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.