THE ROLE OF CHEMICAL FLOCCULANTS IN THE DISPOSAL OF RED MUD

Flocculants are important chemical additives in the treatment of red mud. They are used to control particulate slurry rheology to achieve a high recovery of caustic and a high solids waste for disposal. This work investigates the mode of action of polymeric flocculants used in the clarification and washing stages of the Bayer process that feed the final thickening and waste disposal stages.

The Atomic Force Microscope (AFM) allows the interactions between approaching surfaces, similar to the interactions that occur between particles in a slurry, to be measured. In this study, a ‘model’ red mud surface, developed specifically for use in the AFM, was used to investigate the role of the chemical composition of the polymers on flocculation under Bayer conditions. AFM and electrokinetic techniques have been successful in providing an understanding of the molecular role of additives in controlling floc structure. The results provide an understanding of the molecular role of flocculants in controlling the surface chemistry and subsequently, the floc structure and rheology of the red mud. An understanding of the mechanism of interaction of the flocculants with bauxite residue surfaces under process conditions should enable the solid-liquid separation to be optimized with subsequent improvements in washing performance.