EVALUATION OF LEAD-BEARING PHASES IN MUNICIPAL WASTE COMBUSTOR FLY-ASH

The understanding of the physical and chemical processes involved in t he transport of heavy metals during municipal waste combustion is inco mplete. As part of efforts to improve this understanding this research focuses on determining the composition, morphology, and distribution of lead-bearing phases in municipal solid-waste combustor fly ash. Thi s research uses scanning electron microscopy coupled with energy dispe rsive spectrometry, an electron microprobe analyzer, and digital imagi ng software to automatically search, locate, and evaluate lead-bearing phases. Results indicate the presence of lead in several types of par ticles with various compositions and morphologies. Lead was observed i n two forms including Pb-Cl rich inclusions that exhibit no specific c rystal habit and in lower concentrations in K-Cl-Pb and Na-Cl-Pb inclu sions that exhibit a cubic habit. Several elements including K, Na, S, Ca, Cl, and Zn were common to all lead-bearing phases. Although previ ous leaching studies have indicated lead to be predominant in the smal ler-size ash particles, lead identified in this study was found to be reasonably well distributed throughout all size fractions studied. Res ults obtained in this study are a necessary part of engineering effort s to improve the process of municipal waste combustion including the c ontrol and transport of heavy metals.