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Extraction of Metals

Extraction of Aluminium.

Aluminium ore is called bauxite.
Bauxite contains aluminium oxide, water, iron oxide and other impurities.
The purified dry ore, called alumina, is aluminium oxide - Al₂O₃.

The alumina must be molten for electrolysis to work,
since the ions are not free to move in the solid state.
Unfortunately, alumina has a high melting point (2040 °C)
and it is not practical to do electrolysis at such a high temperature.

In the middle of the nineteenth century
it was found that alumina dissolved in cryolite.
Cryolite is sodium aluminium fluoride - Na₃AlF₆.
A solution of alumina in cryolite melts at about 900 °C
and electrolysis is done at about 950 °C.

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