The effect of thermal activation of kaolinite on its dissolution and re-precipitation as zeolites in alkaline aluminate solution

Abstract

Abstract In this study, kaolinite was heated to temperatures in the range of 400–700 °C to investigate the relationship between thermal activation of kaolinite and its dissolution and re-precipitation as zeolites. Heat treatment with temperature above 600 °C converted the kaolinite to amorphous metakaolin. This treatment substantially increases its dissolution rate and also changes the phase composition of its re-precipitation products in alkaline aluminate solution. The re-precipitate of kaolinite was found to be only sodalite when the heat treatment was below 600 °C. With temperatures above 600 °C, dissolution of metakaolin is followed by rapid precipitation of an amorphous phase, then zeolite LTA which finally transforms to sodalite. UV-Raman spectroscopy can clearly discern between kaolinite and metakaolin despite the presence of small amounts of anatase by focussing on the hydroxyl region.