LiCl-KCl Eutectic Melt Research Articles

Separation of uranium from lanthanides (La, Ce, Nd) and purification of waste salt via aluminum electrodes with different structures in LiCl-KCl eutectic

Aluminum is an ideal cathode material for the pyrochemical reprocessing of spent nuclear fuels. However, there is a lack of large-scale experiments to further assess its performance. Here we designed several Al electrodes with sheet, rod, and porous morphologies, and employed them in separating actinides (An) from lanthanides (Ln) and purifying the waste salts in about 500 g of LiCl-KCl eutectic melt at 773 K. By applying a constant potential of −1.2 V vs. Ag/AgCl, U can be separated from Ln (La, Ce, and Nd) by forming Al-U alloys consisting of Al3U and Al4U with high separation factors and current efficiency. Among all Al electrodes used in our experiments, the porous-shaped ones show the fastest electrochemical reaction rate, and hence only 56 h were required to achieve the separation. Subsequently, the purification of the waste salts from U-Ln separation was conducted via constant potential electrolysis at −1.5 V vs. Ag/AgCl on porous-shaped Al electrodes. About 99.9 % of Ln was extracted via forming Al-Ln alloys, leaving a purified electrolyte that can be reused. In all, about 17 g of U metals and 1 kg of waste salts were successfully reprocessed in our large-scale experiments, which envisions the feasibility of applying Al electrodes in engineering-scale pyrochemical reprocessing.

Permeation Tendency of Rare-earth Elements through a Ni-based Alloy Diaphragm in LiCl–KCl Eutectic Melts

Permeation Tendency of Rare-earth Elements through a Ni-based Alloy Diaphragm in LiCl–KCl Eutectic Melts

Radiochemical and chemical characterization of fuel, salt, and deposit from the electrorefining of irradiated U-6 wt% Zr in hot cells

Abstract Metal fuels are considered as the promising candidates for future fast breeder reactors. Pyro-chemical reprocessing is the ideal method for reprocessing spent metallic fuels due to the inherent process advantages. Electrorefining run was demonstrated in a hot cell facility with irradiated U-6 wt% Zr alloy at 500 °C using LiCl–KCl eutectic melt. In order to understand the behavior of the actinides and various fission products during high-temperature electrolysis, various process streams, viz., irradiated metal alloy fuel, the eutectic salt, and the cathode deposit were analyzed for the uranium, plutonium, and other fission product contents. Various methods employed for characterizing the process streams and the behaviors of some of the fission products during the electrolysis process are highlighted. The major gamma emitting radionuclides present in the irradiated fuel were 106Ru, 125Sb, 134Cs, 137Cs, 144Ce, and 154Eu. During electrorefining, cesium, cerium and europium were oxidized and dissolved in the molten media, whereas ruthenium and antimony remained in the anode basket. A minor contamination of zirconium was found in the cathode deposit.

Electrochemical investigations on cathodic reduction processes at graphite electrode in LiCl-KCl eutectic melt

Sequence of redox processes in LiCl-KCl eutectic at graphite electrode was studied in temperature range 698-798 K using cyclic voltammetry and electrochemical impedance spectroscopy. There were two reduction steps observed when potential was scanned from −0.25 to −1.50 V (vs.▪); a single-step two-electron transfer process due to reduction of carbon to ▪ followed by reduction of ▪. Electrolysis at −1.20 V at 773 K led to formation of ▪ on graphite surface. Complex impedance data were modelled using equivalent circuits and it was established that ▪ film formed around graphite electrode restricting both diffusion of ▪ in melt and metallic ▪ into graphite framework. These results are relevant in terms of their consequences in molten salt electrorefining of metal fuels.

Long-life mullite and boron nitride membranes Ag/AgCl and Pb/PbCl2 reference electrodes for LiCl-KCl eutectic melt

In the pyrochemical reprocessing of spent nuclear fuel (SNFs), a reference electrode with long life and high stability is extremely important for the electrochemical extraction actinides (An). In this work, Ag/AgCl and Pb/PbCl2 reference electrodes using boron nitride (BN) and mullite tubes as reference electrode membrane materials in LiCl-KCl eutectic melt at different temperature (723 ∼ 773 K) were reported. The stability of reference electrodes immersed in melt for a long time and under electrolysis conditions was systematically studied by different electrochemical methods including cyclic voltammetry (CV), open-circuit chronopotentiometry (OCP) and chronoamperometric (CA). The results showed that BN membrane reference electrodes have excellent ions conductivity and can obtain smooth electrochemical curves. But when it was used for a long time (about 30 h), potential drift would occur. Thus, the stability of the membrane was excellent in short time. On the contrary, the ionic conductivity of mullite membrane reference electrodes was more inferior than that of BN. However, this could be improved as the temperature increased. At the same time, the potential was stable during reference electrodes immersed in melt for 48 h and there was only slight drift (145 h, 80 mV for Ag/AgCl and 40 h, 40 mV for Pb/PbCl2 reference electrodes) under long-term electrolysis, which shows that mullite membrane reference electrodes have extremely high stability and practical application prospects.

(Invited) Electrochemical Synthesis of Diamond from Carbon Dioxide in Molten Lithium Chloride-Potassium Chloride Systems

IntroductionIn order to achieve carbon neutrality by 2050, not only the CO2 capture and storage (CCS) but also the CO2 capture and utilization (CCU) is necessary. Here, electrochemical CO2 conversion technology in molten salt is considered to be one of the promising candidates for CCU [1,2]. In this study, we aimed to convert CO2 into diamond, which is one of the most valuable carbon materials. As a first step, we investigated the electrochemical synthesis of diamond in molten LiCl-KCl systems containing K2CO3 and KOH, based on the premise that CO2 dissolves as CO3 2- in molten salts containing O2-. As a result, micro-Raman spectroscopy and scanning electron microscopy (SEM) confirmed that a part of the deposits obtained by electrolysis were diamonds. As a second step, we attempted the electrochemical synthesis of diamond using CO2 as the actual raw material. Here, H2O was also bubbled in the molten salt in order to produce KOH. The deposits obtained by electrolysis were then analyzed by micro-Raman spectroscopy and SEM, which confirmed the synthesis of diamond.ExperimentalCyclic voltammetry and potentiostatic electrolysis were performed after adding K2CO3 and KOH to LiCl-KCl eutectic melts under an Ar atmosphere at 973 K. The working electrode was a Ni flag (Φ 3 × 0.1 mm) or Ni plate (5 mm × 10 mm × 0.1 mm), the counter electrode was a glass-like carbon rod, and the reference electrode was an Ag+/Ag electrode. The potential was calibrated with Li+/Li potential. After electrochemical measurements were performed, samples were prepared by potentiostatic electrolysis using the Ni plate electrodes. In the case where CO2 was used as a raw material, LiCl-KCl eutectic molten salt containing Li2O was prepared, and CO2 and H2O were bubbled into it in predetermined amounts, respectively. After electrochemical measurements, potentiostatic electrolysis was performed to prepare samples. The obtained samples were analyzed by SEM, EDX, and micro-Raman spectroscopy.Result and DiscussionFirst, electrochemical measurements in baths containing only K2CO3, only KOH, or both indicated that carbon deposition and hydrogen evolution proceed simultaneously in the potential range more negative than 1.2 V. Then, samples were prepared by potentiostatic electrolysis using Ni plate electrodes at 1.0 to 1.2 V (vs. Li+/Li). The charge density was unified at 10 C cm-2. As an example, the surface SEM image of a deposit obtained at 1.1 V in a bath containing 0.05 mol% K2CO3 and 1.0 mol% KOH is shown in Fig. 1(a). The EDX analysis of this area showed that only C and Ni from the substrate were detected. The result of micro-Raman spectroscopy of the sample is shown in Fig. 1(b), which shows a spectrum characteristic of diamond with a sharp peak at 1332 cm-1. Based on the results of these three analyses, the electrochemically synthesized angular particles were identified as diamond.On the day of the meeting, we will also present the results of electrolysis using CO2 as the raw material.AcknowledgmentA part of this work was supported by JSPS KAKENHI Grant Number 21K19024.

Accelerated Separation of Uranium from Lanthanides (La, Ce, Sm) in LiCl-KCl Eutectic by Porous Aluminum Electrodes

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.

Conversion of UO2 to UCl3 using AlCl3 in LiCl–KCl eutectic melt in presence of lanthanide (Nd, Pr, Ce, La) oxides: a spectroscopic study

Conversion of UO2 to UCl3 using AlCl3 in LiCl–KCl eutectic melt in presence of lanthanide (Nd, Pr, Ce, La) oxides: a spectroscopic study

Promising Method of Sm–Co Magnet Reprocessing in Alkali Chloride Melts

Developing new, efficient methods for samarium and cobalt recovery from scraps/rejects and swarf at Sm–Co magnet manufacturing sites during shaping and finishing is an important task in terms of meeting their growing demand. In this work, the reaction of oxygen with a solution of samarium and cobalt chlorides in a LiCl–KCl eutectic melt was studied at 400–600 °C to explore possible methods for the separation and recovery of samarium and cobalt from these waste products. The pyrochemical reaction resulted in the formation and precipitation of samarium oxychloride, while the cobalt remained in the melt in a soluble chloride form. The effect of temperature and the amount of oxygen passed through the melt (oxygen-to-samarium molar ratio) on the course of the reaction were studied. Kinetic parameters of the oxygen with samarium chloride reaction were determined.

Electrochemical behaviour of LiCl-KCl eutectic melts containing moisture as impurity. Part I: Inert tungsten electrode

• Acid-base titration method for estimation of moisture in LiCl-KCl eutectic melts developed. • Redox behaviour of moisture in LiCl-KCl melts at tungsten electrode investigated by EIS. • Suitable equivalent circuit models selected for fitting of complex impedance data. • Contribution of capacitive effects in moisture containing LiCl-KCl melts explored. • Complex impedance data validated by Kramers-Kronig transforms. Voltammetric response of purified LiCl-KCl eutectic melt at 500 ° C is uncomplicated in which cathodic and anodic limits are known to be due to Li + | Li and Cl - | Cl 2 redox couples, respectively. Presence of H 2 O as impurity adds newer characteristics to voltammetric and impedance responses of the melt, as a result of faradaic processes involving formation of OH - and O 2 - in potential region −0.40 to −2.30 V as well as non-faradaic process involving adsorption of OH - at around −1.25 V. Present work was focussed on characterization of moisture containing LiCl-KCl eutectic melts using electrochemical impedance spectroscopy. LiCl-KCl eutectic melts thermally equilibrated with different amounts of H 2 O at 500 ° C were further analysed for residual moisture content by acid-base titration method developed as part of this experimental work. Complex impedance response of different LiCl-KCl eutectic melts at inert tungsten electrode was recorded in potential range −0.50 to −2.50 V to explore contributions of various faradaic and non-faradaic processes due to secondary impurities formed as a result of H 2 O as primary impurity in the melt. Equivalent circuit models were selected to fit complex impedance data of different melts. Validation of impedance data was also performed by Kramers-Kronig transforms in which pseudo- χ 2 values in range 10 - 6 to 10 - 4 were obtained.

Electrochemical behaviour of LiCl-KCl eutectic melts containing moisture as impurity. Part II: Uranium electrode

In Part I, LiCl-KCl eutectic melt purified by chlorine and LiCl-KCl + xwt.% H2O prepared by thermal equilibration of eutectic mixture with H2O at 500 °C were analysed for moisture content using acid-base titration. They were further investigated by electrochemical impedance spectroscopy (EIS) at inert tungsten electrode. It was established that cathodic reduction of H2O led to formation of OH- that adsorbed on tungsten electrode in potential range −0.80 to −1.50 V. The OH- film contributed to capacitive response as well as it offered a resistance to any other faradaic process occurring in that potential range. In this work, same LiCl-KCl eutectic melts were used to explore the anodic dissolution of uranium electrode in potential range −1.40 to −0.90 V by EIS. Complex impedance data in all melts were fitted to different equivalent circuit models. Presence of OH- film, which influenced the dissolution of uranium in LiCl-KCl + H2O melts, was modelled using additional resistor and constant phase elements in the equivalent circuit. Impedance data were further validated by Kramers-Kronig transforms where pseudo-χ2 values varied from 8.5×10−6 to 1.2×10−4 confirming a good compliance with spread of fit residuals across logω limited to less than ±3%. After EIS measurements, melts were again analysed by cyclic voltammetry and additional voltammetric features complicating the redox behaviour of U3+|U couple were analyzed.

Electrochemical extraction kinetics of Nd on reactive electrodes

• Pyroprocessing technology is a promising technology for the reprocessing of spent fuel. • It is critical to pursue electrode materials with high An / Ln separation efficiency. • The electrochemical reduction of Nd 3+ on the W electrode is a two-step reduction process. • The kinetic properties of Nd 3+ on W, reactive electrodes were measured. • Cd was evaluated as a favorable electrode material for electrochemical extract ion of Nd. Pyroprocessing technology with molten salt electrolysis as the core is a promising technology for the reprocessing of spent fuel. In this work, the electrochemical reduction mechanism and kinetic properties of Nd 3+ on various electrodes (inert W and reactive Al, Ga, Bi, Cd, Zn, Pb, and Sn electrodes) were systematically investigated and compared in LiCl-KCl eutectic melts using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel techniques. The electrochemical reduction of Nd 3+ was a two-step process on the W electrode including Nd 3+ →Nd 2+ and Nd 2+ →Nd, while it became a one-step process involving three electrons on the reactive electrodes with obvious depolarization effects. Furthermore, the connections between the reduction potentials of Nd 3+ on these reactive cathodes and the formation energies of the electrode-rich alloy phases (Al 11 Nd 3 , Cd 11 Nd, Pb 3 Nd, Zn 17 Nd 2 , Ga 6 Nd, Sn 3 Nd, BiNd 2 ) were established. After evaluating the physicochemical, depolarization and kinetic properties of these reactive electrodes, liquid Cd was considered as the most favorable material for the electrochemical extraction of Nd. In addition, Al, Cd, and Bi are also promising candidates for An / Ln separation.

(Invited) A Novel Electrochemical Recycling Method for Rare Earth Metals from Scrap Magnets Using Molten Salt Electrolysis and Alloy Diaphragms

Today, rare earths (RE) are indispensable as industrial materials all over the world. At the same time, the world is facing a shortage of rare earth resources and a sharp rise in rare earth prices. In order to alleviate this situation and establish a more sustainable use of RE metals, it is necessary to develop a simple, inexpensive, and environmentally friendly process for the recovery and separation of RE metals. In particular, the recovery of RE from Nd-Fe-B magnet scraps is very important because a large amount of magnet scraps are expected to be disposed of from EVs and HEVs in 10 years. For use in EVs and HEVs, Dy must be added to Nd-Fe-B magnets in order to maintain strong magnetic properties even at temperatures above 473 K. Therefore, the recovery and separation of Dy and Nd, which is generally difficult, is required for the new recycling process.With this background, we proposed a process for the separation and recovery of RE metals from magnet scraps using molten salt and alloy diaphragms (Figure 1) [1-4, 6-11]. The proposal was based on our previous finding that certain RE metals can be rapidly alloyed and de-alloyed with iron group (IG) metals in molten salt by electrochemical methods [5].As a candidate molten salt, we used LiCl-KCl eutectic melt at 723 K. We first investigated the electrochemical formation of Dy-Ni, Nd-Ni, and Dy-Nd-Ni alloys in the molten salts containing DyCl3, NdCl3, and DyCl3-NdCl3, respectively, and achieved a high separation mass ratio of Dy/Nd = 72 in the alloy samples [6]. As a next step, we demonstrated the selective permeation of Dy through the alloy diaphragm using a primitive-type electrolytic cell [7]. Recently, we further investigated the selective permeation of Dy through an alloy diaphragm made of RENi2 [8].Considering that molten fluorides such as LiF-REF3 and LiF-CaF2-REF3 are used for smelting RE metals, we also investigated the electrochemical formation of Dy-Ni, Nd-Ni, and Dy-Nd-Ni alloys in LiF-CaF2 eutectic melts containing DyF3, NdF3, and DyF3-NdF3, respectively, at 1123 K [2-4]. The results showed that the Dy/Nd ratio in Dy-Nd-Ni alloys has a potential dependence. The highest value of Dy/Nd was 5.6, which is lower than the value obtained for the LiCl-KCl melt [2].We originally focused on RE-Ni alloy, which has both high alloy formation rate and high Dy/Nd separation rate, and started to investigate it as an alloy diaphragm. However, RE-Ni alloy is not suitable for long-term use because of its brittleness and low durability. In order to develop a more durable alloy diaphragm, iron-group alloys such as Ni-Cr, Ni-Mo, and Ni-Cr-Mo alloys were selected as candidates for the base material [9,10]. Since Cr and Mo are difficult to alloy with RE elements, these components are expected to reinforce the mechanical strength of the alloy diaphragm. The shear stress measurements of the Dy-alloyed samples showed that the Ni-Cr-Mo alloy is the most suitable base material to improve mechanical strength [10]. We are also investigating the use of liquid alloys as another candidate for the diaphragm material [11].AcknowledgementA part of this study was conducted as commission research with the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Selective Permeation of Neodymium Through an Alloy Diaphragm in Molten Chloride Systems

The selective permeation of Nd through an RE–Ni (RE = Nd and Dy) alloy diaphragm was investigated in LiCl–KCl eutectic melts containing NdCl3 and DyCl3 or LaCl3 at 450 °C. The investigation was a part of an ongoing study on a new recycling process for Nd–Fe–B permanent magnets. Selective permeation of Nd was achieved by controlling the potential of the alloy diaphragm, which functioned as a bipolar electrode. Interestingly, energy dispersive X-ray analysis revealed that the Nd content in the alloy diaphragm was less than 2 at%. These results suggest that the transportation rate of Nd atoms in the alloy diaphragm was extremely high compared to that of Dy atoms. To obtain further insights into the transportation mechanism of the RE atoms in the alloy diaphragm, transmission electron microscopy (TEM) was performed. The TEM results suggest that the transportation of RE atoms cannot be explained only by simple grain boundary diffusion, and that a large number of dislocations formed in the alloy diaphragm contribute to the rapid transportation of the RE atoms.

<i>In-situ</i> Observation of Bubble Through Each Interface of a KCl Aqueous Solution / Hg and a Molten Salt / Sn by Controlling Applied Potential

In-situ observation of Ar bubble through each interface of a KCl aqueous solution / Hg and a molten salt / liquid Sn were conducted by controlling applied potential in order to simulate the behavior of bubble at interface of slag / metal. In a KCl aqueous solution, the rate of Ar bubble through each interface of a KCl aqueous solution / Hg became slow with applying −2.0 V at 298 K. This behavior caused by the stabilization of interface with deceasing the interfacial tension, and a lot of Hg droplet formed by rupture of bubble was drawn into Hg phase under the interface in seconds. In a LiCl-KCl eutectic melt, the interfacial tension of the molten salt / liquid Sn were measured by the in-site observation of contact angle with applying −2.0~0 V(vs. Ag+/Ag) at 793 K. The behavior of interfacial tension corresponded to typical electrocapillary curve. The interfacial tension at −0.75 V became highest, 310 (dyn/cm = mN/m), and the interfacial tension at −2.0, 0 V became lowest, 210 (dyn/cm = mN/m), and the Ar bubble through the interface became slowest with applying at −2.0 V. This behavior was same as that through the interface of KCl aqueous solution / Hg.

Selective Permeation of Dysprosium Through an Alloy Diaphragm in Molten Chloride Systems

To develop a new separation technique for rare earth (RE) elements based on alloy diaphragms and molten salt electrolysis, a permeation experiment was conducted in LiCl–KCl eutectic melts containing RECl3 (RE = Dy, Nd, and La, 0.5 mol%) at 450 °C. In this technique, the alloy diaphragm functions as a bipolar electrode and RE ions permeate via three steps: (a) reduction of RE ions to form alloys on the anolyte side of the diaphragm, (b) diffusion of RE atoms in the diaphragm, and (c) oxidation of RE atoms to dissolve into the catholyte on the other side of the diaphragm. The experiment indicated that Dy selectively permeated through the alloy diaphragm consisting of RENi2. The permeated Dy/Nd molar ratio was ∼5, which was mainly determined by the selective alloy formation on the anolyte side of the diaphragm. However, the obtained Dy/Nd ratio was lower than that suggested by the preliminary experiment, in which a Ni substrate was simply alloyed in a LiCl–KCl–NdCl3–DyCl3 melt. Scanning electron microscopy observation and energy dispersive X-ray analysis of the diaphragm revealed that the lower selectivity compared to the preliminary experiment was attributable to the high diffusion rate of Nd atoms inside the alloy diaphragm.

Selective Actinides Recovery over Lanthanides Using Liquid Gallium Cathode

1. Introduction Pyroprocessing is a promising technology for a fast reactor cycle with a highly concentrated minor actinides (MA: Np, Am and Cm)-bearing metallic fuel. Separation of actinides (An) from fission products such as lanthanide elements (Ln) is one of the difficult challenges to establish practical pyroprocessing. Liquid Cd cathode (LCC) with LiCl-KCl bath has been generally used for An recovery in our process [1], however, An/Ln separation performance using LCC was not high enough to fabricate a highly concentrated MA-bearing fuel from materials having a high ratio of Ln/An. Our recent studies showed that a combination of liquid Ga cathode with LiCl-KCl bath had potential to give a higher An/Ln separation performance, and currently we are developing an innovative pyroprocessing using the liquid Ga electrode. Solubility of U and Pu in liquid Ga is smaller than in liquid Cd. Therefore, the solid precipitates (An-Ga alloy) formation could have a significant influence on designing the process compared to the case of using LCC. However, the influence of the solid precipitates formation on An/Ln separation performance is unclear.In this study, galvanostatic electrolysis test on the recovery of U, Pu and Am in liquid Ga was carried out to investigate the influence. Precipitation of Pu-Ga alloy was observed by SEM/EDX on the cross section of Ga electrode after the electrolysis, and separation factors (SFs) for each metallic elements (M) based on Ce, which is defined as (M/Ce concentration ratio in liquid Ga)/(M/Ce concentration ratio in the salt phase), were calculated to evaluate An/Ln separation performance. 2. Experiment All experiments were performed in glove boxes with high-purity Ar atmosphere. Cd-0.1wt%Li alloy anode, liquid Ga cathode and Ag/AgCl reference electrode were used in LiCl-KCl eutectic melt at 773K. Two runs of galvanostatic electrolysis experiments were carried out applying the constant current of 5~10 mA (cathodic current densities: 3.76~7.53 mA/cm2). In the first experiment, An were recovered in the liquid Ga electrode from LiCl-KCl melt containing An chlorides, where concentrations of recovered An in the liquid Ga were almost the solubility. In the second experiment, two times larger amounts of An than the solubility were recovered in liquid Ga from LiCl-KCl melt containing both An and Ln chlorides. After the electrolysis, the Ga and the molten salt were sampled and dissolved into nitric acid. Concentrations of elements in the samples were analyzed by ICP-AES. γ spectrometry was also used to analyze Am concentration in samples. Cross section of solidified Ga electrode was observed by SEM/EDX. 3. Results and discussion It was confirmed that SFs of An seen in Table 1 were around ten times higher values than those obtained in the case of LCC. Furthermore, the SFs of An in the case of the amount of An recovered in liquid Ga exceeding solubility (second experiment) were comparable to those in the case of the An concentration below solubility. The SEM/EDX observation showed that grain shaped precipitates with 1～10 μm was formed homogeneously inside the Ga and the size of the precipitates increased with the amount of recovered An in liquid Ga. Chemical form of the precipitates was assigned to be Pu-Ga alloy by the EDX. It was also found that the precipitates did not accumulate on the surface of liquid Ga. In the present experimental conditions, the amount of An in the liquid Ga had an influence on the precipitation formation, while the precipitation had no influence on An/Ln separation performance.AcknowledgementThis work is supported by the Innovative Nuclear Research and Development Program from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Reference [1] S. Kitawaki, et al. Nucl. Technol., 162 (2008) 118-123.[2] T. Murakami et al., J. Nucl. Radiochem. Sci., 16 (2016) 5-10. Figure 1

Thermodynamic and Kinetic Properties of Mg(II) in LiCl-KCl Melt and the Formation of Zn-Mg Alloy on Liquid Zn Electrode

Thermodynamic and kinetic properties of Mg(II) in LiCl-KCl eutectic melt were investigated by electrochemical techniques. The diffusion coefficients of Mg(II) in the melt at various temperatures were studied by cyclic voltammetry, and the activation energy of Mg(II)/Mg was calculated to be (48.5 ± 3.7) kJ mol−1. The exchange current densities and reaction rate constants of Mg(II)/Mg at different temperatures from 773 K to 873 K were calculated by testing polarization curves on Mo electrode, and results showed that the exchange current densities became larger as the temperature increased. Equilibrium potentials of Mg(II)/Mg on Mo electrode and liquid Zn electrode were also tested by open circuit potential method. Subsequently, the apparent standard potential of Mg(II)/Mg, apparent standard Gibbs energy for the formation of MgCl2 and activity coefficients of Mg in the liquid Zn were calculated. Finally, metallic Mg was extracted in the form of Zn-Mg alloys by galvanostatic electrolysis on liquid Zn electrode. The deposit was analyzed by X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and Mg2Zn11 was detected in the deposit.

Electrochemical Reduction Behavior of Boron in Molten LiCl–KCl–KBF4

1. Introduction The consumption and demand of Nd-Fe-B magnets, so-called neodymium magnets, is increasing year by year. Since the rare earth elements such as Nd can be obtained from sparse mineral resources, the technology for the recycling system of Ne-Fe-B magnets are highly required. The authors have been developing a technique to separately recover Nd and Dy from used Ne-Fe-B magnets using alloy diaphragm and molten salt [1].Although the electrochemical behavior of Nd and Dy was intensively investigated, the Ne-Fe-B magnet contains B as well as Fe, and the behavior of B in molten salt has not been clarified yet. Therefore, in this study, we investigated the behavior of B in LiCl–KCl eutectic melts at 723 K. The LiCl–KCl eutectic melt was chosen because a high separation ratio of Nd and Dy was obtained in our past experiments [2]. 2. Experimental The experiments were conducted in LiCl–KCl (44:56 wt%) eutectic melt in a dry Ar atmosphere at 723 K inside a glove box with an electronic furnace. 300 g of LiCl–KCl was vacuum dried at 473 K for more than 24 hours before elevating the temperature. As working electrodes, Ni, and Ag wire (φ1 mm) electrodes were used for cyclic voltammetry. Ni and Ag plate electrodes (5 mm×15 mm×0.1 mm(t)) were used for electrodeposition. A glassy carbon rod was used as a counter electrode. A reference electrode was an Ag+/Ag electrode, which was prepared by immersing an Ag wire in a LiCl−KCl melt containing 1 mol% of AgCl set in a Pyrex glass tube. The potential of the reference electrode was calibrated by the Li+/Li potential obtained by open circuit potential measurement on a Mo wire (φ1 mm) electrode just after electrodepositing Li metal. All the potential hereafter is described in reference to this Li+/Li potential.Cyclic voltammetry was conducted at KBF4 concentrations of 0, 0.5 and 2.0 mol%. Potentiostatic and galvanostatic electrolysis was conducted at KBF4 concentrations of 2.0 mol%. After the electrolysis, the plate electrodes were rinsed by distilled water, and then characterized by SEM and XRD. 3. Results and Discussion 3-1. Cyclic Voltammetr y Cyclic voltammograms (CV) obtained by Ni and Ag electrodes are shown in Fig.1(a) and (b), respectively. In the case of Ni electrode, cathodic current was observed at around 1.2 V shown “a” in the figure. The couple of peaks “b” and “c” at around 0.0 V correspond to Li metal deposition and dissolution, respectively. In addition to current peak “a”, a small current peak “e” appeared at 1.8 V, which seems to correspond to a formation of Ni-B compounds. Except for the peak “e”, essentially the same results were obtained in the case of Ag electrode. In both cases, the peak current at around 1.2 V increased with the concentration of KBF4 (shown as “a” in the figures). This peak can correspond to the reduction of B(III) to B(0), although further investigation is needed to confirm it. 3-2. Characterization of Products Prepared by Potentiostatic and Galvanostatic Electrolysis Fig. 2 shows a microscope image and a surface SEM image of the deposit on the Ni plate electrode obtained by potentiostatic electrolysis at 1.2 V, Q= −50 C. The granules with a diameter of c.a. 1-2 μm were observed. From XRD measurement, the diffraction peaks coincided to Ni, Ni2B, and NiCl2 was confirmed. Weak peaks that might correspond to B were partially observed.Next, the galvanostatic electrolysis was conducted at −9.8 mA cm−2, Q= −15 C for a Ni and an Ag plate electrode, respectively. In the case of Ni electrode, Ni, Ni2B, NiCl2 and KCl were detected by XRD analysis. This is almost the same result as the potentiostatic electrolysis at 1.2 V. Ag was selected as the substrate because no alloys of Ag and B exist in phase diagram. From the XRD results, only clear diffraction peaks coincided to Ag was confirmed. Other peaks were also detected, but they did not correspond to elemental B or other expected compounds. From the observation by sight, some deposits were actually formed. Therefore, the deposit can be amorphous B. In the future, further analysis and experiments are needed to clarify the behavior of B on Ag electrode. Acknowledgement This work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Selective Permeation of Neodymium Through an Alloy Diaphragm in Molten Chloride Systems

The authors have been investigating a new RE (RE=Dy and Nd) recycling process from Nd-Fe-B permanent magnets, which is characterized by the use of RE-IG (IG=Fe, Ni, Co) alloy diaphragms for separation of REs in molten salts (Fig. 1) [1, 2]. In this process, the RE-IG alloy diaphragm performs as a bipolar electrode and RE ions permeate via three steps: (1) reduction of RE ions to form alloy on the anolyte side of the diaphragm, (2) diffusion of RE atoms in the diaphragm, and (3) oxidation of RE atoms to dissolve into the catholyte as RE ions on the other side of the diaphragm. Because the reaction and diffusion rates depend on the kinds of RE elements and the electrolytic conditions, selective permeation of Dy and/or Nd is possible under an appropriate condition. Using this selective permeation phenomenon through the alloy diaphragms, Dy and Nd can be separately recovered from Nd-Fe-B permanent magnets only by molten salt electrolysis, as shown in Fig. 1.Recently, the authors reported selective Dy permeation through a RE-Ni alloy diaphragm in molten LiCl-KCl eutectic melts containing NdCl3 and DyCl3 at 450 ℃ [3]. Whereas, in the present study, selective permeation of Nd was examined using a similar experimental setup at the different electrolytic conditions. The obtained molar ratio of permeated Nd/Dy was around 6. Interestingly, EDX analysis revealed that the molar ratio of Nd/Dy in the alloy diaphragm was less than 0.05, which was two orders of magnitude lower than that of the permeated amount. These results suggested that the diffusion rate of Nd atoms in the alloy diaphragm was extremely high compared to that of Dy.AcknowledgementThis work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.Reference[1] T. Oishi, H. Konishi, T. Nohira, M. Tanaka and T Usui, Kagaku Kogaku Ronbunshu, 36, 299–303 (2010).[2] T. Oishi, Molten Salts (Yoyuen Oyobi Koon Kagaku), 63, 78–83 (2020).[3] T. Oishi, M. Yaguchi, Y. Katasho and T. Nohira, Rare metal technology 2020, 151–156 (2020). Figure 1