Abstract
Municipal solid waste incinerator fly ash (MSWIFA) is considered a hazardous material because of its high content and leachability of heavy metals and soluble salts. In this study, leaching and thermal mobility of four selected heavy metals (Pb, Zn, Cu, and Cd) found in two types of MSWIFA [cyclone ash (CA) and filter ash (FA)] were investigated. Leaching tests indicated that among the examined heavy metals, leaching concentration of Pb in FA exceeds the regulatory limit of TCLP in Taiwan. On the other hand, the leaching concentration of Pb in CA consistently meets the regulatory limit of TCLP even by reducing the particle size or increasing the alkalinity of CA. In looking at the mobile characteristics of heavy metals under thermal treatment, Pb possesses the highest evaporation ratio among the examined heavy metals in the two types of fly ashes. While washing FA with water removes large amounts of Cl in FA and is able to inhibit the evaporation ratio of heavy metals significantly, it still has no effects on Pb. It is experimentally concluded that Pb is the most thermally mobile metal in the two types of fly ashes studied in this paper, and is thus of serious concern for the thermal treatment process, such as sintering or virtrification. Furthermore, chlorides play a key role in the determination of the evaporation of heavy metals in the fly ashes. That is, chloride salts in fly ashes will transform metal oxides into metal chlorides and enhance the evaporation ratio of heavy metals significantly.