Allied Colloids Limited

Christine A Rushforth

Gillian M Moody

Trevor K Hunter

A Bayer alumina recovery process is described in which lime is added at an intermediate or final wash stage of the red mud recovery circuit to improve flocculation, especially with flocculants having lower anionic content. The process is particularly useful with liquors containing high amounts of sodium carbonate and for process where the mud is settled by mud stacking.

Recovery of alumina from bauxite

In a Bayer process for production of aluminum, alumina trihydrate crystals are formed in the pregnant liquor and are flocculated using a combination of dextran and synthetic polymer, usually a homo- or copolymer of acrylic acid. The process is particularly advantageous where the liquor contains organic components such as humate and/or oxalate.

Recovery of alumina trihydrate in the Bayer process

Red mud in Bayer process liquors are flocculated using dextran and synthetic anionic polymer in the same stage, usually added separately to the liquor. The liquor may be the primary settler slurry, the secondary clarification liquor or one or more of the red mud washing stages. The process is of particular advantage where the liquors are high in carbonate content and/or total alkalinity.

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West Yorkshire, United Kingdom

Christine A Rushforth