Rio Tinto Alcan International Limited

Henri Thomas

Guy Forte

Luc Fortin

El Kadi Bassam

Process for manufacturing alumina trihydrate by alkaline attack of bauxite, following the general steps of the Bayer process, and during which, after settling and before decomposition, the aluminate liquor undergoes a filtration, known as security filtration, so that at the end of the filtration it contains less than 10 mg/l of insoluble particles, characterized in that, during said security filtration, a filtration device is used that comprises a zone in which the liquor is subjected, after passing through said filtration media, to a pressure greater than 2 bar, preferably greater than 3 bar. Preferably, this device also comprises a zone in which the liquor is subjected, before passing through the filtration media, to a pressure greater than 5 bar, preferably greater than 6, typically in the vicinity of 7 bar. In this way, the aluminate liquor can be kept at a high temperature during the security filtration, typically greater than 130&#xb0; C., preferably greater than 140&#xb0; C., and be brought to a high degree of supersaturation Rp, typically greater than 1.25, without risk of reversion.

Bayer process for producing alumina trihydrate, said process comprising a step in which the supersaturated liquor is filtered at high temperature before decomposition

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Aix en Provence, France

Henri Thomas