Bauxite, an aluminium ore, is the world's main source of aluminium. It consists mostly of the minerals gibbsite Al(OH)3, boehmite γ-AlO(OH) and diaspore α-AlO(OH), mixed with the two iron oxides goethite and haematite, the clay mineral kaolinite and small amounts of anatase Template:TiO2. In 1821 the French geologist Pierre Berthier discovered bauxite near the village of Les Baux in Provence, southern France. In 1861, French chemist Henri Sainte-Claire Deville named the mineral "bauxite".
Script error Lateritic bauxites (silicate bauxites) are distinguished from karst bauxite ores (carbonate bauxites). The 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 clay layers – dispersed clays which were concentrated as the enclosing limestones gradually dissolved during chemical weathering.
The lateritic bauxites are found mostly in the countries of the tropics. They were formed by lateritization of various silicate rocks such as granite, gneiss, basalt, syenite, and shale. In comparison with the iron-rich laterites, the formation of bauxites depends even more on intense weathering conditions in a location with very good drainage. This enables the dissolution of the kaolinite and the precipitation of the 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.
In the case of Jamaica, recent analysis of the soils showed elevated levels of cadmium, suggesting that the bauxite originates from recent Miocene ash deposits from episodes of significant volcanism in Central America.
In 2009, Australia was the top producer of bauxite with almost one-third of the world's production, followed by China, Brazil, India, and Guinea. Although aluminium demand is rapidly increasing, known reserves of its bauxite ore are sufficient to meet the worldwide demands for aluminium for many centuries. Increased aluminium recycling, which has the advantage of lowering the cost in electric power in producing aluminium, will considerably extend the world's bauxite reserves.
|Country||Mine production||Reserves||Reserve base|
|Template:Country data Guinea||17,400||18,000||7,400,000||8,600,000|
|Template:Country data Australia||68,400||67,000||6,200,000||7,900,000|
|Template:Country data Vietnam||80||80||2,100,000||5,400,000|
|Template:Country data Jamaica||8,540||10,200||2,000,000||2,500,000|
|Template:Country data Brazil||28,100||31,000||3,600,000||2,500,000|
|Template:Country data Guyana||1,760||2,000||850,000||900,000|
|Template:Country data India||18,000||20,000||900,000||1,400,000|
|Template:Country data China||44,000||46,000||830,000||2,300,000|
|Template:Country data Greece||2,100||2,100||600,000||650,000|
|Template:Country data Iran||—||500||—||—|
|Template:Country data Suriname||4,000||5,000||580,000||600,000|
|Template:Country data Sierra Leone||1,090||1,700||180,000||?|
|Template:Country data Kazakhstan||5,310||5,400||160,000||450,000|
|Template:Country data Venezuela||2,500||4,500||320,000||350,000|
|Template:Country data Russia||5,480||5,800||200,000||250,000|
|Template:Country data United States||30||N/A||20,000||40,000|
|World total (rounded)||209,000||220,000||29,000,000||38,000,000|
Bauxite is usually strip mined because it is almost always found near the surface of the terrain, with little or no overburden. Approximately 70% to 80% of the world's dry bauxite production is processed first into alumina, and then into aluminium by electrolysis as of 2010. Bauxite rocks are typically classified according to their intended commercial application: metallurgical, abrasive, cement, chemical, and refractory.
Usually, bauxite ore is heated in a pressure vessel along with a sodium hydroxide solution at a temperature of 150 to 200 °C. At these temperatures, the aluminium is dissolved as an aluminate (the Bayer process). After separation of ferruginous residue (red mud) by filtering, pure gibbsite is precipitated when the liquid is cooled, and then seeded with fine-grained aluminium hydroxide. The gibbsite is usually converted into aluminium oxide, Al2O3, by heating. This mineral is dissolved at a temperature of about 960 °C in molten cryolite. Next, this molten substance can yield metallic aluminium by passing an electric current through it in the process of electrolysis, which is called the Hall–Héroult process, named after its American and French discoverers.
Prior to the invention of this process in 1886, elemental aluminium was made by heating ore along with elemental Na or K in a vacuum. The method was complicated and consumed materials that were themselves expensive at that time. This made early elemental aluminium more expensive than gold.
- Bárdossy, G. (1982): Karst Bauxites: Bauxite deposits on carbonate rocks. Elsevier Sci. Publ. 441 p.
- Bárdossy, G. and Aleva, G.J.J. (1990): Lateritic Bauxites. Developments in Economic Geology 27, Elsevier Sci. Publ. 624 p. ISBN 0-444-98811-4
- Grant, C.; lalor, G. and Vutchkov, M. (2005) Comparison of bauxites from Jamaica, the Dominican Republic and Suriname. Journal of Radioanalytical and Nuclear Chemistry p. 385–388 Vol.266, No.3
- Hanilçi, N. (2013). Geological and geochemical evolution of the Bolkardaği bauxite deposits, Karaman, Turkey: Transformation from shale to bauxite. Journal of Geochemical Exploration