The potential water quality impacts of hard-rock lithium mining: Insights from a legacy pegmatite mine in North Carolina, USA

The global green energy transition has spurred increased lithium exploration and extraction, yet the water quality impacts from lithium mining are understudied. This study investigates the potential water quality impacts from a legacy hard-rock lithium mine through comprehensive geochemical analyses of groundwater, surface waters, ore grade rocks, tailings, and waste rocks from a mine site in North Carolina, USA. The concentrations of regulated contaminants (e.g. As, Pb) in both groundwater and surface water emerging from the mine site were low, below drinking water and ecological standards. Yet Li (up to 46.8 mg/L), Rb (up to 169 μg/L), and Cs (up to 21 μg/L) were elevated relative to local background waters. Leaching experiments of the pegmatite ores, waste rocks, and tailing consistently demonstrate low mobilization of regulated contaminants and high leachability of Li, Rb, and Cs. Leaching experiments also reveal that water-rock interactions of the rocks and solid wastes from the mine site generate alkaline conditions, and that both phosphate and spodumene minerals are primary sources of Li and play a major role in formation of alkaline conditions during early stages of water-rock interactions. Over longer time scales, their direct impact on water quality is decreased. Given the global interest in hard-rock lithium mines, our findings highlight the potential occurrence of Li, Rb, and Cs in water resources adjacent to hard-rock lithium mines.