Abstract: 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° C., preferably greater than 140° C.

Abstract: An improvement in the Bayer process for producing alumina trihydrate in which bauxite ore is digested in a mixture with a digestion sodium aluminate liquor to produce a slurry, the slurry is settled to remove undigested residues therefrom and produce a pregnant liquor of sodium aluminate and alumina trihydrate is precipitated from the pregnant liquor in the presence of alumina trihydrate recycled as seed. When beginning the precipitation, an aliquot of the pregnant liquor with recycled alumina trihydrate is removed, subjected to mechanical action of an intensity and for a time sufficient to cause formation of seeds, and returned with the formed seeds to the beginning of the precipitation.