OCR Text |
Show 18 Pb appear to remain with the larger-sized particulate, in this case sizes of ash that were greater than 1 J.llll. These trace metals were rarely observed in the final filter or impingers, and Ni and Cr were detected in appreciable concentrations associated with iron-sulfur-rich and aluminosilicate-rich ash particles, respectively. More volatile species consisting of Hg, Se, As, and Cd showed greater quantities of mass in the final multicyclone filter and in the impingers, although it was certainly common to find significant quantities of these elements also in the larger greater-than-l-J.Ull size fraction as well. No definite speciation of the trace metals was able to be performed at this time, although changes in the degree of reducing environment cause definite trends in the vapor-phase quantities of the trace metals. Increased OIC ratios caused less Hg, As, and Cd to be shifted into size fractions of the ash that are usually represented by vapor-phase species. Se, on the other hand, may be driven to a more volatile or vaporizable form with increased OIC ratio. There are known reduced forms of Hg that are more volatile and oxidized forms of Se that are more volatile. Increased gas temperature in the reactor caused slightly greater concentrations of As, Hg, Cd, and Se to be pushed into the smaller vapor for fine particulate fractions of the gas-particulate stream. ACKNOWLEDGMENTS The authors would like to acknowledge" the U.S. Department of Energy Morgantown Energy Technology Center and the Environmental Protection Agency Center for Air Toxic Metals for funding this research. |