Electrochemical behaviour of americium ions in LiCl-KCl eutectic melt

摘要

This work presents a study on the electrochemical properties of AmCl{sub}3 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 Am{sup}(3+) ions. The results show that Am{sup}(3+) is reduced to Am metal by a two-step mechanism corresponding to the Am{sup}(3+)/Am{sup}(2+) and Am{sup}(2+)/Am{sup}0 transitions. Formal standard potentials of Am{sup}(3+)/Am{sup}(2+) ((E{sub}(Am{sup}(3+)/Am{sup}(2+))){sup}0' = -2.695 V versus Cl{sub}2/Cl{sup}-at 733 K) and Am{sup}(2+)/Am{sup}0 ((E{sub}(Am{sup}(2+)/Am{sup}0)){sup}0' = -2.911 V versus Cl{sub}2/Cr at 733 K) redox couples as well as diffusion coefficients of Am{sup}(3+) and Am{sup}(2+) (2.4 × 10{sup}(-5) and 1.15 × 10{sup}(-5) cm{sup}2 s{sup}(-1) at 733 K, respectively) have been calculated at three different temperatures. In the studied range of temperature, the D{sub}(Am{sup}(3+))/D{sub}(Am{sup}(2+)) ratio was found to be around 2. In addition, thermodynamic properties have been calculated for Am{sup}(3+) (Δ(G{sub}(AmCl{sub}3)){sup}∞ = -933.7 + 0.152T) and Am{sup}(2+) (Δ(G{sub}(AmCl{sub}2)){sup}∞ = -623.9 + 0.085T) and compared to thermodynamic reference data in order to estimate activity coefficients (Am{sup}(3+) = 4.7 × 10{sup}(-3) and Am{sup}(2+) = 2.7 × 10{sup}(-2) at 733 K) in the molten LiCl-KCl eutectic.