Aluminium is commonly collected after being produced from its ore using an electrolysis process. This method is the primary way pure aluminium metal is extracted and made available for collection.
The Aluminium Extraction Process
The extraction of pure aluminium metal from its ore, bauxite, is a multi-stage process that ultimately yields molten aluminium ready for collection. The key steps involve purifying the ore and then employing electrolysis.
Stage 1: Purification of Bauxite
The initial step is the purification of bauxite ore to obtain pure alumina (aluminium oxide, Al₂O₃).
- This process is often known as the Bayer Process or a modern wet process.
- Bauxite contains various impurities, mainly iron oxides and silica, which must be removed.
- The purification results in a white powder: pure alumina.
Stage 2: Electrolysis of Pure Alumina
Once pure alumina is obtained, it undergoes electrolysis to produce molten aluminium metal. This is the stage where the metal is actually formed.
- This process is known as the Hall-Héroult process (referred to as the Halls process in the reference).
- Pure alumina is dissolved in molten cryolite (Na₃AlF₆). Cryolite lowers the melting point of alumina and improves conductivity, making the electrolysis economically viable.
- The mixture is placed in an electrolytic cell.
- During electrolysis, the molten alumina is decomposed:
- Al³⁺ ions from the alumina gain electrons at the cathode to form molten aluminium metal (Al).
- Oxygen ions (O²⁻) lose electrons at the anode, typically forming carbon dioxide (CO₂) by reacting with the carbon anodes.
- The molten aluminium metal is denser than the cryolite bath and settles at the bottom of the cell.
This molten aluminium metal, collected at the cathode, is then periodically tapped or siphoned off from the cell, making it available for further processing or casting. The electrolysis process described is fundamental to how aluminium is extracted and subsequently collected in its pure metallic form.
