Effect of solid additive on heavy metal vaporization of fly ash from co-incineration of MSW with sludge at high temperature

On the basis of the leaching characteristics of heavy metals in the fly ash collected from a co-combustion plant of MSW and sewage sludge, the volatilization of heavy metals (Pb, Cd, Cu and Zn) were studied at 1 000 ℃with different residence time. Meanwhile, the influence of solid additive agents (CaO, Al₂O₃, SiO₂, kaolinite and coal ash) was studied. The results show that the contents of Zn, Pb, Mn in fly ash are high, Ni is low and Cd content reaches 29.4 mg/kg. The metals concentrations in leaching solution, changing a great with leaching solution pH and extraction time, meet the hazardous waste identification criteria (GB5085.3-1996).The volatilization of heavy metals has great differences with the order of Pb> Cd> Zn> Cu, in which the volatilization rate of Pb is higher than 80% and that of Cu is less than 30%. In the thermal disposal process, the volatilization rate is influenced by the residence time, and the volatile elements Pb and Cd are particularly evident.The volatilization of Cd reduces after adding Al₂O₃ and kaolinite, and that of Pb reduced after adding Al₂O₃. Zn evaporation rate decreases with adding SiO₂, CaO, kaolinite and coal ash, while that of Cu is not changed. This is related to the high Cl content in fly ash and the competitive adsorption selectivity of the trace element compounds on the active sites of solid additives.