DGA-grafting pyridine for ultra-selective and prior extraction of 99 TcO 4 - from simulated spent nuclear fuel.

Selective and prior extraction of ⁹⁹ TcO ₄ ^- 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 TcO ₄ ^- 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 TcO ₄ ^- under high acidic medium. The interactions of the ligands with Tc(VII)/Re(VII) have been investigated in detail using FT-IR, ¹ H 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 TcO ₄ ^- from simulated spent nuclear fuel. The maximum SF _Tc/U and SF _Tc/Pu values were up to 1.29 × 10 ⁴ and 5.08 × 10 ³ , respectively. In the presence of 9 × 10 ⁴ -fold excess of NO ₃ ^- , the extraction of TcO ₄ ^- was almost unaffected. Moreover, the good radiolytic stability further highlights the promising potential of this ligand for ⁹⁹ Tc separation. DFT calculation revealed the dominant role of DAPy and DODGA in TcO ₄ ^- extraction, providing the theoretical evidence for BisDODGA-DAPy (L1) to selectively bind TcO ₄ ^- over NO ₃ ^- .
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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