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In order to optimize the application of Al electrodes in pyrochemical reprocessing of spent nuclear fuel, the feasibility of porous Al electrodes to separate actinides-lanthanides (An-Ln) in LiCl-KCl eutectic melt was explored. The separation efficiencies and rates of U and lanthanides (La, Ce, Sm) on Al electrodes with regular and irregular and without pores were compared. U was selectively recovered in the form of U-Al alloys by controlling the potential (−1.2 V) on both Al rod and porous Al electrodes. X-ray diffraction (XRD) and scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS) showed that the obtained granular alloys were mainly Al3U and Al4U, and inductive coupled plasma optical emission spectrometry (ICP-OES) indicated that there was almost no Ln in the electrolysis products. Positively, the required separation time was greatly shortened, and the separation rate was effectively improved when porous Al electrodes were used. In addition, the Al honeycomb electrode with regular pores has better kinetic performance compared with Al foam electrodes with irregular pores. The results indicate that the specially designed porous Al electrodes may have a good application prospect for the separation of An-Ln in the pyrochemical reprocessing of spent nuclear fuel.

This work presents the electrochemical behaviors of Pr (III) on a liquid Bi electrode and the formation of Bi-Pr intermetallics in LiCl-KCl eutectic melt. Galvanostatic voltammetry and open circuit chronopotentiometry techniques were employed to determine the apparent standard potential of Pr(III)/Pr couple. The reduction of Pr (III) on the liquid Bi electrode is a one step process with three electrons transferred. The activity coefficient of Pr in liquid Bi was also determined by coulometric titration and in-situ open circuit chronopotentiometry at the temperature range of 723 to 813K. In addition, the signals of five intermetallic compounds corresponding to the Bi-Pr binary phase diagram were successively detected by a series of electrochemical techniques. Thermodynamic properties for the formation of Bi-Pr intermetallic compound were measured by open circuit chronopotentiometry. The activities and partial molar Gibbs free energies of Pr in the two phase coexisting system were obtained, from which the Gibbs free energy, the enthalpy and entropy of formation were also calculated. (C) 2018 The Electrochemical Society.

In this work, Raman measurements were performed with quenched LiCl-KCl-LiF-ZrCl4/ZrF4/K2ZrF6 salt mixtures for deciphering the coordination chemistry of zirconium(IV) in the presence of fluoride ion in the melt. The occurrence of ZrCl62-, ZrCl4F22-, ZrF62-, ZrF73- and ZrF84- in melt at different F/Zr molar ratios was confirmed by Raman spectra. The electrochemical redox behaviors of zirconium in LiCl-KCl-LiF-ZrCl4 were also examined at 773 K. Transient methods such as cyclic voltammetry and square wave voltammetry were used. In LiCl-KCl-LiF-ZrCl4 with LiF concentration less than 1.27 wt% (molar ratio F/Zr 101), the reduction of Zr(IV) followed a two-step mechanism of Zr(IV)/Zr(III) and Zr(III)/Zr(0) at the potentials of about -0.85 and -1.40 V versus Pt, respectively. (C) 2018 The Electrochemical Society.

Electrochemical studies of UCl3 and LnCl3 (Ln: La, Ce, Pr, Nd) in LiCl–KCl melt were performed on inert tungsten and reactive bismuth electrodes. Galvanostatic pulse (GP) and electrochemical impedance spectroscopy (EIS) were carried out to investigate the exchange current density j0 of UCl3/U on liquid Bi electrode at the temperature range of 723–873 K. The impedance data were well fitted with the equivalent circuit. The relationship between j0 and the temperature was determined to model the electrowinning by using liquid Bi electrode. In addition, the electrochemical separation in low concentration uranium from multi-component lanthanide chlorides was demonstrated on liquid Bi electrode. Three electrochemical techniques, including coulometric titration, galvanostatic electrolysis and potentiostatic electrolysis, were applied for the separation of uranium. In which, the coulometric titration showed good separation results. The separation of uranium from lanthanides in terms of mole ratio (U/Ln) was determined, and the different values were discussed in detail. In general, the data from this work can provide theoretical reference for the separation process of various metals by electrochemistry.

The aim of this work is to evaluate and compare the possibility of Cd, Hg, Al, Ga, Sn, Pb and Bi as candidate cathode materials based on their physicochemical and electrochemical properties and theoretical separation ability for actinides over lanthanides. First, the comparison of melting points and vapor pressures about those metals shows that Group 12 elements Cd and Zn are more practically suitable for the electrowinning process. Then, cyclic voltammetry conducted at 773 K on these cathodes in LiCl-KCl eutectic presents a trend of electrochemical reactivity (Bi > Sn > Ga ≥ Pb > Zn > Cd > Al), nobility (Bi > Pb ≥ Sn > Ga > Cd > Zn > Al) and electrochemical window (Cd > Al > Pb > Bi > Ga > Sn > Zn), respectively. Moreover, cyclic voltammograms of U3+ and La3+ collected at 773 K on these cathodes demonstrate different electrochemical reactivity scales Ec(U): Ga ≥ Bi > Sn > Al > Zn > Pb > Cd) and Ec(La): Bi > Sn ≥ Ga > Zn > Pb > Cd > Al), respectively, from the anodic to the cathodic side. From these results, a favorable trend for electrochemical separation of U over La can be obtained (Al > Ga > Zn > Bi > Sn > Pb > Cd). In addition, the theoretical Mediema model shows the relationships of the enthalpy of formation and the activity of different alloys as, a U − M : Al < Ga < Sn < Zn < Bi < Pb < Cd, a ( L a − M ) : Bi < Sn < Pb < Al < Ga < Cd < Zn, suggests the interaction of Al and Ga to uranium is the strongest with the best theoretical separation performance.

This work presents a study of electrochemistry of uranium on a liquid gallium in LiCl-KCl eutectic by applying a series of electrochemical techniques. The electrochemical window of the Ga electrode in LiCl-KCl eutectic is about -1.40 to -0.35 V vs. Ag/AgCl. The reduction of U(III) on liquid gallium starts at -0.86 V and is a one step process with the transfer of three electrons. The co-reductive cyclic voltammograms of U(III) and Ga(III) present a couple of sharp redox peaks at about -0.95 and -0.84 V, corresponding to the formation and dissolution of the intermetallic compound UGa3. In addition, the reduction of Ga(III) in LiCl-KCl melt is a two-step process: Ga(III). Ga(I). Ga. The activity coefficient and solubility of U in liquid Ga at the temperature range from 673 to 823 K were determined by coulometric titration and open circuit potential respectively. The Gibbs free energy for the formation of UGa3 was also calculated. The intermetallic compound UGa3 was deposited by potentiostatic electrolysis at -1.0 V in the LiCl-KCl -GaCl3-UCl3 and LiCl-KCl-UCl3 melt on solid W and liquid Ga electrodes at 773 K, respectively. The electrolysis efficiency is about 97% based on the ICP result. Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS) and X-ray diffraction (XRD) characterizations further identified the formation of UGa3. (C) 2016 The Electrochemical Society. All rights reserved.

The electrochemical formation of Ce-Zn alloys in LiCl-KCl eutectic was systematically investigated by cyclic voltammetry (CV), square wave voltammetry (SWV) and open circuit chronopotentiometry (OCP). Due to the decrease of Ce activity in the metal phase of formed Ce-Zn alloys, the deposition potential of Ce(III) at a liquid Zn electrode was found to be 0.64 V more positive than that on an inert W electrode. The co-reduction behaviors of Ce(III) and Zn(II) ions were also studied in LiCl-KCl eutectic. Signals associated with six and nine CexZny intermetallic compounds were detected by CV and OCP techniques, respectively. In addition, potentiostatic electrolyses were carried out to extract Ce at a liquid Zn electrode in LiCl-KCl-CeCl3 melt and on a W electrode in LiCl-KCl-CeCl3-ZnCl2 melt, respectively. Deposited samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The results showed that intermetallic compound CeZn11 was prepared on both the inert W electrode and liquid Zn electrode. (C) The Author(s) 2015. Published by ECS. All rights reserved.

This work presents a comparative study of electrochemical properties of Gd3+ on W and Zn electrodes in LiCl-KCl eutectic. It was found that Gd3+ reduction on a tungsten cathode occurs in a single step pattern. Relevant kinetic properties of the Gd3+/Gd redox reaction were investigated by cyclic voltammetry (CV). The reduction of Gd3+ at a liquid zinc electrode in LiCl-KCl-GdCl3 melt and a film zinc electrode in LiCl-KCl-GdCl3-ZnCl2 eutectic were also studied at 773 K. The diffusion coefficient of Gd3+ at the liquid zinc electrode was calculated to be 5.44 x10(-5) cm(2)s(-1) in LiCl-KCl-GdCl3 melt. The standard rate constants for the charge transfer of Gd3+ at the liquid zinc electrode or on the tungsten electrode was calculated to be about 1 x10(-2) cms(-1) at 773 K by Nicholson method, revealing the redox reaction of Gd3+ to Gd is quasi-reversible based on the Matsuda-Ayabe criteria for practical concept of electrochemical reversibility. Electrodeposition of Gd3+ was carried out on both the film zinc electrode and the liquid zinc electrode. X-ray diffraction (XRD) results showed that intermetallic compounds GdZn12, Gd2Zn17, Gd13Zn58 and GdZn were obtained on the film zinc electrode, whilst intermetallic compound GdZn12 was gained at the liquid zinc electrode. The morphological properties of all the intermetallic compounds were characterized by scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). (c) 2015 The Electrochemical Society. All rights reserved.