A Green and Innovative Approach to Separate Hexafluorophosphate from Wastewater

Effluent derived from spent lithium-ion batteries (LIBs) electrolyte or discarded ionic liquids (ILs) is a potentially resource of hexafluorophosphate (PF6-) which can be recovered through solvent extraction. In this study, an efficient extraction approach was proposed to recover the hexafluorophosphate from solutions. The effects of extractant (Alamine336) and modifier (TBP), common anions and metallic ions in waste-streams, initial pH, and temperature on the extraction efficiency were explored. The organic phase exhibited an excellent extraction capability of more than 95% under optimal condition. Moreover, it was found that the use of sodium hydroxide as stripping reagent presented a superb stripping and cycling properties. Thermodynamic analysis and spectral data indicated that PF6- was extracted into the organic phase in the form of R3NHâ‹…PF6, which is a spontaneous exothermic process. The novel extraction method provides a broad application perspective for the removal and recovery of valuable hexafluorophosphate from aqueous system.