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Cyclic voltammetry (CV), square wave voltammetry (SWV) and other electroanalytical methods have been applied to molten chloride salts to study metal ion behavior. These studies have been useful for understanding and optimizing the electrorefining and electrowinning of metals. Notable ions that have been studied are rare earth (RE) and actinide metals in eutectic KCl-LiCl salts. However, the behavior of lanthanum (La3+) ions (a RE metal commonly used as a glass additive, component in electric motor vehicle batteries, etc.) in some molten chlorides or chloride mixtures, such as CaCl2, has not been studied. To facilitate the study of La3+ ion behavior, electroanalytical measurements in molten salts require improved experimental techniques to perform appropriate measurements. CV experiments were conducted to evaluate La3+ behavior in eutectic LiCl-CaCl2 and CaCl2 and are compared to La3+ behavior in LiCl-KCl and CaCl2-NaCl eutectics from other studies. The electrochemical reaction was checked for reversible, quasi-reversible, and irreversible transitions in scan rate by examining the relationship between the scan rate applied and the peak current and potential for La3+ reduction. Properties such as diffusion coefficient (Do) and electrons exchanged (n) are calculated from data demonstrating reversible or irreversible behavior. The electrochemical setup was also checked for radial diffusion via error measurements for semi-infinite linear diffusion, which led to the observation that natural convection possibly effected the La3+ reduction peak at low scan rates. For more accurate electroanalytical measurements of La3+ reduction, CVs with and without LaCl3 added to CaCl2 and eutectic CaCl2-LiCl were compared to establish baselines for the La3+ reduction peak. The impact of resistance (IR) compensation on the La3+ reduction peak is also explored. Techniques and practices that optimized electroanalytical performance include placing the electrolytic cell in a Faraday cage, distancing electrodes from the heating coils, and melting the chlorides twice prior to measurements.

A comparison of square-wave voltammetry models for calculating the number of electrons exchanged in a metal deposition reaction. Square-wave voltammetry is extremely useful for isolating the behavior of a single reaction in a mixed solution of many reacting species. Being able to identify the number of electrons exchanged in a reaction is extremely useful for identifying and characterizing unknown compounds in a process, such as electrorefining, molten salt reactors, and electrolytic oxide reduction. Experiments were conducted for silver deposition on platinum in an aqueous HNO3 solution and for nickel and lanthanum deposition in molten chloride environments. Diffusion coefficients for Ni2+ in CaCl2 and for La3+ in LiCl-CaCl2 eutectic are calculated. Accuracy of the soluble-soluble model versus the soluble-insoluble model is discussed. Nucleation dynamics, natural convective and radial diffusive effects, and amount of ohmic drop compensation are all found to impact the resulting calculation for the number of electrons exchanged. A simplified model for determining the number of electrons exchanged under the constraint of well-compensated ohmic drop is proposed and evaluated.