LiCl-KCl System Research Articles

Investigate of Electrochemical Properties of Nd(II) and Nd(III) in Eutectic LiCl-KCl Molten Salt

Pyroprocessing is one of the promising methods to reprocess the spent nuclear fuel. Neodymium (Nd) constitutes about one third of rare earth in fission products, however, the electrochemical properties of Nd have not been thoroughly understood, especially the exchange current. In the present study, the transit electrochemical methods of cyclic voltammetry and square wave voltammetry were applied to study the properties of Nd in LiCl-KCl system. The reduction of Nd3+ was determined as a two-step reaction with Nd3+/Nd2+ to be a reversible but Nd2+/Nd to be a quasi or irreversible reactions. Additionally, parameters such as the diffusion coefficient, exchange current, and apparent potential were derived from the cyclic voltammetry curves. Their relationship with temperature and concentration was investigated under 723 K, 773 K, 823 K with concentrations of 3 wt%, 6 wt% and 9 wt%. The present study contributes significantly to rich the database of Nd in LiCl-KCl molten salt and to understand the electrochemical behaviors of Nd during electrochemical separation of spent nuclear fuel.

Mass Transfer Process by Diffusion of RE(III) (RE=La, Pr) in Eutectic LiCl-KCl Salt

Mass transfer is an important link in the entire electrode process. To investigate mass transfer process by diffusion of trivalent rare Earth ions in molten LiCl-KCl system, the electroreduction mechanism, mass transfer kinetics and diffusion layer thicknesses of RE(III) (RE = La and Pr) were studied by a series of electrochemical methods. It was found that RE(III) underwent one-step reduction reaction with the exchange of 3-electron and reversible processes. The diffusion coefficients (D) of RE(III) and limiting current densities (j l ) for RE(III)/RE pair were measured at different temperatures and concentrations by cyclic voltammetry and chronoamperometry, respectively. Based on the results of D and j l , the diffusion layer thickness (δ) of RE(III) was calculated using the simplified Nernst-Planck formula. Furthermore, the impacts of temperature and concentration on δ were explored. The results indicated that as the temperature declined and ions concentration increased, δ decreased. Meanwhile, the relationships between δ and temperature and concentration were also obtained.

Electrochemical behavior and effective extraction of Er in fused LiCl-KCl eutectic

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.

(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.

Electrochemical synthesis of Co–Pr intermetallic compounds by the co-reduction of Co(II) and Pr(III) ions in a molten LiCl–KCl eutectic

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.

Electrochemical Formation of Dy-Ni Alloys in a Molten Cesium Chloride System

Dy-added Nd-Fe-B magnets are widely used for high-performance motors in battery electric vehicles (BEVs), hybrid electric vehicles (HEVs) and so on. The demand for these magnets is increasing due to the spread of BEVs and HEVs. However, Dy resources are scarce and unevenly located in the earth crust. Thus, it is necessary to develop an inexpensive and effective recovery/separation process of Dy from scraps of the Dy-added Nd-Fe-B magnet. From this background, we have been investigating a new recovery process of Dy and Nd from the magnet scraps using molten salt electrolysis and alloy diaphragms [1-3]. The key step in this process is the alloying and de-alloying of rare earth (RE) elements on both sides of the diaphragm in order to effectively separate them in the molten salt. So far, we have reported that Dy can be selectively alloyed with Ni by potentiostatic electrolysis in a molten LiCl-KCl-DyCl3(0.50 mol%)-NdCl3(0.50 mol%) system at 723 K [2]. The selective permeation of Dy through the RE-Ni alloy diaphragm from an anolyte containing DyCl3 and NdCl3 to a catholyte has been also confirmed [3]. However, the current density was of the order of 10 mA/cm2 or less, which is insufficient for industrial electrolysis. So, we focused on the CsCl system as a candidate melt to achieve a higher current density due to its high operation temperature. Since the alloying and de-alloying of REs in this system is unknown, the electrochemical formation of Dy-Ni alloys was investigated in a molten CsCl-DyCl3 system at 973 K as a first step in the investigation of this system.All experiments were conducted under a dry Ar gas atmosphere at 973 K in a glove box. Mo, Ni wires and Ni plates were used as working electrodes. A glassy carbon rod was used as a counter electrode. The reference electrode was a Ag wire immersed in a molten CsCl containing 1 mol% of AgCl. All the potentials are referred to the Cs+/Cs electrode potential. The alloy samples were prepared by potentiostatic electrolysis. After electrolysis, the samples were analyzed by XRD and were also observed by SEM-EDS. First, cyclic voltammetry was conducted with a Ni wire electrode in a molten CsCl-DyCl3(0.50 mol%) system. During the cathodic potential scan, a large cathodic current was observed from 0.50 V. Since this potential was more positive than that of Dy metal deposition on a Mo wire electrode, the cathodic current was suggested to correspond to the formation of Dy-Ni alloys. Then, open-circuit potentiometry was carried out with a Mo electrode after electrodepositing Dy metal at 0.11 V for 150 s. A potential plateau was observed at 0.26 V. Since Mo does not form any intermetallic compounds with Dy, the observed potential is interpreted as the Dy3+/Dy potential. Also, open-circuit potentiometry was performed with a Ni electrode after depositing Dy metal at 0.18 V for 90 min. As a result, four potential plateaus were observed at 0.29, 0.42 V, 0.52 V, 0.77 V and 0.90 V, which possibly correspond to the potentials of two-phase coexisting states of different Dy–Ni alloys. Based on these results, potentiostatic electrolysis was conducted at 0.38 V for 1 h with a Ni plate electrode. XRD analysis indicated the formation of DyNi2 on the Ni plate electrode. The thickness of DyNi2 layer was estimated to be 50 μm from cross-sectional SEM observations. The growth rate of this DyNi2 layer, 50 µm h-1, was higher than that obtained in a molten LiCl-KCl system at 700 K, 28 µm h-1 [4]. After the formation of DyNi2 on the Ni plate electrode, potentiostatic electrolysis was also conducted at 0.46 V, 0.66 V and 0.82 V for 1 h. These potential values were selected from the observed plateau potentials. The formed DyNi2 were transformed to other phases such as DyNi3 at 0.46 V, Dy2Ni7 at 0.66 V and DyNi5 at 0.82 V due to anodic dissolution of Dy, depending on the applied potentials.

Evaluation of thermophysical properties of the LiCl-KCl system via ab initio and experimental methods

Molten Salt Reactors (MSRs) are envisioned as a potential pathway to safer, more economical nuclear electricity generation and supply of industrial heat. MSRs under consideration today are either solid-fueled salt-cooled designs or liquid-salt-fueled designs with chloride or fluoride based salts. A significant knowledge gap exists in the data for the fundamental properties relevant to fuels and coolants for MSRs that needs to be addressed in order to expedite the technical readiness level of the MSR design concepts. With the rapid development and improvement of computational materials science, computational methods such as Density Functional Theory (DFT) calculations and ab initio Molecular Dynamics (AIMD) simulations are widely used as an effective and reliable tool to investigate the atomic interaction in materials. In this article, the density of the LiCl-KCl system was determined via AIMD calculations and verified using new experimental analyses. AIMD was further utilized to calculate the compressibility , heat capacity, enthalpy of mixing, and Gibbs free energy of mixing. This work spans a wider range of compositions and temperatures than have previously been explored computationally for this pseudo-binary system and provides the basis for further advanced thermophysical property evaluation utilizing AIMD methods.

Coordination and Thermophysical Properties of Transition Metal Chlorocomplexes in LiCl-KCl Eutectic.

Eutectic LiCl-KCl molten salt is often used in molten salt reactors as the primary coolant due to its high thermal capacity and high solubility of fission products. Thermophysical properties, such as density, heat capacity, and viscosity, are important parameters for engineering applications of molten salts but may be significantly influenced by metal solutes from corrosion of metallic structural materials. The behavior of the LiCl-KCl eutectic composition is well researched, yet the effects on these properties due to chlorocomplex formation from metals dissolved in the salt are less well known. These properties are often difficult to accurately measure from experimental methods due to the issues arising from the dissolved species, such as volatility. Here, we applied a combination of quantum mechanics molecular dynamics (QM-MD) and deep machine learning force field (DP-FF) molecular dynamics simulations to investigate the structural and thermophysical properties of LiCl-KCl eutectic as well as the influence of dissolved transition metal chlorocomplexes NiCl2 and CrCl3 at low concentrations. We find that the dissolution of Ni and Cr in the LiCl-KCl system forms the local tetrahedral (NiCl4)2- and octahedral (CrCl6)3- chlorocomplexes, respectively, which do not have a significant impact on the overall liquid salt structures. In addition, the thermodynamic properties including diffusion constant and specific heat capacity are not significantly affected by these chlorocomplexes. However, the viscosity significantly increases in the temperature range of 673-773 K. This study thus provides essential information for evaluating the effects of dissolved metals on the thermophysical and transport properties of molten salts.

Redox behavior of indium in molten chlorides

An electrochemical study on the redox behavior of indium in the eutectic LiCl-KCl system at 450 °C was carried out with the transient techniques of cyclic voltammetry and chronopotentiometry on an inert molybdenum electrode. The reduction of In(III) was found to be a two-step process involving In(III)/In(I) and In(I)/In couples at the potentials of about −0.4 and −0.8 V versus Ag/AgCl, respectively. The redox mechanism was further confirmed by the theoretical evaluation of the number of transferred electrons based on cyclic voltammetry and characterizations of the precipitates generated by the potentiostatic electrolysis. The diffusion coefficients of indium ions in the eutectic LiCl-KCl melt at 450 °C were estimated by cyclic voltammetry and chronopotentiometry. The results obtained through the two methods are in fair agreement, delivering an average diffusion coefficient of approximately 1.8×10−5 cm2/s for In(III), and 1.4×10−4 cm2/s for In(I).

Real-Time Monitoring for Electrochemical Analysis in Molten LiCl-KCl Eutectic Salt

Molten salts are one of the promising alternative classes of new materials for electrochemical processing. They have high chemical stability and offer much wider electrochemical window than conventional aqueous media. This enables various electrochemical reactions to be conducted without decomposing background media. In addition, the high operation temperature of molten salt boosts the mass transfer of reactant of electrochemical reaction, so that the processing time is shortened. Owing to such advantages, the molten salt media have intensively dealt with the electrowinning of metal and electrochemical separation processes. However, knowing the chemical behavior of electrodes during such processes is crucial to understanding the mechanism of electrochemical reactions that occur during the process. One of the most powerful methods of examining the system is to monitor the visual status of electrodes in real time while the electrochemical process is running. However, due to some practical limitations, it has rarely been applied to the molten salt electrochemical system.In the present work, the real-time monitoring system for molten LiCl-KCl eutectic salt medium is set up. Instead of an optically opaque ceramic crucible, a cylindrical quartz tube is chosen for the electrochemical cell of our experimental system. With four optically accessible quartz windows mounted on the electrical furnace, a commercially available CMOS camera can be installed externally to monitor the molten salt system without any special modifications.Real-time monitoring was carried out to investigate the electrode behavior in various electrochemical systems. First, the deposition behavior of cobalt in molten CoCl2-LiCl-KCl system (1wt% CoCl2) is compared on a tungsten working electrode. As shown in Figure 1, there is a clear morphological structural difference in the cobalt deposit between the galvanostatic and the potentiostatic electrodeposition. While the metallic cobalt was deposited evenly on the surface of the working electrode by galvanostatic electrodeposition, rapid growth of the dendritic structure was observed using the potentiostatic electrodeposition. This suggests that the structural properties of deposits can vary significantly due to the nature of the electrodeposition methods.In electrochemical experiments in molten salt system that do not produce solid phase products, it is difficult to elaborately understand the behavior of chemical species during the experiment. However, real-time monitoring enables noteworthy observation from these experiments. During the galvanostatic lithium reduction in the molten LiCl-KCl system, the liquefied metallic lithium formed the oval bulge on the surface of the tungsten working electrode. At the same time, the unknown indigo-colored flow was observed on the surface of the deposited metallic lithium. The clear mechanism remains to be explored, but it appears to be related to the re-oxidization of metallic lithium to Li(I) ions. In the molten ZrCl4-LiCl-KCl system (1wt% ZrCl4) with tungsten working electrode, the reduction of Zr(IV) ions to Zr(III) ions during the potentiostatic electroreduction was visualized and identified by the formation of brown-colored flow near the surface of the working electrode. This confirms the result of our previous work and suggests that Zr(IV) is reduced to Zr(III) with a brown color in the first step of CV [1].Furthermore, with the video signal from the CMOS camera to the PC that controls the potentiostat, the visual changes can be synced with the measured current or potential during the experiment. This enables us to compare the visualized morphological properties on the surface of the working electrode under different applied potential conditions during the CV experiment (Figure 2).[1] H. L. Cha, J.-I. Yun, Electrochem. Commun. 84, 86 (2017) Figure 1

The distillation behavior of fluorides in LiCl–KCl molten salt

The distillation behaviors of some fission product fluorides in LiCl–KCl system were investigated. For rare earth element, the corresponding decontamination factors (DFs) of Ce in 5 wt% CeF3–LiCl–KCl salts were over 100 at 1040 K and 13 Pa. For SrF2, the very poor DFs was deduced for the presence of more volatile SrClF, while Zr4+ was observed to complex easily with F− and Cl−, which affected its evaporation rate and the separation efficiency. F ion concentration in condensate salt was 1–2 level higher than the metal ion due to the stronger covalent band.

Dissolution of Rare Earth Elements from Nd Magnet Scraps Using Gas Electrodes in Molten Chlorides

Here we study the dissolution of rare earth elements from Nd magnet scraps using Cl2 or O2 gas electrodes in order to achieve new rare earth recycle process. The anodic polarization of Nd magnet scraps and cathodic polarization of O2 gas electrodes were investigated in molten LiCl-KCl systems at 723 K. The anodic polarization was carried out by potentiostatic electrolysis of Nd magnet scraps electrode from 0.69-2.39 V(vs. Li+/Li) at every 0.050 V interval. The large anodic current was observed at 1.80-2.00 V due to anodic reaction of dissolution of rare earth elements. On the other hand, the cathodic polarization was carried out by potentiostatic electrolysis of O2 gas electrode using porous Ni from 1.20-2.30 V at every 0.10 V interval in a molten LiCl-KCl added Li2O(0.50 mol%) system. The large cathodic current was observed from 1.40-1.90 V due to cathodic reaction from O2 to O2-. It was possible to dissolve rare earth elements selectively from Nd magnet scraps using O2 gas electrodes.

Investigation of Molten Salt Chemical Cell Using Nd Magnet Scraps and Gas Electrodes in Molten Chlorides

Here we study the molten salt chemical cell using Nd magnet scraps and Cl2 or O2 gas electrodes in order to achieve new rare earth recycle process. The anodic polarization of Nd magnet scraps and cathodic polarization of O2 gas electrodes were investigated in molten LiCl-KCl systems at 723 K. The anodic polarization was carried out by potentiostatic electrolysis of Nd magnet scraps electrode from 0.69-2.39 V(vs. Li+/Li) at every 0.050 V interval. The large anodic current was observed at 1.80-2.00 V due to anodic reaction of dissolution of rare earth elements. On the other hand, the cathodic polarization was carried out by potentiostatic electrolysis of O2 gas electrode using porous Ni from 1.20-2.30 V at every 0.10 V interval in a molten LiCl-KCl added Li2O(0.50 mol%) system. The large cathodic current was observed from 1.40-1.90 V due to cathodic reaction from O2 to O2-.

Thermodynamic properties of ternary Me-Ga-In (Me = La, U) alloys in a fused Ga-In/LiCl-KCl system

This work presents the results of a study of apparent standard potentials of La-(Ga-In) and U-(Ga-In) alloys vs. Cl−/Cl2 reference electrode at the temperature range (723–823) K in fused Me(Ga-In)/LiCl-KCl (3:2 mol ratio) system by potentiometric method at zero current. Lanthanum and uranium activity coefficients and La/U separation factor in gallium-indium alloys containing 40 and 70 wt% indium were determined. Partial excess free Gibbs energy, partial enthalpy of mixing and partial excess entropy of La-(Ga-In) and U-(Ga-In) alloys were calculated. The efficiency of separation of La from U was estimated.

Electrochemical Formation of Dy and Nd Alloys Using Liquid Metal Electrodes in Molten LiCl-KCl Systems

We proposed new separation and recovery process for RE metals from Nd magnet scraps using molten salt electrolysis and an alloy diaphragm. This new process was first applied to chloride melts, and the separation of Dy and Nd were investigated using Ni cathodic electrodes in molten LiCl-KCl-DyCl3-NdCl3 systems. The highest mass ratio of Dy/Nd in Dy-Nd-Ni alloy samples was found to be 72. We focused on the liquid metals as the alloy diaphragms. Liquid metals have higher diffusion rates of elements than those of solid metals during the electrolysis. In this work, Bi, Sn and Zn electrodes were used as liquid metal electrodes. The alloy samples were prepared by potentiostatic electrolysis using liquid Bi, Sn and Zn electrodes in molten LiCl-KCl added DyCl3(0.50 mol%) and NdCl3(0.50 mol%) at 723 K.

Electrochemical Formation of RE-Sn (RE=Dy, Nd) Alloys Using Liquid Sn Electrodes in a Molten LiCl-KCl System

We proposed new separation and recovery process for RE metals from Nd magnet scraps using molten salt electrolysis and an alloy diaphragm(1-3). This new process was first applied to chloride melts, and the separation of Dy and Nd were investigated using Ni and Cu cathodic electrodes in molten LiCl-KCl-DyCl3-NdCl3systems(4-6). The highest mass ratio of Dy/Nd in Dy-Nd-Ni alloy samples was found to be 72 by ICP-AES. But there is a problem in the process. In this process, an alloy diaphragm can’t be durable against a long electrolysis.In order to solve this problem, we focused on the liquid metals as the alloy diaphragms. Liquid metals have higher endurance and diffusion rates of elements than solid metals during the electrolysis. Therefore, liquid metals are desirable for our process. For the first step, in this work a Sn electrode was used as a liquid metal electrode. The alloy samples were prepared by potentiostatic electrolysis using liquid Sn electrodes in a molten LiCl-KCl added DyCl3(0.50 mol%) and NdCl3(0.50 mol%) at 723 K.All experiments were performed in LiCl-KCl eutectic melts under dry argon atmosphere at 723 K. DyCl3 or NdCl3 was added directly to these melts. The working electrodes were liquid Sn electrodes for the investigation of electrochemical behavior. The reference electrode was a Ag+/Ag electrode. All the potentials given hereafter were referred to Li+/Li electrode potential on a Mo wire. The counter electrode was a glassy carbon rod. The alloy samples were prepared by potentiostatic electrolysis. After the electrolysis, the samples were analyzed by SEM and XRF. Before the investigation of RE-Sn(Re=Dy, Nd) alloys formation, the electrochemical behavior of Li was investigated using a liquid Sn electrode as a working electrode in a molten LiCl-KCl system at 723 K. Cyclic voltammetry was conducted with a liquid Sn electrode. The scanning rate was set at 0.05 Vs-1. During the scan in the negative direction, a cathodic current was observed from 1.10 V. Since Sn can form alloy with Li, the cathodic current corresponds to the formation of Li-Sn alloy. On the other hand, taking into account the possibilities of the formation of various Dy, Nd-Sn alloys, the electrochemical behaviors of Dy(III) and Nd(III) were investigated using liquid Sn electrodes as working electrodes. In the negative scan for the DyCl3 added system, a cathodic current was observed from 1.15 V. This cathodic current might correspond to the formation of Dy-Sn alloy. In the negative scan for the NdCl3 added system, a cathodic current was observed from 1.30 V. This cathodic current might correspond to the formation Nd-Sn alloys. In the voltammogram using a liquid Sn electrode after the addition of both DyCl3(0.50 mol%) and NdCl3(0.50mol%), a cathodic current of the formation RE-Sn alloy was observed from 1.30 V. Based on the above results, alloy samples were prepared by potentiostatic electrolysis at 0.50-0.80 V for 0.50 h in a molten LiCl-KCl-DyCl3-NdCl3 system. From the XRF analysis of all samples, the existence of Dy and Nd in liquid Sn electrodes were confirmed. This result indicated the formation Dy-Nd-Sn alloys. The highest mass ratio of Nd/Dy in the alloy sample was 2.08 at 0.60 V. References T. Oishi, H. Konishi, T. Nohira, M. Tanaka and T. Usui, Kagaku Kogaku Ronbunshu, 36, 299 (2010). S. Kobayashi, K. Kobayashi, T. Nohira, R. Hagiwara, T. Oishi and H. Konishi, J. Electrochem. Soc., 158, E142 (2011). S. Kobayashi, T. Nohira, K. Kobayashi, K. Yasuda, R. Hagiwara, T. Oishi and H. Konishi, J. Electrochem. Soc., 159, E193 (2012). H. Konishi, H.Ono, T. Nohira and T. Oishi, MOLTEN SALTS, 54, 21 (2011). H. Konishi, H. Ono, T. Nohira and T. Oishi, ECS Transactions, 50, 463 (2012). H. Konishi, H. Ono, T. Nohira and T. Oishi, ECS Transactions, 53, 37 (2013).

Dy Permeation through an Alloy Diaphragm Using Electrochemical Implantation and Displantation

The molten salt electrochemical process has been studied by Ito and co-workers including the present authors (1-12) and many other researchers (13-16). The present authors reported a unique phenomenon during the electrochemical formation of Dy-Ni alloys in molten LiCl-KCl-DyCl3: DyNi2 film with thickness of 60 µm was formed in 2 h at 700 K (1). The growth rate of DyNi2 was extremely high, compared with the conventional solid phase diffusion at temperatures lower than half of the melting temperature of DyNi2, i.e., 1531 K (17). In addition, the growth rate was found to be strongly affected by electrochemical parameters such as potential and current density. This phenomenon was termed “electrochemical implantation” (1), because it was different from the ordinary concepts of electrodeposition followed by solid phase diffusion. The authors also reported that anodic polarization of the formed DyNi2resulted in the rapid dissolution of Dy to form other Dy-Ni phases. The obtained phase and morphologies were dependent on the applied potential. This phenomenon was named “electrochemical displantation” (1).We proposed a new separation and recovery process for RE metals from scraps using molten salt and an alloy diaphragm (18-20). The new process is based on our previously discovered phenomena, i.e., “electrochemical implantation” and “electrochemical displantation” (1).This new process was first applied to chloride melts, and the separation of Dy from Nd and Pr were investigated using Cu, Ni and Zn cathodic electrodes in molten LiCl-KCl-DyCl3-NdCl3 (21-24) and LiCl-KCl-DyCl3-NdCl3-PrCl3 systems (25). The highest mass ratio of Dy/Nd+Pr in Dy-Nd-Pr-Ni alloy sample was found to be 50 at 0.65 V (vs. Li+/Li) for 1 h by ICP-AES. In this study, the investigation of Dy permeation through an alloy diaphragm using electrochemical implantation and displantation was investigated. The Dy permeation experiment was conducted with two kinds of electrolytic cell in molten LiCl-KCl systems at 723 K in order to confirm the theoretical feasibility of the present process.

Methods for Determining the Working Electrode Interfacial Area for Electroanalytical Measurements of Metal Ions in Molten LiCl-KCl

In this paper, we present an empirical evaluation of methods for determining the interfacial area between a working electrode and molten salt—specifically demonstrated using the eutectic LiCl-KCl system. Approaches studied include dipping a cold electrode into the molten salt, using a vertical translator to adjust the height of the electrode, partially coating the electrodes with an insulating material, and integrating a pre-peak which may represent formation of a monolayer of metal on the electrode. Salt mixtures investigated include LiCl-KCl-UCl3, LiCl-KCl-UCl3-MgCl2, LiCl-KCl-LaCl3-GdCl3, and LiCl-KCl-LaCl3-MgCl2. With accurate determination of the electrode-salt interfacial area, concentration correlations can be developed with error below 2%.

Electrochemical separation of Dy from Nd magnet scraps in molten LiCl–KCl

We proposed a new separation and recovery process for RE metals from Nd magnet scraps using molten salt electrolysis. The present study focused on the electrochemical formation of RE–Ni (RE = Dy, Nd, Pr) alloys in a molten LiCl–KCl system at 723 K. Cyclic voltammetry was conducted using a Ni electrode in molten LiCl–KCl–RECl3 systems at 723 K. In the negative scan for the DyCl3 added system, a large cathodic current was observed from 0.70 V (vs. Li+/Li) as a result of the formation of Dy–Ni alloys. In contrast, large cathodic currents as results of the formation of Nd–Ni and Pr–Ni alloys were observed from 0.60 V. On the basis of these results, an alloy sample was prepared by potentiostatic electrolysis at 0.65 V for 1 h using a Ni plate cathode in a molten LiCl–KCl–DyCl3–NdCl3–PrCl3 system. The mass ratio of Dy/Nd+Pr in the alloy sample was found to be 50 by ICP-AES. Finally, a Dy permeation experiment was conducted with a new electrolytic cell.

Electrochemical Formation of RE-Zn (RE=Dy, Nd) Alloys Using Liquid Zn Electrodes in a Molten LiCl-KCl System

Introduction We proposed new separation and recovery process for RE metals from Nd magnet scraps using molten salt electrolysis and an alloy diaphragm (1). This new process was first applied to chloride melts, and the separation of Dy and Nd were investigated using Ni and Cu cathodic electrodes in molten LiCl-KCl-DyCl3-NdCl3 systems (2, 3). The highest mass ratio of Dy/Nd in Dy-Nd-Ni alloy sample was found to be 72 by ICP-AES. Moreover, in the present study we focused on the electrochemical formation of RE-Zn (RE=Dy, Nd) alloys with solid and liquid Zn electrodes in a molten LiCl-KCl system at 653-723 K (4). The alloy samples were prepared by potentiostatic electrolysis for 1 h using solid Zn plates in a molten LiCl-KCl added DyCl3(0.50 mol%) and NdCl3(0.50 mol%) at 653 K. The mass ratio of Nd/Dy in the alloy sample was the highest value 3.3 at 1.00 V(vs. Li+/ Li). In this study, the electrochemical formation of RE-Zn (RE=Dy, Nd) alloys was investigated with liquid Zn electrodes in a molten LiCl-KCl system at 723 K. Experimental All experiments were performed in LiCl-KCl eutectic melts under dry argon atmosphere at 723 K. DyCl3 or NdCl3 was added directly to these melts. The working electrodes were liquid Zn electrodes for the investigation of electrochemical behavior. The reference electrode was a Ag+/Ag electrode. All the potentials given hereafter were referred to Li+/ Li electrode potential on a Mo wire. The counter electrode was a glassy carbon rod (50 mm × f 5 mm). The alloy samples were prepared by potentiostatic electrolysis. After the electrolysis, the samples were analyzed by XRD, SEM and ICP-AES. Results and discussion Before the investigation of RE-Zn (RE=Dy, Nd) alloys formation, the electrochemical behavior of Li (I) was investigated using a liquid Zn electrode as a working electrode in a molten LiCl-KCl system at 723 K. The scanning rate was set at 0.05 Vs-1. During the scan in the negative direction from 1.60 V, a small cathodic current was observed. Since Zn can form alloy with Li, the cathodic current corresponds to the formation Li-Zn alloy. On the other hand, taking into account the possibilities of the formation of various Dy,Nd-Zn alloys, the electrochemical behaviors of Dy (III) and Nd(III) were investigated using liquid Zn electrodes as working electrodes in molten LiCl-KCl systems at 723 K. A cathodic current was observed from 1.60 V using a liquid Zn electrode after the addition of NdCl3(0.50 mol%). This cathodic current was larger than that cathodic current obtained before the addition of NdCl3. Therefore, this cathodic current might corresponds to not only the formation Li-Zn alloy but also the reduction from Nd(III) to Nd(II). Moreover, a cathodic current peak was observed at 1.15 V. This cathodic current peak correspond to the formation of Nd-Zn alloys. When the potential was shifted to 0.80 V, a large cathodic current was observed. This cathodic current suggested the formation of Li-Zn and Nd-Zn alloys. When the potential scan direction was reversed at 0.50 V, two anodic peaks were observed. These anodic peaks suggested the Li and Nd dissolution from the different Li-Zn and Nd-Zn alloys. During the scan in the negative direction using a liquid Zn electrode after the addition of DyCl3(0.50 mol%), a cathodic current was observed from 1.15 V. Since Zn can form alloy with Dy, the cathodic current corresponds to the formation of Dy-Zn alloys. When the potential was shifted to 0.80 V, a large cathodic current was observed. This cathodic current also suggested the formation of Li-Zn and Dy-Zn alloys. When the potential scan direction was reversed at 0.50 V, two anodic peaks were also observed. These anodic peaks also suggested the Li and Dy dissolution from the different Li-Zn and Dy-Zn alloys. Based on the above results, an alloy sample was prepared by potentiostatic electrolysis at 0.60 V, 0.80 V and 1.0 V for 1 h in a molten LiCl-KCl-DyCl3-NdCl3 system. From the EDX analysis, the alloy phases were identified as DyZn12 or NdZn11. References H. Konishi, H.Ono, T. Nohira and T. Oishi, MOLTEN SALTS, 54, 21 (2011). H. Konishi, H.Ono, T. Nohira and T. Oishi, ECS Transactions, 50, 463 (2012). H. Konishi, H.Ono, T. Nohira and T. Oishi, ECS Transactions, 53, 37 (2013). H. Konishi, H.Ono, T. Nohira and T. Oishi, ECS Transactions, 61, 19 (2014).