Title: Process for effecting seeding in two phases for producing large-grain alumina
Application Number: 85108237 Application Date: 1985.11.22
Publication Number: 1000684 Publication Date: 1986.05.10
Approval Pub. Date: 1990.09.05 Granted Pub. Date: 1990.09.05
International Classifi-cation: C01F7/14
Applicant(s) Name: Aluminium Pechiney Address:
Inventor(s) Name: Maurice Veyrier
Attorney & Agent: LUO YINGMING CHEN JIZHUANG
Abstract:
    The invention concerns a process for the precipitation of aluminium hydroxide by seeding in two phases, which is intended to produce at a high level of productivity alumina with large grains by precipitation in a succession of tanks in cascade relationship of a supersaturated solution of sodium aluminate coming from alkaline attack on bauxite in accordance with the BAYER process. The process comprises three stages: the supersaturated aluminate liquor is introduce into the tank, with an equivalent amount of terms of Na2O of between 110 and 175 g/liter, at a temperature of between 65 DEG and 80 DEG C., and seeding is effected with an amount of washed seed of between 20 and 120 g/l of aluminate. In the second stage, selective retention of the largest crystals of aluminium trihydrate formed is effected in the tanks, so as to produce a content of dry matter of between 300 and 800 g/liter of suspension, the whole production of the aluminium trihydrate is extracted in the second stage. In a third stage, referred to as a liquor depletion stage, an amount of seed of between 400 and 800 g/l of suspension, that is to say between 480 and 1200 g/liter of liquor, is introduced, at the end of the third stage, separation of liquid and very fine grains is effected, a small portion of which is recycled after washing as a seed for the agglomeration stage while the remainder is recycled as a seed to the liquor depletion stage.
Time: 9
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