Concentration, enrichment, and partitioning behavior of heavy metals in ash from a down-fired furnace burning anthracite coal

Abstract

The concentrations, enrichment, partitioning behavior, emission factors, and leaching characteristics of heavy metals (Pb, Cd, Cu, Zn, Ni, and Cr) emitted from a 3.25 MW pilot-scale down-fired furnace burning a typically Chinese anthracite coal are studied in this study. The results show that all six heavy metals are highly enriched in the fine fly ash, whereas they are depleted in the bottom ash. The enrichment of heavy metals increases significantly as the fly ash particle size decreases, which is found to be in the order of Pb, Cd > Cu, Zn > Ni, Cr. A surface deposition model is developed in the study to describe the correlation between metal concentrations and particle sizes, which shows that surface reactions are the rate-limiting step in condensation of heavy metals on fly ash surface. The study also shows that the removal efficiency could exceed 98% for Cd, Cu, and Ni when using an electrostatic precipitator, while it drops to 85–92% for Pb, Zn, and Cr. In addition, the study also finds that the extractable concentrations of heavy metals in the fly ash are relatively low according to the leaching tests; even acids are used as the leachant.