Refinement of brine for lithium extraction using ion concentration polarization

The surge of electric vehicle deployment in response to the global climate crisis has marked tremendous increase in the demand of lithium-ion batteries. Lithium brine has gained much attention as a critical primary lithium resource over mineral sources due to cheaper processing and greater abundance. However, reducing the Mg2+:Li+ ratio of brines remains a challenge, as magnesium contaminates lithium precipitates. Solar evaporation ponds are traditionally employed to concentrate Li and reduce Mg content to tackle this issue, but typically require 1–2 years to process a batch of feed solution, and require much land area disturbing the local environment near brine resources. Here we present a continuous, scalable ion separation technique for reducing the Mg2+:Li+ ratio of brine as an alternative to solar evaporation. The device utilizes ion concentration polarization to induce a locally amplified electric field. The amplified electric field separates ions into streams according to electrophoretic mobility. We demonstrate reduction of a 25:1 Mg2+:Li+ lab brine to below 10:1 Mg2+:Li+, which is an acceptable lithium production purity by industrial standards. Reduction of a 60:1 Mg2+:Li+ to ∼ 10:1 and a 100:1 Mg2+:Li+ brine to approximately 20:1 are also demonstrated. The system suffers a high specific energy consumption (8.804 kWh/g Li+ for 25:1 reduction to 9:1) due to low lithium recovery (9.9%) and microfluidic system size. However, an economic scaling analysis shows that this work is within an order of magnitude of the state-of-the-art separation technologies in the literature after various process parameters are normalized. Ultimately, this work demonstrates a potential novel process for continuous lithium extraction from brines, which is a generalizable ion separation tool utilizing differences in electrophoretic mobility.