FLiBe熔盐中铀与镧系(Eu、Sm、Yb、La、Ce和Ho)氟化物的电化学性质及分离

Electrochemical properties and separation of uranium from lanthanide(Eu,Sm,Yb,La,Ce,and Ho)fluorides in FLiBe molten salt

利用电化学方法在熔盐介质中进行乏燃料的后处理分离是干法后处理中研究最广泛的技术之一,其核心内容就是采用电解法实现锕系元素和镧系元素分离。本文采用循环伏安法、方波伏安法和恒电位电解法研究了FLi Be(Li F-Be F_(2))熔盐中UF_(4)和Ln F_(3)(Ln=Eu、Sm、Yb、La、Ce和Ho)的电化学行为和分离可行性,在FLi BeUF_(4)-Ln F_(3)混合熔盐体系中使用W电极开展了UF_(4)与Ln F_(3)电解分离研究。结果表明:在惰性钨(W)电极上U4+的氧化还原反应分为两步,分别是U^(4+)+e^(-)→U^(3+)和U^(3+)+3e^(-)→U^(0),而Yb^(3+)、Sm^(3+)、Eu^(3+)只能发生一电子转移还原为+2价态的Yb^(2+)、Sm^(2+)、Eu^(2+)的离子,La^(3+)、Ce^(3+)和Ho^(3+)离子在FLi Be熔盐电化学窗口内则没有明显的电化学信号;X射线衍射(X-ray Diffraction,XRD)和能量色谱仪(Energy Dispersive Spectrometer,EDS)结果证明了W电极上的电解产物为金属U、UF_(3)和夹带的熔盐,而不含有Ln F_(3)的电解产物。这些研究结果为熔盐堆燃料中锕系元素和镧系元素的分离提供了基础数据。

[Background]Molten salt electrochemical separation of spent fuel in molten salt medium is one of the most widely studied technologies in pyroprocessing.It is based on the use of electrolysis to achieve the separation.[Purpose]This study aims to investigate the separation of actinides and lanthanides in situ using high-temperature molten salt media.[Methods]Cyclic voltammetry(CV),square wave voltammetry(SWV),and constant potential electrolysis were employed to study the electrochemical behavior and separation feasibility of UF_(4) and LnF_(3)(Ln=Eu,Sm,Yb,La,Ce,and Ho)in FLiBe molten salt.Firstly,the eutectic salt was prepared,followed by the precise measurement and mixing of FLiBe molten salt and UF_(4) or LnF_(3)powder in accordance with the desired concentration ratio.Then,the electrochemical behavior of uranium and lanthanide elements in FLiBe molten salt was experimentally studied using electrochemical CV and SWV.Subsequently,the constant potential electrolysis method was employed to achieve the electrochemical deposition of uranium or lanthanide elements.Finally,the feasibility of separating uranium and lanthanide elements in FLiBe molten salt was evaluated through X-ray diffraction(XRD)and energy-dispersive X-ray spectroscopy(EDS)analysis of the electrolysis products.[Results]Experimental results show that U4+undergoes two electron transfer reductions on an inert tungsten electrode,namely U^(4+)+e^(−)→U^(3+)and U^(3+)+3^(e−)→U^(0),while Yb^(3+),Sm^(3+),and Eu^(3+)have only one electron transfer reduction,leading to the+2 valence state of Yb^(2+),Sm^(2+),and Eu^(2+)ions,respectively.In addition,La^(3+),Ce^(3+),and Ho^(3+)ions do not exhibit significant electrochemical signals within the electrochemical window of FLiBe molten salt.The findings from XRD and EDS analyses verify that the electrolysis products presented on the W electrode consist of metal U,UF_(3),and entrain molten salt,with no lanthanide(Ln=Eu,Sm,Yb,La,Ce,and Ho)electrolytic deposition product detected.[Conclusions]The suitable electrolytic separation method developed in this study provides basic data to separate actinides and lanthanides from molten salts.