1.Purification of bauxite
2.Electrolysis of aluminium oxide
3.Refining
As aluminium is placed relatively high up in the reactivity series, it cannot be extracted from its ore using carbon reduction. Thus it can only be extracted by electrolysis, which is a process of using electricity to break down or decompose a compound. The ore is first converted into pure aluminium oxide by the Bayer Process(the principal industrial means of refining bauxite to produce aluminium oxide) as bauxite is essentially an impure aluminium oxide. It is then electrolysed in molten cryolite(another aluminium ore) as the aluminium oxide has too high a meting point to electrolyse on its own.
Thereafter, crushed bauxite is treated with moderately concentrated sodium hydroxide solution which is hot, reacting to give a solution of sodium tetrahydroxoaluminate.
The impurities in the bauxite remain as solids which are separated out from the solution by filtration.The aluminium oxide is dissolved in a mixture of molten cryolite and fluorspar which lowers the melting point. It is then electrolysed in a rectangular steel tank with carbon lining, which serves as cathode.
Aluminium formed at the cathode gets collected at the bottom of the electrolytic cell, where it is removed periodically. As the metal obtained by this metal is only about 99% pure, further purification can be carried out by Hoop's electrolytic method.
http://www.chemguide.co.uk/inorganic/extraction/aluminium.html
http://entrancechemistry.blogspot.sg/2011/05/extraction-of-aluminium-from-bauxite.html
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