Lithium brine re-injection in salar environments: Perspectives for a sustainable implementation of direct lithium extraction (DLE) technologies

The growing demand for lithium, driven by the global energy transition, has intensified pressure on brine resources in arid salar environments, where conventional evaporation-based production is associated with low recovery efficiencies, substantial water losses, and socio-environmental conflicts. Direct Lithium Extraction (DLE) technologies are increasingly promoted as a cleaner production pathway due to their higher selectivity, reduced land use, and potential for lower freshwater consumption. However, the environmental credibility of DLE critically depends on the technical feasibility and long-term safety of re-injecting processed (spent) brines into salar aquifers to mitigate hydrological imbalances. Large-scale re-injection may induce hydrogeochemical and hydrodynamic perturbations, altering aquifer structure, density-driven flow regimes, pressure propagation, mixing processes, and groundwater-dependent ecosystems. Despite extensive industrial experience with subsurface fluid re-injection, hypersaline lithium brine systems present distinct challenges related to extreme salinity, complex water–rock interactions, and uncertain hydraulic connectivity. This review synthesizes the geological, hydrogeological, geochemical, and operational controls governing re-injection feasibility in salar basins. It evaluates how DLE and complementary lithium brine concentration (LBC) processes modify brine chemistry and define acceptable re-injection envelopes. We identify key environmental risks, including mineral precipitation, metal mobilization, and the introduction of non-native compounds, as well as governance challenges related to receptor protection, uncertainty management, and adaptive monitoring. By integrating basin-scale system characterization with operational validation, we propose a structured roadmap to support science-based decision-making and advance DLE as a genuinely sustainable cleaner production strategy.