Pure LiCl Research Articles

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.

Peculiarities of the potentiometric response of ISEs with membranes containing two neutral ionophores and an excess of ion-exchanger: Experiment and modeling

The potentiometric response of ion-selective electrodes (ISEs) with membranes simultaneously containing two ionophores: valinomycin and lithium ionophore Li VIII, as well as the cation exchanger potassium tetrakis(p-Cl-phenyl) borate in different concentrations is studied in KCl, LiCl and KCl + LiCl solutions. It is shown that ISEs with a membrane containing an excess of ionophores over the ion-exchanger provide Nernstian response to K+ and to Li+ ions. However, membranes with an excess of the ion-exchanger over valinomycin show Nernstian response to K+ only in mixed KCl + LiCl solutions with constant ratios of the concentrations of these electrolytes. On the contrary, the response to Li+ is obtained both in mixed and pure LiCl solutions. The results are semi-quantitatively explained using a simple mathematical model and respective computer simulation.

A Liquid Alloy Anode for the Electrolytic Reduction of Uranium Oxide in Molten Lithium Chloride

A cost-effective anode material for uranium oxide electrolytic reduction in lithium chloride is still in deficiency. In this work, the application of liquid lithium-bismuth alloy anode was investigated. In the LiCl electrolyte at 923 K, UO2 was reduced electrochemically in cathode, while Li-Bi alloy served as counter electrode. Partial reduction of UO2 was verified by X-ray powder diffraction when the cathode potential was intentionally controlled above the lithium reduction potential. In contrast, when the precipitation of lithium metal was intentionally controlled, the reduction of UO2 was significantly improved. The charge transfer coefficient of UO2/U reaction was also calculated. Regeneration of Li-Bi alloy in LiCl-Li2O through electrolysis was proposed. Carbon, gold, and platinum had been investigated as anode materials. According to the potential variation curve, lithium was not effectively reduced into bismuth as in pure LiCl when oxygen ion was present in the molten salt. These three materials failed to demonstrate advantage in the regeneration of Li-Bi alloy.

Experimental study and thermochemical assessment of the reciprocal system Li+, K+//Cl−, CO32−

In this work a new thermodynamic dataset of the reciprocal system Li+, K+//Cl−, CO32− was generated by using Calphad method with FactSage. After collecting and analyzing the available thermodynamic data in the literature, experiments were designed to improve the comprehensiveness of the new database. Specifically, Differential Thermal Analysis (DTA) was used (1) to confirm the eutectic temperature of the K2CO3–KCl system, (2) to check the solid solubility in the K2CO3–Li2CO3 system and (3) to measure the phase equilibria of the diagonal sections (i.e. Li2CO3–(KCl)2 and K2CO3–(LiCl)2) in the reciprocal system. In addition, the heat capacity of the intermediate compound LiKCO3 was measured by three types of Differential Scanning Calorimetry (DSC) and its phase transformation was studied by High temperature X-ray Diffractometry (HTXRD). Based on the literature data and the present experimental results, the thermodynamic data on pure LiCl, all sub-binary systems and the reciprocal system were reassessed in the new database, which can be used to calculate and predict the thermodynamic properties of the salt mixtures in the reciprocal system Li+, K+//Cl−, CO32− more precisely and reliably.

Efficient Atmospheric Water Harvesting of Superhydrophilic Photothermic Nanocapsule.

Drought and water scarcity are two of the world's major problems. Solar-powered sorption-based atmospheric water harvesting technology is a promising solution in this category. The main challenge is to design materials with high water harvesting performance while achieving fast water vapor adsorption/desorption rates. Here, a superhydrophilic photothermic hollow nanocapsule (SPHN) is represented that achieves efficient atmospheric water harvesting in outdoor climates. In SPHN, the hollow mesoporous silica (HMS) is grafted with polypyrrole (PPy) and also loaded with lithium chloride (LiCl). The hollow structure is used to store water while preventing leakage. The hydrophilic spherical nanocapsule and the trapped water produce more free and weakly adsorbed water. Significantly lower the heat of desorption compared to pure LiCl solution. Such SPHN significantly improves the adsorption/desorption kinetics, e.g., absorbs 0.78-2.01g of water per gram of SPHN at 25°C, relative humidity (RH) 30-80% within 3h. In particular, SPHN has excellent photothermal properties to achieve rapid water release under natural sunlight conditions, i.e., 80-90% of water is released in 1h at 0.7-1.0kWm-2 solar irradiation, and 50% of water is released even at solar irradiation as low as 0.4kWm-2 . The water collection capacity can reach 1.2gg-1 per cycle by using the self-made atmospheric water harvesting (AWH) device. This finding provides a way to design novel materials for efficient water harvesting tasks, e.g., water engineering, freshwater generator, etc.

Morphological Plasticity of LiCl Clusters Interacting with Grignard Reagent in Tetrahydrofuran.

Ab initio molecular dynamics simulations are used to explore tetrahydrofuran (THF) solutions containing pure LiCl and LiCl with CH3MgCl, as model constituents of the turbo Grignard reagent. LiCl aggregates as Li4Cl4, which preferentially assumes compact cubane-like conformations. In particular, an open-edge pseudotetrahedral frame is promoted by solvent-assisted Li-Cl bond cleavage. Among the Grignard species involved in the Schlenk equilibrium, LiCl prefers to coordinate MgCl2 through μ2-Cl bridges. Using a 1:1 Li:Mg ratio, the plastic tetranuclear LiCl cluster decomposes to a highly solvated mixed LiCl·MgCl2 aggregate with prevalent Li-(μ2-Cl)2-Mg rings and linear LiCl entities. The MgCl2-assisted disaggregation of Li4Cl4 occurs through transient structures analogous to those detected for pure LiCl in THF, also corresponding to moieties observed in the solid state. This study identifies a synergistic role of LiCl for the determination of the compounds present in turbo Grignard solutions. LiCl shifts the Schlenk equilibrium promoting a higher concentration of dialkylmagnesium, while decomposing into smaller, more soluble, mixed Li:Mg:Cl clusters.

Study on the regeneration process and overall performance of a microencapsulated phase change material slurry dehumidification system

Building on previous findings that showed the efficacy of microencapsulated phase change materials (MicroPCM) in augmenting liquid desiccant dehumidification performance, this study endeavors to further explore the extent of the impact of MicroPCM in the regeneration and the entire dehumidification system. The results of the regeneration experiment on the microencapsulated phase change material slurry (MPCMS) reveal that the addition of MicroPCM impedes regeneration. Specifically, as the concentration of MicroPCM increases, both the regeneration rate and the MPCMS concentration after regeneration decrease, while the regeneration effectiveness exhibits an initial decline followed by an increase. An empirical correlation was proposed to predict the regeneration rate of MPCMS for their future application. The results showed that the addition of MicroPCM led to a decrease in the regeneration rate by as much as 48.1%, when compared to a pure LiCl solution. However, a simulation analysis of the entire system revealed that within a certain concentration range of MicroPCM addition, the coefficient of performance (COP) of the system could still be increased by up to 4.28%. This finding suggests that if a more suitable non-heating regeneration method were used, the addition of MicroPCM could further enhance the overall performance of the liquid desiccant dehumidification system.

Fine analysis of the component effect on the microstructure of LiCl solution

Lithium resources are abundant in Chinese salt lakes, but the high Mg/Li ratio in such aqueous natural sources has brought difficulties to the separation and purification of lithium. Crystallization processes are highly affected by the solution microstructure, which, in turn, depends on its composition. Synchrotron X-ray scattering, Raman spectroscopy, and molecular dynamics simulation methods were used to study the microstructure of aqueous LiCl solutions with different concentrations. In the reduced structure function, F(Q), the double peak around the scattering vector Q = 2.5 Å−1 becomes a single peak, which indicates the addition of LiCl changes the tetrahedral hydrogen bond structure in the aqueous solution. The deconvolution fitting of the Raman spectra show that the DDAA-type (double donor-double acceptor) hydrogen bonds tend to be transformed into DA-type (single donor–single acceptor) hydrogen bonds, confirming that the addition of LiCl breaks the tetrahedral hydrogen bond structure. This hydrogen-bond transformation was confirmed by pair distribution function analysis from molecular dynamics simulations of aqueous KCl solutions. In addition, considering the large number of magnesium ions coexisting with LiCl in the Salt Lake, the microstructure of mixed LiCl-MgCl2 solution was also studied. According to the X-ray scattering results, the peak in the reduced pair distribution function G(r) near r = 3.25 Å shifted from 3.25 Å to 3.10 Å with increased Mg/Li ratio. This change is likely to result from the Cl-O and OO interactions in the mixed aqueous solution. The deconvolution fitting results of Raman spectra show that the DDAA type hydrogen bond increases with the Mg/Li ratio, while the DA + DDA type hydrogen bond decreases. The molecular dynamics results showed that chlorine ions have a higher tendency to form contact ion pairs with Mg2+ than Li+. We propose this to be one of the processes retarding the separation of pure LiCl crystal from mixed LiCl-MgCl2 systems.

Performance investigation of LiCl·H2O-γ-Al2O3 composite materials for low-grade heat storage.

In this study, the influences of nano γ-Al2O3 on the thermal storage performance of LiCl were experimentally investigated. The XRD results show that a complex of lithium aluminium oxychloride (LiAlOCl2) was formed through the LiCl·H2O and γ-Al2O3 composites preparation process. The in situ diffuse reflectance infrared Fourier transform spectroscopy measurement reveals that the addition of γ-Al2O3 accelerated the hydration rate of LiCl composites, concentrated the spectrum utilization range, and promoted the desorption rate of physical adsorbed H2O and low-frequency structural -OH in the materials. The highest specific surface area of the composite is 34.5 times higher than that of pure LiCl. The addition of γ-Al2O3 can increase the conversion rate of LiCl·H2O to approximately 100% at the hydration time of 1 h and the addition content of γ-Al2O3 at 15 wt%. A maximum heat storage density (HSD) for the LiCl·H2O-γ-Al2O3 composite can reach 714.7 kJ kgLiCl·H2O-1 in 1 h when the addition content of γ-Al2O3 was 15%wt and its water uptake can reach 0.26 g g-1 in 1 h. It also can be found that the addition of Al2O3 in LiCl resulted in a decrease of the activation energy from 90.89 kJ mol-1 to 79.76 kJ mol-1. However, the thermal conductivity of the LiCl·H2O-γ-Al2O3 composite slightly decreased with the increase of nano γ-Al2O3 content.

Single LiCl-driven synthesis of heptazine-/triazine-based crystalline carbon nitride homojunction for enhanced solar hydrogen evolution

LiCl-based molten salts have been widely used to induce the polymerization of melamine-derived monomer or intermediate into triazine-based or heptazine-based crystalline carbon nitride. Nevertheless, the role of LiCl beyond lowering melting point has not been fully revealed, and pure LiCl was exclusively reported to induce the formation of triazine-based crystalline counterpart. Herein, we firstly found that single LiCl can promote the deep deamination of melon-based pristine carbon nitride (PCN) to heptazine-based crystalline counterpart. As a result, a heptazine-/triazine-based crystalline carbon nitride homojunction was in situ formed by single LiCl-induced deamination and phase transition of PCN. It exhibits a favorable photocatalytic H2 evolution reaction rate 18.3 times higher than PCN, which benefits from the promoted charges separation between heptazine and triazine units in phase homojunction. This work emphasizes that single LiCl can realize diverse modulation of carbon nitride framework with advanced photocatalytic activity.

Experimental study of the surface vapor pressure of a microencapsulated phase change material slurry liquid desiccant within the entire temperature range of a dehumidification system

The surface vapor pressure is a critical physical property of a liquid desiccant, which has a direct influence on the mass transfer driving force in the dehumidification and regeneration process. In this study, a measurement system for the surface vapor pressure of the microencapsulated phase change materials slurry (MPCMS) was built using a static method. The surface vapor pressure of the MPCMS at 293.2 K–353.2 K was measured, which covered the entire range of dehumidification and regeneration. Experimental results showed that the surface vapor pressure of the MPCMS decreased compared with that of the pure LiCl solution. The surface vapor pressure drop ratio of the MPCMS increased with increasing MicroPCM and LiCl mass concentrations. The phase transition of the MicroPCMs intensified the drop in the MPCMS surface vapor pressure. When the MicroPCM and LiCl mass concentrations were 2 % and 40 %, respectively, and at the phase transition temperature of 303.2 K, the vapor pressure drop ratio reached a maximum of 17 %. A correlation for the MPCMS surface vapor pressure calculation was proposed, and the deviation between the calculated and measured values was less than 10 %. The results of this study provide basic data for the future development of the MPCMS liquid desiccant system.

Feasibility study of electrochemical conversion of solid ZrO2 to Zr metal in LiCl-(0-1 wt%)Li2O melts with graphite and platinum anodes

Direct electrochemical reduction of solid ZrO2 to Zr metal assumes importance in the context of pyrochemical reprocessing of spent oxide nuclear fuel. In this context, electrochemical reduction experiments were carried out with powder compacted and sintered ZrO2 pellets as cathode in LiCl-x wt.% Li2O (x = 0, 0.1, 0.25 and 0.5) melts against graphite anode and in LiCl-(0.5 and 1.0) wt.% Li2O melts against platinum anode at 650 °C and the samples were analysed using XRD and SEM combined with EDS techniques. The pellets were found reduced to Zr in pure LiCl melt and to Zr and smaller amounts of Li2ZrO3 in LiCl-Li2O melts under specific experimental conditions. Similar cathodic polarization experiments carried out with Li2ZrO3 pellets converted those to a mixture of Zr and Li2ZrO3. Contrary to the results reported in the literature by earlier workers, the results of this study make it quite clear that both solid ZrO2 and Li2ZrO3 can be electro-reduced to Zr in LiCl-Li2O melts. However, the study carried out with two different cathode configurations reveal that the efficiency of electro-reduction is strongly influenced by the design of the oxide electrode and to some extent the Li2O content of the melt.

Influences of the mixed LiCl-CaCl2 liquid desiccant solution on a membrane-based dehumidification system: Parametric analysis and mixing ratio selection

The membrane-based liquid desiccant dehumidification system has high energy efficiency without the traditional liquid system carry-over problem. The performance of such a system strongly depends on solution's temperature and concentration, which have direct relationship to the solution surface vapour pressure. Compared with the pure liquid desiccant solution, the mixed liquid desiccant solution has lower surface vapour pressure, better system performance and lower material cost. In this paper, the performance of a flat-plate membrane-based liquid desiccant dehumidification system with the mixed solution (LiCl and CaCl2) is investigated through theoretical and experimental approaches. A mathematical model is established to predict the system performance, while the electrolyte non-random two-liquid (NRTL) method is applied to calculate the mixed solution properties. The influences of the solution mixing ratio, temperature Tsol and concentration Csol are evaluated, and it is found that the regeneration heat Qreg can be dramatically reduced by either applying a high concentration solution or increasing CaCl2 content in the mixed solution. Compared with the pure LiCl solution system, the mixed solution system COP can be improved up to 30.23% by increasing CaCl2 content for a 30% concentration solution. The optimum mixing ratio varies with the solution concentration. For the mixed LiCl-CaCl2 solution, the system highest COPs appear at the mixing ratios of 3:1, 2:1 and 1:1 for 20%, 30% and 40% concentrations respectively.

Separation of CsCl and SrCl2 from a ternary CsCl-SrCl2-LiCl via a zone refining process for waste salt minimization of pyroprocessing

The purification of LiCl salt mixture has traditionally been carried out by a melt crystallization process. To improve the throughput of zone refining, three heaters were installed in the zone refiner. The zone refining method was used to grow pure LiCl salt ingots from LiCl-CsCl-SrCl2 salt mixture. The main investigated parameters were the heater speed and the number of passes. A change in the LiCl crystal grain size was observed according to the horizontal direction. From each zone refined salt ingot, samples were collected horizontally. To analyze the concentrations of Sr and Cs, an inductively coupled plasma optical emission spectrometer and inductively coupled plasma mass spectrometer were used, respectively. The experimental results show that Sr and Cs concentrations at the initial region of the ingot were low and reached their peak at the final freezing region of the salt ingot. Concentration results of zone refined salt were compared with theoretical results yielded by the proposed model to validate its predictions. The keff of Sr and Cs were 0.13 and 0.11, respectively. The decontamination factors of Sr and Cs were 450 and 1650, respectively.

Solubility of Oxide Ion in Molten Chloride and Carbonate Containing Li, Na, K and/or Ca Added with Li2O or CaO

The solubility of oxide ions in LiCl-based and CaCl2-based melts was estimated by double-tracer technique as part of the CO2 capture and conversion process. The solubility of oxide ions in pure LiCl and CaCl2 is 10.6 mol% at 600°C and 12.5 mol% at 800°C, respectively. The solubility of oxide ions increases with escalating temperature. The solubility of oxide ions encounters serious decrease when NaCl or KCl is added to the melts. In the case of LiCl-CaCl2 eutectic, the solubility of CaO firstly descends and then ascends with the increasing mole fraction of CaCl2. Intriguingly, the excess addition of Li2O into alkali carbonates leads to a floating layer while, on the contrary, the addition of Li2O into chlorides gives a Li2O precipitate. It is deduced that the Li2O solubility in Li-Na-K carbonates (43.5:31.5:25 in molar ratio) is slightly lower than 5 mol% at 500°C.

High temperature (35)Cl nuclear magnetic resonance study of the LiCl-KCl system and the effect of CeCl3 dissolution.

This paper examines the dynamics of the LiCl-KCl system over a range of temperatures in order to understand the local structure surrounding chlorine, which is the common ion in these systems, during molten salt pyro-processing. Chlorine-35 nuclear magnetic resonance (NMR) is sensitive to the local environments of the resonant nuclei and their motion on a diffusive timescale. Thus, it is a good probe of the atomic scale processes controlling the viscosities, diffusivities and conductivities of these molten salts. The average isotropic chemical shifts (((35)Cl)δ) and spin-lattice relaxation times (T1) of (35)Cl in (Li,K)Cl salt mixtures have been obtained over a compositional range of 0-100 mol% KCl with an interval of 10 mol% using high temperature nuclear magnetic resonance (NMR) spectroscopy from room temperature up to 890 °C. The ((35)Cl)δ in the two end member salts are consistent with the cation-anion radius ratio as previously measured on the solid halides and the average radius ratio of cation to anion, can be used to explain the variation of ((35)Cl)δ with composition. The quadrupolar interaction is found to be responsible for the spin-lattice relaxation of the (35)Cl, and the activation energies for T1 relaxation have been obtained for all compositions. The measured T1 ((35)Cl) activation energies do not vary linearly with composition and peak at 50% KCl, which also coincides with the Chemla point for this system. They also are in good agreement with the values from equivalent conductivity measurements. To investigate the response of the system to solutes, 8 wt% of CeCl3 was added to the pure LiCl as a surrogate actinide. The shift induced was 120 ppm and the activation energy for the T1 ((35)Cl) increased by a factor of four. This is a promising preliminary result for probing the effect of actinide dissolution on the dynamics of these pyro-processing salts.

The solid–liquid separation characteristics of pure LiCl–KCl eutectic salt using different types of crucibles

Uranium deposits were recovered at the solid cathode of an electrorefining system, and deposited uranium dendrite normally contains about 30–40 wt% LiCl–KCl eutectic salts. Therefore, a separation of the eutectic salts from deposited uranium is essential for reusing these salts and uranium. A process such as distillation was employed for cathode processing due to the advantages of a minimal generation of secondary waste, a compact unit process, and simple and low-cost equipment. However, the realization of a wide evaporation area or high distillation temperature is limited by various factors such as the material or structure of a distiller. Also, the electrical energy flow from outside has a lot of consumption to maintain the high temperature. Hence, in this study, solid–liquid separation experiments are proposed to increase the throughput of the salt removal process by the separation of the liquid salt prior to the distillation of the LiCl–KCl eutectic salt. The solid–liquid separation of salt was carried out in a vertical type distiller. The behavior of the solid–liquid separation of pure eutectic salt was investigated as a function of temperature, pressure, sieve size, and crucible shape. From the experimental results using pure eutectic salts, the amount of salt separation was achieved at more than 94 wt%. The rate of solid–liquid separation of salt using 600 °C is higher than that of 500 °C under the same condition. The influence of a vacuum for solid–liquid separation can be disregarded, and the separation rate of a 100 mesh was higher than that of a 150 mesh. In addition, the rate of separation for salts using a porous crucible is higher than that in a non-porous crucible.

Vacuum evaporation of LiCl–BaCl2–SrCl2 system

Vacuum evaporation of a LiCl–BaCl2–SrCl2 system was investigated to design a process for waste reduction and salt recycling. Through thermo-gravimetric analysis (TGA) tests of pure LiCl at a reduced pressure, a model equation for LiCl vaporization was established. As results of TGA tests of pure BaCl2 and SrCl2, it was confirmed that they were very stable at 900°C and 0.5Torr. At 1Torr, evaporation of the LiCl–BaCl2–SrCl2 system looked similar to the pure LiCl vaporization results. Co-evaporation of BaCl2 or SrCl2 with LiCl was very slight in this study.

Study on a separation method of radionuclides (Ba, Sr) from LiCl salt wastes generated from the electroreduction process of spent nuclear fuel

In this paper, a separation method of radionuclides (Ba, Sr) from LiCl salt wastes generated from the electroreduction process of spent nuclear fuel was studied to recover pure LiCl salts and reduce radioactive wastes. The method consisted of chemical conversion process of BaCl2 and SrCl2 in LiCl molten salts by using lithium compounds and vacuum distillation process of LiCl salts. In the chemical conversion, BaCl2 and SrCl2 in LiCl molten salts were mainly converted into (Ba,Sr)CO3 or (Ba,Sr)SO4. Contents of Ba and Sr in LiCl salts recovered from the vacuum distillation process were equal to about 0.01 of initial concentrations of Ba and Sr in LiCl molten salts. These results will be utilized to recycle the LiCl salt wastes.

Rechargeable Aqueous Lithium-Ion Battery of TiO2/LiMn2O4 with a High Voltage

Rechargeable aqueous TiO2/LiMn2O4 lithium-ion battery is fabricated by combining the TiO2 nanotube arrays on metallic titanium foil as anode and LiMn2O4 as cathode in aqueous solution with mixed lithium salts (LiCl and Li2SO4). It is shown from cyclic voltammograms that the lithium insertion/extraction peaks of the cathode are highly symmetrical before the oxygen evolution, which can ensure a good lithium utilization of the LiMn2O4. Importantly, a higher anodic hydrogen evolution overpotential in TiO2 anode is observed, which is essential for the facile lithium insertion in preference to the hydrogen evolution. Meanwhile, the gas (hydrogen and oxygen) evolution in the anodic and cathodic processes can be effectively suppressed in aqueous electrolyte with mixed lithium salts as compared with that in pure LiCl and Li2SO4 solution, respectively. Correspondingly, the fabricated TiO2/LiMn2O4 battery presents a high discharge voltage plateau of above 2 V, which is well beyond the average discharge voltage of current aqueous battery system. Therefore, the combination of the appropriate anode/cathode-active materials with a relatively large potential difference and high gas evolution overpotential is an ideal strategy for developing new aqueous battery system based on reversible lithium insertion/extraction reactions in aqueous electrolyte.