Aluminium is the most abundant metallic element, and the third most abundant of all elements in the Earth’s crust, making up 8% of the crust by weight. In fact, only silicon and oxygen are more plentiful. Actually, many common minerals, including feldspars, contain aluminium but extracting the aluminium from most minerals is very energy-intensive and therefore prohibitively expensive. This means that economically viable deposits of aluminium are limited.
The most economic ore for the extraction of aluminium is bauxite, the source of over 99% of the world’s metallic aluminium. The word bauxite comes from “les Baux de Provence” a village located in South of France where bauxite was discovered in 1821 by Professor Pierre Berthier.
Because it is a mixture of minerals, bauxite itself is a rock or compound, not a mineral. Actually, bauxite is a general term for an ore composed of a mixture of similar materials that contain hydrated aluminium oxides, primarily alumino-silicate. Bauxite is reddish-brown, white, tan, and tan-yellow in colour, it is dull to earthy in luster looking very much like clay or soil. Bauxite forms when the silica in aluminium-bearing rocks is leached away, a weathering process which occurs in tropical and subtropical climates.
Bauxite is usually strip mined because it is almost always found near the surface of the earth’s crust with little or no waste soil and rock (overburden). Approximately 70% to 80% of the world's dry bauxite production is processed first into alumina, and then into aluminium by electrolysis. Bauxite rocks are typically classified according to their intended commercial application: metallurgical, abrasive, cement, chemical, and refractory.
Bauxite is the feedstock for alumina refineries where it is first processed to make alumina, or aluminium oxide, a white granular material. The alumina is, in turn, reduced to produce aluminium metal in a highly energy intensive smelting process. Sometimes, raw bauxite is shipped overseas for processing to alumina, while in other cases it is processed near the mine. Alumina is lighter than bauxite because the water has been removed, and it flows readily in processing plants, unlike bauxite which can have a sticky, muddy consistency.
It is the specific mineral composition which determines the bauxite ore’s classification, and hence its value. The size of the market for bauxite is determined by the global demand for aluminium and the most extensive reserves of, and highest quality, bauxite are found in Guinea which hosts over one third of the world’s known economically viable deposits.