Highly Selective, exothermic and ligand free separation of plutonium from uranium and americium into ionic liquids

Highly efficient and selective separation of Pu from its mixture with U and Am was demonstrated using ionic liquids containing ammonium and phosphonium cations with maximum separation factors of 320 and 2400 from U and Am, respectively. At 8 M HNO3, the D-Pu(IV) values followed the order: tri-n-hexyl-n-tetradecyl phosphonium bis(trifluoromethylsulfonyl)imide (Hex(3)TDecP center dot NTf2) > n-butyl trimethyl bis(trifluoromethylsulfonyl)imide (BuMe3N center dot NTf2) > methyl-tri-n-butyl ammonium bis(trifluoromethylsulfonyl)imide (Bu3MeN center dot NTf2) though the mass transfer rates were slow. The Pu extraction from different mineral acids at 8 M showed the following trend: D-HNO3 > D-HCl > D-H3PO4 > D-HClO4 > D-H2SO4. At 8 M HNO3, the anionic species of plutonium Pu(NO3)(6)(2-) was extracted into the ionic liquid phase by forming an 1:2 stoichiometric complex like (R4N)(2).Pu(NO3)(6) or (R4P)(2).Pu(NO3)(6) species with these ionic liquids. The extraction process was spontaneous and showed similar trend in Delta G values (Hex(3)TDecP center dot NTf2 similar to -21.48 kJ mol(-1); BuMe3N center dot NTf2 similar to -21.04 kJ mol(-1) and Bu3MeN center dot NTf2 similar to -15.43 kJ mol(-1)) calculated from their respective D-Pu(IV) values. The extraction process was found to be exothermic (Delta H values for Hex(3)TDecP center dot NTf2 similar to -9.47 kJ mol(-1); BuMe3N center dot NTf2 similar to -8.84 kJ mol(-1) and Bu3MeN center dot NTf2 similar to -7.58 kJ mol(-1)) with reduction in the overall entropy of the system. Three to four contacts of 0.5 M sodium carbonate successfully back extracted the extracted plutonium from the ionic liquid phases in a quantitative manner (>99.99 %). The following trend was observed for the radiolytic stability of these solvent systems: Hex(3)TDecP center dot NTf2 > BuMe3N center dot NTf2 > Bu3MeN center dot NTf2.