A newly improved sorbent could offer an environmentally friendly way to get lithium from a relatively untapped resource in the U.S.: the brine produced by geothermal power plants (Environ. Sci. Technol. 2017, DOI: 10.1021/acs.est.7b03464).
These plants pump hot water from deep geothermal deposits and use it to generate electricity, leaving behind a salty solution that can contain hundreds of parts per million lithium—a commodity in demand for lithium-ion batteries. Passing the brine through a sorbent that captures the lithium ions before pumping the brine back underground could collect the metal without the heavy environmental impacts of typical extraction methods, which can generate large amounts of acid or salt waste.
The sorbent in the new study is made out of layers of [LiAl2(OH)6]+ with chloride ions and water in between them. Voids in the structure can fill with additional lithium ions but are too small to let in competing cations like sodium.
Using a simulated brine solution, Parans Paranthaman of Oak Ridge National Laboratory and colleagues captured 91% of the initial lithium in the brine with the improved sorbent and found that the material is strongly selective for lithium over sodium and potassium.
York R. Smith, a metallurgical engineer at the University of Utah, notes that this sorbent has a lower capacity than alternative sorbents that have been tested. He adds, however, that the researchers’ use of lithium chloride to release lithium from the sorbent instead of acid, as is required for other sorbents, is attractive from an environmental perspective.