熔盐脉冲电解精炼Pb-Bi(Zn)-U-Ln合金过程的原位监测及机理的研究

In-situ monitoring of molten salt pulse electrorefining of Pb-Bi(Zn)-U-Ln(Ln=Sm,Ce) alloys was carried out in chloride molten salt system, in view of the deficiency of kinetic data and separation efficiency of lanthanide (Ln) and actinide (An) at present. The electrochemical behavior of U, Ln on the liquid Pb-Bi and Pb-Zn binary alloys cathodes was studied, and the effect of Bi and Zn content in liquid lead on the potential difference between U and Ln was investigated. The activity, activity coefficient and diffusion coefficient of U and Ln in alloys were determined, and the thermodynamic properties of multicomponent alloys were evaluated. Selective electrodeposition and anodic oxidation were employed by pulse electrorefining to achieve high efficient extraction and separation of U and Ln. The U(III) and Ln(III) ions concentration calibration curve was drawn, and the electrorefining process was in-situ monitoring by electrochemical method combined with the calibration curve. A comprehensive analysis on the extraction and separation efficiency of U and Ln were made during the electrorefining process, the control steps, kinetics, thermodynamics of electrorefining process were investigated, and further revealing the electrochemical mechanism of U selective electrodeposition and selective anodic dissolution. The research results can provide the basic data and promising cathode candidate materials for the separation between the lanthanides and actinides in molten salt reactor spent fuel reprocessing process.

针对目前镧系元素(Ln)和锕系元素(An)的动力学数据匮乏、分离效率不够高的缺憾，开展原位监测氯化物熔盐脉冲电解精炼Pb-Bi(Zn)-U-Ln(Ln=Sm,Ce)合金的研究工作。研究U、Ln在液态Pb-Bi、Pb-Zn二元合金阴极上的电化学行为，以及液态Pb中Bi、Zn的含量对U和Ln电位差的影响，测定金属U、Ln在合金中的活度、活度系数，评估多元合金的热力学性质。采用脉冲电解精炼选择性电沉积及阳极溶解实现U和Ln的高效分离。绘制U(III)、Ln(III)离子浓度校准曲线，结合校准曲线，通过电化学方法原位监测电解精炼过程。综合分析电解精炼过程中影响U、Ln的提取、分离效率因素，找出电解精炼过程的控制步骤，研究电解精炼过程的动力学和热力学，进而揭示选择性电沉积、选择性阳极溶解的电化学机理，为熔盐堆乏燃料后处理过程中提高镧系元素和锕系元素之间的分离提供基础数据和有前途的阴极候选材料。

本项目基于目前铀和镧系元素的动力学数据匮乏、分离效率不够高的缺憾，开展了原位监测液态合金阴极熔盐脉冲电解提取分离的研究工作。.（1）研究了铀、镧系元素(Sm, Eu, Gd, Dy, Yb)在LiC1-KCl熔盐中液态Pb、液态Pb-Bi合金阴极上的电化学行为、热力学、动力学和选择性电沉积机理，测定了研究温度下的Pb(Bi)-U(Sm, Eu, Gd, Dy, Yb)金属间化合物的峰电位、平衡电位、热力学和动力学性质。.（2）U和镧系元素在液态Pb阴极和液态Pb-Bi合金阴极上均发生欠电位沉积，铀比镧系元素的析出电位更正，铀在合金阴极上的析出电位比液态Pb更正，这是由于液态铅中铋的引入改变了它们的活度，进而改变了沉积电位。.（3）对比分析了Gd、Eu在液态Pb阴极和液态Pb-Bi合金阴极上的动力学性质，发现固溶体Eu(Pb-Bi)/Eu(II)和Gd(Pb-Bi)/Gd(III)电对的交换电流密度均大于Eu(Pb)/Eu(II)和Gd(Pb)/Gd(III)，而Eu(Pb-Bi)/Eu(II)和Gd(Pb-Bi)/Gd(III)电极反应的活化能小，所以Eu(II)和Gd(III)在液态Pb-Bi合金阴极上比Pb上的反应速度更快动力学结果与热力学研究结果相同。.（4）系统的评估并比较了不同参数的脉冲电位电解、恒电流电解、恒电位电解法对电流效率、分离因子、提取效率、晶体的形貌、晶体尺寸的影响，研究结果表明脉冲电位电解法更适合干法后处理流程。.（5）研究并比较了三种电化学方法结合误差分离和ICP-MS原位监测熔盐脉冲电解提取分离镧系裂片元素的过程，建立了快速、准确的原位监测乏燃料干法后处理过程中金属离子浓度的方法。