Patent ID: 7807119

Claim:
In a process for production of alumina trihydrate by alkaline digestion of bauxite using the Bayer process, comprising the steps of grinding and then bringing the ground bauxite into contact with a sodium aluminate liquor to digest the ground bauxite by forming a slurry, diluting the slurry and treating the diluted slurry in a liquid/solid separation device to separate insoluble residues from the sodium aluminate liquor, obtaining thereby a pregnant aluminate liquor from which alumina trihydrate is precipitated by crystallization, separating the precipitated alumina trihydrate from the pregnant aluminate liquor and then recycling the separated liquor as a green liquor, the improvement comprising passing at least a portion of the diluted slurry, upstream or downstream of the liquid/solid separation device, and before said precipitation by crystallization, through a hydrocyclone having an overflow and an underflow to accelerate and improve separation of the sodium aluminate liquor from insoluble residues having a particle size smaller than 106 μm.