MULTIPLE ISOTOPES AS POTENTIAL TRACERS FOR CONTAMINANTS DERIVED FROM LITHIUM MINE WASTES

Demand for batteries for electric vehicles and grid storage have led to increases in global exploration and extraction of lithium from various deposit types, including lithium-rich pegmatites. Spodumene is often the primary lithium-bearing mineral in such pegmatites and is separated from the bulk pegmatite for lithium extraction. Lithium extraction from pegmatites produces several waste sources, including: (1) residual pegmatite depleted in spodumene, and (2) solid and liquid wastes from lithium extraction. Due to this generation of waste, there is a need to evaluate the potential environmental concerns of lithium mining and extraction, and to develop tracers to monitor for such contamination.

To evaluate the potential environmental effects of spodumene-rich pegmatites, we analyzed whole rock pegmatites, spodumene concentrate, and wastes generated from laboratory-simulated Li extraction experiments on samples from the Tin-Spodumene Belt (TSB) in North Carolina. Experiments show that, in addition to Li, some potentially hazardous elements (i.e., Cr, As, and Th) are also highly leachable (>65% of bulk concentrations) during simulated spodumene processing with an H₂SO₄ leach, suggest that effluents from Li-pegmatite mine waste could be elevated in contaminants that pose environmental and human health risks.

To distinguish between contamination from different waste products induced from lithium mining, we evaluate the potential use of multiple isotope systems (⁸⁷Sr/⁸⁶Sr, ^206,207,208Pb ratios, and ²²⁶Ra/²²⁸Ra activity ratios) and elemental ratios as environmental tracers. We show large variations between the isotopic and elemental compositions of whole rock pegmatite, spodumene concentrate, and lithium extraction by-products including the sulfuric acid leachate and residual solids. Elemental ratios and ⁸⁷Sr/⁸⁶Sr of the H₂SO₄ leachate and the residual waste solids are largely different from natural variations as reflected by a local background stream water sample. Overall, ⁸⁷Sr/⁸⁶Sr paired with Pb isotopes, ²²⁶Ra/²²⁸Ra activity ratios, and elemental ratios (ie. Rb/Sr) could be sensitive tracers for monitoring and delineating the environmental impacts of different wastes from Li-pegmatite mining.