Résumé - Abstract
A composite cover with a Geosynthetic Clay Liner (GCL) was placed over a tailings impoundment at the abandoned Kam Kotia Mine, ON in 2008 as a part of the rehabilitation efforts to reduce the production of acid mine drainage (AMD) at this site. Cores and pore water samples were collected in 2017 and 2018 at various depths from five test locations. Analyses of major and trace elements and stable isotopes were conducted along with PHREEQC modeling to characterize pore water geochemistry. Tailings mineralogy was identified through total carbon and sulfur analysis, X-ray diffraction (XRD), and X-ray fluorescence (XRF). Seasonal water table variations constrained the depths of the oxidation zone and induced spatial fluctuations in tailings geochemistry. Dissolution of secondary Al-hydroxide and Fe(III) (oxy)hydroxide was evident as an acid neutralization mechanism in the oxidation zone, which strongly influenced the fate of trace metal(loid)s, including As, Cu, Zn, Co, and Ni. Reductive dissolution of Fe(III) (oxy)hydroxide was also a potential mechanism for metal(loid) release as the cover likely imposed changes in tailings redox conditions. Continuing research at this site will focus on further geochemical and mineralogical characterization and reactive transport modeling to assess and quantify processes of sulfide oxidation, primary and secondary mineral dissolution and precipitation, metal reduction, and sulfate reduction. In addition to filling the research gap on the long-term tailings geochemical changes under a composite cover, this study can provide insight into cover design, mine closure, and remediation planning.