Tributyl Phosphate-Ionic Liquid System for Selective Lithium Extraction from Acid Leachate of Waste LiFePO4 Battery Cathode

The rapid expansion in the demand for LiFePO 4 (LFP) batteries has created a pressing need for recycling waste LFP batteries. However, the direct extraction of lithium from their acid leachate remains a significant challenge. This study developed a novel extraction system using tributyl phosphate (TBP) as extractant and ionic liquids (ILs) as co-extractant for selective recovery of Li + from H 2 SO 4 leachate of waste LFP cathode. The single-factor experiment results demonstrated that TBP-[C 4 mim][NTF 2 ] (1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide) exhibited higher lithium extraction efficiency under acidic conditions compared to TBP-[C 4 mim][PF 6 ] (1-Butyl-3-methylimidazolium hexafluorophosphate). Moreover, a four-stage cross-current extraction process utilizing the TBP-[C 4 mim][NTF 2 ] system was demonstrated to efficiently and selectively extract lithium from a real H 2 SO 4 leachate, achieving extraction efficiency and separation factor of 92.39% and 197.95, respectively. Mechanism insights from Fourier transform infrared spectroscopy (FT-IR) and theoretical calculations indicate that cationic exchange and a synergistic effect between TBP and IL enhance the selective extraction of lithium. The cation of IL (C 4 mim + ) enters aqueous phase, and Li + are extracted into organic phase in the form of Li + -TBP-[NTF 2 ] - with a larger binding energy. Furthermore, five cycles of extraction and stripping experiments not only yielded a lithium-enriched solution but also demonstrated the excellent stability of the TBP-[C 4 mim][NTF 2 ]. Finally, the Li + was ultimately recovered as high-purity Li 3 PO 4 via the chemical precipitation method. This study provides theoretical and technical references for efficient extraction of lithium from LFP acid leachate, which is crucial for comprehensive utilization of waste LFP cathodes.