Extraction of aluminium

Aluminium is one of the most abundant metals in the Earth's crust, but it is highly reactive, so it does not occur naturally as a pure element. Instead, it is extracted from its ore, bauxite, which contains aluminium oxide (Al2O​3). The extraction process involves electrolysis of aluminium oxide to produce pure aluminium metal.

Key steps in the extraction process

1. Purification of Bauxite

   • Purified aluminium oxide (Al2O3​) is obtained from bauxite as the starting material for electrolysis.

2. Electrolysis Process

   • Aluminium oxide is dissolved in molten cryolite, a substance that lowers the melting point of aluminium oxide from ~2000°C to ~950°C. This makes the process more energy-efficient.

   • The mixture is placed in an electrolytic cell with carbon electrodes.

3. Reactions at the Electrodes

   • At the Cathode (Negative Electrode):
     Aluminium ions (Al3+) are reduced to molten aluminium metal by gaining electrons.

     • Half-Equation: Al3+ + 3e- → Al

   • At the Anode (Positive Electrode):
     Oxide ions (O2-) are oxidised to form oxygen gas (O2).

     • Half-Equation: 2O2- → O2 + 4e-

4. Regukar replacement of carbon anodes

   • The oxygen gas produced at the anode reacts with the carbon electrode, forming carbon dioxide. Over time, this reaction erodes the carbon anodes, requiring frequent replacement.

     • Reaction: C(s) + O2(g) → CO2(g)

Application and context