Aluminum Electrolysis Research Articles

Feasibility of reuse of modified electrolytic aluminium spent refractory material in asphalt and assessment of its environmental stability

The central toxic part of the aluminum industry's overhaul slag, as high value-added recycling of spent refractory material (SRM), contributes to environmental protection and resource recycling. Herein, a “bayberry"-like hexamethyldisilazane-tannic acid-SRM (HMDS-TA-SRM) modifier was prepared by a simultaneous “precipitation-TA wrapping” reaction design and a secondary grafting reaction with HMDS. The design allows the material to be treated with a concentration of F− (5.93 mg/L) that meets the Chinese primary wastewater discharge standard (10 mg/L). HMDS-TA-SRM with hydrophobic (water contact angle = 104.3°) nano-sized microsphere stacking surface exhibited good interfacial interaction with the matrix bitumen. At 64 °C and 0.1 kPa and 3.2 kPa pressures, the deformation recovery capacity of the HMDS-TA modified asphalt was increased by 34.9% and 45.6% compared to that of the pristine SBS-modified asphalt, respectively. At the same time, the double wrapping of the modified film and bitumen significantly improved the sequestration capacity of hazardous substances, with a cumulative F− exudation of only 0.45% after 180 d of immersion. Attributed to the green, cost-effective and efficient modification method, the new SRM-asphalt system could be deemed of great promise for the safe application of SRM.

Population-based discrete state transition algorithm with decomposition and knowledge guidance applied to electrolytic cell maintenance decision

With continuous scale expansion and higher safety requirements in modern aluminum electrolysis, it is more and more necessary to realize an intelligent decision-making for shutting-down and running of aluminum reduction cells (SRARC). However, this realization needs to solve a special single-objective constrained integer optimization problem (SCIOP), where the key challenge is a high requirement for the constraint-handling ability. In this paper, based on a high-scalability intelligent optimization algorithm called discrete state transition algorithm (DSTA), a population-based DSTA with decomposition and knowledge guidance (PDSTA/D-S) is proposed. This PDSTA/D-S improves the constraint-handling ability of DSTA from three aspects. Firstly, a hybrid framework combining DSTA with genetic algorithm is proposed. Secondly, a decomposition-based multi-objective optimization for constrained problems with uniformly-angled weighted sum vector is proposed. Thirdly, the manual decision-making is transferred to a knowledge-based transformation operator of DSTA. Therefore, a high-level performance of decision-making for SRARC can be obtained. The related experiments on a SRARC which is built from the practical production have demonstrated that the proposed PDSTA/D-S not only makes an effective improvement of DSTA from three aspects, but also has a more advanced performance compared with other existing high-performance intelligent optimization algorithms.

Numerical simulation study of the effect of anodic bubble behavior in aluminum electrolysis cell

During the aluminum electrolysis process aluminum is produced at the cathode and CO2 gas bubbles are generated on the anode and released. The bubbles reduce the active surface area of the anode, which increases energy consumption. They also cause the liquid aluminum to fluctuate and oxidize again. The study of anodic bubble behavior is important to reduce power consumption and improve current efficiency. In this paper, the phase field, laminar flow and tertiary current distribution modules in COMSOL Multiphysics are applied to simulate the growth and motion patterns of anodic bubble in the electrolytic cell to visualize and analyze the behavior of anode bubble.

Superheat Degree Recognition of Aluminum Electrolysis Cell Using Unbalance Double Hierarchy Hesitant Linguistic Petri Nets

Superheat degree is a core technical parameter and management index of aluminum electrolysis cell. However, the exiting methods have limited abilities when applied to superheat degree recognition of aluminum electrolysis cell (SDRAEC). In addition, the important hesitant degree is ignored in the unbalance double hierarchy linguistic term set. To address these issues, an unbalance double hierarchy hesitant linguistic Petri net model and extended TOPSIS is proposed for SDRAEC. In this model, the coupling relationships among variables is made to be explicit knowledge, and the unbalance double hierarchy hesitant linguistic term set is proposed to represent the value of knowledge parameter. The relative entropy is introduced to enhance the performance of extended TOPSIS. Moreover, hybrid averaging unbalance double hierarchy hesitant linguistic term set concurrent reasoning algorithm is proposed to improve reasoning efficiency. Finally, thermal analysis experiments conducted in a real-world aluminum electrolysis plant are used to demonstrate the effectiveness of the proposed method. Compared with other methods, the accuracy of SDRAEC has been increased to 89.00%.

Study on the effect of an ultrasound assisted reaction on the crystallization properties of recovered cryolite.

During the treatment of spent cathode carbon from electrolytic aluminum, a large amount of fluoride containing wastewater is generated. By adding different sodium source and aluminum source reagents, under the conditions of different addition order, pH, temperature and time, the effects of conventional static reaction, stirring reaction and ultrasonic assisted reaction on the crystallization properties of recovered cryolite were investigated. The results showed that under the optimum reaction conditions (sodium source: NaCl, aluminum source: AlCl3, the molar ratio of AlCl3 to NaCl is 1 : 3, addition order: first addition of AlCl3 and then NaCl, pH is 8.57, time is 40 min, temperature at room temperature), the removal efficiency of fluoride ions was the highest when ultrasound assisted treatment was used. The cryolite products with ultrasound assisted crystallization and without ultrasound assisted crystallization were characterized using SEM and TEM. The results showed that the crystal particles obtained by ultrasound assisted crystallization were relatively concentrated, and the morphology was regular and the surface was smooth. Design Expert orthogonal software was used to design the response surface test, it was found that ultrasound time has the most significant impact on the content of recovered cryolite among single factors, and the interaction between ultrasound frequency and ultrasound power, ultrasound power and ultrasound time was highly significant among multiple factors.

Analysis of anode current distribution in aluminum electrolysis cell based on equivalent circuit numerical simulation

The development of modern industrial aluminum reduction cell towards the direction of higher line current and more anodes. The distribution of anode current and the stability of the fluid in reduction cell are directly affected by the busbar configuration. In this paper, a simulation model of the multi-loop equivalent circuit of aluminum electrolysis cell was established by using MATLAB/Simulink, and the distribution characteristics of anode current under three different current risers were analyzed. The results show that with the increase of the number of terminals, the cell voltage decreases and anode current distribution is more uniform. The anode current is positively correlated with the distance from the terminal and the current of the nearest column busbar.

Modelling of the Aluminium Electrolysis Process: Feeding and Dissolution of Alumina Particles

The present numerical study describes the feeding and dissolution behaviour of alumina particles in the electrolytic bath of industrial Hall-Héroult cells. The dissolution rate is controlled by thermal and chemical conditions as well as the transport and mixing of particles in the electrolyte. The model presented is implemented in the OpenFOAM® framework using the Lagrangian approach for the coupling of continuous (electrolyte and liquid aluminium) and dispersed phase (alumina particles). The model solves the particle motion, mass transfer from dispersed to continuous phase, the energy equation, and the transport of dissolved concentration. Moreover, the influence of thermal conditions and turbulent mixing due to gas bubbles arising under the anodes is considered by the model. The velocity field is adopted from a previously executed magnetohydrodynamic (MHD) simulation. With the help of the model developed, various studies are carried out. The focus corresponding to the increased flexibility of electric power consumption is on the thermal behaviour during cold operating conditions of the electrolysis cell. It is important to ensure that all the alumina feed is dissolved. The sinking of undissolved alumina to the bottom of the cell must be prevented as it impairs cell efficiency. The results show that the dissolution rate and total dissolution time depend on the bath temperature. A greater effect is observed for the bath superheat defined by the difference of bath temperature and liquidus temperature of the bath. Furthermore, the influence of process parameters like grain size and feeding masses are studied in detail.

Separation and conversion of fluoride salts in aluminum electrolysis flue gas by one-step ammonia purification

Separation and conversion of fluoride salts in aluminum electrolysis flue gas by one-step ammonia purification

Study on ultrasonic leaching and recovery of fluoride from spent cathode carbon of aluminum electrolysis.

Under the assistance of ultrasound, the fluoride in the spent cathode carbon of aluminum electrolysis was recovered by the process of washing first and then leaching. The effects of time, temperature, liquid-solid ratio, ultrasonic power, alkali amount and acid concentration on the leaching rate of fluoride were investigated. The useful components in the leaching solution were recovered by evaporation crystallization and cryolite regeneration. The tests of X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy combined with energy dispersive spectroscopy (SEM-EDS) showed that under the optimal experimental conditions (water washing: 50 s, 3 : 1, 420 W; alkaline leaching: alkali amount 1 g, 60 min, 70 °C, 7 : 1, 480 W; acid leaching: acid concentration 0.6 mol L-1, 60 min, 5 : 1, 70 °C, 480 W), the leaching rate of fluoride was 82.99%, and the fluoride contents recovered in the water washing and leaching processes are 94.67% and 95%, respectively. There is no solid waste and waste water in the whole experimental process.

Evaluation of the Performance of Low-Temperature Naf-Kf-Alf3 Electrolytes for Aluminium Electrolysis Using Vertical Inert Cu-Ni-Fe Alloy Anodes

Evaluation of the Performance of Low-Temperature Naf-Kf-Alf3 Electrolytes for Aluminium Electrolysis Using Vertical Inert Cu-Ni-Fe Alloy Anodes

Efficient CF4 adsorption on porous carbon derived from polyaniline

BackgroundAs a significant greenhouse gas emitted in large quantities from the electrolytic aluminum and semiconductor industries, tetrafluoromethane (CF4) has an extremely high global warming potential (GWP) and a fairly long atmospheric lifetime. MethodsIn this study, porous carbon was prepared via a thermochemical process involving the carbonization and K2CO3 activation of precursor polyaniline (PANI). The activation temperature (600–800 ℃) and K2CO3/carbonized PANI mass ratio (1–4) had significant influences on the porous structure and CF4 uptake of the PANI-derived porous carbon (PDC). Significant findingsThe prepared PDC-3-800 adsorbent exhibited the largest specific surface area (2268 m2 g−1) and highest pore volume (1.48 cm3 g−1), whereas PDC-2-700 adsorbent demonstrated the highest CF4 uptake of up to 2.16 mmol g−1 at 25 ℃ and 1 bar. Notably, CF4 uptake was predominantly dependent on the presence of narrow micropores with diameters below 0.9 nm at atmospheric pressure. The CF4 adsorption isotherms were well fitted by the dual-site Langmuir (DSL) model. Moreover, the isosteric heat of adsorption and CF4/N2 selectivity of PDCs were investigated. These experimental results demonstrate that PDCs with high CF4 adsorption capacity, excellent CF4/N2 selectivity, and good recyclability, have immense potential for practical CF4 capture applications.

Aluminum-Based Fuels as Energy Carriers for Controllable Power and Hydrogen Generation—A Review

Metallic aluminum is widely used in propellants, energy-containing materials, and batteries due to its high energy density. In addition to burning in the air, aluminum can react with water to generate hydrogen. Aluminum is carbon-free and the solid-phase products can be recycled easily after the reaction. Micron aluminum powder is stable in the air and enables global trade. Aluminum metal is considered to be a viable recyclable carrier for clean energy. Based on the reaction characteristics of aluminum fuel in air and water, this work summarizes the energy conversion system of aluminum fuel, the combustion characteristics of aluminum, and the recycling of aluminum. The conversion path and application direction of electric energy and chemistry in the aluminum energy conversion system are described. The reaction properties of aluminum in the air are described, as well as the mode of activation and the effects of the aluminum-water reaction. In situ hydrogen production is achievable through the aluminum-water reaction. The development of low-carbon and energy-saving electrolytic aluminum technology is introduced. The work also analyzes the current difficulties and development directions for the large-scale application of aluminum fuel energy storage technology. The development of energy storage technology based on aluminum is conducive to transforming the energy structure.

The quaternary fluoride LiNaCa2Al2F12 in aluminum electrolytes: synthesis, structure, thermal stability

The quaternary fluoride phase LiNaCa2Al2F12 has been obtained by quenching a melt consisting of a stoichiometric mixture of the corresponding simple fluorides at a temperature of 850 ​°C in air. Previously, the phase has been observed by authors as unknown impurity in cooled samples of aluminum production electrolyte. It has been established that the phase does not form solid solution regions with the initial components. The crystal structure has been solved by X-ray powder diffraction technique: a ​= ​5.053(2) Å, c ​= ​17.546(7) Å, V ​= ​448.02 ​Å3, Z ​= ​2, SG. P-421c. Calcium cations and isolated octahedral [AlF6]3- anions form mixed layers, which are separated by flat nets of lithium and sodium cations. Lithium cations occupy positions with a tetrahedral environment of fluorine atoms. The short interatomic distance Li⋯F 1.89 ​Å makes the position unavailable for other cations. Thermal decomposition has been studied by high-temperature X-ray diffraction and thermal analysis. The LiNaCa2Al2F12 phase is stable up to 600 ​°C in air, and then decomposes in the solid state. The final products of decomposition are fluorite and aluminum oxides and aluminates. It has been concluded that the phase was metastable and it was the result of rapid cooling of the melt. The stability at low temperatures has explained by high potential barrier for transformation. The formation of LiNaCa2Al2F12 indicates the presence in the melt with fluorine deficiency of isolated [AlF6]3- anions, the concentration of which increases due to the existence of coordinated Li+-[AlF6]3- pairs in the melt. It is suggested that the presence of [AlF6]3- anions in acidic electrolyte melts ensures the dissolution of alumina.

Extremely high corrosion resistance of ZnxNi1–xCr2O4 spinel as sidewalls in the aluminum electrolyte

The sidewall material is a key component in new electrolytic cell with an inert electrode for the aluminum electrolysis industry. The continuous development of novel sidewall materials with excellent corrosion resistance in molten salts electrolyte is an important topic. Herein, a new system of sidewall material, spinel structured ZnxNi1–xCr2O4 (x = 0 – 1), is prepared by solid-phase reaction and the corrosion-resistance enhancement is investigated. The results prove that Zn2+ plays two roles in the ZnxNi1–xCr2O4 spinels. Firstly, Zn2+ tunes the surface energies of spinels resulting in the octahedral grains, which suppresses the cation diffusion in the corrosion process. Secondly, Zn2+ stabilizes the Cr3+ in the spinels. As a result, the Zn0.5Ni0.5Cr2O4 spinel displays an extremely low corrosion rate ∼0.007 cm·a–1 in NaF-KF-AlF3 bath at 800 °C comparing with other sidewall materials. The as-obtained spinel shows great potential as a novel sidewall material for the new electrolytic cell.

Molecular Dynamics Simulation of the Effect of Zr and b on Cryolite Molten Salt System 78%Na<sub>3</sub>AlF<sub>6</sub>-9.5%AlF<sub>3</sub>-5.0%CaF<sub>2</sub>-7.5%Al<sub>2</sub>O<sub>3</sub>

The analysis of high temperature physical and chemical properties of molten salt system of aluminum electrolysis has guiding significance for practical production In this paper, the molecular dynamics calculation method was used to simulate the physical and chemical properties of 78%Na3AlF6-9.5%AlF3-5.0%CaF2-7.5%Al2O3 molten salt electrolyte system with Zr and B as additives at 1200K and standard atmospheric pressure. The effects of Zr and B elements on the radial distribution function, coordination number, diffusion coefficient, viscosity, and conductivity of electrolyte system were discussed in detail. The simulation results showed that Zr4+ weakened the connection between Al3+, while the addition of B3+ enhanced the interaction between Al3+, Na+, and F-. In the electrolyte system without impurities, the order of self-diffusion coefficient is Na+ > O2- > F- > Ca2+ > Al3+. And the addition of Zr4+ is conducive to the diffusion of ions in the system, while the addition of B3+ is not conducive to the diffusion of ions in the system. What’s more, the addition of Zr improves the conductivity of the system, while the addition of B reduces the conductivity of the system.

Dimensional reduction of a 3D thermoelectric model to create a reliable and time-efficient 2D model representing an aluminum electrolysis cell

In order to optimize the use of their assets, aluminum smelters aim at increasing the line current. In addition, the fluctuations of the energy market push the industry to exploit power modulation strategies. These variable operating conditions directly affect the thickness of the protective layer (ledge) inside the electrolysis cell. Continuous monitoring of the energy balance is therefore of utmost importance, although physical measurements are difficult due to the hostile environment. The 3D thermoelectric slice digital model is the most frequently used to solve the energy balance, but its high computation time prevents it from being used in a control system. For the first time, the creation of a novel 2D model from an existing 3D slice model is proposed for online thermal diagnosis and process control purposes. The creation starts with a detailed dimensional reduction protocol, which is a significant industrial contribution since it can be applied to any industries relying on 3D physical models. The rigorous methodology developed involves the identification of adjustable parameters that are inserted in the 2D model to minimize deviations caused by physical differences between models and ensure its reliability. Once calibrated, the 2D model is tested using a ± 5% input current variation. The results show minor differences (below 1%) between 3D and 2D models for the predicted behavior of the heat losses distribution and generated heat distribution. Side ledge profiles are very close in both models, the largest difference (1.8 cm) being in an acceptable range for this key operational parameter. During all simulations, the 2D model computing time was 40 to 60 times faster than the 3D model. With the 4.0 era, this is a reliable and time-efficient tool for industries wishing to turn to digital twins.

A Method of Optimizing Cell Voltage Based on STA-LSSVM Model

It is challenging to control and optimize the aluminum electrolysis process due to its non-linearity and high energy consumption. Reducing the cell voltage is crucial for energy consumption reduction. This paper presents an intelligent method of predicting and optimizing cell voltage based on the evaluation of modeling the comprehensive cell state. Firstly, the Savitzky–Golay filtering algorithm(SGFA) is adopted to denoise the sample data to improve the accuracy of the experimental model. Due to the influencing factors of the cell state, a comprehensive evaluation model of the cell state is established. Secondly, the model of the least squares supports vector machine (LSSVM) is proposed to predict the cell voltage. In order to improve the accuracy of the model, the state transition algorithm (STA) is employed to optimize the structure parameters of the model. Thirdly, the optimization and control model of the cell voltage is developed by an analysis of the technical conditions. Then, the STA is used to realize the optimization of the front model. Finally, the actual data were applied to the experiments of the above method, and the proposed STA was compared with other methods. The results of experiments show that this method is efficient and satisfactory. The optimization value of average cell voltage based on the STA-LSSVM is 3.8165v, and it can be used to guide process operation. The DC power consumption is 11,971 KW·h per tonne of aluminum, with a reduction in power consumption of 373 KW·h. This result guarantees the reduction of aluminum electrolysis energy consumption.

Environmentally Friendly Strategy for Treating In Situ Leaching Solutions of Ion-Adsorption Type Yttrium-Rich Heavy Rare-Earth Ore by a Bubble-Supported Organic Liquid Membrane

A novel environmentally friendly strategy based upon bubble-supported organic liquid membrane (BSOLM) extraction using saponified naphthenic acid as extractant is proposed in the present work for treating the in situ leaching solutions of ion-adsorption type yttrium-rich heavy rare-earth ores in South China. It was revealed that selectively preferential separation of non-yttrium rare earths from yttrium can be achieved, while the electrolyte aluminum salt can be retained in the raffinates for subsequent return as the leaching reagent for performing in situ leaching of ion-adsorption type heavy rare-earth ores. The BSOLM extraction exhibits an obvious advantage over conventional extraction in promoting the competitive mass transfer and separation of coexisting rare earths from yttrium and other non-rare-earth impurity ions. Using erbium as a representative of heavy rare earths, it was found that the differences in diffusive mass transfer rate of Er3+, Y3+, and Al3+ ions in the boundary layer of laminar flow near the surface of the extractant liquid membrane result in their enhanced separation. The BSOLM extraction prevents the convective disturbance along the normal vertical direction of the interface due to the irregular movement of dispersed oil droplets in the conventional extraction and therefore inhibit the co-extraction of Al3+ ions. The effects of Al3+ ion concentrations in aqueous feed solutions, initial aqueous pHs, concentrations of naphthenic acid, and its saponification degree on the separation efficiency were investigated. Experimental results confirmed that competitive hydration and adsorption of Al3+ ions at the interface play an important role in increasing the difference in concentration distribution of Er3+ and Y3+ ions near the interface during BSOLM extraction; therefore, the separation of rare earths from yttrium can be controllable.

Plasma electrolytic oxidation behavior and corrosion resistance of brass in aluminate electrolyte containing NaH2PO4 or Na2SiO3

Plasma electrolytic oxidation (PEO) of brass was carried out in aluminate electrolytes with the addition of NaH2PO4 (S1) and Na2SiO3 (S2), respectively, with the aim to investigate the effect of additives on the coating formation and corrosion resistance. For the PEO in S1 electrolyte, a mixed layer of AlPO4 and Al2O3 is formed at the initial stage, which leads to fast plasma discharges and formation of black coatings with the compositions of Al2O3, CuO, Cu2O and ZnO. However, in S2 electrolyte, plasma discharges are delayed and the coatings show a reddish color due to more Cu2O. Mott-Schottky tests show that the S1 coatings are p-type semiconductors; while the S2 coatings can be adjusted between n-type and p-type. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests show that the PEO treatment can significantly improve the corrosion resistance of brass, with protection efficiency up to 91.50% and the largest charge transfer resistance of 59.95 kΩ·cm2 for the S1 coating.

A demand side controller of electrolytic aluminum industrial microgrids considering wind power fluctuations

Direct wind power purchase for large industrial users is a meaningful way to improve wind power consumption and decrease industrial production costs. Short-term wind power fluctuations may lead to large-scale wind power curtailment problems. To promote use of wind energy, a demand side control method is proposed based on output regulator theory for a grid-connected industrial microgrid with electrolytic aluminum loads to continuously track and respond to wind power fluctuations. The control model of the EALs and the dominant frequencies of the wind power fluctuation signals are analyzed and incorporated into the demand side control plant. The feedback control signals with active power deviations on the tie-line are used to design the demand side controller. Simulations are conducted for an actual industrial microgrid to validate the feasibility and effectiveness of the proposed method. The results demonstrate that the proposed controller based on output regulator theory is able to effectively track wind power fluctuations.