Eutectic LiCl-KCl Research Articles

Radiation-Driven Reactivity of Metal Ions in Molten Salts

Molten salts are proposed as liquid fuels or coolants in a new fleet of molten salt nuclear reactors that would have operational and safety advantages over present reactor systems. Under those conditions, the salt will be exposed to high radiation levels, and understanding the chemical effects of radiolysis on the molten salt fuel or coolant is essential to reliable, efficient and sustainable reactor operation. Building this understanding begins with identifying primary salt radiolysis products (solvated electrons (esolv –) and Cl2 •–) and characterizing their reactivities, for which we conduct high-temperature pulse radiolysis transient absorption spectroscopy at the BNL Laser-Electron Accelerator Facility. Here we report on the reaction kinetics of reactions of metal ions with esolv – and Cl2 •– in different molten salt compositions. Salt mixtures containing mono- and divalent cations are particularly interesting because of their tunable Lewis acidity-basicity that can be used to control the solubility and redox poise of dissolved metal ions in the reactor. Previously we showed how varying the MgCl2:KCl mixing ratio alters the absorption spectra of radiolytically-produced excess electrons, with increasing blue shifts related to the likely number of Mg2+ ions adjacent to the cavity electron. The strong blue shifts indicate significant changes in the electron’s energetics and reactivity that we now have probed by measuring reaction kinetics with metal ion electron acceptors. We observed that reaction rates of the solvated electron depend strongly on the composition of the salt. Reactivity trends among first-row transition metals in eutectic LiCl-KCl will be discussed. This work was supported as part of the Molten Salts in Extreme Environments Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.

Electrochemical Synthesis of Carbon Materials from Carbon Dioxide in Molten Chloride Systems

1. IntroductionTo achieve carbon neutrality by 2050, significant attention has been paid to the development of CO2 capture and utilization (CCU) technologies in addition to CO2 capture and storage (CCS) technologies. Here, electrochemical CO2 conversion technology in molten salt is considered one of the promising candidates for CCU because it can reduce CO2 to elemental carbon [1,2]. In recent years, we have been working on the conversion of CO2 into a variety of valuable carbon materials. For example, we reported the electrochemical synthesis of diamond from molten LiCl-KCl-K2CO3-KOH [3]. In the present study, we report recent results on the electrochemical synthesis of various carbon allotropes, including diamond, in molten chlorides.2.ExperimentalAs a typical molten salt among the chloride systems, we used eutectic LiCl-KCl. Cyclic voltammetry and potentiostatic electrolysis were performed after adding K2CO3 to the molten salt. For diamond synthesis, KOH was also added to the molten salt. 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, molten LiCl-KCl 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. In addition to the LiCl-KCl, we used several other chloride-based molten salts for use at higher temperatures.3. Results and DiscussionFor diamond synthesis, CO2 and H2O were introduced into molten LiCl-KCl-Li2O at 973 K. Then, CO2 was converted into CO3 2− and H2O into OH−. 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 to 10 C cm−2. As an example, optical images of the sample obtained at 1.2 V is shown in Fig. 1. The electrode surfaces were covered with black deposits, but most of the deposits, except for the edges, were detached during the water rinsing. Raman spectra were measured at the points indicated by the crosses in Fig. 1. As shown in Fig. 2, sharp peaks were observed at 1332 cm−1, overlapping the spectra characteristic of amorphous carbon. The results indicate that the majority of the product was amorphous carbon, but a small amount of diamond was synthesized electrochemically.On the day of the meeting, we will also present the results obtained in other chloride-based molten salts.AcknowledgmentA part of this work was supported by JSPS KAKENHI Grant Number 21K19024. A part of this study was conducted in collaboration with Cosmo Oil Co., Ltd.

Corrosion Behavior of High-Chromium Alloys in Molten LiCl–KCl Eutectic

Corrosion Behavior of High-Chromium Alloys in Molten LiCl–KCl Eutectic

Electrochemical Identification of Metal Chlorides in Eutectic LiCl-KCl Without Prior Knowledge of Analyte Identities

The identities of unknown analytes within four eutectic LiCl-KCl melts were determined using electrochemical methods, simulating the uncertainty of electrochemically probing an electrorefiner salt bath or molten salt nuclear reactor. With a variety of electrochemical methods (e.g. cyclic voltammetry, chronopotentiometry, and square-wave voltammetry), and electroanalytical techniques (e.g. semi-differentiation), every analyte was positively identified, although one false positive occurred because of an unexpected chemical interaction. This study highlights some remaining challenges for the use of electrochemical sensors in nuclear material control and accountability in molten salts: (1) quantification of analytes without the use of calibration curves (e.g. error in property values, such as diffusion coefficient) and (2) additional and interfering electrochemical signals due to interaction and alloying of multiple species.

Investigate of electrochemical properties of Nd(II) and Nd(III) in eutectic LiCl–KCl molten salt

Investigate of electrochemical properties of Nd(II) and Nd(III) in eutectic LiCl–KCl molten salt

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

Experimental determination of the electrochemical properties of bismuth chloride in eutectic LiCl–KCl and LiCl–KCl–CaCl2 molten salts

Experimental determination of the electrochemical properties of bismuth chloride in eutectic LiCl–KCl and LiCl–KCl–CaCl2 molten salts

Electrochemical and thermodynamic properties of Pu(III) ions at the Mo electrode in LiCl–KCl eutectics

Electrochemical and thermodynamic properties of Pu(III) ions at the Mo electrode in LiCl–KCl eutectics

Synthesis and characterization of super occluded LiCl-KCl in zeolite-4A as a chloride salt waste form intermediate

Synthesis and characterization of super occluded LiCl-KCl in zeolite-4A as a chloride salt waste form intermediate

(Invited) Thermodynamic Properties of Rare-Earth Alloys Relevant for Efficient Rare-Earth Recovery in Molten Salts

Electrode materials of Fe, liquid Bi, and Sn were investigated to enhance the electrochemical recovery of rare-earth elements in molten salts (eutectic LiCl-KCl) at 500‒700 °C, leveraging their chemical interactions with rare-earth elements. Using Nd as a prototypical example, the degree of interactions was quantified based on electromotive force (emf) measurements of Nd alloys (Nd-Fe, Nd-Bi, and Nd-Sn). Temperature-dependent emf values of the Nd alloys were used to determine the thermodynamic properties such as the partial molar Gibbs energy (chemical potential), entropy, and enthalpy of Nd. In addition, the phase behavior of Nd alloys was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) to determine transition temperatures and microstructures of Nd alloy electrodes. Based on these fundamental properties of Nd alloys, the Nd-Sn alloy at mole fraction, x Nd = 0.10 was selected as the reference electrode and employed for electrochemical measurements in three-electrode cells in molten chloride salt (LiCl-KCl-NdCl3). The stability of Nd-Sn reference electrode was maintained less than 1 mV deviation between identical constructs during entire measurements, originating from the two phase (liquid + NdSn3) stability of the binary Nd-Sn alloy at 500‒700 °C. Finally, electrodeposition of Nd onto these interacting electrode materials was conducted to assess the recovery efficiency of Nd from molten chloride salt.

Electrochemical Recovery of Lithium-Ion Battery Materials from Molten Salts: Microstructural Characterisation Using X-Ray Imaging

Recycling spent Li-ion batteries (LiBs) guarantees the conservation of important metal resources by reducing demands on raw supply and offsetting the energy and environmental costs associated with its manufacture. However, selecting practical end of life solutions for battery waste management remains a challenge. Molten salts, on the other hand, are a well-established group of inorganic compounds and are understood to be one of the leading candidates in the recovery of valuable metals. They offer a much greener and simpler route to metal recovery by electrochemical means compared with the use of reducing agents for hydrometallurgical recovery [1]. Yet, the current mechanistic understanding of the electrochemical recovery of metals in molten salts needs to be improved.SEM, EDS and XRD are some of the most employed characterisation techniques used to reveal material composition and surface topography; however, they are known to expose the final product to air and moisture obscuring the results. X-ray computed tomography offers a non-destructive approach for 3D microstructure visualisation and subsequent quantification [2]. This technique can be used to study the morphological evolution of metal deposits from their oxide particles in a representative high-temperature medium to provide a wealth of information on the fundamentals of the electrochemical reduction process.Here, we demonstrate a study into the electrochemical deposition of recovered Co metal from lithium cobalt oxide, LiCoO2 in LiCl-KCl eutectic (LKE) which has been previously studied by the authors’ using a fluidised cathode arrangement [3]. This novel diagnostic approach has been applied to LiCoO2-LKE samples before and after electrolysis at 450 °C, yielding key insights into the morphological evolution of product formation. Different morphologies of recovered Co metal such as dendrite features and agglomerates have been captured and quantified. It has also been observed that CO/CO2 gas formation occurs in copious quantities at the anode surface leading to operational consequences such as the required overpotential needed to drive the reaction. For the first time, the application of X-ray imaging offers the ability to understand the role of process conditions and cell configurations to optimise a pyro-electrochemical reprocessing technology that can play a key role in sustainable battery recycling as well as refractory metal recovery.[1] B. Zhang, H. Xie, B. Lu, X. Chen, P. Xing, J. Qu, Q. Song, H. Yin, A Green Electrochemical Process to Recover Co and Li from Spent LiCoO2-Based Batteries in Molten Salts, ACS Sustain Chem Eng. 7 (2019) 13391–13399.[2] P.J. Withers, C. Bouman, S. Carmignato, V. Cnudde, D. Grimaldi, C.K. Hagen, E. Maire, M. Manley, A. du Plessis, S.R. Stock, X-ray computed tomography, Nature Reviews Methods Primers. 1 (2021) 1–21.[3] M. Mirza, R. Abdulaziz, W.C. Maskell, C. Tan, P.R. Shearing, D.J.L. Brett, Recovery of cobalt from lithium-ion batteries using fluidised cathode molten salt electrolysis, Electrochim Acta. 391 (2021) 138846.

Effect of Metal Chloride Impurities on Equilibrium Potential of Fe/FeCl2 in Eutectic LiCl-KCl

Abstract In this study, interaction of dilute metal chloride solutes in molten eutectic LiCl-KCl was studied via equilibrium potential measurements. Open circuit potential (OCP) was measured between a pure iron rod and a Ag/AgCl reference electrode with concentration of FeCl2 varying from 0.2-1 mol% at 530oC. The Nernst equation was used to calculate activity coefficient of FeCl2 based on OCP. Measurements were made in LiCl-KCl-FeCl2 with and without additions of 0.5 mol% CsCl, NaCl, and LaCl3. The activity coefficient of FeCl2 was found to be unaffected by these small concentrations of CsCl, LaCl3, and NaCl. However, there was observed evidence that the activity coefficient of FeCl2, above 0.8 mol% Fe, may be affected by the presence of LaCl3 at higher concentrations beginning around 0.5 mol% La. Over the full range of conditions tested, the activity coefficient of FeCl2 in molten LiCl-KCl ranged from 2.95x10-5 to 1.01x10-4.

Determination and Comparison of Parameters from Cyclic Voltammetry of LaCl3 in Eutectic LiCl-KCl

Electrochemical measurements of LaCl3 were obtained in eutectic LiCl-KCl at 773 K. Cyclic voltammetry data were acquired using a tungsten electrode LaCl3 amounts in the molten salt in the range of 0.5 to 3.0 wt%. Both cyclic voltammetry and Tafel analyses of the data resulted in calculation of values for the charge transfer coefficient (0.262), diffusion coefficient (1.67 × 10-5 cm2 s-1), exchange current density (0.0148 to 0.0473 A cm-2), and charge transfer resistance (0.404 to 1.99 Ω) related to lanthanum ions in the molten salt. Calculated values were compared to those available in the literature. The values of parameters found in literature varied significantly in comparison to those in the present study due to dissimilar experimental conditions, e.g., electrode material, temperature, and LaCl3 concentration.

Thermodynamic modeling of KCl-PrCl3 and KCl-LiCl-PrCl3 systems

Thermodynamic modeling of KCl-PrCl3 and KCl-LiCl-PrCl3 systems

Time dependent chlorination of CeO2, La2O3 and Nd2O3 by ZrCl4 dissolved in eutectic LiCl–KCl

Time dependent chlorination of CeO2, La2O3 and Nd2O3 by ZrCl4 dissolved in eutectic LiCl–KCl

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.

Thermodynamic Simulation of UCl3 Oxidation with Lead Chloride and UCl4 Reduction with Metallic Uranium in the Molten LiCl–KCl Eutectic

Thermodynamic Simulation of UCl3 Oxidation with Lead Chloride and UCl4 Reduction with Metallic Uranium in the Molten LiCl–KCl Eutectic

Microsecond-scale staircase voltammetry for measuring the electrical conductivity of highly conductive liquids

Microsecond-scale staircase voltammetry for measuring the electrical conductivity of highly conductive liquids

CORROSION PERFORMANCE OF PLASMA SPRAYED ALUMINA–40 wt.% TITANIA COATED HIGH-DENSITY GRAPHITE IN MOLTEN LiCl–KCl EUTECTIC SALT

The corrosion performance of plasma sprayed alumina–40[Formula: see text]wt.% titania (A40T) coated high-density graphite was investigated in molten LiCl–KCl eutectic salt at [Formula: see text]C for periods of 500, 1000, and 2000[Formula: see text]h under argon atmosphere. The microstructural and compositional investigations of corrosion-tested A40T coatings by scanning electron microscopy and energy dispersive X-ray spectroscopy showed that the samples exhibited better corrosion resistance up to 500[Formula: see text]h. The poor corrosion behavior and failure of A40T coating from graphite substrate in the long-term (1000 and 2000[Formula: see text]h) immersion was discussed in detail based on the microstructure and composition analysis. The phases existing in the as-sprayed coating ([Formula: see text]-Al2TiO5, [Formula: see text]-Al2O3, R-TiO2, and [Formula: see text]-Al2O3) remained in the detached coating after 1000[Formula: see text]h exposure to the molten salt. The reaction between molten salt and A40T coating was not evident from XRD analysis. A40T coatings with chromium carbide–nichrome (Cr3C2–NiCr) bond coat showed complete spallation of the top coating and oxidation of the bond coat as evident from the X-ray diffraction analysis. Detachment of the A40T coating occurred due to the penetration of the molten salt into the coating through the voids and pores present on the surface, which weakened the adhesion strength between the substrate and the A40T coating or top coat-bond coat interfaces.

Multi-cationic molten salt electrolyte of high-performance sodium liquid metal battery for grid storage

Multi-cationic molten chloride salt mixtures such as LiCl–KCl–NaCl are promising molten salt electrolytes for sodium liquid metal batteries (Na-LMBs). In this work, the melting temperature of LiCl–KCl–NaCl was determined with Differential Scanning Calorimetry (DSC), assisted by FactSage™ simulation and confirmed by a melting point apparatus OptiMelt™. It is founded that the eutectic LiCl–KCl–NaCl can be considered as a pseudo-binary system with LiCl–KCl eutectic (59.2–40.8 mol.%) as the solvent and NaCl as the solute. When NaCl is not more than 9 mol.%, the eutectic LiCl–KCl–NaCl salt mixture has a melting temperature of ∼350 °C as that of LiCl–KCl eutectic. In addition, the exchange reactions between anode Na metal with LiCl–KCl–NaCl molten salt electrolyte were studied at the temperature of 400–500 °C quantitatively. The equilibrium constants of the exchange reactions were determined by chemical analysis on the salt and metal phases with Ion Chromatography (IC). A one ampere-hour (Ah) Na-LMB test cell shows promising energy storage performance. Moreover, the phenomena in the cell test can be explained convincingly, combining the results of exchange reactions and the pseudo-binary-system theory. The findings on the multi-cationic molten salt electrolytes for Na-LMBs in this work could support further development of other liquid metal batteries. • Phase diagram of NaCl–LiCl–KCl was investigated with simulations and experiments • Exchange reactions of Na anode with NaCl–LiCl–KCl influence battery performance • Equilibrium constants of exchange reactions at 400–500 °C were determined • Cell tests confirmed influence of exchange reactions on battery performance • Suggestions on molten salt electrolyte were given to improve cell performance