Solvent systems containing diglycolamide-functionalized calix[4]arenes in room temperature ionic liquid for metal ion extraction: studies with simulated high-level wastes

The extraction of actinide ions such as Am(III), Pu(IV), Np(IV), U(VI) and Pu(VI) was studied from simulated high-level waste (SHLW) solutions using several diglycolamide-functionalised calix[4]arene (Calix-DGA) ligands dissolved in the room temperature ionic liquid (RTIL) [C8mim][NTf2]. The Calix-DGA ligands were three lower-rim functionalised ligands with varying alkyl substituents (L-I, L-II and L-III), an upper-rim functionalised ligand (L-IV) and an upper- and lower-rim functionalised ligand (L-V). The SHLW solutions used contained 0.5 M HNO3 and the extraction trend of the actinides was found out to be Am(III) > Pu(IV)∼Np(IV)≫ and the extraction efficiency of the Calix-DGA ligands for Am(III) being L-V>L-I>L-II>L-IV>L-III. Reasonably, good extraction of Am(III) was obtained with 5.0 × 10− 4 M ligand solutions suggesting that higher concentrations of the ligand can be used for a higher loading of the metal ions. The extraction of other metal ions representing fission products, structural materials and process chemicals was studied by Inductively Coupled Plasma –Atomic Emission Spectroscopy analysis. The extraction mechanism follows the cation-exchange mechanism often observed with RTIL-based extraction systems. Enthalpy changes were measured from van't Hoff plots and were found to be significantly different than those observed with tracer studies reported previously.