Flue gas desulfurization by-product weathering by acidic mine drainage

We examined the suitability using a flue gas desulfurization grout (FGDG) f or the attenuation and abatement of acidic mine drainage (AMD). The FGDG us ed was a mixture of fly ash (FA) and filter cake (FC),vith a FA/FC ratio of 1:1 to improve handling. Five percent of lime (CaO) was added to improve s trength development and allow the use of this FGDG as a hydrologic seal for underground mines. Acidic mine drainage solutions collect from wells locat ed within mine voids were reacted with samples of FGDG for up to 168 d, to evaluate the potential for grout dissolution subsequent to subterranean imp lacement. Shortly upon reaction with AMD, FGDG released a number of ions in to solution (As, B, Ca, K, Na, Se, SO4), concomitant with a rapid increase in solution pH (8.5), causing decreases in the solubility of most cations ( Al, Fe, Mn, Zn). Significant increases in dissolved As and B concentrations were noted. Both elements were present in solution at levels below respect ive regulatory limits for drinking water. Of the original quantities of As and B present in FGDG, 1.3 and 45.6%, respectively, were released to soluti on over a 168-d reaction period. Concomitant with changes in solution compo sition, reaction of FGDG with AMD resulted in a loss of ettringite and hann ebachgite and a growth of gypsum. Additional changes in mineralogy were obs erved as FGDG equilibrated with AMD solutions. From these reactions, the lo ng-term stability of FGDG in underground acidic mine environments is questi onable and warrants study in situ.