Domestic production of lithium, the lightest of elemental metals, is considered a priority for the US. It is essential for the manufacturing of lithium-ion batteries commonly used for everything from electric vehicles to cell phones and laptops. However, lithium is sourced almost exclusively from other countries, either concentrated using a solar evaporation process from natural brine sources or recovered from ore. The United States imported 4,000 metric tons of lithium in 2018, according to the US Geological Survey, a figure expected to grow exponentially.

In work for DOE’s Critical Materials Institute, scientists at Oak Ridge National Laboratory (ORNL) are working to refine a lithium-aluminum-layered double hydroxide chloride (LDH) sorbent that can more effectively recover lithium salts from concentrated brines at geothermal plants. These plants pump hot water from geothermal deposits and use it to generate electricity. Concentrated brines left over from the operation are then pumped back into the ground.

Those brines can contain as much as 250 to 300 parts-per-million lithium. By some estimates, as much as 15,000 metric tons per year of lithium carbonate could be recovered from a single geothermal power plant in the Salton Sea area of California—one of the most mineral-rich brine sources in the United States. There are currently 13 geothermal plants in the region and more are planned.

The lithium-aluminum-layered double hydroxide chloride (LDH) sorbent being developed by ORNL targets recovery of lithium from geothermal brines—paving the way for increased domestic production of the material for today’s rechargeable batteries. Credit: Oak Ridge National Laboratory

The LDH sorbent is made up of layers of the materials, separated by water molecules and hydroxide ions that create space, allowing lithium chloride to enter more readily than other ions such as sodium and potassium. After the sorbent loads with lithium chloride, it is selectively washed to remove unwanted ions, and then to unload the remaining lithium chloride. In a bench-scale demonstration, the LDH sorbent recovered more than 91% of lithium from a simulated brine.

ORNL scientists recently used inelastic neutron scattering to explore the structure of different variants of the sorbent. The technique is very sensitive to hydrogen atoms, making it ideal for studying water. It allowed researchers to probe deep into the material and explore the ordering of water molecules between the sorbent’s layers, providing information on the material’s stability and its lithium recovery efficiency. The work was performed on the VISION instrument at the Spallation Neutron Source—a DOE Office of Science User Facility at ORNL.

The sorbent’s thermochemical properties were also characterized using differential scanning calorimetry and thermogravimetry at the University of California-Davis. The tests explored how the ordering of water molecules in the sorbent has a direct impact on the material’s stability and effectiveness. The scientists confirmed that by replacing some of the aluminum with iron in the sorbent, the material is made more thermodynamically stable and can be used as an alternate sorbent for extracting lithium.

The work was described in a paper in The Journal of Physical Chemistry C.

With a better understanding of the molecular structure and behavior of the material, we can create sorbents with greater throughput that could reduce the size and cost of plant construction, for instance, or develop variants that would work with lower-temperature brines. The more versatile the sorbent is, the more options there are for industry to supply the lithium we’re going to need for energy storage.

—Bruce Moyer, a project team member and leader of the Chemical Separations Group at ORNL

ORNL scientists are also working on a membrane to concentrate the geothermal brines before they’re exposed to the sorbent, which increases the efficiency of the process. The next steps are to scale up the process and run tests that simulate real-world conditions, the researchers noted.

The work is being conducted with industry partner All American Lithium, which is seeking to refine the technology in preparation for a commercial lithium plant in California.

The CMI, a DOE Energy Innovation Hub, funds the work as part of its mission to encourage supply diversity for critical materials. CMI is led by DOE’s Ames Laboratory and supported by DOE’s Office of Energy Efficiency and Renewable Energy’s Advanced Manufacturing Office. CMI seeks ways to eliminate or reduce our nation’s reliance on rare-earth metals and other materials critical to the success of clean energy technologies.

Resources

• Lili Wu, Samuel F. Evans, Yongqiang Cheng, Alexandra Navrotsky, Bruce A. Moyer, Stephen Harrison, and M. Parans Paranthaman (2019) “Neutron Spectroscopic and Thermochemical Characterization of Lithium–Aluminum-Layered Double Hydroxide Chloride: Implications for Lithium Recovery” The Journal of Physical Chemistry C 123 (34), 20723-20729 doi: 10.1021/acs.jpcc.9b04340