Leaching kinetics of thermally-activated, high silica bauxite

Abstract

Thermal activation of bauxite has been proposed to enable removal of organic carbon and reducing boehmite digestion temperature. However, there is limited published research about how thermally activated bauxite behaves at pre-desilication (<100 °C) conditions. Combining x-ray diffraction and scanning electron microscopy energy dispersive spectroscopy analysis of cross-sectioned samples, key differences in the desilication of bauxite and thermally activated bauxite are identified. The results show that the silicate dissolution rate of activated bauxite is fast and desilicated products do not appear within the first half an hour. At the same time and temperature, the leaching rate of aluminium bearing phases is inhibited by thermal activation. The subsequent filtration rate for activated bauxite residue is significantly shorter than for bauxite residue. Energy dispersive elemental mapping indicated thermal activation enables the dis-association of kaolinite phases from hematite and inert alumina phases.