Geochemistry of zinc and cadmium in coal waste rock, Elk Valley, British Columbia, Canada

Abstract Weathering of mine waste rock can result in high concentrations of zinc (Zn) and cadmium (Cd) in surface and ground water. Design and implementation of mitigation measures requires an understanding of the mineralogical occurrence of Zn and Cd within the waste rock as well as the subsequent weathering and leaching processes. Recent geochemical studies have focused on the characterization of selenium and arsenic leaching from sphalerite and pyrite in waste rock from coal mines in the Elk Valley, British Columbia, Canada. Data collected from these studies provide an opportunity to evaluate the distribution and behavior of Zn and Cd. The abundance and mineralogical association of Zn and Cd were determined in waste rock placed at different times in the dump and leaching of Zn and Cd at the dump-scale was estimated by analyzing porewater and effluent water samples in a rock drain. Mean contents of Zn and Cd in the waste rock samples (n = 260) were 152 mg/kg (range: 48.4–591 mg/kg) and 3.02 mg/kg (range: 0.97–7.56 mg/kg), respectively. Electron microprobe analysis showed Zn and Cd are present in rock samples as primary sphalerite and sorbed onto secondary Fe oxides. The mean concentrations of Zn and Cd in porewater in the dump (n = 121) were 231 μg/L (range: 4.27–1046 μg/L) and 0.61 μg/L (range: