БОКСИТОВ

Bauxite is the major source of aluminum sesquioxide (alumina, Al₂O₃) worldwide. Bauxite is a soft and red clay, rich in alumina. From a geological point of view bauxite is defined as a residual sedimentary rock in the laterite family that results from in situ superficial weathering in moist tropical climates of clays, clayey limestones, or high-alumina-content silicoaluminous igneous and metamorphic rocks containing feldspars and micas.
Bauxite is a sedimentary rock, so it has neither a precise definition nor chemical formula. From a mineralogical point of view, bauxite is mainly composed of hydrated alumina minerals such as gibbsite [Al(OH)₃ or Al₂O₃.3H₂O, monoclinic] in recent tropical and equatorial bauxite deposits, while boehmite [AlO(OH) or Al₂O₃.H₂O, orthorhombic] and, to a lesser extent, diaspore [AlO(OH) or Al₂O3 .H₂O, orthorhombic] are the major minerals in subtropical and temperate bauxite old deposits. The average chemical composition of bauxite is 45 to 60 wt.% Al₂O₃ and 10 to 30 wt.% Fe₂O₃, the remainder consisting of silica, calcia, titanium dioxide, and water.

Bauxite consists mainly of gibbsite, Al(OH)3, and varying amounts of kaolinite, and iron and titania impurities. Because the loss on ignition is high, bauxite must be calcined to high temperatures before use. During calcination, it is converted to a dense grain consisting mainly of corundum, Al2O3, and mullite.

Absorbent catalysts

A natural aggregate of aluminumbearing minerals, more or less impure, in which the aluminum occurs largely as hydrated oxides. It is usually formed by prolonged weathering of aluminous rocks. Contains 30–75% Al2O 3 , 9–31% H2O, 3–25% Fe2O 3 , 2–9%, SiO2, 1–3% Ti O 2 .

Bauxite is the best raw material for the production of alumina and aluminium. More than 95 per cent of the world's alumina is extracted from bauxite using the Bayer process. Therefore, it is mainly used for the production of primary aluminium metal. The following diagram shows the flow chart for aluminium production:

Bauxite can be considered to be a nuisance particulate; long experience with mining and refining of bauxite has not revealed significant adverse health effects.
Nuisance particulates have little adverse effect on lungs and do not produce significant organic disease or toxic effect when exposures are kept under reasonable control.

A nuisance dust. Human systemiceffects by inhalation: fibrosis, focal (pneumoconiosis).