Scalable Membrane-Based Lithium-Ion Sieve Sorbent for Selective Lithium Extraction from Brines

The escalating global demand for lithium, driven by the rapid growth of production of electric vehicles and portable electronics, requires the development of selective and scalable extraction technologies capable of recovering lithium from complex liquid resources such as geothermal-, oilfield-, or low-grade salar brines. This study presents the development and characterization of a novel composite membrane adsorbent based on a monoclinic β-Li2TiO3 (LTO) lithium-ion sieve embedded within a poly(vinyl chloride) (PVC) and silica (SiO2) matrix. The incorporation of SiO2 as a structural component enhances mechanical stability, processability, and wettability of the membrane enabling fabrication via industrially scalable extrusion and calendaring techniques and promoting contact of the Li-bearing brine with LTO particles inside the pore system of the membrane. Three membrane compositions with varying SiO2:LTO ratios (50:50, 40:60 and 30:70 wt %) were systematically investigated. Among the investigated compositions, the 40% SiO2-60% LTO membrane achieved the highest equilibrium adsorption capacity of approximately 37 mg Li+ g-1 HTO at 45 °C from a dilute feed solution (C0 = 100 mg L-1), consistent with endothermic, chemisorption-controlled Li+/H+ exchange kinetics best described by the pseudo-second-order model. Selectivity evaluation in a mixed-cation solution simulating geothermal brine composition yielded a Li+ distribution coefficient (Kd) of 304 mL g-1, with separation factors of 12 over Na+ and Mg2+, and 8 over K+. The membrane retained stable adsorption capacity over several consecutive adsorption-desorption cycles, confirming good chemical and structural stability. These results demonstrate the potential of PVC/SiO2/LTO composite membranes as a promising, cost-effective, and industrially scalable platform for selective lithium recovery from complex brines.