How it works
The Bayer process was invented by Austrian scientist Karl Josef Bayer in 1887. The diagram below shows the process of producing alumina.
Our process
QAL produces alumina. Alumina is the common name for the compound, aluminium oxide, which is extracted from bauxite using a four stage chemical process known as the Bayer process.
Key steps to the Bayer process
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Digestion: Dissolving bauxite's alumina contentBauxite is finely ground in mills, and then mixed with a hot, caustic soda solution. This dissolves the alumina contained in the bauxite. The solution is then cooled in a series of flash tanks.
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Clarification: Settling out undissolved impuritiesThe solid impurities settle as a fine mud in thickening tanks. This red mud is a by-product of the process. After several washing stages to recover caustic soda, this residue is neutralised with sea water and pumped to storage dams. The clear solution is transferred to Precipitation to recover the alumina contained in it.
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Precipitation: Forming alumina crystalsPrecipitation involves the recovery of alumina crystals from the caustic solution. In open-top tanks, the solution is stirred by mechanical agitation and seeded with previously precipitated alumina to assist crystal growth.
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Calcination: High-temperature drying of aluminaThe precipitated material (called hydrate) is washed, filtered and then heated at temperatures exceeding 1,000°C. This removes bound water molecules, creating a fine white powder known as alumina.
Learn more about our approach