Electrochemistry of thorium in LiCl-KCl eutectic melts

This work presents a study of the electrochemical properties of Th chloride ions dissolved in a molten LiCl-KCl eutectic, in a temperature range of 693-823 K. Transient electrochemical techniques such as cyclic voltammetry chronopotentiommetry and chronoamperometry have been used in order to investigate the reduction mechanism on a tungsten electrode and;he diffusion coefficient of dissolved Th ions. All techniques showed that only one valence state was stable in the melt. The reduction into Th metal was found to occur according to a one-step mechanism, through a nucleation-controlled process which requires an overpotential of several 100 mV. At 723 K, the diffusion coefficient is D-Th(723 K) = 3.15 +/- 0.15 x 10(-5) cm(2) s(-1). ENIF measurements indicated that, at 723 K, the standard apparent potential is E-ThCl4/Th(*0) (723 K) = -2.582 V versus Cl-2/Cl-, and the activity coefficient gamma(ThCl4), (723 K) = 4.6 x 10(-4) on the mole fraction scale (based on a pure liquid reference state). (c) 2007 Elsevier Ltd. All rights reserved.