Efficient separation of Li+/Mg2+ via positively charged TFN membrane based on the PEI interlayer

Abstract

Nanofiltration (NF) technology has exceptional mono/divalent ion separation performance, providing considerable application potential for lithium extraction. However, polymeric NF membranes provided only restricted amounts of practical applications since of their low permeability and limited selectivity. Herein, a positively charged membrane designed for Li+/Mg2+ separation was developed, this achievement was accomplished by incorporating NH2-MIL-101(Cr) nanoparticles (NPs) into the polyamide (PA) layer situated atop the polyethyleneimine (PEI) interlayer. The PEI interlayer controlled the amine monomer distribution, regulated the PA nanofilm morphology, and improved the membrane positively charged properties. Meanwhile, the NH2-MIL-101(Cr) could provide Li+ with fast transport paths to further enhance the membrane Li+/Mg2+ separation capability. The improved membrane possessed MgCl2 rejection of 96.1 %, LiCl rejection of 42.3 %, and Li+/Mg2+ separation factor of 102 with outstanding permeance of 17.0 L m-2h−1 bar−1. This research made a valuable contribution to applying NF membranes in lithium extraction processes.