The fate and transport of lead in a municipal waste combustor

This dissertation addresses the fate and transport of lead in a municipal waste combustor (MWC). When subjected to leaching test procedures, MWC fly ash often releases heavy metals including lead and cadmium above EPA regulatory limits. Currently, there is not common agreement regarding the behavior of metals including lead in an MWC. A clear understanding of this behavior is necessary for evaluation of input stream sources and to explore the possibility of modifying combustion operating conditions to ultimately produce an ash that does not leach appreciable amounts of heavy metals.; The composition, morphology, and distribution of lead bearing phases in an MWC fly ash were determined using a combination of chemical leaching and electron beam analytical techniques. Lead distribution as a function of particle size was determined. Scanning electron microscopy coupled with energy dispersive spectrometry and digital imaging software was used to automatically locate and determine the distribution of lead bearing phases as a function of particle size. General phase composition was determined using an electron microprobe analyzer (EMPA).; 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 Ca, Cl, K, Na, S, and Zn were found to be common to all lead bearing phases.; Results indicate that catalytic distillation, whereby metals are transported via chloride formation, may be a possible transport mechanism for several elements including Ca, K, Na, Pb, and Zn. Results obtained from both the leaching and electron beam analyses suggest adsorption as a dominant mechanism controlling the leaching of lead from the MWC fly ash studied. Analysis of leached fly ash samples showed an increase in the areal fraction of lead bearing phases.; The results of this research also indicate that the plastics fraction of municipal solid waste may be a significant contributor to the total lead content in MWC fly ash.