Preparation method of low-sodium high-purity aluminum hydroxide

Abstract

The application relates to a preparation method of low-sodium high-purity aluminum hydroxide, and belongs to the technical field of aluminum hydroxide preparation. By using aluminum hydroxide with a purity of greater than or equal to 99% and industrial ion membrane alkali with a mass concentration of 32% as raw materials, the high purity of the raw materials is ensured, so that the introduction of impurities is reduced. The impurity rejection effect in the crystallization process is utilized to improve the purity of the aluminum hydroxide seed raw material by circulating decomposition. In the decomposition stage, the crystal growth kinetics is regulated, the epitaxial growth is promoted, the impurity inclusion is reduced, and the crystal structure easy to wash is formed by accurately controlling the temperature, stirring speed and feeding speed. Finally, based on different occurrence forms of sodium impurities in the product, different forms of sodium impurities are targetedly removed by using the physical displacement and diffusion principles through multi-stage washing.

Description

Technical Field

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

[0002] In the semiconductor materials and related high-tech fields, high-purity aluminum hydroxide serves as a crucial precursor material, and its quality and performance have a vital impact on the application of the final products. Specifically, high-purity aluminum hydroxide with a purity of 99.9% or higher is not only the basic raw material for preparing 3N to 5N grade high-purity alumina, but also plays an irreplaceable role in many high-end technology fields such as sapphire crystal growth, electronic ceramic manufacturing, and lithium battery separator coating. Furthermore, this material can be directly dissolved in acids to prepare electronic-grade aluminum salts, further broadening its application scope.

[0003] However, sodium content is a particularly critical parameter among the performance indicators of high-purity aluminum hydroxide. The presence of sodium oxide significantly increases the dielectric loss of alumina ceramics, leads to grain coarsening, and reduces the material's refractoriness. These negative effects are especially prominent in fields with extremely stringent material performance requirements, such as 5G communication and semiconductor manufacturing, severely limiting the application potential of high-purity aluminum hydroxide in these high-end technologies.

[0004] Currently, the production of high-purity aluminum hydroxide mainly relies on the modified Bayer process. However, this method is limited by the impurity content in the bauxite raw material and the caustic soda process conditions, resulting in a sodium content in the product often exceeding 1000 ppm, making it difficult to meet the stringent performance requirements of the mid-to-high-end market. Although other preparation methods exist, such as aluminum powder hydrolysis and alkoxide hydrolysis, each has its own significant limitations. Aluminum powder hydrolysis relies on the use of high-purity aluminum powder and generates hydrogen gas during the process, posing safety hazards; alkoxide hydrolysis faces problems such as high raw material costs and complex organic matter recovery and treatment. Summary of the Invention

[0005] This application provides a method for preparing low-sodium, high-purity aluminum hydroxide to solve the following technical problem: how to develop a method for preparing low-sodium, high-purity aluminum hydroxide. This application provides a method for preparing low-sodium, high-purity aluminum hydroxide, the method comprising: A sodium aluminate solution is obtained by mixing and dissolving aluminum hydroxide with a purity of ≥99% and industrial ion-exchange membrane alkali with a mass concentration of 32%. The sodium aluminate solution is subjected to impurity removal and filtration to obtain a high-purity sodium aluminate solution. The high-purity sodium aluminate solution was diluted to obtain a high-purity decomposition and purification solution; Aluminum hydroxide seed raw materials and deionized water are mixed and crushed to obtain seed slurry; The seed slurry is added to the decomposition tank, and the temperature of the decomposition tank is controlled within a first temperature range; At a set stirring speed, the high-purity decomposition and refining liquid is pumped into the decomposition tank at a set speed. When the feed amount of the high-purity decomposition and refining liquid reaches a set ratio of the total volume of the decomposition tank, the temperature of the decomposition tank is adjusted to the second temperature range, and feeding continues until the tank is full. The material in the decomposition tank is further decomposed to obtain aluminum hydroxide slurry; The aluminum hydroxide slurry was filtered and washed sequentially to obtain low-sodium, high-purity aluminum hydroxide.

[0006] Optionally, the aluminum hydroxide seed material is obtained by cyclically decomposing and purifying the high-purity sodium aluminate solution with aluminum hydroxide of ≥99% purity 8 to 9 times.

[0007] Optionally, the solid content of the seed slurry is 150 g / L to 300 g / L, the seed particle size of the seed slurry is 1 μm to 10 μm, and the mass of the seed slurry is 4 g to 30 g.

[0008] Optionally, the mixing and dissolution temperature is 102℃~105℃, and the mass ratio of the 32% industrial ion-exchange membrane alkali to the aluminum hydroxide with a purity ≥99% is (1.5~2.2):1.

[0009] Optionally, the dilution is performed by diluting the high-purity sodium aluminate solution with a diluent, wherein the volume ratio of the high-purity sodium aluminate solution to the diluent is 1.2 to 1.5.

[0010] Optionally, the first temperature range is 70℃~75℃, and the second temperature range is 65℃~69℃.

[0011] Optionally, the decomposition reaction takes 8 to 16 hours.

[0012] Optionally, the set stirring speed is 50 rpm to 60 rpm.

[0013] Optionally, the set speed is 2L / h to 3L / h.

[0014] Optionally, the set ratio is 1 / 8 to 1 / 4.

[0015] Optionally, the impurity removal includes adding an impurity removal additive to the sodium aluminate solution, wherein the impurity removal additive is at least one of activated carbon, EDTA, PAM, chitosan, and aluminum hydroxide.

[0016] Optionally, the step of sequentially filtering and washing the aluminum hydroxide slurry to obtain low-sodium, high-purity aluminum hydroxide includes: The aluminum hydroxide slurry is first filtered to obtain aluminum hydroxide filter cake; The aluminum hydroxide filter cake was subjected to a static washing process using hot water at 55℃~85℃ and a pressure of 0.2MPa~0.5MPa. The aluminum hydroxide filter cake after static washing is first dried by blowing. The aluminum hydroxide filter cake after the first drying is subjected to a second stage of agitation and washing using hot water at 55℃~85℃. The aluminum hydroxide filter cake after two stages of agitation and washing is subjected to a second filtration and a second drying process to obtain low-sodium, high-purity aluminum hydroxide.

[0017] Optionally, during the static washing process, the amount of hot water used per kilogram of aluminum hydroxide filter cake is 15L to 35L.

[0018] Optionally, during the two-stage washing process, the amount of hot water used per kilogram of aluminum hydroxide filter cake is 5L to 30L.

[0019] Optionally, during both the first and second drying processes, the moisture content of the filter cake is controlled to be below 15%.

[0020] Optionally, the purity of the low-sodium high-purity aluminum hydroxide is ≥99.95%, and the sodium content of the low-sodium high-purity aluminum hydroxide is ≤500 ppm.

[0021] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing low-sodium, high-purity aluminum hydroxide. The method includes: mixing and dissolving aluminum hydroxide with a purity ≥99% and industrial ion-exchange membrane alkali with a mass concentration of 32% to obtain a sodium aluminate solution; removing impurities and filtering the sodium aluminate solution to obtain a high-purity sodium aluminate solution; diluting the high-purity sodium aluminate solution to obtain a high-purity decomposition and refining liquid; mixing and crushing aluminum hydroxide seed raw materials and deionized water to obtain a seed slurry; adding the seed slurry to a decomposition tank and controlling the temperature of the decomposition tank within a first temperature range; pumping the high-purity decomposition and refining liquid into the decomposition tank at a set speed under a set stirring speed; when the feed amount of the high-purity decomposition and refining liquid reaches a set proportion of the total volume of the decomposition tank, adjusting the temperature of the decomposition tank to a second temperature range and continuing to feed until the tank is full; continuing the decomposition reaction of the material in the decomposition tank to obtain an aluminum hydroxide slurry; and sequentially filtering and washing the aluminum hydroxide slurry to obtain low-sodium, high-purity aluminum hydroxide. By using aluminum hydroxide with a purity ≥99% and industrial ion-exchange membrane alkali with a mass concentration of 32% as raw materials, high purity of the raw materials is ensured, thereby reducing the introduction of impurities. In the sodium aluminate solution stage, by adding impurity removal additives and utilizing the principles of adsorption and complexation chemistry, most soluble impurities are directly removed from the liquid phase before crystallization, cutting off the main channel for impurities to enter the solid phase. The aluminum hydroxide seed raw material is obtained through 8-9 cycles of high-purity sodium aluminate solution decomposition and purification, achieving the ultimate purity of the seed crystal itself and ensuring the lower limit of the final product's purity from the growth source. In the decomposition and crystallization stage, through staged cooling and extremely slow feeding, and precise control of supersaturation, epitaxial and orderly growth of crystals on the surface of ultrapure seeds is achieved. This growth reduces lattice defects and impurity inclusions, while the resulting dense structure creates conditions for subsequent deep sodium removal. Finally, based on the different occurrence forms of sodium impurities in the product, a multi-stage washing strategy is used for specific removal. The first stage of static washing utilizes the principle of macroscopic displacement, using a large amount of hot water under pressure to penetrate the filter cake, displacing the high-sodium mother liquor trapped in the intercrystalline spaces and removing free sodium. Intermediate drying reduces moisture content, minimizing the dilution of washing efficiency by free water. The second stage of agitation washing utilizes the principles of diffusion and desorption, enhancing mass transfer through stirring, allowing hot water to penetrate deep into the particle surface and micropores, deeply eluting adsorbed sodium ions. The prepared high-purity aluminum hydroxide achieves a purity of over 99.95% and a sodium content below 500 ppm, meeting the requirements of high-end applications such as 5G and semiconductors. Attached Figure Description

[0022] 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.

[0023] 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.

[0024] Figure 1 This is a schematic flowchart illustrating a method for preparing low-sodium, high-purity aluminum hydroxide, as provided in an embodiment of this application. Detailed Implementation

[0025] 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.

[0026] 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.

[0027] Figure 1 This is a schematic flowchart illustrating a method for preparing low-sodium, high-purity aluminum hydroxide, as provided in an embodiment of this application.

[0028] Please see Figure 1 This application provides a method for preparing low-sodium, high-purity aluminum hydroxide, the method comprising: S1. Mix and dissolve aluminum hydroxide with a purity ≥ 99% and industrial ion-exchange membrane alkali with a mass concentration of 32% to obtain sodium aluminate solution; S2. The sodium aluminate solution is subjected to impurity removal and filtration treatment to obtain a high-purity sodium aluminate solution; S3. Dilute the high-purity sodium aluminate solution to obtain a high-purity decomposition and purification solution; S4. Mix and crush the aluminum hydroxide seed raw material with deionized water to obtain seed slurry; S5. Add the seed slurry to the decomposition tank and control the temperature of the decomposition tank within a first temperature range; S6. Under a set stirring speed, the high-purity decomposition and refining liquid is pumped into the decomposition tank at a set speed. When the feed amount of the high-purity decomposition and refining liquid reaches a set ratio of the total volume of the decomposition tank, the temperature of the decomposition tank is adjusted to the second temperature range, and feeding continues until the tank is full. S7. The material in the decomposition tank is further decomposed to obtain aluminum hydroxide slurry; S8. The aluminum hydroxide slurry is filtered and washed sequentially to obtain low-sodium, high-purity aluminum hydroxide.

[0029] This application uses aluminum hydroxide with a purity ≥99% and industrial ion-exchange membrane alkali with a mass concentration of 32% as raw materials, ensuring high purity and reducing impurity introduction. The aluminum hydroxide seed raw material is purified through cyclic decomposition, utilizing the impurity repulsion effect during crystallization to improve its purity. During the decomposition stage, precise control of temperature, stirring speed, and feed rate regulates crystal growth kinetics, promoting epitaxial growth, reducing impurity inclusion, and forming an easily washable crystal structure. Finally, based on the different occurrence forms of sodium impurities in the product, multi-stage washing is used to target and remove sodium impurities of different forms using physical displacement and diffusion principles.

[0030] In some embodiments, the temperature for mixing and dissolving is 102°C to 105°C, and the mass ratio of the 32% industrial ion-exchange membrane alkali to the aluminum hydroxide with a purity ≥99% is (1.5 to 2.2):1.

[0031] Controlling the mixing and dissolution temperature to 102℃~105℃ is beneficial for accelerating the dissolution reaction of aluminum hydroxide with a purity ≥99% in 32% industrial ion-exchange membrane alkali, promoting the formation of a homogeneous sodium aluminate solution, and simultaneously inhibiting the hydrolysis or precipitation of impurities. Controlling the mass ratio of 32% industrial ion-exchange membrane alkali to aluminum hydroxide with a purity ≥99% to (1.5~2.2):1 provides a slightly higher alkali content than theoretically expected, ensuring complete dissolution of aluminum hydroxide with a purity ≥99% and the formation of a stable sodium aluminate solution. This prevents undissolved aluminum hydroxide from entering subsequent processes and provides a suitable chemical environment for subsequent impurity removal steps.

[0032] In some embodiments, the impurity removal includes adding an impurity removal additive to the sodium aluminate solution, the impurity removal additive being at least one of activated carbon, EDTA, PAM, chitosan, and aluminum hydroxide.

[0033] Adding activated carbon to sodium aluminate solution can remove organic impurities and some colored substances through adsorption. Adding EDTA (ethylenediaminetetraacetic acid) allows it to form stable water-soluble complexes with heavy metal ions such as calcium, magnesium, and iron in the solution, preventing them from entering the aluminum hydroxide crystals during subsequent decomposition. Adding PAM (polyacrylamide) helps to aggregate suspended particles, facilitating subsequent filtration. Adding chitosan removes various impurity ions and colloidal substances through flocculation and adsorption. When aluminum hydroxide (Al(OH)3) is used as a purifying additive, it partially dissolves and then precipitates in the sodium aluminate solution; this dynamic process helps to "replace" or "remove" impurities from the original solution structure. At least one of activated carbon, EDTA, PAM, chitosan, and aluminum hydroxide is used as a purification additive to specifically remove certain types of impurities from sodium aluminate solutions. After adding the purification additive, the purified sodium aluminate solution is filtered to achieve solid-liquid separation, separating the impurities from the solution, thereby obtaining a high-purity sodium aluminate solution.

[0034] In some embodiments, the dilution is performed by diluting the high-purity sodium aluminate solution with a diluent, wherein the volume ratio of the high-purity sodium aluminate solution to the diluent is 1.2 to 1.5.

[0035] The high-purity sodium aluminate solution is diluted with a diluent to adjust its concentration to a range suitable for subsequent decomposition processes. The diluent can be deionized water or recycled alkaline water from the production line. Maintaining a volume ratio of 1.2 to 1.5 between the high-purity sodium aluminate solution and the diluent allows for precise control of the alumina concentration and caustic ratio in the resulting high-purity decomposition and refining solution. This ratio also ensures a suitable supersaturation level in the high-purity decomposition and refining solution, which is beneficial for controlling the nucleation and growth rate of aluminum hydroxide crystals when added to the decomposition tank and seed slurry for subsequent decomposition. The high-purity decomposition and refining solution obtained at this ratio promotes stable and uniform growth of aluminum hydroxide crystals on the seed surface, resulting in an aluminum hydroxide product with a concentrated particle size distribution, regular morphology, and easy filtration and washing.

[0036] In some embodiments, the aluminum hydroxide seed material is obtained by cyclically decomposing and purifying the high-purity sodium aluminate solution with aluminum hydroxide of ≥99% purity 8 to 9 times.

[0037] A batch of aluminum hydroxide with a purity ≥99% was mixed with a batch of high-purity sodium aluminate solution and reacted under decomposition conditions to generate a first-generation seed material. The generated first-generation seed material was mixed with deionized water, crushed, filtered, and washed to obtain primary purified aluminum hydroxide. The primary purified aluminum hydroxide was then mixed, reacted, crushed, filtered, and washed again with a fresh batch of high-purity sodium aluminate solution. This process was repeated 8–9 times. Impurities were expelled to the liquid phase in each cycle of decomposition reaction and removed through filtration and washing after each cycle, resulting in a final aluminum hydroxide seed material with a purity significantly higher than the initial aluminum hydroxide with a purity ≥99%. Through 8–9 cycles of decomposition and purification, the aluminum hydroxide seed material was ensured to have extremely high chemical purity and structural consistency. The aluminum hydroxide seed material was used to subsequently prepare seed slurry, thus providing pure crystal nuclei for the decomposition process of the high-purity decomposition and refining solution.

[0038] In some embodiments, the solid content of the seed slurry is 150 g / L to 300 g / L, the seed particle size of the seed slurry is 1 μm to 10 μm, and the mass of the seed slurry is 4 g to 30 g.

[0039] Solid content refers to the mass concentration of solid particles (i.e., aluminum hydroxide seed raw material) in the seed slurry, usually expressed in grams per liter (g / L). Controlling the solid content of the seed slurry to 150 g / L to 300 g / L ensures that the seed slurry has a suitable suspension concentration and fluidity, facilitating the transportation and addition of the seed slurry to the decomposition tank.

[0040] Seed particle size refers to the size of particles in aluminum hydroxide seed raw materials, usually expressed in micrometers (μm). Controlling the particle size of aluminum hydroxide seed raw materials in the seed slurry to 1μm to give the aluminum hydroxide seed raw materials a large specific surface area can provide a large number of uniform crystallization sites for the high-purity decomposition and refining liquid in the subsequent decomposition process.

[0041] The seed slurry mass in this embodiment typically refers to the total amount of seed slurry added to the decomposition tank, expressed in grams (g). Controlling the seed slurry mass to 4g–30g limits the absolute amount of aluminum hydroxide seed material added to the decomposition tank. The seed slurry mass range is matched to the total volume of the decomposition tank and the feed rate of the high-purity decomposition refining solution, ensuring effective initiation and maintenance of the decomposition reaction while avoiding abnormal crystal growth due to excessive or insufficient seed content.

[0042] In some embodiments, the set stirring speed is 50 rpm to 60 rpm.

[0043] The stirring speed in the decomposition tank is set at 50 rpm to 60 rpm to create a uniform and stable hydrodynamic environment for the decomposition reaction. This speed ensures the seed slurry remains uniformly suspended, preventing sedimentation of the aluminum hydroxide seed material. When the high-purity decomposition and refining liquid is pumped into the decomposition tank at the set speed, the 50 rpm to 60 rpm stirring speed facilitates rapid and uniform dispersion of the high-purity liquid throughout the entire material system, preventing localized over-concentration near the feed point. Uniform mixing helps maintain consistent concentration and temperature within the decomposition tank, providing consistent reaction conditions for crystal growth on the surface of the aluminum hydroxide seed material and promoting the formation of aluminum hydroxide crystals with uniform particle size distribution. Simultaneously, the 50 rpm to 60 rpm stirring speed provides the necessary mixing intensity while avoiding excessive shear force that could break up the already grown aluminum hydroxide crystals or induce excessive secondary nucleation.

[0044] In some implementations, the set speed is 2L / h to 3L / h.

[0045] The set pumping rate of the high-purity decomposition and refining solution into the decomposition tank is 2 L / h to 3 L / h, which is a precise control of the feed rate for the decomposition reaction. This feed rate of 2 L / h to 3 L / h is coordinated with the total volume of the decomposition tank, the set stirring speed, and the temperature control of the decomposition tank. This set rate means that the high-purity decomposition and refining solution is added to the decomposition tank containing the seed slurry at a slow and constant rate. The slow feed rate avoids excessively high local concentrations of the high-purity decomposition and refining solution within the decomposition tank, thus maintaining a stable and suitable supersaturation level in the entire decomposition reaction system. Stable supersaturation promotes uniform and continuous crystal growth on the surface of the aluminum hydroxide seed material, inhibiting the spontaneous formation of numerous new crystal nuclei. Controlling the set feed rate to 2 L / h to 3 L / h ensures that the entire feeding process matches the crystal growth rate, which is one of the key operating conditions for obtaining uniformly sized and densely structured aluminum hydroxide crystals and reducing impurity inclusions.

[0046] In some implementations, the set ratio is 1 / 8 to 1 / 4.

[0047] The set ratio refers to the cumulative volume of the high-purity decomposition and refining liquid pumped into the decomposition tank, representing a fraction of the total volume of the decomposition tank. Controlling the set ratio to 1 / 8 to 1 / 4 defines the timing of critical temperature switching during the feeding and decomposition processes in the decomposition tank. When the feed volume of the high-purity decomposition and refining liquid reaches 1 / 8 to 1 / 4 of the total volume of the decomposition tank, a temperature adjustment operation is triggered, shifting the temperature of the decomposition tank from the first temperature range to the second temperature range. The selection of this 1 / 8 to 1 / 4 ratio range is based on process control during the crystal growth stage. In the initial feeding stage, the decomposition tank mainly contains seed slurry. At this stage, the first temperature range (70℃ to 75℃) is required to maintain the activity of the aluminum hydroxide seed material and initiate decomposition. When the feed volume reaches 1 / 8 to 1 / 4 of the total volume, a certain volume of mixed slurry has formed in the decomposition tank, and crystal growth enters a stable period. At this time, adjusting the temperature to the lower second temperature range (65℃ to 69℃) can effectively reduce the supersaturation of the high-purity decomposition and refining liquid, keeping it within a metastable zone. Within this region, the high-purity decomposition and refining solution tends to precipitate aluminum hydroxide, but this is insufficient to spontaneously generate a large number of new crystal nuclei; instead, it tends to grow only on the surface of existing seed crystals. This allows the crystals to grow uniformly and orderly, resulting in a product with coarse particle size and uniform distribution. The coarse particles are easier to separate from the mother liquor during subsequent filtration and washing, and carry fewer sodium impurities. Setting a ratio of 1 / 8 to 1 / 4 as a process control point ensures a smooth transition from the initial "induced start-up" stage to the later "controlled growth" stage of the decomposition process. This is a crucial parameter for optimizing the decomposition reaction path and ensuring the quality of the final low-sodium, high-purity aluminum hydroxide product.

[0048] In some embodiments, the first temperature range is 70°C to 75°C, and the second temperature range is 65°C to 69°C.

[0049] The initial temperature of the decomposition tank is controlled within a first temperature range of 70℃ to 75℃ to provide suitable thermodynamic conditions for the initiation of the decomposition reaction. This first temperature range of 70℃ to 75℃ maintains the surface activity of the aluminum hydroxide seed material in the seed slurry, promoting effective nucleus attachment and growth of the high-purity decomposition and refining solution on the surface of the aluminum hydroxide seed material during the initial feeding stage. When the feed amount of the high-purity decomposition and refining solution reaches a set proportion of the total volume of the decomposition tank, the temperature of the decomposition tank is adjusted from the first temperature range to a second temperature range of 65℃ to 69℃. This is because with the continuous addition of a large amount of high-purity decomposition and refining solution, the supersaturation of the entire reaction system increases sharply. Excessive supersaturation is the root cause of the generation of a large number of new, fine crystal nuclei (spontaneous nucleation), which leads to finer, less uniform product particle size and easy encapsulation of impurities (such as sodium ions) in the mother liquor. Lowering the temperature from 70℃ to 75℃ to 65℃ to 69℃ effectively reduces the supersaturation of the sodium aluminate solution, keeping it within a metastable region. Within this region, the solution tends to precipitate aluminum hydroxide, but this is insufficient to spontaneously generate a large number of new crystal nuclei; instead, it tends to grow on the surface of existing seed crystals. In this way, all newly precipitated aluminum hydroxide grows onto the pre-added seed particles, allowing the crystals to grow uniformly and orderly, resulting in a product with large and evenly distributed particles. The large particles are easier to separate from the mother liquor during subsequent filtration and washing, and contain fewer entrained sodium impurities. Simultaneously, the temperature adjustment strategy enables a controllable transition from rapid initiation in the early stages of the decomposition process to stable growth in the later stages, contributing to obtaining aluminum hydroxide products with the desired particle size and morphology. The precise setting and switching between the first and second temperature ranges are key process techniques for controlling the decomposition reaction kinetics, optimizing the crystal growth environment, and ultimately ensuring the performance of the final low-sodium, high-purity aluminum hydroxide product.

[0050] In some embodiments, the decomposition reaction takes 8 to 16 hours.

[0051] The decomposition reaction time is controlled at 8 to 16 hours, which refers to the total time during which the material in the decomposition tank continues to crystallize and grow under the second temperature range and the set stirring speed after the high-purity decomposition refining liquid has filled the tank and feeding has stopped. This 8-16 hour decomposition reaction time ensures that the sodium aluminate component in the decomposition tank has sufficient time to fully decompose on the surface of the aluminum hydroxide seed material and complete crystal growth. The 8-16 hour time range, combined with the second temperature range (65℃-69℃) and the set stirring speed (50 rpm-60 rpm), ensures a stable and sufficient growth process for the aluminum hydroxide crystals. Sufficient decomposition reaction time is beneficial for forming aluminum hydroxide crystals with a complete crystal structure and concentrated particle size distribution, and promotes the full diffusion of impurity ions from the solid phase to the liquid phase. A decomposition reaction time of less than 8 hours may lead to incomplete decomposition, affecting the yield and crystal properties of aluminum hydroxide; a decomposition reaction time exceeding 16 hours may lead to reduced production efficiency and no longer significantly improve product quality. Controlling the decomposition reaction time to 8 h to 16 h is a necessary condition for achieving high conversion rate and obtaining aluminum hydroxide slurry with excellent physicochemical properties, laying the material foundation for obtaining low-sodium, high-purity aluminum hydroxide through subsequent filtration and washing.

[0052] In some embodiments, the step of sequentially filtering and washing the aluminum hydroxide slurry to obtain low-sodium, high-purity aluminum hydroxide includes: The aluminum hydroxide slurry is first filtered to obtain aluminum hydroxide filter cake; The aluminum hydroxide filter cake was subjected to a static washing process using hot water at 55℃~85℃ and a pressure of 0.2MPa~0.5MPa. The aluminum hydroxide filter cake after static washing is first dried by blowing. The aluminum hydroxide filter cake after the first drying is subjected to a second stage of agitation and washing using hot water at 55℃~85℃. The aluminum hydroxide filter cake after two stages of agitation and washing is subjected to a second filtration and a second drying process to obtain low-sodium, high-purity aluminum hydroxide.

[0053] Through segmented, multi-mode washing and efficient solid-liquid separation, this method aims to systematically and deeply remove various forms of sodium impurities from solid aluminum hydroxide. The first stage of static washing, under pressure, primarily removes free mother liquor from the macroscopic gaps in the filter cake. The intermediate drying stage reduces free water, creating more effective solid-liquid contact conditions for subsequent agitation washing. The second stage of agitation washing, through mechanical stirring and diffusion, targets and removes sodium ions adsorbed on the particle surface and encapsulated in microcrystals. Finally, a second filtration and a second drying stage ensure the product's moisture content meets specifications.

[0054] In some embodiments, during the static washing process, 15L to 35L of hot water is used per kilogram of aluminum hydroxide filter cake.

[0055] A static wash of 15 L to 35 L of hot water per kilogram of aluminum hydroxide filter cake is used to provide sufficient but not excessive washing medium. This water volume range ensures that, under a pressure of 0.2 MPa to 0.5 MPa, the hot water has enough volume to fully penetrate and saturate the entire aluminum hydroxide filter cake layer, effectively displacing the high-sodium decomposition mother liquor trapped between the filter cake particles. The minimum dosage of 15 L / kg guarantees basic washing and displacement effects; the maximum dosage of 35 L / kg avoids increased load and wasted heat energy in subsequent treatments due to excessive water usage. This washing ratio efficiently removes most of the sodium ions in free form, representing the first crucial step in achieving deep sodium removal. The 15 L to 35 L dosage range, combined with the hot water temperature (55℃ to 85℃) and washing pressure (0.2 MPa to 0.5 MPa), optimizes the mass transfer efficiency of the static wash, preparing an aluminum hydroxide filter cake with initially reduced sodium content for subsequent first-stage drying and second-stage agitation washing processes.

[0056] In some embodiments, during the two-stage washing process, the amount of hot water used per kilogram of aluminum hydroxide filter cake is 5L to 30L.

[0057] The aluminum hydroxide filter cake is washed in two stages using 5 L to 30 L of hot water per kilogram of filter cake, aiming to provide a precise solid-liquid ratio for deep washing. This water volume range of 5 L to 30 L allows the first-drying aluminum hydroxide filter cake to redisperse into a slurry suspension of suitable concentration. The minimum water volume of 5 L / kg ensures the formation of an effectively agitated slurry, allowing for sufficient contact between the hot water and the aluminum hydroxide particles; the maximum water volume of 30 L / kg avoids an excessively thin slurry due to excessive water volume, which would reduce washing efficiency and increase the load on the subsequent second filtration. The two-stage washing with 5 L to 30 L of hot water per kilogram of aluminum hydroxide filter cake enhances mass transfer between the hot water and the aluminum hydroxide particles through mechanical agitation, effectively desorbing and washing away residual sodium ions adhering to the particle surface and internal micropores. The 5 L to 30 L volume range, combined with the hot water temperature (55℃ to 85℃), promotes the diffusion of sodium ions from the solid phase to the liquid phase.

[0058] In some embodiments, the moisture content of the filter cake is controlled to be below 15% during both the first and second drying processes.

[0059] Controlling the moisture content of the aluminum hydroxide filter cake to below 15% during the first drying process creates the optimal material state for the subsequent second-stage washing step. After the first static washing, a large amount of washing liquid still adheres to the internal pores and particle surfaces of the aluminum hydroxide filter cake. Reducing the moisture content of the aluminum hydroxide filter cake to below 15% through the first drying significantly reduces the total amount of free water in the filter cake. This makes it easier for the aluminum hydroxide filter cake to be uniformly dispersed and wetted by fresh hot water when entering the second-stage washing, thereby greatly improving the mass transfer efficiency and sodium removal effect of the second-stage washing.

[0060] Controlling the moisture content of the aluminum hydroxide filter cake to below 15% during the second drying process is a direct requirement for obtaining a qualified final product. After completing the two-stage washing and second filtration, the aluminum hydroxide filter cake becomes a deeply washed, low-sodium, high-purity aluminum hydroxide wet cake. The second drying process strictly controls the moisture content of the final product to below 15%, achieving the product dryness quality standard.

[0061] In some embodiments, the purity of the low-sodium high-purity aluminum hydroxide is ≥99.95%, and the sodium content of the low-sodium high-purity aluminum hydroxide is ≤500 ppm.

[0062] A purity of ≥99.95% and a sodium content of ≤500 ppm together define the core quality characteristics of low-sodium high-purity aluminum hydroxide. The low-sodium high-purity aluminum hydroxide prepared in this application combines extremely high chemical purity with extremely low content of characteristic impurities (sodium), meeting the stringent requirements for material performance in high-end applications.

[0063] 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 / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0064] Example 1 A sodium aluminate solution was prepared by dissolving 32% (w / w) industrial ion-exchange membrane alkali and 99% (purity) aluminum hydroxide in a 2.2:1 ratio at 100°C. Activated carbon, an impurity-removing additive, was added to the sodium aluminate solution and stirred for 60 minutes. The solution was then filtered to remove the activated carbon and adsorbed / flocculated impurities, yielding a clear, transparent, high-purity sodium aluminate solution. This high-purity sodium aluminate solution was then diluted with deionized water (as a diluent) at a volume ratio of 1.4:1 and stirred until homogeneous to obtain a high-purity decomposition and purification solution.

[0065] Preparation of aluminum hydroxide seed raw materials and seed slurry: (1) Preparation of seed raw materials: High-purity sodium aluminate solution and 99% pure aluminum hydroxide were used for cyclic decomposition and purification in a small decomposition tank. Specifically, aluminum hydroxide was mixed with high-purity sodium aluminate solution and decomposed to obtain first-generation seed raw materials. The generated first-generation seed raw materials were mixed with deionized water, crushed to 1.5 μm, filtered, and washed to obtain first-purified aluminum hydroxide. This aluminum hydroxide was used as the raw material for the next batch and decomposed, crushed, filtered, and washed again with fresh high-purity sodium aluminate solution. The cycle was repeated 9 times to finally obtain ultra-high purity aluminum hydroxide seed raw materials.

[0066] (2) Preparation of seed slurry: The seed raw material of aluminum hydroxide is mixed with deionized water and crushed to obtain seed slurry. The seed particle size is controlled to 1.5μm and the solid content of seed slurry is controlled to 150g / L.

[0067] Add 14g of the prepared seed slurry to the decomposition tank, start the stirring and heating system of the decomposition tank, and control the temperature of the material in the decomposition tank at 74℃, maintaining the stirring speed of the decomposition tank at 52 rpm. Pump the prepared high-purity decomposition and refining liquid into the decomposition tank at a constant rate of 3L / h. When the cumulative volume of the pumped high-purity decomposition and refining liquid reaches 1 / 8 of the total volume of the decomposition tank, adjust the temperature control system of the decomposition tank to steadily reduce the temperature of the material in the tank from 74℃ to 66℃. After temperature adjustment, continue pumping high-purity decomposition and refining liquid at a rate of 3 L / h until the decomposition tank is full. After the tank is full, maintain the temperature of the material in the decomposition tank at 66℃ and the stirring speed at 52 rpm, and continue the decomposition reaction for 16 hours. After the reaction is completed, an aluminum hydroxide slurry containing a large amount of suspended solids is obtained.

[0068] The aluminum hydroxide slurry was subjected to a first filtration, a first static washing, a first drying, a second stirring washing, a second filtration, and a second drying in sequence to obtain low-sodium, high-purity aluminum hydroxide.

[0069] in: The static washing water temperature is 60℃ and the pressure is 0.25MPa. 15L of washing water is used per ton of aluminum hydroxide filter cake.

[0070] Two-stage washing: 10L of washing water is used per ton of aluminum hydroxide filter cake.

[0071] After each drying process, the moisture content of the filter cake is below 15%.

[0072] Chemical composition analysis was performed on the prepared low-sodium, high-purity aluminum hydroxide product.

[0073] Purity determination: The purity of the product was determined by a combination of X-ray fluorescence spectroscopy (XRF) and loss on ignition method, and the purity result was 99.95%.

[0074] Sodium content determination: The sodium content of the product was determined by inductively coupled plasma mass spectrometry (ICP-MS) and the result was 485 ppm.

[0075] Example 2 A sodium aluminate solution was prepared by dissolving 32% (w / w) industrial ion-exchange membrane alkali and 99% (purity) aluminum hydroxide in a 2.2:1 ratio at a dissolution temperature of 102℃. An impurity removal additive (activated carbon + aluminum hydroxide) was added to the obtained sodium aluminate solution and stirred for 60 minutes. Subsequently, the sodium aluminate solution with the additive was filtered to remove activated carbon and adsorbed / flocculated impurities, yielding a clear and transparent high-purity sodium aluminate solution. This high-purity sodium aluminate solution was then diluted with deionized water (as a diluent) at a volume ratio of 1.3:1 and stirred until homogeneous to obtain a high-purity decomposition and purification solution.

[0076] Preparation of aluminum hydroxide seed raw materials and seed slurry: (1) Preparation of seed raw materials: High-purity sodium aluminate solution and 99% pure aluminum hydroxide were used for cyclic decomposition and purification in a small decomposition tank. Specifically, aluminum hydroxide was mixed with high-purity sodium aluminate solution and decomposed to obtain first-generation seed raw materials. The generated first-generation seed raw materials were mixed with deionized water, crushed to 3μm, filtered, and washed to obtain first-purified aluminum hydroxide. This aluminum hydroxide was used as the raw material for the next batch and decomposed, crushed, filtered, and washed again with fresh high-purity sodium aluminate solution. The cycle was repeated 9 times to finally obtain ultra-high purity aluminum hydroxide seed raw materials.

[0077] (2) Preparation of seed slurry: The seed raw material of aluminum hydroxide is mixed with deionized water and crushed to obtain seed slurry. The seed particle size is controlled to 3μm and the solid content of seed slurry is controlled to 220g / L.

[0078] Add 30g of the prepared seed slurry to the decomposition tank, start the stirring and heating system of the decomposition tank, and control the temperature of the material in the decomposition tank at 75℃, maintaining the stirring speed of the decomposition tank at 52 rpm. Pump the prepared high-purity decomposition and refining liquid into the decomposition tank at a constant rate of 3L / h. When the cumulative volume of the pumped high-purity decomposition and refining liquid reaches 1 / 4 of the total volume of the decomposition tank, adjust the temperature control system of the decomposition tank to steadily reduce the temperature of the material in the tank from 75℃ to 69℃. After temperature adjustment, continue pumping high-purity decomposition and refining liquid at a rate of 3 L / h until the decomposition tank is full. After the tank is full, maintain the temperature of the material in the decomposition tank at 69℃ and the stirring speed at 52 rpm, and continue the decomposition reaction for 8 hours. After the reaction is completed, an aluminum hydroxide slurry containing a large amount of suspended solids is obtained.

[0079] The aluminum hydroxide slurry was subjected to a first filtration, a first static washing, a first drying, a second stirring washing, a second filtration, and a second drying in sequence to obtain low-sodium, high-purity aluminum hydroxide.

[0080] in: The static washing water temperature is 85℃ and the pressure is 0.25MPa. 15L of washing water is used per kilogram of aluminum hydroxide filter cake.

[0081] Two-stage washing: 10L of washing water is used per kilogram of aluminum hydroxide filter cake.

[0082] After each drying process, the moisture content of the filter cake is below 15%.

[0083] Chemical composition analysis was performed on the prepared low-sodium, high-purity aluminum hydroxide product.

[0084] Purity determination: The purity of the product was determined by a combination of X-ray fluorescence spectroscopy (XRF) and loss on ignition method, and the purity result was 99.95%.

[0085] Sodium content determination: The sodium content of the product was determined by inductively coupled plasma mass spectrometry (ICP-MS) and the result was 423 ppm.

[0086] Example 3 A sodium aluminate solution was prepared by dissolving 32% (w / w) industrial ion-exchange membrane alkali and 99% (purity) aluminum hydroxide in a 1.7:1 ratio at a dissolution temperature of 105°C. An impurity-removing additive (activated carbon + aluminum hydroxide) was added to the obtained sodium aluminate solution and stirred for 60 minutes. Subsequently, the sodium aluminate solution with the additive was filtered to remove activated carbon and adsorbed / flocculated impurities, yielding a clear and transparent high-purity sodium aluminate solution. This high-purity sodium aluminate solution was then diluted with deionized water (as a diluent) at a volume ratio of 1.5:1 and stirred until homogeneous to obtain a high-purity decomposition and purification solution.

[0087] Preparation of aluminum hydroxide seed raw materials and seed slurry: (1) Preparation of seed raw materials: High-purity sodium aluminate solution and 99% pure aluminum hydroxide were used for cyclic decomposition and purification in a small decomposition tank. Specifically, aluminum hydroxide was mixed with high-purity sodium aluminate solution and decomposed to obtain first-generation seed raw materials. The generated first-generation seed raw materials were mixed with deionized water, crushed to 2μm, filtered, and washed to obtain first-purified aluminum hydroxide. This aluminum hydroxide was used as the raw material for the next batch and decomposed, crushed, filtered, and washed again with fresh high-purity sodium aluminate solution. The cycle was repeated 5 times to finally obtain ultra-high purity aluminum hydroxide seed raw materials.

[0088] (2) Preparation of seed slurry: The seed raw material of aluminum hydroxide is mixed with deionized water and crushed to obtain seed slurry. The seed particle size is controlled to 2μm and the solid content of seed slurry is controlled to 300g / L.

[0089] Add 5g of the prepared seed slurry to the decomposition tank, start the stirring and heating system of the decomposition tank, and control the temperature of the material in the decomposition tank at 72℃, maintaining the stirring speed of the decomposition tank at 52 rpm. Pump the prepared high-purity decomposition and refining liquid into the decomposition tank at a constant rate of 3L / h. When the cumulative volume of the pumped high-purity decomposition and refining liquid reaches 1 / 4 of the total volume of the decomposition tank, adjust the temperature control system of the decomposition tank to steadily reduce the temperature of the material in the tank from 72℃ to 66.5℃. After temperature adjustment, continue pumping high-purity decomposition and refining liquid at a rate of 3 L / h until the decomposition tank is full. After the tank is full, maintain the temperature of the material in the decomposition tank at 66.5℃ and the stirring speed at 52 rpm, and continue the decomposition reaction for 12 hours. After the reaction is completed, an aluminum hydroxide slurry containing a large amount of suspended solids is obtained.

[0090] The aluminum hydroxide slurry was subjected to a first filtration, a first static washing, a first drying, a second stirring washing, a second filtration, and a second drying in sequence to obtain low-sodium, high-purity aluminum hydroxide.

[0091] in: The static washing water temperature is 85℃ and the pressure is 0.25MPa. 15L of washing water is used per kilogram of aluminum hydroxide filter cake.

[0092] Two-stage washing: 10L of washing water is used per kilogram of aluminum hydroxide filter cake.

[0093] After each drying process, the moisture content of the filter cake is below 15%.

[0094] Chemical composition analysis was performed on the prepared low-sodium, high-purity aluminum hydroxide product.

[0095] Purity determination: The purity of the product was determined by a combination of X-ray fluorescence spectroscopy (XRF) and loss on ignition method, and the purity result was 99.95%.

[0096] Sodium content determination: The sodium content of the product was determined by inductively coupled plasma mass spectrometry (ICP-MS) and the result was 479 ppm.

[0097] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: The high-purity aluminum hydroxide obtained by the preparation process provided in this invention has a purity of over 99.95%, which is significantly higher than the purity of products on the general market and can meet the strict requirements for material purity in high-end fields.

[0098] The embodiments of the present invention reduce the sodium (Na) content in aluminum hydroxide products to below 500 ppm, effectively solving the adverse effects of excessive sodium content on material performance.

[0099] 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 method for preparing low-sodium, high-purity aluminum hydroxide, characterized in that, The method includes: A sodium aluminate solution is obtained by mixing and dissolving aluminum hydroxide with a purity of ≥99% and industrial ion-exchange membrane alkali with a mass concentration of 32%. The sodium aluminate solution is subjected to impurity removal and filtration to obtain a high-purity sodium aluminate solution. The high-purity sodium aluminate solution was diluted to obtain a high-purity decomposition and purification solution; Aluminum hydroxide seed raw materials and deionized water are mixed and crushed to obtain seed slurry; The seed slurry is added to the decomposition tank, and the temperature of the decomposition tank is controlled within a first temperature range; At a set stirring speed, the high-purity decomposition and refining liquid is pumped into the decomposition tank at a set speed. When the feed amount of the high-purity decomposition and refining liquid reaches a set ratio of the total volume of the decomposition tank, the temperature of the decomposition tank is adjusted to the second temperature range, and feeding continues until the tank is full. The material in the decomposition tank is further decomposed to obtain aluminum hydroxide slurry; The aluminum hydroxide slurry was filtered and washed sequentially to obtain low-sodium, high-purity aluminum hydroxide. The first temperature range is 70℃~75℃, and the second temperature range is 65℃~69℃; The set stirring speed is 50 rpm to 60 rpm; The set speed is 2L / h to 3L / h; The set ratio is 1 / 8 to 1 / 4.

2. The method according to claim 1, characterized in that, The aluminum hydroxide seed material is obtained by cyclically decomposing and purifying the high-purity sodium aluminate solution with aluminum hydroxide of ≥99% purity 8 to 9 times; and / or, The solid content of the seed slurry is 150 g / L to 300 g / L, the seed particle size of the seed slurry is 1 μm to 10 μm, and the mass of the seed slurry is 4 g to 30 g.

3. The method according to claim 1, characterized in that, The mixing and dissolution temperature is 102℃~105℃, and the mass ratio of the 32% industrial ion-exchange membrane alkali to the aluminum hydroxide with a purity ≥99% is (1.5~2.2):

1.

4. The method according to claim 1, characterized in that, The dilution is performed by diluting the high-purity sodium aluminate solution with a diluent, wherein the volume ratio of the high-purity sodium aluminate solution to the diluent is 1.2 to 1.

5.

5. The method according to claim 1, characterized in that, The decomposition reaction takes 8 to 16 hours.

6. The method according to claim 1, characterized in that, The impurity removal includes adding an impurity removal additive to the sodium aluminate solution, wherein the impurity removal additive is at least one of activated carbon, EDTA, PAM, chitosan, and aluminum hydroxide.

7. The method according to claim 1, characterized in that, The step of sequentially filtering and washing the aluminum hydroxide slurry to obtain low-sodium, high-purity aluminum hydroxide includes: The aluminum hydroxide slurry is first filtered to obtain aluminum hydroxide filter cake; The aluminum hydroxide filter cake was subjected to a static washing process using hot water at 55℃~85℃ and a pressure of 0.2MPa~0.5MPa. The aluminum hydroxide filter cake after static washing is first dried by blowing. The aluminum hydroxide filter cake after the first drying is subjected to a second stage of agitation and washing using hot water at 55℃~85℃. The aluminum hydroxide filter cake after two stages of agitation and washing is subjected to a second filtration and a second drying process to obtain low-sodium, high-purity aluminum hydroxide.

8. The method according to claim 7, characterized in that, During the aforementioned static washing process, 15L to 35L of hot water is used per kilogram of the aluminum hydroxide filter cake; and / or, During the two-stage washing process, the amount of hot water used per kilogram of aluminum hydroxide filter cake is 5L to 30L; and / or, During both the first and second drying processes, the moisture content of the filter cake is controlled to be below 15%.

9. The method according to claim 1, characterized in that, The purity of the low-sodium high-purity aluminum hydroxide is ≥99.95%, and the sodium content of the low-sodium high-purity aluminum hydroxide is ≤500 ppm.

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