Aluminium life cycle
Aluminium is the most abundant metal in nature and the third most common element in the Earth’s crust after oxygen and silicon.
The principle raw material in the production of aluminium is the clay soil bauxite – named after the French region of Les Baux where it was first discovered. The largest bauxite deposits today are in Australia, West Africa, Brazil and Jamaica.
Bauxite is formed when certain rocks rich in aluminium crumble. While 8% of the Earth’s crust is aluminium on average, bauxite consists of 50 to 60% aluminium. The bauxite is converted to aluminium oxide through a cleaning process, often in plants close to the bauxite mines.
Aluminium is then extracted from the aluminium oxide by electrolysis (reduction). This involves dissolving the aluminium oxide in cryolite at a high temperature when aluminium and oxygen ions are formed. The application of a DC current in the electrolysis furnace deposits the aluminium on the cathode while carbon dioxide is released at the anode. The aluminium sinks to the bottom of the electrolysis cell from where it is transferred by vacuum to a crusible for transport to the casthouse. Aluminium made from the mining of bauxite via aluminium oxide is called primary aluminium.
The liquid aluminium is cleaned in the casthouse and alloying materials are added. The starting materials for future production are then made as required – extrusion logs, foundry alloys, wire rod or sheet logs.
The extrusion log is the raw material used in extrusion. The logs are cast in lengths of up to 8m with a diameter up to 331mm. The logs are made in a wide range of alloys and qualities to meet the demands made for various product properties and tensile strength etc.
The production of primary aluminium is an energy demanding process. When viewed from the perspective of its life cycle where the metal’s energy saving properties are taken into account, however, another picture emerges. The energy consumed in producing the raw material is more than compensated for by savings at a later stage through lighter products with longer service life and reduced maintenance requirements. The energy gains are quite easy to see with the use of aluminium in the transport sector.
Vehicles with lower weights – cars, lorries, buses, trains, boats etc – require less fuel and/or can increase their payloads. Aluminium and the extrusion production technique are an especially powerful combination. This material and this technique make it possible to produce extrusions with integrated, labour-saving functions that cut costs in the form of reduced requirements for fabrication and simplified assembly.
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