Macroscopic and microscopic approach to the study of enrichment phenomena in the electrostatic precipitation of coal fly ash particles

Ordinary PIXE analysis of fly ash samples collected at the inlet and outlet of the electrostatic precipitators of coal-fired power plants, shows the occurrence of enrichment phenomena for several elements. This is usually attributed to the volatile nature of compounds associated with these elements and to the decreasing electrostatic precipitator efficiency versus particle size. A microscopic approach to the study of enrichment phenomena, based on the analysis of hundreds of individual fly ash particles collected at the inlet and outlet of the electrostatic precipitators of coal-fired power plants, indicates the occurrence of an additional mechanism, besides that shown by ordinary PIXE analysis. In particular, the enriched trace element concentrations at the outlet of the electrostatic precipitators can be related also to the preferential penetration of particles with higher concentrations of trace elements because of their influence on the electrical properties of the particle themselves.