(308e) Fabrication of Lithium/Magnesium Selective Tethered Electrolyte Active Layer Membranes for Lithium Production from Brine Water Sources

This study investigates novel tethered electrolyte active-layer membranes (TEAMs) for selective lithium recovery from magnesium-rich brine sources, which is a critical mineral extraction challenge for the clean energy transition. Using controllable surface-initiated atom transfer radical polymerization (SI-ATRP), we systematically developed and characterized three distinct membrane architectures: conventional single-block polyelectrolytes (positive, negative, and mixed charges), bottlebrush polyelectrolytes, and bionic crown ether-modified membranes.

Positively charged PMAC-grafted TEAMs demonstrated exceptional lithium selectivity (up to 30-fold) at 2 mM salt concentrations, with selectivity increasing to 120-fold at higher magnesium feed ratios (75-95%). However, these conventional membranes showed performance limitations at higher salt concentrations that are more typical of natural brine sources. To address this challenge, we developed novel bottlebrush architectures by grafting positively charged polyelectrolytes from a PHEMA backbone on cellulose substrates. These bottlebrush TEAMs maintained substantial lithium selectivity across a broad concentration range (15-fold at 2 mM, 8-fold at 20 mM, and 3-fold at 200 mM), representing a significant advancement for practical lithium extraction applications.

Negatively charged membranes exhibited different transport mechanisms, with PSVBS bottlebrush membranes achieving 10-fold lithium selectivity at 2 mM salt concentration through combined lithium transport and ion exchange processes. Bionic crown ether-incorporated membranes demonstrated modest but pressure-dependent lithium selectivity (1.5-fold at 2 bar, increasing to 3-fold at 50 bar) due to compaction effects on the selective layer.

The selectivity mechanisms were explored through systematic testing of various charge configurations, polymer architectures, and feed compositions under controlled dead-end filtration conditions. The bottlebrush structure proved particularly effective for concentrated brines (up to 200 mM), addressing a critical gap in current membrane technology. Process parameters including pressure, pH, and feed composition were systematically varied to elucidate governing transport phenomena. This research establishes a foundation for developing tailored membrane technologies for lithium extraction from diverse brine compositions, addressing both fundamental transport mechanisms and practical separation challenges in concentrated salt environments. The membrane design principles demonstrated here offer a promising pathway toward more efficient, scalable lithium production technologies essential for meeting growing demand in battery technologies and clean energy applications.