Aluminium is extracted primarily by the electrolysis of aluminium oxide (alumina), which is derived from the ore bauxite. The extraction process involves several key steps:
- Purification of Bauxite: Bauxite ore is purified to produce aluminium oxide (Al2O3), a white powder.
- Dissolving Aluminium Oxide: Because aluminium oxide has a very high melting point (over 2000°C), it is dissolved in molten cryolite, a compound that reduces the melting point of the mixture and helps lower energy costs.
- Electrolysis: The molten mixture is placed in an electrolysis cell lined with graphite electrodes. At the cathode (negative electrode), aluminium ions gain electrons and form molten aluminium, which sinks to the bottom and is periodically siphoned off. At the anode (positive electrode), oxide ions lose electrons to produce oxygen gas. The oxygen reacts with the graphite anode, producing carbon dioxide and causing the anode to wear away and need replacement.
- Collection: The extracted molten aluminium is collected, and fresh aluminium oxide is continuously added to the cell.
This process is known as the Hall-Héroult process and is energy-intensive, requiring a large amount of electricity, which is a significant cost factor in aluminium production.
