Bauxite Types and Uses
Bauxite is aluminium-rich ore that is used for aluminium production (the metallurgical bauxites) and for production of refractory materials, chemicals or cements (the non-metallurgical bauxites).
Metallurgical bauxites are sub-divided into two basic types based on the processing methods that must be applied to them at the alumina refinery stage, namely:
1. low temperature gibbsite (aka: tri-hydrate or tropical bauxite); and
2. high-temperature boehmite (aka: mono-hydrate or European bauxite)
Note: ABx bauxites are predominantly the gibbsite-rich type.
Alumina refineries extract pure alumina from bauxite by dissolution in hot caustic soda followed by purification and precipitation of alumina powder which is aluminium oxide (Al2O3) – the raw material for smelting into pure aluminium metal by electrolytic reduction in a molten bath at aluminium smelters.
The gibbsite mineral is alumina tri-hydrate and is the most valuable of alumina ore minerals because it readily dissolves at low temperatures and pressures at the alumina refinery stage (the Bayer process).
The boehmite mineral is alumina mono-hydrate which must be processed at high temperatures and high pressures in more expensive pressure vessels. Some unwanted non-alumina minerals are also dissolved so that additional processing stages to remove the non-alumina contaminants are required. The additional processing stages to remove contaminants can also be associated with alumina loss.
Boehmite bauxites are sourced from Weipa in far northern Queensland, Gove in NT and from west African states, including parts of Guinea in northwest Africa.
Gibbsite bauxites are sourced from southwest Western Australia, the Republic of Guinea in northwest Africa, Indonesia, Caribbean islands and South America, mainly in Brazil, Guyana and other parts of tropical Amazonia. Gibbsite ores are in short supply.