The Water Quality Impacts of Legacy Hard-Rock Lithium Mining and Processing

Hard-rock Li mining from Li-pegmatites is rapidly expanding to support the clean energy transition, yet associated water-quality impacts remain understudied. Here, we evaluate surface water and groundwater in the Tin-Spodumene Belt (TSB), a legacy Li mining and processing district in North Carolina. Streams emerging from legacy Li mining and processing sites show markedly elevated total dissolved solids (TDS), Li, and Rb, and circumneutral pH, but no exceedances of regulated contaminants. These solute increases are attributed to gypsum dissolution from historical processing wastes. Groundwater across the TSB exhibits widespread enrichment in Li, Rb, and Cs due to natural pegmatite water-rock interaction, although groundwater within a mine shows greater degrees of interaction. A geospatial analysis reveals no effects on quality of domestic wells located near the historic Li mining and processing. Our results indicate that the waste gypsum residues from Li processing drive the long-term surface water quality impacts, while groundwater chemistry is governed by natural geochemical processes between the Li pegmatite and its host rocks. The global abundance of Li pegmatite deposits and the increasing demand for Li exploration suggests that similar water quality issues may become widespread as new mines and processing facilities open and expand.