基于电化学方法的水溶液中高价态镅的分离研究

Separation between trivalent lanthanides, Ln(III) and actinides, An(III) is a key step in “partitioning and transmutation” of spent fuel reprocessing, and is of great importance for advanced nuclear fuel cycle. However, the separation remains one of the most challenging tasks in radiochemistry historically due to the similarities of physico-chemical properties between these trivalent ions. Traditional liquid-liquid extraction is the basic separation method, whose key point lies in finding proper ligands with “soft” donor atoms such as S/N as they preferentially complex An(III) in favor of Ln(III). For now each extractant has its own shortcomings nonetheless and needs to be further investigated (esp. the anti-radiation stability is quite desired)..Other than its common +III oxidation state, americium (Am) can be brought to +V/+VI valence with the help of strong oxidants, existing as actinyl cations (AnO2+ and AnO22+) in aqueous phase that exhibit solution chemistries quite different from that of the trivalent lanthanides and curium. Hence to utilize higher oxidation state of Am becomes a feasible approach to solve aforementioned problem. Given the various limitations of chemical oxidation of Am(III), we have proposed to study the electrochemical pathway of such Am-oxidation reactions in this project. The application of electrode modified by appropriate Am binding ligand can lower the redox potentials and facilitate the reaction kinetics than conventional method in noncomplexing media, followed by well-developed solvent extraction, solid phase extraction, ion exchange etc. which may potentially lead to new Ln(III)/An(III) and Am/Cm separation strategies and development of radionuclide partitioning technologies.

三价镧系元素与锕系元素的分离是“分离-嬗变”法进行乏燃料后处理的一环，对建立先进核燃料循环意义重大。由于这些元素的电子结构、半径与化学性质极为相似，实现其有效分离一直是放射化学领域最富挑战性的研究内容之一。溶剂萃取是三价镧锕分离的基本方法，但目前各萃取剂均有不足，使用条件较复杂且辐照稳定性不佳，面临不少挑战。鉴于镅在强氧化剂作用下可呈现+V/+VI价且在水溶液中以酰基离子形式存在，与水合镧系离子及锔离子有较大性质差异，故实现高价态镅的富集与分离成为解决此难题的可行之道。常规化学方法氧化有诸多限制条件，本项目拟以电化学手段进行水溶液中Am(III) 氧化至高价态的研究，用选择性配位基团修饰的电极直接电解可有效降低氧化还原势垒，加快反应速率，随后进行溶剂萃取、固相萃取、离子交换等，可引申出崭新的镧锕分离及锕系组内分离（尤其是镅锔分离）的方略，具有良好的应用前景。