镅的化学氧化及电化学氧化研究进展

Advances in Chemical and Electrochemical Oxidation of Americium

三价锕系/镧系元素(Am^(3+)/Ln^(3+))的分离是开发先进核燃料循环以实现核能可持续应用的关键。由于二者在水溶液中的化学行为相似,通过液-液萃取来实现二者的有效分离仍然面临挑战。镅的氧化分离作为替代方法因其高效率和大的改进空间而受到越来越多的关注。由于Am(Ⅳ/Ⅲ)电对的氧化电势高,使得高价态镅制备困难,并且新生成的高价态镅具有强氧化性,需要调控其种态以避免被溶液中存在的还原性物质还原。因此,研究Am的氧化分离途径需要解决两个问题:(1)降低Am的氧化电势,实现在较温和条件下的选择性氧化;(2)稳定高价态Am并及时进行分离。本文综述了近年来面向镧锕分离的Am的化学氧化和电化学氧化研究进展。在Am的化学氧化中,高碘酸铜(Ⅲ)表现出比铋酸盐和过硫酸盐更高的活性和氧化效率。在Am的电化学氧化中,通过选择合适的配体对电极进行修饰,可显著降低Am(Ⅳ/Ⅲ)的氧化电势,避开电解水等影响电化学氧化效率的副反应。这些新的认识为镧锕分离提供了新的思路,也提出了对深入理解微观机制的需求。

Efficient trivalent actinides/lanthanides(Am^(3+)/Ln^(3+))separation is one of the key components of advanced nuclear fuel cycle.Owing to their similar chemical behavior in condensed phase,it remains a challenge to adopt traditional liquid-liquid extraction techniques.The strategy of separating Am by oxidizing Am(Ⅲ)to its penta-and hexa-valent states has the benefit of high efficiency and large space of improvement and is attracting growing attention.The obstacle to adopt this strategy is the high oxidation potential,which impedes the efficient conversion of Am(Ⅲ)to Am(Ⅴ,Ⅵ)under mild conditions,and the low stability of high oxidation states of Am.This poses two questions to solve:(1)how to minimize the oxidation potential of Am?(2)how to stabilize Am in its high oxidation state?In this work,we surveyed the advances in the chemical and electrochemical oxidation of Am towards its separation from lanthanides.In its chemical oxidation,copper(Ⅲ)periodate was identified as a superior oxidants over bismuthate and persulfate in view of its high oxidizing power and high yield of Am(Ⅴ,Ⅵ).In its electrochemical oxidation,functionalization of electrode by appropriate ligands can significantly decrease the oxidation potential of Am and increase the overpotential of water,which circumvents the side reactions,e.g.oxidation of water.These results provide insights for the design and optimization of novel protocols for Am/Ln separation,and calls for improved understanding of the underlying mechanisms to stimulate extensive advances of efficient Am/Ln separation.