Bauxite with a US Cent Bauxite with core of unweathered rock

Bauxite is the most important aluminium ore. It consists largely of the minerals gibbsite Al(OH)₃, boehmite γ-AlO(OH), and diaspore α-AlO(OH), together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO₂. It was named after the village Les Baux-de-Provence in southern France, where it was first discovered in 1821 by geologist Pierre Berthier.

Bauxite information

Lateritic bauxites (silicate bauxites) are distinguished from karst bauxites (carbonate bauxites). The early discovered carbonate bauxites occur predominantly in Europe and Jamaica above carbonate rocks (limestone and dolomite), where they were formed by lateritic weathering and residual accumulation of intercalated clays or of clayey dissolution residues of the limestone.

The lateritic bauxites occur in many countries of the tropical belt. They were formed by lateritization of various silicate rocks such as granite, gneiss, basalt, syenite and shale. Compared with iron-rich laterites, the formation of bauxites demands even more intense weathering conditions with a very good drainage. This enables dissolution of kaolinite and precipitation of gibbsite. Zones with highest aluminium content are frequently located below a ferruginous surface layer. The aluminium hydroxide in the lateritic bauxite deposits is almost exclusively gibbsite.

Production trends

In 2007, Australia was the top producer of bauxite with almost one-third world share, followed by China, Brazil, Guinea and Jamaica. Although aluminum demand is rapidly increasing, known reserves are sufficient to meet the needs for a considerable time. Increased aluminum recycling, which has the advantage of lowering the energy costs of production, will help extend Bauxite reserves.

(in '000 tonne, Numbers for 2007 estimated)
Country	2006	2007	Reserves	Reserve base
Australia	62,300	64,000	5,800,000	7,900,000
China	21,000	32,000	700,000	2,300,000
Brazil	21,000	24,000	1,900,000	2,500,000
Guinea	14,500	14,000	7,400,000	8,600,000
Jamaica	14,900	14,000	2,000,000	2,500,000
India	12,700	13,000	770,000	1,400,000
Russia	6,600	6,000	200,000	250,000
Venezuela	5,500	5,500	320,000	350,000
Suriname	4,920	5,000	580,000	600,000
Kazakhstan	4,800	4,900	360,000	450,000
Greece	2,450	2,400	600,000	650,000
Other countries	5,460	6,800	3,400,000	4,000,000
World total (rounded)	178,000	190,000	25,000,000	32,000,000
Source: U.S. Geological Survey, Mineral Commodity Summaries, January 2008

Processing

Bauxite is strip mined (surface mining) because it is found at the surface, with little or no overburden. Approximately 95% of the world's bauxite production is processed into aluminium. Bauxites are typically classified according to their intended commercial application: metallurgical, abrasive, cement, chemical and refractory.

Bauxites are heated in pressure vessels with sodium hydroxide solution at 150-200 °C through which aluminium is dissolved as aluminate (Bayer process). After separation of ferruginous residue (red mud) by filtering, pure gibbsite is precipitated when the liquor is cooled and seeded with fine grained aluminium hydroxide. Gibbsite is converted into aluminium oxide by heating. This is molten at approx. 1000 °C by addition of cryolite as a flux and reduced to metallic aluminium by a highly energy-consumptive electrolytic process (the Hall-Héroult process).