Studies on extraction equilibrium of rare earths in ion liquid extraction system using 1-butyl-3-methyl-imidazolium hexafluorophosphate and 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5

The extraction equilibrium of four rare earth ions (REn+, n = 3 or 4) was investigated in ionic liquid (IL) extraction system using 1-butyl-3-methyl-imidazolium hexafluorophosphate ([Bmim]PF6) ionic liquid as extraction solvent and 1-pheny1-3-methy1-4-benzoyl-pyrazolone-5 (HPMBP, HP) as extractant. The extraction percentage could be higher than 99%. The extracted species in the REn+[Bmim]PF6-HP system was neutral REPn (n = 3 or 4) and complete recovery of REn+ extracted into [Bmim]PF6 can be achieved using diluent HCl as stripping agent. [Bmim]PF6 can be recycled in the experiment. The extraction equilibrium constants and the pH(1/2) values of four REs and their separation factors between adjacent rare earths were estimated and comparatively studied.