From the ground
Aluminium is the third most abundant element and the most plentiful metal in the Earth’s crust. It is most commonly present as ‘bauxite’, the ore from which primary aluminium metal is produced. Bauxite is a reddish mineral that is normally found about half a metre under the topsoil in a layer between three and five metres deep. The presence of bauxite so close to the Earth’s surface allows the ore to be extracted by a process known as open-cast strip mining.
Through the ‘Bayer’ chemical refining process bauxite is transformed into aluminium oxide or ‘alumina’, the feedstock for the aluminium smelting process. Refining can be carried out close to the bauxite supply mine thus reducing transport costs and increasing efficiency; alternatively some mines ship their ore in bulk to major refineries.
Alumina is dissolved into molten cryolite (sodium aluminium fluoride) within a large carbon lined container known as a ‘pot’. A carbon anode (positive) is lowered into the cryolites and, with the pot lining acting as a cathode, (negative) a direct current with very high amperage and low wattage is passed through the electrolyte. The electrolytic process strips the alumina of its oxygen atoms, reacting with the anode to produce carbon dioxide and depositing molten aluminium at the bottom of the pot. The aluminium is regularly drawn off into a holding furnace for further processing.
From the Ground
Prior to extraction of the bauxite from the strip mine much of the topsoil and some of the original flora is gathered for safe keeping in nurseries. In some instances endangered species of animals and reptiles are also gathered. Once the bauxite has been removed the site is quickly restored using the original materials thereby minimising the environmental impact. This process is known as the ‘rehabilitation process’ and it forms a major part of any mining undertaken in all parts of the globe.