Influence of unburned carbon on mercury chemical forms in fly ash produced from a coal-fired power plant

Abstract

The chemical forms of mercury in coal-fired power plant fly ash were determined qualitatively and quantitatively using X-ray absorption near edge structure (XANES) analysis. Mercury content in the fly ash increased linearly with an increase in the content of unburned carbon. The inflection point method, using the first and second derivatives of XANES spectra, was used to estimate the type and abundance of chemical forms present. The XANES spectrum of fly ash mercury was modeled by a linear combination fitting of control mercury compounds, with their abundance ratios used as fitting parameters. The inflection point difference in energy was used as the requirements for simulation. The fly ash sample contained 2.6 ppm of mercury which combined with sulfur, chlorine and oxygen. The determined abundance ratios of C-Hg-S, C-Hg-Cl and C-Hg-O were 18, 27 and 36%, respectively. The unburned carbon in the fly ash was impregnated with sulfur and exposed to gaseous mercury oxide. The amount of captured mercury increased dramatically with the increase in sulfur content while chlorine and oxygen in the unburned carbon also influenced on the mercury chemical forms.