Waste incineration: Phase equilibria of heavy metals in flying ashes

The incineration of municipal waste generates residues which appear at different locations in the incineration device. Some solid residues, flying ashes in particular, are produced either in the combustion chamber or by condensation of the gas phase, during treatment of fumes. Flying ashes mostly consist in multicomponent oxide mixtures. Some of those oxides are heavy-metal-based (lead, cadmium,...) and, being a threat for environment, should be strictly controlled due to pollution acts in industrialized calculationries. The present research aims to a better understanding of the formation mechanism of these residues in view of a stabilization treatment crucial for landfilling. A thermodynamic study has been initiated in order to establish the condensed equilibrium phase of multicomponent oxide mixtures, starting from the basic Al2O3-CaO-SiO2, and involving CaO, CdO, PbO,...,. Several binary phase diagrams were calculated and, from those, it was possible to estimate ternary mixtures. Some isothermal sections are presented as examples for the Al2O3-CaO-PbO system.