Quality of Wastewater from Lithium-Brine Mining

Abstract

The sustainability of lithium mining is one of the critical factors for a successful transition to renewable energy. A potential practice to alleviate brine level decline and loss of adjacent fresh groundwater from brine pumping in the salt pans (salars) is through injection of spent brines into the subsurface. The quality and possible impacts of injecting spent brines have not been fully investigated. Here we present data for major and trace elements in natural brines, brines and salts from evaporation ponds, and wastewaters from a lithium processing plant at the Salar de Uyuni in Bolivia, the largest known global lithium deposit. The investigation reveals that evaporation of natural brines results in highly saline brines (TDS ≈ 360 g/kg) with low pH (3.2) and elevated concentrations of lithium, boron, and arsenic (up to ∼50 mg/kg) that could modify the chemical composition and mineral saturation upon release to the environment. The extremely high arsenic concenrations and low pH also have potential environmental impacts. In contrast, the processing plant generates saline and low-saline wastewater streams with high pH (∼10) and lower solute concentrations that could dilute the natural lithium reservoir, while the high pH limits their disposal options.