THE MICROSCOPIC NATURE OF COAL FLY-ASH PARTICLES INVESTIGATED BY MEANS OF NUCLEAR MICROSCOPY

Individual fly ash particles collected at the outlet of a pilot electrostatic precipitator of a coal-fired power plant have been analysed by a proton microprobe. Major and trace element concentrations have been obtained for about one hundred particles in the 0.5-5 mu m size range. As a result of the combustion of the different components of the mineral matter in the parent coal, particles can be grouped in seven classes showing characteristic matrix compositions and different trace element concentrations. The relative abundances of these groups seem to have a size dependence. Trace elements are found to be non-uniformly distributed over all particles: a size dependence as well as some preferential association with the particle matrix have been found. Enriched concentrations of potentially toxic elements exist on smaller, most respirable particles examined in this study, Possible reasons for this are suggested.