Mechanical dewatering of red mud

Red mud is a by-product of alumina extraction from bauxite ore. It contains high quantities of alkali, minerals, and metal ions, which are typically pumped as thick slurry to a residue disposal area. Dry cake disposal is the most preferred technique for the disposal of red mud, which reduces the environmental impact. Dry cake disposal also improves recoveries of caustic soda and alumina. In order to perform dry cake disposal economically, filtration, de-watering, and final cake washing become mandatory. Further drying, though adds to the cost may be the future norm for proper resources mobilization and further value addition. This paper is an attempt to review various methods available for filtration & dewatering of red mud . It includes various design, operational and maintenance parameters that influence the solid-liquid separation. The traditional rotary drum vacuum filters can produce the final cake solids content up to 65 wt%, whereas, the results of pressure filtration tests using FLSmidth AFP IV (TM) and Outotec Larox (R) membrane filter press produce the final cakes containing up to 75 wt% solids. In recent times, HiBar steam filtration seems to be the most benevolent technology that could produce extremely dry granular solids of up to 78-80 wt% with very low soda content. Red mud cake with high solids content provides several benefits such as long-term storage, future utilization for the recovery of valuable metals such as aluminium, iron, titanium, and rear earth elements.