DGA-grafting pyridine for ultra-selective and prior extraction of 99TcO4− from simulated spent nuclear fuel

Selective and prior extraction of ⁹⁹TcO₄^- ahead of uranium and plutonium separation is a beneficial strategy for the modern nuclear fuel cycle. Herein, a novel DGA-grafting pyridine ligand BisDODGA-DAPy (L1) was tailored for the efficient separation of TcO₄^- from simulated spent nuclear fuel based on the selectivity of pyridine and synergistic effect of diglycolamide (DGA) group. Compared to the ligands BisDOSCA-DAPy (L2) and BisDODGA-MPDA (L3) with similar structure, BisDODGA-DAPy (L1) demonstrated the better separation performance including good extraction efficiency, reusability, and high loading capacity for TcO₄^- under high acidic medium. The interactions of the ligands with Tc(VII)/Re(VII) have been investigated in detail using FT-IR, ¹H NMR titration, UV-Vis spectrophotometric titration, ESI-HRMS and DFT simulations. The extraction mechanism affected by the protonation of ligand was elucidated under different acidity. BisDODGA-DAPy (L1) demonstrated the ultra-selective extraction ability for TcO₄^- from simulated spent nuclear fuel. The maximum SF_Tc/U and SF_Tc/Pu values were up to 1.29 × 10⁴ and 5.08 × 10³, respectively. In the presence of 9 × 10⁴-fold excess of NO₃^-, the extraction of TcO₄^- was almost unaffected. Moreover, the good radiolytic stability further highlights the promising potential of this ligand for ⁹⁹Tc separation. DFT calculation revealed the dominant role of DAPy and DODGA in TcO₄^- extraction, providing the theoretical evidence for BisDODGA-DAPy (L1) to selectively bind TcO₄^- over NO₃^-.