Highly Selective Lithium-Ion Separation by Regulating Ion Transport Energy Barriers of Vermiculite Membranes
Lina Zhang, Ziqing Huang, Yanzhe Chen, Fangzhou Li, Guanghe Li, Fang Zhang
Abstract
Selective extraction of lithium from brines faces significant challenges due to the difficulty of separating Li + from competing Mg 2+ by using conventional membranes. Taking inspiration from natural mineral ion-recognition mechanisms, we developed a vermiculite-based membrane functionalized with copper-coordinated sodium alginate (Cu-SA) to regulate ion transport energy barriers and overcome limitations in selectivity. The incorporation of Cu-SA serves a dual function by reinforcing interlayer covalent networks to stabilize the membrane structure with minimal spacing fluctuation (0.55 Å) and by enhancing ion selectivity through unreacted carboxyl groups. Thermodynamic analysis revealed a higher enthalpic barrier (Δ H ) for Mg 2+ than for Li +, due to the energy required to break Mg 2+ –COOH coordination bonds. Cu 2+ cross-linking generated a denser and more ordered channel structure, increasing the spatial confinement for Mg 2+ while maintaining a more favorable entropy (Δ S ) profile for Li + transport. This design achieved a Li + permeation rate of 1.02 mol m –2 h –1 and a Li + /Mg 2+ selectivity of 34 in single-ion systems. When applied in an electrodialysis system at an external field of 0.8 V cm –1, the Li + flux increased to 1.8 mol m –2 h –1, six times higher than diffusion-driven transport. This work not only offers a practical route for lithium recovery from complex brines but also provides a general strategy for designing next-generation ion-selective membranes through thermodynamic and structural tuning.