Development and applications of nuclear methods for the analysis of mercury and other trace elements in coal.

摘要

Trace elements in coal are of great interest because of the potentially hazardous impact on human health and the environment resulting from their release during coal combustion. Given that 85-90% of the one billion tons of coal mined annually in the United States is consumed by coal-fired power plants, large quantities of a potentially toxic element can be released into the environment as a result of coal combustion even if its concentration is as low as a few ;Because of its toxicity, mercury is an element of major concern. A novel radiochemical neutron activation analysis technique has been developed for the determination of mercury in coal based on pyrolysis followed by double gold amalgamation. The system has been shown to yield accurate results for mercury determinations in a variety of standard reference materials certified for mercury, including coal. Linearity up to mercury concentrations of 10,000 ng/g was demonstrated, with a detection limit of 5 ng/g. A high level of reproducibility was exhibited when analyses were repeated over a period of several months. When homogeneous samples were analyzed, the precision of the system was excellent.;A hydrothermal leaching coal cleaning procedure was shown to provide only minor reductions in the concentrations of most elements beyond that provided by both froth flotation and column flotation. These studies yielded indirect information on the modes of occurrence for some elements in coal. Of greatest interest were the results obtained for the Upper Freeport coal which suggest that mercury may be only weakly associated with pyrite in this coal; this result contradicts the general consensus of a significant mercury-pyrite association for all coals.;Investigations into whether or not quantitative information could be derived from X-ray absorption fine structure (XAFS) spectroscopy showed a strong correlation between the XAFS step height and elemental concentrations for manganese, arsenic, and zinc. These results warrant further research into the possibility of using XAFS to obtain quantitative information on elemental concentrations.