Preparation of LiOH through BMED process from lithium-containing solutions: Effects of coexisting ions and competition between Na+ and Li+

Abstract Bipolar membrane electrodialysis (BMED) is a promising method to produce LiOH from lithium containing solutions. However, the coexisting ions will significantly affect the current efficiency of preparing LiOH. Herein, the influence of the ion's property on the mass transfer behavior of the BMED was investigated, establishing the relations between hydration number and ion's migration as well as water osmosis. Effects of coexisting ions on the lithium migration and current efficiency were studied. The results show that the competition from Na+ and K+ reduced the migration rate of Li+ and increased the energy consumption of producing LiOH, and the coexisting K+ had greater impact compared with Na+. The coexisting SO42− in feed solution generated severer lithium leakage into the acid compartment than Cl− did. In addition, influences of the Na/Li molar ratio in feed solution, current density, and characteristics of cation exchange membrane (CEM) on competitions between Na+ and Li+ were discussed. With increasing the Na/Li molar ratio, lithium concentration in base solution decreased, while the energy consumption increased, owing to the dominant role of Na+ in competitive migration and backward diffusion. Larger ion exchange capacity and lower resistivity of CEMs were beneficial for avoiding negative-transfer and enhancing current efficiency.