LiCl-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

Investigation of the corrosion behavior of 29NC alloy in LiCl-KCl melt at 500 oC depending on the content of Li2O and LiOH from 0 to 2 mol. %

Molten chloride salt electrolytes are promising for use as a working medium for the implementation of high-temperature technologies. Alkali metal chlorides are an aggressive environment in relation to structural materials. One of the possible methods of reducing the corrosion damage of a structural material is the method of oxygen passivation of the surface of a metal or alloy by introducing a certain amount of oxygen-containing additives into the melt. The article considers the effect of oxygen-containing impurities (lithium oxide and lithium hydroxide) on the corrosive behavior of a metal material — an alloy of the composition iron–cobalt–nickel. To assess the corrosion resistance of materials, gravimetric analysis, micro-X-ray spectral analysis (XRSA) of the surface and cross-section sections, and X-ray phase analysis (XRF) of the sample surface were used. The dependences of the corrosion rate of the material on the concentration of oxygen-containing additives Li2O and LiOH are presented. Based on the data set of gravimetric, MRSA and XRF data, it was found that 29NC alloy samples in the LiCl–KCl–nLi2O salt melt are not susceptible to corrosion, but in the LiCl–KCl–nLiOH melt, the speed of the 29NC alloy increases significantly due to the interaction of the LiOH additive with the most electronegative component of the alloy — iron.

Compositional transferability of deep learning potentials: a case study for LiCl-KCl melt.

One of the crucial issues related to machine learning potentials is the formation of representative dataset. For multicomponent systems, it is a general methodology to scan the composition range with a certain step. However, there is a lack of information on the compositional transferability of machine learning potentials. In this paper, we extend the knowledge in this area by studying the transferability of deep learning potential over the range of compositions of LiCl-KCl molten mixtures. The training dataset was formed using only the near-eutectic composition of 60% LiCl-40% KCl. Then, we tested the ability of the model to predict physicochemical properties of the melts far from the reference composition. It was found that for the composition range from 0 to 100% of LiCl, the calculated properties concur closely with those of other studies and ab initio calculations. Therefore, the model shows prominent non-intuitive compositional transferability. Moreover, the solid states and solid-liquid coexistence were reproduced. The calculated melting temperatures of LiCl and KCl show the errors of 6.6% and 0.4%, respectively. We argue that such good transferability stems from the local structure configurations that are typical both for pure LiCl and for pure KCl which are implicitly presented in the training dataset because of local fluctuations in composition. To collect the data for the initial dataset, density functional theory was employed. Then, the DeePMD package was used to train a neural network potential. To calculate the properties of the melts, standard equilibrium and non-equilibrium molecular dynamic approaches were utilized.

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.

Investigation of electrochemical characteristics and nucleation mechanism of cerium influenced by F− in LiCl-KCl-CsCl melts

The present study investigated the influence of F− on the electrochemical characteristics and nucleation mechanism of cerium in LiCl-KCl-CsCl molten salts, a new electrolyte medium for pyroprocessing of spent nuclear fuel with lower melting point that reduces the temperature tolerance demand of operating equipment compared with LiCl-KCl melts. By employing different electrochemical techniques, the electrochemical reaction of Ce(III)/Ce in LiCl-KCl-CsCl melts containing F− was found to be a diffusion-controlled, electrochemical reversible and three electrons transfer redox reaction at 653 K (CCe(III) = 4.94 × 10−2 mol/kg). It was also discovered that exchange current density and the diffusion coefficient of Ce(III)/Ce dropped in the presence of F−, while shifting negatively the equilibrium potential and subsequently resulting in the change of thermodynamic characteristics. The electrodeposition mechanism of Ce was also studied, demonstrating that the nucleation mode of Ce successfully transformed into progressive nucleation when F− was added. The affected electrochemical characteristics and the mechanism of electrodeposition nucleation of Ce in LiCl-KCl-CsCl molten salts at lower temperatures were attributed to the stronger complex ion [CeCl5F]3− formed after the addition of F−, being illustrated by the mathematic analysis of the molten salt structure. The formation of complex ion [CeCl5F]3− provides a new solution to inhibit the dendrite growth issue in the pyroprocessing of spent nuclear fuel at lower temperatures.

Selective separation of Y and Nd with similar electrochemical properties by pulsed electrolysis on Sn electrode

Selective separation of Y and Nd from LiCl-KCl melt was systematically investigated on W and Sn electrodes by various electrochemical methods. The electrochemical properties of Y and Nd on W and Sn film electrodes were firstly analyzed and compared by cycle voltammetry (CV), square wave voltammetry (SWV), reverse chronopotentiometry (RCP), etc. The results indicate that the deposition potentials of Y and Nd on W electrode are very close, while the deposition potential difference could reach 0.15 V on Sn film electrode. The selective separation of Y and Nd was conducted by potentiostatic electrolysis (PE) on W electrode assisted by Sn(II), and the product is composed of Sn and NdSn3 phases. In addition, the electrochemical properties and kinetic parameter of Y and Nd on liquid Sn electrode were also studied. The results prove that Nd has a more positive deposition potential, larger exchange current density and smaller reaction activation energy than Y, illustrating that Nd is more easily extracted on liquid Sn electrode. Thus, PE and potentiostatic electrolysis + pulse potential electrolysis (PE + PPE) were used to separate Y and Nd on liquid Sn electrode. The results show that the application of PPE effectively reduced the extraction efficiency of Y from 16.75 ± 1.50 % to 8.36 ± 1.13 %, and increased the separation factor β from 4.98 ± 0.46 to 9.64 ± 0.58.

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).

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%.

Effects of F- on the electrochemical properties and electrodeposition nucleation mechanism of Ce(III) in LiCl-KCl melts

The purpose of this work is to systematically investigate the effect of F− on the electrochemical properties and electrodeposition nucleation of Ce(III) in LiCl-KCl molten salt. Electrochemically reversible, three-electron transfer and diffusion-controlled Ce(III)/Ce redox reactions were still observed by using Cyclic voltammetry (CV), Square wave voltammetry (SWV), and Chronopotentiometry (CP) methods in the LiCl-KCl molten salt containing F−. With the addition of F−, a negative shift in peak and equilibrium potentials were observed, indicating that F− could interact with Ce(III) via the coordination competition with Cl−. Also, F− ions were found to decrease both the diffusion coefficient and exchange current density j0 of Ce(III). In addition, the thermodynamic data of Ce(III)/Ce at multiple F− concentrations were calculated theoretically, which showed that Ce(III) preferred to form [CeCl5F]3−complexes in chlorine molten salts. Finally, the effect of F− on the electrodeposition nucleation mechanism of Ce(III) at tungsten electrodes was studied. The results showed that the nucleation and growth mechanism shifted from instantaneous nucleation to between instantaneous and progressive nucleation with the addition of F−. The current research paves a new way for changing the nucleation mode of electrodeposition, which provides a new direction to retrieve the uranium dendrites during the electrorefining of spent nuclear fuel.

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.

Electrochemical and kinetic analysis of Ce recovery using Ga electrode in LiCl-KCl melt

Electrode material is an obstacle to the application of molten salt electrolysis in Ce recovery. Liquid Ga is a potential candidate for the cathode, but the corresponding reaction process on the electrode in the melt has yet to be fully understood and systematically studied. Herein, the electrochemical reaction and the kinetics of recovering Ce using Ga electrodes were investigated by various electrochemical methods. A concentration-dependent test of the co-deposition reaction revealed the continuous alloying process of reduced Ce. The electrolytic reduction of Ce ions on liquid Ga was studied by electrochemical impedance spectroscopy (EIS). The result shows that the reaction is controlled by diffusion. In addition, some important parameters such as exchange current density, activity coefficient and solubility were determined by pulsed electrolysis and coulomb titration, allowing a preliminary assessment of the electrolytic extraction of Ce on the Ga electrode.

Corrosion Performance of Commercial Alloys and Refractory Metals in Conditions for Electrorefining of Spent Nuclear Fuels

Molten LiCl-KCl salt and liquid cadmium are proposed as the electrolyte and the reactive cathode for the electrorefining of spent nuclear fuels, but they can be corrosive to the structural alloys. The down-selection of existing materials through corrosion testing is necessary to ensure the longevity of the electrorefiner vessel and electrode assemblies. Haynes C276, Inconel 600, AISI 316L stainless steel, and 42CrMo low-alloy steel were exposed to a LiCl-KCl melt at 500 °C for 500 h in an argon atmosphere. All alloys suffered from dissolution attacks with the presence of oxide islands or a porous oxide layer on the surface. AISI 316L, T91 steel, and tungsten specimens were submitted to corrosion tests in liquid cadmium at 500 °C for 120 h. The corrosion of AISI 316L and T91 stainless steel was predominated by chemical oxidation, with the additional occurrence of severe Ni dealloying and Cd penetration on AISI 316L. Destabilization of the Cr oxide layer by cadmium was discovered, resulting in the formation of CdCrO4. Tungsten only suffered from a dissolution attack at a rate of 0.50 mm/a.

Direct electrochemical formation of carbonaceous material from CO2 in LiCl-KCl melt

The electrochemical reduction of CO2 on a Ni electrode in LiCl-KCl melt at 723 K was studied. The Ni electrode which was partially immersed in the melt was used for electrochemical measurement in order to investigate the relationship between electrical wettability and electrodeposition behavior of carbon from CO2 at the three-phase interface of the Ni electrode/LiCl-KCl melt/CO2 gas. It was found that solid carbon was obtained in the wetted area of the Ni electrode by potentiostatic electrolysis. Under high polarization, a super meniscus was formed at the three-phase interface where the direct electrochemical reduction of CO2 to solid carbon progressed. In addition, SEM and TEM observations with EDS analyses showed that electrodeposited carbon was multi-walled carbon nanotubes with a diameter of 30–50 nm. The dependence of applied potential and electrolytic time on morphology and crystallinity of electrodeposited carbon was also investigated. Based on the experimental results, we have proposed the model of the formation mechanism of the multi-walled carbon nanotube on the Ni electrode. The reported data indicate that carbonaceous materials from CO2 can be obtained by electrochemical technique in molten salt and suggest that the technique contributes to developing the carbon recycling system against global warming.

КОРРОЗИЯ КОНСТРУКЦИОННЫХ МАТЕРИАЛОВ В РАСПЛАВЛЕННЫХ ХЛОРИДАХ ЩЕЛОЧНЫХ МЕТАЛЛОВ

The corrosion process of 12X18H10T steel in a KCl-Nacl melt with the addition of Li2O (0-11000 ppm O2-), as well as lanthanum, cerium and neodymium trichlorides, was investigated. The concentration interval of lithium oxide in the LiCl-KCl melt is determined in the range from 0 to 0.2 % by weight of Li2O, at which the corrosion rate decreases by 5–6 times. The concentration interval of lithium oxide in the LiCl-KCl melt is in the range from 0 to 0.2 % by weight of Li2O, at which the corrosion rate decreases by 5–6 times.

Electrochemical Deposition with Redox Replacement of Lanthanum with Uranium in Molten LiCl-KCl

Electrochemical recovery of dilute concentrations of actinides from spent nuclear fuel would reduce the longevity of storing high-level nuclear waste. Electrochemical deposition with redox replacement (EDRR) is used in a molten salt medium for the selective electrochemical recovery of uranium in the presence of excess concentrations of lanthanum. In each EDRR cycle, after a short electrodeposition pulse, the deposited lanthanum is spontaneously replaced by uranium at open circuit. After repeated cycles, uranium metal was obtained on a tungsten electrode immersed in a LiCl-KCl melt that contained 1 wt% lanthanum chloride—0.15 wt% uranium (IV) chloride. Scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) analysis revealed uranium particles approximately 0.5−1 μm with well-defined rectangular shapes; and with 20–60 times more uranium recovered on the surface of the electrode than lanthanum.

(Digital Presentation) Anodic Formation of Oxide Film on MoSi2 Containing Al or Nb in LiCl-KCl Molten Salt

Li and Mg metals are produced by electrolysis in a molten chloride bath. Currently carbon-based material is used as anode. However, carbon-based anode reacts electrochemically with oxide ions dissolved in the bath, which causes its undesirable consumption. In our laboratory, a new type of inert anode by forming a thin and dense oxide film has been studied. It was shown that a SiO2 film was formed on MoSi2 anode in molten LiCl-KCl melt with Li2O, and that the dissolution of MoSi2 was inhibited by the formation of oxide film. However, sufficient electrolytic current was hardly applied. In this study, the modification of the anodic properties of MoSi2 has been attempted by the addition of Nb or Al in MoSi2. A MoSi2 rod containing Nb(0.1~1.0mol%) or Al(0.1~0.5mol%) was prepared by sintering from MoSi2, Nb and Al powder. The prepared rod was pre-oxidized (1573K, 4h) to form a SiO2 film in advance, and then used as working electrode. An Al plate and Ag/AgCl were used as counter and reference electrode, respectively. The potential of the Ag/AgCl electrode was calibrated against the Li metal deposition potential measured by cyclic voltammetry. Electrolysis was conducted at 700K in an Ar atmosphere. Anodic behavior of MoSi2 was investigated by cyclic voltammetry, and potentio-static electrolysis was performed. The weight change in MoSi2 anode was measured, and the surface and cross section of the MoSi2 electrode were observed and analyzed by SEM-EDX and XRD.The shape of the cyclic voltammogram did not change significantly by the addition of Nb or Al in the MoSi2. Anodic peaks were seen around 2.5V (vs. Li / Li+, the same hereinafter) and around 3.6V. Above 3.6V, anodic current continued to flow with gas bubble formation. The current at 3.6V in the cyclic voltammogram changed with the added amount of Nb or Al as shown in Fig.1, which suggests the Nb or Al addition strongly influenced the anodic property of MoSi2.Current during potentio-static electrolysis at 4.2V increased with current oscillation. It was seen that a black film peeled periodically, and the current oscillation seemed to link the peeling. The quantity of electricity increased with Ni or Al addition in MoSi2. An oxide layer was observed on the MoSi2 surface after potentio-static electrolysis, and a dense layer was formed on MoSi2 containing 0.5~1.0mol% Nb. The weight of MoSi2 decreased by potentio-static electrolysis, and Nb or Al addition in MoSi2 clearly inhibited the weight change. The addition of 0.5~1.0mol%-Nb seemed suitable from the improvement of the anodic property of MoSi2.It was indicated that Nb or Al addition in MoSi2 influenced its anodic property, and that the addition inhibited its anodic consumption in molten LiCl-KCl. However, it was shown that the formation and peeling of the surface film occurred repeatedly, so the formation of a durable surface film should be necessary.The results of this research were obtained as a result of the commissioned work (JPNP 14004) of the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

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.

Evaluation of the local structure and electrochemical behavior in the LiCl-KCl-SmCl3 melt

This present work evaluates the local structure and electrochemical behavior of the LiCl-KCl-SmCl3 melt to facilitate the efficient reprocessing of spent nuclear fuel (SNF). At 723 K, the radial distribution function, coordination number, and structure factors were adopted to understand the local structure of LiCl-KCl and LiCl-KCl-SmCl3 based on first-principles molecular dynamics (FPMD) simulation. We found the SmCl3 slight effect on LiCl-KCl melts in short-range order and its influence on the distribution of Li-Li intermediate-range order. Moreover, the diffusion coefficient of Sm(III) 2.012 × 10-5 cm2/s in LiCl-KCl melts was determined by analyzing the mean square displacement. The electrochemical behavior of Sm(III) was conducted in the temperature range from 673 K to 823 K by a series of electrochemical methods. According to the theory of Matsuda and Ayabe, the Sm(III) + e- = Sm(II) is a quasi-reversible process. The diffusion coefficient of Sm(III) was measured by the chronoamperometry method, which verified the credibility of the FPMD simulation. Furthermore, this work explored the exchange current density of Sm(III)/Sm(II), whose value is between 0.826 × 10-3 and 2.383 × 10-3 A·cm−2, by the linear polarization.