Coupling enlarged sub-nanoporous membrane with EDTA complexation for efficient Li+/Mg2+ separation

A synergistic membrane–solution strategy combining enlarged sub-nanoporous PI membrane with EDTA complexation achieves high Li + flux (73 mmol h -1  m -2 ) and exceptional Li + /Mg 2+ selectivity (351). • The EDTA-induced size and charge transformation of Mg 2+ enables effective electrostatic and steric rejection by negatively charged sub-nanopores, breaking the permeability–selectivity trade-off. • The system demonstrates robust separation performance (selectivity > 284) even at Mg 2+ /Li + ratio up to 60, with EDTA 4- being efficiently regenerated and reused over multiple cycles. Efficient extraction of lithium-ion from salt-lake brine remains a significant challenge, primarily due to the similar physicochemical properties of Li + and Mg 2+ , and the inherent trade-off between permeability and selectivity in conventional membrane processes. Herein, we propose a synergistic membrane–solution strategy that integrates an enlarged sub-nanoporous polyimide membrane (ESN-PI) with ethylenediaminetetraacetate (EDTA 4- ) complexation to enhance the Li + flux and Li + /Mg 2+ selectivity simultaneously. The ESN-PI membrane, fabricated via heavy-ion irradiation and controlled alkaline etching, provides enlarged transport channels that significantly improve Li + permeation. Meanwhile, EDTA 4- selectively chelates Mg 2+ to form a bulky, negatively charged [EDTA-Mg] 2- complex, which is electrostatically repelled and sterically hindered by the negatively charged sub-nanopores, thereby greatly suppressing Mg 2+ transmembrane transport. The coupled system delivers a high Li + flux of up to 73 mmol h -1 m -2 and an exceptional Li + /Mg 2+ selectivity of 351. Notably, the separation performance remains robust (selectivity > 300) even at a high feed Mg 2+ /Li + ratio of 60, and EDTA 4- can be efficiently regenerated and reused over multiple cycles. This research utilized heavy ion irradiation technology to prepare a more economical cation exchange membrane. By coupling the membrane with the EDTA complexation strategy, it was able to resolve the contradiction between permeability and selectivity in the ion separation process based on the membrane, providing a promising strategy for extracting lithium from brines with high magnesium ion content. Polymer membranes are widely used for the extraction of lithium resources from salt-lake. The enlarged sub-nanoporous polyimide membranes (ESN-PI) combined with EDTA 4- to achieve efficient Li + /Mg 2+ separation. EDTA 4- can combine with Mg 2+ to form a bulky, negatively charged [EDTA-Mg] 2- complex. The lithium flux and Li + /Mg 2+ selectivity reaches 0.073 mol·h -1 ·m -2 and 351, respectively. This work demonstrates a viable and economically feasible route to decouple the permeability–selectivity trade-off in membrane-based ion separation, offering a promising strategy for lithium extraction from high-Mg 2+ brines. Download: Download high-res image (86KB) Download: Download full-size image