Dissolution of the glassy phase in low-calcium fly ash during alkaline activation

Abstract

An experimental investigation on the dissolution of low-calcium fly ashes in an alkaline solution is presented. Fly ashes collected directly from different sources are used in the study. Changes in the elemental concentrations in the solution are determined using optical emission spectroscopy and the residue is characterised using X-ray-based techniques. The increase in the concentration of ions in the alkaline solution is primarily associated with the dissolution of the glassy phase and the crystalline content of fly ash is largely unaffected by the alkaline exposure. The increase in the concentration of Si in the solution relative to the concentration of Al is not influenced by the solution molarity or the temperature. The glass that contains Ca is more reactive and dissolves earlier than the aluminosilicate glass present within the fly ash. The X-ray diffraction pattern of the fly ash glassy phase is adequately fit using a single pseudo-Voigt (PV) peak. The peak position of the PV fit is invariant of the dissolution of the glassy phase and an intensity-based measure of the X-ray diffraction analysis intensity pattern with the PV fit provides an accurate estimate of the undissolved glassy content present in the fly ash.