Enhanced lithium recovery from simulated lithium-ion battery (LIB) leachate using supported liquid membrane contactors: effects of organophosphorus extractants and real-time wetting monitoring

Spent lithium-ion batteries (LIBs) represent a valuable secondary resource containing strategically important metals, particularly lithium-ion (Li⁺), which plays a critical role in electric vehicles and energy storage systems. As global demand for Li⁺ continues to rise, efficient recovery from end-of-life LIBs has become essential for sustainable resource recycling and supply chain stability. Supported liquid membrane contactors (SLMCs) offer a promising alternative to conventional liquid–liquid extraction owing to their low energy and chemical requirements and capability for continuous operation. In this study, hydrophobic polytetrafluoroethylene (PTFE) membranes impregnated with organophosphorus extractants, di-(2-ethylhexyl)phosphoric acid (D₂EHPA) and trioctylphosphine oxide (TOPO), were evaluated for Li⁺ recovery from simulated LIB leachate. Among the tested systems, PTFE-D₂EHPA exhibited the highest Li⁺ recovery efficiency (76.7 %), compared with only 0.5 % for the virgin PTFE membrane, primarily due to a proton–Li⁺ exchange mechanism facilitated by D₂EHPA. Continuous operation for 24 h demonstrated the excellent stability of the extractant-impregnated membrane. Water contact angle and optical coherence tomography (OCT) analyses revealed severe wetting and pore collapse in virgin PTFE, whereas PTFE-D₂EHPA maintained high hydrophobicity, stable porosity, and structural integrity, with porosity reduction limited to 13.5 % (vs. 74.7 % for virgin PTFE). These findings highlight the potential of functionalized SLMCs as a scalable, energy-efficient, and stable platform for sustainable lithium recovery from waste battery resources, providing a mechanistic foundation for next-generation circular resource technologies.