Production of alumina

Aluminium minerals are abundant in the earth’s crust with equatorial lateritic bauxites the dominant Al bearing resource used as the raw material for alumina production. The Bayer process, essentially unchanged for more than 100 years, accounts for much of this production. The process involves ore digestion in a hot caustic soda solution, the clarification of a sodium aluminate solution and the precipitation of aluminium hydroxide, subsequently calcined to produce alumina. Refinery operation and particularly the processes of gibbsite precipitation and calcination have a profound effect on the properties of the product alumina, and its use in the production of aluminium metal in the Hall-Héroult process. Although around 95% of alumina production is used in primary metal production, there are also increasing specialist markets for alumina in applications as diverse as catalysis, in microelectronics and as an absorbent.