A method for producing high-whiteness aluminum hydroxide micropowder by dissolving bauxite with liquid caustic soda

Abstract

The present invention provides a method for producing high - white aluminum hydroxide fine powder by dissolving bauxite in liquid caustic soda, which mainly includes alkali dissolution, solid - liquid separation, purification separation, seeding and drying; for purification separation, the overflow obtained from solid - liquid separation is refined to obtain sodium aluminate solution by removing impurities with a leaf filter, and the content of suspended matter in the refined sodium aluminate solution is < 0.02 g / L; alumina is added to the refined sodium aluminate solution for adsorption purification to obtain a high - light - transmittance purified solution; the purified solution is separated to obtain the decomposition mother liquor, and the content of suspended matter in the decomposition mother liquor is < 0.015 g / L. The method of the present invention can treat various bauxites. Compared with the re - dissolution method and the decolorization method, the method of the present invention has extremely strong applicability to raw materials. By using this method to treat various bauxites, high - white aluminum hydroxide fine powder with a whiteness greater than 98% can be directly obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of special alumina production, and particularly relates to a method for producing high-whiteness aluminum hydroxide micropowder by leaching bauxite with liquid caustic soda. Background Art

[0002] High-whiteness aluminum hydroxide micropowder has the advantages of high whiteness, good dispersibility, and low iron and sodium contents, and has excellent properties such as flame retardancy, smoke elimination, modification, and non-toxicity, making it widely used in various fields. For example, it is used as a flame retardant in products such as polyvinyl chloride, epoxy resin, polyester resin, polyurethane resin, polyvinyl chloride resin, and electrical appliances; as a filler in products such as fiberglass, epoxy potting compound, and flame retardant carpet; as a colorant in the raw materials of artificial stone and high-grade ceramic colorants. Especially when used as a colorant, it can be evenly dispersed into the organic resin, thereby obtaining a stable pigment distribution, making it very popular.

[0003] With the increasing understanding of high-whiteness aluminum hydroxide micropowder, the research on it has also increased accordingly. In the patent document with the application number CN201110222296.8 and the theme name of a method for controlling the chromaticity of carbonated high-whiteness filler aluminum hydroxide, the process of the disclosed chromaticity control method is relatively complex, and the rotary kiln process is used in the clinker sintering process, resulting in large energy consumption and high production costs; in the patent document with the application number CN201410530157.5 and the theme name of a method for preparing high-whiteness ultrafine aluminum hydroxide from Bayer process aluminum hydroxide, the aluminum hydroxide product is used as the raw material, and a redissolution device needs to be added, with the disadvantages of high environmental protection pressure and large equipment investment; in the patent document with the application number CN201110346835.9 and the theme name of a method for preparing high-whiteness aluminum hydroxide micropowder from sodium aluminate solution of the Bayer process, the sodium aluminate solution is used as the raw material, relying on the large production process of the Bayer process, and the raw material source is restricted, and there are certain limitations in industrial promotion. Summary of the Invention

[0004] In view of the above deficiencies of the prior art, the present invention provides a method for producing high-whiteness aluminum hydroxide micropowder by leaching bauxite with liquid caustic soda. The method includes alkali leaching, solid-liquid separation, purification separation, seeding, and drying. This method has the advantages of simple process, low energy consumption, small investment, low cost, and easy availability of raw materials; using this method, aluminum hydroxide micropowder with a whiteness > 98% can be obtained.

[0005] The technical solution of the present invention is as follows:

[0006] A method for producing high-whiteness aluminum hydroxide micropowder by leaching bauxite with liquid caustic soda mainly includes alkali leaching, solid-liquid separation, purification separation, seeding, and drying;

[0007] Purification and separation: The overflow obtained from solid-liquid separation is refined to obtain a sodium aluminate solution using a leaf filter to remove impurities, and the content of suspended matter in the refined sodium aluminate solution is < 0.02 g / L; alumina is added to the refined sodium aluminate solution for adsorption purification to obtain a purified solution with high light transmittance; the purified solution is separated to obtain the decomposition stock solution, and the content of suspended matter in the decomposition stock solution is < 0.015 g / L;

[0008] In this process, alumina has the advantages of a large specific surface area, making it have good adsorption effect, strong impurity removal ability and obvious decolorization effect.

[0009] Preferably, the method for producing high-whiteness aluminum hydroxide micropowder by leaching bauxite with liquid caustic soda is as follows:

[0010] S1, caustic leaching:

[0011] The liquid caustic soda and bauxite are proportioned according to the digestion α k for batching; the batched bauxite is subjected to pipe digestion to obtain a slurry; after pipe digestion, the alumina in the bauxite enters the slurry, while iron oxide, silicon oxide, etc. form insoluble red mud residues;

[0012] S2, solid-liquid separation:

[0013] The slurry is sent to a conical tank for solid-liquid separation to separate the red mud from the slurry, obtaining an underflow and an overflow; the solid content of the underflow is 400 - 600 g / L, and it is returned to the Bayer process for red mud washing; the content of suspended matter in the overflow is 0.05 - 1.0 g / L;

[0014] S3, purification and separation:

[0015] The overflow is purified and decontaminated using a leaf filter with lime milk as a filter aid to obtain a refined sodium aluminate solution and filter cake A;

[0016] Alumina is added to the refined sodium aluminate solution for adsorption purification to obtain a purified solution with high light transmittance;

[0017] The purified solution is separated by pressure filtration to obtain the decomposition stock solution and filter cake B; filter cake B is washed and calcined to remove organic matter to obtain alumina, which enters the purification and separation process for recycling;

[0018] Among them, the decomposition stock solution can be subjected to repeated pressure to make the content of suspended matter < 0.015 g / L;

[0019] S4, seeding precipitation:

[0020] The decomposition stock solution is subjected to seeding precipitation under the condition of adding seeds, and then filtered and washed by a flat plate filter to obtain the mother liquor after seeding and the aluminum hydroxide filter cake. The mother liquor after seeding is returned to the Bayer process for recycling;

[0021] S5, drying:

[0022] The aluminum hydroxide filter cake is dried to remove the attached water. The drying conditions are 100 °C and 60 min, and high-whiteness aluminum hydroxide fine powder with a whiteness greater than 98% is obtained. After packaging, it can be sold as a product.

[0023] Preferably, in step s1, the liquid caustic soda is a 32% sodium hydroxide solution or a 50% sodium hydroxide solution; the bauxite is a trihydrate or a monohydrate ore; the digestion α k is 1.3 - 1.6; the digestion temperature during the caustic digestion process is 140 - 260 °C, and the digestion time is 15 - 60 min. The specific digestion temperature and time depend on the type of bauxite.

[0024] Preferably, in step s3, the addition amount of alumina is 1 - 10 g / L, the purification temperature is 50 - 70 °C, and the purification time is 30 - 60 min.

[0025] Preferably, in step s4, the decomposition mother liquor is seeded under the conditions that α k is 1.3 - 1.6, the temperature is 50 - 70 °C, the time is 4 - 12 h, the seed ratio is 0.02 - 0.12, and the AO concentration is 110 - 160 g / L.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The method of the present invention can treat various bauxites. Compared with the re-dissolution method and the decolorization method, the method of the present invention has extremely strong applicability to raw materials. Using this method to treat various bauxites can directly obtain high-whiteness aluminum hydroxide fine powder with a whiteness greater than 98%.

[0028] 2. In the present invention, alumina is obtained by washing and calcining the filter cake B to remove organic substances, and then enters the purification and separation process for recycling, reducing the later input of alumina and lowering the cost; the filter cake A and the underflow are returned to the red mud washing system in the Bayer process large-scale production process and participate in the alumina production, improving the utilization rate and thus reducing the cost.

[0029] 3. In the present invention, the Bayer process is adopted, and the bauxite does not need to be calcined, so the energy consumption is low; physical methods are used for purification twice, with conventional lime milk and alumina as purification agents respectively, and the purification effect is good and the impurity removal efficiency is high; the mother liquor of seeding can be recycled, and the production cost is low; in addition, no additional equipment needs to be invested, and the treatment method uses existing equipment, reducing the equipment investment cost and thus reducing the production cost.

[0030] 4. The method of the present invention is reasonably designed, simple to operate, the process is easy to control, and it is suitable for wide promotion and application. Brief Description of the Drawings

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 It is a flowchart of the method of the present invention. Specific embodiments

[0033] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0034] Embodiment 1

[0035] Combined with Figure 1 , the present invention provides a method for producing high-white aluminum hydroxide micropowder by caustic soda digestion of bauxite, and the process is as follows:

[0036] s1, caustic digestion:

[0037] Mix bauxite trihydrate and 32% sodium hydroxide solution according to a digestion α k 1.3 for batching, and subject the batched bauxite to pipe digestion at a digestion temperature of 140 °C and a digestion time of 30 min to obtain a slurry; after pipe digestion, the alumina in the bauxite enters the slurry, while iron oxide, silicon oxide, etc. form insoluble red mud residues;

[0038] s2, solid-liquid separation:

[0039] Send the slurry to a conical tank for solid-liquid separation to separate the red mud from the slurry, obtaining an underflow with a solid content of 400 g / L and an overflow with a suspended matter content of 0.05 g / L; the underflow is returned to the Bayer large-scale production process for red mud washing;

[0040] s3, purification and separation:

[0041] Purify and remove impurities from the overflow using a leaf filter with lime milk as a filter aid to obtain a refined sodium aluminate solution with a suspended matter content of 0.02 g / L and filter cake A; the lime milk forms a secondary filter cake on the surface of the filter assembly;

[0042] Add 5 g / L of alumina to the refined sodium aluminate solution for adsorption purification at a purification temperature of 50 °C and a purification time of 60 min; obtain a high-transparency purification solution;

[0043] The purification liquid is separated by pressure filtration to obtain a decomposed stock solution with a suspended matter content of 0.015 g / L and filter cake B; after the filter cake B is washed and calcined to remove organic matter, alumina is obtained and recycled into the purification and separation process;

[0044] S4, seed precipitation:

[0045] The decomposed stock solution is subjected to seed precipitation under the condition of adding seeds. Specifically, in this embodiment, the decomposed stock solution is subjected to seed precipitation under the conditions of α k 1.3, temperature 50 °C, time 12 h, seed ratio 0.05, and AO concentration 110 g / L; then, after filtration and washing by a flat plate filter, mother liquor for seed precipitation and a filter cake of aluminum hydroxide are obtained, and the mother liquor for seed precipitation is returned to the Bayer process for recycling;

[0046] S5, drying:

[0047] The filter cake of aluminum hydroxide is dried to remove the attached water. The drying conditions are 100 °C and 60 min, and high-whiteness aluminum hydroxide fine powder with a whiteness greater than 99.2% is obtained. After packaging, it can be sold as a product.

[0048] Example 2

[0049] A method for producing high-whiteness aluminum hydroxide fine powder by leaching bauxite with liquid caustic soda, the process is as follows:

[0050] S1, alkali leaching:

[0051] Bauxite trihydrate and 50% liquid caustic soda are proportioned according to the digestion α k 1.5, and the proportioned bauxite is subjected to pipe digestion at a digestion temperature of 140 °C and a digestion time of 20 min to obtain a slurry; after pipe digestion, the alumina in the bauxite enters the slurry, while iron oxide, silicon oxide, etc. form insoluble red mud residues;

[0052] S2, solid-liquid separation:

[0053] The slurry is sent to a conical tank for solid-liquid separation to separate the red mud from the slurry, obtaining an underflow with a solid content of 450 g / L and an overflow with a suspended matter content of 0.1 g / L; the underflow is returned to the Bayer large-scale production process for red mud washing;

[0054] S3, purification and separation:

[0055] The overflow is purified and decontaminated by a leaf filter with lime milk as a filter aid to obtain a refined sodium aluminate solution with a suspended matter content of 0.015 g / L and filter cake A; the lime milk forms an auxiliary filter cake on the surface of the filter element;

[0056] Add 5 g / L of alumina to the refined sodium aluminate solution for adsorption purification. The purification temperature is 60 °C and the purification time is 50 min to obtain a purified solution with high light transmittance.

[0057] The purified solution is separated by pressure filtration to obtain a decomposition stock solution with a suspended matter content of 0.010 g / L and filter cake B. After washing and calcining filter cake B to remove organic substances, alumina is obtained and recycled into the purification and separation process.

[0058] S4, seed precipitation:

[0059] The decomposition stock solution is subjected to seed precipitation under the condition of adding crystal seeds. Specifically, in this embodiment, the decomposition stock solution is subjected to seed precipitation under the conditions of α k 1.5, temperature 60 °C, time 10 h, seed ratio 0.08, and AO concentration 120 g / L. Then, after filtration and washing by a flat plate filter, a mother liquor for seed precipitation and a filter cake of aluminum hydroxide are obtained. The mother liquor for seed precipitation is returned to the Bayer process for recycling.

[0060] S5, drying:

[0061] The filter cake of aluminum hydroxide is dried to remove the attached water. The drying conditions are 100 °C and 60 min to obtain high-whiteness aluminum hydroxide fine powder with a whiteness greater than 99.5%. After packaging, it can be sold as a product.

[0062] Example 3

[0063] A method for producing high-whiteness aluminum hydroxide fine powder by dissolving bauxite with liquid caustic soda, the process is as follows:

[0064] S1, alkali dissolution:

[0065] Mix boehmite and 32% liquid caustic soda according to the dissolution α k 1.3 for batching, and subject the batched bauxite to pipe digestion at a digestion temperature of 240 °C and a digestion time of 30 min to obtain a slurry. After pipe digestion, the alumina in the bauxite enters the slurry, while iron oxide, silicon oxide, etc. form insoluble red mud residues.

[0066] S2, solid-liquid separation:

[0067] Send the slurry to a conical tank for solid-liquid separation to separate the red mud from the slurry, obtaining an underflow with a solid content of 500 g / L and an overflow with a suspended matter content of 0.5 g / L. The underflow is returned to the Bayer process for red mud washing.

[0068] S3, purification and separation:

[0069] Purify and remove impurities from the overflow using a leaf filter with lime milk as a filter aid to obtain a refined sodium aluminate solution with a suspended solid content of 0.015 g / L and filter cake A; the lime milk forms an auxiliary filter cake on the surface of the filter assembly;

[0070] Add 10 g / L of alumina to the refined sodium aluminate solution for adsorption purification at a purification temperature of 50 °C and a purification time of 60 min; obtain a purified solution with high light transmittance;

[0071] Separate the purified solution by pressure filtration to obtain a decomposition stock solution with a suspended solid content of 0.010 g / L and filter cake B; after washing and calcining filter cake B to remove organic matter, alumina is obtained and recycled into the purification and separation process;

[0072] S4, seed precipitation:

[0073] The decomposition stock solution is subjected to seed precipitation under the condition of adding crystal seeds. Specifically, in this embodiment, the decomposition stock solution is subjected to seed precipitation under the conditions of α k 1.3, temperature 55 °C, time 8 h, seed ratio 0.10, and AO concentration 130 g / L; then, after filtration and washing by a flat plate filter, a mother liquor for seed precipitation and a filter cake of aluminum hydroxide are obtained, and the mother liquor for seed precipitation is returned to the Bayer process for recycling;

[0074] S5, drying:

[0075] Dry the filter cake of aluminum hydroxide to remove the attached water under the drying conditions of 100 °C and 60 min to obtain high - white aluminum hydroxide micropowder with a whiteness greater than 99.3%, which can be sold as a product after packaging.

[0076] Example 4

[0077] A method for producing high - white aluminum hydroxide micropowder by leaching bauxite with liquid caustic soda, the process is as follows:

[0078] S1, alkali leaching:

[0079] Mix boehmite and 50% liquid caustic soda according to a digestion α k 1.5 for batching, and subject the batched bauxite to pipe digestion at a digestion temperature of 240 °C and a digestion time of 20 min to obtain a slurry; after pipe digestion, the alumina in the bauxite enters the slurry, while iron oxide, silicon oxide, etc. form insoluble red mud residues;

[0080] S2, solid - liquid separation:

[0081] Send the slurry to a conical tank for solid - liquid separation to separate the red mud from the slurry, obtaining an underflow with a solid content of 550 g / L and an overflow with a suspended solid content of 0.8 g / L; the underflow is returned to the Bayer process for red mud washing;

[0082] s3, Purification and separation:

[0083] The overflow is purified and removed impurities by a leaf filter with lime milk as filter aid to obtain a sodium aluminate refined liquid with a suspended matter content of 0.012 g / L and filter cake A; the lime milk forms an auxiliary filter cake on the surface of the filter component;

[0084] 8 g / L of alumina is added to the sodium aluminate refined liquid for adsorption purification, the purification temperature is 60 °C, and the purification time is 50 min; a high light transmittance purified liquid is obtained;

[0085] The purified liquid is separated by pressure filtration to obtain a decomposition mother liquor with a suspended matter content of 0.008 g / L and filter cake B; after filter cake B is washed and calcined to remove organic matter, alumina is obtained and recycled into the purification and separation process;

[0086] s4, Seed precipitation:

[0087] The decomposition mother liquor is subjected to seed precipitation under the condition of adding seeds. Specifically, in this embodiment, the decomposition mother liquor is subjected to seed precipitation under the conditions of α k 1.5, temperature 50 °C, time 6 h, seed ratio 0.05, and AO concentration 140 g / L; then after filtration and washing by a flat plate filter, a seed precipitation mother liquor and a cake of aluminum hydroxide are obtained, and the seed precipitation mother liquor is returned to the Bayer process for recycling;

[0088] s5, Drying:

[0089] The aluminum hydroxide cake is dried to remove the attached water, and the drying conditions are 100 °C and 60 min to obtain high white aluminum hydroxide micropowder with a whiteness greater than 99.2%, which can be sold as a product after packaging.

[0090] Example 5

[0091] A method for producing high white aluminum hydroxide micropowder by liquid caustic soda digestion of bauxite, the process is as follows:

[0092] s1, Alkaline digestion:

[0093] The diaspore and 32% liquid caustic soda are proportioned according to the digestion α k 1.4, and the proportioned bauxite is subjected to pipe digestion, the digestion temperature is 260 °C, and the digestion time is 50 min to obtain a slurry; after pipe digestion, the alumina in the bauxite enters the slurry, while iron oxide, silicon oxide, etc. form insoluble red mud residues;

[0094] s2, Solid-liquid separation:

[0095] The slurry is sent to a conical tank for solid-liquid separation to separate the red mud from the slurry, obtaining an underflow with a solid content of 600 g / L and an overflow with a suspended matter content of 0.8 g / L; the underflow is returned to the Bayer process for red mud washing;

[0096] s3, Purification and separation:

[0097] The overflow is purified and impurity-removed by a leaf filter with lime milk as filter aid to obtain a refined sodium aluminate solution with a suspended matter content of 0.015 g / L and filter cake A; the lime milk forms an auxiliary filter cake on the surface of the filter assembly;

[0098] 6 g / L of alumina is added to the refined sodium aluminate solution for adsorption purification at a purification temperature of 55 °C and a purification time of 40 min; a high-transparency purified solution is obtained;

[0099] The purified solution is separated by pressure filtration to obtain a decomposition stock solution with a suspended matter content of 0.012 g / L and filter cake B; after filter cake B is washed and calcined to remove organic substances, alumina is obtained and recycled into the purification and separation process;

[0100] s4, Seed precipitation:

[0101] The decomposition stock solution is subjected to seed precipitation under the condition of adding crystal seeds. Specifically, in this embodiment, the decomposition stock solution is subjected to seed precipitation under the conditions of α k 1.4, temperature 60 °C, time 10 h, seed ratio 0.05, and AO concentration 125 g / L; then, after filtration and washing by a flat plate filter, a mother liquor for seed precipitation and a filter cake of aluminum hydroxide are obtained, and the mother liquor for seed precipitation is returned to the Bayer process for recycling;

[0102] s5, Drying:

[0103] The filter cake of aluminum hydroxide is dried to remove the attached water under the drying conditions of 100 °C and 60 min to obtain high-whiteness aluminum hydroxide fine powder with a whiteness greater than 99.5%, which can be sold as a product after packaging.

[0104] Example 6

[0105] A method for producing high-whiteness aluminum hydroxide fine powder by leaching bauxite with liquid caustic soda, the process is as follows:

[0106] s1, Alkaline leaching:

[0107] The diaspore and 50% liquid caustic soda are proportioned according to the digestion α k 1.5, and the proportioned bauxite is subjected to pipe digestion at a digestion temperature of 260 °C and a digestion time of 40 min to obtain a slurry; after pipe digestion, the alumina in the bauxite enters the slurry, while iron oxide, silicon oxide, etc. form insoluble red mud residues;

[0108] s2, Solid-liquid separation:

[0109] The slurry is sent to a conical tank for solid-liquid separation to separate the red mud from the slurry, obtaining an underflow with a solid content of 580 g / L and an overflow with a suspended matter content of 1.0 g / L; the underflow is returned to the Bayer process for red mud washing;

[0110] S3, purification and separation:

[0111] The overflow is purified and decontaminated by a leaf filter with lime milk as a filter aid, obtaining a refined sodium aluminate solution with a suspended matter content of 0.01 g / L and filter cake A; the lime milk forms a secondary filter cake on the surface of the filter assembly;

[0112] 8 g / L of alumina is added to the refined sodium aluminate solution for adsorption purification, the purification temperature is 50 °C, and the purification time is 60 min; a high light transmittance purified solution is obtained;

[0113] The purified solution is separated by a pressure filtration method, obtaining a decomposition stock solution with a suspended matter content of 0.009 g / L and filter cake B; filter cake B is washed and calcined to remove organic matter to obtain alumina, which enters the purification and separation process for recycling;

[0114] S4, seeding and precipitation:

[0115] The decomposition stock solution is subjected to seeding and precipitation under the condition of adding seeds. Specifically, in this embodiment, the decomposition stock solution is subjected to seeding and precipitation under the conditions of α k 1.5, temperature 50 °C, time 8 h, seed ratio 0.12, and AO concentration 138 g / L; then, after filtration and washing by a flat plate filter, a mother liquor for seeding and a filter cake of aluminum hydroxide are obtained, and the mother liquor for seeding is returned to the Bayer process for recycling;

[0116] S5, drying:

[0117] The aluminum hydroxide filter cake is dried to remove the attached water, and the drying conditions are 100 °C and 60 min, obtaining high-white aluminum hydroxide micropowder with a whiteness greater than 99.1%, which can be sold as a product after packaging.

[0118] Although the present invention has been described in detail by referring to the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those of ordinary skill in the art can make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions should all be within the scope of the present invention. / Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for producing high - white aluminum hydroxide micropowder by dissolving bauxite in liquid caustic soda, characterized in that, it mainly includes caustic soda dissolution, solid - liquid separation, purification separation, seeding and drying; Purification separation: The overflow obtained from solid - liquid separation is refined to obtain sodium aluminate solution by removing impurities with a leaf filter. The content of suspended matter in the refined sodium aluminate solution is < 0.02 g / L; Alumina is added to the refined sodium aluminate solution for adsorption purification to obtain a high - light - transmittance purified solution; The purified solution is separated to obtain the decomposition mother liquor, and the content of suspended matter in the decomposition mother liquor is < 0.015 g / L; The specific process is as follows: s1, Caustic soda dissolution: The liquid caustic soda and bauxite are proportioned according to the digestion αk; The proportioned bauxite is subjected to pipeline digestion to obtain a slurry; s2, Solid - liquid separation: The slurry is sent to a conical tank for solid - liquid separation to separate the red mud from the slurry, obtaining an underflow and an overflow; The solid content of the underflow is 400 - 600 g / L; The content of suspended matter in the overflow is 0.05 - 1.0 g / L; s3, Purification separation: The overflow is purified and de - impurities by a leaf filter with lime milk as a filter aid to obtain a refined sodium aluminate solution and filter cake A; Alumina is added to the refined sodium aluminate solution for adsorption purification to obtain a high - light - transmittance purified solution; The purified solution is separated by pressure filtration to obtain the decomposition mother liquor and filter cake B; s4, Seeding: The decomposition mother liquor is seeded under the condition of adding crystal seeds, and then filtered and washed by a flat - plate filter to obtain the seeding mother liquor and aluminum hydroxide filter cake; s5, Drying: The aluminum hydroxide filter cake is dried under the conditions of 100 °C and 60 min to obtain high - white aluminum hydroxide micropowder with a whiteness greater than 98%. After packaging, it can be sold as a product; In step s1, the liquid caustic soda is a 32% sodium hydroxide solution or a 50% sodium hydroxide solution; The bauxite is a trihydrate or monohydrate ore; The digestion αk is 1.3 - 1.6; In step s1, the digestion temperature during the caustic soda dissolution process is 140 - 260 °C, and the digestion time is 15 - 60 min; In step s3, the addition amount of alumina is 1 - 10 g / L, the purification temperature is 50 - 70 °C, and the purification time is 30 - 60 min; In step s4, the decomposition mother liquor is seeded under the conditions of αk being 1.3 - 1.6, temperature being 50 - 70 °C, time being 4 - 12 h, seed ratio being 0.02 - 0.12, and AO concentration being 110 - 160 g / L.

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