Quantifying the modes of occurrence of mercury in coal using a selective leaching procedure

Using a selective solvent leaching procedure the modes of occurrence of mercury (Hg) have been quantitatively determined in eight as-mined coals and six commercially cleaned coals from major coal producing areas of the U.S. (Northern Appalachian, Eastern Interior, and Powder River Basin). Samples were sequentially leached with 1N ammonium acetate, 3N HCl, 48% HF, and 2N HNO{sub 3}. Residues from each step were analyzed by cold vapor atomic absorption (CVAA). Most of the Hg in the Northern Appalachian and Eastern Interior samples was leached by HNO{sub 3} (50-75% and 60-65%, respectively), indicating an association with pyrite. Up to 25% of the Hg in the Northern Appalachian coals and up to 20% of the Hg in the Eastern Interior coals was leached by HCl. This HCl-soluble Hg may be associated with mono-sulfides or oxidized pyrite. Fifteen to 50% of the Hg in the Northern Appalachian coals and 15-25% of the Hg in the Eastern Interior coals was not removed by leaching. This residual Hg may be present as organically-bound Hg or, less likely, as organically-encapsulated Hg-bearing pyrite. Results from the Powder River Basin samples were variable. In one sample, 30% of the Hg was HCl-soluble, 25% was associated with pyrite, and more » 40% remained unleached. In the other sample, no Hg was leached, possibly indicating that all of the Hg in this sample is organically associated. « less