Wang Zhipeng, Lu Jun-Bo, Dong Xue, Yan Qiang, Feng Xiaogui, Hu Han-Shi, Wang Shuao, Chen Jing, Li Jun, Xu Chao
Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China.
Department of Chemistry, Southern University of Science and Technology, Shenzhen 518055, China.
J Am Chem Soc. 2022 Apr 13;144(14):6383-6389. doi: 10.1021/jacs.2c00594. Epub 2022 Mar 30.
Lanthanide/actinide separation is a worldwide challenge for atomic energy and nuclear waste treatment. Separation of americium (Am), a critical actinide element in the nuclear fuel cycle, from lanthanides (Ln) is highly desirable for minimizing the long-term radiotoxicity of nuclear waste, yet it is extremely challenging given the chemical similarity between trivalent Am(III) and Ln(III). Selective oxidation of Am(III) to a higher oxidation state (OS) could facilitate this separation, but so far, it is far from satisfactory for practical application as a result of the unstable nature of Am in a high OS. Herein, we find a novel strategy to generate stable pentavalent Am (Am(V)) through coordination of Am(III) with a diglycolamide ligand and oxidation with Bi(V) species in the presence of an organic solvent. This strategy leads to efficient stabilization of Am(V) and an extraordinarily high separation factor (>10) of Am from Ln through one single contact in solvent extraction, thereby opening a new avenue to study the high-OS chemistry of Am and fulfill the crucial task of Ln/Am separation in the nuclear fuel cycle. The synergistic coordination and oxidation process is found to occur in the organic solvent, and the mechanism has been well elucidated by quantum-theoretical modeling.
镧系元素/锕系元素的分离是全球在原子能和核废料处理方面面临的一项挑战。在核燃料循环中，将关键的锕系元素镅（Am）与镧系元素（Ln）分离，对于将核废料的长期放射性毒性降至最低非常有必要，但鉴于三价镅（Am(III)）和镧系元素（Ln(III)）之间的化学相似性，这极具挑战性。将Am(III)选择性氧化至更高氧化态（OS）有助于这种分离，但到目前为止，由于处于高氧化态的Am性质不稳定，在实际应用中远不能令人满意。在此，我们发现了一种新策略，即通过在有机溶剂存在下，使Am(III)与二甘醇酰胺配体配位并与Bi(V)物种发生氧化反应，生成稳定的五价镅（Am(V)）。该策略实现了Am(V)的有效稳定，并在溶剂萃取中通过一次接触实现了Am与Ln高达10以上的超高分离因子，从而为研究Am的高氧化态化学以及完成核燃料循环中Ln/Am分离这一关键任务开辟了一条新途径。研究发现协同配位和氧化过程发生在有机溶剂中，并且通过量子理论建模对其机理进行了很好的阐释。
