Electrochemistry of thorium in LiCl–KCl eutectic melts

Abstract

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 and chronopotentiommetry have been used in order to investigate the reduction mechanism on a tungsten electrode and the 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 an irreversible reaction controlled by a nucleation process which requires an overpotential of several 100 mV. At 723 K, the diffusion coefficient is D Th(723K) = 3.7 ± 0.2·10 -5 cm 2 .s -1 . EMF measurements indicated that, at 723 K, the standard apparent potential is 0(723 K) = -2.582 V vs. Cl 2 /Cl -, and the activity coefficient γ ThCl4 (723 K) = 8·10 -3 on the mole fraction scale (based on a pure liquid reference state).

Electrodeposition of metals from non-aqueous solutions

“…The electrode reactions of U and Pu were complicated by the formation of an alloy. The properties of thorium chloride ions were investigated on a W electrode in a molten eutectic LiCl-KCl in the temperature range 420-550 • C. Here the electrochemistry of thorium was only examined [110]. Electrorefining experiments of uranium were successfully carried out in the LiCl-KCl eutectic molten salt at 500 • C with a graphite cathode.…”

Electrochemistry of thorium fluoride in LiCl-KCl eutectic melts and methodology for speciation studies with fluorides ions

“…In the literature, most of authors mention for the dissolved forms of thorium only thorium at the valence state (IV) [7][8][9][10]. Only one mentions the existence of Th (II) [11].…”

Thin-Layer Electrodeposition of Thorium Metal from Molten LiCl-KCl

“…Many different overpotentials were selected along with two different cathode materials (2 mm diameter nickel or tungsten rods), however the result was always a simple cottrellian decay of current with no maximum. The only relevant literature available is the work of Cassayre 18 which determined progressive nucleation of thorium on tungsten. However, tungsten is inert as opposed to the reactive nickel electrode which is used here.…”

“…According to literature, [16][17][18][19][20] the reduction should be a onestep, four electron transfer [Th 4+ /Th]. The cyclic voltammogram for both materials is displayed in Figure 3.…”