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Studying the electrodeposition mechanism of La3+ in LiCl-KCl salt is extremely important for understanding the main characteristics of the deposition of An/Ln in the pyrochemical reprocessing of spent nuclear fuels. In this work, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel methods were employed to investigate the electrodeposition mechanism and kinetic processes of La3+ on Al, Ga and Al-Ga alloy cathodes in LiCl-KCl eutectic salt at the temperature range of 723-873 K. The EIS spectra were measured by applying a minimum overpotential near the equilibrium potential, and the suitable equivalent circuits were fitted. The values of exchange current density (i0) calculated by EIS ranged from 0.078 to 0.42 A cm-2. Finally, Al2Ga2La ternary and Al3La, Ga6La binary alloys were obtained by the potentiostatic electrolysis, which were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). [ABSTRACT FROM AUTHOR]

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, ${a}_{\left({\rm{U}}-{\rm{M}}\right)}:$ Al < Ga < Sn < Zn < Bi < Pb < Cd, ${a}_{(La-{\rm{M}})}:$ 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. [ABSTRACT FROM AUTHOR]

The objective of this work is to explore the electrochemical and electrodeposition behaviors of Eu (III) cation at the liquid binary Al-Ga alloy cathode. In addition, the co-reduction behaviors of Eu (III), Al (III) and Ga (III) were also systematically studied on a W electrode. The results indicated that Eu (III) can be reduced on the binary Al-Ga alloy cathode, and Eu (III), Al (III) and Ga (III) also can be co-reduced on the W electrode to form Al-Eu/Ga-Eu intermetallic compounds. At the same time, the isothermal section phase diagram of the Al-Ga-Eu ternary system at 773 K was also calculated. In addition, Al-Eu and Ga-Eu alloys were prepared by potentiostatic and galvanostatic electrolyses in the LiCl-KCl-EuCl3 melt. Finally, the electrodeposition products were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS). [ABSTRACT FROM AUTHOR]

Uranium-molybdenum (U-Mo) alloys especially the γ-U-Mo phase,with excellent irradiation performance at high temperatures, have been extensively studied as low-enriched-uranium candidate fuels for strengthening nuclear security and nonproliferation worldwide. Herein, we provide a facile method to successfully prepare the γ-U-Mo alloys (U-10Mo and U-8Mo) directly from oxide precursors via electro-reduction by constant cell voltage electrolysis in LiCl molten salt at 986 K. The reduction mechanism was elucidated through cyclic voltammetry using the metallic cavity electrode (MCE) combined with XRD, SEM and EDS characterizations toward the electrolysis products under different conditions. It was found that the reduction of mixed MoO3-UO2 oxides may take place in three steps. Firstly, MoO3 was reduced to Li4Mo5O12, and then Li4Mo5O12 was converted into Mo. Finally, the U-Mo alloys were formed due to the underpotential deposition of U on the pre-formedMo. In addition, the effects of cell voltage, sintering temperature and mixture composition on the electrochemical reduction were investigated. The results found that the reduction rate increased with the augmentation of applied potential and the decrease of sintering temperature. Moreover, the favorable composition of the mixed precursor varied from 24 at% to 21at%. The reduction conversion rate was determined to be 93.7% by ICP and TGA. [ABSTRACT FROM AUTHOR]

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 ZrC16 2-, ZrCl4F2 2-, ZrF4 2-, ZrF7 3- and ZrF8 4- 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 < 9.1), the reduction behavior was found to be largely dependent on the formed Zr(I) species; In LiCl-KCl-8.0 wt% LiF (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. [ABSTRACT FROM AUTHOR]

The aim of this work is to explore the electroextractions and related thermodynamic properties of Ln (Ce and Nd)as actinide surrogates on the liquid Ga media, aiming at further Ln/An separation. The activities, activity coefficients and solubilities of Ce and Nd in the liquid Ga media were determined by open circuit potential at the temperature range from 698 to 798 K. The electroextractions of Ce and Nd and their corresponding current efficiencies on a static liquid Ga electrode were investigated by gavanostatic electrolysis. The electrochemical behaviors of Ce and Nd on a liquid Ga electrode in LiCl-KCl eutectic were explored by the cyclic voltammetry. It was found that both of the reductions of Ce(III) and Nd(III) on a liquid gallium electrode start at about -1.1 V at 773 K and are a one-step process with three electrons transferred. Semi-differential method was applied so as to more accurately determine the apparent standard potential of Nd(III)/Nd(II) which actually hadn't been well clarified in literatures. Open circuit potential technique was also utilized to determine the apparent standard potentials of Ce(III)/Ce and Nd(III)/Nd redox couples and to evaluate the thermodynamic properties of Ce and Nd in the liquid Ga media. Galvanostatic electrolyses on the static liquid Ga electrode were conducted to extract the Ln elements with or without the formation of intermetallic compounds at 723 or 773 K. The current efficiencies for the electroextraction of Ce and Nd were calculated to be about 90%. X-ray diffraction (XRD) characterizations identified the formation of intermetallic compounds CeGa6 and NdGa6 after the electrolysis. The Gibbs free energies for the formation of LnGa6 were also calculated. [ABSTRACT FROM AUTHOR]

This work presents an electrochemical study of La(III) in the LiCl-KCl-LaCl3 melt on a liquid gallium electrode. The reduction of the La(III) on a liquid gallium starts at -1.13 V (vs. Ag/AgCl) and is a one step process with three electrons transferred. The activities, activity coefficients and solubilities of La in La-Ga alloys were calculated by open circuit potential technique at the temperature range of 673 to 823 K. Moreover, galvanodynamic methods was also applied on a W electrode to evaluate the apparent standard potential of La(III)/La couple, the Gibbs free energy for the formation of LaCl3 and the activity coefficient of La(III) in the LiCl-KCl-LaCl3 melt. The co-reductive cyclic voltammograms of La(III) and Ga(III) present several redox couples which correspond to the formation and dissolution of different La-Ga intermetallic compounds. Finally, potentiostatic electrolysis was employed to deposit La on a liquid Ga electrode and the intermetallic compound LaGa6 was identified by Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS) and X-ray diffraction (XRD) characterizations. [ABSTRACT FROM AUTHOR]

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 5.44x 10-5 cm2s-l 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 x 10 -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). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]