The earliest production methods used very reactive metals in a mercury amalgam to displace aluminium from its compounds. Only small quantities could be produced by this method, and so aluminium was an expensive luxury metal.
Two significant developments were:
Bauxite ore is now the principal source of aluminium. The ore usually
contains oxides of aluminium, iron, silicon and titanium, and the presence
of iron (III) oxide gives it a characteristic red/orange colour. It
is found relatively close to the surface, and so is extracted by opencast
Aluminium is present as the oxide (Al2O3), which is needed in a pure
form for electrolysis. It is extracted from crushed bauxite using the
method originally developed by Karl Bayer.
The position of aluminium in the reactivity series indicates that, unlike iron, it could not be extracted by reducing the oxide using carbon or carbon monoxide. Electrolysis of molten aluminium oxide ("alumina") will, however, give aluminium and oxygen.
Aluminium production consumes huge quantities of electrical energy. For this reason plants are sited where hydroelectric power can be utilised, or close to sources of fuel for electricity generation.