Patent ID: 7217408
Filing Date: 2007-05-15
Classification: C01F

Abstract:
1. Alumina production process from bauxite containing a diaspore or boehmite alumina monohydrate with more than 1.5% by weight of calcium carbonate, comprising the steps of: a) digesting the ore at a temperature of more than 220° C. using an aluminate liquor with a soda concentration of more than 200 g of Na b) diluting the aluminate slurry thus obtained; c) separating insoluble residues obtained by settling and filtering; d) crystallizing the liquor by seeding with aluminum trihydroxide particles in order to cause precipitation of alumina in solution in the form of aluminum trihydroxide, to obtain thereby a spent liquor; and e) restoring the soda concentration of the spent liquor and recycling the spent liquor to the bauxite digestion step; wherein the ore digestion step comprises the steps of: a1) transferring the slurry comprising ground bauxite ore and concentrated alumina liquor to an installation comprising a series of n digesters (A a2) passing the slurry first through the series of digesters (A a3) passing the slurry through the series of flash tanks (D a4) directing the slurry to stations for said dilution (C) and said separating (F); and wherein the slurry (S