Alumina Refining and Air Quality
Aluminium is one of the key commodities in modern society. The processes required to produce aluminium include mining of bauxite, refining of the bauxite to produce alumina through the Bayer process, and then smelting of the alumina to produce the aluminium.
In recent years there has been work carried out to understand the influence on air quality of alumina smelting, which can produce fluorides and fluorocarbons. Little work has been published on the influence on air quality of alumina refining.
The key processes from a typical alumina refinery that could have an influence on air quality are: (a) generation of electricity and heat for the plant; (b) storage of bauxite and lime prior to their use; (c) digestion of the bauxite in hot caustic soda and subsequent precipitation of alumina; (d) calcining (roasting) the alumina; (e) storage of the alumina prior to shipping; (f) purifying the caustic soda solution by burning the organic material in it; (g) removing unwanted heat; (h) disposing of unwanted water; (i) storing the residue from the bauxite after it has had the alumina removed in the residue disposal area, and (j) operating and maintaining the plant, involving vehicular travel and many minor activities. There are efficient pollution control procedures for many of these processes.
The air quality components include odour, dust and fine particles, NOx, air toxics and volatile organic compounds. Examples will be provided from Australian alumina refineries. Outstanding uncertainties will be discussed.