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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 (continued).
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