The Aqueous Geochemistry of Lithium Deposits and Environmental Effects of Lithium Mining

Abstract

Critical raw materials are essential to the global clean energy transition as the foundational components of emerging energy technologies. Among these, lithium is particularly important due to its central role in lithium-ion batteries used in electric vehicles and grid-scale energy storage. Rapidly increasing demand for lithium has intensified mining and exploration efforts worldwide, highlighting the need to better understand the geochemical processes governing lithium deposit formation and the potential environmental impacts of lithium extraction.This dissertation investigates the geochemistry of the two dominant lithium deposit types, continental closed-basin lithium-rich brines and hard-rock lithium-rich pegmatites, and evaluates the water-quality implications associated with mining these resources. The first three chapters focus on the origins, enrichment, and geochemical evolution of lithium and associated solutes in closed-basin brines of the Lithium Triangle in South America. Using a combination of new and compiled geochemical data, including major and trace element concentrations and isotopic tracers (δ7Li, δ11B, 87Sr/86Sr, δ18O, δ2H), this work refines existing models of brine evolution. Specifically, it (1) updates the mineral precipitation sequence of evaporating inflows into the salar systems to include ulexite, a borate mineral common to salars of the Lithium Triangle; (2) demonstrates that progressive evaporative evolution of inflows removes dissolved inorganic carbon, allowing boron species to become the dominant control on alkalinity and pH of the lithium brines; (3) shows that halite dissolution and precipitation exert a primary control on lithium concentrations of surface brines while deeper brines are instead composed of residual fossil brines at different stages of evaporation within closed-basins; and (4) develops a geochemical framework linking Mg/Li ratios of the lithium brines to the relative contributions of high-temperature geothermal water and near-surface low-temperature water-rock interactions. These processes are examined in detail at the Salar de Uyuni in Bolivia and evaluated in the broader context of Lithium Triangle brines. The latter chapters assess the potential environmental impacts of lithium mining. At the Salar de Uyuni, evaporation-based lithium extraction generates chemically distinct waste streams, including highly saline and acidic spent brines enriched in rubidium, cesium, boron, and arsenic, as well as alkaline processing wastewaters from the lithium processing plant. The contrasting geochemistry of these fluids constrains disposal and reinjection options and highlights the importance of geochemical controls in sustainable brine management. Beyond brine systems, this dissertation evaluates water-quality impacts associated with legacy hard-rock lithium mining in the Carolina Tin-Spodumene Belt of North Carolina. Results show that while elevated concentrations of lithium, rubidium, and cesium occur both naturally and in association with mining, hard-rock lithium operations are likely to generate alkaline effluents enriched in lithium with relatively high salinity derived from processing wastes but are unlikely to produce widespread exceedances of regulated contaminants under typical conditions. Together, this work provides an integrated geochemical framework linking lithium enrichment, extraction processes, and environmental outcomes across the two principal lithium resource types. These findings inform both lithium resource development and the sustainable management of water resources in critical mineral systems and environmental protection.