Bauxite

Bauxite is a naturally occurring, heterogeneous material composed primarily of one or more aluminium hydroxide minerals, plus various mixtures of silica, iron oxide, titania, aluminium silicates, and other impurities in minor or trace amounts. Bauxite is a sedimentary rock produced by in situ chemical weathering typically under tropical to subtropical climate conditions.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The principal aluminium hydroxide minerals found in varying proportions with bauxites are gibbsite and the polymorphs boehmite and diaspore. Bauxites are typically classified according to their intended commercial application: abrasive, cement, chemical, metallurgical, refractory, etc.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The bulk of world bauxite production (approximately 85%) is used as feed for the manufacture of alumina via a wet chemical caustic leach method commonly known as the Bayer process. Subsequently, the majority of the resulting alumina produced from this refining process is in turn employed as the feedstock for the production of aluminium metal by the electrolytic reduction of alumina in a molten bath of natural or synthetic cryolite (Na3AlF6), the Hall-Heroult process.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Bauxite is the raw material most widely used in the production of alumina on a commercial scale. Other raw materials, such as anorthosite, alunite, coal wastes, and oil shales, offer additional potential alumina sources. Although it would require new plants using new technology, alumina from these nonbauxitic materials could satisfy the demand for primary metal, refractories, aluminium chemicals, and abrasives. Synthetic mullite, produced from kyanite and

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

sillimanite, substitutes for bauxite-based refractories. Although more costly, silicon carbide and alumina-zirconia

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

substitute for bauxite-based abrasives.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Aluminium: x...

Hydroxide: Hydroxide is a polyatomic ion consisting of oxygen and hydrogen:...

Mineral: This article is about minerals in the geologic sense; for nutrient minerals see dietary mineral; for the band see Mineral (band)....