Patent ID: 8628738

Claim:
A manufacturing process for alumina trihydrate by alkaline attack of bauxite, following the general stages of the Bayer process, the process comprising: a) attacking bauxite ore by means of a sodium aluminate liquor at a suitable concentration, thereby causing alumina within the bauxite ore to become soluble in said sodium aluminate liquor and obtaining a suspension including said liquor enriched with dissolved alumina and red mud formed of particles of ore which were not dissolved during the attack; b) separating the sodium aluminate liquor from said red mud; c) placing said sodium aluminate liquor in a highly unbalanced state of supersaturation to form a supersaturated liquor; d) introducing alumina trihydrate particles into said supersaturated liquor, causing decomposition of the supersaturated liquor, and causing alumina to precipitate in the form of alumina trihydrate; e) after decomposition, concentrating the sodium aluminate liquor, depleted in alumina as a result of precipitation, and f) recycling said liquor to the bauxite attack stage a), said process during which, between stage b) and stage c), the aluminate liquor undergoes safety filtration, so that on leaving the filtration stage, the aluminate liquor contains less than 10 mg/l of insoluble particles, said process being characterized in that, during said safety filtration stage, a filtering device is used including a zone in which the liquor is subjected, after going through a filtration medium, to a pressure greater than 2 bar.