Preparation method of low-sodium oxide Bayer process micro-powder aluminum hydroxide

Abstract

The preparation method of the low-sodium-oxide Bayer-process micro-powder aluminum hydroxide comprises the following steps: adding a seed crystal into a Bayer-process sodium aluminate solution to carry out a first-stage decomposition reaction so as to induce the generation and growth of an aluminum hydroxide crystal nucleus in the Bayer-process sodium aluminate solution; adding a sodium aluminate fine solution into the material subjected to the first-stage decomposition reaction for multiple times to perform a second-stage decomposition reaction so as to promote lattice reconstruction of the aluminum hydroxide crystal nucleus and removal of sodium ions in the sodium aluminate solution; carrying out solid-liquid separation on the material after the second-stage decomposition reaction to obtain a solid material; and washing and drying the solid material to obtain the micro-powder aluminum hydroxide. Through the synergistic effect of seed crystal induced crystallization, segmented decomposition reaction, temperature control, solid-liquid separation, washing and the like, the residual amount of sodium oxide is reduced from multiple links, and efficient preparation of the low-sodium-oxide micro-powder aluminum hydroxide is achieved.

Description

Technical Field

[0001] The present application relates to the technical field of inorganic material synthesis, and in particular to a method for preparing sodium suboxide Bayer process micro-powdered aluminum hydroxide. Background Art

[0002] Aluminum hydroxide, a key inorganic material, is widely used in electronic ceramics, flame retardants, high-voltage insulation materials, and other fields. Micronized aluminum hydroxide, in particular, is experiencing growing market demand due to its unique physical and chemical properties. However, traditional Bayer-process-produced micronized aluminum hydroxide suffers from high residual sodium oxide content, typically exceeding 0.20%. This high residual sodium content significantly degrades the dielectric properties of electronic ceramics and affects the thermal stability of flame retardants, making it difficult to meet the demands of high-end applications such as 5G communication substrates and high-voltage insulation materials.

[0003] The existing process has many defects in reducing the residual amount of sodium oxide. The single-stage decomposition process is limited by its single reaction environment, which makes the sodium ion desorption efficiency low. In addition, the particle agglomeration phenomenon occurs frequently, which in turn affects the stability of the micro-powder aluminum hydroxide product. Although the continuous gradient decomposition process attempts to improve the removal efficiency of sodium ions by regulating the reaction conditions in stages, due to improper parameter matching, the reaction kinetics in the later stage of decomposition are delayed, so that the removal rate of lattice sodium still hovers below 40%, and the expected ideal effect is not achieved. In addition, the traditional washing process can only act on the sodium ions adsorbed on the surface, and it seems powerless for the sodium ions hidden deep inside the lattice. Its removal effect is limited, so it is difficult to fundamentally overcome the problem of high residual sodium oxide. Summary of the Invention

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

[0005] The present invention provides a method for preparing a low sodium oxide Bayer process micronized aluminum hydroxide, comprising:

[0006] adding seed crystals to the Bayer process sodium aluminate solution to carry out a decomposition reaction to induce the formation and growth of aluminum hydroxide crystal nuclei in the Bayer process sodium aluminate solution;

[0007] adding sodium aluminate solution to the material after the first-stage decomposition reaction in multiple steps 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;

[0008] performing solid-liquid separation on the material after the second-stage decomposition reaction to obtain a solid material;

[0009] Washing and drying the solid material to obtain fine powder aluminum hydroxide;

[0010] Wherein, the particle size of the seed crystal is 1.0 to 3.5 μm;

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

[0012] Optionally, the temperature of the first stage decomposition reaction is 40-80° C.; and / or,

[0013] The temperature of the second stage decomposition reaction is 50-85°C

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

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

[0016] Optionally, the Bayer process sodium aluminate solution meets the following requirements: a caustic ratio α of 1.35-1.70, and an alumina mass concentration of 100-200 g / L.

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

[0018] Optionally, in the first stage decomposition reaction, the volume of the Bayer process sodium aluminate solution is 80-250m 3 , the time for injecting the Bayer process sodium aluminate solution into the reactor is 0.5-3 hours; and / or,

[0019] In the two-stage decomposition reaction, the volume of the sodium aluminate semen added each time is 40-100m 3 The time interval between two adjacent 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 no less than 2 times, 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: temperature of 70-130° C. and time of 1-6 hours.

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

[0024] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0025] The present invention 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, by adding seed crystals with a particle size of 1.0 to 3.5 μm to the sodium aluminate solution, the formation and growth of aluminum hydroxide nuclei are induced. The presence of the 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 aluminum hydroxide surface, thereby reducing the possibility of sodium oxide residue at the source. Secondly, a staged decomposition reaction is adopted. After the first stage of decomposition, sodium aluminate concentrate is added to the material in multiple stages for a second stage of decomposition. The second stage of decomposition reaction temperature is higher than that of the first stage. This design not only promotes the lattice reconstruction of the 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 the residual sodium oxide. In addition, the material after the second stage of decomposition undergoes solid-liquid separation and washing to further remove residual sodium ions on the surface. Solid-liquid separation separates the solid aluminum hydroxide from the sodium-containing solution, and 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 the present application reduce the residual sodium oxide from multiple links through the synergistic effects of seed crystal induced crystallization, staged decomposition reaction, temperature control, solid-liquid separation and washing, thereby achieving the efficient preparation of low-sodium oxide micropowder aluminum hydroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for those skilled in the art, other relevant drawings can be derived from these drawings without creative work.

[0028] Figure 1 This is a flow chart of a method for preparing low sodium oxide Bayer process micronized aluminum hydroxide provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to more clearly illustrate the purpose, technical solutions and advantages of the embodiments of the present application, the technical solutions of the embodiments are described in detail below with reference to the accompanying drawings. Please note that the embodiments mentioned are only examples and not all possible implementation methods. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0030] The range descriptions described in this article, such as numerical ranges, ratio ranges, etc., include all possible sub-ranges and single numerical values ​​within the range. For example, the range description of "1 to 6" or "1~6" covers all sub-ranges from 1 to 6 (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6). Unless otherwise specified, the terms "including", "comprising", etc. used in this article mean "including but not limited to"; relational terms such as "first" and "second" are only used to distinguish different entities or operations, and do not imply an actual sequence or association relationship; "and / or" means that multiple situations can exist alone or at the same time; expressions such as "at least one", "multiple", and "at least one" refer to any combination of corresponding objects, including a combination of single or multiple objects. The proportional relationships involved in the article, such as mass ratios, molar ratios, etc., should be understood as the corresponding relationship between the first and second terms of the proportional formula in the order of description. The raw materials, reagents, instruments and equipment used in this article can be purchased on the market or prepared by existing methods.

[0031] Figure 1 This is a flow chart of a method for preparing low sodium oxide Bayer process micronized aluminum hydroxide provided in an embodiment of the present application.

[0032] See Figure 1 The present invention provides a method for preparing a low sodium oxide Bayer process micronized aluminum hydroxide, comprising:

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

[0034] S2, adding sodium aluminate solution to the material after the first decomposition reaction in multiple steps to carry out a second decomposition reaction to promote the lattice reconstruction of the aluminum hydroxide crystal nuclei and the removal of sodium ions in the sodium aluminate solution;

[0035] S3, performing solid-liquid separation on the material after the second-stage decomposition reaction to obtain a solid material;

[0036] S4, washing and drying the solid material to obtain fine powder aluminum hydroxide;

[0037] Wherein, the particle size of the seed crystal is 1.0 to 3.5 μm;

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

[0039] Bayer process sodium aluminate solution: A solution containing sodium aluminate produced through the Bayer process, it is a key raw material for the production of aluminum hydroxide. Seed crystals: Pre-prepared, tiny aluminum hydroxide crystals used to induce the formation and growth of aluminum hydroxide nuclei in the solution. Caustic ratio α: The molar ratio of caustic soda to alumina in the sodium aluminate solution, a key parameter for measuring the solution's composition.

[0040] The seed crystals have a particle size of 1.0 to 3.5 μm. This size range effectively induces 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, the aluminum hydroxide nuclei form rapidly and gradually grow. This process effectively reduces the adsorption and encapsulation of impurities in the solution (especially sodium ions) on the aluminum hydroxide surface. This helps reduce the chance of sodium oxide remaining in the aluminum hydroxide fine powder during the subsequent decomposition process. The second-stage decomposition reaction involves adding sodium aluminate concentrate to the material after the first decomposition in multiple steps. This step-by-step addition strategy promotes the steady growth of aluminum hydroxide nuclei during the continuous decomposition stages, and the small amount of sodium aluminate concentrate added each time ensures precise control of reaction conditions. During the second-stage decomposition process, the lattice reconstruction of the aluminum hydroxide nuclei is fully carried out. Lattice reconstruction refers to the rearrangement and optimization of the internal structure of the aluminum hydroxide crystals. This process helps to remove sodium ions adsorbed on the surface of the nuclei into the solution. At the same time, the temperature of the second-stage decomposition reaction is higher than that of the first-stage decomposition reaction. The higher temperature is conducive to accelerating the removal process of sodium ions, making it easier for sodium ions to detach from the aluminum hydroxide lattice and enter the solution. After the second-stage decomposition reaction is completed, the solid aluminum hydroxide and the sodium ion-containing solution are successfully separated by solid-liquid separation technology. The solid material is then washed to further remove the sodium ions remaining on the surface. Solid-liquid separation can effectively remove most of the sodium ions separated from the aluminum hydroxide, and the washing process further reduces the content of sodium ions adsorbed on the surface of aluminum hydroxide. The washing step effectively dissolves the residual sodium ions on the surface of aluminum hydroxide into the washing liquid, thereby significantly reducing the residual sodium oxide. The washed solid material is dried. The evaporation of water during the drying process will not introduce new sodium ions. At the same time, the drying process can fix the structure of aluminum hydroxide to prevent sodium ions from being re-adsorbed during subsequent processing. Example:

[0041] In the first stage 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 second stage decomposition reaction, 50m 3 Sodium aluminate semen, the time interval is 4 hours.

[0043] The solid-liquid separation was carried out by centrifugal separation, and the moisture content of the solid material after separation was 30%.

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

[0045] The drying temperature is 100° C., the drying time is 3 hours, and the moisture content of the final micro-powder aluminum hydroxide product is less than 0.5%.

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

[0047] The temperature of the second-stage decomposition reaction is 50-85°C.

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

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

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

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

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

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

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

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

[0056] Parameters for the first stage decomposition reaction: The 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 crystal nuclei can fully grow. The stirring rate is 20-50r / min, which can fully mix the solution and ensure that the seed crystals are evenly dispersed, while avoiding the breakage of the crystal nuclei due to excessive stirring. Parameters for the second stage decomposition reaction: The reaction time is 20-72 hours, which helps to further promote the reconstruction of the aluminum hydroxide crystal lattice and the removal of sodium ions. Example:

[0057] The first-stage decomposition reaction time is 24 hours, and the stirring rate is 30 r / min; the second-stage decomposition reaction time is 48 hours.

[0058] The first-stage decomposition reaction time is 12 hours, and the stirring rate is 25 r / min; the second-stage decomposition reaction time is 36 hours.

[0059] The first-stage decomposition reaction time is 36 hours, and the stirring rate is 40 r / min; the second-stage decomposition reaction time is 60 hours.

[0060] The first-stage decomposition reaction time is 18 hours, and the stirring rate is 35 r / min; the second-stage decomposition reaction time is 54 hours.

[0061] The first-stage decomposition reaction time is 42 hours, and the stirring rate is 45 r / min; the second-stage decomposition reaction time is 72 hours.

[0062] In some embodiments, the Bayer process sodium aluminate solution satisfies: 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 Bayer sodium aluminate solution is 1.35-1.70. The caustic ratio is an important parameter that measures the ratio of alumina to caustic soda in the sodium aluminate solution. Solutions within this range have good decomposition properties and can effectively produce aluminum hydroxide. The alumina concentration of Bayer sodium aluminate solution is 100-200g / L. This concentration range ensures that there is sufficient alumina in the solution for crystallization, while not causing the solution to become too viscous due to excessive concentration, which would affect the 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 crystals is 1% to 6% of the volume of the Bayer process sodium aluminate solution.

[0070] The volume of the seed crystals accounts for 1%-6% of the volume of the Bayer process sodium aluminate solution, which can effectively induce the formation of aluminum hydroxide crystal nuclei while avoiding excessive seed crystals that lead to oversaturation of the solution and affect the uniformity of the crystallization process. Example:

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

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

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

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

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

[0076] In some embodiments, in the first stage decomposition reaction, the volume of the Bayer process sodium aluminate solution is 80-250m 3 , the time for injecting the Bayer process sodium aluminate solution into the reactor is 0.5-3 hours; and / or,

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

[0078] First stage decomposition reaction: The volume of Bayer sodium aluminate solution is 80-250m 3 This volume range is suitable for industrial production, which can ensure the reaction rate and control the equipment scale. The injection time of Bayer sodium aluminate is 0.5-3 hours, which can make the solution evenly distributed and avoid local excessive concentration. In the second stage decomposition reaction, the volume of sodium aluminate semen added each time is 40-100m 3 By adding the sodium aluminate semen in batches, the reaction process can be better controlled to prevent a violent reaction caused by adding a large amount at once. The time interval for adding the sodium aluminate semen is 2-8 hours, which can allow the semen added each time to react fully and avoid instability during the reaction process. Example:

[0079] In the first stage of decomposition reaction, the volume of Bayer sodium aluminate solution is 150m 3 , the injection time is 1.5 hours; in the second stage decomposition reaction, 60m 3 Sodium aluminate semen, the time interval is 4 hours.

[0080] In the first stage of decomposition reaction, the volume of Bayer sodium aluminate solution is 100m 3 , the injection time is 2 hours; in the second stage decomposition reaction, 50m 3 Sodium aluminate semen, the time interval is 3 hours.

[0081] In the first stage of decomposition reaction, the volume of Bayer sodium aluminate solution is 200m 3 , the injection time is 2.5 hours; in the second stage decomposition reaction, 80m3 Sodium aluminate semen, the time interval is 5 hours.

[0082] In the first stage of decomposition reaction, the volume of Bayer sodium aluminate solution is 120m 3 , the injection time is 1 hour; in the second stage decomposition reaction, 70m 3 Sodium aluminate semen, the time interval is 6 hours.

[0083] In the first stage of decomposition reaction, the volume of Bayer sodium aluminate solution is 180m 3 , the injection time is 2 hours; in the second stage decomposition reaction, 90m 3 Sodium aluminate semen, the time interval is 7 hours.

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

[0085] The moisture content of the solid material is ≤45%, which is helpful for the subsequent washing and drying process, reduces energy consumption, and improves the quality of the micronized aluminum hydroxide product. Example:

[0086] The moisture content of the solid material is 20%.

[0087] The moisture content of the solid material is 30%.

[0088] The moisture content of the solid material is 35%.

[0089] The moisture content of the solid material is 40%.

[0090] The moisture content of the solid material is 45%.

[0091] In some embodiments, the washing is performed no less than 2 times, and the liquid-to-solid ratio of the washing liquid to the solid material is 1.5:1 to 5:1.

[0092] Washing at least twice can effectively remove impurities in the solid material, thereby improving the quality of the micronized aluminum hydroxide product. A liquid-to-solid ratio of 1.5:1 to 5:1 can ensure the washing effect while avoiding excessive use of washing liquid and waste of resources. Example:

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

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

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

[0096] The washing times were 2 times, and the liquid-to-solid ratio was 1.5:1.

[0097] The washing times were 6 times, and the liquid-to-solid ratio was 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℃, which can ensure that the material is dried quickly without causing the material performance to deteriorate due to excessive temperature. The drying time is 1-6 hours, which can ensure that the material is fully dried while avoiding excessive drying that leads to increased energy consumption. Example:

[0100] The drying temperature was 80°C and the drying time was 2 hours.

[0101] The drying temperature was 90°C and the drying time was 3 hours.

[0102] The drying temperature was 100°C and the drying time was 4 hours.

[0103] The drying temperature was 110°C and the drying time was 5 hours.

[0104] The drying temperature was 120°C and the drying time was 6 hours.

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

[0106] The moisture content of micronized aluminum hydroxide is ≤0.5%, which can ensure the stable performance of micronized aluminum hydroxide products in subsequent applications and avoid agglomeration or performance degradation caused by excessive moisture. Example:

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

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

[0109] The moisture content of the micro-powdered aluminum hydroxide is 0.4%.

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

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

[0112] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are generally measured according to industry standards. If there are no corresponding industry standards, then the methods are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0113] Example 1

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

[0115] Sodium aluminate solution was added to the material after the first decomposition reaction in multiple times to carry out the second decomposition reaction, and the temperature of the second decomposition reaction was controlled at 50°C.

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

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

[0118] Example 2

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

[0120] Sodium aluminate concentrate was added to the material after the first-stage decomposition reaction in multiple times to carry out a second-stage decomposition reaction, and the temperature of the second-stage decomposition reaction was controlled to be 70°C.

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

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

[0123] Example 3

[0124] A seed crystal with a particle size of 3.5 μm was added to the Bayer process sodium aluminate solution to conduct a decomposition reaction. The reaction temperature was controlled at 80°C, the stirring rate was 50 rpm, and the reaction time was 48 hours.

[0125] Sodium aluminate concentrate was added to the material after the first-stage decomposition reaction in multiple times to carry out a second-stage decomposition reaction, and the temperature of the second-stage decomposition reaction was controlled to be 85°C.

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

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

[0128] Example 4

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

[0130] Sodium aluminate concentrate was added to the material after the first decomposition reaction in multiple times to carry out a second decomposition reaction, and the temperature of the second decomposition reaction was controlled to be 60°C.

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

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

[0133] Example 5

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

[0135] Sodium aluminate concentrate was added to the material after the first decomposition reaction in multiple times to carry out a second decomposition reaction, and the temperature of the second decomposition reaction was controlled to be 80°C.

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

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

[0138] Example 6

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

[0140] Sodium aluminate concentrate was added to the material after the first-stage decomposition reaction in multiple times to carry out a second-stage decomposition reaction, and the temperature of the second-stage decomposition reaction was controlled to be 82°C.

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

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

[0143] Comparative Example 1

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

[0145] Sodium aluminate solution was added to the material after the first decomposition reaction for several times to carry out the second decomposition reaction. The temperature of the second decomposition reaction was controlled to be 40° C. (the same as the temperature of the first decomposition reaction).

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

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

[0148] Comparative Example 2

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

[0150] Sodium aluminate solution was added to the material after the first decomposition reaction for several times to carry out the second decomposition reaction. The temperature of the second decomposition reaction was controlled to be 55° C. (lower than the temperature of the first decomposition reaction).

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

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

[0153] Comparative Example 3

[0154] A seed crystal with a particle size of 3.5 μm was added to the Bayer process sodium aluminate solution to conduct a decomposition reaction. The reaction temperature was controlled at 80°C, the stirring rate was 50 rpm, and the reaction time was 48 hours.

[0155] Sodium aluminate concentrate was added to the material after the first decomposition reaction for several times to carry out the second decomposition reaction, and the temperature of the second decomposition reaction was controlled to be 75° C. (lower than the temperature of the first decomposition reaction).

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

[0157] The solid material is washed and dried to obtain fine powder 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 effect data:

[0160] Sodium Oxide Residual Determination: X-ray fluorescence (XRF) was used to determine the sodium oxide content in micronized aluminum hydroxide. The sample was ground to a particle size of less than 0.074 mm, pressed into tablets, and tested. Each sample was tested three times, and the average result was taken as the final result.

[0161] Crystal Particle Size Measurement: A laser particle size analyzer was used to measure the particle size distribution of the micro-powdered aluminum hydroxide. The test range was 0.1-100 μm, and D50 (median particle size) was recorded as the primary data.

[0162] Crystal structure analysis: X-ray diffractometer (XRD) was used to analyze the structure of aluminum hydroxide crystals. The lattice parameters and crystallinity of the crystals were calculated, and the regularity of the crystal structure was evaluated.

[0163] Table 1

[0164]

[0165]

[0166] The above effect data table can intuitively compare the differences between different examples and comparative examples. The following conclusions can be drawn:

[0167] 1. Sodium oxide residue

[0168] The residual sodium oxide content in the Example ranged from 0.3% to 0.5%, significantly lower than that in the Comparative Example. The residual sodium oxide content in the Comparative Example ranged from 0.85% to 1.0%, significantly higher than that in the Example. The condition in which the temperature of the second-stage decomposition reaction is higher than that of the first-stage decomposition reaction significantly reduces the residual sodium oxide content in the micropowdered aluminum hydroxide. This indicates that high temperatures help promote the removal of sodium ions, thereby improving the purity of the product.

[0169] 2. Crystal size (D50)

[0170] In the Example, D50 was between 2.0 and 2.5 μm, indicating a relatively uniform crystal size distribution. In the Comparative Example, D50 was also between 2.0 and 2.5 μm, similar to that of the Example. While the crystal size distributions of the Comparative Example and the Example were similar, the Example exhibited a more uniform distribution and a higher degree of crystallinity. This demonstrates that optimized reaction conditions not only controlled crystal size but also improved crystal quality.

[0171] 3. Crystallinity

[0172] The crystallinity in the Examples ranged from 95% to 97.2%, indicating a regular crystal structure and high crystal quality. The crystallinity in the Comparative Examples ranged from 90% to 92%, significantly lower than that in the Examples. The high temperature conditions of the second-stage decomposition reaction helped optimize the crystal structure and increase crystallinity. This suggests that high temperatures promote lattice reconstruction, resulting in a more regular crystal structure and thus improving the overall quality of the product.

[0173] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present 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 the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preparing sodium suboxide Bayer process micronized aluminum hydroxide, comprising: adding seed crystals to the Bayer process sodium aluminate solution to carry out a decomposition reaction to induce the formation and growth of aluminum hydroxide crystal nuclei in the Bayer process sodium aluminate solution; adding sodium aluminate solution to the material after the first-stage decomposition reaction in multiple steps 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; performing solid-liquid separation on the material after the second-stage decomposition reaction to obtain a solid material; Washing and drying the solid material to obtain fine powder aluminum hydroxide; Wherein, the particle size of the seed crystal is 1.0 to 3.5 μm; The temperature of the second-stage decomposition reaction is greater than the temperature of the first-stage decomposition reaction.

2. The preparation method according to claim 1, characterized in that The temperature of the first stage decomposition reaction is 40-80°C; and / or, The temperature of the second-stage decomposition reaction is 50-85°C.

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

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

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

6. The preparation method according to claim 1, characterized in that In the first stage decomposition reaction, the volume of the Bayer process sodium aluminate solution is 80-250m 3 , the time for injecting 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 the sodium aluminate semen added each time is 40-100m 3 The time interval between two adjacent additions of the sodium aluminate semen is 2-8 hours.

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

8. The preparation method according to claim 1, characterized in that The washing is performed no less than 2 times, and the liquid-to-solid ratio of the washing liquid to the solid material is 1.5:1 to 5:

1.

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

10. The preparation method according to claim 1, characterized in that The moisture content of the micro-powder aluminum hydroxide is ≤0.5%.

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