QAL’s bauxite supplies are mined at Weipa in far north Queensland. The bauxite is loaded onto specially designed, and QAL chartered, coal-fired ships that transport the bauxite around Cape York and 2000 kilometres down to Gladstone.

Alumina is produced at QAL through the continuous four stage “Bayer Process” involving:

1. Digestion – Dissolving bauxite’s alumina content
Bauxite is finely ground in mills, then mixed with a recycled caustic soda solution and steam in digester vessels operating at high temperature and pressure. This dissolves the alumina content of the bauxite and the solution is then cooled in a series of flash tanks.

2. Clarification – Settling out undissolved impurities
The impurities, which remain undissolved, are allowed to settle as a fine mud in thickening tanks. After several washing stages to recover caustic soda, this residue is pumped to storage dams. The solution of alumina in caustic soda is further clarified by filtration.

3. Precipitation – Forming alumina crystals
The next step 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.

4. Calcination – High-temperature drying of alumina
The precipitated material (called hydrate) is washed and calcined at temperatures exceeding 1000 degrees Celsius. This forms the dry white anhydrous aluminium oxide powder, alumina, which is cooled and conveyed to storage.