Abstract
The treatment of anionic 99TcO4− in the waste tank with high alkalinity is still very challenging. In this work, a new temperature-responsive alkaline aqueous biphasic system (ABS) based on (tri-n‑butyl)-n-tetradecyl phosphonium chloride (P44414Cl) was developed to remove radioactive 99TcO4−. The phase transition mechanism was studied by cloud point titration, small-angel X-ray scattering, dynamic light scattering, and molecular dynamic simulations. As the NaOH concentration or temperature increased, the P44414+ micelle could grow and aggregate. This micelle showed a particularly high affinity toward ReO4−/99TcO4− compared to other competing anions and could directly extract more than 98.6% of 99TcO4− from simulated radioactive tank waste supernatant. Furthermore, the loaded 99TcO4− could be easily stripped by using concentrated nitric acid rather than metal salt-based reductants. This work clearly demonstrates that the alkaline ABS is a promising separation system for solving the technetium problem in the alkaline waste tank.
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