Lithium extraction from synthetic brine with high Mg2+/Li+ ratio using the polymer inclusion membrane

Lithium extraction from brines with the high Mg2+/Li+ ratio is crucial for sustainable lithium resource and environmental protection. This study incorporated the classic tributylphosphate (TBP)/FeCl3 system into the polyvinyl chloride (PVC) based polymer inclusion membrane (PIM) to extract Li+ from the solution which is rich of Mg2+ (The initial Mg2+/Li+ molar ratio is 15). The morphology and composition of PIMs were characterized systematically, and the content of TBP/FeCl3 carrier in the PIM was optimized. Compared to liquid-liquid extraction, the extraction ratio of Li+ for PIM extraction increases by 20% and the separation factor of Li+ over Mg2+ increases by 5%. Besides, the loss ratio of Fe3+ after one loop of liquid-liquid extraction is 17.79%, which is close to that of PIM extraction after three loops (18.30%), demonstrating that the PIM showed a good stability. Furthermore, the separation factor of Li+ over Mg2+ for the PIM with 50 wt% TBP/FeCl3 is as high as 176 and the initial flux for Li+ is 8.12 × 10−4 mol m−2 h−1. This study displays a TBP/FeCl3 based PIM with high selectivity for Li+, providing a possible membrane technology for lithium extraction from brines.