00/00015 The use of sequential leaching to quantify the modes of occurrence of elements in coal

Abstract

Sequential leaching can be used to rapidly and accurately quantify the modes of occurrence of inorganic elements in coal. Nine as-mined coals and seven commercially cleaned coals from major coal producing areas (Appalachian, Eastern Interior and the Powder River basins) were sequentially leached with 1 N ammonium acetate, 2N HCl, 48% HF and 2N HNO{sub 3}. The reproducibility of the technique is about {+-}5 to 10% absolute. The resulting mass balances from the multi-technique analyses of both the leachates and the residual solids provide a high degree of confidence in the procedure. Modes of occurrence were quantified for 15 environmentally sensitive elements. Generally more than 50 percent of the As and Fe are leached by HNO{sub 3} indicating an association with pyrite. With few exceptions, more than 50% of the Be and 40% of the Cr was leached by HF indicating an association with the aluminosilicates. Se and Hg are associated with disulfides in most coals but as much as 95% of the Se and 70% of the Hg in some cases remained unleached by any solvent indicating an organic association. Co, Ni, Sb, Th and U have multiple modes of occurrence in each coal. Mn is primarily associated withmore » the carbonates. Pb, Zn and Cd are primarily associated with mono- and di-sulfides but also have a significant organic association.« less