Zinoveev, Dmitry Viktorovich

Khanna R., Konyukhov Y., Zinoveev D., Li K., Maslennikov N., Burmistrov I., Kargin J., Kravchenko M., Mukherjee P.S.

The present study developed a novel approach for transforming red mud (RM) into soft magnetic materials (SMMs) for applications in advanced electrical devices in the form of Fe-Si and Fe-Si-Al alloys. A total of ten blends were prepared based on two RMs, three iron oxide additives (Fe2O3, black and red mill scales), alumina and carbonaceous reductants in a range of proportions. Carbothermic reduction of the blends was carried out in a vertical Tamman resistance furnace at 1600–1650 °C for 30 min in an argon atmosphere; synthetic graphite was used as a reductant. Reaction products were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray fluorescence (XRF) and X-ray diffraction (XRD). Significant amounts of Fe-rich metallic droplets/regions of different grain sizes (0.5 to 500 μm) were produced in these studies. The formation of Fe-Si alloys with Si contents from 3.9 to 6.7 wt.% was achieved in 8 out of 10 blends; the optimal levels of Si for SMMs ranged from 3.2 to 6.5 wt.%. There was clear evidence for the formation of Fe-Si-Al (up to 1.8 wt.% Al) alloys in 4 out of 10 blends. In addition to lowering operating challenges associated with RM processing, blending of RMs with iron oxide additives and alumina presents a novel recycling approach for converting RMs into valuable SMMs for possible emerging applications in renewable energy, storage, electrical vehicles and other fields. Along with reducing RM stockpiles across the globe, this approach is expected to improve resource efficiency, mitigating environmental impacts while generating economic benefits.

Kostina V.S., Kostina M.V., Zinoveev D.V., Kudryashov A.E.

The processability of a material is directly related to the possibility of its production, operation and maintainability. One of the most important indicators of the processability of any metal is weldability. Austenitic steels with a high nitrogen content proved themselves as high-strength, corrosion- and cold-resistant materials, but the issue of their weldability is still not fully understood. The lack of welding filler materials on the market specifically designed for welding high-nitrogen steels is the primary obstacle to solving this problem. Thus, the goal of the work was to develop and obtain a laboratory sample of high-nitrogen welding wire. Based on calculations of nitrogen solubility and the phase composition of the weld metal, the chemical composition of Cr – Mn – Ni – Mo – V, N steel was selected for this wire. A defect-free ingot with 0.57 % N was obtained, and wire with a nitrogen content of 0.57 wt. % was produced using hot plastic deformation and drawing methods. Testing of this wire to obtain a welded joint of austenitic cast steel, close to it in chemical composition, with the welding process carried out according to the developed technological recommendations, made it possible to obtain a defect-free welded joint without loss of nitrogen in the weld metal. With a microhardness of the base metal of 252 HV50 , due to the alloying of the welding wire steel with nitrogen and vanadium, the metal of the weld and fusion line had a high microhardness (278 and 273 HV50 , respectively), significantly exceeding the microhardness of Cr – Ni cast austenite. The metal of the welded joint has high strength (0.9 of the base metal strength) and high impact toughness. The fracture of impact samples is characterized by a dimple structure characteristic of viscous materials. According to the obtained results, the new welding wire showed itself to be a promising material for welding austenitic high-nitrogen steels.

Khanna R., Konyukhov Y., Li K., Jayasankar K., Maslennikov N., Zinoveev D., Kargin J., Burmistrov I., Leybo D., Kravchenko M., Mukherjee P.S.

Primary and secondary mill scales (MSs) are waste products produced by the surface oxidation of steel during the hot (800 to 1200 °C) rolling process in downstream steelmaking. While the primary MS is comprised of FeO, Fe3O4, and Fe2O3 in a range of proportions, the secondary MS primarily contain red ferric oxide (Fe2O3) (red MS). We report a novel route for extracting iron from red MS and transforming it into ferro-aluminium alloys using carbothermic reduction in the presence of alumina. The red MS powder was blended with high-purity alumina (Al2O3) and synthetic graphite (C) in a range of proportions. The carbothermic reduction of red MS-Al2O3-C blends was carried out at 1450 °C and 1550 °C under an argon atmosphere for 30 min and then furnace-cooled. The red MS was completely reduced to iron at these temperatures with reduced iron distributed around the matrix as small droplets. However, the addition of alumina unexpectedly resulted in a significant increase in the number and sizes of iron droplets generated, much higher reactivity, and the formation of ferrous alloys. A small amount of alumina reduction into metallic aluminium was also observed at 1450 °C. There is an urgent need to identify the true potential of industrial waste and the materials within it. This study showed that red MS is a valuable material source that could be transformed into ferro-aluminium alloys. These alloys find application in a range of industrial sectors such as construction, automotive, infrastructure, etc.

Zinoveev D., Grudinsky P., Dyubanov V.

In recent years, the proper management and recycling of metallurgical waste have become increasingly important due to their significant environmental impact and the potential for the recovery of valuable metals in order to save natural resources [...]

Grudinsky P., Zinoveev D., Kondratiev A., Delitsyn L., Kulumbegov R., Lysenkov A., Kozlov P., Dyubanov V.

Waelz slag is an iron-containing waste generated during electric arc furnace (EAF) dust processing in a rotary kiln named the Waelz process. This study focuses on the reduction smelting of the Waelz slag to produce iron-based alloy. The thermodynamic simulation using FactSage 8.0 software was carried out to predict temperatures of the metal and slag obtained as well as their compositions. Based on the simulation results, reduction smelting experiments were performed on a laboratory scale using two approaches, with and without preliminary froth flotation of carbon, respectively. The experiments have confirmed the technological possibility of reduction smelting of the Waelz slag from EAF dust processing. The approach using preliminary flotation of carbon and reduction smelting at 1500 °C resulted in high-copper cast iron production, while the approach without flotation, where the Waelz slag was smelted at 1650 °C with the addition of SiO2 flux, led to obtaining low-silicon ferrosilicon with high Cu content, as well as slag attractive for construction industry.

High-quality academic publishing is built on rigorous peer review [...]

Zinoveev D., Pasechnik L., Grudinsky P., Yurtaeva A., Dyubanov V.

The main waste formed during the production of alumina by the Bayer method is red mud. This waste has a high content of iron, which can be effectively extracted by the carbothermic reduction and magnetic separation methods. The crucial factors affecting the commercial efficiency of this process are the iron reduction rate and the size of reduced iron particles. This study considers the influence of sodium sulfate addition to red mud on the kinetics of iron reduction and the iron grain growth process. The isothermal kinetics of the iron reduction process at 1000–1200 °C and 5–30 min of time was investigated for the red mud processing without additives and with 13.65% Na2SO4 addition. It was shown that the activation energy value for the reduction without additives was 65 kJ·mol−1, while it was 39 kJ·mol−1 for the reduction with Na2SO4 addition, respectively. Based on the microstructure study of the roasted samples, models were obtained for the calculation of the average diameter of iron grains without and with the additives. The iron grain growth process was thoroughly discussed, and its main mechanism was proposed.

Grudinsky P., Pasechnik L., Yurtaeva A., Dyubanov V., Zinoveev D.

Bauxite residue is a high-iron waste of the alumina industry with significant contents of scandium, aluminum, and titanium. This study focuses on the recovery of Sc, Al, Ti, and Si from iron-depleted bauxite residue (IDBR) into valuable products. Iron depletion was carried out using reduction roasting followed by low-intensity magnetic separation to enrich bauxite residue in Al, Ti, and Sc and reduce an adverse effect of iron on scandium extraction. Hydrochloric high-pressure acid leaching, aluminum precipitation by saturation of the acid leachate, solvent extraction of scandium using di(2-ethylhexyl) phosphoric acid (HDEHP) and tributyl phosphate (TBP), alkaline leaching of the acid residue with subsequent silica precipitation were used to obtain appropriate selective concentrates. As a result, scandium concentrate of 94% Sc2O3, crude alumina of 93% Al2O3, titanium concentrate of 41.5% TiO2, and white carbon of 77% SiO2 were prepared and characterized. Based on the characterization of the treatment stages and the obtained valuable products, the prospect for the application of the suggested flowsheet was discussed.

Khanna R., Konyukhov Y., Zinoveev D., Jayasankar K., Burmistrov I., Kravchenko M., Mukherjee P.S.

Managing red mud (RM), a solid waste byproduct of the alumina recovery process, is a serious ecological and environmental issue. With ~150 million tons/year of RM being generated globally, nearly 4.6 billion tons of RM are presently stored in vast waste reserves. RM can be a valuable resource of metals, minor elements, and rare earth elements. The suitability of RM as a low-grade iron resource was assessed in this study. The utilization of RM as a material resource in several commercial, industrial operations was briefly reviewed. Key features of iron recovery techniques, such as magnetic separation, carbothermal reduction, smelting reduction, acid leaching, and hydrothermal techniques were presented. RMs from different parts of the globe including India, China, Greece, Italy, France, and Russia were examined for their iron recovery potential. Data on RM composition, iron recovery, techniques, and yields was presented. The composition range of RMs examined were: Fe2O3: 28.3–63.2 wt.%; Al2O3: 6.9–26.53 wt.%; SiO2: 2.3–22.0 wt.%; Na2O: 0.27–13.44 wt.%; CaO: 0.26–23.8 wt.%; Al2O3/SiO2: 0.3–4.6. Even with a high alumina content and high Al2O3/SiO2 ratios, it was possible to recover iron in all cases, showing the significant potential of RM as a secondary resource of low-grade iron.

Grudinsky P., Zinoveev D., Yurtaeva A., Kondratiev A., Dyubanov V., Petelin A.

Red mud is a hazardous waste of alumina production by the Bayer method, which can be used for recovery of valuable elements such as iron, aluminum, titanium, and scandium. In this study, carbothermic roasting of red mud followed by dry or wet magnetic separation was applied with addition of alkaline salts to enhance iron extraction. A comparative influence of the use of sodium and potassium carbonates and sulfates, as well as the effects of roasting temperature and amounts of the additives on iron recovery and the iron concentrate grade were studied experimentally on two industrial red mud samples. The general mechanism of the roasting process in the presence of alkali metals was proposed in terms of temperature and iron extraction. Influence of the grinding fineness of the roasted samples and magnetic field strength during wet magnetic separation on iron extraction was also studied. It was shown that the addition of sodium and potassium carbonates and sulfates during carbothermic roasting of red mud improves the magnetic separation of metallic iron. The composition and microstructure of the separation products were examined, and their possible application was discussed.

Zinoveev D., Pasechnik L., Fedotov M., Dyubanov V., Grudinsky P., Alpatov A.

Bauxite residue, known as red mud, is a by-product of alumina production using the Bayer process. Currently, its total global storage amounts to over 4.6 billion tons, including about 600 million tons in Russia. The total global storage of red mud occupies large areas, leading to environmental damage and increasing environmental risks. Moreover, it contains a significant amount of sodium, which is easily soluble in subsoil water; therefore, a sustainable approach for comprehensive recycling of red mud is necessary. The bauxite residue contains valuable elements, such as aluminum, titanium, and scandium, which can be recovered using liquid media. In recent years, many methods of recovery of these elements from this waste have been proposed. This paper provides a critical review of hydrometallurgical, solvometallurgical, and complex methods for the recovery of valuable components from red mud, namely, aluminum, titanium, sodium, and rare and rare-earth elements. These methods include leaching using alkaline or acid solutions, ionic liquids, and biological organisms, in addition to red mud leaching solutions by extraction and sorption methods. Advantages and disadvantages of these processes in terms of their environmental impact are discussed.

Zinoveev D.V., Delicyn L.M., Ryabov Y.V., Kulumbegov R.V., Zakunov A.S., Dyubanov V.G.

Abstract Coal fly ash is a hazardous waste of heat power engineering. The complex processing of it includes several stages, such as carbon flotation and magnetic separation of iron. This study focuses on carbon extraction by flotation method and iron by magnetic separation method from Kashirskaya GRES coal fly ash with subsequent reduction smelting of it. At optimal conditions were obtained carbon concentrate with 37% C and magnetic concentrate with 61% Fe2O3. The high-quality steelmaking pig iron with low P and S and high alumina slag were obtained at 1400 °C after reduction smelting mixture magnetic, and carbon concentrates.

Zinoveev D., Grudinsky P., Zhiltsova E., Grigoreva D., Volkov A., Dyubanov V., Petelin A.

Red mud is a hazardous waste of the alumina industry that contains high amounts of iron, aluminum, titanium and rare-earth elements (REEs). One of the promising methods for the extraction of iron from red mud is carbothermic reduction with the addition of sodium salts. This research focuses on the process of hydrochloric high-pressure acid leaching using 10 to 20% HCl of two samples of non-magnetic tailings obtained by 60 min carbothermic roasting of red mud at 1300 °C and the mixture of 84.6 wt.% of red mud and 15.4 wt.% Na2SO4 at 1150 °C, respectively, with subsequent magnetic separation of metallic iron. The influence of temperature, leaching duration, solid-to-liquid-ratio and acid concentration on the dissolution behavior of Al, Ti, Mg, Ca, Si, Fe, Na, La, Ce, Pr, Nd, Sc, Zr was studied. Based on the investigation of the obtained residues, a mechanism for passing valuable elements into the solution was proposed. It has shown that 90% Al, 91% Sc and above 80% of other REEs can be dissolved under optimal conditions; Ti can be extracted into the solution or the residue depending on the leaching temperature and acid concentration. Based on the research results, novel flowsheets for red mud treatment were developed.

Zinoveev D., Petelin A., Grudinsky P., Zakunov A., Dyubanov V.

Kologrieva U., Volkov A., Zinoveev D., Krasnyanskaya I., Stulov P., Wainstein D.

Vanadium containing sludge is a by-product of vanadium pentoxide obtained by hydrometallurgical methods from vanadium slag that can be estimated as a promising technogeneous raw material for vanadium production. The phase analysis of vanadium-containing sludge by the X-ray diffraction method showed that it contains vanadium in spinel form (FeO∙V2O3). The various oxidation roasting methods for sludge treatment were studied for increasing vanadium extraction into the solution. It showed that the most effective additive is 1% CaCO3 at a roasting temperature of 1000 °C. Oxidation roasting of vanadium-containing sludge with the additive led to an increase in the acid-soluble form of V2O5 from 1.5% to 3.7% and a decrease in the content of FeO∙V2O3 from 3% to 0.4%. These results confirm the efficiency of the application of oxidation roasting to convert vanadium compounds into acid-soluble forms. The conversion mechanism of spinel to acid-soluble phases during oxidation roasting with additives was investigated by thermogravimetric analysis and thermodynamic simulation. It showed that the formation of acid-soluble calcium vanadates during oxidation roasting without additives occurs at temperatures above 800 °C while CaCO3 addition allows one to reduce this temperature to 600 °C.

Harini K., Karthiyaini S., Shanmugasundaram M.

Khanapur N.V., Tripathi B., Chandra T.

Shen H., Lou B., Liu B., Zhang J., Zhang X., Liu J., Hu Y., Zhang S.

Liu M., Zeng A., Mao R., Yu H., Zhou F., Zhang H.

Prozorov D.A., Afineevskii A.V., Smirnov D.V., Gordina N.E., Rumyantsev R.N.

Comprehensive studies of physicochemical properties, including textural and morphological, of iron-containing waste from the landfill of the Zavolzhsky Chemical Plant (Ivanovo region, Russia) were carried out. The data on changes in elemental and phase composition of red mud depending on the depth of occurrence and time of storage at the landfill were obtained. Methods of primary treatment of iron-containing wastes of Zavolzhsky Chemical Plant to obtain iron-containing intermediates for synthesis of catalysts were proposed. Morphology and distribution of elements on the surface of red mud after its thermal treatment at different temperatures, as well as porosity of iron-containing wastes after their thermal treatment in air oxygen environment were studied. The use of iron-containing wastes from Zavolzhsky Chemical Plant as a semi-product of iron-containing catalysts and chemisorbents for deep processing of process gases is recommended.

Li X., Li L., Huang Z., Chang Z., Tu Z., Tian L., Du W., Li H., Zhang P., Pan B.

Sun T., Aslam M.M., Chen G., Peng C.

Vielma C.A., Svobodova-Sedlackova A., Chimenos J.M., Fernández A.I., Berlanga C., Rodriguez R., Barreneche C.

Red mud (RM), the primary waste product of the aluminium industry, is notable for its high concentrations of metals and rare earth elements (REE). Efforts have been made to develop extraction methods for REE recovery from RM, aiming to enhance its valorisation and reduce the European reliance on external REE sources—particularly crucial for technological advancements and the transition to renewable energy. However, these methods have only been limited to low technology readiness levels (TRLs), with no economically or technically viable processing routes yet defined to enable large-scale industrialisation within a circular economy model. This study characterised RM samples from the Seydişehir region in Türkiye using different techniques and explored the experimental process for recovering metals and REE. Moreover, the study assessed the global prospective potential of RM based on technical and economic data, as well as the sustainability of the implemented process through the life cycle assessment (LCA) tool. Results showed a total REE concentration of up to 1600 ppm, with Ce, being the most abundant (426 ± 27 ppm), followed by La, Nd, and Sc. Concentration efficiencies for La and Nd ranged between 240–300%. Sc, Y, Ce, La, and Nd have significant usage in European markets and represent prime RM targets for further prospecting. The LCA revealed that the highest global warming potential of the sequential extraction process was attributed to hydroxylamine hydrochloride and hydrogen peroxide. The findings highlight the need to explore alternative, more eco-friendly reagents to improve RM valorisation.

Khanna R., Konyukhov Y., Zinoveev D., Li K., Maslennikov N., Burmistrov I., Kargin J., Kravchenko M., Mukherjee P.S.

The present study developed a novel approach for transforming red mud (RM) into soft magnetic materials (SMMs) for applications in advanced electrical devices in the form of Fe-Si and Fe-Si-Al alloys. A total of ten blends were prepared based on two RMs, three iron oxide additives (Fe2O3, black and red mill scales), alumina and carbonaceous reductants in a range of proportions. Carbothermic reduction of the blends was carried out in a vertical Tamman resistance furnace at 1600–1650 °C for 30 min in an argon atmosphere; synthetic graphite was used as a reductant. Reaction products were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray fluorescence (XRF) and X-ray diffraction (XRD). Significant amounts of Fe-rich metallic droplets/regions of different grain sizes (0.5 to 500 μm) were produced in these studies. The formation of Fe-Si alloys with Si contents from 3.9 to 6.7 wt.% was achieved in 8 out of 10 blends; the optimal levels of Si for SMMs ranged from 3.2 to 6.5 wt.%. There was clear evidence for the formation of Fe-Si-Al (up to 1.8 wt.% Al) alloys in 4 out of 10 blends. In addition to lowering operating challenges associated with RM processing, blending of RMs with iron oxide additives and alumina presents a novel recycling approach for converting RMs into valuable SMMs for possible emerging applications in renewable energy, storage, electrical vehicles and other fields. Along with reducing RM stockpiles across the globe, this approach is expected to improve resource efficiency, mitigating environmental impacts while generating economic benefits.

Huang Z., Li A., Zhou W., Li J., Zhang J.

The effects of red mud on the microstructures and high-temperature tensile properties of the ZL109 aluminum alloy have been investigated. Red mud/ZL109-based composite materials with added red mud (a major byproduct of the aluminum industry), which has been coated with nickel by chemical deposition, have been prepared through gravity casting. The results show that the addition of red mud promotes the alloy’s microstructure and helps to uniformly distribute the eutectic silicon. It also increases the content of heat-resistant phases, such as the Q-Al5Cu2Mg8Si6 and γ-Al7Cu4Ni phases. These changes significantly enhance the alloy’s high-temperature tensile properties. The alloy with 1% (wt.%) red mud exhibits the best tensile strength at both room temperature and 350 °C, reaching 295.4 MPa and 143.3 MPa, respectively. The alloy with 1.5% (wt.%) red mud demonstrates excellent performance at 400 °C, achieving a tensile strength of 86.2 MPa through the cut-through method and Orowan mechanism. As a reinforcing material, red mud not only improves the high-temperature resistance of the aluminum alloy but also provides a way to recycle industrial waste. This study offers a new way to address the red mud waste problem and helps develop high-performance, heat-resistant aluminum alloys. It shows the potential of these alloys in high-temperature applications.

Kurniawati R., Dahani W., Subandrio S., Palit C., Kisal Albrian Gheraldy S.

Abstract Red mud is classified as hazardous waste due to its high alkalinity and the presence of radioactive materials. This study aims to investigate the leaching properties of major metals and rare earth elements in red mud at pH levels of 2, 7, and 13. We performed XRD, XRF, and ICP analyses to determine the effect of pH on metal leaching in red mud. The findings revealed that the pH of the solution substantially affected the concentration of dissolved metals. Metal dissolution increases dramatically at an acidic pH (pH 2), but metal concentration drops quickly at a neutral pH (pH 7). At alkaline pH (pH 13), Al dissolves significantly, whereas Fe remains reasonably stable. These findings indicate that the red mud processing industry can utilize pH modulation to enhance the leaching effectiveness of specific metals, a crucial step towards developing more efficient and environmentally friendly purification procedures.

Wang Y., Hassan H.M., Nisar A., Zahara S.S., Akbar A., Al-Emam A.

Sharma S.K., Girdwood M.L., Arif T., Pearcy A.C., Tiffin C.M., Marshall A.T., Bumby C.W.

Gudkova S.A., Zhivulin V.E., Taskaev S.V., Kostishin V.G., Chernukha A.S., Zirnik G.M., Solizoda I.A., Pankratov D.A., Agafonov S.A., Vinnik D.A.

Li Q., Lv G., Wang S., Li X., He X., Zhang T.

The Bayer method of alumina production generates highly alkaline solid waste known as red mud, which is challenging to utilize and can only be disposed of in stockpiles. This practice leads to environmental pollution and safety hazards, posing a significant barrier to the bauxite industry’s transition towards green and sustainable development. In light of the diminishing availability of high-quality iron ore resources, Bayer red mud is increasingly viewed as a potential resource due to its high iron content. Consequently, utilizing red mud as a raw material for iron extraction presents both challenges and opportunities. This study systematically reviews the methods of iron extraction and recovery from red mud, categorizing them into physical sorting methods, wet leaching, pyrometallurgy method, and biometallurgy. This paper elaborate on the mechanisms of iron extraction from red mud in these processes, the transformation of mineral phases, and the challenges that exist. Additionally, it analyze and compare the characteristics, advantages, and disadvantages of the various technologies. It propose a novel low-carbon process for iron extraction from red mud—“calcified transformation—vortex reduction—cement preparation”, achieving an iron recovery rate exceeding 95%. This recovered iron can be directly utilized in steel production, while the molten reduction slag can be modulated for the preparation of low-carbon cement clinker. This approach not only facilitates the reduction and high-value utilization of solid waste but also provides valuable insights into the recovery of iron and the effective use of red mud resources.

Shen H., Lou B., Liu B., Zhang J., Zhang X., Liu J., Zhang R., Chen M., Zhang S.

Aluminum dross (AD) and red mud (RM) are waste discharged from aluminum industry. AD and RM contain 5-15 wt% of hazardous aluminum nitride (AlN) and 20–50 wt% of iron oxide , respectively. In this work, alumina-based cermet was in-situ prepared from AD and RM, after reduction of iron oxide with AlN by pyrometallurgy . Cermet was consisted of metal reinforcement phase about 1 μm, alumina matrix phase and low-melting aluminosilicate binder. Mechanism of in-situ preparation was studied after exploring phase composition of the cermet powder. Iron, silicon and titanium oxide from RM was reduced into Fe 3 Si and TiN, which acted metal reinforcement phase in cermet. Reaction was consisted of two steps, Fe 2 O 3 , TiO 2 and AlN dissolving into low-melting aluminosilicate and electron transferring from AlN to Fe 2 O 3 , SiO 2 and TiO 2 . Content of Fe in ceramic phase was decreased from 6 at.% to 1 at.% after reduction reaction. Low-melting aluminosilicate acted both reaction solvent for reduction reaction, and binder for metal reinforcement phase and alumina matrix phase. More low-melting aluminosilicate was formed when temperature was increased from 1200 °C to 1400 °C, which made more metal balls be formed. The metal ball and alumina were bonded by low-melting aluminosilicate, which increased the bond strength between reinforcement phase and ceramic phase in cermet. This work achieved a total recycle of AD and RM into cermet. It was proposed a novel idea of in-situ preparing cermet, which was generating metal reinforcement phase in ceramic matrix phase.

Khanna R., Konyukhov Y., Li K., Jayasankar K., Maslennikov N., Zinoveev D., Kargin J., Burmistrov I., Leybo D., Kravchenko M., Mukherjee P.S.

Primary and secondary mill scales (MSs) are waste products produced by the surface oxidation of steel during the hot (800 to 1200 °C) rolling process in downstream steelmaking. While the primary MS is comprised of FeO, Fe3O4, and Fe2O3 in a range of proportions, the secondary MS primarily contain red ferric oxide (Fe2O3) (red MS). We report a novel route for extracting iron from red MS and transforming it into ferro-aluminium alloys using carbothermic reduction in the presence of alumina. The red MS powder was blended with high-purity alumina (Al2O3) and synthetic graphite (C) in a range of proportions. The carbothermic reduction of red MS-Al2O3-C blends was carried out at 1450 °C and 1550 °C under an argon atmosphere for 30 min and then furnace-cooled. The red MS was completely reduced to iron at these temperatures with reduced iron distributed around the matrix as small droplets. However, the addition of alumina unexpectedly resulted in a significant increase in the number and sizes of iron droplets generated, much higher reactivity, and the formation of ferrous alloys. A small amount of alumina reduction into metallic aluminium was also observed at 1450 °C. There is an urgent need to identify the true potential of industrial waste and the materials within it. This study showed that red MS is a valuable material source that could be transformed into ferro-aluminium alloys. These alloys find application in a range of industrial sectors such as construction, automotive, infrastructure, etc.

Vilarinho I.S., Dias A.C., Carneiro J., Pinto C., Labrincha J.A., Seabra M.P.

Red mud (RM), resulting from alumina production by Bayer process, is classified as hazardous waste and is, nowadays, one of the most abundant industrial waste worldwide. Currently, over 4 billion tons are stored in ponds/dried mounds and is of utmost importance to tackle this problem. This work aims to recycle RM as colouring agent in stoneware products. For this purpose, several proportions of RM (0–10 wt%) were added to ceramic pastes. The developed products with RM exhibit a reddish/brown colour. Further, the technical characteristics of the specimens with 10 wt% of RM (RM10) are within the industrial limits: firing shrinkage (7.1%), weight loss (6.9%) and water absorption (1.38%). RM10's density and flexural strength are higher than RM0, 2.16 g/cm3 and 2.07 g/cm3, and 416 kgf/cm2 and 388 kgf/cm2 respectively. Leaching tests performed in cups industrially prepared indicated that all the values were below the maximum permitted. Lastly, through a life cycle assessment, it was concluded that the carbon footprint decreases 18% when RM10 is incorporated into the stoneware paste. Therefore, this work provides a viable alternative for the management of considerable amounts of this waste and reduces the carbon footprint associated with the ceramic production process.

Li H., Shi B., Fu X., Zhang H., Yang H.

As an abundant hazardous waste, red mud needs a simple and effective mean of resource utilization. Herein, a novel zero-valent iron heterogeneous Fenton catalyst RMB-900 was synthesized by pyrolysis (900 °C) using red mud and straw with a facile solvent-free carbothermal redox approach. X-ray diffraction analysis showed that Fe2O3 in the red mud was reduced to Fe0. Characterization data showed that RMB-900 was a zero-valent iron loaded porous material. Under the conditions of 2.86 mM H2O2, 100 mg/L acid red G, and 1 g/L RMB-900, 98% of acid red G was removed within 10 min, the reaction rate constant is 6.7 folds higher than that of commercial zero-valent iron. The RMB-900/H2O2 system also showed good degradability to antibiotics (Sulfamethoxazole, Ibuprofen and Carbamazepine). H2O2 is mainly catalysed by Fe0 in RMB-900 to generate •OH for ARG degradation. RMB-900 still showed excellent catalytic performance after standing for four months and after being reused nine times. This study not only prepared a catalyst with low cost, high stability, and great potential for wastewater treatment through a simple and green solvent-free method, but also provided a research basis for further exploration of red mud-based catalysts.

Liu Z., Fan C., Yang C., Ming Z., Hua Z., Lin S., Wang L.

Dissimilar welding of high nitrogen steel and low alloy martensitic steel has a large application prospect in power plants and offshore structures. In this paper, the weldability was studied by comparing and analyzing the metallurgical characteristics and mechanical properties of the dissimilar joints by three types of consumables. Among the welding materials of austenitic ER 307Mo, duplex ER 2209, and martensitic ER 120S-G, macroscopic gas pores appeared in the weld with ER 2209 and ER 120S-G, which were both caused by the mix of the nitrogen-containing molten metal and low alloy steel, where the elements that promote nitrogen solubility were rapidly diluted, resulting in a violent escape of nitrogen. In ER 307Mo weld, because of the high content of alloying elements and the minimal fusion ratio, nitrogen only escaped as the micropores and small precipitates, which have no obvious effect on the performance of the weld. It is a good solution to solve the problems of dissimilar welding by selecting a filler metal that does not contain nitrogen but can dissolve nitrogen, and using the dissolution of high nitrogen steel to strengthen the weld based on controlling the fusion ratio. Finally, nitrogen behavior during the welding process was discussed and analyzed combined with porosity distribution, nitrogen distribution, and microstructure.

Chiweshe T.T., Welman-Purchase M.

The fusion method of using ammonium phosphate salt as flux was assessed for its ability to precipitate metaphosphate compounds containing trivalent ions M3+ = Al, Cr, Fe, Ti, and V as M(PO3)3 in inorganic salts and a certified reference material (CRM) mineral ore sample. Fusion analysis using mixtures of inorganic salts containing AlCl3, CrCl3, FeCl3, and VCl3 showed variable amounts of precipitates isolated as metaphosphate compounds in the order of iron (12%) < vanadium (13%) < chromium (30%) < (44%) aluminum. However, an analysis of the CRM (AMIS 0368) where magnetite (Fe3+/Fe2+) and ilmenite (Ti4+) are the dominant phases, showed that the obtained precipitates were in the order of chromium (less than 0.1%) < vanadium (1%) < aluminum (2%) < titanium (9%) < iron (68%). The metaphosphate compounds isolated via the use of this method were identified using XRD analysis. SEM–EDX analysis showed micro-crystalline particles from the inorganic salts that were irregular and clustered, contrary to the amorphous micro particles which were produced from the CRM. The degree of specificity improved considerably using CRM ore (AMIS 0368) with high iron content (~76%, Fe3+/Fe2+). This method was shown to be highly selective towards metals with a stable trivalent oxidation state. No other elements of a different oxidation state were precipitated.

Grudinsky P., Zinoveev D., Kondratiev A., Delitsyn L., Kulumbegov R., Lysenkov A., Kozlov P., Dyubanov V.

Waelz slag is an iron-containing waste generated during electric arc furnace (EAF) dust processing in a rotary kiln named the Waelz process. This study focuses on the reduction smelting of the Waelz slag to produce iron-based alloy. The thermodynamic simulation using FactSage 8.0 software was carried out to predict temperatures of the metal and slag obtained as well as their compositions. Based on the simulation results, reduction smelting experiments were performed on a laboratory scale using two approaches, with and without preliminary froth flotation of carbon, respectively. The experiments have confirmed the technological possibility of reduction smelting of the Waelz slag from EAF dust processing. The approach using preliminary flotation of carbon and reduction smelting at 1500 °C resulted in high-copper cast iron production, while the approach without flotation, where the Waelz slag was smelted at 1650 °C with the addition of SiO2 flux, led to obtaining low-silicon ferrosilicon with high Cu content, as well as slag attractive for construction industry.

Zinoveev D., Pasechnik L., Grudinsky P., Yurtaeva A., Dyubanov V.

The main waste formed during the production of alumina by the Bayer method is red mud. This waste has a high content of iron, which can be effectively extracted by the carbothermic reduction and magnetic separation methods. The crucial factors affecting the commercial efficiency of this process are the iron reduction rate and the size of reduced iron particles. This study considers the influence of sodium sulfate addition to red mud on the kinetics of iron reduction and the iron grain growth process. The isothermal kinetics of the iron reduction process at 1000–1200 °C and 5–30 min of time was investigated for the red mud processing without additives and with 13.65% Na2SO4 addition. It was shown that the activation energy value for the reduction without additives was 65 kJ·mol−1, while it was 39 kJ·mol−1 for the reduction with Na2SO4 addition, respectively. Based on the microstructure study of the roasted samples, models were obtained for the calculation of the average diameter of iron grains without and with the additives. The iron grain growth process was thoroughly discussed, and its main mechanism was proposed.

Li W., Li Z., Wang N., Gu H.

Red mud is an alkaline industrial solid waste discharged from alumina production via the Bayer process and can be considered a kind of potential resource of rare earth elements (REEs). Many valuable metals such as iron, aluminum, and titanium also exist in red mud. A multi-stage extraction method was proposed in this study by taking full account of the REEs’ occurrence in red mud. Firstly, the pretreatments of oxalic acid leaching, roasting, and dilute hydrochloric acid leaching were employed to recover iron and enrich REEs in the residue. Subsequently, sulfuric acid leaching was used to selectively dissolve REEs into the leaching solution. Finally, the effects of sulfuric acid concentration, liquid-solid ratio, reaction temperature, and reaction time on the leaching efficiency of REEs were then investigated. The results show that the maximum extraction of the REEs reached 80% and less than 4% of Fe, Na, Ca, Ti and Al were extracted under the experimental conditions of 1 mol/L H 2 SO 4 , 3 h, 95 °C, and the liquid-solid ratio of 5:1 mL/g. The practicable approach by multi-stage extraction of acid leaching and roasting can split iron and REEs from red mud. • Oxalic acid was introduced to dissolve iron and to enrich REEs in form as oxalates. • Calcium was removed by roasting and HCl leaching to further enrich REEs. • Effects of H 2 SO 4 leaching condition on REEs leaching efficiency were investigated. • Approximately 80% Sc and less than 4% of Fe, Na, Ca, Ti and Al were extracted.

Wang K., Dou Z., Liu Y., Li X., Lv G., Zhang T.

Bayer red mud is a strong alkaline solid waste discharged during alumina production. Due to large emissions and strong alkalinity, red mud is now mostly dammed or buried, which not only occupies huge land but also contaminates the surrounding ecosystem, causing the risk of collapse and landslide. In addition to its overall utilization in building materials, agriculture, the environment, and the chemical industry, red mud also contains valuable metals such as sodium, aluminum, iron, titanium, and scandium and is considered to be an important secondary resource. In this paper, the physicochemical properties and hazards of red mud are first introduced, and then, the overall utilization of red mud is summarized. Then, the latest research progress on the separation and extraction of valuable metals from red mud is reviewed in detail and a new comprehensive utilization method is recommended and evaluated. This paper also provides suggestions for the future development direction of the comprehensive utilization technology of red mud.

Grudinsky P., Pasechnik L., Yurtaeva A., Dyubanov V., Zinoveev D.

Bauxite residue is a high-iron waste of the alumina industry with significant contents of scandium, aluminum, and titanium. This study focuses on the recovery of Sc, Al, Ti, and Si from iron-depleted bauxite residue (IDBR) into valuable products. Iron depletion was carried out using reduction roasting followed by low-intensity magnetic separation to enrich bauxite residue in Al, Ti, and Sc and reduce an adverse effect of iron on scandium extraction. Hydrochloric high-pressure acid leaching, aluminum precipitation by saturation of the acid leachate, solvent extraction of scandium using di(2-ethylhexyl) phosphoric acid (HDEHP) and tributyl phosphate (TBP), alkaline leaching of the acid residue with subsequent silica precipitation were used to obtain appropriate selective concentrates. As a result, scandium concentrate of 94% Sc2O3, crude alumina of 93% Al2O3, titanium concentrate of 41.5% TiO2, and white carbon of 77% SiO2 were prepared and characterized. Based on the characterization of the treatment stages and the obtained valuable products, the prospect for the application of the suggested flowsheet was discussed.

Bai B., Bai F., Li X., Nie Q., Jia X., Wu H.

This study aims to treat heavy metal pollutants in water by applying red mud particle waste. An experiment on the static adsorption of heavy metal ions Pb 2 + (or Cd 2 + and Cu 2 + ) by red mud particles was carried out, and the influences of the type of heavy metal ion, ion concentration, pH value, red mud dosage, reaction time, and temperature on adsorption performance were explored. The competitive adsorption mechanisms of various coexisting heavy metal ions by red mud particles were compared. The red mud samples loaded and not loaded with heavy metal ions were detected by zeta potential measurement, scanning electron microscopy, and Fourier transform infrared spectrometry. The adsorption strength of red mud particles for heavy metal ions was ranked in the sequence of Pb 2 + , Cd 2 + , and Cu 2 + , while increasing temperature enhanced their adsorption. When the initial pH values were 4.3, 5.0, and 3.6 for Pb 2 + , Cd 2 + , and Cu 2 + solutions, the removal peaks were 94.5%, 92.8%, and 78.1%, respectively. The preferred order of adsorption for red mud was Pb 2 + , Cd 2 + and then Cu 2 + under the competitive mechanism of binary/ternary systems due to the discrepancy in the functional groups of red mud particles loaded with different heavy metal ions. • A concept for purifying heavy metal pollutants in water using red mud is proposed. • The competitive adsorption mechanism of various heavy metal ions is revealed. • The influence of temperature on the interaction of heavy metal ions and red mud is emphasized. • An adsorption–desorption model with hysteresis is verified by experimental results.

Salman A.D., Juzsakova T., Jalhoom M.G., Abdullah T.A., Le P., Viktor S., Domokos E., Nguyen X.C., La D.D., Nadda A.K., Nguyen D.D.

The aim of this study was to recover Sc as the main product and Fe as a by-product from Hungarian bauxite residue/red mud (RM) waste material by solvent extraction (SX). Moreover, a new technique was developed for the selective separation of Sc and Fe from real RM leachates. The presence of high Fe content (∼38%) in RM makes it difficult to recover Sc because of the similarity of their physicochemical properties. Pyrometallurgical and hydrometallurgical methods were applied to remove the Fe prior to SX. Two protocols based on organophosphorus compounds (OPCs) were proposed, and the main extractants were evaluated: bis(2-ethylhexyl) phosphoric acid (D2EHPA/P204) and tributyl phosphate (TBP). The results showed that SX using diethyl ether and tri-n-octylamine (N235) was efficient in extracting Fe(III) from the HCl leachate as HFeC14. Over 97% of Sc was extracted by D2EHPA extractant under the following conditions; 0.05 mol/L of D2EHPA concentration, A/O phase ratio of 3:1, pH 0-1, 10 min of shaking time, and a temperature of 25 °C. Sc(OH)3 as a precipitate was efficiently obtained by stripping from the D2EHPA organic phase by 2.5 mol/L of NaOH with a stripping efficiency of 95%. In the TBP system, 99% of Sc was extracted under the following conditions: 12.5% vol of TBP, an A/O phase ratio of 3:1, 10 min of shaking time, and a temperature of 25 °C. The Sc contained in the TBP organic phase could be efficiently stripped by 1 mol/L of HCl with a stripping efficiency of 92.85%.

Lv X., Yan Z.

The physicochemical properties of slag at high temperature are closely related to its structure, which are mainly reflected in the following aspects: (1) Melting property refers to the chemical reaction of each other to form liquid phase under the appropriate temperature and atmosphere conditions, and it is the process of the transition of ordered oxide crystal into a disordered liquid phase. (2) The fluidity and conductivity reflect the migration of ions and ion clusters and the adjustment of slag structure. (3) The surface properties are also related to the distribution of ions and clusters in slag structure of the surface layer. (4) The desulfurization performance is related to the distribution of free oxygen ions in slag.

Valeev D., Bobylev P., Osokin N., Zolotova I., Rodionov I., Salazar-Concha C., Verichev K.

Coal combustion used by the Combined heat and power plants (CHPs) generates solid wastes - coal fly ash (CFA). Up to 22% of the total electricity supply in Russian is coal-generated, this value is forecasted to not decrease until 2035, which in the next 14 years will translate into the accumulation of more than 260 Mt of CFA on the CHPs landfills. Following the Government recently presenting a roadmap towards the ramp-up of the CFA utilization from the current 8%–50% by 2035, the highly developed aluminum industry in Russia amidst the lack of its own bauxite sources is currently considering the utilization of CFA as an aluminum oxide-rich raw material for the alumina production. The present review localizes the largest sources of CFA in Russia, summarizes the annual CFA accumulation rates, and its stored volumes, and the chemical composition of the CFA generated in Russia. In this review, the actual acidic methods for alumina production (hydrochloric acid and ammonium bisulfate/sulfuric acid) were considered. Alumina powder obtained by acid methods was analyzed for the quality requirements of the Russian aluminum smelters to forward the case for the CFA's wide adoption as the raw material in both Russia's and worldwide aluminum industry. • Worldwide practices of the utilization of large volumes of CFA. • Localization of coal-fired power plants in Russia. • Characteristics of the chemical compositions of CFA formed in Russia. • Description of HCl and NH 4 HSO 4 + H 2 SO 4 for alumina production from CFA. • Characterization of alumina samples obtained by acidic methods.