Extracting lithium from currently underutilized brines, such as geothermal and oilfield brines, will be necessary to meet the growing demand for lithium in energy-storage applications in the future. Technical hurdles for extracting lithium from these sources include the relatively low concentration of Li+ and high concentrations of competing cations (such as Na+, K+ and Mg2+).
Recent experiments by a team of engineers at Columbia University (New York, N.Y.; www.columbia.edu) have demonstrated a direct-extraction method for selectively removing lithium from brines containing low lithium concentrations and high levels of other cations. The method, which takes advantage of a solvent system that changes its affinity for water based on temperature, could unlock lithium resources that are not practically accessible with conventional technologies.
The Columbia researchers developed a technique called switchable solvent selective extraction (S3E), which utilizes a moderate temperature swing to “toggle switchable hydrophilicity solvents between water-affinity and water-aversion states,” the researchers say.
In the extraction step, brine is combined with low-polarity amine solvents, forming a biphasic system with an organic and aqueous phase. Crucially, the system is designed such that the organic phase preferentially extracts lithium ions over other cations.
At elevated temperatures, the solvent produces a lithium-enriched aqueous stream and the solvent is regenerated for reuse.
The researchers tested the technique using a simulated brine similar to that found in the Salton Sea, a geothermal brine reservoir in California. Even with feed concentrations of Li+ that are 1,000 times lower than competing alkali metal cations, the technique was able to demonstrate practical Li+ recovery yields over several rounds using the same solvent, the researchers say.