Molten Salt Electrolysis Method Research Articles

Study on separation and purification of titanium alloys (TC4-6Al-4V) by molten salt electrolysis

With the widespread expansion of titanium applications and its significant increase in usage, the issue of recycling titanium resources after consumption has emerged. Focusing on titanium alloys with high usage, such as TC4 (Ti-6Al-4V), this article proposes a titanium separation and recovery method based on molten salt electrolysis. This method thoroughly analyzes the characteristics of elements in TC4 and electrochemical principles, ensuring that vanadium in the TC4 alloy does not undergo electrochemical dissolution when the electrolysis potential is below 0.3 V vs Pt. Subsequently, through electrochemical analysis, it was discovered that the precipitation of aluminum ions is influenced by concentration. Therefore, by controlling the concentration of aluminum in the eutectic molten salt, such as increasing the electrolyte concentration and shortening the electrolysis time, the precipitation of aluminum can be effectively avoided. Under the experimental conditions mentioned above, vanadium elements deposit at the bottom of the crucible in the form of anode slime, while aluminum dissolves and remains in the electrolyte. Meanwhile, titanium ions in the cathode region undergo electron reduction and deposit in the cathode area in the form of titanium, thus achieving precise separation of alloy elements. Experimental verification shows that the purity of the obtained titanium reaches 99.17 atomic percent. Therefore, this molten salt electrolysis method, which combines the physical properties of alloy elements with electrochemical principles, not only provides a new perspective for the separation and recovery of titanium and other critical metals, but also offers new research directions for the recovery technology of other alloy elements.

Summary of the Research Progress on Advanced Engineering, Processes, and Process Parameters of Rare Earth Green Metallurgy.

The addition of rare earth metals to aluminum alloys can effectively improve their corrosion resistance and has been widely used in the aerospace and military industries. However, the current methods for the preparation of rare earth metals involve long processing steps, high energy consumption, and high carbon emissions, which severely constrains the development of aluminum alloys. Its output is further developed. To this end, this paper reviews mainstream rare earth production processes (precipitation methods, microemulsion methods, roasting-sulfuric acid leaching methods, electrochemical methods, solvent extraction methods, and ion exchange methods) to provide basic information for the green smelting of rare earth metals and help promote the development of green rare earth smelting. Based on the advantages and disadvantages of each process as well as recent research results, the optimal process parameters and production efficiency were summarized. Studies have concluded that the precipitation method is mostly used for the recovery of rare earth elements and related valuable metals from solid waste; the microemulsion method is mostly used for the preparation of nanosized rare earth alloys by doping; the roasting-sulfuric acid leaching method is mostly used for the treatment of raw rare earth ores; and the molten salt electrolysis method is a more specific method. This is a green and environmentally friendly production process. The results of this study can provide direction for the realization of green rare earth smelting and provide a reference for improving the existing rare earth smelting process.

Upcycling of spent LiMn2O4 cathode towards sodium-ion battery cathode through molten salt electrolysis approach

Recycling and valorizing spent lithium-ion batteries (LIBs) are requisite to achieve resource sustainability and environment safety. Herein, we reported a molten salt electrolysis method to recycle degraded LiMn2O4, synergistically achieving the selective leaching of lithium (Li) and high-valued reutilization of manganese (Mn). In molten Na2CO3-K2CO3, 94.3 % of Li from LiMn2O4 was released into molten salt by the electrolysis at 1.2 V for 7 h, while in-situ forming Na0.55Mn2O4⋅1.5H2O. During the electrolysis, LiMn2O4 at the cathode was electrochemically decomposed to Li2O and manganese oxide, accompanied by the reaction of resultant Mn oxide with Na2CO3 salt to generate Na0.55Mn2O4⋅1.5H2O. Finally, Li2CO3 in molten salt can be selectively extracted by water leaching. The obtained Na0.55Mn2O4⋅1.5H2O material as a sodium-ion battery (SIB) cathode delivers a discharge specific capacity of 58.9 mAh g−1 at 100 mA g−1, showing good cycle performance with a capacity retention of 93.9 % after 100 cycles. Hence, molten salt electrolysis achieves both extraction of Li and high-value reutilization of Mn, offering an electricity-driven materials separation, recovery, and reutilization with reduced environmental impact.

Oxygen removal and silicon recovery from polycrystalline silicon kerf loss by combining vacuum magnesium thermal reduction and hydrochloric acid leaching

With the strengthened awareness of environmental protection and the growing interests of wastes recycling, silicon recovery from polycrystalline silicon kerf loss (PSKL) has drawn extensive attentions all over the world. In this paper, an efficient and environmental friendly approach for oxygen removal and silicon recovery from PSKL by combining vacuum magnesium thermal reduction (VMTR) and hydrochloric acid leaching was proposed. The effects of temperature, duration and particle size on the reduction of PSKL were investigated thoroughly. It is proved that the amorphous SiO2 in PSKL can be reduced by magnesium vapor at 923 K to generate MgO, and then the produced MgO can be dissolved by hydrochloric acid to eliminate the impurity oxygen. The oxygen removal fraction and the silicon recovery efficiency attained 98.43% and 94.46%, respectively, under the optimal conditions, indicating that a high efficiency recovery of silicon from PSKL was achieved. Compared to the existing PSKL deoxidation technologies, e.g., the high temperature process and the hydrofluoric acid leaching method, this method requires a relatively lower temperature and the waste acid can be easily recovered. Additionally, by taking into accounts the fact that the MgCl2 in leaching liquor can be recycled for cyclic utilization with a molten salt electrolysis method, it should be suggested that an efficient and environmental friendly process for PSKL recycling was obtained, which shows good prospects for commercial application.

Molten salt electrosynthesis of Cr2GeC nanoparticles as anode materials for lithium-ion batteries.

The two-dimensional MAX phases with compositional diversity are promising functional materials for electrochemical energy storage. Herein, we report the facile preparation of the Cr2GeC MAX phase from oxides/C precursors by the molten salt electrolysis method at a moderate temperature of 700°C. The electrosynthesis mechanism has been systematically investigated, and the results show that the synthesis of the Cr2GeC MAX phase involves electro-separation and in situ alloying processes. The as-prepared Cr2GeC MAX phase with a typical layered structure shows the uniform morphology of nanoparticles. As a proof of concept, Cr2GeC nanoparticles are investigated as anode materials for lithium-ion batteries, which deliver a good capacity of 177.4mAhg-1 at 0.2 C and excellent cycling performance. The lithium-storage mechanism of the Cr2GeC MAX phase has been discussed based on density functional theory (DFT) calculations. This study may provide important support and complement to the tailored electrosynthesis of MAX phases toward high-performance energy storage applications.

From CO2 capture to high-efficient and over-stable core-shell bimetallic catalysts for eliminating sulfamethoxazole

Herein, we prepare a series of core-shell bimetallic catalysts NixCo1-x@C (x = 0–1) with different graphitized degrees by the one-step molten salt electrolysis (MSE) method. During the catalytic oxidation experiments, sulfamethoxazole (SMX) degradation rates reach 85.60%, 100%, 100%, 98.79%, and 57.60%, respectively, as the x values increases from 0 to 1. Therefore, the alloying of Ni significantly increases the catalytic elimination performance of SMX by the NixCo1-x@C catalyst (x = 0.3) with a reaction rate (kobs) of 0.153 min−1. In addition, increasing the Ni content increases the graphitization of the carbon shell. The value of ID/IG decreases to 0.81 when the x value is 0.7, reducing the metal Ni and Co leaching of Ni0.7Co0.3@C catalyst to as low as 0.45 and 0.16 mg L−1 during the cycle's experiments, respectively. The electron paramagnetic resonance (EPR) tests and classical quench experiments show that SO4•–, •OH, O2•–, and 1O2 co-degrade the SMX.

Effect of Electrolysis Temperature on the Preparation of FeO by Molten Salt Electrolysis

FeO is a low-price material with high charge storage capacity, biocompatibility and other characteristics. It has been applied in the fields of catalysts, capacitors, electrodes and composite materials. However, the current method of preparing FeO needs to control the temperature and reducing atmosphere, which increase the production difficulty and cost. In this experiment, the molten salt electrolysis method was used to prepare FeO by using the NaCl-KCl molten salt system and Fe2O3 and Al2O3 as raw materials, and the influence of temperature on the preparation process was explored. The results showed that the electrolysis process of Fe2O3 to FeO is mainly divided into the following three stages: the electric double-layer charging process, Fe2O3 to Fe3O4 process and Fe3O4 to FeO process. The increase in temperature can improve the reaction speed and strengthen the electrolysis effect. The higher the temperature, the less Fe3O4 and more FeO in the sample. Through analysis, it was found that the increase in temperature will affect the theoretical voltage of the electrolytic reaction in thermodynamics, resulting in the increase in the overall potential provided by the power supply. In terms of kinetics, the increase in temperature will affect the viscosity of molten salt, so that O2− transport has better kinetic conditions.

Separation of antimony from lead-antimony alloy by molten salt electrolysis

Lead-acid batteries (LABs) are widely used in electric motorcycles, uninterruptible power systems, and stationary energy storage devices. However, spent LABs should be recycled to reuse lead (Pb) and thereby close the Pb cycle and avoid Pb contamination. In order to reuse the recovered Pb, the purity of recovered Pb should meet the required standard. Since antimony (Sb) is a common alloying element in Pb alloy grid such as the Pb-Sb alloy, separating Sb from the recovered Pb is necessary. In this paper, we proposed a molten salt electrolysis method to separate Sb from liquid Pb-Sb alloys in terms of forming a solid Ca-Sb intermetallic at the top of the liquid Pb-Sb cathode. The electrochemical separation process was performed in molten NaCl-CaCl2. The content of Sb (atomic percent) in the Pb-Sb alloy was reduced from 1% to less than 0.01% (atomic ratio). The recovery principle lies in the different alloying potentials between Ca-Sb and Ca-Pb. Hence, molten salt electrolysis is a promising separation method to recover pure Pb from spent Sb-containing Pb alloys.

Electrochemical Growth of High-Strength Carbon Nanocoils in Molten Carbonates.

The reported mechanical strength of carbon nanocoils (CNCs) obtained from traditional preparation of catalytic acetylene pyrolysis is far below its theoretical value. Herein, we report a molten salt electrolysis method that employs CO32- as feedstock to grow CNCs without using metal catalyst. We meticulously mediate the alkalinity of molten carbonate to tune the electrochemical reduction of CO32- on graphite electrode to selectively grow CNCs in Li2CO3-Na2CO3-K2CO3-0.001 wt %Li2O. Graphite substrate, current density, and alkalinity of molten salt dictate the growth of CNCs. In addition, the electrolytic CNCs shows a spring constant of 1.92-39.41 N/m and a shear modulus of 21-547 GPa, which are 10-200 times that of CNCs obtained from catalyst-assisted gas-to-solid conversions. Overall, this paper opens up an electrochemical way to prepare CNCs through liquid-to-solid conversion without using catalysts and acetylene, providing new perspectives on green synthesis of 1D carbon nanomaterials with high mechanical strength.

U(VI) adsorption behavior onto polypyrrole coated 3R-MoS2 nanosheets prepared with the molten salt electrolysis method

U(VI) adsorption behavior onto polypyrrole coated 3R-MoS2 nanosheets prepared with the molten salt electrolysis method

Study on the Synergistic Extraction of Lithium from Spent Lithium Cobalt Oxide Batteries by Molten Salt Electrolysis and Two-Step Precipitation Method

With the continuous development of society, the number of spent lithium-ion batteries has also increased, and the recovery of valuable metals such as Ni, Co, and Li has become the main research direction of many scholars. In this paper, the extraction process of lithium that enters the molten salt after LiCoO2 electrolysis is studied. Oxalic acid and phosphate are added to molten salt containing lithium ions to realize the two-part precipitation method to extract lithium. The influence of pH value, temperature, reaction time, and oxalic acid (or phosphate) addition on the process of oxalic acid calcium removal and phosphate lithium precipitation is analyzed. The results show that the calcium removal rate of oxalic acid has reached 99.72% (Initial conditions: PH = 7.0, T = 70 °C, t = 1.5 h, n(H2C2O4):n(Ca2+) = 1.2:1). The precipitation of Li3PO4 obtained in the phosphate extraction experiment of lithium is as high as 88.44% (Initial conditions: PH = 8.0, T = 70 °C, t = 1.5 h, n(actual dosage of Na3PO4):n(theoretical dosage of Na3PO4) = 1.2:1). The obtained lithium phosphate crystals show regular spherical particles, which can be seen by SEM.

The electrochemical dissolution mechanism and treatment process in the molten-salt electrolytic recovery of WC-Co two-phase scraps

The use and scrap of cemented carbide, especially WC-Co series cemented carbide, are increasing every year. Recycle of cemented carbide scrap is paid attention to more and more by researchers. In this paper, the molten salt electrolysis method was employed to extract tungsten and cobalt. The focal points of this study were the electrochemical dissolution mechanism of WC-Co two-phase scraps and the treatment process of multiple pieces of WC-Co scrap. Electrochemical impedance spectroscopy indicated that the dissolution mechanism of WC-Co composite had the anodic potential dependence. The equivalent circuit model of WC-Co two-phase composite can adopt the “Rct parallel model” of cobalt and tungsten carbide. At the case of surface area evolution or multiple anodes electrolysis, the equivalent circuit model can also adopt the “Rct parallel model”, which built a bridge between single WC-Co anode and multiple WC-Co anodes. Consequently, we designed and achieved the recovery process of multiple WC-Co anodes. The XRD analysis and elemental analysis showed that the products were pure cobalt and pure tungsten, respectively.

Molten salt electrolysis method to achieve Ni/MoS2 with activity sulfur enhance the hydrogen evolution reaction performance under alkaline condition

The main problem in the application of molybdenum disulfide (MoS2) in hydrogen evolution reaction (HER) is difficult to optimize the active site and promote the charge transfer. The decoration of Ni can improve the intrinsic activity and increase the number of active sites of MoS2 efficiency. An electrode of Ni/MoS2 nanosheets or nanoflowers on carbon fiber cloth is designed via a facile one-pot molten salt electrolysis method. The amount of doped Ni was controllable during the molten salt electrolysis process. Two specially structures of nanosheets and nanoflowers were compared to confirm the effect by structure. Benefiting from Ni decoration and its unique crystal structure, the Ni/MoS2 electrode exhibits excellent electrocatalytic performance in alkaline solution (1 M KOH). As a result, the designed electrocatalyst of Ni/MoS2 nanosheets shows the best catalytic performance with low overpotentials (109.0 mV for the current density of 10.0 mA cm−2) and the small Tafel slope (41.2 mV dec−1). Test results of electrocatalytic hydrogen evolution and density functional theory (DFT) calculation revealed that Mo was substituted by Ni. S near the top position is activated by two doping Ni atoms to adsorb H. The Hydrogen is adsorbed on the surface with the lowest free energy of adsorption ΔGH* (ΔGH*= 0.13). When the S atom is at the far end, the free energy of adsorption increases. These findings open an effective and propagable strategy for nanostructure HER catalysts synthesis.

Engineering Electrolytic Silicon–Carbon Composites by Tuning the In Situ Magnesium Oxide Space Holder: Molten-Salt Electrolysis of Carbon-Encapsulated Magnesium Silicates for Preparing Lithium-Ion Battery Anodes

Fabricating hollow space between a Si core and C shell has been recognized as an efficient strategy for tailoring lithium-storage performances of the silicon–carbon composite anode by resolving the extreme volume expansion of Si. Here, we report a molten-salt electrolysis method for electroreducing carbon-encapsulated magnesium silicate to prepare a Si@void@C composite in MgCl₂-containing molten salt. The void space between carbon and silicon comes from the transition from silicate to Si as well as the removal of the in situ generated MgO, and the SiC is suppressed by tailoring the electrode potentials in MgCl₂-containing molten salt. In other words, MgO serves as an inert space holder that can be removed by an acid leaching process to create void space. The obtained Si@void@C composite delivers a specific discharge capacity of 900 mAh/g at 1 A/g, even after 300 cycles with a discharge capacity retention rate of 75.5%. Therefore, this study paves an electrochemical pathway to prepare Si@void@C composite anodes using inexpensive feedstocks, and the void space can be tuned by adjusting the amount of MgO space holder.

Preparation of petaloid graphite nanoflakes in molten salt for high-performance lithium-ion batteries

The high value-added utilization of inferior resources has grown up an urgent need. Artificial graphite with petaloid nanoflakes was prepared from inferior coal by molten salt electrolysis method. The as-prepared graphite was used in lithium-ion batteries, which exhibited a high reversible specific capacity of 848.26 mA h g−1 after 120 cycles with a current density of 1 A g−1. Even at an ultra-high current density of 10 A g−1, it still delivered a high specific capacity of 277.2 mA h g−1 as well as an excellent rate performance. These superiorities make synthetic graphite based on inferior coal a very promising anode materials for high-performance lithium-ion batteries.

Effective adsorption of uranyl ions with different MoS2-exposed surfaces in aqueous solution

An understanding of the impacts regarding on two-dimensional materials on radionuclide removal is indispensable, owing to the intrinsic structure of materials can affect its properties. In this work, MoS2 nanosheets and nanoflowers were prepared by molten salt electrolysis method. The distinct adsorption behaviors of U(VI) on MoS2 was theoretically and experimentally investigated. The adsorption properties of MoS2 material including equilibrium isotherms, kinetics and effects of pH and temperature were explored. Batch experiments results show that MoS2 nanosheets and nanoflowers achieved excellent U(VI) adsorption capacities, which were 45.7 and 37.1 mg/g at 298 K, respectively. According to the computational results, U(VI) have formed more stable complexes on MoS2. Interestingly, the molybdenum group could significantly improve the binding energy through U-S bond. Therefore, the MoS2 material has potential applications in the elimination of uranyl ion from radioactive wastewater.

One-step electrochemical reduction of stibnite concentrate in molten borax

In this study, antimony production from a stibnite concentrate (Sb2S3) was performed in one step using a molten salt electrolysis method and borax as an electrolyte. Electrochemical reduction of the stibnite concentrate was performed at 800°C under galvanostatic conditions and explained in detail by the reactions and intermediate compounds formed in the borax. The effects of current density (100–800 mA·cm−2) and electrolysis time (10–40 min) on cathodic current efficiency and antimony yields were systematically investigated. During the highest current efficiency, which was obtained at 600 mA·cm−2, direct metal production was possible with 62% cathodic current efficiency and approximately 6 kWh/kg energy consumption. At the end of the 40-min electrolysis duration at 600 mA·cm−2 current density, antimony reduction reached 30.7 g and 99% of the antimony fed to the cell was obtained as metal.

Production and electrochemical characterization of Mg[sbnd]Ni alloys by molten salt electrolysis for Ni–MH batteries

MgNi alloys are produced by molten salt electrolysis and diffusion method on a nickel plate in KClNaCl based melts. Structure, alloy composition and electrochemical properties of these alloys are evaluated. Electrolyte composition and applied current density parameters are studied for the characterization of the alloys. It is found that MgNi alloys with 45 wt% to 49 wt% Ni content which can be defined as MgNi–type alloys, have both higher discharge capacity and good retaining rate (72%). These alloys are mainly composed of Mg2Ni phases and displayed a maximum discharge capacity of 384 mAhg−1. Increased Ni content is advantageous for the enhancement of the cycle life. At the same time, the discharge capacity of MgNi alloy electrode is found to be decreasing. The highest capacity retaining (85%) rate is observed in the highest Ni content alloys (72 wt% Ni).Electrochemical impedance spectroscopy and potentiodynamic polarization measurements show that the controlling–step of the discharge process changed from a mixed rate–determining process at lower depth of discharge to a mass transfer controlled process at higher depth of discharge. The charge transfer resistance increases from 0.5 Ω to 23 Ω with increasing depth of discharge.

Rapid Production of Ln2O2S:Eu3+/Tb3+ (Ln = Sm, La, Gd, and Y) Phosphors by Molten Salt Electrolysis

In this paper, a facile one-pot molten salt electrolysis method has been proposed for the synthesis of hexagonal sheet-like Ln2O2S:Eu3+/Tb3+ (Ln = Sm, La, Gd and Y) phosphors. The phase, composition, morphology, and optical properties of the phosphors were characterized by X-ray powder diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and photoluminescence. The results showed that doping Eu3+ or Tb3+ causes no great changes to the crystal structure. Under the excitation of 394 nm light, sheet-like Ln2O2S:Eu3+ (Ln = Sm, La, Gd, and Y) exhibited predominantly red emission at around 627 nm, which corresponds to the absorption of host crystals and the energy level transitions of 5D0 to 7F2 configuration of Eu3+ ions. The sheet-like Ln2O2S:Tb3+ exhibited characteristic excitation of Tb3+ under 364 nm. The emission spectra of Ln2O2S:Tb3+ (Ln = Sm, La, Gd, and Y) were measured, and those emission lines between 450 and 650 nm corresponded to the transitions of 5D4 to 7FJ (J = 0–6) groun...

A Molten Salt Electrolysis Procedure to Form Al-Sc Alloys

Recently, alloys such as Al-Sc and Al-Mg-Sc came to the forefront due to the reinforcement effect of scandium on the properties of aluminum such as mechanical strength, thermal stability, resistance to recrystallization, resistance to intergranular fracture and corrosion [1]. The main scandium source for these aluminum alloys is the Sc2O3 by-product obtained during uranium (U), tungsten (W) or tantalum (Ta) production. It has been shown that it is possible to produce Sc by the molten salt electrolysis method with dissolution of Sc2O3 in Na3ScF6 as in the Hall-Héroult process [2]. This scandium can be used to produce Al-Sc alloy in-situ, provided that required amount of aluminum was already present in the reactor. Furthermore, the production of Al-Sc alloy by the dissolution of Sc2O3 in a molten salt containing CaCl2, in which the solubility of oxide ions is very large has been reported [3]. The Al-Sc alloy formation by the reduction of other Sc containing compounds in a molten salt containing CaCl2 was investigated in this study. The preliminary tests revealed that Al3Sc intermetallic was successfully formed and distributed homogeneously throughout the Al matrix as confirmed by the XRD, SEM-EDS and optical microscopy analyses. As can be seen in the optical micrograph shown in Figure (a), due to the long electrolysis and the high voltage applied, calcium contamination was observed by the presence of black Al4Ca eutectics in between the white faceted Al3Sc intermetallics. On the other hand, in the optical micrograph shown in Figure (b), it can be seen that the calcium contamination was inhibited by changing the electrolysis duration and the voltage while keeping the homogeneous distribution of Al3Sc.