Molten Salt Electrolysis Research Articles

Economics of Electrowinning Iron from Ore for Green Steel Production

The transition to green steel production is pivotal for reducing global carbon emissions. This study presents a comprehensive techno-economic analysis of various green steel production methods, including hydrogen reduction and three different electrolysis techniques: aqueous hydroxide electrolysis (AHE), molten salt electrolysis, and molten oxide electrolysis (MOE). By comparing process flow diagrams, capital and operational expenditures, specific energy consumption, and production footprint, this work provides a high-level assessment of the economic viability of these processes as they mature. The analysis reveals that MOE, despite its ongoing development, offers a promising route for iron production given its ability to process a wide range of ore qualities and the potential to sell electrolyte as a cement product. However, the best balance between deployment ready technology and economic benefit is AHE. Operational challenges are also discussed, such as electrolyte loss and slag handling. We suggest that the sale of by-products like oxygen may not significantly impact the economics due to market saturation. The findings underscore the importance of continued research and development in process optimization to realize the full potential of green steel technologies. All the calculations have been released as supplementary electronic material (MS Excel workbook). The format has been inspired by the techno-economic assessment template (TECHTEST) distributed by the US Dept. of Energy.Graphical

Molten Salt Electrodeposition: Review

Molten salt electrodeposition is the process of producing impressively dense deposits of refractory metals using the electrolysis of molten salts. However, predicting which electrochemical parameters and setup will best control different kinds of deposition (density, homogeneity, etc.) is an ongoing challenge, due to our limited understanding of the properties and mechanisms that drive molten salt electrodeposition. Because these advancements have been made rapidly and in different arenas, it is worth taking the time to stop and assess the progress of the field as a whole. These advancements have increasing relevance for the energy sector, the development of space materials and engineering applications. In this review, we assess four critical facets of this field: (1) how the current understanding of process variables enhances the electrodeposition of various molten salts and the quality of the resulting product; (2) how the electrochemical setup and the process parameters (e.g., cell reactions) are known to impact the electrodeposition of different metal coatings and refractory-metal coatings; (3) the benefits and drawbacks of non-aqueous molten salt electrodeposition, and (4) promising future avenues of research. The aim of this work is to enhance our understanding of the many procedures and variables that have been developed to date. The expectation is that this review will act as a stimulant, motivating scientists to delve further into the investigation of refractory-metal alloys by utilizing molten salt electrodeposition.

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.

CO2 transformed into highly active catalysts for the oxygen reduction reaction via low-temperature molten salt electrolysis

The implementation of a technology capable of capturing and converting CO2 into valuable products is one of the key requirements for limiting the effects of our carbon-intensive industries. At the same time, future CO2 emissions need to be reduced to combat climate change, meaning that new devices capable of storing and converting energy without CO2 emissions have to be adopted widely. In this work, we demonstrate catalysts made directly from CO2 for fuel cells and zinc-air batteries. The molten salt electrolysis process is used to electrodeposit solid carbon from CO2 in two mixtures, a known eutectic mixture of Li2CO3, Na2CO3, K2CO3 and a new mixture containing 0.1 mol of LiOH in addition. The effects of the electrolyte towards the final carbon product and its electrocatalytic activity are analysed using the rotating disk electrode method, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The porosity of the materials is described by N2 adsorption and the best performing catalyst is compared to the activity of a commercial 20 wt% PtRu/C material in a zinc-air battery.

Evaluating Phase Relations in Molten Oxides for Electrochemical Operating Windows for Selective Metal Reduction

AbstractMolten oxide electrolysis is a promising pathway to decarbonize primary metal production. The oxide electrolyte is less hazardous and eco‐toxic than halides (molten salt electrolysis) and, with the use of renewably generated electricity and an inert anode, oxygen is produced as a by‐product instead of CO2. Building fundamental understanding of electrolytic operating windows requires starting with simple chemistries. Here we investigate a simplified binary oxide system as an electrolyte for titanium oxide reduction to metal. The TiO2−Na2O binary system forms a eutectic, reducing the liquidus temperature over a wide composition range. FactSage 8.1 predictions suggested Ti reduction would become favorable over Na reduction for compositions greater than 0.49 mole fraction TiO2. The prediction was validated by the detection of metallic Ti after electrolysis experiments. However, the reduction efficiency was too low (0.24±0.08 % at −0.1 V vs Ti reference electrode) for the TiO2−Na2O system to be a viable industrial electrolyte for Ti production. Scoping for other binary oxide systems was performed for electrolytic production of two critical metals, tantalum and neodymium. Based on TiO2−Na2O system's predicted behavior, candidate binary oxide systems were identified that contained congruently melting line compounds flanked by eutectic reactions from the ACerS‐NIST Phase Equilibria diagrams database.

Mixed rare earth metals production from surface soil in Idaho, USA: Techno-economic analysis and greenhouse gas emission assessment

Rare earth elements are crucial for the development of cutting-edge technologies in various sectors, such as energy, transportation, and health care. Traditional extraction of rare earth elements from soil and ore deposits primarily involves chemical leaching and solvent extraction. Environmental-based biological rare earth element extraction, such as bioleaching, can be a promising alternative to mitigate pollution and hazardous wastes. We investigated the sustainability aspects (techno-economic and environmental impact) of mixed rare earth metals production from soil in Idaho, USA. We focused on the bioleaching of surface soil using techno-economic analysis and “cradle-to-gate” life cycle assessment. The system boundary included collection, transportation, bioleaching, and molten salt electrolysis. Our results revealed that the mixed rare earth metals (including Nd, Ce, and La) production costs approximately $10,851 per metric ton and generates 1.9 × 106 kg CO2 eq./ton. Our results showed that most emissions are due to energy consumption during bioleaching. Over a 100-year time horizon ultrasound-assisted bioleaching can reduce greenhouse gas emissions by approximately 91 % compared to the traditional bioleaching process by decreasing the organic acid leaching process time and energy consumption. Our work demonstrates that higher solids loading in leaching with biological reactions can promote economic feasibility and reduce chemical wastes.

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

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

Mechanical and Electrochemical Corrosion Behaviors of Porous Ti-6Al-4V Alloys Prepared by an Electrochemical Sintering Approach

Titanium alloys have been widely used in bone implants, but the mechanical properties, elastic modulus mismatch between bone and metal, and stress shielding effects can occur. However, porous materials can effectively overcome this problem. In recent years, porous structures have attracted enough attention from researchers. Adjustment of the porous structure may make the titanium alloys better able to meet the requirements of the implant. In this study, we have successfully prepared Ti-6Al-4V alloys by combining powder metallurgy with electrolysis in molten salt. At the same time, CaCl2 was used as a sacrificial space holder to adjust the porosity and porous structure. The Ti-6Al-4V alloys prepared by this method contain 29%–60% porosity and elastic modulus has been controlled between 1.8 GPa to 7.8 GPa, which is suitable for cancellous bone, trabecular, and other parts with low elastic modulus. In addition, the higher porosity also showed better corrosion resistance in the Hank’s solution. The potentiodynamic polarization curves show that the corrosion resistance increases significantly with an increase in porosity.

Rare Earth Chlorides in Low-Hydration Magnesium Chloride Electrolysis: Mechanistic Insights

During the molten salt electrolysis of magnesium production, water in the magnesium chloride (MgCl2) feedstock poses significant interference, reducing the current efficiency. Employing rare earth chlorides (RECl3) to assist in dehydrating MgCl2 and producing Mg-RE master alloys emerges as an effective strategy. This study investigated the transformation process in the hydrolysis reaction of low-hydrate MgCl2 within the molten salt, examining the electrochemical activity of its hydrolysis products using Cyclic voltammetry (CV). Additionally, a thermodynamic analysis of the reaction between hydrolyzate MgO and RECl3 was performed at electrolysis temperatures. By integrating CV and Square wave voltammetry (SWV) with X-ray diffraction (XRD) analysis, the study explored the alterations in the electrochemically active components of the molten salt system following the addition of RECl3 to the KCl-NaCl molten salt containing MgO.

Electrometallurgical Extraction of Silicon Using Solid Oxide Membrane—Molten Salt Electrolysis

Electrometallurgical Extraction of Silicon Using Solid Oxide Membrane—Molten Salt Electrolysis

Electrochemical separation of tungsten from scrap cemented carbide WC in FLiNaK melt

Molten salt electrolysis is an innovative technology applied to recover tungsten from the scrap of cemented carbide, which enables the realization of energy saving and consumption reduction goals. Currently, numerous studies have focused on the molten salt electrolysis of chlorine salt systems, but still face challenges including low electrolysis efficiency and salt volatilization. Here, we propose to employ the FLiNaK molten salt system for recovering tungsten from the scrap cemented carbide and analyze the feasibility of the dissolution of WC occurring at the anode from the perspective of thermodynamics and electrochemical polarization curves. Moreover, the influence of electrolysis temperature on the dissolution of the anode is also investigated and the productions are identified as nano-flake tungsten powder by characterizing the cathode product using XRD, SEM, EDS, and XPS. A two-step reduction mechanism of W ions was analyzed by electrochemical means such as CV, SWV, etc., and the ionic groups stabilized by W6+ and W4+, and F− in the molten salts were deduced to be WF33+ and WF3+ by DFT simulation calculations. This work provides new guidance for the application of molten salt electrolysis in the recovery of tungsten from scrap cemented carbide.

Research Progress of Preparing Titanium Alloy By Molten Salt Method

Titanium alloy has excellent characteristics that cannot be compared with other metals such as light specific gravity, high specific strength, wide applicable temperature range, corrosion resistance, and hydrogen storage. The traditional titanium alloy smelting process is mainly based on titanium sponge as raw material, which has a long process, high energy consumption, heavy pollution, and other problems, which seriously restricts the sustainable development of titanium alloy in the world. The common methods of preparing titanium alloy are alloy melting, metal thermal reduction, powder metallurgy, and the gradually emerging molten salt electrolysis. Among them, molten salt electrolysis is recognized as the most promising method to replace the traditional titanium alloy production process, and certain achievements have been made in recent years in terms of both process and basic theory research. In this paper, the common processes of titanium alloy preparation by molten salt electrolysis at home and abroad, such as molten salt electrolytic co-deposition method, cathodic alloying method and liquid cathode method, new FFC method, and its derived SOM method, etc., will be summarized systematically, and the future research will be put forward.

Modeling electrolysis in reduced gravity: producing oxygen from in-situ resources at the moon and beyond

Molten Regolith Electrolysis, as an in situ resource utilization (ISRU) technology, has the potential to enable the production of oxygen and metallic alloys on the Lunar surface; opening new doors in Cis-Lunar, and eventually Martian space exploration. This research studies the fundamental physics which govern the formation, growth, detachment, and rise of electrolytic bubbles. To this end, computational fluid dynamic (CFD) models were developed and run, to simulate water electrolysis, molten salt electrolysis (MSE), and molten Lunar regolith (MRE) electrolysis across multiple reduced gravity levels. The results demonstrate that reduced gravity, electrode surface roughness (possibly due to surface degradation), fluid properties, and electrode orientation can all affect electrolytic efficiency and possibly even stall electrolysis by delaying bubble detachment. The findings of this research must be considered when designing and operating electrolysis systems at reduced gravity levels.

Unveiling the dual tunability of dimension and pore structure in MAX-derived carbon via molten salt electrolysis

3D construction or pore-forming of carbon nanosheets brings the materials exceptional energy storage performance. However, these strategies involve complicated procedures and challenging conditions. Herein, based on the structural regulation of a MAX phase, a facile method was proposed to prepare MAX-derived carbon (MDC) with dual tunability of dimension and pore structure via molten salt electrochemical etching-gaseous sulfur delamination coupling. Polyhedral structure Ti2SC and highly oriented structure Ti2SC were transformed into 3D Mesopore carbon nanoshells (3D Meso-CNSL) and 2D Mesopore carbon nanosheets (2D Meso-CNST) in one step. By matching the decomposition voltage of TiClx with that of PS-Ti2SC, Cl2 gas generated in situ was employed to enhance the porosity of the 3D Meso-CNSL, resulting in the formation of 3D meso/macro-porous carbon nanoshells (3D Meso/Macro-CNSL) with doubled pore volume (1.45 cm3 g−1) and specific surface area (649.97 m2 g−1). The 3D Meso/Macro-CNSL exhibits excellent capacity performance and cycle stability under high current density. The capacities are 674.8 mAh g−1 and 501.5 mAh g−1 after 1000 cycles at 5 A g−1 and 10 A g−1, respectively. It is the first report on the direct delamination of MAX phases into 3D nanomaterials, presenting a new pathway for the precise regulation of the nanostructure of the MDCs.

The impact of 3-dimensional anode geometry on the electrochemical response of high temperature gas evolution reactions in molten salts

Bulk electrodes are used in molten salt electrolysis as consumable graphite anodes for existing aluminium production (producing CO2) as well as for oxygen evolution anodes in future zero emission manufacturing processes, such as direct iron electrolysis. Here, graphite electrodes with different geometry, roughness, density, and size were assessed for their kinetic behaviour and gas evolution stability in a molten alkali-metal (Li-Na-K) carbonate salt at 600 °C. It is suggested through comparative assessment of controlled electrode sizes and geometry that radial diffusion at a small (5 mm diameter disc) electrode is likely to influence performance. Roughened electrodes and electrodes of varying porosity also impacted polarisation behaviour which was ascribed to changes in electrolyte wetting observed in separate studies, conducted under similar conditions. It was also seen that 3-dimensional cone and slant type electrodes on angles of 75° increased the electrode performance. Enhanced kinetics were observed by a decreasing Tafel slope from 254 mV.decade−1 to 188 mV.decade−1 for 45° and 75° slant electrodes, respectively. The apparent improved performance for identical electrode material is discussed to involve influence from radial diffusion of reactants, modified via electrode geometry. Additional work is required to confirm this. It was concluded that to fairly compare oxidation of graphite materials in molten carbonate salts, electrodes of 10 mm diameter equivalent should have the same geometry and consistent inclination angle (of below 45°), as well as control of bulk density and resulting porosity. This observation may well also apply to other systems and should be considered in experimental design.

Advances in Understanding of Unit Operations in Non-Ferrous Extractive Metallurgy in 2023

Advances in Understanding of Unit Operations in Non-Ferrous Extractive Metallurgy in 2023

In Situ Chlorine Generation and Rare Earth Chlorination by Molten Salt Electrolysis

Chloride volatility processes for purifying actinide and rare earth elements have historically required the use of Cl2 tanks. To minimize the hazards associated with these processes, an apparatus was designed to produce Cl2 via molten salt electrolysis. Within this apparatus, one can generate Cl2, chlorinate metals, and consume excess Cl2. Here, electrode materials were tested for their ability to generate Cl2, the composition of the gaseous electrolysis product was evaluated using a quadrupole mass spectrometer, and a Ce foil sample was successfully chlorinated using the electrochemically generated Cl2.

Electrolysis in Chloride Molten Salts for Sustainable Critical Metals Production and Recovery

Critical materials, such as rare-earth metals, are essential to numerous applications, including clean energy; however, the present industrial practices for producing rare-earth metals involve environmentally damaging and thus unsustainable chemical and electrochemical processes. An alternative moderate-temperature chloride-based molten salt electrolysis process can address these issues, providing energy efficient and sustainable metal production. While it is being developed presently for rare-earth electrowinning, one can easily envision its broader application to rare-earth electrorefining and the electrolytic production of high-volume metals like Fe and Al. Presently, these high-volume metals industries account for nearly 10% of global greenhouse gas emissions. Thus, the chloride MSE process presents a huge opportunity for truly achieving sustainability if it is developed further for producing Fe, Al, Ti, Mg, and other commodity metals.

Self-Assembly of Silicon Nanotubes Driven by a Biphasic Transition from the Natural Mineral Montmorillonite in Molten Salt Electrolysis.

Silicon nanotubes (SNTs) have been considered as promising anode materials for lithium-ion batteries (LIBs). However, the reported strategies for preparing SNTs generally have special requirements for either expensive templates or complex catalysts. It is necessary to explore a cost-effective and efficient approach for the preparation of high-performance SNTs. In this work, a biphasic transformation strategy involving "solid-state reduction" and "dissolution-deposition" in molten salts is developed to prepare SNTs using montmorillonite as a precursor. The rod-like intermediate of silicon-aluminum-calcium is initially reduced in solid state, which then triggers the continuous dissolution and deposition of calcium silicate in the inner space of the intermediate to form a hollow structure during the subsequent reduction process. The transition from solid to liquid is crucial for improving the kinetics of deoxygenation and induces the self-assembly of SNTs during electrolysis. When the obtained SNTs is used as anode materials for LIBs, they exhibit a high capacity of 2791mAhg-1 at 0.2Ag-1, excellent rate capability of 1427mAhg-1 at 2Ag-1, and stable cycling performance with a capacity of 2045mAhg-1 after 200 cycles at 0.5Ag-1. This work provides a self-assembling, controllable, and cost-effective approach for fabricating SNTs.

Molecular dynamics simulations of the local structure and physicochemical properties of CaCl2molten salt

AbstractCaCl2molten salt, as a common electrolyte in the process of molten salt electrolysis, has a high decomposition potential and a strong ability to bind O2−. So the study of the structure and properties of CaCl2is significant for the molten salt electrolysis. In this paper, molecular dynamics simulations (MD) method was used to investigate the variation rule of the local structure and physicochemical properties of CaCl2molten salt with temperature. The results show that the temperature has less effect on the heterozygous ion pairs and more effect on the homozygous ion pair. With the increase of temperature, the interaction between ion pairs is weakened, the coordination number decreases, the local structure changes a little, and the structural configuration tends to be an irregular octahedral structure with vacancies. The calculated self-diffusion coefficients, viscosities, and ionic conductivities are consistent well with the reality, but there is a significant error in densities due to the strong polarization effect of Ca2+compared to the reality. The local structure directly determines the thermodynamic properties of the molten salts. This study promotes the basic theoretical research on alkaline earth metal-containing molten salts and is an important reference for the study of molten salt electrolysis process.