Process for producing alumina from gibbsitic bauxites

Abstract From the Canadian patent

An improvement in the process for extracting alumina from gibositic bauxitesl wherein the basic, known process comprises mixing the bauxites with a sodium hydroxide-sodium aluminate digestion liquor, digesting the bauxites at a temperature in the range of 100-180 °C, diluting the resulting slurry separating the, red mud therefrom, precipitating alumina hydrate through cooling and agitation of the sodium aluminte liquor and calcining the, alumina hydrate precipitate to obtain alumina wherein the, improvement characterized by so controlling the process that in, the liquid phase of the slurry leaving the digestion reactor the, reactive hydroxide ion concentration is maintained below 6 g/l and …