There are numerous bauxite deposits, mainly in the tropical and subtropical regions, but also in Europe. Bauxite is generally extracted by open cast mining from strata, typically 4-6m thick under a shallow covering of topsoil and vegetation. In most cases, the topsoil is removed and stored.

In nearly all commercial operations, alumina is extracted from bauxite by the Bayer Process. This process consists of four stages.

1. Digestion
The finely ground bauxite is pumped into a very large pressure vessel called a digester. It is then mixed with a hot solution of caustic soda and steam at a temperature in excess of 250^oC. The alumina in the bauxite react with the caustic soda and a sodium aluminate solution is formed.

2. Clarification
The alumina-bearing solution is separated from the insoluble impurities that were part of the original bauxite.

3. Precipitation
The alumina is precipitated or crystalllised from the solution as crystals of alumina(III) hydrate. The solution is mixed with recycled seed crystals. .When completed the solid alumina hydrate is passed on to the next stage and the remaining liquor, containing caustic soda and some alumina, goes back to the digesters.

4. Calcination
The alumina(III) hydrate is washed to remove any remaining caustic. It is then heated in special calciners or kilns to drive off the water of crystallisation, leaving the alumina, a dry, white, sandy material. The alumina is now ready for the aluminium smelting process.

The Aluminium Smelting Process..

Alumina is dissolved in an electrolytic bath of molten cryolite (sodium aluminium fluoride) within a large carbon or graphite lined steel container known as a "pot". An electric current is passed through the electrolyte at low voltage, but very high current, typically 150,000 amperes. The electric current flows between a carbon anode (positive), made of petroleum coke and pitch, and a cathode (negative), formed by the thick carbon or graphite lining of the pot.

Molten aluminium is deposited at the bottom of the pot and is siphoned off periodically, taken to a holding furnace, often but not always blended to an alloy specification, cleaned and then generally cast.