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

Extraction of U(VI) in HNO₃ to 1-butyl-3-methylimidazolium nonafluorobutanesulfonate (BMINfO) by using N-dodecyl-2-pyrrolidone as an extractant has been investigated. With increasing the concentration of HNO₃ from 0.01 to 3.0 mol/dm³ (M), distribution ratio decreased. This suggests that uranyl ions are extracted by ion exchange with a cation component of BMINfO, i.e. BMI⁺. The amount of BMI⁺ transferred to aqueous phase accompanied by extraction of U(VI) was evaluated with ¹H NMR measurement. Plots of the amount of U(VI) extracted versus the amount of BMI⁺ transferred from BMINfO phase to the aqueous phase indicated linear relationship. The slope of the line was about 1.0 and 0.63 in the extraction system of U(VI) performed in 0.1 and 1.0 M HNO₃, respectively. This result means that two types of extraction mechanisms exist depending on the concentration of HNO₃. One is the ion exchange mechanism. Another is the ion-pair extraction mechanism.