Effect of Various Saturation Levels, Leaching Solution pH, and Leaching Cycle on Electrical Conductivity from Coal Mine Spoil Leachate
Parker, John Martin
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Historically, environmental research associated with Appalachian coal surface mines focused on acid mine drainage and reclamation. Recent studies suggest that electrical conductivity (EC) levels above 500 ?S cm-1 can impair Appalachian streams, shifting the focus towards limiting release of total dissolved solids (TDS) and associated elements of concern. Previous column studies utilized an unsaturated bi-weekly leaching design to evaluate the behavior of overburden with respect to TDS, pH, and trace metals. The objective of this study was to determine the effects of column saturation, leaching solution chemistry, and leaching cycle on the release of TDS and associated elements from an unweathered sandstone. Treatments evaluating potential saturation, leaching solution pH, and leaching cycle included saturated, standard method, vacuum, and standpipe fitted columns; simulated acid rain, de-ionized water, and CaCO3 leaching solutions; and 2x week-1, 1x week-1, 2x month-1, and 1x day-1 leaching cycles. Saturation level in the column significantly impacted leachate pH, EC level, and the release of sulfate, bicarbonate, and associated cations by potentially affecting trace sulfide oxidation and carbonate dissolution reactions. Little evidence of saturation was noted with the standard method. Leaching solution bulk chemistry did not alter leachate chemistry. Longer times between dosing cycles corresponded to higher EC, bicarbonate, and associated cation levels, especially over time. Sulfate, Ca, and Se exhibited the greatest percent release based on total mass losses during peak elution. For managing TDS, time between precipitation events and saturation level can strongly affect short and long-term EC level, its major contributors, and elements of concern.
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