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Quantifying the modes of occurrence of elements in coal is necessary for the development of models to predict an element's behavior during in-ground leaching, weathering, coal cleaning, and combustion. Anticipating the behavior of the trace elements is necessary for evaluating the environmental and human health impacts, technological impacts, and economic byproduct potential of coal use. To achieve the goal of quantifying element modes of occurrence, an international round robin project was initiated. Four bituminous coal samples (from the United States, England, Australia and Canada) were distributed to participating laboratories (9 labs from 5 countries) for analysis. Preliminary results indicate that there is good agreement among six laboratories for the chemical analyses. Using selective leaching, quantitative electron microprobe analyses, and semi-quantitative X-ray diffraction, the authors found that many elements have similar modes of occurrence in all four samples. For example, at least 75% of the Al, K, and Li and about 50% of Be, Sc, V, and Cr are leached by HF. Because HF dissolves silicates, the authors infer that these elements are in the clays. As, Hg, Cu, Zn, Cd, and Pb are leached primarily by HCl and HNO{sub 3}, indicating that they are associated with mono- (such as sphaleritemore » and galena) and di-sulfides (pyrite). Leaching results indicate that small amounts of these metals may be associated with clays and organics. Iron behaves differently in each three of the samples, likely due to different proportions of iron in sulfide, carbonate, and silicate phases. Results from the other laboratories (using selective leaching and density separations) appear to be consistent with these results.« less

Semi-quantitative determination of the modes of occurrence of elements in coal: Results from an international round robin project