Kinetic Mechanism of La3+ Reaction in LiCl-KCl-LaCl3 Molten Salt System

Abstract

In this paper, the reaction kinetic mechanism of La3+ was studied in the LiCl-KCl eutectic salt at various temperatures. First, the diffusion coefficient of La3+(D) measured by cyclic voltammetry(CV) increases from 3.06×10-5 cm2/s to 6.08×10-5 cm2/s with the temperature ranging from 723 K to 873 K, and the activation energy of La3+ diffusion(ED) in the molten salts is 34.51 kJ/mol calculated by the Arrhenius equation. Subsequently, the kinetic parameters of La3+ on the W electrode were studied by the electrochemical impedance spectroscopy(EIS). In the temperature range of 723-873 K, the exchange current density(i0) is measured to be 0.48-1.39 A/cm2, and the reaction rate constant(k0) is determined as 2.04×10-4-5.90×10-4 cm/s. Moreover, the corresponding reaction activation energy(Ea) is found to be 35.04 kJ/mol. The Nyquist plots and the fitted circuit diagrams explored the reaction kinetic mechanism of La3+ on a W electrode. It was illustrated that the electrochemical reduction rate of La3+ in the LiCl-KCl eutectic salt is controlled by diffusion and charge transfer, and it is positively correlated with temperature.

Keywords

• licl-kcl
• lacl3
• diffusion coefficient
• electrochemical impedance spectroscopy
• kinetic parameters