Modification of cation exchange membranes for enhanced extraction of lithium from magnesium and sodium brine solutions via selective electrodialysis

Selective extraction of Li + ions from highly saline solutions is challenging due to the presence of competing ions like Mg2+ and Na+. This study employed a straightforward interfacial polymerization technique to modify cation exchange membranes (CEM, CR671) to enhance Li+ transport selectivity and capacities. The modification involved a two-layer coating, with polydopamine (PDA) as the initial layer facilitating subsequent coating with polyethyleneimine (PEI). The second layer, comprising PEI and 2-OH-15-crown-5 ether (15CE), created the channels for selective Li transport through crosslinking with 1,3,5-benzenetricarbonyl trichloride. Fourier transform infrared spectroscopy confirmed the presence of 15CE coating on the modified membranes (15CE-PEIPDA-CR671), while zeta-potential analysis indicated a positive surface charge attributed to PEI to increase the electrostatic repulsion of divalent cations. Electrochemical impedance spectroscopy demonstrated a reduced impedance of 15CE/PEI-PDA-CR671 for Li transport, indicating its high transport potential and selectivity for Li. Bench-scale electrodialysis experiments simulating high Mg2+ and Na + brine conditions demonstrated promising results that 15CE/PEI-PDA-CR671 membrane achieved up to 80% and 90% Li+ recovery efficiency in Mg2+/Li+ and Na+/Li+ mixtures, respectively. The modified membranes exhibited enhanced selectivity, as evidenced by reduced relative transfer numbers (tMg/Li and tNa/Li). Specifically, 15CE/PEI-PDA-CR671 demonstrated significant improvements in Li+ permselectivity and flux compared to CR671 and PEI-PDA-CR671, highlighting its potential for enhancing Li+ recovery effectively from brine water sources.