Selective separation of Li from Mg rich brine using supported betaine ionic liquid membranes with ultrasonic assisted forward osmosis process

Abstract

The increasing global demand for lithium (Li + ) in energy storage systems requires effective and selective extraction methods from complicated, magnesium-rich brines. This study investigates the design, characterization, and performance optimization of supported ionic liquid membranes (ILMs) for selective Li + extraction from magnesium-rich brines under ultrasonic-assisted forward osmosis (FO) conditions. Four composite ILMs were prepared by incorporating betaine-based ionic liquids ([Bet-butyl][PF 6 ], [Bet-hexyl][PF 6 ], [Bet-butyl][SCN], and [Bet-hexyl][SCN]) with tributyl phosphate (TBP) into polyvinylidene fluoride (PVDF) membranes, further sealed with a polyvinyl chloride (PVC) layer. Membrane morphology, crystallinity, and stability were characterized via XRD, FESEM, and EDX analyses. ILMs with PF 6 anions produced dense, crystalline membranes with high mechanical strength and selectivity, while ILMs with SCN anions led to more amorphous, porous structures with elevated permeance. Hydrophilicity and ILM stability were enhanced by PVC sealing, reducing ILM loss to less than 2.4% under ultrasonication. Through Bayesian network learning, key ultrasonic parameters including amplitude, sonication time, and pulse sequence were searched for their effects on Li and Mg ions fluxes through composite membranes. High ultrasonic amplitudes (157.5 μm) and moderate frequencies (150 kHz) maximized lithium permeance and selectivity, while elevated magnesium (Mg 2+ ) concentrations hindered performance. The [Bet-butyl][SCN]:TBP membrane exhibited the highest selectivity ( S Li/Mg > 349). These findings demonstrate that tailored ILM chemistry, combined with optimized ultrasonic conditions and PVC sealing, enables efficient, selective, and robust Li + extraction from complex brines.