Rusal

A series of controlled chemical reactions, this is how the process works:. The bauxite is washed and crushed, reducing the particle size and increasing the surface area for the upcoming digestion stage in the alumina refinery. Lime and spent liquor are added at the mills to make a pumpable slurry. Because silica can cause problems with the quality of the final product, bauxites with high levels of silica go through a process to remove as much of this impurity as possible.

Alcoa

Next, a hot caustic soda sodium hydroxide solution dissolves the aluminium-bearing minerals in the bauxite to form a sodium aluminate supersaturated solution, known as pregnant liquor. Clarification separates the bauxite residue from the pregnant liquor via sedimentation. The bauxite residue sinks to the bottom of the settling tanks and is transferred to the washing tanks to recover the caustic soda.

Further separation of the pregnant liquor from the bauxite residue is performed, utilising a series of security filters to ensure the final product is not contaminated with impurities present in the residue. In this stage, the alumina is recovered by crystallisation from the pregnant liquor, which is supersaturated in sodium aluminate. The chemical industry can use alumina in applications such as industrial and medical ceramics, sandpapers, pigments, cosmetics and pharmaceuticals.

It is important to note that cyclical steps within the Bayer Process make it more energy efficient. For example, in the precipitation stage, the spent liquor is heated and then cooled, and the resulting condensate is re-used as boiler feed water or for washing bauxite residue. Meanwhile, much of the remaining caustic soda is washed and recycled back into the digestion process.

Search Close this search box. Refining: Refining Process. After the bauxite is mined, it is refined into alumina before it is ready to be reduced to primary aluminium.