This study aims to develop a methodology for the thermal characterization of MSWI fly ash. We performed TGA-DTA and component variation analysis, microstructure transfer of sintered fly ash, as well as leaching toxicity, volatilization ratio and specification transformation of heavy metals as a function of temperature. It is found that content of crystal phases first increases between room temperature and 800 degrees C and then decreases between 800 degrees C and 1200 degrees C, while that of glass phases registers a reverse trend. Fly ash registers a SiO(2)-Al(2)O(3)-metal oxides system and its content of glass phases is around 57%. Increase of sintering temperature between 600 degrees C and 1200 degrees C is conducive to the reduction of soluble As, Cd, Cu, Hg, Pb, Ni and Zn, while content of soluble Cr increases as temperature rises from 800 degrees C to 1200 degrees C. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.