Alumina Production Process Research Articles

Technology of production of aluminosilicate refractories for units processing fluorinated waste

The aluminium production process through the electrolysis of cryolite-alumina melts involves a series of interconnected, sequential, and parallel technological operations, each defined by a specific level of engineering and technological advancement. The development of the modern aluminum industry is closely tied to the adoption of resource-efficient and environmentally friendly technologies, which focus on recycling secondary materials and industrial waste. Fluorinated carbon-based materials release fluorine into the gas phase at relatively low temperatures when heated, and in thermal units processing fluorinated waste, this fluorine, along with alkali metals, will remain in the gas phase. To enhance the durability of furnace linings against the corrosive atmosphere, refractories with the highest possible density (low porosity) and a high concentration of mullite in the matrix (the finely ground component of the batch) are required. These properties can only be achieved in refractory products produced by the semi-dry pressing method, which ensures high grain packing density and leads to the formation of a ceramic mullite bond after firing.

Development of sustainable aluminum alloy‑tungsten carbide hybrid composites using industrial waste - An experimental analysis

The research article focuses on the development of aluminum alloy 6061 sustainable composites with the utilization of industrial waste through the use of the stir casting process. Recycling industrial waste is essential for reducing environmental impact. Thus, the red mud waste came from the aluminum production process, which was considered for producing sustainable metal matrix composites (MMCs). Also, tungsten carbide (WC) microparticles have been used to develop hybrid aluminum composite materials. The concentrations of red mud and tungsten carbide were 2 wt%, 4 wt%, and 6 wt%, respectively, and were used to achieve the desired strength performance of aluminum metal matrix composites. The elemental and bonding analyses of hybrid composites were analyzed using X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) analysis. Mechanical characterizations of aluminum hybrid sustainable composites were also investigated, including tensile, compression, and microhardness testing. The results show that increasing reinforcement by up to 4 wt% increases the mechanical strength of aluminum alloy composites. The tensile, compression, and microhardness of metal matrix composites are increased by 25.24 %, 40.2 %, and 20.6 %, respectively, as compared to the aluminum alloy 6061 alloy. The surface morphology of metal matrix composites was analyzed by utilizing Field emission scanning electron microscopy. The proposed sustainable aluminum composites have the potential to develop structural and automotive components due to their higher strength-to-weight ratio.

Impact of red mud on soil properties and revegetation species growth in bauxite mining land reclamation

Bauxite mining, a key aluminum production process, can cause environmental degradation, soil erosion, and biodiversity loss. Reclamation measures like reforestation and water management can restore balance. Red mud, a by-product of alumina production, can enhance soil fertility and plant growth in post-bauxite mining reclamation areas. Its alkalinity and mineral composition reduce reliance on synthetic fertilizers, promoting sustainable soil management and addressing environmental challenges. This study aimed to examine the impact of red mud on soil characteristics and the growth of plants in areas during bauxite mining land reclamation. This study was conducted in the post-reclamation area of bauxite mining in West Kalimantan. The experiment involved two treatments: red mud application and a species of revegetation plant. Plant species consist of the plants Embeng, Forest Guana, Johar, and Rambutan. The study used a randomized block design with 24 experimental units. The parameters measured in the study included pH, organic carbon, nitrogen, phosphorus, exchangeable cations, cation exchange capacity, and base saturation, while growth parameters included a high percentage of plant growth and percentages of increased stem diameter. The findings showed that adding red mud to the planting hole increased soil pH and base saturation, improved nutrient availability, and enhanced plant growth in the areas post-mining bauxite at PT Antam, UBPB West Kalimantan. The Embeng Plant is highly regarded as a suitable plant species for re-vegetating areas after bauxite mining.

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.

Mechanism of ultrasonic-enhanced leaching for separating organic impurities from the surface of bauxite and H2O2 oxidation-CaO precipitation for purifying the leaching solution

The existence of organic impurities in bauxite significantly hampers the regular production of alumina. This study proposes a low-temperature ultrasonic-enhanced alkali leaching to directly separate organic impurities from bauxite, and purify the leaching solution through H2O2 oxidation and CaO precipitation. Under the optimal conditions of 550 W ultrasonic power, 80 °C, 60 min, and 200 g/L NaOH concentration, the leaching rate of organic carbon in bauxite is 91.02 %, which is 19.01 % higher than conventional alkali leaching, and the organic carbon content in the bauxite decreased from 0.59 % to 0.06 % after leaching. Kinetic studies indicate that the limiting factors of the leaching rate vary under different leaching temperatures and leaching times. Characterization of bauxite before and after leaching using various detection techniques demonstrates the effective separation of organic impurities while basically no loss of alumina and increasing the alumina to silica ratio to 34.13. Subsequently, H2O2 and CaO are introduced to the leaching solution with 20 % and 800 mL/g, respectively. The oxidation process under 550 W ultrasonic power at 90 °C for 60 min achieves an 71.35 % removal rate of organic carbon. GC-MS analysis confirms the successful removal of the main organic substances in the leaching solution, while XRD analysis of the oxidation residue indicates that organic substances are ultimately removed as CaC2O4·H2O and CaCO3. Additionally, a proposed free radical reaction mechanism of H2O2 oxidizing organic substances is discussed. In conclusion, this study providing valuable insights for the removal of organic pollutants in the alumina production process.

Evaluation of fluoride emissions and pollution from an electrolytic aluminum plant located in Yunnan province

The monitoring and evaluation of fluoride pollution are essentially important to make sure that concentrations do not exceed threshold limit, especially for surrounding atmosphere and soil, which are located close to the emission source. This study aimed to describe the atmospheric HF and edaphic fluoride distribution from an electrolytic aluminum plant located in Yunnan province, on which the effects of meteorological conditions, time, and topography were explored. Meanwhile, six types of solid waste genereted from different electrolytic aluminum process nodes were characterized to analyze the fluoride content and formation characteristics. The results showed that fluoride in solid waste mainly existed in the form of Na3AlF6, AlF3, CaF2, and SiF4. Spent electrolytes, carbon residue, and workshop dust are critical contributors to fluoride emissions in the primary aluminum production process, and the fluorine content is 17.14 %, 33.30 %, and 31.34 %, respectively. Unorganized emissions from electrolytic aluminum plants and solid waste generation are the primary sources of fluoride in the environment, among which the edaphic fluoride content increases most at the sampling sites S1 and S7. In addition, the atmospheric HF concentration showed significant correlations with wind speed, varying wildly from March to September, with daily average and hourly maximum HF concentrations of 4.32 μg/m3 and 9.0 μg/m3, respectively. The results of the study are crucial for mitigating fluorine pollution in the electrolytic aluminum industry.

Preparation and Research on Mechanical Properties of Eco-Friendly Geopolymer Grouting Cementitious Materials Based on Industrial Solid Wastes.

Red mud (RM), a hazardous solid waste generated in the alumina production process, of which the mineral composition is mainly hematite, is unable to be applied directly in the cement industry due to its high alkalinity. With the rise of geopolymers, RM-based grouting materials play an essential role in disaster prevention and underground engineering. To adequately reduce the land-based stockpiling of solid wastes, ultrafine calcium oxide, red mud, and slag were utilized as the main raw materials to prepare geopolymers, the C-R-S (calcium oxide-red mud-slag) grouting cementitious materials. The direct impact of red mud addition on the setting time, fluidity, water secretion, mechanical properties, and rheological properties of C-R-S were also investigated. In addition, a scanning electron microscope (SEM), X-ray diffraction (XRD), three-dimensional CT (3D-CT), Fourier transform infrared spectroscopy (FT-IR), and other characterization techniques were used to analyze the microstructure and polymerization mechanism. The related results reveal that the increase in red mud addition leads to an enhanced setting time, and the C-R-S-40 grouting cementitious material (40% red mud addition) exhibits the best fluidity of 27.5 cm, the lowest water secretion rate of 5.7%, and a high mechanical strength of 57.7 MPa. The C-R-S polymer grout conforms to the Herschel-Bulkley model, and the fitted value of R2 is above 0.99. All analyses confirm that the preparation process of C-R-S grouting cementitious material not only substantially improves the utilization rate of red mud, but also provides a theoretical basis for the high-volume application of red mud in the field of grouting.

Gallium distribution between slag and metal phases during the carbothermal reduction of bauxite

This article investigated the recoverability of the Ga in bauxite by carbothermal reduction. Currently, Ga is mostly manufactured from bauxite through the Bayer process as a by-product of alumina, but it is worthwhile to consider alternative processes under stricter environmental regulations and a shortage of high-quality bauxite. This study focused on the Pedersen process, which is the alumina production process consisting of carbothermal reduction and alkaline leaching. The metal and slag phases were prepared by carbothermal reduction of bauxite at 1873 K, and then aluminium in the slag was leached with (Na2CO3 + NaOH) solution at 348 K. Evaluation by inductively coupled plasma atomic emission spectroscopy and inductively coupled plasma mass spectrometry revealed that almost all Ga in bauxite was transferred to the metal phase, and the distribution to the slag phase was negligible in carbothermal reduction, which agrees with the thermodynamic consideration. These results suggest that the gallium recovery from pig iron is necessary to produce Ga in the Pedersen process.

Research Progress of New Generation of Aluminum–Lithium Alloys Alloying

Aluminum–lithium alloy, being the lightest aluminum‐based alloy, holds significant potential for applications in the aerospace and military sectors. Currently, alloying treatment stands as a crucial method for enhancing the comprehensive performance of aluminum–lithium alloy. This article provides an overview of the production process of aluminum–lithium alloys, encompassing smelting and deformation processing characteristics. Additionally, it outlines the developmental history of the chemical composition for the primary grades of aluminum–lithium alloy, detailing the copper (Cu) and lithium (Li) content of the main alloying elements. And discusses the influence of various microalloying elements on the alloy's properties. Additionally, it summarizes the structure, properties, and precipitation morphology of the three primary strengthening phases formed by the alloying of aluminum–lithium alloys: T1 (), (), and (). The analysis also examines the impact of anisotropy on the mechanical properties of the primary dispersion. Finally, the article addresses the challenges involved in alloying aluminum–lithium alloys and proposes key research directions for element composition design.

Application of ultrasonic-enhanced active seed crystals in the removal of sodium oxalate from alumina refinery waste liquor

When organic matter, especially sodium oxalate (Na2C2O4), accumulates to a certain extent, it will seriously affect the alumina production process in the refinery and therefore urgently needs to be removed. This work attempts to illuminate the benefits of ultrasonic intensification of the crystallization process of Na2C2O4, taking the alumina refinery waste liquor, i.e., flat plate washing liquor, as a case study. The effects of different operating parameters (seed crystal addition amount, caustic soda concentration, reaction time, ultrasonic power) on the crystallization behavior and yield are discussed, and it is found that ultrasonic can increase the Na2C2O4 removal rate to 70.4%. The addition of ultrasonic promotes the morphological evolution of Na2C2O4 and is of great significance to the optimization of the components of the precipitated Na2C2O4. Specifically, the proportion of Na2C2O4 in the crystallized product reaches 64% with conventional conditions, while it reaches 77% with ultrasonic conditions. Therefore, ultrasonic can greatly reduce the alkali loss caused by the crystallization process of Na2C2O4 in flat plate washing liquor, which has great economic benefits.

The TPRF: A Novel Soft Sensing Method of Alumina–Silica Ratio in Red Mud Based on TPE and Random Forest Algorithm

The online measurement of the aluminum–silicon ratio of red mud in the dissolution stage of the Bayer alumina production process is difficult to achieve. The offline assay method has a high cost and strong time delay. Soft sensors are an effective and economical method to solve such problems. In this paper, a hybrid model (TPRF model) based on a tree-structured Parzen estimator (TPE) optimized random forest (RF) algorithm is proposed to measure the Al–Si ratio of red mud. The probability distribution of the hyperparameters of the random forest model is estimated by combining the TPE optimization algorithm with the random forest algorithm. According to this probability distribution, the hyperparameters of the random forest algorithm are adjusted in the parameter search space to obtain the best combination of hyperparameters. We established a TPRF soft sensing model based on the optimal combination of hyperparameters. The results show that the best performance of the TPRF model is a mean absolute percentage error (MAPE) of 0.0015, a root-mean-square error (RMSE) of 0.00378, a mean absolute error (MAE) of 0.00162, and a goodness of fit (R2) of 0.9893. The goodness of fit improved by 93.2% compared to the linear model, 39.1% compared to the SVR model, about 21.2% compared to the GRU model, and 5.5% compared to the RF model. This level of performance is demonstrated to be better than traditional soft sensors.

Green production management in the aluminum industry: A sustainable approach towards environmental performance

Implementing green production management (GPM) practices has become increasingly vital for ensuring a sustainable future. Integrating green scientific research into the aluminum industry is imperative for achieving economic and environmental benefits. Despite being touted as a "green metal," the aluminum production process presents significant sustainability challenges. Notably, the industry contributes a substantial 3% to global carbon emissions, with the production of one metric ton of primary aluminum releasing 10-20 metric tons of CO2. Thus, reducing these emissions is critical to promoting environmental sustainability within the industry. This article meticulously examines this pressing issue and analyzes potential strategies to foster a greener aluminum production process. The intrinsic value of this study lies in its capacity to make substantive contributions towards environmentally sustainable practices in this specific industrial domain.

Sustainable Management of Red Mud: Life Cycle Assessment and Treatment Techniques

Red mud is a strongly alkaline leaching solid hazardous waste material generated in the Bayer process of alumina production. India ranks 4th place in alumina production. According to the Ministry of Mines (Oct 2022), India produces 9 million tonnes of red mud annually. In nature, red mud is highly alkaline. The high alkalinity and caustic content of red mud will contaminate the groundwater and fertile soil, and also there is a limitation on the utilization of red mud. Due to its low utilization ratio, large amounts of red mud are stacked in disposal areas, which may cause water pollution, soil salinization and heavy metal pollution. Red mud contains toxic metals such as arsenic, chromium, lead, nickel, zinc and radioactive elements such as thorium, potassium, and uranium, which cause severe effects on the environment and also on our health. The objective is to examine the environmental impact, utilization methods and treatment process of the red mud (bauxite residue). Also, scrutinize the biodegradation of heavy metals in red mud.

Proper Material Tracking for a Continuous Aluminum Production Process

Proper Material Tracking for a Continuous Aluminum Production Process

Efficient rhodamine B dye degradation by red mud-grapefruit peel biochar catalysts activated persulfate in water.

The continuous and rapid development of textile industry intensifies rhodamine B dye (RhB) wastewater pollution. Meanwhile, massive red mud (RM) solid waste generated by the industrial alumina production process poses detrimental effects to the environment after leaching. For resource utilization and to reduce the expansion of RhB pollution, RM and peel red mud-biochar composite (RMBC) catalyst were synthesized in activating peroxydisulfate (PDS) for RhB degradation. Firstly, characterization results showed that compared to RM, RMBC had a higher content of catalytically active metals (Fe, Al, Ti) (higher than 0.92-4.18%), smaller pore size, and larger specific surface area (10 times), which verified RMBC had more potential catalytic oxidation activity. Secondly, under optimal dosage (catalyst, PDS), pH 4.6, and 20 mg L-1 RhB, it was found that the RhB degradation ratio of RM was 76.70%, which was reduced to 41% after three cycles, while that of RMBC was 89.98% and 67%, respectively. The results indicated that the performance of RMBC was significantly superior to that of RM. Furthermore, the quenching experiments, electron paramagnetic resonance spectroscopy tests, FTIR, and XPS analysis showed the function of O-H, C=O, C-O, Fe-O, and Fe-OH functional groups, which converted the PDS to the active state and hydrolyzed it to produce free radicals ([Formula: see text], 1O2, [Formula: see text]) for RhB degradation. And, Q Exactive Plus MS test obtained that RhB was degraded to CO2, H2O, and intermediate products. This study aimed to raise a new insight to the resource utilization of RM and the control of dye pollution.

Study on the removal of iron (II) and manganese (II) in acidic mine drainage by red mud: Performance and mechanism.

Red mud is an environmental burden during the alumina production process. To mitigate the hazards associated with red mud storage, this study investigated the utilization of alkaline red mud as a treatment agent for acidic mine drainage (AMD) with high concentrations of Fe(II) and Mn(II). This study explored the influence of reaction times, addition amounts of red mud, and pH values on the removal efficiency of Fe (II) and Mn(II) from high-concentration AMD. Various parameters such as suspended solids levels, effluent pH, and zeta potentials were measured to meet discharge standards. The adsorption mechanism of red mud was examined using SEM, XRD, EDX, XPS, and 3D-EEM analysis. Optimal conditions were determined as a reaction time of 2 h, pH value of 5.01 and the addition of 100 g/L red mud, achieving effective removal of Fe(II) (reduced from 1000 to 0.224 mg/L) and Mn (II) (reduced from 20 to 1.03 mg/L). The treated AMD meets discharge standards with reduced suspended matter content of 37.4 mg/L. These findings provided valuable insights for the utilization of red mud waste in engineering applications.

Distinct Extraction Behaviors of La/Ce and Sc/Y in the Phosphoric Acidic Leachate of Bauxite Residues and Their Sequential Extraction with Di-(2-Ethylhexyl) Phosphoric Acid as Extractant

Bauxite residue is a hazardous solid waste produced in the alumina production process and has also become a significant rare earth resource. The extraction behaviors of La, Ce, Sc and Y solubilized in the phosphoric acidic leachate of bauxite residue were investigated in this study with di-(2-ethylhexyl) phosphoric acid as the extractant. With a relatively low concentration of 2% at an aqueous solution pH of 1.5, 90% Sc and 98% Y were extracted by di-(2-ethylhexyl) phosphoric acid. Less than 5% La and Ce and impurities of Fe, Al, Ti and Ca were extracted in this situation. As the concentration of di-(2-ethylhexyl) phosphoric acid increased to 20%, almost all the Sc and Y were extracted and the extraction ratios of La and Ce were 87% and 95%, respectively. A good separation of REEs against impurities was simultaneously obtained in the solvent extraction process and their separation coefficients were much higher than 1. A stepwise extraction process was proposed and established to extract Sc/Y and La/Ce sequentially from the phosphoric acidic leachate. It was further revealed that the Sc and Y in the acidic leachate were extracted by di-(2-ethylhexyl) phosphoric acid through an ion exchange process, and that the extraction of La and Ce was due to an antagonistic process where both an ion exchange reaction and a solvation reaction occurred.

Effect of Nanopillars on the Wetting State and Adhesion Characteristics of Molten Aluminum Droplets.

To solve the adhesion problem between molten aluminum and vacuum ladle liner during the electrolytic aluminum production process, the wetting state and adhesion properties of molten aluminum droplets on substrate surfaces with different nanopillars are investigated based on molecular dynamics. The results show that the adhesion strength of molten aluminum droplets in different wetting states has the pattern Young state > Wenzel state > Cassie state. Effects of increasing nanopillar height or interval are poles apart in the wetting state and adhesion characteristics of aluminum molten droplets. The critical height and critical interval of the nanopillar where the wetting state transition occurs are obtained. The increase of the nanopillar width can induce the wetting state transition from the Cassie state to the Wenzel state. In addition, the phantom wall method is applied to study the variation of the separation force. It is found that a peak in the separation force curve occurs when the molten droplet separates from the bottom of the nanopillar interval or the top of the nanopillar. The separation force curves of the droplets in the Young state and the Cassie state have single peaks, while the droplets in the Wenzel state have double peaks.

Developing a Comprehensive Mathematical Model for Aluminium Production in a Soderberg Electrolyser

The technological process of aluminium electrolysis is a complex scientific and technical task. This is due to a large number of internal, external and resultant factors. The aim of this work is to analyse these factors, assess them and their influence on the technological process of electrolysis and develop a comprehensive and mathematical model of aluminium production in the Soderberg electrolyser. The work analyses the technological process of primary aluminium production on the basis of the Bayer method and then on the basis of the Hall–Eru method. The existing methods and technologies for computer modelling of the technological process are analysed. The modern methods of analysis for thermal and electromagnetic fields in electrolysers are considered. On the basis of an in-depth analysis, a number of factors influencing the process of primary aluminium production are identified. Using the methods of system analysis to analyse the identified factors, a ranked list of factors according to the degree of influence is obtained. Using the Pareto diagram, we obtain a list of factors with maximum impact. A conceptual model of the technological process is derived. Based on the obtained conceptual model, the mathematical model of the technological process is derived. The conducted research may be useful to specialists in the field of metallurgy for the analysis of the technological processes of primary aluminium production.

Generating porous metal surfaces as a mean to incorporate thymol-loaded nanoparticles

Porous metals have gained interest in many fields such as biomedicine, electronics, and energy. Despite the many benefits that these structures may offer, one of the major challenges in utilizing porous metals is to incorporate active compounds, either small molecules or macromolecules, on these surfaces. Coatings that contain active molecules have previously been used for biomedical applications to enable the slow release of drugs, e.g., with drug-eluting cardiovascular stents. However, direct deposition of organic materials on metals by coatings is very difficult due to the challenge of obtaining uniform coatings, as well as issues related to layer adherence and mechanical stability. Our study describes an optimization of a production process of different porous metals, aluminum, gold, and titanium, using wet-etching. Pertinent physicochemical measurements were carried out to characterize the porous surfaces. Following the production of porous metal surface, a new methodology for incorporating active materials onto the metals by using mechanical entrapment of polymeric nanoparticles in metal pores was developed. To demonstrate our concept of active material incorporation, we produced an odor-releasing metal object with embedded particles loaded with thymol, an odoriferous molecule. Polymer particles were placed inside nanopores in a 3D-printed titanium ring. Chemical analysis, followed by smell tests, indicated that the smell intensity lasts significantly longer in the porous material containing the nanoparticles, compared with the free thymol.