Long-Term Behavior of Fixated Flue Gas Desulfurization Material Grout in Mine Drainage Environments

In this research, we examine the long-term ( ～ 4 years) behavior of fixated flue gas desulfurization (FGD) material grout following placement within the Roberts–Dawson underground coal mine. Surface water and groundwater samples were collected to examine the impact of grouting on water quality, and core samples were obtained to assess the geochemical stability of the grout material. Surface water samples collected from the main seep at the Roberts–Dawson mine indicated that 4 years after grout placement the long-term fluxes of acidity, iron, sulfur, and calcium were slightly elevated compared to pregrout conditions. The long-term discharge of these constituents was likely due to continued dissolution of grout material (for Ca and S) as well as changes in flow paths and subsequent solubilization of metal salts accumulated within the mine voids (for acidity, Fe, Al, and S). Although the fluxes of these elements were elevated, no measurable deleterious impact was observed for the underlying groundwater or adjacent surface water reservoir. Groundwater samples collected from monitoring wells installed within the grout material indicated that acid mine drainage waters were neutralized by the grout material. Mineralogical analyses demonstrated minimal penetration of mine drainage water into the high strength fixated FGD material grout, and little weathering of the material was observed. These data indicate that the high strength fixated FGD material grout injected into the Roberts–Dawson mine was geochemically stable and could locally neutralize mine drainage waters. However, more complete grouting and more extensive mine flooding is likely needed in order to bring about significant improvements in seep water quality.