentration of the first sodium aluminate solution to obtain the second sodium aluminate solution; The second sodium aluminate solution was finely filtered to obtain a refined sodium aluminate solution with a concentration of 120 g / L.

[0069] High-purity aluminum hydroxide was prepared by the above method, and the specific indicators are shown in Table 1.

[0070] Example 5 Example 5 provides a method for preparing high-purity aluminum hydroxide for alkyl aluminum hypophosphite, comprising the following steps: Step 1: Provide a refined sodium aluminate solution; The refined sodium aluminate solution includes Refined Sodium Aluminate Solution I and Refined Sodium Aluminate Solution II; the concentration of alumina in the refined sodium aluminate solution is 130 g / L, and the caustic ratio of the refined sodium aluminate solution is α. K It is 1.55; Step 2: Place 5m 3 A refined sodium aluminate solution is mixed with high-purity aluminum hydroxide seed crystals and subjected to a decomposition reaction to obtain a seed slurry. The purity of the high-purity aluminum hydroxide seed crystals is ≥99.9%; the particle size of the high-purity aluminum hydroxide seed crystals is 3.2μm; the mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals is 100:2.5; the reaction temperature of the decomposition reaction is 64℃, and the reaction time of the decomposition reaction is 24h. Step 3: Pump the seed slurry into the decomposition tank; then add 150m... 3 A refined sodium aluminate solution was added to the seed slurry to carry out a seed decomposition reaction, yielding aluminum hydroxide solid-liquid product. The volume ratio of refined sodium aluminate solution II to seed slurry was 30:1; the reaction temperature for the seed decomposition reaction was 69℃; the reaction time for the seed decomposition reaction was 20 h; refined sodium aluminate solution II was added to the seed slurry in 7 equal volumes over 18 h, with each addition being 21.4 m³. 3 The time interval between two consecutive additions of refined sodium aluminate solution to the seed slurry was 3 hours; the seed decomposition reaction was carried out at a stirring rate of 20 r / min. Step 4: Separate the solid and liquid components of aluminum hydroxide sequentially, wash and dry them to obtain high-purity aluminum hydroxide; Wash with 85℃ high-purity water; the mass ratio of reagent to high-purity aluminum hydroxide is 8:1. The preparation method of refined sodium aluminate solution includes the following steps: Industrial aluminum hydroxide and sodium hydroxide solutions were mixed and reconstituted to obtain a reconstituted sodium aluminate solution; the reconstitution temperature was 110℃; the caustic ratio α of the reconstituted sodium aluminate solution was... K It is 1.46; The sodium aluminate solution was mixed with a purifying agent and then purified and filtered sequentially to obtain the first sodium aluminate solution. The purifying agent included any one or more of aluminum hydroxide hydrate, polyaluminum chloride, activated alumina, and calcium hydroxide. The purification temperature was 58℃ and the purification time was 55 min. The solid-liquid ratio of the purifying agent to the sodium aluminate solution was 7 g: 1 L. The concentration of the first sodium aluminate solution was adjusted to obtain a second sodium aluminate solution with a concentration of 130 g / L; The second sodium aluminate solution was finely filtered to obtain a refined sodium aluminate solution.

[0071] High-purity aluminum hydroxide was prepared by the above method, and the specific indicators are shown in Table 1.

[0072] Comparative Example 1 Comparative Example 1 provides a method for preparing aluminum hydroxide, which differs from Example 1 in that the particle size of the high-purity aluminum hydroxide seed crystals is different. In Comparative Example 1, the particle size of the high-purity aluminum hydroxide seed crystals is 4.5 μm.

[0073] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0074] Comparative Example 2 Comparative Example 2 provides a method for preparing aluminum hydroxide, which differs from Example 1 in that the particle size of the high-purity aluminum hydroxide seed crystals is different. In Comparative Example 2, the particle size of the high-purity aluminum hydroxide seed crystals is 1 μm.

[0075] The other steps and parameters are the same as in Example 1, and will not be repeated here.

[0076] In addition, acid solubility tests were performed on the products obtained in Example 1 and Comparative Example 2, and the results are as follows: Figure 3 As shown.

[0077] Comparative Example 3 Comparative Example 3 provides a method for preparing aluminum hydroxide, which differs from Example 2 in that the concentration of the second sodium aluminate solution is different when preparing the refined sodium aluminate solution. In Comparative Example 3, the concentration of the second sodium aluminate solution is 170 g / L (i.e., the concentration of aluminum oxide in the refined sodium aluminate solution is 170 g / L).

[0078] The other steps and parameters are the same as in Example 2, and will not be repeated here.

[0079] Comparative Example 4 Comparative Example 4 provides a method for preparing aluminum hydroxide, which differs from Example 3 in that the reaction temperature of the decomposition reaction is different. In Example 4, the reaction temperature of the decomposition reaction is 75°C.

[0080] The other steps and parameters are the same as in Example 3, and will not be repeated here.

[0081] The product particles obtained in this comparative example agglomerated, resulting in a coarse particle size. This is because although high temperature is conducive to agglomeration, excessively high temperature will lead to accelerated growth, thus making the particle size of the sample coarser.

[0082] The method for determining acid solubility specifically includes the following steps: 1) Provide 100 mL of a 75% phosphoric acid solution and place the phosphoric acid solution in a water bath at 75°C; 2) Weigh 34.16g of the aluminum hydroxide sample to be tested and add it to 100mL of 75% phosphoric acid solution at 75℃, so that the mass ratio of aluminum hydroxide in the reaction system is 18%; after the aluminum hydroxide sample to be tested is added, stop heating and let it cool naturally in a water bath. 3) After the reaction has proceeded for 1 hour (i.e. 1 hour after the feeding is completed), add 100 mL of distilled water to dilute the reaction solution, then filter it. The resulting solid residue is thoroughly washed with distilled water and dried at a constant temperature to a constant weight. The mass of the residual solid is Ag. 4) Calculate the acid solubility of the sample using the following formula: (1-A÷34.16)×100%.

[0083] Table 1 Performance results of the products obtained from each embodiment and comparative example.

[0084] Experimental results: Comparing Example 1 and Comparative Examples 1-2, it can be seen that if the particle size of the high-purity aluminum hydroxide seed crystals exceeds 3.5 μm, its surface activation energy is too low, making aluminum hydroxide precipitation difficult and resulting in a lack of crystal nuclei in the system. This leads to a larger particle size in the resulting product, reducing the acid dissolution rate. The larger particle size also increases the amount of alkali encapsulated in each particle, further reducing product purity and acid dissolution rate. If the particle size of the high-purity aluminum hydroxide seed crystals is less than 1.5 μm, its surface activation energy is too high, causing rapid and disordered precipitation of a large amount of product. This large amount of precipitation leads to an excessive number of crystal nuclei in the system, resulting in a finer particle size in the final product. Rapid precipitation also increases the amount of alkali in the product lattice, reducing purity and further affecting the acid dissolution rate. Disordered precipitation makes it difficult to control the product morphology, thus affecting the stability of the acid dissolution rate of batch products.

[0085] Comparing Example 2 and Comparative Example 3, it can be seen that if the concentration of the second sodium aluminate solution is higher than 150 g / L when preparing the refined sodium aluminate solution, the sodium content in the product is likely to increase during subsequent seeding processes, resulting in the aluminum hydroxide purity failing to reach 99.96%. If the concentration of alumina in the refined sodium aluminate solution is lower than 80 g / L, the system is not sufficiently supersaturated, limiting crystal nucleation and growth, leading to a significant reduction in product yield. Furthermore, the crystals are small and agglomeration is insufficient, making it difficult to form highly active aluminum hydroxide with a loose structure and uniform particle size, thus affecting its acid solubility and application suitability.

[0086] Comparing Example 3 and Comparative Example 4, it can be seen that if the reaction temperature of the decomposition reaction exceeds 70°C, the aluminum hydroxide particles undergo significant agglomeration, resulting in a coarser particle size in the product. This is because the higher temperature accelerates the crystal growth rate on the one hand, and promotes the agglomeration between particles on the other, thereby forming aggregates with larger particle sizes.

[0087] It is evident that the excellent results of the high-purity aluminum hydroxide preparation method provided in this application are based on the combined effect of various parameters, none of which can be omitted.

[0088] In summary, this invention provides a high-purity aluminum hydroxide, its preparation method, and its applications. This high-purity aluminum hydroxide combines high purity, excellent acid solubility, and controllable particle size distribution, successfully solving the key challenge of "difficulty in synergistically achieving high purity and high acid solubility" in existing technologies. It provides a high-quality raw material foundation for the green, efficient, and large-scale preparation of high-performance phosphorus-based flame retardants. This method, through the synergistic effect of multiple steps including deep purification of heavy solutions, precise control of refined sodium aluminate solution, induction of high-purity aluminum hydroxide crystals, optimization of agglomeration conditions, and controlled decomposition of sodium oxide, successfully prepares small-crystal agglomerated, easily soluble high-purity aluminum hydroxide, possessing both high purity and high acid solubility, fully meeting the stringent requirements for raw materials in the synthesis of alkyl aluminum hypophosphite. The obtained product has a purity ≥99.96%, a particle size of 40μm~60μm, and an acid solubility of 99.99%. The solution after acid dissolution is clear and transparent, without residue, significantly improving the quality stability of downstream flame retardant products. Among them, the concentration of Al2O3 in the refined sodium aluminate solution is limited to 80 g / L~150 g / L, and the caustic ratio α is... KThe alkalinity is controlled between 1.30 and 1.60 to avoid co-precipitation of impurities caused by high alkalinity and to maintain a suitable supersaturation, ensuring the stability of the seeding process and forming loosely structured, porous particles, thus enhancing reactivity. Aluminum hydroxide seed crystals with a purity ≥99.9% and a particle size of 1.5μm~3.5μm are used as nucleation centers to effectively guide orderly crystal growth, inhibit spontaneous nucleation and disordered aggregation, resulting in more uniform crystallization and significantly reducing the adsorption and encapsulation of sodium ions on the crystal faces, thus reducing Na2O residue from the source. Combined with a deeply purified sodium aluminate solution, efficient solid-liquid separation, and high-temperature, high-purity water multi-stage washing (80℃~90℃, reagent to high-purity aluminum hydroxide mass ratio of (7~10):1), sodium and other soluble impurities remaining in the mother liquor and on the particle surface are thoroughly removed, ensuring that the Na content of the product is <350ppm. In summary, this method overcomes the technical bottleneck of balancing high purity and high acid solubility in traditional high-purity aluminum hydroxide, providing a green, controllable, and scalable process for preparing easily soluble high-purity aluminum hydroxide. This lays a crucial raw material foundation for the high-quality production of high-end phosphorus-based halogen-free flame retardants. Based on the high purity, high acid solubility, and uniform particle size distribution of this high-purity aluminum hydroxide, it exhibits excellent reactivity and stoichiometric controllability during the reaction with alkyl hypophosphite, significantly improving the reaction conversion rate and reducing the formation of unreacted aluminum sources and byproducts. The resulting alkyl hypophosphite aluminum flame retardant possesses advantages such as high thermal decomposition temperature, pure white color, and good batch-to-batch consistency. It not only effectively ensures the stability of high-purity aluminum hydroxide during high-temperature processing but also significantly improves the flame retardant efficiency, mechanical property retention, and overall processing safety of engineering plastics and other end materials, fully meeting the stringent requirements of high-end applications for halogen-free flame retardants.

[0089] 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 in this application.

Claims

1. A high-purity aluminum hydroxide, characterized in that, The high-purity aluminum hydroxide has an acid solubility ≥99.99%; a purity ≥99.96%; and a particle size of 40μm~60μm. The impurity content in the high-purity aluminum hydroxide, by mass percentage, meets the following requirements: Ca < 3 ppm, Fe < 1 ppm, Si < 10 ppm, Mg < 1 ppm, Ga < 10 ppm, Na < 350 ppm.

2. A method for preparing high-purity aluminum hydroxide as described in claim 1, characterized in that, Includes the following steps: A refined sodium aluminate solution is provided, wherein the concentration of alumina in the refined sodium aluminate solution is 80 g / L to 150 g / L, and the caustic ratio of the refined sodium aluminate solution is α. K The value is between 1.30 and 1.

60. A second refined sodium aluminate solution is provided, wherein the concentration of alumina in the second refined sodium aluminate solution is 80 g / L to 150 g / L, and the caustic ratio of the second refined sodium aluminate solution is α. K The value is between 1.30 and 1.

60. The refined sodium aluminate solution and high-purity aluminum hydroxide seed crystals are mixed and decomposed to obtain seed slurry; The refined sodium aluminate solution was added to the seed slurry to carry out a seed decomposition reaction, resulting in aluminum hydroxide solid-liquid product. as well as, The aluminum hydroxide solid-liquid mixture is subjected to solid-liquid separation, washing, and drying in sequence to obtain the high-purity aluminum hydroxide.

3. The method for preparing high-purity aluminum hydroxide according to claim 2, characterized in that, The purity of the high-purity aluminum hydroxide seed crystals is ≥99.9%; and / or, The high-purity aluminum hydroxide seed crystals have a particle size of 1.5 μm to 3.5 μm; and / or, The mass ratio of the equivalent alumina in the refined sodium aluminate solution to the equivalent alumina in the high-purity aluminum hydroxide seed crystals is 100:(1~3).

4. The method for preparing high-purity aluminum hydroxide according to claim 3, characterized in that, The decomposition reaction is carried out at a temperature of 55°C to 70°C; and / or, The decomposition reaction takes 12 to 36 hours.

5. The method for preparing high-purity aluminum hydroxide according to claim 4, characterized in that, The volume ratio of the refined sodium aluminate solution II to the seed slurry is (30~40):1; and / or, The reaction temperature for the seed decomposition reaction is 63℃~75℃; and / or, The reaction time for the seed decomposition reaction is 10 h to 20 h; and / or, The refined sodium aluminate solution II is added to the seed slurry in equal volumes multiple times within 15h to 20h, with a time interval of 3h to 5h between two consecutive additions of the refined sodium aluminate solution II to the seed slurry.

6. The method for preparing high-purity aluminum hydroxide according to claim 2, characterized in that, The preparation method of the first or second refined sodium aluminate solution includes the following steps: Industrial aluminum hydroxide and alkaline solution are mixed and redissolved to obtain a redissolved sodium aluminate solution. The redissolved sodium aluminate solution is mixed with a purifying agent and then subjected to purification and filtration in sequence to obtain a first sodium aluminate solution. Adjust the concentration of the first sodium aluminate solution to obtain a second sodium aluminate solution; and, The second sodium aluminate solution is subjected to fine filtration to obtain either the first refined sodium aluminate solution or the second refined sodium aluminate solution.

7. The method for preparing high-purity aluminum hydroxide according to claim 6, characterized in that, The alkaline solution includes a sodium hydroxide solution; and / or, The remelting treatment temperature is 95℃~115℃; and / or, The caustic ratio α of the redissolved sodium aluminate solution K The value is 1.30~1.

60.

8. The method for preparing high-purity aluminum hydroxide according to claim 7, characterized in that, The purifying agent includes any one or more of aluminum hydroxide hydrate, polyaluminum chloride, activated alumina, and calcium hydroxide; and / or, The purification process is performed at a temperature of 50℃~65℃; and / or, The purification process takes 45 to 90 minutes; and / or, The solid-liquid ratio of the purifying agent to the redissolved sodium aluminate solution is (3g~7g):1L.

9. The method for preparing high-purity aluminum hydroxide according to any one of claims 2 to 8, characterized in that, The washing reagent includes any one or more of high-purity water and ultrapure water; The temperature of the washing reagent is 80℃~90℃; The mass ratio of the reagent to the high-purity aluminum hydroxide is (7~10):

1.

10. The application of the high-purity aluminum hydroxide according to claim 1, wherein the high-purity aluminum hydroxide can be used in the preparation of alkyl aluminum hypophosphite.

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