Sergio Carrero

The increasing demand of Li, required in the electrification of motoring industry, has intensified the exploitation of brines in salt flats, as one of the main known sources of this element. Continental salt falt are hydrogeological systems characterized by extreme salinity gradients that generate significant spatial variations in groundwater density and give rise to complex flow patterns dominated by thermohaline circulation. Despite their relevance, density-dependent processes are often simplified or neglected in hydrogeological models used to assess brine exploitation, introducing substantial uncertainty in the interpretation of system behavior and associated impacts.In this contribution, a coupled numerical modelling approach is presented to analyze the hydrogeological response of a salar subject to brine exploitation under variable-density flow conditions. First, a three-dimensional regional-scale groundwater model was developed and calibrated against observed hydraulic heads and salinity distribution. The model represents basin-scale flow patterns and incorporates existing brine pumping associated with exploitation, providing a reference framework for evaluating anthropogenic perturbations.Building on the calibrated regional model, the system response to a controlled brine injection test associated with Direct Lithium Extraction (DLE) schemes was investigated. The simulations allow assessment of the spatial and temporal evolution of the injected brine plume, as well as the interaction between pumping- or injection-induced hydraulic gradients and buoyancy forces related to density contrastsResults indicate that both brine extraction and reinjection induce non-linear and spatially propagated responses that are strongly controlled by density contrasts and hydrostratigraphic architecture, and that differ markedly from predictions obtained using constant-density approaches. The study highlights the necessity of explicitly accounting for density-dependent flow when evaluating the impacts of brine exploitation and reinjection strategies, and provides a physically consistent modelling framework to support the assessment and management of salars under conventional and DLE schemes. Those models would help to predict not only the evolution of phreatic level in a strategy based on DLE, but also would predict groundwater flow paths and the stability of the freshwater–brine mixing zone in marginal areas.

The climate emergency impacts settlements, infrastructures and ecosystems both through permanent flooding of the lowest‐lying areas and by increasing the frequency and/or severity of storm surges over a much larger region. In response to these challenges, the urgency in green renewable energies transition and vehicle electrifications to reduce the greenhouse gases emissions aligns with the growing need for enhanced electrical storage capacity, predominantly reliant on Li-based batteries. Notably, Li extraction is predominantly sourced from brine pumping and evaporation in salt flats, arid environments necessitating a shift toward Zero-Water consumption in extraction procedures. With this objective, mining companies have proposed a new extraction methodology based on Li recovery without evaporation and later brine reinjection in the aquifer, reducing at the same time cost and environmental impact, aligning with Horizon Europe cluster 5 of agenda 2030. Our research aims to develop a novel hydrogeochemical framework that helps to understand the effect of brine reinjection in salt flat, combining 3 fundamental research plans: 1) the hydrogeological characterization in salt flat focused to fiend the most favorable areas for brine injections, as well as monitoring the evolution of hydrological parameters at the aquifer during injection test for later implementation in 3D models. 2) the hydromechanical analysis of surface deformation associated with brines injection, looking to calculate the storage capacity and identify hydrogeological discontinuities. 3) the geochemical framework around brine mixing and brine-rock interactions affronted by modeling, lab and field samples characterization for later implementation in reactive transport models. A reinjection test carried out at a salt flat has studied by analyzing the generated hydrogeological and geochemical data, combined with historical deformation data. Descents in phreatic level influenced by injection has been characterized and included in a transport model. Geochemical reactions, including brine mixing and brine-rock interactions has ben also characterized by reactive transport models calibrated with field data. Elucidating the whole set of geochemical processes that affect salt flats, as well as their combination with hydrogeologic and interferometric analysis will help to adapt predicting 3D models to new extraction strategies.

This study advances the understanding of hydrological and hydrogeological processes in fractured and karstified carbonate massifs by systematically characterizing the isotopic composition of precipitation, surface water, and groundwater in the headwaters of the Llobregat River (Spain). A total of 115 water samples, collected between April 2024 and February 2025, were analyzed to assess temporal and spatial isotopic variability, examine the relationships between stable isotopes and meteorological variables, reconstruct backward air-mass trajectories of moisture sources, and delineate groundwater recharge zones.Results reveal an isotopic gradient linked to moisture conditions, and show that thermodynamic processes and air-mass origin exert a primary control on d-excess values. Moisture sources contributing to precipitation were identified as the Atlantic Ocean (44%), the Mediterranean Sea (24%), France (18%), and the Cantabrian Sea (14%). Backward trajectory analysis highlights a strong link between moisture provenance and isotopic signatures; however, accumulated precipitation samples represent integrated mixtures of multiple moisture sources.Groundwater and surface water isotopic signatures suggest dominant winter recharge occurring above 1,800 m a.s.l., consistent with regional topography and the highly karstified structure of the Moixeró massif. Seasonal precipitation signals preserved in groundwater further suggest short residence times and rapid recharge responses.These findings provide valuable insights for water-resource management and highlight the sensitivity of alpine karst systems to climatic variability, underscoring the need for continued long-term isotopic monitoring and expanded future hydrogeological studies.

Rare earth elements (REEs) behavior in acid mine drainage (AMD) during neutralization in estuaries is controlled by adsorption onto schwertmannite and basaluminite surface.

Fractures are integral to the hydrology and geochemistry of watersheds, but our understanding of fracture dynamics is very limited because of the challenge of monitoring the subsurface. Here we provide evidence that long-term, high-frequency measurements of the river concentration of the ultra-trace element thorium (Th) can provide a signature of bedrock fracture processes spanning neighboring watersheds in Colorado. River Th concentrations show abrupt (subdaily) excursions and biexponential decay with approximately 1-day and 1-week time constants, concentration patterns that are distinct from all other solutes except beryllium and arsenic. The patterns are uncorrelated with daily precipitation records or seasonal trends in atmospheric deposition. Groundwater Th analyses are consistent with bedrock release and dilution upon mixing with river water. Most Th excursions have no seismic signatures that are detectable 50 km from the site, suggesting the Th concentrations can reveal aseismic fracture or fault events. We find, however, a weak statistical correlation between Th and seismic motion caused by distant earthquakes, possibly the first chemical signature of dynamic earthquake triggering, a phenomenon previously identified only through geophysical methods.

Schwertmannite is a common nanomineral in acid sulfate environments such as Acid Mine Drainage (AMD) and Acid Sulfate Soils (ASS). Its high surface area and positively charged surface result in a strong affinity towards toxic oxyanions such as arsenate in solution. However, natural precipitation of schwertmannite also involves the accumulation of other impurities, in particular aluminum, an element that is often incorporated into the structure of Fe-oxide minerals, such as goethite and ferrihydrite, affecting their structural and surface properties. However, little is known about the effect of Al incorporation in schwertmannite on the removal capacity of toxic oxyanions found in AMD and ASS (e.g. arsenate). In this paper, schwertmannite samples with variable Al concentration were synthetized and employed in arsenate adsorption isotherm experiments at a constant pH of 3.5. Solid samples before and after arsenate adsorption were characterized using high energy X-ray diffraction and pair distribution function analyses in order to identify structural differences correlated with the Al content as well as variations in the coordination of arsenate adsorbed on the mineral surface. These analyses showed limited Al accumulation on schwertmannite (up to 5%) with a low effect on its structure. The maximum arsenate sorption capacity (258 mmol H₂AsO₄ mol_Fe ⁻¹) was in the range of that with pure schwertmannite, but a higher proportion of inner-sphere coordination was observed. Finally, Al was found to desorb from schwertmannite, with adsorbed arsenate preventing this effect and increasing the stability of the mineral. These results are useful to interpret observations from the field, in particular from river water affected by AMD and ASS, where similar conditions are observed, and where aluminum incorporation is expected.