Production of aluminium – material for eternity
Aluminium is the third most common element and the most abundant metal in the Earth’s crust. However, because of its affinity to combine with other elements it was difficult at first to extract pure aluminium. It was only in 1827 that the German chemist Friedrich Wöhler managed to obtain pure aluminium in powder form. At the time, the price of aluminium was higher than that of gold. Photo credit: Norsk Hydro
Bauxite as starting point
The starting material today is usually bauxite containing large quantities of aluminium in combined form. Aluminium oxide is first separated out using the so-called Bayer process, and aluminium for further processing is then extracted from the oxide in smelters using the fused-salt electrolysis process.
Nowadays, a large part of the bauxite is processed to aluminium oxide in its country of origin. The powdery oxide is then broken down into aluminium and oxygen in alumina-reduction cells using electric current. Although 21 kWh of energy used to be needed to extract a kilogram of aluminium, the figure is now only 13-14 kWh. Today hydroelectric power is used to produce about 60 per cent of the electricity used in aluminium production.
Bauxite mining areas are rehabilitated systematically by the aluminium industry. Some 70 per cent of the area is reforested, 20 per cent is used for forestry or agricultural purposes and ten per cent is developed for residential, recreational and industrial areas.
Some facts about aluminium
- After oxygen and silicon, the metal is the third most frequently occurring element, accounting for 7.57 per cent of the Earth’s crust.
- Aluminium occurs in nature exclusively in the form of chemical compounds, e.g. as aluminium silicate in feldspars and micas.
- The mineral corundum (ruby, sapphire) contains aluminium oxide.
- The most important aluminium ore is bauxite, which consists mainly of a mixture of hydroxides and oxides of aluminium.
Strange parallel discovery on the road to mass production
In 1846, Henri Sainte-Claire Deville optimised a process for aluminium production that had been described by Wöhler, and he published this process in book form in 1859. The curious parallel discovery of the electrolysis process was apparently based on this book. Charles Martin Hall developed it in the United States and Paul Héroult developed it in France. Both laid claim to the discovery as they foresaw its future economic value. Hall patented his idea in the USA and Héroult was granted patent rights for the rest of the world.
The electrolysis process laid the foundation stone for the large-scale economic production of aluminium. The price of aluminium fell by 90 per cent within ten years and aluminium was predestined for use in many fields of application.