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

摘要

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) [C_8mim][NTf_2]. 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 0.5M HNO_3 and the extraction trend of the actinides was found out to be Am(III). Pu(IV), Np(IV) q UO~(-2)_2, PuO~(-2)_2 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 cationexchange 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.