Extraction mechanisms of uranyl ions by 1-butyl-3-methylimidazolium nonafluorobutanesulfonate containing N-dodecyl-2-pyrrolidone

► Extraction of U(VI) in HNO3 to ionic liquids (ILs) has been investigated. ► As an IL, 1-butyl-3-methylimidazolium nonafluorobutanesulfonate (BMINfO) is used. ► BMINfO is containing N-dodecyl-2-pyrrolidone as an extractant of U(VI). ► Extraction mechanisms depending on the concentration of HNO3 are discussed. ► The ion exchange mechanism and the ion-pair extraction mechanism are suggested.