Large-Scale Preparation of Fluorinated Antifouling Nanofiltration Membranes with High Ion Selectivity for Li+/Mg2+ Separation

Developing high-efficiency antifouling nanofiltration (NF) membranes is crucial to address the dual challenges of low separation selectivity and severe membrane fouling in lithium extraction from high Mg 2+ /Li + ratio salt-lake brines. This study presents an efficient strategy based on one-step dip-coating surface modification. By grafting 1, 2-epoxy-3,3,3-trifluoropropane (TFO) molecules onto a PEI-TMC polyamide (PA) base membrane, a unique bipolar electrostatic potential reconstruction was triggered, simultaneously and significantly enhancing both the separation selectivity and antifouling performance of the membrane. In simulated high Mg 2+ /Li + ratio brine (2000 ppm, Mg 2+ /Li + = 30:1), the PA-TFO 0.75 membrane demonstrated exceptional integrated performance by achieving a high Li + /Mg 2+ selectivity of 20.5 (9.76 times higher than commercial NF membranes) while maintaining a high water permeance of 14.65 L m −2 h −2 bar −1 , and exhibiting an outstanding flux recovery ratio (FRR) approaching 100.6% (a 151% improvement over the pristine membrane), thereby meeting industrial fouling resistance standards. Critically, this strategy enabled the continuous fabrication of large-area membranes (60 m × 0.298 m). The assembled spiral-wound module (1812-type) retained a Li + /Mg 2+ selectivity of 19.5 in the same simulated brine, providing an efficient, antifouling, and scalable industrial-scale solution for lithium extraction from high Mg 2+ /Li + ratio salt lakes.