Patent ID: 6296819
Filing Date: 2001-10-02
Classification: C01F,C01P

Abstract:
A process for manufacturing coarse aluminium hydroxide by decomposition of a supersaturated alkaline aluminate liquor in a two stage precipitation process having an agglomeration stage in agglomeration tanks, connected in series, where the liquor is seeded with fine aluminium hydroxide to induce precipitation and formation of a suspension, the feed of the supersaturated alkaline aluminate liquor to the agglomeration stage is split into a first substream and said first substream is fed to a single first agglomeration tank or to the first and more of a series of first agglomeration tanks, at a higher liquor temperature of 70.degree. to 100.degree. C. and to a second substream and said second substream is fed to a second agglomeration tank or to a series of 2 or more second agglomeration tanks at a lower liquor temperature of 50.degree. to 80.degree. C., the residence time of the suspension in the agglomeration stage tanks is 3 to 12 hours, all of the supersaturated alkaline aluminate liquor being added during the agglomeration stage, followed by a growth stage, where the suspension is seeded with a coarse aluminium hydroxide, yielding at the end of precipitation a strong coarse product hydrate, giving after calcination a sandy alumina with low occluded soda content, compatible with a high liquor productivity.