Bayer process

Developed by Carl Josef Bayer Bayer process is used in aluminum production, in order to convert bauxite in sufficient purity alumina.

Firstly, bauxite is separated from the iron oxide contained in hematite, and boehmite. The method exploits the fact that can be easily solved at a higher temperature, the aluminum hydroxides of the finely ground bauxite in sodium hydroxide solution. The finely ground bauxite is mixed with concentrated sodium hydroxide solution at about 7 bar and about 180 ° C.

The undissolved residue ( containing mainly insoluble iron compounds, and the red mud -called mass presents a disposal problem ) is separated. Here, the recovery may be interposed by the gallium contained in admixture. From the dilute aluminate pure aluminum hydroxide is precipitated on cooling. The filtrate is diluted with sodium hydroxide solution, the temperature is lowered to 78 ° C and the pressure is reduced again to atmospheric pressure. Through so-called " seeding " with solid aluminum hydroxide as a crystallization nucleus then falls from the aluminum hydroxide.

The resulting solid of aluminum hydroxide is calcined in rotary kilns at a temperature of 1200 to 1300 ° C, wherein aluminum oxide is formed.

For this pure bauxite can then be recovered by electrolysis in the Hall - Heroult process, metallic aluminum.