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Aluminium Extraction

Aluminium is normally extracted from its the ore (mineral) bauxite that contains
aluminium oxide, Al2O3. Bauxite is not soluble in water and must be melted to release its ions. Cryolite (sodium hexafluoroaluminate Na3AlF6) is added to lower the melting point of aluminium oxide to 9000C from 20450C. Using carbon electrodes, the molten aluminium oxide is electrolysed (subjected to electrolysis). The ions available in the electrolyte are aluminium Al3+ ions and oxide O2- ions.

The
aluminium cations Al3+ migrate to the cathode (carbon lining) and are discharged.
Al3+(l) + 3e- → Al(s) .

Gain of Electrons ⇨ Reduction (GER)
Reduction happens at the cathode.


The oxide anions
O2- migrate to the anode (carbon electrodes) and are discharged.
2O2-(l)  → O2(g) + 4e-

Loss of Electrons ⇨ Oxidation (LEO)
Oxidation happens at the anode.

==========================
The overall equation for the above is

2Al2O3 → 4Al(l) + 3O2(g)
==========================

The
carbon anode has to be replaced from time to time as it is corroded in the electrolysis process.
C(s) + O2(g) →  CO2(g)


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