Solvent extraction of plutonium(IV) in monoamide – ammonium ionic liquid mixture

• First time evaluation of diluent behavior of [N1888][NTf2] for Pu(IV) extraction.
• Efficient extraction of Pu(IV) by ionic liquid alone.
• Mechanistic pathway is different as compared to imidazolium ionic liquid diluents.
• Easy stripping from ionic liquid phase by dilute nitric acid.

The extraction behavior of plutonium(IV) was studied in the room temperature ionic liquid, trioctylmethylammonium bis(trifluoromethanesulfonyl)imide ([N1888][NTf2]) containing a monoamide, N,N-dihexyloctanamide (DHOA). The unusual extraction of Pu(IV) observed in this ionic liquid system was reported in this paper. The extraction behavior of plutonium(IV) was investigated as a function of various parameters, such as feed acid concentration, extractant and ionic liquid concentration, type of the extractants, equilibration time and temperature. Changing the extractant from DHOA to tri-n-butyl phosphate reduced the distribution ratio of Pu(IV). The extraction trend of Pu(IV) in neat [N1888][NTf2] was compared with those observed in other ionic liquids such as 1-alkyl-3-methylimidazolium bistriflimide ([Cnmim][NTf2]). Pu(IV) extraction in [N1888][NTf2] was found to follow a combination of anion exchange mechanism and neutral solvation pathway at feed acidities above 2 M HNO3. The extraction of Pu(IV) in DHOA/[N1888][NTf2] was also compared with those observed in a molecular diluent system, DHOA/n-DD. All thermodynamic parameters governing the extraction of plutonium(IV) in [N1888][NTf2] was determined and discussed in detail. Stripping of Pu(IV) from the loaded ionic liquid phase was performed using dilute nitric acid.