Feature Article

22-Jan-2020

ORNL develops sorbent to recover lithium from geothermal brines

DOE/Oak Ridge National Laboratory

In the quest for domestic sources of lithium to meet growing demand for battery production, scientists at the Department of Energy's Oak Ridge National Laboratory are advancing a sorbent that can be used to more efficiently recover the material from brine wastes at geothermal power plants.

Domestic production of lithium, the lightest of elemental metals, is considered a priority for the nation. It is essential for the manufacturing of lithium-ion batteries commonly used for everything from electric vehicles to cell phones and laptops. Yet it 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 U.S. Geological Survey, a figure expected to grow exponentially.

In work for DOE's Critical Materials Institute, scientists at ORNL are working to refine a 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.

ORNL and its research partners are working to improve the capacity and selectivity of a sorbent that could extract the lithium from these brines. The lithium-aluminum-layered double hydroxide chloride (LDH) sorbent they're developing is a low-cost, reusable option for large-scale industrial plants.

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.

By putting the sorbent through these paces, "we get valuable information on how water is accommodated in the sorbent's layers and how that dictates separation and stability," said Parans Paranthaman, principal investigator for the project and leader of the Materials Chemistry Group at ORNL.

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

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.

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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.

ORNL is managed by UT-Battelle for the U.S. Department of Energy's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. DOE's Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit https://energy.gov/science.