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

Abstract

Abstract

The 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.

Keywords:

• Solidification/stabilisation
• APC residue
• Co-fired PFA
• Leaching
• Alkali activation

Notes

This paper is part of a special issue on Cement and Concrete Research