Liquid metal gallium (Ga), utilized as a reactive cathode, has garnered extensive attention in the field of molten salt electrolysis due to its exceptional separation performance. Therefore, the electrochemical redox process of holmium (Ho) ions was investigated using molybdenum (Mo) and liquid Ga as cathodes in a 3LiCl-2KCl melt. The diffusion coefficient during the reaction process on a Mo electrode at 773 K was calculated using cyclic voltammetry (CV) and semi-integration methods. Additionally, the reaction activation energy associated with the target reaction was quantified as 34.249 kJ mol−1. Subsequently, the thermodynamic and kinetic properties of Ho(III) on a Ga electrode were studied, achieving multiple objectives simultaneously. Notably, a linear correlation between the standard apparent electrode potential of Ho-Ga alloys and temperature was established. Meanwhile, the exchange current density of Ho(III)/Ho(Ga) was calculated using linear polarization (LP) and Tafel techniques. The separation factor (SF) for uranium (U) and Ho surpassed 104 throughout the range of experimental temperatures, indicating excellent separation efficiency. Finally, the influence of electrolysis temperature on the Ga electrode performance was investigated, demonstrating a maximum Ho extraction rate of 98.5% under optimized conditions. The electrolysis products formed were characterized by XRD and SEM-EDS and were found to be HoGa6.

Electrochemical reduction of U(III) ions on a liquid reactive Al electrode in molten 0.34 NaCl–0.66 CsCl eutectic was investigated using cyclic voltammetry, open-circuit potentiometry and galvanostatic electrolysis. These data are interest for the application of molten salt electrolysis in pyrochemical reprocessing of spent nuclear fuel. Electrode reaction of uranium deposition was proceeded in one step with a significant depolarization with formation of UAl3 and UAl4 intermetallic compounds. Conditions for electrochemical alloy production were determined. The activity, solubility of uranium in liquid aluminum, and basic thermodynamic properties of uranium compounds in molten salt media were calculated.

The electrochemical drawdown of U(III) ions in molten low melting non-hygroscopic NaCl-2CsCl eutectic using liquid reactive Pb and Pb-Sn cathodes was investigated by cyclic voltammetry and open-circuit potentiometry over the temperature range of 823-973 K. The reduction of U(III) ions on these electrodes take place with considerable depolarization and formation of various intermetallic compounds: UPb3, UPb, U(Pb-Sn)3 and USn3. The conditions of the electrochemical production of individual intermetallic compounds by galvanostatic electrolysis were found and principal thermodynamic characteristics of the alloys of different composition were calculated. The extraction conditions of uranium from the electrolyte in the form of alloys on bimetallic liquid Pb-Sn electrode via galvanostatic electrolysis with an efficiency of more than 96 % were found.

The electrorefining of spent nuclear fuel is a key step for extraction of uranium with the application of liquid reactive cathodes. The electrochemical extraction of uranium on W and Sn electrodes in molten NaCl-2CsCl (0.36-0.64) eutectic at the temperature range 823-973 K was investigated. The electroreduction mechanism of U(III) ions on W inert electrode was studied by cyclic voltammetry technique to verify that this process is a one-step reaction. On reactive liquid Sn electrode this reaction took place with the considerable depolarization with the formation of USn3 intermetallic compound. The conditions of the electrochemical production of alloy of a given composition were found. The apparent standard potentials of U(III)/U couple and USn3 alloy were determined by open-circuit potentiometry. The activity, solubility of uranium in liquid tin and the principal thermodynamic properties of uranium compounds in molten salt media were calculated. The electrochemical extraction of U on liquid Sn electrode in low melting non-hygroscopic NaCl-2CsCl eutectic was studied.The conditions of production USn3 intermetallic compound were determined.The thermodynamic properties of uranium compounds in molten salt media were calculated.The solubility of uranium in liquid tin in NaCl-2CsCl eutectic was found.

Abstract—The electrochemical reduction of U(III) ions to the metal in molten LiCl–KCl eutectic in a temperature range of 673–793 K on cadmium and gallium electrodes under an inert gas atmosphere is studied by cyclic voltammetry, square-wave voltammetry, and zero current potentiometry. Reagents containing no traces of moisture, oxygen, and products of their interaction are used in the experiments. All main procedures are carried out in a dry glove box under a purified argon atmosphere. As shown by cyclic and square-wave voltammetry, the cathodic reduction of uranium(III) ions on the active cadmium and gallium electrodes in the “electrochemical window” under study occurs with a depolarization of 0.2–0.4 V and depends on the cathode material. The potential shift to the electropositive range is found to be related to the formation of intermetallic compounds of uranium with the material of the active electrodes. The potentiostatic electrolysis of the melt at the potentials of the current peaks observed on the cyclic voltammograms using the active electrodes is conducted to identify the compositions of the cathodic deposits. The X-ray diffraction (XRD) data show that the intermetallic compound UCd11 is formed on the cadmium electrode and UGa3 and UGa2 are formed on the gallium electrode. SEM image and EDS analysis of the sample surface confirm the presence of fine fragments of the U–Cd and U–Ga intermetallic compounds. The conditions for the formation of alloys of a specified composition are determined by potentiostatic electrolysis. The equilibrium potentials of the U–Cd and U–Ga alloys are measured by zero current potentiometry, and the temperature dependences of the apparent standard potentials of the alloys are calculated. The electrochemical extraction of uranium from the LiCl–KCl–UCl3 melt is studied. The determined degree of extraction of uranium from the electrolyte on the active liquid electrodes at various electrolysis times exceeds 97

Liquid metallic gallium demonstrates great potential as a reactive cathode with its excellent ability for the effective separation of fission products during the recovery of spent nuclear fuel in the "liquid metal-salt melt system". In this study, advanced electrochemical methods were utilized to investigate the deposition mechanism of Er(iii) ions, along with the kinetic and thermodynamic properties of Er(iii) ions on both an inert molybdenum (Mo) electrode and a liquid gallium (Ga) electrode. Results indicated that the reduction reaction of Er(iii) belonged to a one-step process involving the transfer of three electrons, and the process was reversible within the range of scanning rates investigated on the Mo electrode. The diffusion coefficients were calculated at different temperatures on the inert Mo electrode, and the activation energy of the diffusion process was calculated to be 35.575 kJ mol-1. Subsequently, the electrochemical co-deposition of Ga(iii) and Er(iii) ions on the inert Mo cathode and the reduction of Er(iii) ions on the reactive Ga cathode were investigated, and the electrochemical mechanisms of the two reactions were determined. Additionally, the oxidation-reduction potentials of the Er-Ga intermetallic compounds that appeared during the reaction were determined. The main thermodynamic properties of Er-Ga alloy were obtained using open circuit potentiometry, and the separation factors of the U/Er couple were explored. Meanwhile, Er was effectively extracted as ErGa6 through potentiostatic electrolysis at -2.0 V for 12 h, achieving an extraction rate of approximately 98.3%.

Radioisotope thermoelectric generators for biomedical purposes require high-purity 238Pu. The present article examines a model for its production in NaCl–2CsCl eutectic melt. For this purpose, physicochemical properties of plutonium, americium, and curium treated with an oxygen-chlorine-argon mixture in NaCl-2CsCl melt were studied at the JSC “SRC RIAR” (Dimitrovgrad, Russian Federation). The developed model provides for determining the modes of plutonium dioxide precipitation without americium and curium, as well as for assessing its possible contamination with actinides.

For the efficient electrolytic extraction of Er from spent nuclear fuel, a series of electrochemical methods was used to research the electrochemical behavior of Er(III) in the LiCl-KCl system on inert (Mo) electrode and on reactive (Ni) electrodes. On the inert Mo electrode, the reduction of Er(III) to Er(0) is a one-step with three-electron and quasi-reversible reaction process. Meanwhile, the apparent generation Gibbs free energy and activity coefficients of Er(III) on the inert electrode were determined. Thereafter, the electrochemical reduction of Er(III) on the Ni electrode was emphatically investigated. Er(III) is reduced at a corrected potential owing to the formation of Ni-Er alloys. In addition, thermodynamic parameters such as partial excess Gibbs free energy change of Er in Ni, activity and apparent generation Gibbs free energy of the Ni-Er alloys were determined by the electromotive force method. Finally, different Ni-Er alloys were produced using potentiostatic electrolysis on the Ni cathode by controlling different potentials. Moreover, electrolytic extraction was carried out on the Ni cathode at the potential of –2.0 V, and the separation efficiency of Er reaches 99.72%, which proves the practicability of separating Er from LiCl-KCl eutectic on the reactive Ni cathode.

The efficient separation of the rare earth element Sm from spent nuclear fuel is of strategic importance for the nuclear industries. This study explored the feasibility of a novel liquid Ga-Pb hybrid electrode for electrochemical extraction of samarium compounds, and the electrochemical reduction mechanism and dynamic properties of Sm(III) ions were provided in NaCl-2CsCl molten salt. It was established that the reduction mechanisms of Sm(III) to Sm(II) and Pb(II) to Pb(0) on the Mo cathode were a one-step reaction processes, respectively, while Ga(III) to Ga(0) was a two-step reaction process. The co-deposition mechanisms of Sm(III), Ga(III) and Pb(II) ions on the Mo cathode were identified, and the types of intermetallic compounds, formation potentials and reaction processes were analyzed. The deposition potential of Sm on Ga-Pb mixed cathode is determined, and the value of its depolarization was greater than on the liquid Pb electrode. Simultaneously, Sm ions have higher exchange current densities and lower activation energies for electrode reactions on the liquid Ga-Pb mixed electrodes than on the liquid Pb electrodes. Furthermore, the electro-separation of NaCl-2CsCl-SmCl3 molten salt was executed via potentiostatic electrolysis technique, and the separation efficiency and the effect of cathode product type were analyzed and compared in Ga-Pb hybrid electrode and Pb electrode. It was obtained that the maximum extraction efficiency on the Ga-Pb hybrid electrode and the separation efficiency of Sm could reach 91.3 % after 8 h of electrolysis.

This work presents the electrochemical study of LiCl-KCl-UCl3 solutions at the temperature range 673–823 K on inert and reactive electrodes, i.e. W and Cd, respectively. On inert electrode, U(III) ions were reduced to metallic uranium through one step and the mechanism of the cathode reaction was irreversible. The diffusion coefficients of U(III) ions in molten chloride eutectic and liquid cadmium were calculated. On reactive electrode, U(III) ions were reduced with depolarization and were accompanied by the formation of intermetallic compound UCd11. The reactions of the cathodic deposition and anodic dissolution of the U-Cd alloy were studied and the conditions of the alloy formation via galvanostatic electrolysis were found. The solubility and the activity of uranium in liquid cadmium were determined.

The electrochemical and thermodynamic properties of uranium compounds were studied in molten ultra-pure LiCl–KCl eutectic at 723–823 K on inert W and reactive Ga electrodes by different electrochemical techniques. The mechanism of the cathode reaction was determined and the diffusion coefficients of U(III) complex ions were calculated for reversible and irreversible systems. The deposition of uranium(III) on reactive Ga electrode was proceeded with depolarization and accompanied by the formation of intermetallic compounds. The conditions of the alloy formation via potentiostatic electrolysis were found. Thermodynamic properties of UCl3 and UGa3 were calculated.

The interaction mechanism between Sm 3+ and O 2− in NaCl–2CsCl eutectic has been investigated by potentiometric titration, and Pourbaix diagram has been drawn to determine the types of samarium compounds.

The electrochemical extraction of uranium in ternary low melting LiCl–KCl–CsCl eutectic on inert and reactive electrodes via different electrochemical techniques was investigated. It was established that the electrochemical reduction process of U(III) ions on the inert W electrode was irreversible and proceeded in one stage. On reactive liquid Ga and liquid Cd electrodes the reduction of uranium ions took place with the considerable depolarization with the formation of UGa2, UGa3 and UCd11 intermetallic compounds. Thermodynamic characteristics of uranium compounds and alloys were calculated. The conditions for the extraction of uranium from the electrolyte in the form of alloys on both liquid reactive electrodes via potentiostatic electrolysis were found.

The processes of cathodic reduction of U(III) ions to metal in a low–melting LiCl–KCl–CsCl eutectic at the temperature range 650–850 K on tungsten, gallium and cadmium electrodes in an inert gas atmosphere have been studied by non-stationary and stationary electrochemical methods. Reagents without contain impurities of moisture, oxygen and their compounds were used in the experiments. All major operations were performed in a dry glove box. The following methods were used to analyze the electrochemical processes: cyclic voltammetry, square-wave voltammetry and potentiometry at zero current. On cyclic voltammogram of the molten LiCl–KCl–CsCl–UCl3 solution on an inert tungsten electrode, one cathode current peak corresponding to the deposition of metallic uranium and one anode current peak associated with its dissolution were recorded. It was found that the potential of the cathode peak was shifted to a region of more negative values with an increase of the scan rate. The value of the cathode peak current was directly proportional vs. the square root of the polarization rate, but this dependence does not pass through the origin. Consequently, the system of U(III)/U(0) couple was irreversible and proceeds in one stage. It was found that on square-wave voltammograms in the studied “electrochemical window” the deposition of uranium on liquid reactive gallium and cadmium electrodes was carried out at more positive values than on inert tungsten electrode. It was established that this potential shift was associated with the formation of intermetallic compounds of uranium with the material of reactive electrodes. The values of the alloy formation potentials were determined. For identification of the composition of cathode deposits, potentiostatic electrolysis was performed. By X–ray diffraction analysis, it was found that the formation of the intermetallic compounds Ga3U and Ga2U occurs on the gallium reactive electrode, and Cd11U occurs on the cadmium one. The conditions of their formation during the electrolysis of molten LiCl–KCl–CsCl–UCl3 solutions were established. The reaction of the electrochemical extraction of uranium from molten LiCl–KCl–CsCl–UCl3 electrolyte was investigated on liquid reactive electrodes at different duration of electrolysis. It was found that the electrochemical extraction of uranium exceeds 97% on both Ga and Cd electrodes.

The electrochemical behavior of Pr(III) ions in molten NaCl-2CsCl solutions was investigated via different electrochemical techniques on Mo inert and Ga, Ga-Pb and Pb reactive electrodes. It was determined that the electrochemical reduction process on inert electrodes proceeds in one stage. It is reversible at low scan rates below 0.1 V/s, whereas it is irreversible at high scan rates. The diffusion coefficients of PrCl63- complex ions were determined at different temperatures, and the activation energy of this process was calculated as 42.2 kJ mol(-1). The co-reduction of Pr(III), Ga(III) and Pb(II) ions was investigated, and the redox potentials of forming different alloys were determined. The electrodeposition of Pr(III) ions was studied on three reactive electrodes, and one-step electrode processes were determined. The current exchange density of Pr(III) ions increased in the order of Pb < Ga-Pb < Ga. The composition of Ga2Pr and Pb3Pr intermetallic compounds was formed on reactive electrodes and their specific thermodynamic characteristics were calculated. Finally, praseodymium was successfully extracted from the molten salt in the form of Ga2Pr and Pb3Pr intermetallic compounds on three liquid reactive electrodes via potentiostatic electrolysis.

The electrochemical behaviour of Nd(III) ion was investigated on inert W, active Ga and Ga–Al cathodes. It is established that the reduction of Nd(III) ion on the inert electrode is a consecutive two-step process while that on the active electrodes is a one-step process. The apparent standard potential of the Nd(III)/Nd redox couple at different temperatures was determined by open-circuit chronopotentiometry and semi-differential method, and the relationship between temperature and apparent standard potential was further discussed. The thermodynamic properties of Nd in Ga and Ga–Al electrodes such as activity coefficient and activity were evaluated via intermittent coulomb titration and temperature dependence test, and the effect of temperature on activity coefficient was verified. Finally, Nd was successfully extracted in form of alloy from molten salt by galvanostatic electrolysis, in which the current efficiency of 91.7% for the electroextraction indicates that the binary liquid Ga–Al electrode has favorable performance.

For effective recovery of the fission element Pr from spent nuclear fuel (SNF) by using molten salt electrolysis technology, the electrochemical behavior of Pr(III) on inert Mo electrode in the molten LiCl–KCl system was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques, indicating that the reduction of Pr(III) on the Mo electrode is a one-step reaction process with three electrons. Subsequently, electrochemical methods were used to reveal and calculate the kinetic and thermodynamic parameters of the Pr(III) ion reduction process. The co-reduction reaction of Pr(III) and Co(II) ions was explored, and five different CoxPry intermetallic compounds were detected. Meanwhile, only one Co2Pr intermetallic compound was obtained by galvanostatic and potentiostatic electrolysis with the best electrochemical parameters, and the thermodynamic properties of the Co2Pr intermetallic compound were calculated at different temperatures. The co-reduction product was verified using X-ray diffraction (XRD), and the composition was determined by scanning electron microscopy (SEM) with energy spectrum analysis (EDS) and X-ray photoelectron spectroscopy (XPS). In addition, the produced Co2Pr intermetallic compound has magnetic properties with a saturation magnetization of 10.3 emu/g.

Cathodic processes in Li2MoO4–K2MoO4–MoO3 and K2MoO4–MoO3 melts containing added UO2MoO4 were investigated at 550–800 °C using cyclic voltammetry, cathodic polarization and bulk electrolysis. Cathodic reduction of molybdate melts (not containing uranium) resulted in formation of molybdenum dioxide. Products of the cathodic reactions in the melts containing uranium molybdate predominantly consisted of crystalline uranium oxides (mostly UO2 and U4O9) and MoO2. Minor products formed included other uranium oxides (U3O8, U13O34), mixed uranium-molybdenum oxides (U1.5Mo10O32, Mo2UO8) and molybdates (provisionally attributed to K2U(MoO4)3). Effect of temperature, cathodic current density 0.05–1 A cm−2), excess MoO3 concentration (30–50 mol%) on the composition of the cathodic reaction products were analyzed. Oxygen-to-uranium atomic ratio (oxygen coefficient) for primary uranium oxide phases was determined and varied from 1.963 to 2.161 for UO2±x and from 2.209 to 2.287 for U4O9±y. The effect of the electrolysis regime on the composition of the cathodic product was also considered. Constant-current and constant-potential electrolysis, as well pulsed-current, pulsed-potential and pulsed-reversed-current electrolysis were investigated with varying the parameters of alternating pulses (duration, current density or potential). Chemical and phase composition of the products produced by bulk electrolysis was fully characterized.

Speciation and behavior of uranium (III) chloride in the ternary low melting LiCl–KCl–CsCl eutectic was studied by electrochemistry and spectroscopy techniques. Cathodic reduction of U(III) ions on inert (tungsten) and reactive (gallium, cadmium) electrodes was investigated at 623–923 K using cyclic and square wave voltammetry. The potential scan rate was changed from 0.075 to 0.5 V s −1 in all experiments. It was established that the electrochemical reduction process on the inert electrode was irreversible, proceeded in one stage, and was controlled by the charge transfer. Formation of uranium alloys with gallium and cadmium was studied using active liquid Ga and Cd electrodes. Reduction of uranium ions of the reactive electrodes proceeded with considerable depolarization. The effect of current density on the composition of the cathodic product was considered. Conditions for the electrochemical production of alloys of a given composition were determined.