Alumina refining
Aluminium oxide is extracted from bauxite in an oil refinery. Alumina is then used to produce primary aluminium.
4-7 tons of bauxite = 2 tons of alumina = 1 tons of aluminium.
Bauxite, in addition to alumina, also contains silica, iron and titanium dioxide. Alumina extraction from bauxite by Bayer process:
Using heat treatment, caustic soda (sodium hydroxide) and lime (calcium oxide) decompose alumina from bauxite.
The mixture is injected into a high pressure vessel and heated.
Caustic soda dissolves alumina and alumina precipitates from a saturated solution. Then wash and heat it to the alumina to make it evaporate.
The sediment is filtered and cleaned to keep the solution corrosive.
Everything else is filtered out, and alumina is a dry white powder.
Most of the alumina refineries are located near the bauxite, or in the nearest port, alumina can be easily transported to the aluminum production plant.
How does alumina production affect the environment?
The extraction of alumina from bauxite, bauxite residue produced the same amount of this process, also known as the red mud. This requires proper use to protect the environment, and is a challenging part of alumina production.
The aluminum industry is from the storage in the lake to dry material accumulation, because it is more effective, there will be a more secure environment.
The alumina refinery has different storage methods for the residue produced by bauxite. The model is based on reports of 17 refineries in 2007, with 17 refineries accounting for 44% of global output (source: review of current bauxite residue management, processing and storage: practice, engineering and science. CSIRO document DMR - May 36082009).