As the importance of rare earth metals in high-tech equipment and defense industries continues to increase, optimizing the performance of rare earth electrolytic cells has become increasingly crucial for enhancing energy efficiency and production effectiveness. Based on the issue of gas stagnation at the anode bottom in the bottom cathode rare earth electrolytic cells, this study proposes an optimized anode structure aiming to improve bubble emission, flow field characteristics, and the stability of the electrolysis process. The bubble dynamics and flow field characteristics of three anode structure designs (conventional anode, single slotted anode, and double slotted anode) were comparatively analyzed by using room-temperature electrolysis experimental and numerical simulation. The results of the room-temperature electrolysis experiment and numerical simulation show that the optimization of the anode structure significantly reduces both the bubble coverage rate and the maximum bubble layer thickness at the anode bottom. Notably, under the double slotted anode design, the bubble emission rate and overall fluid circulation were significantly enhanced. Furthermore, high-temperature molten salt electrolysis experiments validated the optimization effect of anode slotting, demonstrating its ability to significantly improve current efficiency and the stability of the electrolysis process. The numerical simulations align with experimental results, indicating that optimizing the anode structure can effectively enhance the performance of the rare earth electrolytic cell, providing a theoretical foundation and practical reference for the design and improvement of the novel bottom cathode rare earth electrolytic cell.

The emissions of waste coal fly ash from thermal power generation have increased in tandem with the growing demand for electric energy, which has had a negative impact on both the environment and human health. The extraction of aluminum oxide from coal fly ash by the hydrochloric acid method presents a viable avenue for the repurposing of coal fly ash. However, a major obstacle in the manufacturing process is the removal of iron from the leachate of coal fly ash. This study proposes a cost-effective, efficient, and environmentally sustainable electrolysis method for iron removal. Specifically, the ion exchange membrane electrolysis technique is employed to remove iron from the leachate of coal fly ash, with Fe being deposited on the cathode surface as iron, minimizing aluminum loss and primarily incurring costs associated with electrical energy. The by-products are hydrogen and chlorine, both of which have considerable economic value, while the catholyte following electrolysis is an aluminum chloride solution that can be directly utilized for aluminum oxide production. Under optimal conditions, the concentration of iron in the catholyte can be reduced to 125 mg/L, achieving a removal efficiency of 98.3 %. Furthermore, it is found that an increase in current density and electrolysis temperature resulted in a more regular morphology of the iron. The mechanism of the electrolysis process is proposed indicating that hydrolysis reactions occur in the catholyte, while hydrogen and iron reduction reactions take place at the cathode surface.

To address the issues of gas film blocking at the anode bottom, poor electrolyte circulation, and instability during the electrolysis process in the bottom cathode rare earth electrolytic cell, this study introduces structural modifications to the anode. Furthermore, the effects of different anode structure configurations on the molten electrolyte flow behavior, gas volume fraction distribution, and the concentration distribution of Nd2O3 (neodymia) particle dissolution-diffusion process are systematically investigated. Based on the ANSYS Fluent 2023R2 software platform, a coupled numerical model integrating gas–liquid–solid multiphase flow and mass transfer was established through simulation and comparative analysis of three distinct anode configurations: conventional anode, single slotted anode, and double slotted anode. The results clearly demonstrate that slotted anode designs significantly enhance electrolyte circulation and facilitate efficient gas release at the anode bottom. Notably, the double slotted anode exhibits superior performance in promoting the transport and dissolution diffusion of neodymia particles. Moreover, model validation confirmed good agreement between the simulation results and experimental data, demonstrating the reliability of the established model in predicting neodymia concentration distributions in industrial-scale rare earth electrolytic cells. This research not only deepens the understanding of multiphysics coupling mechanisms during rare earth electrolysis but also provides a substantial scientific foundation for structural optimization and process parameter regulation in industrial electrolytic cell design.

The Anode Effect (AE) in primary aluminum production is a critical issue for the industry, contributing significantly to greenhouse gas emissions and current efficiency. This study investigates the role of the bubble layer and fluorocarbon (CFx) passivation film on a 50 cm2 industrial carbon anode during AE initiation, using in-situ video observation in a high-temperature transparent electrolytic cell at 940 degrees C, combined with non-in situ X-ray photoelectron spectroscopy (XPS) and gas chromatography techniques. Additionally, it analyzes the reasons for gas changes before and after AE. Video observations combined with XPS analysis confirm that the bubble-free region formed during the electrolysis stage contains a complex high-resistance and insulating CFx film, which is the root cause of AE. CFx cannot continuously generate and cover the electrode surface, nor can it quickly trigger new AE again. The bubble layer covering the anode is a secondary phenomenon resulting from the deterioration of wettability caused by CFx. CFx plays a central role in impeding current flow, increasing cell voltage, and halting electrochemical activity in the affected areas. The composition of CFx can be altered by AE, leading to variations in back electromotive force(BEMF). Gas chromatography detection confirms that even after AE, the partial CFx film remains on the anode surface, where it forms a "memory effect" and decomposes at high temperatures to produce PFC. In industrial testing, the changes in anode gas composition before and after AE can be attributed to the CFx film formed on the anode surface and its degree of fluorination. This study suggests that targeting CFx layer formation, rather than bubble layer dynamics, could be a more effective strategy for reducing AE frequency, enhancing energy efficiency, and minimizing emissions in aluminum smelting. These insights offer a refined understanding of AE mechanisms for improving the sustainability and stability of industrial aluminum production processes.

The rapid dissolution of lithium iron phosphate (LFP) in fluoride provides a possibility for the recycling of spent lithium battery cathode materials through molten salt electrolysis. In this article, the dissolution behavior and mechanism of LFP in cryolite based molten salts are studied in detail. The dissolution behavior of LFP in NaF-AlF3 molten salt with a cryolite ratio (CR) of 1.8 was observed and recorded using a custom-made see-through cell. LFP has high solubility, and its tablets rapidly diffuse and dissolve in cryolite, causing the transparent molten salt to display an orange-yellow color indicative of Fe ions. The XRD results of the cooled molten salt indicate that LFP decomposes into AlPO4, LiNa2AlF6, and Fe2(PO4)F phases after dissolution in fluoride. Due to the instability of LFP, some ferrous elements are easily oxidized by oxygen, forming Li3Na3Fe2F12 and Fe2O3. The complex ion cluster structure of LFP at high temperatures was investigated using high-temperature Raman spectroscopy and quantum chemical calculations. Comparative analysis of high-temperature Raman spectra with the addition of LFP, Fe2O3, Li3PO4, and blank molten salt suggests that ion clusters containing Fe may include Fe2OF4, Fe2OF84- , and Fe2O2F3- , while ion clusters containing P may include PO2F, PO2F32- , POF4- , and POF52- .

This study uses three-dimensional finite element analysis to investigate the mechanical behavior of aluminum reduction cell cathodes subjected to breakage and repair, with a focus on preventing corrosion at the molten aluminum–cathode interface. Cathode breakage, driven by thermal expansion and corrosion, is a significant challenge in aluminum production, increasing maintenance costs and reducing lifespan. We analyze how breakage size, repair material properties, and graphitization levels affect stress distribution, deformation, and structural integrity. Our results show that graphitized cathodes reduce stress and deformation, improving stability. Additionally, the choice of repair material influences performance, with magnesia lowering stress and alumina sludge minimizing deformation. These findings offer a framework for selecting optimal repair materials, improving both efficiency and cost-effectiveness in aluminum reduction cells. By linking processing, structure, and properties, this study enhances understanding of repair processes and their impact on cathode durability.

This study presents a groundbreaking approach to modeling the Hall-Héroult cathode used in aluminum production. Our innovative model is grounded in a sophisticated porous electrode methodology coupled with state-of-the-art numerical simulations. This enables us to capture the intricate physicochemical processes within the system precisely, encompassing the migration, diffusion, and convection of ionic species. A key feature of our model is the integration of detailed electrochemical reaction kinetics at the microscale, providing a nuanced understanding of the internal dynamics of the cathode. Furthermore, we have incorporated a unique penalization method that rigorously enforces the principles of electroneutrality and ionic thermodynamic equilibrium, ensuring the model's fidelity to real-world phenomena. Computational simulation using the finite element method (FEM) serves as the backbone of our model, offering unparalleled accuracy and robustness. This has been confirmed through validation against empirical data, underlining the model's potential to significantly enhance both the efficiency and sustainability of aluminum production processes. • Development of an advanced porous electrode model for the Hall-Héroult process, utilizing numerical simulations42 to unravel complex physicochemical dynamics. • Incorporation of a novel penalization method for ensuring electroneutrality and thermodynamic equilibrium, enhancing 44 model accuracy. • Validation of the model against empirical data using FEM, demonstrating potential improvements in aluminum 46 production efficiency and sustainability.

Currently, there are two research focuses in aluminum electrolysis industry: process control based on individual anodic current and current modulation. These two novel technologies share the same core mechanisms: precise control of energy balance and heat balance of aluminum electrolysis cells, which is closely linked to the changes in inter-electrode processes when the anodic current changes. In this study, the correlation between inter-electrode characteristics, including characteristics of the aluminum-electrolyte interface and anode-electrolyte interface, and current density as well as anode–cathode distance during aluminum electrolysis were investigated using the scanning reference electrode method and a see-through electrolytic cell. The obtained variation patterns of inter-electrode voltage components may serve as a reference for current balance control and precise thermal balance management in the multi-anode aluminum electrolysis system. The see-through lab-scale electrolytic cell was used to statistically analyze size distribution of gas bubbles released from the bottoms of three types of anodes during aluminum electrolysis process, aiding in understanding the resistance of the gas bubble layer.

In view of the existing bottom cathode rare earth electrolytic cell has problems such as easy accumulation of gas bubbles at the bottom of the anode, poor overall fluidity of the electrolyte, and unstable electrolysis. In this study, the anode of the bottom cathode rare earth electrolytic cell was improved, and three-dimensional numerical simulation was carried out using the VOF model to investigate the effects of different structures of anodes on the gas-liquid flow characteristics in the electrolytic cell. The results clearly show that the use of slotted anodes can significantly promote the bubble discharge behavior and thus affect the overall flow pattern, in which the double slotted anode having the optimal effect.

Around the world the number of scrapped lithium-ion batteries (LIBs), which are rich in valuable elements worthy of recycling, is increasing. In this study, a method using cryolite-based electrolyte to recycle cathode materials from spent lithium nickel-cobalt-manganese oxide (LNCM) batteries is proposed. Firstly, a molten cryolite-based electrolyte is used to decompose the microstructure of spent LIB cathode material, releasing valuable lithium element into the electrolyte, which can be used in aluminum electrolysis industry. As nickelcobalt-manganese oxides have low solubilities in the cryolite-based electrolyte, they sink to the bottom of the molten electrolyte, which is then cooled down, forming an upper and lower layer. Lithium element can be quickly and conveniently separated from nickel-cobalt-manganese oxides, which are enriched in the lower layer of the electrolyte. Then, a hydrochloric acid solution is used to leach nickel-cobalt-manganese components from the lower layer of the cryolite-based electrolyte. The effects of acid concentration, liquid-solid ratio, and temperature on the leaching process are investigated through single factor experiments. The highest leaching rates of nickel, cobalt, and manganese elements reach 99.47%, 98.94%, and 98.27%, respectively. By using NaOH + NH3 center dot H2O to adjust the pH of the leaching solution, coprecipitation of nickel, cobalt, and manganese elements occur, producing a hydroxide precursor and resulting in recovery rates of over 99%. The recycled hydroxide precursor and new lithium source are then roasted to regenerate an LNCM811 cathode material, which has a layered microstructure and is assembled into a battery. Test results show that the battery has a discharge capacity of 200.8 mAh center dot g(-1) initially and 170.4 mAh center dot g(-1) after 100 cycles.

The corrosion of carbon cathodes in aluminum reduction cells operating at about 950°C significantly impacts the cells’ lifespan. This issue is exacerbated when graphitized cathodes are used. In this paper, a volume-of-fluid electric (VOF) model was developed to investigate the evolution of corrosion in graphitized cathodes and explore the influence of sludge and different cathode materials on corrosion. Cathode corrosion (CC) initiates at the ledge toes and spreads to the central channel. The maximum corrosion depth for graphitized cathodes reaches − 0.2 m at the ledge toes after 2100 days. The presence of a solid ledge effectively protects the cathode underneath. When sludge is introduced, it alters the local electric current density (ECD) distribution without significantly affecting the overall pattern. Sludge in the central channel protects the cathode beneath but slightly intensifies corrosion at the ledge toes, with a maximum corrosion depth of − 0.203 m, which reduces to − 0.196 m with sludge placed in the side channel. Transitioning to a semi-graphite cathode material reduces the maximum ECD at the ledge toes, resulting in a reduced maximum corrosion depth of − 0.187 m. This research provides valuable insights into the development of cathode corrosion in graphitized cathodes, highlighting the importance of cathode material selection.

The present study investigates the impact of erosion holes and subsequent repairs on the current distribution at the cathode-metal interface in aluminum reduction cells. The research focuses on examining the effects of erosion hole location, size, repair material properties, and the modification of cathode collector bars to optimize cathode repair strategies. The findings indicate that erosion holes lead to a localized concentration of current distribution in the metal at the erosion site. Notably, the maximum current density observed reaches 46125 A/m2, and the maximum horizontal current in the lateral cell direction at the cathode-metal interface increases with the depth of the erosion hole. Furthermore, the study reveals that the electrical conductivity of repair materials significantly influences current distribution. Materials with high resistivity behave similarly to insulators. Post-repair actions, including the cutting off of the collector bar, result in a noticeable reduction in current density, with a maximum horizontal current of 5860 A/m2. These results provide valuable insights into optimizing cathode repair processes, offering implications for enhancing aluminum reduction cells' efficiency, productivity, and cost-effectiveness.

AluminumAluminum–scandiumScandium master alloysMaster alloy are highly demanded products used to create multi-functional aluminum alloysAluminum alloys and composites. A high cost of Al-Sc master alloysMaster alloy stops the automotiveAutomotive industry from using them widely. This research investigates the possibility to produce Al-ScAl-Sc master alloysMaster alloy via electrolysisElectrolysis of the LiF-AlF3-Sc2O3 melt. The kinetic parameters of the aluminumAluminum and scandiumScandium electrowinningElectrowinning were studied by means of voltammetryVoltammetry, stationary polarization, and electrolysisElectrolysis tests. The apparent limiting current density for co-deposition of AluminumAluminum and ScandiumScandium on tungsten cathodeCathode was in the range from 1.28 to 1.97 A.cm–2 in the temperature range from 860 to 940 °C. Based on the electrochemical measurements, the parameters for galvanostatic electrolysisElectrolysis were selected and electrolysisElectrolysis tests were carried out to obtain Al-Sc master alloysMaster alloy. The microstructureMicrostructure of the obtained Al-Sc master alloysMaster alloy was studied. It was possible to obtain Al-Sc alloysAl-Sc alloys with the concentration of Sc 0.68 wt.%.

Aluminum electrolyte is a necessity for aluminum reduction cells; however, its stock is rising every year due to several factors, resulting in the accumulation of solid waste. Currently, it has become a favorable material for the resources of lithium, potassium, and fluoride. In this study, the calcification roasting–two-stage leaching process was introduced to extract lithium and potassium separately from aluminum electrolyte wastes, and the fluoride in the form of CaF2 was recycled. The separation behaviors of lithium and potassium under different conditions were investigated systematically. XRD and SEM–EDS were used to elucidate the phase evolution of the whole process. During calcification roasting-water leaching, the extraction efficiency of potassium was 98.7

An extraction and recovery method is developed based on leaching in Al3+ solution media, neutralization for fluoride precipitation, and lithium recovery to solve the accumulation problem of spent bottom sedimentation in aluminum reduction cells. The maximum extraction efficiencies of Li, Na, K, Ca, and F were 96.6 %, 98.1 %, 95.3 %, 30.9 %, and 91.7 %, respectively, under the optimized leaching conditions initial Al3+ concentration 1.0 mol/ L, liquid to solid ratio of 10:1, and leaching temperature 50 degrees C for 120 min. Upon analysis of the leaching residues and thermodynamics, the results demonstrated that the Al3+ solution could effectively dissolve fluoride in bottom sedimentation. After neutralization, the high recovery rate of F and acceptable purities of aluminum hydroxyfluoride hydrate product was obtained, which was used to produce aluminum fluoride. Lithium was recycled in the form of Li2CO3, which has a good purity. These results indicate that the process is a promising method for treating and utilizing spent bottom sedimentation in the aluminum reduction cell.

为了研究高铝粉煤灰盐酸法制备氧化铝工艺中部分杂质的去除工艺,除杂(Na,K,Ca,Mg)实验以某企业提供的低铁结晶氯化铝固体为原料,采用氯化铝低温热解-水解产物高压水洗方法,探究了焙烧过程中温度、时间对物料焙烧前后失重率的影响,采用正交实验研究了温度、时间、固液比对杂质去除率的影响,得到最佳实验条件为 140℃,20 min,1 ∶ 10,去除率达 90％以上.除Fe实验以自配含铁物料为原料,采用氯化铝低温热解-水解产物常压酸洗的方法,探究了焙烧过程中温度、时间对物料焙烧前后失重率、Fe氧化率及产物物相组成的影响,采用正交实验研究了时间、pH值、固液比对杂质去除率的影响,得到最佳实验条件为 120 min,pH=2,1 ∶ 10,此时Fe可部分去除,去除率在 50％以上.

As China's aluminum electrolysis industry expanded its production capacity, it produced a large amount of bath materials– cryolite based molten salt, which is not utilized fast enough and piled up in aluminum factories. It is of great significance to find a proper way to process the accumulated bath materials. Through the method introduced in this paper, aluminum fluoride can be produced from cryolite-based electrolyte and fed back into the aluminum electrolysis cell as a necessary additive. This method includes four steps: Calcination of crystalline aluminum nitrate with cryolite. Cryolite and crystalline aluminum nitrate are mixed and preheated. The main chemical reaction that occurs in this step will produce sodium nitrate (NaNO3), β-aluminum fluoride (β-AlF3), chiolite (Na5Al3F14) and the aluminum hydroxyfluoride hydrate (AHF). After calcination, the products are washed with water to separate soluble NaNO3 from the other products. The insoluble products obtained after washing are calcined with ammonium bifluoride to convert AHF into AlF3. The mixture obtained after preheating is then washed with an aqueous solution of aluminum salt (such as Al(NO3)3) to remove Na5Al3F14. Aluminum fluoride of high purity is obtained in the end. Calcination step is the most important among the four steps. The effects of calcination temperature (85 – 135 ℃) and molar ratio of crystalline aluminum nitrate to cryolite (0.5 – 2) on the conversion rate of cryolite were studied. The experimental results show that the highest conversion rate of cryolite can reach 97.03%. Through SEM, EDS, ICP and other analysis methods, it was found the final products contained more than 98.8 wt% aluminum fluoride and less than 0.4 wt% sodium, and the average particle size of aluminum fluoride is approximately 15 – 20 µm.

The present study employs a three-dimensional (3D) finite element method (FEM) to investigate erosion holes' impact and subsequent repairs on current distribution at the cathode-metal interface in aluminum reduction cells. The research objectives include examining the effects of erosion hole location, size, repair material properties, and cut-off cathode collector bar on current distribution to optimize cathode repair. The findings reveal that erosion holes induce local concentration of current distribution in the metal at the erosion site, with the maximum current density reaching 46125A/m2 and the maximum horizontal current at the cathode-metal interface increasing with erosion hole depth. Furthermore, the electrical conductivity of repair materials plays a significant role in current distribution, with high-resistivity materials behaving like insulators. After repairing and cutting off the collector bar, the current density significantly reduces, with a maximum horizontal current of 5860A/m2 and a decrease in a cathode voltage drop (CVD) to about 90mV. These results offer valuable insights for optimizing cathode repair and have significant implications for enhancing efficiency, productivity, and cost-effectiveness in aluminum reduction cells.

This paper focuses on preparation of Al–Zr master alloy and Al3Zr intermetallic compound. A method is proposed to obtain Al3Zr intermetallic compound from Al–Zr master alloy by leaching. The alloy was prepared by electrolysis in 2.4NaF–AlF3–5 wt

The electrochemical behavior of Zr(IV) on a molybdenum (Mo) electrode in a KF-AlF3-Al2O3-ZrO2 molten salt system was studied using cyclic voltammetry (CV), square-wave voltammetry (SWV) and chronopotentiometry (CP). The reduction process of Zr(IV) was found to follow a two-step, two-electron transfer mechanism: Zr(IV)+2e−→Zr(II) and Zr(II)+2e−→Zr(0). The reduction process was quasi-reversible and controlled by diffusion. Al-Zr alloys were successfully obtained on Mo and liquid aluminum electrodes by potentiostatic electrodeposition. Flower-like AlZr3 and irregular granular Al3Zr were obtained on the Mo electrode, which were mainly attributed to the electrochemical co-reduction of Al(III) and Zr(IV) in the molten salt. Three Al-Zr alloy phases, Al3Zr, Al3Zr2, and Al2Zr, were obtained on the liquid aluminum electrode, among which Al3Zr was dominant in the product, followed by Al3Zr2.