Charactertstics of red mud generated at NALCO refinery, Damanjodi, India

Abstract

Red mud generated at Alumina Refinery of NALCO, Damanjodi, India, has been characterised in respect of particle size, settling properties, mineralogy, mineral chemistry and chemistry and the reason for loss of some alumina value in the rejects established. Red mud comprising fine solid particles (av.: 5 mu) is alkaline, poor in settling and has 13-16m(2)/g specific surface area. Its mineral constituents are hematite, gibbsite, goethite, boehmite, rutile/ilmenite grains, specs of lithorelics like kaolinite, sillimanite etc and minor sodalite. Electron probe analysis on selective particles indicated the presence of up to 64-mole % of boehmite coexisting with gibbsite crystals and up to 18% of alumina in goethite lattice. Red mud samples generated at different stages of the refinery, such as: Digested Mud (DM), Desilicated Mud (DSM), Settler Mud (SM), Washer Mud (WM) and Mud to Pond (MTP), are more or less similar in their physical and mineralogical properties but exhibit minor but distinguishable difference in their chemical characteristics. In the alumina refinery, some phases like dehydroxylated gibbsite, boehmite, alumo-goethite, Al-rich lithorelics etc, do not dissolve during the industrial treatment of bauxite and get released as constituents of red mud and thereby reduce the recovery of alumina significantly.