The Hall-Héroult process is the primary industrial method for smelting aluminium. It involves electrolysis of molten aluminium oxide (Al₂O₃) dissolved in molten cryolite (Na₃AlF₆).

Key points about the cathode:

• The cathode is where reduction occurs: ${\mathrm{Al}}^{3+}+3e^{-}\to \mathrm{Al}$
• It must withstand extremely high temperatures (around 950°C) and the corrosive molten electrolyte.
• It must be electrically conductive.
• It is typically made of carbon (graphite). The carbon lining of the electrolytic cell itself acts as the cathode.

Platinum is too expensive and would dissolve. Copper has a lower melting point (1085°C) and would melt. Pure aluminium would melt at these temperatures (mp: 660°C). Carbon is ideal because it is refractory, conductive, and cost-effective.

Related Topics:

• Electrolysis: The process of using electrical energy to drive a non-spontaneous chemical reaction.
• Extraction of Metals: Methods used to obtain pure metals from their ores, especially reactive metals like aluminium.

Important Formulae:

The main reduction reaction at the cathode: ${\mathrm{Al}}^{3+}+3e^{-}\to \mathrm{Al}$

The oxidation reaction at the carbon anode: $2O^{\mathrm{2-}}+C\to \mathrm{CO}2+4e^{-}$