Tests were performed in simulated flue gas streams using two fly ash samples from the electrostatic precipitators of two full-scale utility boilers. One fly ash was derived from a Powder River Basin (PRB) coal, while the other was derived from Blacksville coal (Pittsburgh No. 8 seam). The tests were performed at temperatures of 120 and 180°C under different gas compositions using whole fly ash samples as well as magnetic and nonmagnetic concentrates from sized fly ash. Only the Blacksville ash

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... ontained magnetic phases. The whole and fractionated fly ash samples were analyzed for morphology, chemical composition, mineralogical composition, total organic carbon, porosity, and surface area. Mineralogically, the Blacksville ash was composed predominantly of magnetite, hematite, quartz, and mullite, while the PRB ash contained mostly quartz with lesser amounts of lime, periclase, and calcium aluminum oxide. The iron oxides in the Blacksville ash were concentrated almost entirely in the largest size fraction. As anticipated, there was not a clean separation of magnetic (Fe-rich) and nonmagnetic (aluminosilicate-rich) phases for the Blacksville ash. The Blacksville ash had a significantly higher surface area and a much higher unburned carbon content than the PRB ash. Elemental mercury (Hg) streams were injected into the simulated flue gas and passed over filters (housed in a convection oven) loaded with fly ash. Concentrations of total, oxidized, and elemental Hg downstream from the ash samples were determined by the Ontario Hydro Method. The gas stream composition and whether or not ash was present in the gas stream were the two most important variables. Based on the statistical analyses, the presence of HCl, NO, NO 2 , and SO 2 and all two-way gas interactions were significant. In addition, it appears that even four-factor interactions between those gases are significant. The HCl, NO 2 , and SO 2 were critical gases resulting in Hg oxidation, while the presence of NO appeared to suppress oxidation. The Blacksville fly ash tended to show slightly more catalytic activity than the PRB fly ash, but this could be largely due to the higher surface area of the Blacksville ash. Temperature was not a statistically important factor. The magnetic (Fe-rich) phases did not appear to be more catalytically active than the nonmagnetic phases, and unburned carbon did not appear to play a critical role in oxidation chemistry. iv