The Bayer Process
The primary aluminum industry is dependent on a regular supply of alumina for four functions:
-Basic raw material for aluminum production
-Thermal insulator for the top of electrolytic cells
-Coating for prebaked anodes
-Absorbent filter for cell emissions
Alumina Production
Bauxite is washed, ground and dissolved in caustic soda (sodium hydroxide) at high pressure and temperature. The resulting liquor contains a solution of sodium aluminate and undissolved bauxite residues containing iron, silicon, and titanium. These residues sink gradually to the bottom of the tank and are removed.
The clear sodium aluminate solution is pumped into a huge tank called a precipitator. Fine particles of alumina are added to seed the precipitation of pure alumina particles as the liquor cools. The particles sink to the bottom of the tank, are removed, and are then passed through a rotary or fluidised calciner at 1100°C to drive off the chemically combined water. The result is a white powder, pure alumina. The caustic soda is returned to the start of the process and used again.
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