Selective ion separation from acid mine drainage (AMD) under extreme acidic conditions presents a critical environmental challenge. While membrane-based technologies show promise for advancing water treatment processes, implementation in AMD treatment requires membranes that combine exceptional acid stability with precise ion sieving capabilities. Inspired by the ion retention characteristics of natural clay minerals, we have developed cation-selective membranes using vermiculite nanosheets as building blocks. The vermiculite membranes (VM) featured high acid stability and well-ordered two-dimensional nanochannels (2 Å), achieving a high H + permeation rate of 3.24 mol m −2 h −1 . The VM demonstrated exceptional selectivity between monovalent and metals ions, with a H + /Fe 3+ selectivity factor of 1284 in single-cation transport process. In complex multi-ion environments, the VM maintained stable separation performance, achieving a H + /Fe 3+ selectivity of 1000 in mixed solutions containing H + , K + , Na + , Ca 2+ , Mg 2+ and Fe 3+ . Additionally, VM effectively blocked other common AMD metals, including Cu 2+ , Co 2+ , Ni 2+ and Mn 2+ , while maintaining stable separation performance even at extreme low pH values (pH = 1). Through integrated theoretical calculations and experiments, we revealed that the synergistic effects of ultra-confined nanochannels (4∼5 Å) and surface charge created enhanced energy barriers for trivalent ion transport, resulting in high ion selectivity. Beyond providing an effective solution for AMD remediation, this work establishes vermiculite-based membranes as promising candidates for ion separation applications.
Selective extraction of lithium from brines faces significant challenges due to the difficulty of separating Li+ from competing Mg2+ 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 (ΔH) for Mg2+ than for Li+, due to the energy required to break Mg2+–COOH coordination bonds. Cu2+ cross-linking generated a denser and more ordered channel structure, increasing the spatial confinement for Mg2+ while maintaining a more favorable entropy (ΔS) profile for Li+ transport. This design achieved a Li+ permeation rate of 1.02 mol m–2 h–1 and a Li+/Mg2+ 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.
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