INCREASING THE STABILITY OF BAYER PROCESS LIQUOR USING LOW MOLECULAR WEIGHT DEXTRAN

Liquors supersaturated with alumina relative to total caustic concentrations are required for efficient and cost-effective precipitation of alumina tri-hydrate. However, the efficiency is reduced when dissolved alumina precipitates prior to (and during) filtration, reducing the time for which filters remain operable and negatively impacting on the cost of operation and alumina and soda recovery. Most refineries operate within a preferred range of liquor supersaturation, above which alumina losses are incurred and maintenance costs increase.

Addition of ppm levels of Alclar^® 5000, a low molecular weight dextran, to the filter feed slurry allows the upper limit of the operational window for liquor supersaturation to be increased without affecting filter availability.

This paper presents an overview of the method of increasing the stability of Bayer process liquor by suppressing the precipitation of alumina tri-hydrate, using the application of Alclar^® 5000 at an Alcoa refinery in Western Australia as a case study.