Electrochemistry of redox potential of the couple Tm3+/Tm2+ and the formation of a Tm–Al alloy in fused NaCl–2CsCl eutectic

Abstract This work presents the electrochemical study of TmCl 3 solutions in NaCl–2CsCl eutectic at the temperature range 823–973 K using inert and reactive electrodes, i.e. Mo and Al, respectively. On an inert electrode, Tm 3+ ions are reduced to metallic thulium through two consecutive steps: Tm 3+  + e −  → Tm 2+ and Tm 2+  + 2e −  → Tm. The electroreduction of Tm 3+ to Tm 2+ ions was found to be reversible at low scan rates being controlled by the rate of the mass transfer and irreversible at high scan range (>0.1 V s −1 ) being controlled by the rate of charge transfer. The diffusion coefficient of [TmCl 6 ] 3− complex ions was determined at different temperatures. Arrhenius law was verified by plotting the variation of the logarithm of the diffusion coefficient vs. reverse temperature. The apparent standard potential of the soluble-soluble redox system Tm 3+ /Tm 2+ was obtained by cyclic voltammetry. The electrode reactions of Tm 3+ solutions at an Al electrode were also investigated. The results showed that for the extraction of thulium from molten chlorides, the use of a reactive electrode made of aluminum leading to Al–Tm alloys seems to be a pertinent route.