Electrochemical behaviour of americium ions in LiCl–KCl eutectic melt

This work presents a study on the electrochemical properties of AmCl3 in a molten LiCl–KCl eutectic, at a temperature range of 733–833 K. Transient electrochemical techniques, such as cyclic voltammetry and chronopotentiometry, on inert metallic tungsten working electrode have been used to investigate the reduction mechanism of Am3+ ions. The results show that Am3+ is reduced to Am metal by a two-step mechanism corresponding to the Am3+/Am2+ and Am2+/Am0 transitions. Formal standard potentials of Am3+/Am2+ (EAm3+/Am2+0′=−2.695 V versus Cl2/Cl− at 733 K) and Am2+/Am0 (EAm2+/Am00′=−2.911 V versus Cl2/Cl− at 733 K) redox couples as well as diffusion coefficients of Am3+ and Am2+ (2.4 × 10−5 and 1.15 × 10−5 cm2 s−1 at 733 K, respectively) have been calculated at three different temperatures. In the studied range of temperature, the DAm3+/DAm2+DAm3+/DAm2+ ratio was found to be around 2. In addition, thermodynamic properties have been calculated for Am3+ (ΔGAmCl3∞=−933.7+0.152T) and Am2+ (ΔGAmCl2∞=−623.9+0.085T) and compared to thermodynamic reference data in order to estimate activity coefficients (Am3+ = 4.7 × 10−3 and Am2+ = 2.7 × 10−2 at 733 K) in the molten LiCl–KCl eutectic.