Lithium demand grows as lithium is an essential element for energy storage systems which reduce the exploitation of non-renewable and polluting energy resources for our planet.
Lithium is extracted by conventional mining methods from pegmatitic rocks, and from salt flat systems where the metal is contained in brines and extracted as a fluid.
Salt flat systems have a core formed by brines with high density and high concentrations of minerals (sulfates, nitrates, lithium, carbonates). Towards the borders of the salt flat, these brines coexist with lower-density fresh water from the upper areas of the basin. These two different density fluids collide at the borders of the salt flat where the brine pushes the water towards the surface. The contact zone generates a surface or mixing zone known as a salt wedge or salt interface. The marginal zone of the salt flat where the salt interface is observed is characterized as a sector of low permeability, and with local variations of topography where outcrops of fresh water appear, forming wetlands (vegas) or lacustrine systems. Unique, fragile ecosystems of native flora and fauna develop in these surface water systems.
Brine extraction through wells or ditches generates drawdown in the hydrogeological system that spreads to the borders, displacing and deforming the saline interface. These changes have an undesirable effect on the local flora and fauna which may be reduced or even disappear.
In this context, salt flat lithium extraction projects should consider detailed studies to examine the effect on salt flat borders. It is essential to have accurate groundwater and surface water data, detailed topography, water quality data, porosity and permeability of constituent units, lagoon bathymetry as well as geophysics and hydraulic conductivity profiles in wells to identify the geometry of the salt wedge. This information must be obtained over as long a period as possible in order to understand the seasonal evolution of the system. Furthermore, this monitoring should continue throughout the execution of the project in order to monitor possible changes in these systems and to detect in advance any variation in levels or quality that could bring undesirable consequences in the perimeter lacustrine systems.
At present, environmental regulations demand an understanding of these systems through detailed studies. These investigations are complex and challenge the use of hydrogeological conceptualization tools and numerical approaches to solve variable density systems, which are necessary to ensure the sustainability of lithium mining in salt flat systems.
