Coal combustion for energy generation creates large quantities of solid coal utilization by-products (CUB), including fly ash, bottom ash, and flue gas desulfurization products. These materials are either used in environmental and industrial applications or stored adjacent to power plants. The development of new techniques to track and understand the behavior of CUB in the environment is essential to the safe utilization of coal. In this research, sequential leaching techniques are coupled with strontium (Sr) isotope analysis to investigate the influence of coal type and combustion process on the geochemical characteristics of CUB. Sequential leaches of water, acetic acid, and hydrochloric acid were carried out on a variety of CUB types. Systematic differences in 87Sr/86Sr ratios were observed (1) among different types of CUB, and (2) between leachates and their corresponding bulk CUB values. These differences can help elucidate the origins of the inorganic components of coal, as well as the transformations that occur during combustion. In addition, this study demonstrates for the first time that there are multiple sources of Sr in coal that remain isotopically distinct during combustion. The degree of isotopic homogenization induced during the formation of CUB appears to be controlled by the feed coal chemistry and the particular combustion technology used. The Sr isotope data, when combined with major and trace element results, suggest that a greater fraction of Sr is bound in detrital minerals in higher-rank coals, while authigenic minerals and organic complexes comprise the dominant form of Sr in lower-rank coals. Investigation of CUB produced from fluidized bed combustion (FBC) also demonstrates that the combustion process can strongly impact the behavior of the inorganic components of coal during utilization. The association of potentially toxic trace elements with certain soluble Sr-bearing phases in CUB make Sr isotopes a promising tool to trace the release of these species during interactions with water. Application of Sr isotopes to studies of coal and CUB could facilitate the development of better disposal techniques by serving as a robust tracer of CUB in the environment
