Aluminum Hydroxide CAS 21645-51-2

1. Bayer method: 97% of the bauxite ore produced every year in the world is processed by the Bayer method to obtain alumina. The Bayer process consists of two main processes: heat treatment of bauxite with a caustic soda solution to produce sodium metaaluminate from the alumina in the ore, namely:
   
   Then, the cooled sodium aluminate solution is decomposed by stirring, and then filtered and separated to obtain an aluminum hydroxide product, that is,
   
   
2. Sintering method: In industrial aluminum production, the sintering method is suitable for high-silicon bauxite, that is, Al2O3/SiO2<7. The steps of the sintering method include the following aspects: First, the bauxite and sodium carbonate solution are mixed in a certain proportion for sintering, namely:
   
   Secondly, the sintered bauxite is prepared into sodium aluminate by leaching with sodium carbonate solution; namely:
   
   Finally, CO2 gas is passed into the sodium aluminate solution to generate aluminum hydroxide.
   
   

The aluminum hydroxide synthesized by the hydrothermal method has high purity, small particle size, uniform distribution, easy control of crystal shape, and simple operation. Therefore, it is widely used in the process of synthesizing aluminum hydroxide. Using aluminum isopropoxide as the main raw material, it was mixed with distilled water in a molar ratio of 1:100 to make it hydrolyzed. Heat treatment, and then cooling and centrifuging to obtain nano aluminum hydroxide. The prepared aluminum hydroxide product is a typical boehmite flake structure with a particle size of about 10 nm.

The sol-gel method is currently a commonly used method for the preparation of ultrafine aluminum hydroxide. The most common sol-gel method for preparing aluminum hydroxide is to hydrolyze aluminum salts and alkoxides in water. The mechanism is divided into two steps: the -OR group is first hydrolyzed to produce -OH, and then aluminum hydroxide is precipitated in the form of precipitation.

A highly crystalline aluminum hydroxide product was synthesized by reacting aluminum isopropoxide and monobutyltrimethylimidazolium borofluoride in 1 L of hydrophilic ionic liquid and using (NH)4OH as a catalyst at 30 °C. , and heat treatment at 300 ℃ to obtain highly crystalline alumina particles, and the product is boehmite with low crystallinity when isopropanol is used as a medium, and a new composite material is synthesized by combining the aluminum hydroxide product with polystyrene.

The carbon fractionation method is a method in which CO2 gas is introduced into the sodium metaaluminate solution to precipitate aluminum hydroxide, and the size and morphology of the product are controlled by adjusting the pH value and CO2 concentration.

Microemulsions typically consist of surfactants, cosurfactants, solvents, and water (or aqueous solutions). Microemulsions have properties such as ultra-low interfacial tension and high solubilizing ability. The preparation of nanomaterials by microemulsion technology can precisely control the crystal growth process of nanomaterials, and the microemulsion spheres wrap the crystal particles, effectively preventing the agglomeration of nanoparticles.

• Acid-base method: Zhejiang University of Technology uses industrial solid waste alum pulp as raw material, mainly containing KAl(SO4)2 and SiO2, and a small amount of Fe2O3 in the rest. First, use H2SO4 for acid treatment to obtain Al2(SO4)3, and then add Excess NaOH is filtered to remove iron to obtain sodium metaaluminate, which is then neutralized with H2SO4 to precipitate aluminum hydroxide. According to the discussion of the preparation process, it is considered that the best synthesis conditions are: H2SO4 concentration 16 mol/L, NaOH concentration 5 mol/L L. This method realizes the efficient utilization of industrial solid waste, but the product yield is not high and contains many impurities, which still needs to be purified.
• Ion membrane electrolysis method: Alkaline ion membrane electrolysis MA1(ΟH)4 to obtain aluminum hydroxide, where M represents an alkali metal, and the electrolysis temperature is not less than 40 °C. This method can greatly improve the decomposition efficiency of sodium aluminate, and obtain high-quality, high-yield aluminum hydroxide.
• Homogeneous precipitation method: Using Al(NO) 3 9H2O and anhydrous sodium acetate as raw materials, nano-sodium hydroxide was prepared by homogeneous precipitation in the absence of water. The specific experiment is as follows: 0.3 mmol Al(NO) 3 9H2O and 0.9 mmol anhydrous sodium acetate, with PVP (60 g) as the dispersant, add 30 mL of ethylene glycol together into a beaker and stir at room temperature until it is completely dissolved. The reactants were transferred to a 50 mL autoclave containing Teflon and crystallized at 180 °C for 5 h. This method can achieve the effect of controlling the particle size and morphology of the product by controlling the reaction temperature and the concentration of the reactants.
• Aluminum salt hydrolysis method: add 100 g Na2SO4 to 412 g Al2(SO4)3 solution, and then add the mixed solution to the Na2CO3 solution with a mass fraction of 26% at a rate of 25 mL/min for hydrolysis. When the pH is between 7 and 8, the synthesized BET is 350-450 m2/g, and the pore volume is 0.58-0.9×10-6 m2/g of porous boehmite. When the pH is equal to 9, the synthesized boehmite BET drops to 189 m2/g, while the pore volume increased to 1.27×10-6 m2/g.