Li Xiao-Bo, Wu Qun-Yan, Wang Cong-Zhi, Lan Jian-Hui, Zhang Meng, Chai Zhi-Fang, Shi Wei-Qun
Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, College of Nuclear Science and Technology, Harbin Engineering University, Harbin, Heilongjiang 150001, China.
Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
J Phys Chem A. 2023 Sep 14;127(36):7479-7486. doi: 10.1021/acs.jpca.3c03830. Epub 2023 Sep 5.
The separation of plutonium (Pu) from spent nuclear fuel was achieved by effectively adjusting the oxidation state of Pu from +IV to +III in the plutonium uranium reduction extraction (PUREX) process. Acetaldoxime (CHCHNOH) as a free salt reductant can rapidly reduce Pu(IV), but the reduction mechanism remains indistinct. Herein, we explore the reduction mechanism of two Pu(IV) ions by one CHCHNOH molecule, where the second Pu(IV) reduction is the rate-determining step with the energy barrier of 19.24 kcal mol, which is in line with the experimental activation energy (20.95 ± 2.34 kcal mol). Additionally, the results of structure and spin density analyses demonstrate that the first and second Pu(IV) reduction is attributed to hydrogen atom transfer and hydroxyl ligand transfer, respectively. Analysis of localized molecular orbitals unveils that the reduction process is accompanied by the breaking of the Pu-O bond and the formation of the O-H and C-O bonds. The reaction energies confirm that the reduction of Pu(IV) by acetaldoxime is both thermodynamically and kinetically accessible. In this work, we elucidate the reduction mechanism of Pu(IV) with CHCHNOH, which provides a theoretical understanding of the rapid reduction of Pu(IV).
在钚铀还原萃取（PUREX）过程中，通过有效调整钚（Pu）的氧化态从+IV至+III，实现了从乏核燃料中分离钚。乙醛肟（CHCHNOH）作为一种游离盐还原剂能够快速还原Pu(IV)，但其还原机理仍不明确。在此，我们探究了一个CHCHNOH分子对两个Pu(IV)离子的还原机理，其中第二步Pu(IV)还原是速率决定步骤，能垒为19.24千卡/摩尔，这与实验活化能（20.95±2.34千卡/摩尔）相符。此外，结构和自旋密度分析结果表明，第一步和第二步Pu(IV)还原分别归因于氢原子转移和羟基配体转移。定域分子轨道分析表明，还原过程伴随着Pu - O键的断裂以及O - H键和C - O键的形成。反应能量证实，乙醛肟还原Pu(IV)在热力学和动力学上都是可行的。在这项工作中，我们阐明了乙醛肟还原Pu(IV)的机理，这为理解Pu(IV)的快速还原提供了理论依据。
