Submicron aluminum hydroxide and method for its production

Abstract

This invention belongs to the field of inorganic materials technology, specifically relating to a submicron aluminum hydroxide and its preparation method. The submicron aluminum hydroxide powder has a particle size of 0.6–0.75 μm, exhibiting good dispersibility and complete crystal morphology. Specifically, it is prepared by adding an appropriate amount of dilute acid solution to a sodium aluminate decomposition solution, causing aluminum hydroxide particles to precipitate spontaneously. A seed inhibitor is then added, and the precipitated aluminum hydroxide particles are used as seed crystals for decomposition at a constant temperature of 50–60°C for 40–48 hours. The sodium aluminate decomposition solution described in this invention has extremely high stability, ensuring clarity for 48 hours at the decomposition temperature. This prevents immediate reaction with the added dilute acid, avoiding the formation of large aluminum hydroxide seed crystals due to rapid chemical reaction. Furthermore, the constant-temperature decomposition process ensures that secondary crystallization does not occur during seed crystal growth. The seed inhibitor effectively inhibits the growth of aluminum hydroxide seed crystals.

Description

[Technical Field]

[0001] This invention belongs to the field of inorganic materials technology, specifically relating to a submicron aluminum hydroxide and its preparation method. [Background Technology]

[0002] Submicron powders typically refer to fine-grained powders with an average particle size of 0.1–1.0 μm. Submicron aluminum hydroxide, due to its excellent smokeless flame retardancy, wear resistance, density, fracture toughness, and insulation properties, has wide applications in flame retardants, aluminum salts, papermaking, catalysts, and glass fibers. It can also serve as a precursor for the preparation of high-end powder materials such as submicron boehmite, submicron aluminum nitride, and submicron alumina, resulting in significant market demand and broad application prospects.

[0003] Currently, most ultrafine aluminum hydroxide on the market has an average particle size of over 1.0 μm, and there are no large-scale submicron aluminum hydroxide products available for sale. There are two main methods for preparing submicron aluminum hydroxide: mechanical grinding and seeding decomposition. Mechanical grinding is technically simple, but it requires the use of ball mills and sand mills in series, resulting in high production costs. Furthermore, the aluminum hydroxide produced has a wide particle size distribution, with large particles and poor performance. Seeding decomposition, on the other hand, allows for controllable particle size and distribution, producing samples of better quality and application performance. In the seeding decomposition process, the decomposition of sodium aluminate solution is one of the key steps in producing submicron aluminum hydroxide; however, the final particle size of the submicron aluminum hydroxide product obtained from this method is currently only 1–2 μm.

[0004] There is considerable research in China on the preparation process of ultrafine aluminum hydroxide. For example, patent CN98126371.2 discloses a method for preparing fibrous ultrafine aluminum hydroxide using carbon decomposition and hydrothermal treatment; patent CN200610127935.1 uses polyol additives added to sodium aluminate solution to obtain flake aluminum hydroxide of different particle sizes; patent CN200510110587.2 also prepares ultrafine aluminum hydroxide by precipitation reaction of sodium aluminate aqueous solution with CO2 gas; patent CN00130250.7 uses carbon powder method to prepare seed crystals, and then prepares ultrafine aluminum hydroxide through seed decomposition, which has also been industrialized. However, the aluminum hydroxide products prepared by these methods are only ultrafine aluminum hydroxide with an average particle size of 1.5 micrometers. Currently, there is no research on products and technologies for preparing submicron aluminum hydroxide below 1.0 μm using the Bayer process seed decomposition method in China. [Summary of the Invention]

[0005] The purpose of this invention is to provide a submicron aluminum hydroxide with an average particle size of 0.6-0.75 μm, good dispersibility, and complete crystal morphology, and a method for preparing the same.

[0006] Based on the above objectives, this application adopts the following technical solution:

[0007] The first aspect of the present invention is to provide a submicron aluminum hydroxide, wherein the submicron aluminum hydroxide is obtained by seeding and decomposition using self-precipitated aluminum hydroxide particles obtained by mixing dilute acid with sodium aluminate decomposition stock solution.

[0008] Preferably, the dilute acid is selected from dilute sulfuric acid and dilute hydrochloric acid.

[0009] Preferably, the N in the sodium aluminate decomposition solution k The concentration is 140 g / L to 180 g / L, α k The concentration is 1.50 to 1.55. This decomposition solution is extremely stable and can guarantee that it will not decompose within 48 hours.

[0010] A second aspect of the present invention is to provide a method for preparing the above-mentioned submicron aluminum hydroxide, specifically comprising the following steps:

[0011] (1) Add an appropriate amount of dilute acid solution to the sodium aluminate decomposition stock solution and stir for a certain period of time until the solution turns milky white;

[0012] (2) Add seed inhibitor to the above solution and then decompose at a constant temperature of 50-60℃ for 40-48 hours.

[0013] Preferably, the equivalent concentration of the dilute acid solution in step (1) is 1.0 to 2.0 N, and the added mass is 0.1% to 0.5% of the mass of the sodium aluminate decomposition stock solution.

[0014] Preferably, the seed inhibitor is selected from sodium gluconate.

[0015] Preferably, the mass of sodium gluconate added is 0.1 to 0.2% of the mass of the sodium aluminate decomposition solution.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The sodium aluminate decomposition solution described in this invention has extremely high stability, ensuring that it remains clear for 48 hours at high temperature and that it will not react immediately after the addition of dilute acid, thus preventing the formation of large aluminum hydroxide seed particles due to excessively rapid chemical reaction.

[0018] The sodium aluminate decomposition solution of the present invention will spontaneously precipitate aluminum hydroxide particles in one go after about 20 minutes of adding dilute acid. The resulting particles are finer and more conducive to obtaining aluminum hydroxide powder with a finer average particle size.

[0019] The seed decomposition process of this invention adopts a constant temperature decomposition process, which can ensure that secondary crystallization will not occur during the seed growth process;

[0020] This invention effectively inhibits the growth of aluminum hydroxide seeds by adding a seed inhibitor after seed precipitation, thus obtaining submicron aluminum hydroxide particles.

[0021] The aluminum hydroxide powder obtained by this invention has a particle size of 0.6 to 0.75 μm, and exhibits good dispersion properties and complete crystal morphology.

Detailed Implementation Methods

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described with reference to the following specific embodiments, but these are not intended to limit the invention. The following descriptions are preferred embodiments of the invention and are merely for illustrative purposes. They should not be construed as limiting the invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

[0023] Example 1

[0024] (1) To N k It is 150g / L, α k Add a 1.5N equivalent concentration of dilute sulfuric acid solution to a sodium aluminate decomposition stock solution of 1.50, the added mass being 0.1% of the mass of the sodium aluminate decomposition stock solution; stir for 20 minutes, and seed crystals will precipitate from the solution until the solution turns milky white;

[0025] (2) Then add sodium gluconate to the above solution, the amount of which is 0.1% of the mass of the original solution, and then decompose at a constant temperature of 50°C for 48 hours.

[0026] The final particle size of the aluminum hydroxide obtained is D. 50 =0.63μm, D 90 =1.42μm.

[0027] Example 2

[0028] (1) To N k It is 140 g / L, α k Add a 1.0N equivalent concentration of dilute sulfuric acid solution to the sodium aluminate decomposition stock solution with a concentration of 1.55. The added mass is 0.2% of the mass of the sodium aluminate decomposition stock solution. Stir for 20 minutes, and seed crystals will precipitate from the solution until the solution turns milky white.

[0029] (2) Then add sodium gluconate to the above solution, the amount of which is 0.15% of the mass of the original decomposition solution, and then decompose at a constant temperature of 55℃ for 45 hours.

[0030] The final particle size of the aluminum hydroxide obtained is D. 50 =0.70μm, D 90 =1.49μm.

[0031] Example 3

[0032] (1) To N k It is 160g / L, α k Add a 2.0N equivalent hydrochloric acid solution to the sodium aluminate decomposition stock solution with a concentration of 1.55. The added mass is 0.2% of the mass of the sodium aluminate decomposition stock solution. Stir for 20 minutes. Seed crystals will precipitate from the solution until the solution turns milky white.

[0033] (2) Then add sodium gluconate to the above solution, the amount of which is 0.2% of the mass of the original solution, and then decompose at a constant temperature of 60℃ for 40 hours.

[0034] The final particle size of the aluminum hydroxide obtained is D. 50 =0.75μm, D 90 =1.58μm.

[0035] Example 4

[0036] (1) To N k It is 180g / L, α k A 1.0N equivalent concentration of dilute hydrochloric acid solution was added to the sodium aluminate decomposition stock solution with a concentration of 1.52. The added mass was 0.2% of the mass of the sodium aluminate decomposition stock solution. After stirring for 20 minutes, seed crystals were precipitated from the solution until the solution turned milky white.

[0037] (2) Then add sodium gluconate to the above solution, the amount of which is 0.2% of the mass of the original solution, and then decompose at a constant temperature of 60℃ for 40 hours.

[0038] The final particle size of the aluminum hydroxide obtained is D. 50 =0.74μm, D 90 =1.52μm.

[0039] Comparative Example 1

[0040] Same as Example 1, except that the dilute sulfuric acid in step (1) is replaced with an aluminum sulfate solution with an aluminum oxide content of 3.8%.

[0041] The final particle size of the aluminum hydroxide obtained is D. 50 =4.80μm, D 90 =10.61μm.

[0042] Comparative Example 2

[0043] Same as Example 1, except that sodium gluconate is not added and the decomposition is performed directly.

[0044] The final particle size of the aluminum hydroxide obtained is D. 50 =3.50μm, D90 =8.53μm.

[0045] In summary, the submicron aluminum hydroxide obtained by the method described in this application has a particle size D 50 The particle size is between 0.6 and 0.75 μm, reaching the submicron level. The particle size distribution is uniform and the crystals are complete. It can be directly used as a flame retardant in the fields of rubber and plastic materials. It can also be used as a raw material for submicron boehmite and submicron alumina in the field of lithium battery fillers. It can be seen that the application prospects of submicron aluminum hydroxide with this particle size are broad.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing submicron aluminum hydroxide, characterized in that, The submicron aluminum hydroxide is prepared by seeding and decomposition using self-precipitated aluminum hydroxide particles obtained by mixing dilute acid with sodium aluminate decomposition stock solution. Specifically, the steps include the following: (1) Add an appropriate amount of dilute acid solution to the sodium aluminate decomposition stock solution and stir for a certain period of time until the solution turns milky white; (2) Add seed inhibitor to the above solution and then decompose at a constant temperature of 50°C for 48 hours; The equivalent concentration of the dilute acid solution mentioned in step (1) is 1.5N, and the added mass is 0.1% of the mass of the sodium aluminate decomposition stock solution; The dilute acid is dilute sulfuric acid; The N in the sodium aluminate decomposition solution k It is 150g / L, α k It is 1.50; The seed inhibitor is selected from sodium gluconate; the added mass of sodium gluconate is 0.1% of the mass of the sodium aluminate decomposition solution.