Evaluation of Lead-Bearing Phases in Municipal Waste Combustor Fly Ash

Abstract

The understanding of the physical and chemical processes involved in the transport of heavy metals during municipal waste combustion is incomplete. 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. This research uses scanning electron microscopy coupled with energy dispersive spectrometry, an electron microprobe analyzer, and digital imaging software to automatically search, locate, and evaluate lead-bearing phases. Results indicate the presence of lead in several types of particles with various compositions and morphologies. Lead was observed in two forms including Pb-Cl rich inclusions that exhibit no specific crystal habit and in lower concentrations in K-Cl-Pb and Na-Cl-Pb inclusions that exhibit a cubic habit. Several elements including K, Na, S, Ca, Cl, and Zn were common to all lead-bearing phases. Although previous leaching studies have indicated lead to be predominant in the smaller-size ash particles, lead identified in this study was found to be reasonably well distributed throughout all size fractions studied. Results obtained in this study are a necessary part of engineering efforts to improve the process of municipal waste combustion including the control and transport of heavy metals.