Alcan International Limited

Peter F Bagatto

Donald L Puxley

Gaston M Jean

Pierre C Harrington

Bernard P Dancose

Marc A Lepage

A process and apparatus useful for decanting suspensions at temperatures at and above the atmospheric boiling point of the liquid of the suspension are disclosed. The apparatus is in the form of a vertically elongated vessel of high height to diameter ratio having a cylindrical upper section and a bottom section and arranged to be filled to a predetermined liquid level in an upper region of said cylindrical section; feed means for feeding a suspension into the cylindrical section in a mid-region between the bottom of the vessel and said liquid level, said feed means including means for injecting the feed under a positive pressure sufficient to overcome the hydrostatic head of the liquid in the vessel above the feed inlet; means for adding a flocculant to the suspension feed; liquid outlet means in an upper region of the cylindrical section at or below said liquid level for drawing off clarified liquid; solids discharge means at the bottom of said vessel; means for controlling a slurry-clarified liquid interface at a predetermined level in a lower region of said cylindrical portion below the feed inlet and rotatable rake means in the bottom section adapted to remold the sedimented solids and continuously expose renewed surfaces. It is particularly useful for clarifying caustic liquor containing red mud residues from the Bayer process.

Process for decantation of suspensions

A method of and apparatus for the thickening of mud-like slurries produced during the course of industrial processes, e.g. the thickening of red muds produced during operation of the Bayer process for the production of alumina. The invention involves the step of feeding the slurry, a fluocculating agent and washing liquor to a deep thickening vessel having an underflow outlet for the thickened slurry and an overflow outlet for clarified washing liquor. The solids content of the slurry leaving the underflow outlet is increased and kept constant by the use of a stirrer having a number of generally vertical rod-like members rotated in the vessel above the underflow outlet. The stirrer enhances dewatering of the slurry and prevents undue build up of thick inactive mud which may block the outlet or cause fluctuations in the solids content of the thickened slurry.

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Jonquiere, Canada

Peter F Bagatto