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Bauxite is a naturally occurring, heterogeneous material composed primarily of one or more aluminium hydroxide minerals, plus various mixtures of silica, iron oxide, titania, aluminosilicate , and other impurities in minor or trace amounts. 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 processThe Hall-Heroult process is the major industrial process for the production of aluminum. In the Hall-Heroult process alumina, AlO is dissolved in a carbon-lined bath of molten cryolite, NaAlF. Aluminum fluoride, AlF is also present to reduce the melting p.
Bauxite is the raw material most widely used in the production of alumina on a commercial scale. Other raw materials, such as anorthositeAnorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar (90-100%), and a minimal mafic component (0-10%). Augite, ilmenite, magnetite, and minor olivine are the mafic minerals usually present. In feldspa, aluniteAlunite or alumstone, is a mineral that was first observed in the 15th century at Tolfa, near Rome, where it was mined for the manufacture of alum. First called aluminilite by J. Delametherie in 1707, this name was contracted by F. Beudant in 1824 to alun, coalCoal is a fossil fuel extracted from the ground by mining. It is a readily combustible black or brownish-black sedimentary rock. It is composed primarily of carbon and hydrocarbons, along with assorted other elements, including sulfur. Often associated wi wastes, and oil shaleOil shale is a general term applied to a group of fine black to dark brown shales rich enough in bituminous material (called kerogen) to yield petroleum upon distillation. The kerogen in oil shale can be converted to oil through the chemical process of pys, 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 kyaniteThe mineral kyanite is an aluminium silicate of the sillimanite group (along with andalusite and sillimanite), also called alumino-silicate. It has the formula AlO·SiO (AlSiO). Its hardness varies widely depending on its crystallographic direction, from 5 and
sillimaniteSillimanite is an alumino-sillicate mineral with the chemical formula AlSiO. Sillimanite is named after the American chemist B. Silliman ( 1779- 1824). Occurrence Sillimanite is one of three alumino-sillicate polymorphs, the other two being andalusite and, substitutes for bauxite-based refractories. Although more costly, silicon carbideSilicon carbide (SiC) or moissanite is a ceramic compound of silicon and carbon. Most SiC is man-made for use as an abrasive (when it is often known by the trade name carborundum), or more recently as a semiconductor and moissanite gemstones. The simplest and alumina-zirconia
substitute for bauxite-based abrasives.
1 History
Bauxite was named after the village Les Baux de Provence in southern France, where it was first discovered in 1821 by the geologist Pierre Berthier. Knighted in 1832, Sir Berthier went on to establish the Berthier Museum of Geology in Tours.
Due to the exhaustion of its bauxite mines, France has almost completely ceased the exploitation of bauxite since 1991. French mines were located in the Var, Bouches-du-Rhône and Herault departements.
