Bauxite Processing

Bauxite

With the rapid development of the global alumina industry, bauxite consumption is growing and has reached more than 160 million tonnes per year.  With such a high demand for bauxite alumina production is becoming more difficult due to the gradual global decline of high-grade bauxite resources.

The world’s largest bauxite deposits (reserves) can be found in Guinea, Australia, Brazil and Jamaica. In 2006 the annual world production of bauxite amounted to 184 million tones (World Bureau of Metal Statistics, 2008). The 14 mines which responded to the 2006 survey produced 122 million tones and represent 66% of the respective annual world production.

Bauxite process stages

Bauxite is treated by the Bayer process through the following stages:

1. Bauxite preparation (crushing and grinding).
2. Desiliconization.
3. Leaching.
4. Sedimentation and red mud rinsing.
5. Hydrate dissociation and treatment.
6. Steaming.
7. Calcination.

Milling sizes for bauxite processed in this industry are: on-sieve particles 0.147 mm to 4%, on-sieve particles 0.058 mm to 25%, and particles of ten microns.

Bauxite properties

The average thickness of bauxite deposits varies from 2-20m with a production weighted average of 5m. An average 2m of overburden layer had to be removed before the bauxite deposits could be extracted. The overburden thickness ranged from 0.4-12m and the extracted bauxite had an average available alumina content of 41% that varied from 31-52%.

Processing of bauxit

Unlike other base metal ores, bauxite does not require complex processing, because most of the mined bauxite is of an acceptable grade or can be improved (beneficiated) by a relatively simple but not inexpensive process of removing clay. In many types of bauxite, clay is removed by some combination of washing, wet screening, cycloning and sorting. Beneficiating ore also reduces the amount of material that needs to be transported and processed at the refinery.

However, the benefits of beneficiating need to be weighed against the amount of energy and water used in the process and the environmental impacts of the fine wastes produced and stored in tailing ponds. In 2006, three out of 14 plants beneficiated the bauxite at a local washing plant and two operations dried its bauxite before shipping.

After mining, the bauxite is refined into alumina using the Bayer process (refining). The majority of the alumina is then transformed into aluminium using the Hall/Heroult electrolytic process (smelting). However, some of the alumina is used in non-metallurgical applications. Two to three tonnes of bauxite are required to produce a tonne of alumina and four to six tonnes of bauxite for the production of one tonne of aluminium metal.