Aluminum Electrolysis Research Articles

Thermodynamic modeling of the processes of purification of primary aluminum from vanadium impurities

This article discusses the interaction of chemical elements in the three-component Al-V-B system. Vanadium reduces electrical conductivity in primary aluminum, which requires its reduction during aluminum electrolysis to values less than 0.02%. In order to reduce the concentration of vanadium impurities, thermodynamic calculations were carried out for the reactions of separation of the metallic phase of aluminum and impurities of vanadium intermetallic compounds through the use of a boron-containing flux. The calculation of thermodynamic parameters was carried out in HSC Chemistry 9.0. for AlB2 and VB2 compounds, the chemical reaction AlB2 + V = VB2 + Al within the operating temperatures of electrolysis and casting of primary aluminum of 650–950°С and the conditions of immersion of boron-containing flux into the melt to a ladle depth of 0.5, 1.0, 1.5 and 2 m, i.e. within the pressure range of 102.39–148.99 kPa. Thermodynamic analysis showed that the Gibbs energy (ΔGT) values in the entire range of operating temperatures of the electrolysis and casting of primary aluminum for VB2 are significantly lower than AlB2, therefore, they will be formed predominantly in this temperature range. The order of stability also suggests that vanadium can be easily removed from aluminum melts by adding boron. The results obtained allow us to conclude that chemical reactions of primary aluminum purification from vanadium impurities can occur due to boron additives.

Environmentally friendly recycling of energy storage functional materials from hazardous waste lithium-containing aluminum electrolytes

Low energy consumption and environmentally friendly extraction of high value-added elements from waste aluminum electrolytes are crucial for developing potential mineral resources and reducing environmental hazards. This study aims to propose a new method for resource utilization of retired aluminum electrolytes by combining NH4Cl with CaO-assisted low-temperature calcination. The leaching rates of Li and Na exceed 94.67 % and 98.12 %, respectively. The optimal conditions for roasting transformation were determined to be NH4Cl/CaO: 2, CaO/LWE@Al: 2, T: 550 ℃, t: 1 h. In the leaching stage, liquid–solid ratio: 5, T: 45 ℃, t: 1.0 h were proved to be the most suitable experimental condition. An evaluation was conducted on the economic benefits and creativity of the process. Finally, the regenerated LiCoO2 prepared from recycled Li2CO3 has been proven to have better electrochemical performance than commercial LiCoO2, demonstrating the feasibility of energy storage use. The economic accounting results indicate that this novel process demonstrates significant financial and environmental benefits through high-value lithium recovery. Compared with traditional concentrated acid roasting, this low-temperature roasting method has lower energy consumption, higher element conversion rate, lower corrosiveness, and lower operational difficulty (without the involvement of strong acids/bases). Therefore, this process has been proven to be a green, environmentally friendly, low energy consumption, and high value-added method for comprehensive utilization of waste electrolytes.

Preparation of β-AlF3 from fluorine-containing wastes: Leaching with fluorosilicic acid and crystallization

Numerous fluorine-containing hazardous solid wastes from the electrolytic aluminum process pose a serious threat to the ecosystem and human health. Currently, in the study of leaching on these wastes, Al and F are usually recovered by adjusting the pH of the leaching solution to precipitate aluminium hydroxyfluoride hydrate, which can be used to produce aluminum fluoride by roasting. However, aluminium hydroxyfluoride hydrate is often mingled with cryolite and other impurities when precipitating, which ultimately affects the purity of obtained aluminum fluoride by calcination. Interestingly, herein, the aluminium hydroxyfluoride hydrate residue was digested by fluorosilicic acid to effectively remove impurities and obtain a pure aluminum fluoride solution, from which the β-AlF3 product was produced by crystallization at a high-temperature. The results show that under the conditions of a temperature of 60 °C, time of 35 min, initial fluorine-aluminum molar ratio of 3:1 and initial concentration of fluorosilicic acid of 18 %, the gross yield of fluorine is 86.2 %, and the recovery of silicon in the form of SiO2 is 95.2 %. During crystallization, the product changes from AlF3·3H2O to β-AlF3 with the increase of temperature. Under the conditions of a crystallization temperature of 150 °C, an initial concentration of aluminum fluoride of 191.10 g/L and a stirring speed of 200 rpm, β-AlF3 of an average particle size of 43.22 μm was obtained by adding 5 % seed. The contents of Al and F in β-AlF3 products are 32.57 % and 61.49 % respectively, which meet the requirements of GB/T 4292–2017 (AF-0) about National Standards of China. According to DFT calculation, the β-AlF3 tends to adsorb two or three water molecules in its cavity structure, which explains why the crystallized β-AlF3 contains water of 5.10 % at 180 °C.

Study on dissociation mechanism and process of regenerated cryolite

Solid waste produced in the process of aluminum electrolysis is a substantial secondary source of fluorine, the fluoride electrolyte in aluminum electrolysis carbon slag accounts for about 75%. Regenerative cryolite, extracted from anode carbon residue through flotation or calcination, possesses a significant potential for fluorine recovery. The fluoride in regenerated cryolite is mainly insoluble, making its efficient dissociation crucial for utilizing the solid waste from aluminum electrolysis. This study uses regenerative cryolite and sodium carbonate to examine how roasting temperature, time, and the reagent-to-cryolite ratio (R/C) affect cryolite dissociation. Dissociation efficiency is measured using indices like baking loss, leaching loss, fluoride ion concentration in the leachate, and fluoride ion conversion rate. Optimal dissociation is achieved at 780-820°, 2.0-2.5 hours roasting time, and an R/C ratio of 1.0-1.2. Orthogonal experimental results highlight the predominant influence of R/C, with roasting temperature being the secondary factor and roasting time having the least impact. Notably, at 780°, 2.0 hours, and an R/C ratio of 1.2:1, the fluoride ion conversion rate reaches a peak of 94.23%. This allows for recycling and production of high-value fluoride products, benefiting both the environment and the economy.

Chemical leaching − Flexible precipitation for sustainable recovery of fluoride from aluminum electrolysis multisource hazardous waste

The spent carbon materials, including anode and cathode, generated from the aluminum electrolysis process contain high fluoride levels and are unavoidable hazardous solid wastes. Chemical leaching, as a promising strategy for large-scale industrial treatment, must address the challenge of secondary recovery of the solution. The co-recovery mechanism preparing various fluorides from acidic and alkaline fluoride-aluminum solutions was investigated. In this process, the F/Al molar ratio and the pH value of the substrate environment are critical factors for achieving synergistic recovery. Different acid and alkali adjustment modalities resulted in a diverse array of products. For instance, adding an alkali to an acid solution generated aluminum hydroxyfluoride hydrate, whereas the reverse sequence yielded cryolite. The precipitation mechanism of acidic solutions is characterized by a complex interplay of multiple substances, whereas the process in alkaline solutions is comparatively straightforward. Specifically, as the pH value increases, the sequence of phase transformations progresses through aluminum hydroxyfluoride hydrate, chiolite, aluminum hydroxide, and cryolite. In addition to pH, localized over-alkalinity was the primary factor contributing to impurity generation. The precipitation phase in an alkaline substrate environment is significantly better controlled. During this process, pure cryolite can be synthesized by adjusting the F/Al molar ratio to 6.0 using the neutralization solution. The synergistic synthesis of fluoride from both acidic and alkaline fluorine-containing solutions is not only feasible but also anticipated to effectively address the significant issues of water swelling and secondary solution recovery that are commonly encountered in industrial applications.

Corrosion behavior of magnesium-aluminum spinel in low-temperature electrolytes

Magnesium-aluminum spinel composite is a novel material designed for low-temperature aluminum electrolytic baths without a ledge profile. In this study, multi-doped magnesium-aluminum spinel was successfully prepared, and its corrosion behavior in low-temperature aluminum electrolytes was investigated. The multi-doped magnesium-aluminum spinel exhibited high relative density and homogeneous grain structure. The addition of lithium fluoride and potassium fluoride altered the physical structure of the aluminum electrolytes. A corundum phase was observed on the surface of the corroded multi-doped magnesium-aluminum spinel. The average corrosion depth and static corrosion rate were found to be related to the electrolyte composition and liquidus temperature. Notably, the corrosion rate decreased as the exposure time increased.

Quantitative Analysis of Complex Aluminum Electrolytes by X-Ray Fluorescence.

The future production of electrolytic aluminum will be characterized by low temperature, low carbon emissions, and environmental friendliness, which will result in a more complex electrolyte system. Real-time analysis of electrolytes can significantly enhance the efficiency of the electrolytic process. However, accurately analyzing the composition of complex aluminum electrolytes online has been a technical challenge. This research primarily focuses on determining the ingredient contents of complex aluminum electrolytes based on elemental concentrations measured using X-ray fluorescence (XRF) according to an applicable standard. Calibration curves were established based on 53 standard samples of complex aluminum electrolytes to establish relationships between XRF fluorescence intensity and real concentrations. Analysis conducted on industrial complex electrolytes confirms that these newly constructed curves effectively reduce relative errors to less than 3%. Additionally, a feasible solution is proposed for determining the cryolite ratio (CR) in aluminum electrolytes using XRF. Results demonstrate an average deviation as low as approximately 0.02, fully meeting industrial production requirements. This technique offers numerous benefits including rapid analysis, ease of use, and cost savings.

Clean and efficient lithium recovery from waste electrolytes via an environmentally short process

Low-cost and environmentally friendly recycling methods can incorporate strategic elements from discarded lithium-containing aluminum electrolytes (LiAE), which is crucial for alleviating resource shortages and environmental footprint. This study aims to develop a method for the comprehensive utilization of LiAE through low-temperature leaching of calcification. Unlike traditional high-temperature acidification roasting/ transformation processes (320–850 °C), the calcification leaching method only involves one-step leaching and avoids high heat energy consumption. Besides, this low-temperature calcification method chemically destroys the crystal structure of metal fluorides (Li, Na, K, etc.), ensuring a high leaching rate while ensuring an alkaline environment for lithium extraction from the leaching solution without additional alkaline neutralization. The lithium extraction rate exceeds 96 %, with high-purity Li2CO3 and NaOH prepared. The CaCO3 produced by decalcification has the potential for recycling (in the form of CaO after calcination). Meanwhile, the effects of operating temperature, mass ratio of CaO to LiAE, liquid–solid ratio, and leaching time on the calcium leaching reaction were systematically studied. The economic benefits and creative evaluation of the process were evaluated. Finally, the regenerated LCO prepared from recycled Li2CO3 has been proven to have good electrochemical performance compared to commercial LCO, demonstrating the feasibility of energy storage application. In summary, the comprehensive utilization of LiAE by the calcium leaching method has been proven to be feasible.

Evironmentally friendly comprehensive utilization of retired waste electrolytes of aluminum electrolysis by calcification leaching

Low energy consumption and environmentally friendly recycling methods can extract high-added value and high-demand elements from retired waste fluorinated aluminum electrolytes (RWE-Al), which is crucial for alleviating resource shortages and environmental hazards. This study aims to develop a method for recovering fluorine and aluminum from RWE-Al through calcium leaching transformation combined with acid leaching. Compared to the traditional high-temperature roasting transformation and high-concentration alkali-metal-salt leaching process, this new process only involves one step of low-temperature leaching, purification of fluorine, carbonization of excess calcium, and evaporation extraction of aluminum, avoiding the generation of high energy consumption and secondary hazardous waste (F-containing liquid/ residue). Fluorine and aluminum are effectively separated and purified with extraction rates exceeding 96%. The effects of leaching temperature, CaO addition coefficient, liquid–solid ratio, and leaching time on the leaching process were systematically studied. The effects of acid concentration, liquid–solid ratio, time, and temperature on the acid-leaching process were also investigated. In summary, the comprehensive utilization of RWE-Al by this new process has proved to be feasible.

A Coordinated Emergency Frequency Control Strategy Based on Output Regulation Approach for an Isolated Industrial Microgrid

Constructing isolated industrial microgrids with wind power is beneficial for improving the economic benefits of high-energy-consuming production, such as the electrolytic aluminum industry. Due to the specialized structure of industrial microgrids and the unique characteristics of the electrolytic aluminum load (EAL), the common emergency frequency control methods do not apply to the specific operational requirements of isolated industrial microgrids. Since EALs have huge regulating capacities and fast responses, this paper proposes a coordinated emergency frequency control scheme to deal with power disturbances in isolated industrial microgrids. The coordinated frequency control model of an industrial microgrid considering demand-side participation is derived. With the help of output regulation theory, a practical, feasible coordinated frequency controller is designed by introducing frequency deviation and power disturbance as feedback control signals. The proposed control scheme achieves reserve power distribution between the generation and demand sides. The microgrid frequency can be maintained within a permitted range in the presence of large power imbalances. The simulation results conducted in an actual isolated industrial microgrid validate the effectiveness and dynamic performance of the proposed control scheme.

Study on the wetting characteristics of liquid-Al/ SiO2 interface with Si content in liquid-Al

Aiming to address the issue of aluminum slag adhering to the interior walls of vacuum lifting ladles in the aluminum electrolysis industry, Molecular dynamics simulations are employed to investigate the wetting behavior and adhesion characteristics of aluminum droplets on silica surfaces. Our findings indicate that with an increase in silicon content within the droplets, wetting diminishes and complete wetting of the silica substrate by aluminum droplets is not achieved. The presence of silicon reduces both the melting point temperature and surface tension of aluminum droplets, leading to a significant increase in contact angle and a corresponding decrease in wettability. Moreover, an elevated silicon content within molten aluminum droplets substantially decreases their interaction energy with the substrate surface. The virtual wall method is applied to examine average separation force and work of separation for detaching aluminum droplets from the substrate, revealing that adhesion characteristics are predominantly governed by mutual adhesive forces. This paper presents an atomic-level analysis elucidating how silicon as an alloying element influences adhesion between liquid aluminum and solid surfaces.

Enhanced thermal stability and corrosion resistance of novel high-entropy spinels in cryolite-alumina molten salt applications

The development of spinel oxide materials with high thermal stability and corrosion resistance is essential for thermochemical reactions, particularly in aluminum electrolysis. This study presents the structural design of a family of high-entropy spinels (HESs) with a stable cubic spinel structure (<i>Fd3‾m</i>), specifically formulated as (Cr5/12 Mn5/12 Fe5/12 Co3/8 Y3/8)3O4, (Y = Ni, Cu, or Zn). Our results demonstrate that these high-entropy spinels significantly outperform conventional NiFe₂O₄, exhibiting superior corrosion resistance and thermal properties. Specifically, we observe lower high-temperature weight loss (0.24 %–0.74 % at 1000 °C), reduced thermal conductivity (1.810–2.258 W m−1 K−1 at room temperature), and lower thermal expansion coefficients (8.2 - 10.7 × 10−6 K−1 from 400 °C to 800 °C), while maintaining comparable specific heat capacities (0.51–0.55 J g−1 K−1). Corrosion testing at 800 °C for 20 h in a KF3-AlF3-Al2O3 molten salt environment shows a corrosion layer thickness of less than 150 μm, with minimal corrosion product formation. These findings not only advance our understanding of material properties under extreme conditions but also pave the way for the development of next-generation materials for thermochemical applications, specifically aimed at improving the efficiency of aluminum electrolysis.

Preparation of lithium-ion battery anode materials from graphitized spent carbon cathode derived from aluminum electrolysis

Preparation of lithium-ion battery anode materials from graphitized spent carbon cathode derived from aluminum electrolysis

Pre‐oxidized Recycled MgO–Steel Composite Material for Possible Application in Cryolitic Melts

Recycled MgO–C lining bricks and 316L stainless steel are used to manufacture composite material for inert anode samples for aluminum electrolysis cell. The microstructure of the composite material is characterized after preoxidation thermal treatments at 800, 900, and 1000 °C as well as in its sintered state. Preoxidation (PO) process is designed to enhance the material's corrosion resistance in molten cryolite environments by developing robust Fe–Mg–O, Fe–Cr–O‐ containing phases. Analytical techniques including scanning electron microscopy, electron backscatter diffraction, and energy dispersive X‐ray spectrometry are applied to characterize the phase formation, revealing the potential of these composites for use as inert anodes in aluminum electrolysis cells. PO at 800 °C is not sufficient to form adequate protective oxide layers. Whereas, PO at 900 and 1000 °C leads to the formation of protective oxide layers containing Mg–O Fe–O halite‐like solid solutions and (Cr,Fe)3O4 spinel phase. Sample, preoxidized at 1000 °C is sealed in Mg–Fe–O spinel phase.

Anode process on gold in KF–AlF&lt;sub&gt;3&lt;/sub&gt;–Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; melt

In the conditions of resource saving and carbon footprint reduction, the development of oxygen–releasing anodes for technologies of production of important metals and alloys by electrolysis of molten salts seems to be an urgent task. To determine the degree of “inertness” of a particular anode material, data on the kinetics and mechanism of the anode process on a material not subject to oxidation are required. In this connection, the anodic process on gold in the KF–AlF3–Al2O3 melt for electrolytic aluminum production was investigated by cyclic and square–wave voltammetry methods. The influence of temperature (715 and 775 оC) of the melt, the content of Al2O3 in it (from 0.1 to saturation), as well as the polarization rate (0.05–1 V/s) on the kinetics and some features of the mechanism of the investigated process was determined. An assumption is made that oxygen release on gold without dissolution of the substrate takes place in the region of overvoltages from 0 to 0.8 V. It is shown that the process includes the stages of electrochemical adsorption and desorption of the intermediate product, the first of which is limited by the diffusion of electroactive anions to the anode.

Enhanced thermal insulation and corrosion resistance in Ni-Fe cermet through incorporation of high-entropy spinel oxides

The influence of high-entropy spinel oxide (HESO) content on the microstructure, electrical conductivity, and high-temperature corrosion resistance of HESO/NiFe cermets were investigated. The results found that the addition of 10–30 wt% HESO enhanced sintering densification and thermal insulation, although it also resulted in reduced electrical conductivity. Isothermal oxidation tests conducted at 900 °C for 10 hours revealed that cermets containing 30–50 wt% HESO exhibited significantly lower weight gains (0.954–1.167 mg cm⁻²) and oxidation rate constants (0.1057–0.1525 mg² cm⁻⁴ h⁻¹). Furthermore, static corrosion tests in AlF₃-KF-Al₂O₃ molten salt demonstrated that HESO effectively mitigated the erosion of the metallic phase by the fluoride molten salt. This study holds significant potential by providing new insights for the design of inert anodes for aluminum electrolysis and exploring the practical applications of high-entropy oxide materials.

Methodological Review of Methods and Technology for Utilization of Spent Carbon Cathode in Aluminum Electrolysis

Spent carbon cathode (SCC) is one of the major hazardous solid wastes generated during the overhaul of electrolysis cells in the aluminum production process. SCC is not only rich in carbon resources but also contains soluble fluoride and cyanide, which gives it both recycling value and significant leaching toxicity. In this study, we explore the properties, emissions, and disposal strategies for SCC. Pyrometallurgy involves processes such as vacuum distillation, molten salt roasting, and high-temperature roasting. Hydrometallurgy describes various methods used to separate valuable components from leachate and prepare products. Collaborative disposal plays a positive role in treating SCC alongside other solid wastes. High-value utilization provides an approach to make full use of high-purity carbon-based materials. Finally, we analyze and summarize future prospects for the disposal of SCC. This study aims to contribute to the large-scale treatment and resource utilization of SCC while promoting circular economy principles and green development initiatives.

Lithium recovery from an alumina electrolysis slag leaching solution with strong acidity: Separation of lithium-ion and production of battery grade lithium carbonate

Lithium (Li) with excellent physicochemical properties is widely used in modern industries. However, the shortage and depletion of Li resources has hindered the sustainable economic development. Li recovery from waste resource was an effective approach, in particular, alumina electrolysis slag is exemplified as Li riched solid waste. In this work, separation of Li from alumina electrolysis slag leaching solution (AESLS) via solvent extraction using bis(2-ethylhexyl) hydrogen phosphate (P204) system was explored. Effects of saponification degree, phase ratio, and reaction time on metal ions impurities and Li extraction were investigated. Operational parameters including extraction, scrubbing, saponification and precipitation were optimized. Results showed that the extraction efficiencies of Mg2+, Ca2+, Al3+, Fe3+ and Li+ were 100 %, 100 %, 99.99 %, 100 % and 20.71 %, respectively, under the optimal single extraction conditions. The loss of Li after scrubbing of loaded organic phase using hydrochloric acid was as low as 1.59 %. The P204 extraction process was proved to be a thermodynamic process with spontaneous entropy increase, and the extraction order of metal ions was Al3+ > Fe3+ > Ca2+ > Mg2+ > Li+ according to the extraction driving force (ΔC); The solvent-extracted ligand mechanism was elucidated by infrared spectroscopy and nuclear magnetic resonance. Additionally, battery-grade lithium carbonate was produced. Our study paves a new way for recovery of Li in AESLS.

Simulation and Application of a New Type of Energy-Saving Steel Claw for Aluminum Electrolysis Cells

Aluminum electrolysis is a typical industry with high energy consumption, and the energy saving of aluminum electrolysis cells is conducive to the sustainable development of the ecological environment. The current density distribution on the steel claws of conventional aluminum electrolysis cells is uneven, resulting in a large amount of power loss. Therefore, a new type of current-equalized steel claw (CESC) is designed in this paper. The ANSYS simulation study shows that the CESC can achieve a more uniform current density distribution and reduce the voltage drop by about 36 mV compared with the traditional steel claw (TSC). In addition, the use of CESC optimizes the temperature distribution of the steel claws and reduces the risk of cracking and deformation. The results of the industrial application tests are highly consistent with the simulation results, confirming the accuracy of the simulation results. The economic benefit analysis shows that using CESC saves 114.1 kWh of electricity per ton of aluminum produced. If this technology can be promoted throughout China, it is expected to save up to 4.75 billion kWh of electricity annually. The development of CESC is promising and of great significance for improving the overall technical level of the aluminum electrolysis industry.

Fully-Coupled Electric-Thermal-Flow Modeling and Investigation of Dynamic Thermal-Ledge Behavior in Aluminum Electrolysis Cell

Aluminum electrolysis cells (AECs) require effective thermal regulation to operate flexibly alongside renewable energy sources. Prior to implementing thermal regulation strategies, it is essential to predict the dynamic variations in the thermal field and ledge characteristics of a full-scale cell. This study introduces a transient electro-thermal-flow coupling model for a full-scale AEC, aimed at investigating the interactions between ledge distribution and various operational fields, including thermal, electric, and flow fields. The model facilitates the calculation and assessment of the dynamic properties of the ledge and thermal balance under ±15% flexible current variations. Results indicate that during a current increase, ledge melting predominantly occurs in the electrolyte layer, while ledge solidification is primarily observed in the metal layer during a current reduction. Regions with a thicker ledge and faster velocity tend to melt more during current increases and are less likely to return to their original shape and thickness during current reductions, complicating the rapid restoration of thermal equilibrium. To achieve uniform ledge distribution and real-time adaptation to flexible current variations, it is recommended to install distributed cooling devices on the sides of the AEC to enable differential ledge regulation at various locations.