BAUXITE

Resources

According to the US Geological Survey, the world's bauxite resources are estimated to be 55 to 75 billion tonnes located mainly in South America (33%), Africa (27%), Asia (17%), Oceania (13%), and elsewhere (10%). Today, Australia supplies 35% of the demand worldwide for bauxite, South America 25%, and Africa 15%. The current reserves are estimated at being able to supply worldwide demand for more than two centuries. Note that about 95% of bauxite is of the metallurgical grade and hence used for the production of primary aluminum metal.

Description

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.

Chemical Properties

solid

Chemical Properties

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.

Uses

Absorbent catalysts

Uses

Ore for production of alumina; adsorbent in oil refining

Definition

A mineral hydrated form of aluminum hydroxide; the principal ore of aluminum.

Definition

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 .

Application

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:

Health Hazard

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.

Safety Profile

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

Raw materials

Preparation Products