Alumina is removed from bauxite by means of a reduction process and is transformed into aluminum. Production consists in a series of chemical reactions. Even bauxite is formed by a natural chemical process, from the infiltration of water through decomposing alkaline rocks. This mineral can be found close to the surface in layers that have an average thickness of 4.5 meters. It is normally extracted by open-cast mining means, using backhoe loaders.
Before starting bauxite mining it is necessary to carefully remove the vegetation and fertile soil overlying the deposits, and retain the latter for reclaiming the terrain in the future. This task, which takes place after extraction, is very important for preserving the environment.
After being mined the bauxite is transported to the plant where it arrives still in its natural state. There, the first of many chemical reactions is initiated. The bauxite is crushed and caustic soda in solution is added, which transforms it into slurry. It is heated under pressure and, after receiving fresh amounts of caustic soda, this slurry dissolves and forms a solution that passes through processes of sedimentation and filtration. This stage eliminates all impurities and the remaining solution is ready to have the alumina extracted from it.
In equipment called precipitators, the alumina contained in the solution is precipitated by the process of "seed crystallization". The resulting material needs to be washed and heat-dried. This is the first stage in aluminum production, which results in alumina, which is a white and refined sugar-like powder.
In this phase the chemical process known as Bayer is the most used; bauxite is dissolved in caustic soda and subsequently filtered to separate out the solid material, the filtrate is concentrated to produce crystallization of the alumina. These crystals are dried and calcinated in order to eliminate water. Then the alumina is finally transformed into aluminum by an electrolytic process.
