The process of producing
pure alumina from bauxite - the Bayer Process - haschanged very little since
its invention by Austrian chemist Karl Josef Bayer whileworking in Saint
Petersburg, Russia. He develop a method for supplying aluminato the textile
industry (it was used as a mordant in dyeing cotton), in 1888. Hefound found that
the aluminium hydroxide that precipitated from alkaline solution wascrystalline
and could be easily filtered and washed, while that precipitated fromacid
medium by neutralization was gelatinous and difficult to wash. Figure 1:
Karl Josef BayerThe alumina produced today, can then be used for various
industrial purposes orsmelted to provide aluminum.The first commercial plant
was commissioned in 1893. The Bayer processes can beconsidered in three stages
The aluminium-bearing
minerals in bauxite - Gibbsite, B?hmite and Diaspore -are selectively extracted
from the insoluble components (mostly oxides) bydissolving them in a solution
of sodium hydroxide (caustic soda):The first step in the process is the mixing
of ground bauxite into a solution ofsodium hydroxide. By applying steam and pressure
in tanks containing themixture, the bauxite slowly dissolves. The alumina
released reacts with thesodium hydroxide to form sodium aluminateGibbsite: