Electrochemical behaviour of americium ions in LiCl–KCl eutectic melt

J. Serp (1) , Pierre Chamelot (2) , S. Fourcaudot (1) , Rudy J. M. Konings (1) , R. Malmbeck (1) , Carole Pernel (1, 3) , Jean-Claude Poignet (4) , J. Rebizant (1) , Jean-Paul Glatz (1)

1 ITU - JRC Institute for Transuranium Elements [Karlsruhe]
2 LGC - Laboratoire de Génie Chimique
3 CEA-LETI - Commissariat à l'énergie atomique et aux énergies alternatives - Laboratoire d'Electronique et de Technologie de l'Information
4 LEPMI - Laboratoire d'Electrochimie et de Physico-chimie des Matériaux et des Interfaces

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⁺ (E^0′ _{Am³⁺/Am²⁺} = -2.695 V versus Cl₂/Cl^– at 733 K) and Am²⁺/Am⁰ (E^0′ _{Am²⁺/Am⁰} = -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 D_Am³⁺/D_Am²⁺ ratio was found to be around 2. In addition, thermodynamic properties have been calculated for Am³⁺ (ΔG^∞_AmCl3= -933.7 + 0.152 T) and Am²⁺ (ΔG^∞_AmCl2= -623.9 + 0.085 T) 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.

Mots clés: Americium; Electrochemistry; LiCl–KCl; Cyclic voltammetry; Square wave voltammetry; Diffusion coefficient; Thermodynamic properties

Domaines: Matériaux

J. Serp, Pierre Chamelot, S. Fourcaudot, Rudy J. M. Konings, R. Malmbeck, et al.. Electrochemical behaviour of americium ions in LiCl–KCl eutectic melt. Electrochimica Acta, 2006, 51 (19), pp. 4024-4032. ⟨10.1016/j.electacta.2005.11.016⟩. ⟨hal-00420691⟩