摘要
钍的分离和再利用是熔盐堆钍铀燃料循环的重要组成部分,钍与裂变产物特别是化学性质相似的镧系元素的分离是熔盐堆氟盐燃料处理的关键之一。利用循环伏安法和方波伏安法研究了773 K下多种镧系元素氟化物(w=3%)在LnF_3-LiCl-KCl熔盐中的电化学行为。研究结果表明:Ce^(3+)和Gd^(3+)在惰性电极上均一步还原为金属,Nd^(3+)则是通过两步反应还原为金属,而Sm^(3+)和Eu^(3+)只能还原为低价态的Sm^(2+)和Eu^(2+);Th和Ln在惰性金属阴极上的析出电位差ΔE均大于0.19 V,在LiCl-KCl熔盐体系中实现Th与Ln的电化学分离在理论上是可行的;与纯氯盐体系相比,少量F-的引入不会改变Ln^(3+)在惰性电极上的电极反应过程,F-的存在使得Ln^(3+)在LiCl-KCl熔盐中的活度降低,从而导致扩散系数减小。此研究结果为了解Th4+)和Ln^(3+)在含F-氯盐体系中的电化学行为和建立可行的分离方法提供了基础实验依据。
[Background] The separation and cyclic utilization of thorium is an important part of thorium-uranium fuel cycle for molten salt reactor. Therefore, separation of thorium from fission products, especially lanthanides, is the key step to electrochemical separation of thorium in molten salt because of their similar chemical properties. [Purpose] The aim of this work is to explore the influence of fluorine ion（F^-） on electrochemical properties of 5 lanthanides in LnF3-LiCl-KCl molten salt and to confirm the feasibility of electrochemical separation of thorium from lanthanides in chloride molten salt. [Methods] Transient electrochemical techniques such as cyclic voltammetry and square wave voltammetry were employed to investigate the reduction mechanism and diffusion coefficient of Ln ions on a tungsten inert electrode. [Results] In LnF3-LiCl-KCl molten salt, Ce^3＋ and Gd^3＋ were reduced into metal Ce and Gd according to a one-step process by exchanging 3 electrons; Nd^3＋ was reduced into metal Nd through two steps; Sm^3＋ and Eu^3＋ couldn＇t be reduced into metal in tungsten electrode, and both of them were transformed into divalent state. The existence of F-would not change the electrode reaction process of Ln cations. The differences of deposition potential between Th and the 5 Lns on inert electrode were larger than 0.19 V, which demonstrated theoretically that it was feasible to separate Th from Lns in LiCl-KCl molten salt. Compared with pure chloride molten salt, the existence of F-decreased the activity of Ln^3＋, resulting in the decrease of diffusion efficiency of all Ln ions. [Conclusion] The study provided experimental foundation for feasibility investigation of the separation of thorium fluoride from lanthanides fluoride in LiCl-KCl molten salt.
作者
王先彬
龙德武
朱铁建
郑海洋
蒋锋
佘长锋
黄卫
李晴暖
WANG Xianbin;LONG Dewu;ZHU Tiejian;ZHENG Haiyang;JIANG Feng;SHE Changfeng;HUANG Wei;LI Qingnuan(Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Jiading Campus, Shanghai 201800, China;University of Chinese Academy of Sciences, Beijing 100049, China)
出处
《核技术》
CAS
CSCD
北大核心
2018年第6期22-29,共8页
Nuclear Techniques
基金
中国科学院战略先导科技专项(No.XDA02030200)
中国科学院青年创新促进会课题(No.2017307)资助
国家自然科学基金(No.21601200)~~
