A method for preparing low-sodium-oxide Bayer process micronized aluminum hydroxide

Abstract

This application discloses a method for preparing low-sodium-oxide Bayer process micronized aluminum hydroxide, comprising: adding seed crystals to a Bayer process sodium aluminate solution to induce the generation and growth of aluminum hydroxide crystal nuclei in the Bayer process sodium aluminate solution; adding sodium aluminate concentrate to the material after the first decomposition reaction in multiple stages to induce a second decomposition reaction to promote the lattice reconstruction of the aluminum hydroxide crystal nuclei and the removal of sodium ions from the sodium aluminate solution; performing solid-liquid separation on the material after the second decomposition reaction to obtain a solid material; and washing and drying the solid material to obtain micronized aluminum hydroxide. Through the synergistic effects of seed-induced crystallization, staged decomposition reaction, temperature control, solid-liquid separation, and washing, the residual sodium oxide content is reduced from multiple stages, achieving efficient preparation of low-sodium-oxide micronized aluminum hydroxide.

Description

Technical Field

[0001] This application relates to the field of inorganic material synthesis technology, and in particular to a method for preparing low-sodium-oxide Bayer process micronized aluminum hydroxide. Background Technology

[0002] Aluminum hydroxide, as an important inorganic material, is widely used in electronic ceramics, flame retardant materials, and high-voltage insulation materials. Among these, micronized aluminum hydroxide is experiencing increasing market demand due to its unique physicochemical properties. However, micronized aluminum hydroxide produced using the traditional Bayer process suffers from high sodium oxide residue levels, typically exceeding 0.20%. This high sodium residue significantly reduces the dielectric properties of electronic ceramics and affects the thermal stability of flame retardant materials, making it difficult to meet the demands of high-end applications such as 5G communication substrates and high-voltage insulation materials.

[0003] Existing processes have several shortcomings in reducing sodium oxide residue. Single-stage decomposition processes are limited by their singular reaction environment, resulting in low sodium ion desorption efficiency and frequent particle agglomeration, which in turn affects the stability of the micronized aluminum hydroxide product. While continuous gradient decomposition processes attempt to improve sodium ion removal efficiency by controlling reaction conditions in stages, improper parameter matching leads to sluggish reaction kinetics in the later stages of decomposition, causing the sodium removal rate to remain below 40%, failing to achieve the desired effect. Furthermore, traditional washing processes only target surface-adsorbed sodium ions, proving ineffective against sodium ions deeply embedded within the crystal lattice, thus failing to fundamentally overcome the problem of high sodium oxide residue. Summary of the Invention

[0004] This application provides a method for preparing low-sodium-oxide Bayer process micronized aluminum hydroxide to solve the following technical problem: how to reduce the residual sodium oxide content in micronized aluminum hydroxide produced by the Bayer process.

[0005] This application provides a method for preparing low-sodium-oxide Bayer process micronized aluminum hydroxide, comprising:

[0006] Seed crystals are added to a Bayer process sodium aluminate solution to induce a decomposition reaction, thereby inducing the generation and growth of aluminum hydroxide crystal nuclei in the Bayer process sodium aluminate solution.

[0007] Sodium aluminate concentrate is added to the material after the first stage decomposition reaction in multiple stages to carry out a second stage decomposition reaction, so as to promote the lattice reconstruction of the aluminum hydroxide crystal nuclei and the removal of sodium ions from the sodium aluminate solution.

[0008] The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material;

[0009] The solid material is washed and dried to obtain micronized aluminum hydroxide.

[0010] The seed crystals have a particle size of 1.0 to 3.5 μm;

[0011] The temperature of the second-stage decomposition reaction is higher than the temperature of the first-stage decomposition reaction.

[0012] Optionally, the temperature of the decomposition reaction is 40-80℃; and / or,

[0013] The temperature of the two-stage decomposition reaction is 50-85℃.

[0014] Optionally, the parameters of the decomposition reaction may further include: a reaction time of 10-48 hours, a stirring rate of 20-50 r / min; and / or,

[0015] The parameters for the two-stage decomposition reaction also include: a reaction time of 20-72 hours.

[0016] Optionally, the Bayer process sodium aluminate solution satisfies the following conditions: caustic ratio α is 1.35-1.70, and alumina mass concentration is 100-200 g / L.

[0017] Optionally, the volume of the seed crystal is 1%-6% of the volume of the Bayer process sodium aluminate solution.

[0018] Optionally, in the decomposition reaction, the volume of the Bayer process sodium aluminate solution is 80-250 m³. 3 The Bayer process sodium aluminate solution is injected into the reactor over a period of 0.5-3 hours; and / or,

[0019] In the two-stage decomposition reaction, the volume of sodium aluminate semen added each time is 40-100 ml. 3 The time interval between two consecutive additions of the sodium aluminate semen is 2-8 hours.

[0020] Optionally, the moisture content of the solid material is ≤45%.

[0021] Optionally, the washing is performed at least twice, and the liquid-to-solid ratio of the washing liquid to the solid material is 1.5:1 to 5:1.

[0022] Optionally, the drying parameters include: a temperature of 70-130°C and a time of 1-6 hours.

[0023] Optionally, the moisture content of the micronized aluminum hydroxide powder is ≤0.5%.

[0024] The technical solutions provided in this application have the following advantages compared with the prior art:

[0025] This application provides a method for preparing low-sodium-oxide Bayer process micronized aluminum hydroxide. Its core principle lies in optimizing the crystallization process and enhancing sodium ion removal. First, seed crystals with a particle size of 1.0 to 3.5 μm are added to a sodium aluminate solution to induce the generation and growth of aluminum hydroxide nuclei. The presence of seed crystals provides nucleation centers for crystallization, making the crystallization process more orderly and reducing the adsorption and encapsulation of impurities (including sodium ions) on the surface of aluminum hydroxide, thereby reducing the possibility of sodium oxide residue at the source. Second, a staged decomposition reaction is adopted. After the first stage decomposition, sodium aluminate concentrate is added to the material multiple times for a second stage decomposition. The temperature of the second stage decomposition reaction is higher than that of the first stage. This design not only promotes the lattice reconstruction of aluminum hydroxide nuclei and optimizes the crystal structure, but also accelerates the removal of sodium ions from the lattice, allowing them to enter the solution, further reducing sodium oxide residue. Furthermore, the material after the second stage decomposition undergoes solid-liquid separation and washing to further remove residual sodium ions from the surface. Solid-liquid separation separates solid aluminum hydroxide from the sodium-containing solution, while washing further dissolves the sodium ions adsorbed on the surface, reducing the sodium oxide content. Finally, the drying process stabilizes the aluminum hydroxide structure, effectively preventing the re-adsorption of sodium ions. In summary, the embodiments of this application, through the synergistic effects of seed-induced crystallization, segmented decomposition reaction, temperature control, solid-liquid separation, and washing, reduce the residual sodium oxide content at multiple stages, achieving efficient preparation of low-sodium-oxide micronized aluminum hydroxide powder. Attached Figure Description

[0026] 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.

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings required in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other related drawings can be derived from these drawings without creative effort.

[0028] Figure 1 This is a flowchart illustrating a method for preparing low-sodium-oxide Bayer process micronized aluminum hydroxide, as provided in this application embodiment. Detailed Implementation

[0029] To more clearly illustrate the purpose, technical solutions, and advantages of the embodiments of this application, the technical solutions of this embodiment will be described in detail below with reference to the accompanying drawings. Please note that the mentioned embodiments are merely examples and not all possible implementations. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0030] 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 to 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 "comprise" 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.

[0031] Figure 1 This is a flowchart illustrating a method for preparing low-sodium-oxide Bayer process micronized aluminum hydroxide, as provided in this application embodiment.

[0032] Please see Figure 1 This application provides a method for preparing low-sodium-oxide Bayer process micronized aluminum hydroxide, comprising:

[0033] S1. Add seed crystals to the Bayer process sodium aluminate solution to carry out a decomposition reaction to induce the generation and growth of aluminum hydroxide crystal nuclei in the Bayer process sodium aluminate solution;

[0034] S2. Add sodium aluminate concentrate to the material after the first stage decomposition reaction in multiple stages to carry out a second stage decomposition reaction, so as to promote the lattice reconstruction of the aluminum hydroxide crystal nuclei and the removal of sodium ions from the sodium aluminate solution.

[0035] S3. The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material;

[0036] S4. The solid material is washed and dried to obtain micronized aluminum hydroxide;

[0037] The seed crystals have a particle size of 1.0 to 3.5 μm;

[0038] The temperature of the second-stage decomposition reaction is higher than the temperature of the first-stage decomposition reaction.

[0039] Bayer process sodium aluminate solution: A solution containing sodium aluminate produced by the Bayer process, it is a key raw material for the preparation of aluminum hydroxide. Seed crystals: Pre-prepared microcrystalline aluminum hydroxide, used to induce the formation and growth of aluminum hydroxide nuclei in the solution. Caustic ratio α: The molar ratio of caustic alkali to aluminum oxide in the sodium aluminate solution, an important parameter for measuring the composition of the solution.

[0040] The seed crystals, with a particle size ranging from 1.0 to 3.5 μm, effectively induce the formation and growth of aluminum hydroxide nuclei in the Bayer process sodium aluminate solution. The presence of the seed crystals provides nucleation centers for aluminum hydroxide crystallization, making the crystallization process more orderly and efficient. Under the active guidance of the seed crystals, aluminum hydroxide nuclei rapidly form and gradually grow, effectively reducing the adsorption and encapsulation of impurities (especially sodium ions) on the surface of the aluminum hydroxide. This helps reduce the chance of sodium oxide residue remaining in the aluminum hydroxide powder during subsequent decomposition. The two-stage decomposition reaction involves adding sodium aluminate concentrate to the material after the first-stage decomposition in multiple stages. This stepwise addition strategy promotes the steady growth of aluminum hydroxide nuclei during the continuous decomposition stage, and the small amount of sodium aluminate concentrate added each time ensures precise control of the reaction conditions. During the two-stage decomposition process, the lattice reconstruction of the aluminum hydroxide nuclei is fully realized. Lattice reconstruction refers to the rearrangement and optimization of the internal structure of the aluminum hydroxide crystals, a process that helps to remove sodium ions adsorbed on the surface of the nuclei into the solution. Meanwhile, the temperature of the second-stage decomposition reaction is higher than that of the first-stage decomposition reaction. This higher temperature accelerates the removal of sodium ions, making it easier for them to detach from the aluminum hydroxide lattice and enter the solution. After the second-stage decomposition reaction, solid aluminum hydroxide is successfully separated from the sodium-containing solution using solid-liquid separation technology. The solid material is then washed to further remove residual sodium ions from its surface. Solid-liquid separation effectively removes most of the sodium ions separated from the aluminum hydroxide, while the washing process further reduces the sodium ion content adsorbed on the aluminum hydroxide surface. The washing step effectively dissolves residual sodium ions from the aluminum hydroxide surface into the washing liquid, thus significantly reducing sodium oxide residue. The washed solid material is then dried. The evaporation of water during drying does not introduce new sodium ions, and the drying process also fixes the structure of the aluminum hydroxide, preventing the re-adsorption of sodium ions during subsequent processing. Example:

[0041] In a decomposition reaction, seed crystals with a particle size of 2.0 μm were used, the reaction temperature was 60 °C, and the stirring rate was 30 r / min.

[0042] In the two-stage decomposition reaction, 50m is added each time. 3 Sodium aluminate semen, at 4-hour intervals.

[0043] Solid-liquid separation was performed using centrifugation, and the moisture content of the separated solid material was 30%.

[0044] The liquid-to-solid ratio of the washing liquid to the solid material is 3:1, and the washing is performed 3 times.

[0045] The drying temperature is 100℃, the drying time is 3 hours, and the final micronized aluminum hydroxide product has a moisture content of less than 0.5%.

[0046] In some embodiments, the temperature of the decomposition reaction is 40-80°C; and / or,

[0047] The temperature of the two-stage decomposition reaction is 50-85℃.

[0048] The first-stage decomposition reaction temperature is 40-80℃. This temperature range is optimized to ensure stable formation of aluminum hydroxide crystal nuclei while preventing excessively rapid nuclei growth that could negatively impact the quality of the micronized aluminum hydroxide product. The second-stage decomposition reaction temperature is 50-85℃. The higher temperature helps accelerate the reconstruction of the aluminum hydroxide lattice and the removal of sodium ions, while ensuring both reaction efficiency and the quality of the micronized aluminum hydroxide product. Example:

[0049] The first stage decomposition reaction temperature is 55℃, and the second stage decomposition reaction temperature is 70℃.

[0050] The first stage decomposition reaction temperature is 45℃, and the second stage decomposition reaction temperature is 65℃.

[0051] The first stage decomposition reaction temperature is 75℃, and the second stage decomposition reaction temperature is 80℃.

[0052] The first stage decomposition reaction temperature is 60℃, and the second stage decomposition reaction temperature is 75℃.

[0053] The first stage decomposition reaction temperature is 50℃, and the second stage decomposition reaction temperature is 60℃.

[0054] In some embodiments, the parameters of the decomposition reaction further include: a reaction time of 10-48 hours, a stirring rate of 20-50 r / min; and / or,

[0055] The parameters for the two-stage decomposition reaction also include: a reaction time of 20-72 hours.

[0056] First-stage decomposition reaction parameters: Reaction time is 10-48 hours. This time range provides sufficient time for the formation and growth of aluminum hydroxide crystal nuclei, ensuring that the nuclei can grow sufficiently. The stirring rate is 20-50 r / min, which ensures thorough mixing of the solution, guarantees uniform seed dispersion, and avoids nucleus breakage due to excessive stirring. Second-stage decomposition reaction parameters: Reaction time is 20-72 hours, which helps to further promote the reconstruction of the aluminum hydroxide lattice and the removal of sodium ions. Example:

[0057] The first stage of decomposition reaction lasted 24 hours with a stirring rate of 30 r / min; the second stage of decomposition reaction lasted 48 hours.

[0058] The first stage of decomposition reaction took 12 hours with a stirring rate of 25 r / min; the second stage of decomposition reaction took 36 hours.

[0059] The first stage of decomposition reaction took 36 hours with a stirring rate of 40 r / min; the second stage of decomposition reaction took 60 hours.

[0060] The first stage of decomposition reaction took 18 hours with a stirring rate of 35 r / min; the second stage of decomposition reaction took 54 hours.

[0061] The first stage of decomposition reaction took 42 hours with a stirring rate of 45 r / min; the second stage of decomposition reaction took 72 hours.

[0062] In some embodiments, the Bayer process sodium aluminate solution satisfies the following conditions: a caustic ratio α of 1.35-1.70 and an alumina mass concentration of 100-200 g / L.

[0063] The caustic ratio α of the Bayer process sodium aluminate solution is 1.35-1.70. The caustic ratio is an important parameter for measuring the ratio of alumina to caustic alkali in the sodium aluminate solution. Solutions within this range exhibit good decomposition performance and can effectively generate aluminum hydroxide. The alumina concentration of the Bayer process sodium aluminate solution is 100-200 g / L. This concentration range ensures sufficient alumina for crystallization without making the solution too viscous due to excessive concentration, which would affect reaction efficiency. Example:

[0064] The caustic ratio α is 1.45, and the alumina concentration is 150 g / L.

[0065] The caustic ratio α is 1.50, and the alumina concentration is 180 g / L.

[0066] The caustic ratio α is 1.60, and the alumina concentration is 200 g / L.

[0067] The caustic ratio α is 1.35, and the alumina concentration is 100 g / L.

[0068] The caustic ratio α is 1.70, and the alumina concentration is 120 g / L.

[0069] In some embodiments, the volume of the seed crystal is 1%-6% of the volume of the Bayer process sodium aluminate solution.

[0070] The seed crystal volume is 1%-6% of the volume of the sodium aluminate solution used in the Bayer process. This effectively induces the formation of aluminum hydroxide crystal nuclei while avoiding solution supersaturation due to excessive seed crystals, which would affect the uniformity of the crystallization process. Example:

[0071] The seed crystal volume is 2% of the volume of the Bayer process sodium aluminate solution.

[0072] The seed crystal volume is 3% of the volume of the Bayer process sodium aluminate solution.

[0073] The seed crystal volume is 4% of the volume of the Bayer process sodium aluminate solution.

[0074] The seed crystal volume is 5% of the volume of the Bayer process sodium aluminate solution.

[0075] The seed crystal volume is 6% of the volume of the Bayer process sodium aluminate solution.

[0076] In some embodiments, during the decomposition reaction, the volume of the Bayer process sodium aluminate solution is 80-250 m³. 3 The Bayer process sodium aluminate solution is injected into the reactor over a period of 0.5-3 hours; and / or,

[0077] In the two-stage decomposition reaction, the volume of sodium aluminate semen added each time is 40-100 ml. 3 The time interval between two consecutive additions of the sodium aluminate semen is 2-8 hours.

[0078] A single-stage decomposition reaction: The volume of sodium aluminate solution in the Bayer process is 80-250 ml. 3 This volume range is suitable for industrial production, ensuring both reaction rate and control over equipment scale. The injection time for sodium aluminate in the Bayer process is 0.5-3 hours, ensuring uniform solution distribution and preventing excessively high local concentrations. In the two-stage decomposition reaction, the volume of sodium aluminate concentrate added each time is 40-100 ml. 3 Adding the sodium aluminate to the semen in stages allows for better control of the reaction process and prevents violent reactions caused by adding a large amount at once. The time interval between adding the sodium aluminate to the semen is 2-8 hours, allowing each addition of semen to react fully and avoiding instability during the reaction. Example:

[0079] In one stage of the decomposition reaction, the volume of the sodium aluminate solution in the Bayer process is 150 m³. 3 The injection time is 1.5 hours; in the two-stage decomposition reaction, 60 mg is added each time. 3 Sodium aluminate semen, at 4-hour intervals.

[0080] In a single decomposition reaction, the volume of the sodium aluminate solution in the Bayer process is 100 m³. 3 The injection time is 2 hours; in the two-stage decomposition reaction, 50 mg is added each time. 3 Sodium aluminate semen, with a time interval of 3 hours.

[0081] In one stage of the decomposition reaction, the volume of the sodium aluminate solution in the Bayer process is 200 m³. 3 The injection time is 2.5 hours; in the two-stage decomposition reaction, 80 mg is added each time.3 Sodium aluminate semen, with a time interval of 5 hours.

[0082] In one stage of the decomposition reaction, the volume of the sodium aluminate solution in the Bayer process is 120 m³. 3 The injection time is 1 hour; in the two-stage decomposition reaction, 70 mg is added each time. 3 Sodium aluminate semen, at 6-hour intervals.

[0083] In one stage of the decomposition reaction, the volume of the sodium aluminate solution in the Bayer process is 180 m³. 3 The injection time is 2 hours; in the two-stage decomposition reaction, 90 mg is added each time. 3 Sodium aluminate semen, at 7-hour intervals.

[0084] In some embodiments, the moisture content of the solid material is ≤45%.

[0085] A moisture content of ≤45% in the solid material facilitates subsequent washing and drying processes, reduces energy consumption, and improves the quality of the micronized aluminum hydroxide product. Example:

[0086] The solid material has a moisture content of 20%.

[0087] The solid material has a moisture content of 30%.

[0088] The solid material has a moisture content of 35%.

[0089] The solid material has a moisture content of 40%.

[0090] The solid material has a moisture content of 45%.

[0091] In some embodiments, the washing is performed at least twice, and the liquid-to-solid ratio of the washing liquid to the solid material is 1.5:1 to 5:1.

[0092] At least two washing cycles are necessary to effectively remove impurities from solid materials, thereby improving the quality of micronized aluminum hydroxide. A liquid-to-solid ratio of 1.5:1 to 5:1 ensures effective washing while avoiding excessive waste of washing solution. Example:

[0093] The washing cycle is 3 times, and the liquid-to-solid ratio is 2:1.

[0094] The washing cycle is 4 times, and the liquid-to-solid ratio is 3:1.

[0095] The washing cycle is 5 times, and the liquid-to-solid ratio is 4:1.

[0096] The washing cycle is twice, and the liquid-to-solid ratio is 1.5:1.

[0097] The washing cycle is 6 times, and the liquid-to-solid ratio is 5:1.

[0098] In some embodiments, the drying parameters include a temperature of 70-130°C and a time of 1-6 hours.

[0099] The drying temperature is 70-130℃, a range that ensures rapid drying without degrading material properties due to excessive heat. The drying time is 1-6 hours, ensuring thorough drying while avoiding over-drying and increased energy consumption. Example:

[0100] The drying temperature is 80℃ and the drying time is 2 hours.

[0101] The drying temperature is 90℃ and the drying time is 3 hours.

[0102] The drying temperature is 100℃ and the drying time is 4 hours.

[0103] The drying temperature is 110℃ and the drying time is 5 hours.

[0104] The drying temperature is 120℃ and the drying time is 6 hours.

[0105] In some embodiments, the moisture content of the micronized aluminum hydroxide is ≤0.5%.

[0106] The moisture content of micronized aluminum hydroxide powder is ≤0.5%, which ensures the stable performance of the product in subsequent applications and avoids clumping or performance degradation caused by excessive moisture. Example:

[0107] The moisture content of the micronized aluminum hydroxide is 0.2%.

[0108] The moisture content of the micronized aluminum hydroxide powder is 0.3%.

[0109] The moisture content of the micronized aluminum hydroxide powder is 0.4%.

[0110] The moisture content of the micronized aluminum hydroxide powder is 0.1%.

[0111] The moisture content of the micronized aluminum hydroxide powder is 0.5%.

[0112] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0113] Example 1

[0114] Seed crystals with a particle size of 1.0 μm were added to a Bayer process sodium aluminate solution to initiate a decomposition reaction. The reaction temperature was controlled at 40 °C, the stirring rate at 20 r / min, and the reaction time at 10 hours.

[0115] Sodium aluminate concentrate was added to the material after the first stage decomposition reaction in multiple stages to carry out the second stage decomposition reaction, and the temperature of the second stage decomposition reaction was controlled at 50℃.

[0116] The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material.

[0117] The solid material is washed and dried to obtain micronized aluminum hydroxide.

[0118] Example 2

[0119] Seed crystals with a particle size of 2.0 μm were added to a Bayer process sodium aluminate solution to initiate a decomposition reaction. The reaction temperature was controlled at 60 °C, the stirring rate at 30 r / min, and the reaction time at 24 hours.

[0120] Sodium aluminate concentrate was added to the material after the first stage decomposition reaction in multiple stages to carry out the second stage decomposition reaction, and the temperature of the second stage decomposition reaction was controlled at 70℃.

[0121] The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material.

[0122] The solid material is washed and dried to obtain micronized aluminum hydroxide.

[0123] Example 3

[0124] Seed crystals with a particle size of 3.5 μm were added to a Bayer process sodium aluminate solution to initiate a decomposition reaction. The reaction temperature was controlled at 80 °C, the stirring rate at 50 r / min, and the reaction time at 48 hours.

[0125] Sodium aluminate concentrate was added to the material after the first stage decomposition reaction in multiple stages to carry out the second stage decomposition reaction, and the temperature of the second stage decomposition reaction was controlled at 85℃.

[0126] The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material.

[0127] The solid material is washed and dried to obtain micronized aluminum hydroxide.

[0128] Example 4

[0129] Seed crystals with a particle size of 1.5 μm were added to a Bayer process sodium aluminate solution to initiate a decomposition reaction. The reaction temperature was controlled at 50 °C, the stirring rate at 25 r / min, and the reaction time at 12 hours.

[0130] Sodium aluminate concentrate was added to the material after the first stage decomposition reaction in multiple stages to carry out the second stage decomposition reaction, and the temperature of the second stage decomposition reaction was controlled at 60℃.

[0131] The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material.

[0132] The solid material is washed and dried to obtain micronized aluminum hydroxide.

[0133] Example 5

[0134] Seed crystals with a particle size of 2.5 μm were added to a Bayer process sodium aluminate solution to initiate a decomposition reaction. The reaction temperature was controlled at 70 °C, the stirring rate at 40 r / min, and the reaction time at 36 hours.

[0135] Sodium aluminate concentrate was added to the material after the first stage decomposition reaction in multiple stages to carry out the second stage decomposition reaction, and the temperature of the second stage decomposition reaction was controlled at 80℃.

[0136] The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material.

[0137] The solid material is washed and dried to obtain micronized aluminum hydroxide.

[0138] Example 6

[0139] Seed crystals with a particle size of 3.0 μm were added to a Bayer process sodium aluminate solution to initiate a decomposition reaction. The reaction temperature was controlled at 75 °C, the stirring rate at 45 r / min, and the reaction time at 42 hours.

[0140] Sodium aluminate concentrate was added to the material after the first stage decomposition reaction in multiple stages to carry out the second stage decomposition reaction, and the temperature of the second stage decomposition reaction was controlled at 82℃.

[0141] The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material.

[0142] The solid material is washed and dried to obtain micronized aluminum hydroxide.

[0143] Comparative Example 1

[0144] Seed crystals with a particle size of 1.0 μm were added to a Bayer process sodium aluminate solution to initiate a decomposition reaction. The reaction temperature was controlled at 40 °C, the stirring rate at 20 r / min, and the reaction time at 10 hours.

[0145] Sodium aluminate concentrate was added to the material after the first decomposition reaction in multiple stages to carry out the second decomposition reaction, and the temperature of the second decomposition reaction was controlled at 40℃ (the same as the temperature of the first decomposition reaction).

[0146] The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material.

[0147] The solid material is washed and dried to obtain micronized aluminum hydroxide.

[0148] Comparative Example 2

[0149] Seed crystals with a particle size of 2.0 μm were added to a Bayer process sodium aluminate solution to initiate a decomposition reaction. The reaction temperature was controlled at 60 °C, the stirring rate at 30 r / min, and the reaction time at 24 hours.

[0150] Sodium aluminate concentrate was added to the material after the first decomposition reaction in multiple stages to carry out the second decomposition reaction, and the temperature of the second decomposition reaction was controlled at 55℃ (lower than the temperature of the first decomposition reaction).

[0151] The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material.

[0152] The solid material is washed and dried to obtain micronized aluminum hydroxide.

[0153] Comparative Example 3

[0154] Seed crystals with a particle size of 3.5 μm were added to a Bayer process sodium aluminate solution to initiate a decomposition reaction. The reaction temperature was controlled at 80 °C, the stirring rate at 50 r / min, and the reaction time at 48 hours.

[0155] Sodium aluminate concentrate was added to the material after the first decomposition reaction in multiple stages to carry out the second decomposition reaction, and the temperature of the second decomposition reaction was controlled at 75℃ (lower than the temperature of the first decomposition reaction).

[0156] The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material.

[0157] The solid material is washed and dried to obtain micronized aluminum hydroxide.

[0158] Effect data: The effect data of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1.

[0159] Experimental methods for obtaining effect data:

[0160] Sodium oxide residue determination: The sodium oxide content in micronized aluminum hydroxide was determined using X-ray fluorescence spectrometry (XRF). Samples were ground to a particle size of less than 0.074 mm, pressed into tablets, and then tested. Each sample was tested three times, and the average value was taken as the final result.

[0161] Crystal particle size determination: The particle size distribution of micronized aluminum hydroxide was determined using a laser particle size analyzer. The test range was 0.1-100 μm, and the D50 (median particle size) was recorded as the primary data.

[0162] Crystal structure analysis: The structure of aluminum hydroxide crystals was analyzed using X-ray diffraction (XRD). The lattice parameters and crystallinity of the crystals were calculated, and the regularity of the crystal structure was assessed.

[0163] Table 1

[0164]

[0165]

[0166] The above effect data table provides a clear comparison of the differences between various embodiments and comparative examples. The following conclusions can be drawn:

[0167] 1. Sodium oxide residue

[0168] Example: The sodium oxide residue was between 0.3% and 0.5%, significantly lower than the comparative example. Comparative example: The sodium oxide residue was between 0.85% and 1.0%, significantly higher than the example. The condition that the temperature of the two-stage decomposition reaction was higher than that of the first-stage decomposition reaction significantly reduced the sodium oxide residue in the micronized aluminum hydroxide. This indicates that high-temperature conditions help promote the removal of sodium ions, thereby improving the purity of the product.

[0169] 2. Crystal grain size (D50)

[0170] Example: D50 is between 2.0 and 2.5 μm, and the crystal grain size distribution is relatively uniform. Comparative Example: D50 is also between 2.0 and 2.5 μm, similar to the example. Although the crystal grain size distribution of the comparative example and the example is similar, the particle size distribution of the example is more uniform, and the crystallinity is higher. This indicates that the optimized reaction conditions not only control the crystal size but also improve the crystal quality.

[0171] 3. Crystallinity

[0172] Example: Crystallinity between 95% and 97.2% indicates a regular crystal structure and high crystal quality. Comparative Example: Crystallinity between 90% and 92% is significantly lower than that of the example. The high-temperature conditions of the two-stage decomposition reaction help optimize the crystal structure and increase crystallinity. This indicates that high-temperature conditions promote lattice reconstruction, resulting in a more regular crystal structure and thus improving the overall quality of the product.

[0173] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing low-sodium-oxide Bayer process micronized aluminum hydroxide, comprising: Seed crystals are added to a Bayer process sodium aluminate solution to induce the generation and growth of aluminum hydroxide crystal nuclei in the Bayer process sodium aluminate solution. The temperature of the first-stage decomposition reaction is 40-80℃. Sodium aluminate concentrate is added to the material after the first stage decomposition reaction in multiple stages to carry out a second stage decomposition reaction, so as to promote the lattice reconstruction of the aluminum hydroxide crystal nuclei and the removal of sodium ions in the sodium aluminate solution. The temperature of the second stage decomposition reaction is 50-85℃. The material after the two-stage decomposition reaction is subjected to solid-liquid separation to obtain solid material; The solid material is washed and dried to obtain micronized aluminum hydroxide. The seed crystals have a particle size of 1.0 to 3.5 μm; The temperature of the second-stage decomposition reaction is higher than the temperature of the first-stage decomposition reaction.

2. The preparation method according to claim 1, characterized in that, The parameters for the decomposition reaction also include: a reaction time of 10-48 hours, a stirring rate of 20-50 r / min; and / or, The parameters for the two-stage decomposition reaction also include: a reaction time of 20-72 hours.

3. The preparation method according to claim 1, characterized in that, The Bayer process sodium aluminate solution meets the following requirements: caustic ratio α is 1.35-1.70, and alumina mass concentration is 100-200 g / L.

4. The preparation method according to claim 1, characterized in that, The volume of the seed crystal is 1%-6% of the volume of the Bayer process sodium aluminate solution.

5. The preparation method according to claim 1, characterized in that, In the aforementioned decomposition reaction, the volume of the Bayer process sodium aluminate solution is 80-250 m³, and the injection time of the Bayer process sodium aluminate solution into the reactor is 0.5-3 hours; and / or, In the two-stage decomposition reaction, the volume of sodium aluminate semen added each time is 40-100 m³, and the time interval between two adjacent additions of sodium aluminate semen is 2-8 hours.

6. The preparation method according to claim 1, characterized in that, The moisture content of the solid material is ≤45%.

7. The preparation method according to claim 1, characterized in that, The washing is performed at least twice, and the liquid-to-solid ratio of the washing liquid to the solid material is 1.5:1 to 5:

1.

8. The preparation method according to claim 1, characterized in that, The drying parameters include: temperature of 70-130℃ and time of 1-6 hours.

9. The preparation method according to claim 1, characterized in that, The moisture content of the micronized aluminum hydroxide is ≤0.5%.

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