Electroanalytical Measurements of Binary-Analyte Mixtures in Molten LiCl-KCl Eutectic: Gadolinium(III)- and Lanthanum(III)-Chloride

Abstract

Electroanalytical measurements, such as cyclic voltammetry and chronopotentiometry, have been applied by other researchers to many eutectic LiCl-KCl mixtures containing a single analyte, typically a rare earth or actinide ion. These measurements have demonstrated the applicability of electroanalytical measurements of concentration in molten LiCl-KCl eutectic, which is prevalently used as an electrolyte in the electrorefining of used nuclear fuel (UNF). However, UNF electrorefiners contain multiple actinide and rare earth ions, necessitating the ability to make electroanalytical measurements in multi-analyte mixtures. The presence of multiple analytes creates interferences and overlapping signals. Chronoamperometry, cyclic voltammetry (CV), chronopotentiometry and open-circuit potential measurements were performed in eutectic LiCl-KCl mixtures containing a range of GdCl3 and LaCl3 concentrations to explore the issues associated with applying electroanalytical techniques in multi-analyte molten salt mixtures and to develop possible solutions. CV was found to be most promising for separating and analyzing each ion's signal. CV measurements were semi-differentiated and correlated to concentration using peak heights and principal component regression (PCR) to determine the concentration from electrochemical signals. The lowest average relative error was obtained using PCR for Gd3+ (6.21%) and using peak height correlations for La3+ (10.4%).