Electrochemical reactions of the Th4+/Th couple on the tungsten, aluminum and bismuth electrodes in chloride molten salt

This work concerns the electrochemical behaviors of Th4+ on the tungsten, aluminum and bismuth electrodes in the LiCl-KCl eutectic, respectively, at 773 K. Cyclic voltammetry and square wave voltammetry were employed to investigate the cathodic reduction of Th4+. The results demonstrate that the reduction of Th4+ is a one step process with a transfer of 4 electrons. The reversibility of the Th4+/Th couple on the bismuth film and tungsten electrodes is directly confirmed by the CV. The diffusion coefficient is also calculated to be (2.23 ± 0.16) × 10−5 and (7.19 ± 0.12) × 10−5 cm2/s by applying both cyclic voltammetry and chronopotentiometry, respectively. A series of redox couples were confirmed to be associated with the formation of different kinds of Al-Th intermetallic compounds. Compared to Al electrode, a cathodic shift of the reduction potential of the Th4+ is observed on the Al film electrode which is not conducive for the potentiostatic extraction of thorium. The cathodic depolarization gives a shift of 420 mV on the Al electrode, while 490 mV on the Bi film electrode for the reduction of Th4+ compared to the inert W electrode. The reduction potential of Th4+ on the Bi film electrode is 70 mV more anodic than that on the Al electrode. Potentiostatic electrolyses were carried out on an Al plate and Bi liquid electrode to confirm the formation of the Th alloys. Two Al-Th alloys (Al3Th and Al2Th) and one Bi-Th alloy (Bi2Th) were obtained, respectively.