Geochemical characterization of coal-combustion byproducts and adjacent pore waters fifteen years after emplacement in an abandoned mine land site in southwestern Indiana.

摘要

Coal-combustion byproducts (CCBs) have potential as structural fill and capping materials in coal mine reclamation because of their abundance, engineering properties, and acid-neutralization capacity. However, the potential to leach constituents of concern (COCs) into groundwater hinders their widespread utilization. In 1996, an abandoned mine land (AML) Site in southwestern Indiana was reclaimed using a Fixated Scrubber Sludge (FSS) cap composed of flue gas desulphurization sludge, fly ash, and lime. The cap was placed over pyritic refuse, overburden spoil, and ponded ash. In 2011, 45 samples of FSS and ponded ash extracted from six sediment cores were subjected to laboratory analyses to identify evidence of chemical weathering. Also, samples of groundwater and pore water from the unsaturated and shallow saturated zone were collected during the 2012 water year to find potential leaching of CCBs and calculate mineral saturation indices. X-ray diffractometry indicated that oxidation of hannebachite to gypsum and calcite was restricted to the upper one-to-four centimeters of the FSS cap. Samples of the ponded ash revealed no alteration with depth. Elemental analysis indicated there was no significant change in major oxide or trace element concentrations in FSS or ponded ash. Water chemistry data confirmed historical Site data exhibiting decreasing concentrations of COCs and neutralizing conditions. Calculated saturation indices show that soluble minerals in FSS and ponded ash are in equilibrium with groundwater. The results of this study support previous research indicating that COCs which were initially leached from the CCBs quickly, reached equilibrium with the impacted water and that there was little or no additional alteration of CCBs.