Geochemical interactions of mine seepage water with an aquifer: laboratory tests and reactive transport modeling

Abstract

Laboratory tests and reactive transport modeling were conducted to evaluate the geochemical interactions between the seepage water from a mine waste rock dump and the nearby aquifer. In laboratory tests, the reaction of the mine seepage water with the aquifer materials increased pH, alkalinity, and dissolved Ca and Mg, whereas it decreased dissolved Fe, SO4 2−, and metals (Al, Zn, Cd, Cu, Cr, and Mn). Such results were mainly due to dissolution of carbonate minerals and precipitation of secondary minerals. The geochemical processes inferred from the laboratory tests (i.e., acid neutralization via dissolution of carbonates and retention of metals via precipitation of secondary minerals) were incorporated into a reactive transport model to predict the evolution of a mine seepage plume along a groundwater flow path below the waste rock dump site. The model simulations showed that dissolved metals within the plume were sequestered below non-detectable levels as a result of interactions with aquifer materials. The decreased mobility of metals was closely related to the neutralization of the acidic plume mostly due to dissolution of carbonate minerals, thus resulting in favorable geochemical conditions for the formation of secondary minerals incorporating metals (hydroxides, carbonates, and sulfides). This study helps to understand the geochemical processes governing the fate and transport of acid mine drainage in aquifers.