All types of clay contain aluminium compounds, but bauxite is the ore that can be used to produce pure aluminium. The main component of bauxite is aluminium oxide, which makes up 45–60% of the material. Other impurities include sand, iron, and other metals. Although some bauxite deposits are made of hard rock, the majority are made of relatively soft dirt that can be extracted without difficulty from open-pit mines. More than a third of the world's bauxite supply is produced in Australia. 1 lb (0.5 kg) of aluminium metal can be made from 4 lb (2 kg) of bauxite. The aluminium compounds present in bauxite are dissolved using caustic soda (sodium hydroxide), which allows for their separation from impurities. Relatively little quantities of other chemicals may be used in the extraction process, depending on the makeup of the bauxite ore. The Bayer process, which turns bauxite ore into aluminium oxide, and the Hall-Heroult process, which melts the aluminium oxide to produce pure alumini...
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