Electrochemical behaviors of Dy(III) and its co-reduction with Al(III) in molten LiCl-KCl salts

Peculiarities of Holmium and Iron Triad Ions Co-Reduction: Formation of HoxNiy (HoxCoy, HoxFey) Intermetallic Compounds in Chloride Melts

The present paper is focused on the analysis of Ni2+, Co2+, Fe3+, and Ho3+ ion co-reduction in the background equimolar NaCl-KCl melt at 973 K using the method of cyclic voltammetry. It was found that the co-reduction potentials of Ho3+ and iron triad ions differ greatly. The depolarization of metallic holmium electrodeposition on one of the iron triad metals preliminary deposited on the tungsten electrode was determined. This process resulted in the formation of the HoxNiy, HoxCoy, and HoxFey intermetallic compounds. It was observed that the HoxNiy, HoxCoy, and HoxFey intermetallic compounds may be synthesized in a kinetic regime. The influence of the current density, electrolytic bath composition, and electrolysis time on the composition of the obtained intermetallic compounds was studied. The possibility of synthesizing cathode deposits composed solely of intermetallic compounds is verified. It is demonstrated that the intermetallic compounds may be formed by the addition of the iron triad metals (in particular, metallic iron) via anode dissolution. Synthesized HoxNiy, HoxCoy, and HoxFey samples were characterized by X-ray diffraction analysis, scanning electron microscopy, and photon correlation spectroscopy.

Mechanism of Dy3+ and Nd3+ Ions Electrochemical Coreduction with Ni2+, Co2+, and Fe3+ Ions in Chloride Melts

The present paper is devoted to the study of the processes of the mechanism of electrochemical coreduction of Dy³⁺ and Nd³⁺ ions with Ni²⁺, Co²⁺, and Fe³⁺ ions in the equimolar NaCl-KCl melt at 973 K and characterization of the synthesized samples. The performed voltammetry analysis of the electrochemical coreduction processes elucidated a significant difference in the values of the extraction potentials of the studied metals. This melt testifies that intermetallic compounds of Dy and Nd with Ni, Co, and Fe may be synthesized in the kinetic regime. The intermetallic phases of Dy and Nd with Ni, Co, and Fe are found to be formed along with the phases of metallic Ni, Co, and Fe either during electrolysis at the cathode current densities exceeding the limiting diffusion current of Ni²⁺, Co²⁺, and Fe³⁺ ions or in the potentiostatic regime at the potentials of the corresponding voltammetry curves. Therefore, the following interrelated key parameters affecting the electrochemical synthesis of Dy and Nd intermetallic compounds with Ni, Co, and Fe were determined: (i) composition of the electrolyte, i.e., concentrations of FeCl₃, CoCl₂, NiCl₂, DyCl₃, and NdCl₃; (ii) cathode current density or electrolysis potential and (iii) electrolysis time. The obtained samples were characterized by micro-X-ray diffraction analysis, cyclic voltammetry, and scanning electron microscopy methods.

Separation of actinides from lanthanides associated with spent nuclear fuel reprocessing in China: current status and future perspectives

Developing necessary reprocessing techniques to meet the remarkable increase of spent nuclear fuels (SNFs) is crucial for the sustainable development of nuclear energy. This review summarizes recent research progresses related to the SNF reprocessing in China, with an emphasis on actinides separation over lanthanides through three different techniques, hydrometallurgical reprocessing, pyrometallurgical processes, and selective crystallization based separation. Some future perspectives with respect to advanced actinide separation are also given.

Electrolytic extraction of dysprosium and thermodynamic evaluation of Cu-Dy intermetallic compound in eutectic LiCl-KCl

The electrochemical reduction of dysprosium(iii) was studied on W and Cu electrodes in eutectic LiCl–KCl by transient electrochemical methods. Cyclic voltammogram and current reversal chronopotentiogram results demonstrated that dysprosium(iii) was directly reduced to dysprosium (0) on the W electrode through a single-step process with the transfer of three electrons. Electrochemical measurements on the Cu electrode showed that different Cu–Dy intermetallics are formed. Moreover, the thermodynamic properties of Cu–Dy intermetallic compounds were estimated by open circuit chronopotentiometry in a temperature range of 773–863 K. Using the linear polarization method, the exchange current density (j₀) of dysprosium in eutectic LiCl–KCl on the Cu electrode was estimated, and the temperature dependence of j₀ was studied to estimate the activation energies associated with Dy(iii)/Cu₅Dy and Dy(iii)/Cu_9/2Dy couples. In addition, potentiostatic electrolysis was conducted to extract dysprosium on the Cu electrode, and five Cu–Dy intermetallic compounds, CuDy, Cu₂Dy, Cu_9/2Dy, Cu₅Dy and Cu_0.99Dy_0.01 were identified by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. Meanwhile, the change of dysprosium(iii) concentration was monitored using inductively coupled plasma-atomic emission spectrometry, and the maximum extraction efficiency of dysprosium was found to reach 99.2%.

The electrochemical reduction of dysprosium(iii) was studied on W and Cu electrodes in eutectic LiCl–KCl by transient electrochemical methods.

Estimation of the composition of intermetallic compounds in LiCl–KCl molten salt by cyclic voltammetry

In this work, the compositions of Ce–Al, Er–Al and La–Bi intermetallic compounds were estimated by the cyclic voltammetry (CV) technique. At first, CV measurements were carried out at different reverse potentials to study the co-reduction processes of Ce–Al, Er–Al and La–Bi systems. The CV curves obtained were then re-plotted with the current as a function of time, and the coulomb number of each peak was calculated. By comparing the coulomb number of the related peaks, the compositions of the Ce–Al, Er–Al and La–Bi intermetallic compounds formed in the co-reduction process could be estimated. The results showed that Al₁₁Ce₃, Al₃Ce, Al₂Ce and AlCe could be formed by the co-reduction of Ce(iii) and Al(iii). For the co-reduction of Er(iii) and Al(iii), Al₃Er₂, Al₂Er and AlEr were formed. In a La(iii) and Bi(iii) co-existing system in LiCl–KCl melts, LaBi₂, LaBi and Li₃Bi were the major products as a result of co-reduction.

Electroreduction-based Tb extraction from Tb4O7 on different substrates: understanding Al–Tb alloy formation mechanism in LiCl–KCl melt

This work presents the electroreduction of Tb(iii) ions, and formation mechanisms of Al–Tb alloys in molten chlorides by applying different types of cathodes: Mo, Al and Al-coated Mo.