Bayer process
Dissolving alumina out of bauxite with hot caustic soda — the refining step between the ore and the smelter, and the source of red mud.
Bauxite is not smelted directly. It is a mixture in which the aluminium-bearing minerals are accompanied by iron oxides, silica and titania, and putting that into an electrolytic cell would produce contaminated metal at enormous energy cost.
The Bayer process separates them chemically. Hot concentrated sodium hydroxide dissolves the aluminium hydroxides and leaves almost everything else undissolved; the solution is filtered, cooled and seeded so that pure aluminium hydroxide crystallises back out, and calcining that gives alumina ready for the smelter.
Uses
Essentially all alumina destined for aluminium production, plus the specialty aluminas used as abrasives, refractories, ceramics and catalyst supports.
Its by-product is the process's defining problem. Bauxite residue — red mud — is strongly alkaline, produced in roughly equal mass to the alumina, and has no large-scale use. It is impounded behind dams, and the failure of one at Ajka in Hungary in 2010 released about a million cubic metres and killed ten people. Reducing the alkalinity and finding uses for the residue are active industrial problems rather than solved ones.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
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takes as input
- Bauxite — rock · the ore, dissolved selectively so the iron and silica are left behind
- Sodium hydroxide — compound · hot concentrated caustic soda dissolves the aluminium hydroxides
produces
- Aluminium oxide — compound · crystallised from the liquor and calcined, ready for the smelter
Sources
- Material WorldOur own writing