Short- and Long-Term Behavoir of Fixated FGD Material Grout at the Roberts-Dawson Mine

摘要

Here we examine both the short- (～1 year) and long-term (～4 years) behavior of fixatedrnflue gas desulfurization (FGD) material grout following placement within an undergroundrncoalmine. Immediately after grout injection, significant increases in acidity, Fe, Al, S, and Carnwere observed for most of the surface and groundwater monitoring locations near where groutingrnwas carried out. However, after four years, the long-term fluxes of acidity, iron, sulfur andrncalcium were only slightly elevated compared to pre-grout conditions. We suspect that the initialrnincrease in discharge of inorganic elements was due to dissolution of accumulated iron andrnaluminum sulfate salts and ferrihydrite within the mine voids following the increase in waterrnlevel and/or rerouting of drainage flow. The long-term discharge of these constituents was likelyrncontrolled by the continued dissolution of these soluble salts as well as grout material (for Ca andrnS). Although the long term fluxes of some elements from the main seeps were slightly elevated,rnno measurable deleterious short- or long-term impact was observed for the underlyingrngroundwater or adjacent surface water reservoir. Mineralogical analyses indicate that the fixatedrnFGD material grout injected into the Roberts-Dawson mine was geochemically stable andrngroundwater sampling showed that the grout could locally neutralize mine drainage. However, arngrouting strategy that minimizes the dissolution or transport of accumulated soluble salts withinrnthe mine voids upon changes in water flow paths is likely needed in order to bring aboutrnsignificant improvements in seep water quality.