Novel bifunctional aminophosphonic acid extractants for efficient lithium recovery from spent battery leachates with high sodium interference

The increasing demand for lithium resources has promoted significant advancements in lithium extraction and recovery technologies. This study introduces a series of novel aminophosphonic acid extractants with varying branched-chain structures, designed to enhance lithium recovery from spent battery leachates with high sodium interference. These bifunctional extractants, incorporating both phosphonic acid and amino groups, demonstrated notable efficiency and selectivity. Under optimal conditions, a single-stage extraction achieved a lithium extraction efficiency of 70 %, with a lithium‑sodium separation factor of 139. A four-stage countercurrent extraction process further elevated the lithium recovery to 99 %. The extraction mechanism was elucidated through Fourier-transform infrared (FT-IR) spectroscopy and 31 P nuclear magnetic resonance (NMR) spectroscopy, complemented by density functional theory (DFT) calculations. This research not only provides a feasible method for lithium extraction from high Na/Li ratio leachates but also offers useful insights for industrial applications, highlighting the potential of bifunctional extractants in sustainable lithium recovery.