LiCl-KCl Melt Research Articles

Electrochemical Behavior and Extraction of Yttrium on Cu Electrode in LiCl-KCl Eutectic

The electrochemical behaviors of Y(III) were investigated on inert W and reactive Cu electrodes in LiCl-KCl eutectic by electrochemical technique at 773K. On an inert W electrode, the apparent standard potential of Y(III)/Y(0) couple was studied at different concentration of Y(III) ions using cyclic voltammetry. The result shows the apparent standard potential of Y(III)/Y(0) couple has a dependent on the concentration of Y(III) ions. On a reactive Cu electrode, cyclic voltammetry, stripping voltammetry and square wave voltammetry experiment results indicated that the deposition potential of Y (III) shift toward more positive values than that on W electrode because of the formation of Cu-Y intermetallic compound. Five Cu-Y intermetallic compounds, Cu6Y, Cu4Y, Cu7Y2, Cu2Y and CuY, were found to be formed by transient and steady electrochemical methods. Based on open circuit chronopotentiogram, the intermetallic compounds of Cu7Y2 is easier to form and more stable than the others because its platform is longer. Potentiostatic and galvanostatic electrolysis was conducted on Cu electrode to extract metallic yttrium. Furthermore, the cyclic voltammetry curves showed that the redox signals observed before electrolysis almost disappeared after electrolysis. In addition, the concentration of Y(III) ions in LiCl-KCl melts were detected by inductive coupled plasma atomic emission spectrometer before and after electrolysis, and the current efficiency for the electroextraction of Y was estimated. The results showed that Y(III) ions could be effectively extracted using reactive Cu electrode. Finally, the electrolysis products were characterized by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The results showed that yttrium and copper can form Cu-Y intermetallic compounds during electrolysis and the thickness of alloy layer is about 50 mm. Acknowledgement The work was financially supported by the National Natural Science foundation of China (11675044, 11575047, 21790373, 21271054 and 21173060), the Major Research plan of the National Natural Science Foundation of China (91326113 and 91226201), and the International Exchange Program of Harbin Engineering University for Innovation−oriented Talents Cultivation. Figure 1

Electrochemical and thermodynamic properties of ytterbium and formation of Zn–Yb alloy on liquid Zn electrode

The electrochemical behavior of Yb(III) in LiCl–KCl–YbCl3 melts on W and liquid Zn electrodes was studied at 813 K. On the W electrode, the diffusion coefficient of Yb(III) was determined to be 3.38 × 10−5 cm2 s−1. The apparent standard Gibbs energy of the reaction: YbCl2+1/2Cl2→YbCl3 in LiCl–KCl melts was calculated. On the liquid Zn electrode, the results from cyclic voltammetry, square wave voltammetry and open circuit chronopotentiometry indicated that two electrochemical signals corresponding to the formation of two kinds of Zn–Yb intermetallic compounds were observed. Ytterbium was extracted in the form of Zn–Yb alloys by galvanostatic electrolysis on liquid Zn electrode. The results from XRD show that three kinds of Zn-Yb intermetallic compounds were formed. Moreover, the different phases of Zn–Yb alloys could be controlled by adjusting the concentrations of YbCl3.

Selective formation of Ce-Ni hydrogen storage alloys by electro-deposition in LiCl-KCl-CeCl3 melts using Ni as cathode

The electrochemical formation of Ce-Ni alloy and its nucleation mechanism were researched in LiCl-KCl melts using different electrochemical methods. Cyclic voltammetric and square wave voltammetric results indicated that the electrochemical reduction of Ce (III) appeared at a less negative value on Ni electrode than that recorded on W electrode because of the formation of Ce-Ni alloy compounds. The nucleation mechanism of Ce was found to be the progressive nucleation on Ni electrode based on Scharifker-Hill model. The change of electrode surface morphology with deposited time was observed by SEM, which indicated that the morphology of Ce deposited on Ni electrode was dendritic. Ce-Ni alloys were prepared using potentiostatic electrolysis, and checked by XRD and SEM-EDS. The results showed that hydrogen storage alloys of CeNi2, CeNi3 and CeNi5 were gained by controlling applied potential. Furthermore, the thermodynamic properties of Ce-Ni compounds were estimated in the temperature range of 823–898 K by open circuit chronopotentiometry.

Electrochemical deposition of praseodymium (III) and copper (II) and extraction of praseodymium on copper electrode in LiCl-KCl melts

Cyclic voltammogram and square wave voltammograms indicated that Cu (II) ion being reduced to Cu(0) was a two-electron process: Cu(II) + e− → Cu(I) and Cu(I) + e− → Cu(0). The diffusion activation energy for Cu (I) ions was calculated as 42.85 kJ mol−1. The equilibrium potential and apparent standard potential for Cu (I)/Cu(0) redox couple was measured by open circuit chronopotentiometry at a temperature of 773–923 K. Three reduction peaks, corresponding to the formation of PrxCuy intermetallic compounds, were detected from cyclic voltammogram and square wave voltammogram obtained by co-reduction of Pr (III) and Cu (II) or electrodeposition of Pr (III) on Cu electrode. Furthermore, potentiostatic electrolysis was performed to extract the element Pr on Cu electrode, and the electrolytic products were analyzed by scanning electron microscopy equipped with energy dispersive spectrometry. Meanwhile, the highest extraction efficiency of Pr (III) ions could reach about 99.81% at − 2.20 V for 22 h at 823 K.

Electrorefining of metallic fuel with burn-up of ~7 at% in a LiCl-KCl melt

ABSTRACT Electrorefining of irradiated metallic fuels (burn-up ~ 7 at%) in a LiCl-KCl melt at 773 K was successfully demonstrated: Actinides in the fuels were anodically dissolved in the melt. Both a selective U metal deposition on a solid cathode and a grouped recovery of actinides, U, Pu, Np, Am, and Cm, in a liquid Cd cathode were confirmed. The behavior of fission products, such as lanthanides, alkali metals, alkaline earth metals, and noble metals, were also investigated. It was found that the behaviors of actinides and fission products in the electrorefining of the fuels with ~ 7 at% burn-up were similar to those in electrorefining of fuels with ~ 2.5 at% burn-up.

Electrochemical Formation of Divalent Samarium Cation and Its Characteristics in LiCl-KCl Melt.

The electrochemical reduction of trivalent samarium in a LiCl-KCl eutectic melt produced highly stable divalent samarium, whose electrochemical properties and electronic structure in the molten salt were investigated using cyclic voltammetry, UV-vis absorption spectroscopy, laser-induced emission spectroscopy, and density functional theory (DFT) calculations. Diffusion coefficients of Sm2+ and Sm3+ were electrochemically measured to be 0.92 × 10-5 and 1.10 × 10-5 cm2/s, respectively, and the standard apparent potential of the Sm2+/3+ couple was estimated to be -0.82 V vs Ag|Ag+ at 450 °C. The spectroelectrochemical study demonstrated that the redox behavior of the samarium cations obeys the Nernst equation ( E°' = -0.83 V, n = 1) and the trivalent samarium cation was successfully converted to the divalent cation having characteristic absorption bands at 380 and 530 nm with molar absorptivity values of 1470 and 810 M-1 cm-1, respectively. Density function theory calculations for the divalent samarium complex revealed that the absorption signals originated from the 4f6 to 4f55d1 transitions. Additionally, laser-induced emission measurements for the Sm cations in the LiCl-KCl matrix showed that the Sm3+ ion in the LiCl-KCl melt at 450 °C emitted an orange color of fluorescence, whereas a red colored emission was observed from the Sm2+ ion in the solidified LCl-KCl salt at room temperature.

A particularly simple NH4Cl-based method for the dissolution of UO2 and rare earth oxides in LiCl-KCl melt under air atmosphere

Traditionally, the dissolution of UO2-based spent fuels in molten chlorides is difficult and usually conducted under strict controlling environment. Here, we report a particularly simple method utilizing NH4Cl for the dissolution of UO2 and rare earth oxides (RExOy), which is of potential interest for the pyrochemical reprocessing of UO2-based spent fuels. In this work, NH4Cl is conveniently introduced on the surface of LiCl-KCl melt. The results show that both the UO2 and RExOy can be successfully dissolved into the LiCl-KCl melt in air atmosphere with the assistance of NH4Cl. In addition, the dissolution process and mechanisms are studied in detail by electrochemical and spectroscopic methods. For the dissolution of UO2, UO2Cl2 is finally formed with the intermediates of U3O8 and UO3, and the obtained concentration of UO22+ is about 0.64% in the melt. In contrast, for the dissolution of RExOy, RECl3 is ultimately produced with the main intermediate of RECl3žxNH4Cl.

Electrochemical behavior of Dy(III) on bismuth film electrode in eutectic LiCl-KCl melts

An electrochemical study of dysprosium (III) on Bi film electrode was carried out in eutectic LiCl-KCl melts by transient and steady state electrochemical techniques. The results of transient electrochemical techniques showed that the reduction of Dy (III) appears at a more positive value than the one detected on W electrode owing to the formation of Bi-Dy intermetallic compounds through electrochemical deposition of Dy on bismuth film electrode. The thermodynamic properties of the formation for Dy-Bi intermetallics were estimated by a steady state electrochemical method in a temperature range of 713–803 K. Furthermore, the electrochemical preparation of Bi-Dy alloys was conducted by galvanostatic electrolysis at different current intensities. The Bi-Dy alloys, characterized by scanning electron microscopy equipped with energy dispersive spectrometry and X-ray diffraction, are comprised of DyBi3/5 and DyBi phases.

Solubility of Li2O in an LiCl–KCl Melt

The phase diagrams of the binary LiCl–Li2O system and the quasi-binary [LiCl–KCl]–Li2O systems containing 10 and 20 mol % KCl have been built using thermal analysis of cooling curves and isothermal saturation curves. The solubility of Li2O in LiCl–KCl melts is determined in the temperature range 500–800°C. The solubility of Li2O in the melts LiCl, LiCl–KCl (10 mol %) and LiCl–KCl (20 mol %) decreases as the KCl content increases;at 650°C, it is 11.5, 7.7, and 3.9 mol %, respectively.

Properties of the LiCl-KCl-Li2O system as operating medium for pyro-chemical reprocessing of spent nuclear fuel

Crystallization temperatures (liquidus and solidus) in the LiCl-Li2O and (LiCl-KCl)-Li2O systems with the KCl content of 10 and 20 mol.% were obtained with independent methods of thermal analysis using cooling curves, isothermal saturation, and differential scanning calorimetry. The linear sweep voltammetry was applied to control the time of the equilibrium establishment in the molten system after the Li2O addition, which depended on the composition of the base melt and the concentration of Li2O. The fragments of the binary LiCl-Li2O and quazi-binary [LiCl-KCl(10 mol.%)]-Li2O and [LiCl-KCl(20 mol.%)]-Li2O phase diagrams in the Li2O concentration range from 0 to 12 mol.% were obtained. The KCl presence in the LiCl-KCl-Li2O molten mixture in the amount of 10 and 20 mol.% reduces the liquidus temperature by 30 and 80°, respectively, but the region of the homogeneous molten state of the system is considerably narrowed, which complicates its practical application. The Li2O solubility in the molten LiCl, LiCl-KCl(10 mol.%) and LiCl-KCl(20 mol.%) decreases with increasing the KCl content and is equal to 11.5, 7.7 and 3.9 mol.% at 650°С, respectively. The LiCl-KCl melt with 10 mol.% KCl can be recommended for practical use as a medium for the SNF pyro-chemical reprocessing at temperature below 700 °C.

The kinetics process of a Pb(ii)/Pb(0) couple and selective fabrication of Li-Pb alloys in LiCl-KCl melts.

The electrode reaction of Pb(ii) and co-reduction of Li(i) and Pb(ii) were investigated on a tungsten electrode in LiCl–KCl eutectic melts by a range of electrochemical techniques. From cyclic voltammetry and square wave voltammetry measurements, the reduction of Pb(ii) was found to be a one-step diffusion-controlled reversible process with the exchange of 2 electrons. The diffusion coefficients of Pb(ii) were computed, and they obey the Arrhenius law. Using the linear polarization technique, the kinetic parameters, such as exchange current intensity (j0), standard rate constant (k0) and charge transfer resistance (Rct) for the Pb(ii)/Pb(0) couple on a tungsten electrode were studied at different temperatures, and the activation energy is 27.32 kJ mol−1, smaller than the one for diffusion of Pb(ii), which further confirmed that the reduction of Pb(ii) was controlled by diffusion. A depolarisation effect for Li(i) reduction was observed from the results of cyclic voltammetry, square wave voltammetry and chronopotentiometry due to the formation of Li–Pb alloys by co-reduction of Li(i) and Pb(ii). Furthermore, five Li–Pb intermetallic compounds, LiPb, Li8Pb3, Li3Pb, Li10Pb3 and Li17Pb4 characterized by scanning electronic microscopy and X-ray diffraction, were selectively prepared by potentiostatic electrolysis on a tungsten electrode and galvanostatic electrolysis on a liquid Pb electrode, respectively.

Co-electrodeposition of U and Mo from a LiCl-KCl melt

Co-electrodeposition of uranium and molybdenum from a LiCl-KCl melt was investigated using cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The electrochemical study showed that the electrodeposition of Mo occurred from a molten LiCl-KCl eutectic at potentials more negative than −0.3 V vs. Ag|Ag+. Electrodeposition at a low overpotential range (between −0.3 V and −0.35 V) resulted in flat, thin Mo films, whereas greater overpotentials led to the growth of 3D films. Conditions for simultaneous electrodeposition of U and Mo were then optimized by varying the concentrations of UCl3 and MoCl3 and the electrodeposition method applied. At a constant potential of −1.58 V, a melt containing 1.3 wt% UCl3 and 1.5 wt% MoCl3 resulted in the co-electrodeposition of dendrites due to the high overpotential for Mo electrodeposition. However, diffusion-controlled electrodeposition using the same potential and concentration resulted in a uniform and flat U-Mo film. This co-electrodeposition of U-Mo films could be applied to the preparation of low-cost U-Mo nuclear fuel.

High-Speed Observation of Electrolytic Deposition of Liquid Lithium Droplets in LiCl-KCl Melt

In the case of metallothermic reduction of oxide XOx-1(s) (X=Ti, Ta, etc.) by electro-deposited liquid metal Me(=Ca, Li or their alloys), the it accompanied with dissolved Me at the vicinity of the cathode is essential, where the oxide is placed close to the cathode. In this mechanism, the dissolved Me works effectively to reduce XOx-1, even if these solids do not have any direct electronic contact with the cathode. In the case of Li-LiCl-KCl-Li2O system at 723 K, colloidal microparticle dissolution of Li occurs in addition to true dissolution. Recently, the in-situ Raman spectroscopy was carried out, and obtained from colloidal Li were in agreement with the lithium cluster, Li8. The colloidal Li formation strongly depends on the linear current density and that the current concentration should cause its formation. Although colloidal Li occurs at the liquid Li and molten salt interface, the morphology of liquid Li on the electrochemically precipitated cathode surface has not been well understood as root cause. High-speed photography with high-resolution image quality has been becoming possible by recent C-MOS image sensor which has been improved by recent digital optical technology. In this study, we investigated the morphology of liquid Li in molten LiCl-KCl-Li2O by recording electrode surface image obtained with digital microscope at high speed. To elucidate the mechanisms of interfacial morphology on the basis of three-dimensional shape observations, the electric resistance furnace was designed to allow the phenomena occurring within to be observed directly. The changes induced in the interface of electrodes were recorded at a rate of 500 frames per a second (fps) and a resolution of 640 × 480 pixels using a high-speed microscope (the field of view of 610 μm × 460 μm, and the length per pixel of 1.04 μm) was employed. LiCl (>99.0%) and KCl (>99.5%) were used for the melt. The eutectic mixture of LiCl–KCl (= 59:41 mol%, m.p. = 625 K) contained in a borosilicate glass crucible with flat surface was dried under vacuum at 573 K for more than one night to remove residual water and then melted. Li2O (>99.5%) was directly added to the melt as an O2-ion source in the concentration range of 0.1–1.0 mol%. The experimental temperature was 723 K. The interface temperature was measured with a K–type thermocouple with a glass protection tube. All the experiments were conducted in an Ar atmosphere (>99.9995%). The working electrode was a Mo rod (ϕ 1.5 mm, 99.95%) for cyclic voltammetry and it was used as a cathode for electrodeposition of liquid lithium. The counter electrode was a graphite rod (ϕ 10 mm). The Ag+/Ag reference electrode was employed, i.e. a silver wire (ϕ 1.0 mm, 99.99%) was immersed in the LiCl–KCl eutectic melt containing 0.5 mol% AgCl (>99.5%), which was set in a borosilicate tube. Electrochemical measurements were performed using an automatic polarization system (Hokuto Denko Corp., HZ-5000). From the snapshots corresponding to each potential in cyclic voltammograms, blue “fog” was observed are observed at about −2.46 V (vs. Ag+/Ag) with the electrodeposited Li, notably during Li dissolution reaction. The amount of colloidal Li generation decreased by Li2O addition. Chronoamperometry was conducted at -2.55 V vs. Ag+/Ag using a Mo rod electrode for 1.0 s. Photographs of the transient behavior of electrode surface in LiCl-KCl melt are shown in Fig. 1. It can be seen that droplets are formed and grow on the surface of the Mo electrode as the current is generated. It should be noted that the liquid phase precipitates grow heterogeneity on the Mo surface. Considering the “electrocapillary” theory, due to the electrostatic attraction between the droplets charge and charge in the electrode, the energy of their interface is reduced, and the wetting of the electrode should be enhanced. Nevertheless, metal droplets do not wet and spread on the electrode surface completely. Figure 1

Electrochemical Extraction of Nd from NaCl-KCl Melt by Formation of Cu-Nd Alloys

Electrochemical behavior of Nd was studied in NaCl-KCl melt on W and Cu electrodes via cyclic voltammetry and chronopotentiometry. Generally, the reduction of Nd3+ takes place in two consecutive steps in molten chlorides, such as LiCl-CaCl2, LiCl-BaCl2, CaCl2-NaCl, LiCl-KCl melts. However, the reduction of Nd3+ ions was found to be through a one-step process: Nd3+ + 3e− → Nd. The co-reduction behavior of Nd3+ and Cu2+ ions and the mechanisms of alloy formation were investigated in NaCl-KCl melt on W electrodes at 988 K (715 °C). Four potential plateaus corresponding to four different kinds of Cu-Nd intermetallic compounds were detected. Cu-Nd alloys were prepared on Cu electrodes at 988 K (715 °C) and 1143 K (870 °C). At 988 K (715 °C), Cu5Nd phase was identified by X-ray diffraction. The morphology and micro-zone chemical analysis of the alloys were characterized by scanning electron microscopy equipped with energy-dispersive spectrometry. The alloy film was observed on the Cu electrodes. Moreover, at 1143 K (870 °C), a globate bulk Cu-Nd alloy with Cu5Nd, Cu4Nd, Cu2Nd, CuNd, and Cu phases, as liquid in the melt, was obtained at the bottom of the crucible.

A New Green Approach for Recovery of Metallic Tungsten through Electrolysis of Tungsten Carbide Scrap Anode in Molten Salts

In this study, a new green approach has been developed for the recovery of tungsten by using tungsten carbide (WC) scrap material as consumable anode in LiCl-KCl molten salts at 773 K to produce metallic tungsten. The feasibility of the direct electrochemical dissolution of WC anode into metallic tungsten was evaluated based on the experimental verifications and electrochemical methods. The effects of the main technical parameters, including the cell voltage, electrolysis time and electrolysis temperature, on the dissolved condition of anode were studied and the optimal anode parameters were obtained. It was found that a large electrolytic voltage, high electrolytic temperature and long electrolysis time would be favorable for the dissolved state of the tungsten carbide anode under the same conditions. The cathode product was analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the tungsten particles with a diameter of 100 nm could be prepared by this process in a molten salt bath. Linear sweep voltammetry was applied to investigate the dissolution of WC anode, and showed that the WC scrap material could be used as consumable anode to produce tungsten powder. Other electrochemical techniques including cyclic voltammetry , square-wave voltammetry and chronopotentiometry were employed to explore the electrochemical properties of tungsten ion derived from WC anode in LiCl-KCl melts. These results confirmed that electroreduction of tungsten ion in the melts proceeded in one step with four exchanged electrons.

Corrosion of Zirconium in Halogenide Melts

We propose a method for the evaluation of stability of the corrosion products of zirconium in melts of different compositions. The method is based on the analysis of the dependence of the equilibrium potential of zirconium electrode on the initial concentration of its compounds in the oxidation state 4+. It is discovered that zirconium compounds in the oxidation state 2+ are in equilibrium with the metal in all investigated systems and their stability depends on the composition of the melt and decreases in the following order: (NaBr–KBr) > KBr ≥ KCl > (LiCl–KCl). It is also established that, parallel with zirconium compounds in the oxidation state 2+, the investigated systems contain its compounds in the other oxidation states. The stability of these compounds in bromide melts decreases in the following order: Zr(II) (NaBr–KBr) > Zr(IV) (NaBr–KBr) > Zr(II) (KBr) > Zr(IV) (KBr). In chloride melts, the observed sequence has a somewhat different form: Zr(II) (KCl) > Zr(IV) (KCl) > Zr(II) (LiCl–KCl). Lithium is present among the corrosion products in LiCl–KCl melts. We also determined the thermodynamic characteristics (ΔH and ΔS) of equilibria of the corrosion products of zirconium with the investigated melts.

Electrochemical Extraction of Praseodymium by Formation of Zn-Pr Alloy in LiCl-KCl Melts with the Assistance of ZnCl2 and Liquid Zn

The electrochemical behavior of Zn(II) and Pr(III) in LiCl-KCl melts was investigated by different electrochemical measurements. On W electrode, the reduction of Zn(II) to Zn(0) in LiCl-KCl melts was realized by a single reaction step. In LiCl-KCl-ZnCl2-PrCl3 melts, cyclic voltammetry, square wave voltammetry and open circuit chronopotentiometry showed that six kinds of Zn-Pr intermetallic compounds could be formed at 923 K. However, when the experimental temperature increased to 948 K, eight potential plateaus corresponding to the formation of eight different kinds of Zn-Pr intermetallic compounds appeared in the open circuit chronopotentiogram. Electrochemical extraction of praseodymium was implemented by the formation of Zn-Pr alloys, which were manufactured by galvanostatic electrolysis on W electrodes in LiCl-KCl-ZnCl2-PrCl3 melts and by galvanostatic and potentiostatic electrolysis on liquid Zn electrode in LiCl-KCl-PrCl3 melts, respectively. After electrolysis, the alloys were analyzed by XRD and SEM equipped with EDS analysis.

Electrochemical Synthesis Quaternary Mg−Li−Al−Pr Alloy with and without Whisker on Magnesium Cathode in LiCl−KCl−PrCl3−AlCl3 Melts

The electrochemical behavior of Pr(III) was firstly studied by different electrochemical measurements, and the Mg−Li−Al−Pr alloys with different alloy phases were prepared by galvanostatic electrolysis. Meanwhile, the electrochemical behavior of Mg(II) was also investigated by cyclic voltammetry and chronopotentiometry, and the diffusion coefficient of Mg(II) in LiCl–KCl melts was finally determined by chronopotentiometry. The results from different electrochemical measurements which were measured in LiCl−KCl−MgCl2−AlCl3−PrCl3 melts exhibited that two kinds of Al−Pr intermetallic compounds (Al2Pr and Al3Pr) and one kind of Mg−Pr intermetallic compound (Mg12Pr) were formed. Chronopotentiometry illustrated that the co−deposition of Mg(II), Li(I), Al(III) and Pr(III) ions will be realized when the current intensity is more than −200 mA (S = 0.322 cm2). Quaternary Mg−Li−Al−Pr alloys with and without whiskers were prepared on Mg cathodes by galvanostatic electrolysis in LiCl−KCl−AlCl3−PrCl3 melts. The deposits were finally analyzed by XRD, SEM and TEM with electron diffraction test. The result from the SEM analysis exhibited that the element aluminum existed in the form of Al−Pr intermetallic compound whiskers in the Mg−Li−Al−Pr alloy, which was obtained by galvanostatic electrolysis on liquid magnesium electrode. The micro hardness and corrosion resistance of Mg−Li−Al−Pr alloys were enhanced significantly with the assistance of Al−Pr intermetallic compound whiskers.

Electrochemical and Spectroscopic Monitoring of Interactions of Oxide Ion with U (III) and Ln (III) (Ln = Nd, Ce, and La) in LiCl-KCl Melts

Using cyclic voltammetry and UV-vis absorption spectroscopic methods, we studied the precipitation reactions of trivalent uranium and lanthanides (Nd, Ce, and La) with the oxide ion in LiCl-KCl molten salts, which are likely side reactions during the electrorefining process for nuclear fuel treatment. The in situ electrochemical and spectroscopic monitoring demonstrated that U3+ consumed O2− with the mole ratio of 2:1, whereas the lanthanide ions reacted with O2− with the mole ratio of 1:1. Raman spectroscopy and X-ray diffraction were also employed to analyze the precipitates, confirming that U3+ was precipitated and oxidized into UO2, while the trivalent lanthanide ions formed oxychlorides (LnOCl). As a preliminary study of actinide co-precipitation, we also electrochemically monitored the precipitation reactions in a mixed melt containing uranium and lanthanides, demonstrating a higher reactivity of the former with the oxide ion in LiCl-KCl.

Electrochemical behaviour of erbium(III) and its extraction on Cu electrode in LiCl-KCl melts

The electrochemical behaviour of Er(III) was studied on W and Cu electrodes in LiCl-KCl melts by a series of electrochemical techniques. The studies indicated that Er(III) ions were reduced to Er(0) in a one-step diffusion-controlled process exchanging three electrons. The diffusion coefficient of Er(III) was determined and the activation energy for diffusion of Er(III) ions was found to be 35.2 kJ mol−1. The equilibrium potential of the Er(III)/Er(0) redox couple was measured via open circuit chronopotentiometry in the temperature range of 773–923 K, with subsequent calculation of the apparent standard potential, EEr(III)/Er(0)∗0, and the apparent Gibbs free energy of formation for ErCl3, ΔGf∗0(ErCl3). The cyclic voltammogram and square wave voltammogram obtained on Cu electrode, compared with those on W electrode, showed several new pairs of reduction peaks observed at more positive potential, which means that the underpotential deposition of erbium occurs. The thermodynamic properties of the Cu-Er intermetallic compound, Cu5Er, were estimated by open circuit chronopotentiometry. Potentiostatic and galvanostatic electrolysis was performed on Cu electrode to extract erbium. The extraction products, consisting of CuEr, Cu2Er and Cu5Er, were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). Furthermore, the extraction efficiencies were evaluated during potentiostatic electrolysis at different electrolysis times using an inductive coupled plasma atomic emission spectrometer (ICP-AES), which showed that the highest extraction efficiency of Er(III) could reach about 98.92%.