Bauxite
Introduction
Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO(OH)), mixed with the two iron oxides goethite (FeO(OH)) and haematite (Fe2O3), the aluminium clay mineral kaolinite (Al2Si2O5(OH)) and small amounts of anatase (TiO2) and ilmenite (FeTiO3 or FeO.TiO2).
Formation
Bauxite is formed from the intense lateritic weathering of residual clays, which accumulate in topographic lows on continental surfaces. Bauxite is the primary source of aluminium ore and is also used in the manufacture of synthetic corundum and aluminous refractories.
Composition
About 90% of the bauxite mined worldwide is used to produce alumina for refining into Aluminium metal and the remainder goes towards chemical applications. Bauxite is classified on the basis of its intended commercial application, such as abrasive, cement, chemical, metallurgical and refractory.
Extraction and Processing
Bauxite is usually strip mined (surface mining) because it is almost always found near the surface of the terrain, with little or no overburden. Approximately 70% to 80% of the world's dry bauxite production is processed first into alumina, and then into aluminium by electrolysis. This process is still used to produce nearly all of the world's alumina supply.
Environmental Impact
The extraction of bauxite has significant environmental implications. It can lead to deforestation, loss of biodiversity, erosion, contamination of water sources and creation of vast waste dumps.
Economic Importance
Bauxite is of immense economic importance as it is primarily used in the production of aluminium. The global bauxite market was valued at $9.8 billion in 2019, and is expected to grow at a compound annual growth rate (CAGR) of 3.3% from 2020 to 2027.