Aluminium hydroxide, commonly known as hydrate of alumina, Al(OH)3, is an odourless, white crystalline powder. This substance is stable at standard conditions and is insoluble in water. Aluminium hydroxide is widely known as a material for flame retardant because it can decompose into water and alumina at 200°C. Aluminium hydroxide is also an amphoteric material, it can be base or acid depending on the condition of the solution. It is usually used for the manufacturing of aluminium, fire retardant, and pharmaceuticals. It is also used in the catalytic industry, paper industry, ceramic industry, printing industry and etc.
In 1887, Carl Josef Bayer invented the Bayer Process. He discovered how to separate alumina from bauxite more efficiently. Firstly, bauxite is to be mixed with a hot solution of sodium hydroxide, NaOH. The addition of sodium hydroxide solution causes the precipitation of alumina. Alumina precipitate is then cooled and the resulting solution is calcinated and processed to give Al2O3.
Aluminium hydroxide is the basic material for many other aluminium compounds. In industries, it is added to cement to facilitate the drying. It is also used for the production ceramic and glass as it can increase the melting point of glass. When aluminium hydroxide is combined with a polymer, the newly made material will gain fire retardant properties.
Aluminium hydroxide acts as an extender and bodying agent in the manufacturing of paper. It is used as a filler in paper as it disperses readily and retains for a long time during manufacturing. It is also used as a paper coating agent in the paper industry.
In the pharmaceutical industry, aluminium hydroxide that combines with magnesium hydroxide is used for neutralising acids. It can also help to increase our immune system and also preparing vaccines to combat tetanus, Hepatitis A, and Hepatits B.
Aluminium oxide is important for the manufacturing of pure aluminium metal via the Hall-Héroult process. The Hall-Héroult process involves dissolving aluminium oxide in molten cryolite, and electrolysing the molten salt bath at 940–980°C, giving a 99.5% - 99.8% yield of pure aluminium.