Conventional steel production routes, such as blast furnaces, often involve high emissions of greenhouse gases, which motivates steel producers to continuously explore different routes that could reduce their carbon footprint. One of the alternative sustainable routes for iron- and steelmaking is to produce direct reduced iron (DRI), which can use hydrogen or natural gas instead of coal or coke in the conventional route. However, fayalite (Fe2SiO4) formation may be important, especially when high-silica ore is used to produce DRI. In this work, the current knowledge on fayalite formation and strategies to minimize its formation is presented. Thermodynamic calculations are used to evaluate the conditions for fayalite formation and explore different methods to minimize its effect on iron ore reduction. The results show that two methods could be employed: the addition of calcium oxide to the ore and the substitution of methane for the hydrogen reductant. CaO addition of 10 wt
The conventional production of medium carbon ferromanganese (MCFe-Mn) via the multistage silicothermic route involves high energy consumption, complex infrastructure, and significant environmental impact. This study presents an improved two-stage process (Si-Mn production + direct EAF smelting) that consolidates the traditional three-unit operation (MnO slag production, Si-Mn production, and ladle refining) into a single electric arc furnace (EAF) step after Si-Mn production. The process integrates thermodynamic modeling (FACTSAGE), experimental validation, and circular resource utilization through the incorporation of gas cleaning plant (GCP) sludge. Two commercially available Si-Mn grades (with Si contents of 15.5 wt.
Hydrogen-based fluidized bed reactor (FBR) is a promising low-carbon ironmaking technology that allows for the direct utilization of fine iron ores without prior agglomeration. However, the poor melting behavior of the produced fine direct reduced iron (DRI*) remains a challenge in subsequent electric smelting furnace (ESF) operations. This study explored the potential of utilizing return fines as a partial iron ore feedstock in a FBR process to enhance the melting properties of DRI* without significant deterioration of reduction performance. The direct utilization of return fines in a fluidized bed involves complex interactions between the physical and chemical characteristics of the bed. This study decoupled the fluidization behavior, reduction kinetics, and downstream melting behavior to evaluate the precise feasibility of return fines. The minimum fluidization velocity (Umf) of the return fines in the particle size range of 0.5–1.0 mm was determined to be 0.55 m/s, implying that the return fines can be treated in a FBR process. The return fines showed inferior reduction degrees in atmospheres of CO/CO2 and H2/H2O compared to iron ores due to their relatively dense microstructure and higher gangue content. The increased addition of return fines up to 10 wt
The novel reductive Bayer process is industrially used to treat high-iron bauxite, and tailing with fine particle size is generated during gravity separation of red mud. In this study, the iron in red mud tailing was recovered through deep reduction–magnetic separation, and the effect of blast furnace dust addition on the process was investigated. Phase transformation and iron grain growth during deep reduction were systematically studied via X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS), and metallic iron was further recovered by magnetic separation. Results showed that, during deep reduction of red mud tailing, liquid-phase formation inhibited further improvements in metallization ratio and iron grain size in the products reduced at 1100 °C and 1200 °C. With the addition of blast furnace dust, liquid-phase formation in the reduced products was effectively suppressed, resulting in a metallization ratio greater than 95
Mill scale, a primary byproduct of the steel industry, presents recycling challenges due to the inefficiencies and complexities of conventional methods of reducing mill scale, which demands a high energy input of around 850–1200 °C and additional reductants. This study introduces two feasible and cost-effective recycling approaches via hydrometallurgy and high-energy ball milling, which can respectively be considered as bottom-up and top-down. Despite the heterogeneous composition of mill scale, both approaches allow for efficient synthesis of magnetically-active magnetite nanoparticles. An array of techniques was used, including X-ray diffraction, electron microscopy, and atom probe tomography to reveal the evolution of the phase fractions. In combination with magnetic measurements, this study rationalizes and optimizes the ferromagnetic properties of the particles. Finally, the results demonstrate the upcycling of these wastes into stable ferrofluid. Both fabrication routes yield ferrofluids demonstrating distinct Rosensweig instability under an applied magnetic field flux of 1.45 T. This integrated upcycling strategy not only valorizes steelmaking waste but also enables scalable production of ferrofluids, expanding potential applications in magnetic technologies.
In this study, a TiO2-doped glass–ceramic was successfully synthesized from steel converter slag via an energy-efficient one-step (petrurgic) process for high-temperature thermal energy storage (TES) applications in concentrated solar power (CSP) systems. The effect of TiO2 addition (0–6 wt
The aluminum casting industry plays a pivotal role in modern manufacturing, contributing to sectors such as automotive, aerospace, and construction. However, the increasing demand for aluminum, coupled with environmental concerns, necessitates a critical evaluation of its raw material sourcing and energy-intensive casting processes. This study explores the dual challenges of raw material criticalities and furnace selection choices in primary and secondary aluminum casting, aiming to chart a pathway toward more sustainable foundry practices. The study is based on the definition of criticality and environmental assessments for a more circular and climate-resilient future. Raw material criticality assessment is assessed through six factors: (1) abundance of elements in the Earth’s crust, (2) sourcing and geopolitical risk, (3) environmental country risk, (4) supply risk, (5) economic importance, and (6) recycling input, while the environmental assessment is made through two major loads: (i) embodied energy, and (ii) carbon footprints. A comparative analysis of common furnace types, including crucible, induction, reverberatory, and stack furnaces, with varying in-house return rates, is conducted to examine the trade-offs in performance from a sustainability perspective. The findings of the proposed work will emphasize the importance of material and process selection in foundries to save the reserves of critical raw materials, implement better closed-loop recycling systems, integrate renewable energy sources, and develop smart furnace operations to minimize environmental footprints. This comprehensive approach is vital for transitioning the foundry industry toward a more circular and climate-resilient future.
Deep-sea polymetallic nodules are rich in valuable metals such as Mn, Ni, Cu, and Co, but their high SiO2 content increases the difficulty of subsequent hydrometallurgical extraction. In this study, a continuous pressurized alkaline leaching process was employed to remove acidic oxides from deep-sea polymetallic nodules. The effects of reaction time, temperature, NaOH concentration, and liquid-to-solid (L/S) ratio on silicon leaching were systematically investigated, and the phase transformation, elemental distribution, and microstructural evolution were characterized by X-ray diffraction (XRD) analysis, X-ray fluorescence spectroscopy (XRF), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS). The results showed that under the optimal conditions of the first-stage leaching (200 °C, 30
Electronic waste, particularly lithium-ion batteries (LIBs), poses significant challenges due to its hazardous components. Effective waste management is essential for sustainability, reducing pollution, and conserving critical metals like lithium (Li) and cobalt (Co). Conventional recycling often relies on high temperatures, strong acids, and/or intensive energy consumption with high carbon footprint. This study explores a moderate temperature pyrometallurgical approach for recycling lithium-ion batteries using raw sugarcane bagasse powder (RSBP), an abundant agricultural waste, as a sustainable reducing agent. The carbon content of raw sugarcane bagasse powder facilitates the carbothermic reduction of cobalt compounds in cathode active powder (CAP), promoting the formation of lithium carbonate (Li2CO3). Complete conversion of Li to Li2CO3 occurs at 600 °C, while cobalt is fully converted to its metallic form at 700 °C. Li in Li2CO3, a water-soluble compound, is then extracted via water leaching and recovered by evaporative crystallization, while metallic Co is obtained as a residue and dried. This leads to recovery efficiencies of 97
As a major waste product of bauxite mining, partially laterized khondalite (PLK) causes significant ecological damage. Despite rigorous research into sustainable alternatives to dumping, industries have yet to find an economically feasible solution for its large-scale reprocessing and industrial use. In this paper, refractory bricks were developed from partially laterized khondalite rock. Other materials including silica sand, fly ash, bentonite, and cement were used to increase the strength and strong bond formation. Ten refractory bricks were developed with varying material composition. It was found that brick with PLK (45
Steelmakers worldwide face increasing pressure to adopt sustainable low CO2 emission production routes, with electric steelmaking emerging as a key pathway. Electric arc furnaces (EAF) require high-grade iron ore for direct reduced iron (DRI), whereas electric smelting furnaces (ESF) can tolerate wider variations in iron content and impurities. This makes the ESF suitable for utilizing Western Australia’s Pilbara ores, which are predominately used in blast furnace ironmaking. In the DRI–ESF route, iron ore can be reduced using hydrogen, then smelted in the ESF using electricity before refining in steelmaking processes. However, detailed mechanistic understanding of heat transfer, fluid flow, and chemical reactions in the ESF process for producing iron are currently lacking. This work investigates heat transfer behavior using a combination of simplified analytical approaches and computational fluid dynamic (CFD) simulations, validated using results of a laboratory electrode smelting furnace. First, this study focused on temperature-dependent thermophysical properties of metal and slag, incorporating flexibility for compositional effects. Dimensionless numbers were derived to assess the relative influence of driving forces on heat transfer and flow within the ESF. The scaling analysis revealed thermal diffusion as the dominant heat transfer mechanism, whereas natural convection, bubbling, and Marangoni effects are significant to the motion of the bath. Building on this, a CFD-based sensitivity analysis was carried out for two configurations covering the range of expected behavior: mixed slag–metal and slag-only models. This highlighted the roles of thermal conductivity, reduction reaction heat sink, and arc’s heat distribution temperature gradients in the process.
A continuous counter-current membrane-assisted (CCCMA) extractor used wettable membranes (hydrophobic or hydrophilic properties) to separate organic and aqueous phases. In this study, the CCCMA extractor was evaluated as an alternative to conventional gravity-based phase-disengagement mixer-settlers for solvent extraction (SX) of critical metals, targeting cobalt (Co) and nickel (Ni). The performance of the CCCMA–SX system was investigated for the hydrometallurgical separation of Co from Ni in sulfate media using bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) as the extractant. The effects of operating conditions, including the organic-to-aqueous (O/A) flowrate ratio, extractant concentration, degree of saponification, initial pH, initial Co/Ni ratio, and number of extraction stages, were assessed. Cobalt stripping utilizing the CCCMA–SX system was evaluated, with H2SO4 being the stripping solution. The applicability of the system for different SX chemistry, including Ni extraction from ammoniacal solution utilizing 2-hydroxy-5-nonylacetophenone oxime (LIX 84-I) extractant, was also demonstrated. The results from this study indicate that CCCMA–SX can improve process continuity and lower phase entrainment, while maintaining extraction efficiency and selectivity as in conventional process. This study also highlights key technical challenges for implementation of the CCCMA–SX system.
The electric smelting furnace (ESF) is a crucial technology for decarbonizing steelmaking and ironmaking, especially as the industry shifts toward processing iron ores with higher gangue content. Building on the discussion presented in the introductory paper [1], the present paper reviews commercially available direct reduced iron (DRI) smelting technologies, heat losses due to radiation, mass and energy balance modeling, and various modeling approaches for studying ESF furnaces. Mass and energy balance modeling of an ESF model showed that every 1.0 wt
Electric smelting furnace (ESF)-based smelting of direct reduced iron (DRI), followed by refining in either a basic oxygen furnace (BOF) or an electric arc furnace (EAF) is increasingly recognized as a promising pathway for low-emission iron and steel production. In this study, three hydrogen-based DRIs produced from low-grade Australian iron ores were evaluated using FactSage® thermodynamic modeling to investigate the effects of gangue content in DRI production and key operating parameters on smelting performance. As Part 1 of the two-part study, hot metal chemistry, carbon consumption to reach the target carbon content of hot metal, and specific energy consumption (SEC) are discussed. Base operating conditions for the model were set at a slag basicity of 1.1, a dissolved carbon content of 3.5 wt
To address the large heat loss and poor mineralization behavior of laterite nickel ore during sintering, magnetization roasting was employed to modify the ore. The sintering performance and mineralization behavior of blends containing magnetically modified laterite nickel ore and original laterite nickel ore were investigated using a sintering cup test system. The results indicate that, compared with the sintering of original laterite nickel ore, the addition of 70
Physical processing materials—aluminum and active material (Al-AM) and graphite and active material (G-AM)—were used to study the hydrometallurgical extraction of metals (Li, Co, Ni, Mn, Al, Cu) from cylindrical NMC532, cylindrical NCA, and prismatic NMC-LMO cells from electric vehicle lithium-ion (Li-ion) batteries. Leaching tests with H2SO4 (0.5–2.0 mol L−1) at solid-to-liquid (S:L) ratios of 1:5 and 1:10 were conducted on NMC532 fluxes. Mixtures of aluminum and active material and graphite and active material at ratios of 15–50 wt
Excellent physicochemical properties and high-tech production applications have led to tungsten (W) and its associated minerals being classified as critical raw materials. Currently, scheelite (CaWO4) has become the main global source of tungsten following the depletion of wolframite ((Fe,Mn)WO4) reserves. In flotation systems, the selective concentration of scheelite from associated gangue minerals, particularly Ca-bearing minerals, remains a major challenge owing to their similar surface characteristics and exposed active Ca2+ sites. In this work, the mechanistic role of quebracho as a green and biodegradable reagent in the selective depression of calcite (CaCO3) and fluorite (CaF2) during scheelite flotation was investigated. Various surface characterization techniques including contact angle, zeta potential, and UV–Vis spectroscopy were applied to reveal the adsorption and interaction behavior of quebracho on mineral surfaces. Results demonstrated that quebracho preferentially adsorbs onto fluorite and calcite, leading to significant surface negativity and hydrophilicity, while showing minimal interaction with scheelite. This selective adsorption is mainly attributed to high availability and reactivity of surface Ca2+ sites on gangue minerals. Continuous flotation experiments (rougher and scavenger) on a real low-grade scheelite sample, conducted in the presence of quebracho, revealed enhanced separation efficiencies (S.E.) across the examined pH range of 9–10, with the most favorable performance observed at pH 10, where scheelite recovery and S.E. exceeded 80 and 70
The depletion of mine reserves and environmental concerns over mine tailings highlight the necessity of valorizing mine tailings as a source of critical metals (CMs). Herein, valorization of Burgin sulfide tailings as a source of Zn and Mn was investigated via microscopic and spectroscopic characterization, thermodynamic calculation, acid leaching, and solvent extraction (SX) tests. H2SO4 and HCl leaching tests were conducted at 75 °C under various solid/liquid ratios to evaluate the leaching behavior of Zn, Mn, and other elements. After leachate purification via selective precipitation, two-step SX tests were performed on the 1.0 M H2SO4 leachate to separate Zn and Mn from the remaining contaminants. Results show that the tailings sample mainly comprised quartz, dolomite, rhodochrosite, and sulfides. It contained 8.8
Coal washery tailings are increasingly recognized as a valuable secondary carbon resource owing to their significant residual carbon content despite being discarded as beneficiation waste. Sustainable valorization of these tailings can reduce waste accumulation, recover valuable carbonaceous material, and support circular resource utilization in the coal and metallurgical sectors. In this study, carbon enrichment and ash reduction of coal washery tailings were achieved through low-reagent physicochemical beneficiation techniques, namely Froth flotation and oil agglomeration, employing fatty acid-based reagents, diesel, and kerosene. The raw tailings contained 40.27 wt.
