How is the aluminium extracted from bauxite.

Explanation

Extraction of aluminium form bauxite, .Al. is extracted from bauxite `Al_(2)O_(3)2H_(2)O`
(i) Concentration of bauxite is done by leaching
(ii) Electrolytic Reduction (Hall - Heroult Process). Purified bauxite ore is mixed with cryolite `(Na_(3)AlF_(6))` or `CaF_(6)` which lowers its melting point and increases electrolysed using number of graphite rods as anode and carbon lining as cathode.

The graphite anode is useful for reduction of metal oxide to metal
`2Al_(2)O_(3)+3Crarr4Al+3CO_(2)`
`Al_(2)O_(3)overset("electrolysis")rarr2Al^(3+)+3O^(2-)`
At anode : `Al^(3+)` (melt) `+3e^(-)rarrAl(l)`
At cathode `O^(2-)-2e^(-)rarrO`
`O+OrarrO_(2)`
`C+O_(2)rarrCO_(2)`
Graphite rods gets burnt forming CO and `CO_(2)` the aluminium thus obtained is refined electrolytically using impure Al anode, pure Al as cathode and Molten cryolite as electrolyte.
At anode : `underset(("Impure"))(Al)rarrAl^(3+)+3e^(-)`
At cathode `Al^(3+)+3e^(-)rarrAl` (Pure)