Voltammetric Analysis of Mixtures of Molten Eutectic LiCl-KCl Containing LaCl3 and ThCl4 for Concentration and Diffusion Coefficient Measurement

Several electrochemical techniques, including cyclic voltammetry (CV), chronopotentiometry-open circuit potential (CP-OCP), chronoamperometry (CA) and normal pulse voltammetry (NPV) were applied to the eutectic LiCl-KCl melt containing LaCl3 and ThCl4 at 773K. The dependence of diffusion coefficient of La(III) on concentration of LaCl3 was investigated by using CV, CP and CA. As the concentration of LaCl3 increases, the DLa(III) value obtained from CV gradually decreases, while the values derived from CA and CP exhibit a dome-shaped variation trend. In the LiCl-KCl-LaCl3-ThCl4 system, the diffusion coefficients of La(III) and Th(IV) are both approximately constant regardless of changes in the composition of LaCl3 and ThCl4. Concentration correlations were developed for LaCl3 and ThCl4 using the normalized CV peak heights in addition to the diffusion-limited relationships for CV, CA and NPV. NPV was found to be superior for the concentration prediction over the range studied in this work.