Alkali activated solidification/stabilisation of air pollution control residue using co-fired PFA: mineralogical characterisation

AbstractThe paper characterises the phases formed in a solidification/stabilisation (s/s) matrix resulting from a blend of air pollution control residue and co-fired pulverised fuel ashes, activated with a waste, aluminium containing, NaOH solution. Characterisation was performed by X-ray diffraction, simultaneous thermal analysis (thermogravimetric analysis and differential thermal analysis) and SEM. The effects of varying air pollution control/pulverised fuel ashes ratio, curing temperature and time and liquid phase (NaOH or deionised water) on the hydration products in the s/s matrix were studied, as were the changes in phase composition during regulatory leach testing. The principle phases in the s/s matrix, dependent on the process conditions, included Ca(OH)2, CaCO3, NaCl, C–S–H (I), Friedel’s salt, katoite, zeolitic phases Na–P1 and sodalite, CaClOH and vishnevite. Some retention of chlorides within Friedel’s salt and sodalite during leach testing was observed; however, most was released due to its presence as NaCl. Sulphates were retained as vishnevite during leach tests.