Extracting TcO₄^–/ ReO₄^– from the Alkaline Solution by the Imidazolium-Based Ionic Liquid–Aqueous Biphasic System

With the advancement of the nuclear industry, recovering 99TcO4– from alkaline waste has become urgently necessary. In this study, an alkaline aqueous biphasic system (ABS) based on an imidazolium-based ionic liquid (IL) was developed to meet this demand. The phase transition mechanism was investigated by using cloud point titration, small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS). The ABS was formed through the aggregation and growth of imidazolium micelles, which were influenced by the NaOH/IL concentration and temperature. Furthermore, the anion exchange extraction mechanism was identified through Fourier transform infrared spectroscopy (FT-IR), electrospray ionization mass spectrometry (ESI-MS), Raman spectroscopy, and 1H NMR and 13C NMR analyses. This IL-ABS demonstrated high loading capacity, fast kinetics, and high selectivity for ReO4– (an analogue for radioactive 99TcO4–) and could recover over 95% of ReO4– from a simulated radioactive tank waste supernatant with high concentrations of NaOH and competing anions. Additionally, the loaded ReO4– could be easily stripped by using nitric acid. Compared with traditional separation methods, alkaline ABS is efficient and green, showing promising application prospects for the removal of 99TcO4– from nuclear alkaline waste.