LiCl Molten Salt Research Articles

Li2O concentration influenced local structure and properties of molten LiCl salt by machine learning driven molecular dynamics simulation

Pyroprocessing is one of the promising technologies for the reprocessing of spent nuclear fuel. In the electrolytic reduction process of pyroprocessing, LiCl serves as the electrolyte with a minor addition of Li2O as the initial oxygen ion input. Investigating the impact of Li2O concentration on the molten salt system is essential for enhancing the efficiency of electrolytic reduction. In the present study, the LiCl-Li2O system is simulated using deep potential molecular dynamics simulation. The properties including self-diffusion coefficient, shear viscosity, ionic conductivity, heat capacity, radial distribution functions, coordination numbers, short-range order, medium-range order, Voronoi structure, and angle distribution functions are explored at different Li2O concentrations. This study reveals that the variations of physical properties at different Li2O concentrations in LiCl molten salt can be attributed to the changes in local structure. For example, unnormal high proportions of two Voronoi structures are found in the molten salt when the Li2O concentration increases, which may explain the changes of properties. These findings offer valuable insights for refining the parameters of electrolytic reduction and elucidating the correlation between microscopic and macroscopic phenomena.

Rapid fractionation of noncondensed lignin from birch via acidified LiCl molten salt hydrates

The conventional fractionation of lignocellulose is generally carried out at high temperatures, high acid or alkali, or using organic solvents due to the rigid matrix of lignocellulose and crystallinity of cellulose, leading to the condensation of lignin and environmental pollution, and hindering the further value-added utilization of lignin. In this work, a rapid fractionation method was proposed, in which hemicellulose and cellulose (holocellulose) were first dissolved and partially hydrolyzed in acidified LiCl molten salt hydrates, followed by a filtration process to isolate the lignin solid with a purity of 88.3%. It was found that the dissolution of holocellulose required the addition of a small amount of acid to break the cellulose chain into short chains. Due to the small amount of acid added and the rapid dissolution, the obtained lignin has as high as 89.5% of β-O-4 bond content close to the theoretical value, suggesting that a promising native lignin structure was preserved. The isolated lignin can be selectively depolymerized into monophenol over Ru/C catalyst with a high yield of 24.2%. In addition, the dissolved holocellulose without containing lignin was selectively hydrolyzed into sugars in acidified LiCl molten salt hydrates, giving 63.1% of xylose, 43.9% of glucose, 29.5% of xylan oligomers, and 48.2% of glucan oligomers, respectively.

C@CoSn2 composite prepared through one-step electro-deoxidation method as anode material of lithium-ion batteries with long-cycle-life and high capacity

Tin is widely studied as an alternative anode material of high-energy-density Li-ion batteries owing to its high theoretical capacity of 993 mAh g–1, low discharge potential, large electrical conductivity, and natural abundance. However, Sn-based anode materials still suffer from large changes in volume during lithium intercalation/de-intercalation processes, leading to cracking and pulverization of electrodes. Herein, carbon is in-situ coated on CoSn2 alloys (C@CoSn2) during the electro-deoxidation process of Co3O4 and SnO2 through the reduction of CO32− in the molten salt of LiCl–KCl–K2CO3. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectrometry all confirm CoSn2 alloys coated with a uniform carbon layer. The sizes of CoSn2 particles decrease to 0.2–1.0 µm due to the surface coating of carbon. The galvanostatic charge/discharge tests suggest discharge capacity and Coulombic efficiency of the optimized C@CoSn2 alloy film electrode reaching 991.5 mAh g–1 and 97.6 % after the 5th cycle, respectively. C@CoSn2 alloy also shows a good rate performance at 2 A g–1 along with a superior retained high capacity of 969.6 mAh g–1 after 300th cycles. Meanwhile, this proposed method looks efficient for the electrochemical fixation of CO2 in molten salts.

Electrochemical separation of fission element samarium on lead electrodes from KCl–LiCl molten salts and the kinetic research of the process

Electrochemical separation of fission element samarium on lead electrodes from KCl–LiCl molten salts and the kinetic research of the process

Fabrication of U-Ti alloy through direct electro-reduction from U3O8 and TiO2 mixtures in LiCl molten salt

U-Ti alloys have attracted much attention for its excellent mechanical performance and corrosion resistance. The conventional method to fabricate U-Ti alloy by melting U and Ti metals shows great disadvantages in high energy consumption, excessive impurity content, low security and compositional segregation. Hereby, direct electro-reduction method was employed to fabricate U-Ti alloy from U3O8 and TiO2 mixtures in LiCl molten salt. The co-reduction route and process were also analyzed in detail, which are helpful to comprehend the effects of alloying elements on electro-reduction of uranium oxides, further promoting the application of this technique on nuclear fuel recycling.

Reduction of SiO2 by Metallic Li with a By-Product Soluble in Recyclable Molten LiCl Salt

Reduction of SiO₂ by Metallic Li with a By-Product Soluble in Recyclable Molten LiCl Salt

Preparation of stoichiometric uranium dioxide (UO2.000) via electro-reduction method in LiCl molten salt

Preparation of stoichiometric uranium dioxide (UO2.000) via electro-reduction method in LiCl molten salt

KCl–LiCl molten salt synthesis of LaOCl/CeO2-g-C3N4 with excellent photocatalytic-adsorbed removal performance for organic dye pollutant

A ternary photocatalyst of LaOCl/CeO2-g-C3N4 was designed and firstly synthesized by a facile KCl–LiCl molten salt method. The 60 %LaOCl/40 %CeO2-g-C3N4 with a 6: 4 weight ratio of LaOCl to CeO2 has an optimal degradation ratio (nearly 100%) for methylene blue (MB) with an impressive cyclic stability. Both of adsorption and photodegradation contribute to the high MB removal ratio, and kinetic study results show that the rate constant of photocatalytic degradation route is 0.0174 min−1, which is less than that of adsorption process (2.4406 min−1). The excellent adsorption performance of 60 %LaOCl/40 %CeO2-g-C3N4 is attributed to its negative zeta potential (−35.40 mV) and larger average pore size. The photochemical characterizations suggest that the 60 %LaOCl/40 %CeO2-g-C3N4 form a dual Z-scheme heterojunction, which enhances its separation efficiency of photogenerated e-/h+ with an outstanding redox ability, and further promotes the photocatalytic activity.

Fabrication of U-Ti Alloy Through Direct Electro-Reduction from U3o8 and Tio2 Mixtures in Licl Molten Salt

Fabrication of U-Ti Alloy Through Direct Electro-Reduction from U3o8 and Tio2 Mixtures in Licl Molten Salt

Novel synthesis of single-crystalline TbCu7-type Sm–Fe powder by low-temperature reduction-diffusion process using molten salt

In this study, molten salt was used as a solvent for calcium (Ca) to let a reduction-diffusion (R-D) reaction occur below the melting point of Ca (1115 K), which is the lower limit temperature of the conventional R-D process. When the R-D reaction is conducted below 923 K with LiCl molten salt, submicron-sized TbCu7-type Sm–Fe powder is formed. The c/a ratio of the powder estimated by a synchrotron X-ray diffraction pattern is 0.8456, which is consistent with the Sm0.67Fe5.667(SmFe8.5) phase. An electron backscatter diffraction analysis reveals that single-crystalline TbCu7-type SmFe8.5 powder was synthesized for the first time.

Microsized Red Luminescent MgAl2O4:Mn4+ Single-Crystal Phosphor Grown in Molten Salt for White LEDs.

A single-crystalline defect-less phosphor is desired for efficient luminescence of the therein doped optical activators. In this paper, microsized MgAl2O4:Mn4+ single-crystal phosphors with bright red luminescence were grown in molten LiCl salt at 950 °C, for application in blue LED pumped white lighting. By comparing the phosphor formation from various Mg2+- and Al3+-bearing sources, both the template-formation and the dissolution-diffusion processes were evidenced to account for the formation of the microsized MgAl2O4:Mn4+ crystallites. Using nano γ-Al2O3 as the Al3+-bearing precursor, the uniform MgAl2O4:Mn4+ microcrystallites with a {111} planes-exposed tetragonal bipyramid morphology were obtained. The photoluminescence property was studied at various temperatures, and Mg ↔ Al anti-site disorder induced luminescence broadening was discussed. The Mn4+ 2Eg → 4A2g transition in MgAl2O4 shows a quite short luminescence wavelength peaking at 651 nm and ultrabroadband emission extending to 850 nm. The luminescence is relatively robust against thermal effect with relatively high thermal quenching temperature of 400 K and activation energy of 0.23 eV. Employing the red-emitting MgAl2O4:Mn4+ crystallites, blue LED pumped white lighting prototypes were fabricated which simulate the solar-like spectrum and show neutral to warm white.

Electro-reduction processes of U3O8 to metallic U bulk in LiCl molten salt

U3O8, the most stable state of uranium oxides, is a key intermediate compound for pyroprocessing of used nuclear fuel. However, compared to UO2, the electro-deoxidation mechanism of U3O8 is still cursory due to the complicated U-O intermediate phases. In this paper, the electro-deoxidation processes of U3O8 were investigated via diverse methods. A molybdenum metallic cavity electrode loaded with U3O8 powder was adopted to investigate the electrochemical behavior via cyclic voltammetry and square wave voltammetry. Sintered U3O8 pellets were used as cathodes to obtain electrolytic products with varying applied voltages or duration time. The composition and microstructure of electrolytic products were characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscope and energy dispersive spectrometer. Based on above analysis results, electro-reduction processes of porous U3O8 pellets were proposed. First, U3O8 undergoes a rapid transition to U4O9 (U4O9-y). Then, the intermediate compound was gradually reduced to UO2 from the outer layer to the center of the bulk due to the limited migration rate of O2−. Before the transformation completed, metallic U generated on the surface of the bulk through direct electro-deoxidation and Li metal thermal reduction. With the increase of porosity and the propagation of metal-oxide-electrolyte three-phase interline, the U3O8 pellet was finally reduced to metallic U bulk.

Electrochemical Behavior of CsI in LiCl Molten Salt

The electrochemical behavior of CsI in LiCl molten salt was investigated to identify its impact on the electrolytic oxide reduction of oxide-phase spent nuclear fuels by combined electrolysis and cyclic voltammetry experiments of LiCl-CsI in comparison with LiCl, LiCl-CsCl, and LiCl-LiI. It was found that Cs+ ions were hardly involved in the cathode reaction, and reduction of Li+ ions occurred dominantly in the cathode. In contrast, incorporation of I− ions induced low-potential anode reaction compared with the I− ion-free cases. Such additional electrochemical reaction resulted in the generation of I2 and/or ICl gases, which would increase a process burden for treating 129I with exceptionally long lifetime. In this respect, separating CsI from spent nuclear fuel before the electrolytic oxide reduction is recommended for the purpose of efficient waste management.

Optimization of Electrolysis Conditions for Ti Film Electrodeposition from LiF – LiCl Eutectic Molten Salt

1. IntroductionTitanium is known as a metal which has excellent properties such as high specific strength and high corrosion resistance. However, there are two problems that prevent widespread use of titanium. One is the high smelting cost and the other is the poor workability. As a method to solve these problems, titanium plating is an attractive technique because superior surface properties of titanium can be utilized. For some applications, physical vapor deposition (PVD) is practically used as a titanium plating method. However, the PVD method has high plating cost and can be used for only simple-shaped substrates. On the other hand, electrodeposition of titanium in high-temperature molten salt is a promising plating method which is expected to have lower cost and can be used for complex shaped substrates. Accordingly, there have been many reports on the titanium electrodeposition in high-temperature molten salts [1–3].We have already reported the electrochemical behaviors of Ti(III) ions and the electrodeposition of titanium in KF–KCl and LiF–LiCl molten salts [4–7]. Furthermore, we found that LiF–LiCl has an advantage for electrodepositing smooth titanium films due to its lower melting point (774 K at the eutectic composition [8]); smoother titanium films were obtained at lower temperature by suppressing grain growth of titanium [9]. Thus, in the present study, we investigated the effect of electrolysis conditions such as current density and concentration of Ti(III) ions on smoothness of titanium films in LiF–LiCl eutectic molten salt.2. ExperimentalThe experiments were conducted in LiF–LiCl eutectic molten salt in an Ar glove box at 823 K. Li2TiF6(0.50–5.0 mol%) and Ti sponge (0.33–3.3 mol%) were added to the bath and Ti(IV) ions were converted to Ti(III) ions by comproportionation reaction. Ni plate, Mo flag, and Au flag electrodes were used as the working electrode. The counter and reference electrodes were Ti rods. The potential of the reference electrode was calibrated by Cl2/Cl− potential measured at a glass-like carbon rod electrode. Samples were prepared by galvanostatic electrolysis of Ni plate substrates. The samples were analyzed by SEM/EDX after washing with distilled water and 1M Al(NO3)3 aqueous solution to remove adhered salts.3. Result and DiscussionThe electrodeposition was carried out by changing the added amounts of Li2TiF6from 0.50 to 5.0 mol% and Ti sponge from 0.33 to 3.3 mol%. The cathodic current density was also varied from 25 to 1000 mA cm−2. The surface roughness of the obtained samples was measured by SEM. As a result, smooth Ti films were obtained at high Ti(III) concentrations and low current densities. As a typical example of the smooth film, Fig. 1 shows an appearance of the sample prepared at 50 mA cm−2 and 60 C cm−2 after addition of 3.0 mol% Li2TiF6and 2.0 mol% Ti sponge. The electrodeposited titanium film had metallic luster. Fig. 2 shows a cross-sectional SEM image of the film, indicating the smooth and compact deposit.In the poster session, the solubility of Ti(III) ions will be presented. Also, the effects of Ti(III) ion concentration and cathodic current density on the morphology will be discussed.AcknowledgementThe present address of Kouji Yasuda is Graduate School of Engineering, Kyoto University.

The formation mechanism of nanocrystalline TiC from KCl–LiCl molten salt medium

In this research, an attempt was made to artificially synthesis bulk nanocrystalline TiC using molten salt bath medium. To do so, titanium powder and carbon black (CB) were mixed as precursors with prepared KCl–LiCl eutectic composition and the effect of the synthesis temperature and dwelling time were studied on the final powder. The X-ray diffraction (XRD) patterns revealed that the increase of the temperature and dwelling time has a considerable effect on the purity and crystallinity of the final TiC. Based on results attained from simultaneous thermal analysis (STA) and microscopic micrographs (TEM and SEM), the mechanism of TiC synthesis was determined as “template growth”. The XRD and STA analyses results showed that by increasing the temperature up to 950 °C, some intermediate phases such as LiTiO2 and TiClx (x = 2 and 3) were formed. The results of Rietveld refinement showed that with increasing the temperature from 815 to 950 °C, the crystallite size of the final product decreased from 75 to 30 nm and the lattice parameter of TiC powder increased from 4.298 to 4.324 Å (The lattice parameter of TiC is 4.327 Å). The Energy Dispersive X-ray Spectroscopy (EDS) declared that the nanocrystalline TiC synthesized at 950 °C was with maximum accordance with the composition of the stoichiometric compound.

Simulation of Electrolyzer Processes for the Reprocessing of Spent Nuclear Fuel

The ANSYS software package is used to simulate a functioning electrolyzer for the reprocessing of spent nuclear fuel via electrolysis in LiCl molten salt with the addition of Li2O. The seven considered types of electrolyzer design differ in their mutual arrangement of electrodes and anode thickness. The temperature field, as well as distributions of the current density and electric potential, are calculated. The optimal electrolyzer design is determined in order to achieve the best temperature and electrical characteristics.

Computer modeling of electrochemical processing of waste nuclear fuel

The purpose of the work is to study the influence of the electrodes geometry and the mutual arrangement of functional elements in the working space of a metallization electrolyzer on the distribution of the oxygen flux density in the electrolyte, as well as on the distribution of electric and temperature fields. In a computer model, the stationary operation mode of the electrolyzer for processing spent nuclear fuel immersed into the LiCl molten salt with the addition of Li2O was studied. The calculations were performed using the ANSYS software package. We studied eight designs of the electrolyzer, which differ in the immersion depth of the anodes into the melt as well in the types anode protective covers and the cathode baskets. Verification based on the comparison of the computer modeling with experimental data indicates the adequacy of the models used. The electrolyte velocity field and the temperature field are calculated, as well as the steady-state picture of the distribution of electric current density over the working space of the electrolyzer. The efficiency of the electrochemical cell is determined.

Preparation of Nd-Si alloy by direct electroreduction of solid oxides in molten LiCl

In molten LiCl salt at 973 K, Nd-Si alloy was successfully prepared by direct electro reduction of a mixed oxide of Nd2O3-SiO2 or Nd2O3-Si at a constant potential. The reduction mechanism was studied by CV through metal cavity electrode in conjunction with XRD, SEM and EDS results of the electrolytic products under different conditions. It was found that the reduction process of Nd2O3-SiO2 was carried out in two steps. First, SiO2 was reduced to elemental silicon, and then Nd2O3 was deposited on silicon to form Nd-Si alloys. In addition, the effects of the electrolysis voltage have been investigated. As a result, it was found that the reduction rate increased with the increasing of the electrolysis voltage, and it was easy to prepare pure Nd-Si alloys when the atomic content of silicon was 50% in the mixed oxides. This work first reported the preparation of Nd-Si alloy by direct electroreduction of its oxides.

Electrolytic behavior of SrCl2 and BaCl2 in LiCl molten salt during oxide reduction in pyroprocessing

Ba and Sr elements in spent nuclear fuels are supposed to accumulate in LiCl molten salt electrolyte by forming chlorides (i.e., BaCl2, SrCl2) during oxide reduction in pyroprocessing. An electrochemical examination was performed in a LiCl–BaCl2–SrCl2 system to identify the effect of the BaCl2 and SrCl2 on the C anode-based oxide reduction process. BaCl2 and SrCl2 dissolved in LiCl were electrochemically stable up to 5 wt% with the C anode system, suggesting that no concern for their accumulation is needed in this range in the electrochemical aspect for the process design of the oxide reduction.

Molten salt synthesis and formation mechanism of magnesium aluminate spinel using different shape Al2O3 as the templets

Abstract In order to verify the “Al2O3-template-formation” mechanism of magnesium aluminate (MA) spinel proposed previously using Al2O3 and MgO micro-powders as raw materials, in this work, MA spinel was synthesized by nanograined, plate-like, and fibrous Al2O3 in LiCl molten salt at 1150 °C for 3 h, respectively. The products were characterized by XRD, SEM, TEM, and EDS techniques, and the grain size of the products and raw materials were analyzed. The results showed clearly that the MA spinel was initially nucleated and subsequently developed to octahedral crystal. When the reaction further took place, when using nanograined Al2O3, the newly formed MA spinel seeds initially moved and attached to the surface of the large octahedral MA spinel crystal, and they were subsequently engulfed by the large MA spinel crystal, which further grew via layer-by-layer to become micro-sized crystal. Using plate-like or fibrous Al2O3 raw material, MgO diffused continuously into the interior of Al2O3 to form MA spinel with a gradient growth from surface to depth. These revealed that whatever shape of Al2O3 was used, the synthesis of MA spinel was governed by “Al2O3-template formation mechanism”, i.e., by the reaction of MgO diffusion into the Al2O3 templet in the molten salt.