KCl Melt Research Articles

Cathode processes and uranium electrochemical extraction on W and Ga electrodes in LiCl–KCl melt

Cathode processes and uranium electrochemical extraction on W and Ga electrodes in LiCl–KCl melt

Molten Salt Modulation of Potassium-Nitrogen-Carbon for the Breaking Kinetics Bottleneck of Photocatalytic Overall Water Splitting and Environmental Impact Reduction.

Sluggish interfacial water dissociation and the O2 evolution reaction (OER) kinetics are the main obstacles that limit the photocatalytic overall water-splitting performance. A molten salt modulation of potassium-nitrogen-carbon is herein demonstrated as the formation of highly crystalline potassium-doped poly(triazine imide) (KPTI). The in situ X-ray diffraction patterns and theoretical calculation show that the KCl melt can significantly reduce the free energy for the polycondensation of triazine building blocks owing to the formation of a kinetically stable KPTI. Benefiting from the presence of potassium-carbon-nitrogen moiety, the catalyst not only weakens the excitonic confinement to improve the separation efficiency of photogenerated charge carriers but also enhances the stability of carbon sites by suppressing the undesired C═O formation. Moreover, KPTI accelerates water dissociation by forming interfacial K·H2O clusters with an ordered structure, which supplies sufficient protons for the H2 evolution reaction and lowers the energy barrier to enhance the kinetics of OER. Therefore, a stable photocatalytic overall water-splitting performance can be achieved over KPTI with a stoichiometric generation of products (H2 and O2). Life cycle assessment shows that a carbon-neutral scenario can be achieved on KPTI production in the near term with an increase in green power in the electricity grid.

Solar methane pyrolysis in a liquid metal bubble column reactor: Effect of medium type and gas injection configuration

Solar methane pyrolysis in different molten media and reactor configurations was experimented to improve hydrogen production. Pure Sn, Ni0.18Sn0.82, Cu0.45Bi0.55, and KCl melts were compared at three different temperatures (1030–1130–1230 °C), and no significant difference was observed except for KCl and only at 1230 °C (XCH4 = 72 % vs. 57 % for pure Sn). This enhanced performance was attributed to possible carbon dispersion in the salt, which probably modified the physical properties and enhanced hydrodynamics. A porous quartz sparger (downward injection) did not significantly enhance the bubbles hydrodynamics, mainly because bubbles were trapped and coalesced below the sintered disc. A custom-made sparger (lateral bubbling) did not either improve conversion due to non-uniform pores. A sparger with an upward injection should be preferred to generate small bubbles with longer residence time. When a solid bed of tungsten carbide particles was placed around the injector, overlaid by molten tin, the conversion was improved even at a relatively low temperature (XCH4 = 17 % at 1030 °C). The immersed bed likely behaved as a porous device and increased the gas-solid surface contact. Combining particle bed and liquid bubbling system is very promising for further optimization of methane pyrolysis in molten media. The carbon collected above molten metals showed mostly a sheet-like structure with significant metal contamination. In case of KCl, most carbon was entrained with the gas, while the remaining was mixed with KCl in the reactor. The density of KCl is close to that of carbon, which prevented a good separation.

Electrodeposition of Beta-Tantalum in Alkali Metal Halides and Oxohalide Melts

Data on the electrolytic preparation of β-Ta in halide and oxohalide melts were reported. It was shown that during electrolysis in halide melts containing K2TaF7, the amount β-Ta in the cathodic products can be markedly increased by using a copper cathode with a definite texture. It was found that in chloride-oxofluoride melts the β-Ta content increases monotonically on passing from NaCl to KCl and RbCl melt. The dependencies of the β-Ta content in cathodic products on the ratio of oxygen to tantalum concentrations were studied in chloride-oxofluoride and fluoride-oxofluoride melts. The maxima of these dependences were identified and explained. It was shown that β-Ta could be obtained by electrolysis in molten salts only at temperatures below 850 °C.

Machine learning model to efficiently predict the structure and properties of MgCl2–NaCl–KCl melts

MgCl2–NaCl–KCl ternary melts hold great promise as thermal energy storage and heat transfer fluid for the next generation of concentrating solar power (CSP), offering major advantages such as high-temperature storage capacity, adjustable temperature ranges, and renewable usability. However, a critical challenge is the lack of an accurate model to analyze the structural and property aspects of this complex melt. In response, a machine learning-based model with high accuracy and applicability has been developed for this purpose. Based on DPMD techniques, the trained model is used to investigate the structure information, transport and thermal properties of the melt. Temperature and composition effects are introduced. Radial distribution functions, coordination numbers, and angular distribution functions are applied to investigate the microscopic ionic environment within the melt. Transport properties studied include density, self-diffusion coefficient, ionic conductivity, and viscosity, while thermal properties include heat capacity at constant pressure and volume and thermal conductivity. Our model accurately reproduces the results obtained from FPMD simulations and accurately predicts the macroscopic properties of the melt through validation. The high stability of the Mg2+-Cl- interactions is introduced, which remains relatively unaffected by temperature and concentration changes. The presence of MgCl53− species in the melt was observed. We are devoted to the development of AI for the CSP science field. Due to the application of machine learning strategies, our models have proven to have exceptional accuracy and ease of study for MgCl2–NaCl–KCl ternary melts, and they can provide valuable insights into their properties and ionic behaviors.

Electrochemical and kinetic studies on the electrolytic extraction of Gd on Bi electrode in LiCl–KCl melt

Advancements in science and technology are heavily dependent on the development and utilization of rare earth materials.

PROTECTIVE METAL COATINGS MADE OF MOLYBDENUM ON STEEL 12Cr18Ni10Ti FOR FLUORIDE MELTS. OBTAINING, CERTIFICATION, EFFICIENCY

The successful use of molten alkali metal fluorides as an electrolyte for high-temperature devices requires the development of such reactor materials that have high corrosion resistance in melts with compositions characteristic of liquid-salt mixing reactors. This is one of the most important unresolved problems. One of the effective ways to reduce corrosion losses is to create a layer on the surface of the material that protects the metal from the corrosive effects of the environment. In this paper, molybdenum insulating coatings on steel 12Kh18Ni10Ti obtained in molten salts of various compositions and by various methods are considered as protective layers. Experiments were carried out on the electrodeposition of molybdenum coatings on structural materials based on iron (steel 12Cr18Ni10Ti). The coatings obtained by the electrochemical method are inhomogeneous and easily exfoliating. The thickness of molybdenum coatings obtained from molten salts is 8.15 and 20.34 μm on steel in FLiNaK and LiCl–KCl melt, respectively. Corrosion tests have shown the inefficiency of the molybdenum coating obtained from both chloride and fluoride melts. The corrosion rate of 12Cr18Ni10Ti steel in FLiNaK/FLiNaK + 5% CeF3 melts at 650°C and a holding time of 100 hours decreases in the following row: 12Cr18Ni10Ti + Mo (0.75/0.77 mm/year) 12Cr18Ni10Ti (0.45/0.50 mm/year).

LUMINESCENT DETERMINATION OF EUROPIUM AND CERIUM IN THE JOINT PRESENCE IN SOLUTIONS – MELTS OF EQUIMOLAR MIXTURES NaCl–KCl

Europium and Cerium belong to lanthanides of variable valency and have similar chemical properties. Luminescent method was proposed for the analytical determination of Eu(III) and Ce(III) with the simultaneous presence in the sample of [EuF3–CeF3 (1:1)]–[NaCl–KCl] (2:8), which is a promising material for detecting UV-solar radiation. Determination of Eu(III) was carried out by the method of sensitized 4f-4f luminescence in a complex with nalidixic acid at an emission wavelength of 613 nm, λex =351 nm. During complexation, a standard ratio of Stark components to Europium is observed in the luminescence spectra, in contrast to the spectrum of the sample solution without the reagent. This fact indicates that the formation of complexes not only increases the intensity of Eu(III) luminescence, but also reduces the effect of Cerium present in the solution. To determine Ce(III), its own luminescence caused by 5d-4f electronic transitions was used at an emission wavelength of 351 nm, λex =263 nm. The presence of Europium ions in the solution does not affect the nature of the luminescence excitation spectra and Ce(III) luminescence spectra. For the quantitative determination of these lanthanides, the additive method was used, which allows to level the mutual influence of ions, as well as the influence of Ce(IV) on the determination of Ce(III). It was found that the content of Eu(III) in the melt is 2.44–2.53% weight, which is in good agreement with the data obtained earlier when studying the EuF3 – [NaCl–KCl](1:9) system. Compared to EuF3, the solubility of CeF3 ((0.028–0.032)% weight) is significantly lower than that predicted by previous thermodynamic calculations. The obtained data allow us to conclude that the solubility of fluoride systems containing Eu in the NaCl–KCl melt is almost the same, and the presence of Ce(III) does not significantly affect the EuF3 dissolution process, and therefore does not affect the properties of the systems [EuF3 – CeF3] – [NaCl–KCl] as detectors of ultraviolet solar radiation.

Corrosion Behavior of 12Kh18N10T Steel in the LiCl–KCl Melt Containing f-Element Chloride Additives

Corrosion Behavior of 12Kh18N10T Steel in the LiCl–KCl Melt Containing f-Element Chloride Additives

Electrochemical separation of fission element neodymium using plumbum electrode from molten LiCl–KCl based on spent fuel reprocessing

In order to investigate the application prospects for the extraction of fission products neodymium (Nd) by electrolytic refining at active plumbum (Pb) electrodes, the reduction mechanism of Nd(III)/Pb(II) at inert tungsten, and Nd(III) at Pb thin film electrodes was investigated. This work simultaneously presents the results of kinetic and thermodynamic parameter of Pb(II)/Nd(III). The composition of the Pb–Nd alloy compound formed on the activated Pb electrode was determined by X-ray diffraction analysis (XRD) and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), and the thermodynamic parameters of the formed Pb3Nd alloy were calculated: ΔHf0Pb3Nd=−219.92kJmol−1 and ΔSf0Pb3Nd=−47.48Jmol−1K−1. Nd(III) was extracted in the form of Pb–Nd alloy by constant potential electrolysis (PE) in LiCl–KCl melt. Based on the analysis of inductively coupled plasma-atomic emission spectrometry (ICP-AES) results, the average extraction rate of Nd(III) ions at the liquid Pb electrode could reach 99.03%.

CORROSION BEHAVIOR OF 12Cr18Ni10Ti STEEL IN LiCl–KCl MELT CONTAINING ADDITIVES OF <i>f</i>-ELEMENT CHLORIDES

When reprocessing spent nuclear fuel, it is supposed to use LiCl–KCl melt (0.49:0.51) in an inert atmosphere, all metal materials in this salt melt are extremely susceptible to corrosion, besides, during the processing of spent fuel, both the liquid (melt) and the gas phase are saturated with decay products that can act as additional oxidizing agents, increasing the aggressiveness of the environment. The pyrochemical technology of SNF includes operations such as soft chlorination, electrofining and metallization, implying the presence in the melt of compounds of chlorides of rare earth metals lanthanum, cerium and neodymium, as well as uranium(III, IV) chlorides. In this work, the corrosion behavior of 12CR18NI10TI steel in LiCl–KCl melt containing NdCl3, CeCl3, LaCl3, UCl3 and UCl4 additives up to 2 wt % was investigated. Corrosion tests lasting 100 hours were performed at a temperature of 500°C in an inert argon atmosphere. It was found that the presence of REM chlorides significantly reduces the degradation of the steel under study. The addition of (REM)Cl3 leads to the formation of a compound (REM) on the surface of the samples OCl, the thickness and continuity of which increases in the following row: LaCl3 NdCl3 CeCl3. The formation of such a compound leads to the inhibition of the corrosion process of steel 12CR18NI10TI due to salt passivation of the surface. The addition of UF4 to the melt causes significant corrosion of 12CR18NI10TI intercrystalline steel. The introduction of UF3 into the melt leads to a decrease in the corrosion rate, which is associated with the predominant interaction of trivalent uranium chloride with dissolved molecular oxygen contained in the melt, and the formation of a non-stoichiometric compound with the crystal chemical formula U3O7 on the surface of samples according to microrentgenospectral analysis.

Kinetic and Thermodynamic Properties of Ytterbium Chloride and Fluoride Complexes in Chloride Melts

The electrochemical behavior of trichloride ytterbium in NaCl-KCl, KCl, and CsCl melts was studied in the temperature range 973–1173 K by different electrochemical methods. The diffusion coefficients (D) of Yb(III) and Yb(II) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods. The standard rate constants of charge transfer (k s) for the Yb(III)/Yb(II) redox couple were calculated on the basis of cyclic voltammetry data using Nicholson’s equation. The formal redox potentials E * Yb(III)/Yb(II) in alkali chloride melts were obtained by the cyclic voltammetry and the Gibbs free energy for the reaction: YbCl2(sol.) + 1/2 Cl2(g.) ↔YbCl3(sol.) in alkali chloride melts was calculated. The electrochemical behavior of the Yb(III)/Yb(II) redox couple in the NaCl-KCl- NaF (5 wt%) melt was studied. A comparative analysis of electrochemical behavior of ytterbium chloride complexes in the NaCl-KCl melt and ytterbium fluoride complexes in the NaCl-KCl- NaF (5 wt%) melt was performed. It was shown that the formation of the stronger fluoride complexes reduced diffusion coefficients, standard rate constants of charge transfer for the Yb(III)/Yb(II) redox couple, and shifted the formal standard redox potentials to more electronegative values.

Study on diffusion kinetics of chromium and nickel electrochemical co-deposition in a NaCl–KCl–NaF–Cr2O3–NiO molten salt

Abstract The process of preparing surface composite by molten salt co-deposition is the result of the mass transfer of active particles in molten salt, electrochemical reduction, and solid diffusion. In this study, we prepared Cr–Ni alloy/low-carbon steel surface composites in NaCl, KCl, NaF, Cr2O3, and NiO melt salt system successfully, and analyzed the entire diffusion dynamics process, aiming to find out the limiting links and provide ideas for further improving the preparation efficiency. The results show that chromium and nickel ions are simultaneously reduced on the cathode surface through two and one steps, respectively. And an alloy layer with Fe content of 64.52 wt%, Ni content of 28.96 wt%, and Cr content of 6.52 wt% is formed on the surface of low-carbon steel substrate. The average diffusion coefficients of chromium and nickel atoms in the surface composites are 1.16 × 10−14 and 1.44 × 10−14 m2·s−1. The mass transfer process in molten salt is the limiting link in the whole preparation process.

Formation and Structural Characterization of Spinel‐Phase Zn2TiO4 Synthesized in a High‐Temperature Solution Approach

AbstractSpinel phase Zn2TiO4 powders were prepared by high‐temperature solution, which is a kind of molten salt (such as KCl melt). The effect of Zn2TiO4 synthesis was explored under different holding time, preparation temperature and the mass ratio of salt to raw material in KCl melt. Through experimental analysis, the synthesis temperature range of Zn2TiO4 phase in KCl molten salt system was from 800 to 1000 °C. Compared with the traditional solid‐state reaction, the stable temperature range of Zn2TiO4 phase in KCl molten salt system was wider. The HRTEM image analysis of calcined product was consistent with the XRD result. The TEM analysis showed that the average particle size of Zn2TiO4 powder was 200 nm. The crystallinity of Zn2TiO4 increased with increasing sintering time and Zn/Ti molar ratio. Compared with LiCl+KCl and LiCl melts, the crystallinity of Zn2TiO4 powder synthesized in KCl molten salt system was better. It is determined that the high‐temperature solution (KCl melt) can be successfully applied for large‐scale synthesis of spinel phase Zn2TiO4.

Коэффициенты диффузии комплексов неодима (III) в эквимолярном расплаве NaCl — KCl — NdCl3

The paper presents results of electrochemical behavior of neodymium trichloride in the NaCl — KCl melt. It was shown that the process of neodymium electroreduction in the NaCl — KCl — NdCl3 melt proceeds in two stages. It was established by using the diagnostic criteria of voltammetry that the discharge process of Nd (III) to Nd (II) at the potential sweep rate in the range of 0.6 ≤  ≤ 1.0 V · s-1 is not complicated by reaction disproportionation. In this study diffusion coefficients and activation energy of diffusion for Nd (III) complexes in the NaCl — KCl melt were determined.

Electrochemical and spectroscopic analysis of thermochemical conversion of UO2 to UCl3 using AlCl3 and Al in LiCl–KCl eutectic

Thermochemical conversion of UO2 to UCl3 using AlCl3 and Al metal in LiCl–KCl melt at 773 K is reported here. The reaction product was assessed qualitatively by UV–Vis spectroscopy, cyclic voltammetry (CV) and square wave voltammetry (SWV). The extent of conversion efficiency was quantified through UV–Vis spectroscopy by measuring the absorbance of U(VI) at 420 nm after dissolving the reaction product in 1 M HNO3 + 1 M H3PO4 medium. The conversion process was optimized by varying concentrations of AlCl3 (stoichiometric × 1 to 4) and the duration of reactions (45 min–5 h). About 93% conversion of UO2 was achieved by doubling the stoichiometric requirement of AlCl3 in 50 g of LiCl–KCl salt in 2.5 h.

Kinetic and Thermodynamic Properties of Ytterbium Chloride and Fluoride Complexes in Chloride Melts

The electrochemical behavior of ytterbium in NaCl-KCl, KCl and CsCl melts was studied in the temperature range 973-1173 K by different electrochemical methods. The diffusion coefficients (D) of Yb(III) and Yb(II) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods. The standard rate constants of charge transfer (k s) for the Yb(III)/Yb(II) redox couple were calculated on the basis of cyclic voltammetry data using Nicholson’s equation. The formal redox potentials E* Yb(III)/Yb(II) were obtained in alkali chlorides melts from the cyclic voltammetry data. The influence of fluoride ions on the standard rate constants in the NaCl-KCl melt was investigated.

Effect of fluoride addition on electrochemical behaviors of V(III) in molten LiCl−KCl

X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to analyze the complexes in LiCl−KCl eutectic salt containing VCl3 and KF. The additional fluoride ions would replace chloride ions and combine with V(III) to form VF63−. The electrochemical behavior of V(III) was evaluated under condition of the molar concentration ratio of F− to Vn+ (α) equal to 0:1, 1:1, 2:1, 5:1, 20:1 and 50:1, respectively. The results showed that a new reduction step appeared: VF63−→V2+, and the reduction mechanism of vanadium ions became more complicated. The metallic vanadium was deposited on the tungsten electrode at −2.90 V in the LiCl−KCl melts for 6 h, and the products were characterized by SEM−EDS. It was indicated that the particle size of the product decreased with adding fluoride ions for the forming of the coordination compound VF63−.

A Finite-Element Model for Underpotential Deposition of Ce(III) on an Active Aluminum Electrode in LiCl–KCl Melts

Underpotential deposition on an active Al cathode plays an increasingly important role in pyroprocessing of used nuclear fuel, but most of the developed models are applied to simulate underpotential deposition at atomic level without considering electron transfer process which is a critical step in electrochemical reactions. In this work, a novel finite-element model for the underpotential deposition of Ce(III) in LiCl–KCl melts is developed with the consideration of Ce(III) activity in the Al electrode and the electron transfer process which is described by Butler-Volmer equation. This model was applied to investigate cyclic voltammetry(CV), square wave voltammetry(SWV) and electrodeposition behaviors of Ce(III) on an Al/Mo electrode. Additionally, the effect of temperature and electrode surface area on the electrodeposition thickness was investigated. Simulated CV and SWV curves are obtained and compared with our pervious experimental data. The results also provide the distribution diagrams of current density, electrostatic potential, Ce(III) concentration and electrodeposition thickness. Furthermore, the electrodeposition thickness is found to be linearly proportional to temperature and the inverse of cathode’s area, respectively. This work proposes a new pathway for the further study of underpotential deposition process.

Molten salt/liquid metal extraction: Electrochemical behaviors and thermodynamics properties of La, Pr, U and separation factors of La/U and Pr/U couples in liquid gallium cathode

The electrochemical behavior of lanthanides (La, Pr) and actinide (U) on inert W and liquid Ga electrodes in LiCl–KCl molten salt as well as their related thermodynamic properties were experimentally determined for further Lns/Ans separation. The results indicate that the reductions of La3+ and Pr3+ in LiCl–KCl melts are both one-step process with three electrons exchanged, and the reactions are quasi-reversible processes at low scan rate. Temperature dependencies of apparent standard redox potentials of La(Ga), Pr(Ga) and U(Ga) alloys were determined by open-circuit chronopotentiometry versus Cl-/Cl2 reference electrode. The activity and activity coefficients of lanthanum, praseodymium and uranium on the liquid Ga electrode in the temperature interval 723–813 K were calculated. The separation factors for La/U and Pr/U on the liquid Ga electrode in the molten salt were determined by logθU/La=−10.39+11440.69T±0.0125 and logθU/Pr=−5.84+7763.27T±0.07. The separation factors of La/U and Pr/U on the liquid Ga electrode indicate that lower temperature should be more effective for separating uranium.