Abstract
Tailings with sulphide minerals exposed to oxygen and water can oxidize and produce acid mine drainage (AMD). This study evaluated the impact of natural conditions and of a thin cover deposition on the water table level, with respect to selecting the reclamation technique to control AMD on the elevated portion of an abandoned tailings impoundment. The reactive tailings were partly covered with alkaline tailings transported as a pulp from a nearby mine. A three-dimensional numerical variably saturated groundwater flow model of the tailings impoundment and its surrounding area was built. The simulation results reproduced well the field observations before, during, and after the deposition of a thin layer of tailings. The calibrated model was then used to forecast the evolution of the water table position for the next 100 years under various site conditions, including a period of 5 years with dry summers. The results show that the water table levels are on average several metres below the interface between the reactive tailings and the cover, thus failing to meet the target criterion to control the production of AMD determined from previous column tests. The results are analyzed and discussed in terms of the site configuration and atmospheric recharge.
Highlights
Sulphidic mine tailings exposed to water and oxygen can oxidize and produce acid mine drainage (AMD), which may adversely impact water quality on and beyond the disposal site
It can be seen that for the cases with a recharge of 20% and 30% of the average precipitation applied on the model surface, the water table remains below the interface at most locations, with distances ranging from 0.5 m to more than 6 m
It was shown that the numerical model was capable of reproducing field observations including periods of heavy tailings deposition, with better results obtained using the water retention curves (WRCs) of the coarser fraction of the Manitou tailings
Summary
Sulphidic mine tailings exposed to water and oxygen can oxidize and produce acid mine drainage (AMD), which may adversely impact water quality on and beyond the disposal site. An effective and economic alternative for the closure of tailings ponds under humid climatic conditions is the EWT technique (MEND 1996; Aubertin et al 1999; Dagenais 2005; Dagenais et al 2006; Ouangrawa et al 2006, 2010; Pabst 2011; Ethier et al 2018a, 2018b; Pabst et al 2018) The goal of this method is to raise or maintain the water table at a position allowing the reactive tailings to stay at a sufficiently high degree of saturation (Sr) to prevent sulphide oxidation. The simulated water level position was compared with the elevation target developed from large-scale laboratory column tests, to prevent the production of AMD in the Manitou tailings
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