New Method Optimizes Lithium Extraction From Seawater and Groundwater

Lithium production has more than tripled in the last decade, with the electric vehicle market causing global demand to soar. However, current lithium production methods are rather inefficient – they require huge volumes of energy and often come with significant environmental drawbacks.

To lessen our reliance on these operations, scientists are eager to maximize the potential of alternative lithium sources wherever they exist.

Scientists at the University of Chicago have demonstrated a new method that can effectively draw out lithium from very dilute liquids – including seawater, groundwater and the “flowback water” generated from fracking and offshore oil drilling operations. The method has been described in a paper published in Nature Communications.

“Right now there is a gap between the demand for lithium and the production,” said senior study author Chong Liu, the Neubauer family assistant professor of molecular engineering at the University of Chicago Pritzker School of Molecular Engineering. “Our method allows the efficient extraction of the mineral from very dilute liquids, which can greatly broaden the potential sources of lithium.”

Environmentally friendly lithium extraction

Most of the lithium that makes it into the world today comes from one of two sources: mined lithium ore or dried lithium brine. Lithium mines dig up lithium ore from the ground and treat the ores with acid, leaving behind isolated lithium. Most lithium brine pools are found underneath salt flats, with the lithium being extracted by pumping the brine up to the Earth’s surface and letting the water evaporate off, leaving behind dried lithium.

Both methods have significant pitfalls – mining operations have been linked to air pollution and water contamination, while lithium brine evaporation operations have been criticized for their intensive water use.

“These methods aren’t particularly environmentally friendly to begin with, and if you start trying to work with less concentrated sources of lithium, they’re going to become even less efficient,” explained Liu. “If you have a brine that is 10 times more dilute, you need 10 times more briny water to get the same amount of lithium.”

The new method, developed by Liu and her colleagues, is specifically designed to draw lithium out of these very dilute solutions. Using this method, the team envisions that valuable lithium could be extracted from a more diverse set of liquids than just lithium brine deposits, such as seawater or the flowback generated during fracking.

The “Goldilocks” lithium sponge

The team’s new approach uses particles of olivine iron phosphate to soak up lithium ions as if they were mini sponges. Due to their electrochemical properties, lithium ions are easily drawn into the large channels present in the particles’ crystal lattice structure, where they become trapped.

This type of electrochemical intercalation between lithium and olivine iron phosphate had previously been proposed to selectively isolate lithium from unconventional sources. However, issues with sodium ions outcompeting the lithium ions for space in the lattice structure had always presented a challenge.

To see whether this could be overcome, Liu’s team began to investigate whether variation in the lattice’s channel size could have any significant effects on lithium selectivity. If so, the right lattice structure might be able to soak up lithium while leaving out sodium and any other ions present in briny waters. 

“When you produce iron phosphate, you can get particles that are drastically different sizes and shapes,” explained Gangbin Yan, a graduate student in the Liu Group. “In order to figure out the best synthesis method, we need to know which of those particles are most efficient at selecting lithium over sodium.”

In their synthesis method tests, Liu’s group generated olivine iron phosphate in a range of particle sizes, with internal channel lengths spanning from 20 to 6,000 nanometers. These were sorted into groups based on their channel length and used to build electrodes capable of extracting lithium from a weak solution.

Electrochemical tests found that where the iron phosphate channel sizes were too large or too small, they tended to extract more sodium.

“It turned out that there was this sweet spot in the middle where both the kinetics and the thermodynamics favor lithium over sodium,” said Liu.

This observation could be vital to improving electrochemical lithium extraction and making it a commercial reality. In light of their findings, the team says that researchers should be sure to prioritize not just producing olivine iron phosphate but also producing the right type of olivine iron phosphate when investigating lithium extraction.

“We have to keep this desired particle size in mind as we pick synthesis methods to scale up,” Liu said. “But if we can do this, we think we can develop a method that reduces the environmental impact of lithium production and secures the lithium supply in this country.”

Reference: Yan G, Wei J, Apodaca E, et al. Identifying critical features of iron phosphate particle for lithium preference. Nat Commun. 2024;15(1):4859. doi: 10.1038/s41467-024-49191-3

This article is a rework of a press release issued by the University of Chicago Pritzker School of Molecular Engineering. Material has been edited for length and content.