The demand for electric vehicles is on the rise due to climate change and the impending depletion of fossil fuels. This swelling demand also raises the price of lithium, which is vital to powering electric cars. Lithium is mostly extracted from salt lake brines using evaporation or filtration techniques, but a large amount of magnesium dissolved in the brine has been a challenge for efficient lithium mining.

A POSTECH research team led by Professor Geunbae Lim, PhD candidate Minsoo Lee, and Dr. Hyukjin J, Kwon (Department of Mechanical Engineering), in collaboration with Dr. Woochul Jung of Research Institute of Industrial Science and Technology (RIST) has recently proposed a novel filterless and electrokinetic-driven ion separation mechanism for lithium and magnesium without the use of any extractants. The findings from this study were published as the back cover paper of Journal of Materials Chemistry A, an international journal on materials science.

When extracting lithium from salt lakes brines, magnesium forms a compound with lithium during solar evaporation and co-precipitates during the chemical precipitation process, which leads to a double loss of lithium. Consequently, as the amount of magnesium in the brine increases, the loss of lithium and the cost of extraction sharply increase.

Diverse strategies have been proposed to mitigate this problem over the years, but the extraction process relying on physical or chemical filtration has limited their scalability and applicability.

To this, the researchers focused on the electrokinetic phenomenon that enables precise control over the migration of tiny particles. A strong electric field can be formed in a small area by applying the concept of ion concentration polarization, which is a typical electrokinetic phenomenon. The electric force acts on charged particles that approach this area along the direction of the electric field and at this time, the magnitude of the electric force is proportional to the magnitude of the particle's electrophoretic mobility.

The researchers developed the ion separation mechanism based on this subtle difference in the electrophoretic mobilities of lithium and magnesium. They experimentally demonstrated for the first time a new method for continuous lithium separation and extraction utilizing the electrokinetic manipulation of ion migrations by steering ions onto different paths simply by balancing the diagonally formed electric field intensity and flow rate.

The researchers have also verified that consistent performance can be achieved in this novel force-based ion separation method regardless of brine conditions, which is an improvement on the conventional technique whose performance depends on the brine condition.

 “This novel method can be widely applicable and highly cost-effective since it uses a filterless mechanism,” remarked Lim who led the study. “It may provide an entirely new direction for practical and economical lithium mining from brines that requires magnesium separation in the future.”

This study was conducted with the support from the Mid-Career Researcher Program of the National Research Foundation of Korea.

- This press release was originally published on the Pohang University of Science & Technology website

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