Search Results (110)

The objective of the present work was to investigate a possible processing route for a currently discarded material, niobium mineral tailings containing rare earth elements, from the largest niobium producer worldwide (CBMM), for use as a raw material for valuable products such as ferroniobium and rare earth concentrate. A study was conducted on the kinetics of the carbothermic reduction from hematite to magnetite (magnetizing roasting). Thermogravimetric tests performed in duplicate or triplicate were conducted at three different temperatures (700 °C, 800 °C and 900 °C) for 1 h with two times the stoichiometric quantity of the reductant (charcoal). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed small amounts of magnetite in the samples reduced at 700 °C and 800 °C. At 900 °C, in accordance with the XRD analysis (Rietveld), almost all hematite was reduced to magnetite. The kinetic model that showed the best fitting was the Ginstling–Brounshtein model. The apparent activation energy was evaluated to be 206 kJ/mol, which is similar to the values reported in the literature for the activation energy of the Boudouard reaction. Full article

In the recycling of semiconductor materials like Bi₂Te₃ or CdTe, TeO₂ may form as a by-product that can be directly reduced to recover metallic Te. The hydrogen reduction of TeO₂ offers an eco-friendly alternative to conventional carbothermic reduction by avoiding CO by-products. This study investigates the reduction of 99.99 wt.% purity level TeO₂ using hydrogen in an oscillating kiln furnace (200–800 °C, 2–7 h), with phase composition and microstructure analysed via XRD and SEM. Results demonstrate conversions of up to 89% (solid–gas) and 100% (liquid–gas), revealing that kinetics dominate over thermodynamics in controlling reaction progress. The work proposes a reaction mechanism based on morphological evolution observed in SEM images, suggesting that further parameter optimisation could enhance scalability. As the first lab-scale demonstration of hydrogen-assisted TeO₂ reduction, this study establishes a preliminary process window (temperature/time) and underscores the potential for industrial adoption. Future work should verify the proposed mechanism and refine operational parameters to maximize efficiency. Full article

The present study demonstrates, for the first time, the fundamental possibility of producing electrode materials for sodium-ion batteries through low-temperature carbothermic smelting of ilmenite concentrate fluxed with calcined soda and diatomite, followed by aqueous refining of titanium slag. The primary phase composition of the slag includes Na₂Ti₃O₇ (48.2%), Na_0.23TiO₂ (22.0%), Na₂TiSiO₅ (11%), and Na_0.67Al_0.1Mn_0.9O₂ (8.5%), which, upon hydrolysis, transform into a monophase titanium dioxide with intercalated sodium—Na_0.23TiO₂. Thermodynamic analysis of the heat effects of chemical reactions among raw materials and resulting products substantiates the role of silicon and sodium oxides, carbon, oxygen, and water in the formation of various electrode materials during carbothermic flux conversion and aqueous refining. Insights into the mechanisms of thermochemical formation and hydrothermal phase transformations offer a scientific basis for the development of intercalation systems from abundant and low-cost natural raw materials, bypassing the need for expensive precursor synthesis. Full article

Comparative analysis of red mud reduction techniques was performed using both carbothermal and hydrogen-based reduction methods, combining thermochemical modeling and experimental validation. The reduction process is mostly important because of the high contamination risk assessment of soil with disposed red mud. Therefore, the minimization of red mud during the reduction process can be a novel strategy for the production of metallic iron and solid residue for hydrometallurgical treatment. Different strategies of hydrogen and carbon reduction in static and dynamic conditions were studied between 700 °C and 1700 °C. The separation of solid residue and formed iron was analyzed using magnetic separation. The main aim was to study the advantages and disadvantages of using decarbonizing technologies for the treatment of red mud, aiming to develop an environmentally friendly process. Thermochemical analysis of the reduction offered new data about mass losses during our process through the evaporation, thermal decomposition, and formation of metallic carbide. Full article

Electric arc furnace dust (EAFD) is a zinc-containing solid waste generated during steelmaking, and advanced recycling strategies are needed to facilitate the recovery of valuable zinc. This study investigated the microwave-assisted carbothermic reduction in EAFD using coke as a reductant, with a focus on temperature (900–1100 °C), holding time (0–60 min), and the C/Zn molar ratio (3–5). The results demonstrated that the zinc removal rate exhibited positive correlations with both temperature and time. Under optimized conditions (1100 °C, 60 min), a zinc removal rate of 95.45% was achieved, accompanied by a complete decomposition of the ZnO phases. Furthermore, increasing the C/Zn molar ratio enhanced the zinc recovery efficiency and product purity. Isothermal kinetic analyses indicated that the reaction proceeds in two stages: during the initial stage (0–30 min), the process was governed by three-dimensional diffusion control with an activation energy of 146.50 kJ/mol, while the final stage (30–60 min) transitioned to chemical reaction control with an activation energy of 267.32 kJ/mol. Comparative assessments indicated that microwave processing significantly reduced the activation energy compared to conventional heating methods. These findings suggest that microwave-assisted reduction is capable of attaining a high-grade recovery of Zn from EAFD, thus opening up new avenues for the resource-oriented utilization of EAFD. Full article

To reduce solid waste production and enable the synergistic conversion of solid waste into high-value-added products, we introduce a novel, sustainable, and ecofriendly method. We fabricate nanofiber and nanosheet silicon carbides (SiC) through a carbothermal reduction process. Here, the calcined coal gangue, converted from coal gangue, serves as the silicon source. The carbon sources are the carbonized waste tire residue from waste tires and the pre-treated kerosene co-refining residue. The difference in carbon source results in the alteration of the morphology of the SiC obtained. By optimizing the reaction temperature, time, and mass ratio, the purity of the as-made SiC products with nanofiber-like and nanosheet-like shapes can reach 98%. Based on the influence of synthetic conditions and the results calculated from the change in the Gibbs free energy of the reactions, two mechanisms for SiC formation are proposed, namely the reaction of intermediate SiO with CO to form SiC-nuclei-driven nanofibrous SiC and the SiO-deposited carbon surface to fabricate nuclei-induced polymorphic SiC (dominant nanosheets). This work provides a constructive strategy for preparing nanostructured SiC, thereby achieving “turning trash into treasure” and broadening the sustainable utilization and development of solid wastes. Full article

An innovative approach is reported for recovering Fe and Zn resources from hazardous zinc-bearing electric arc furnace dusts (ZBDs) in a sustainable manner. A combination of carbothermal and H₂ reduction were used to overcome challenges associated with the high temperatures of carbothermal reduction and the high costs/limited supplies of hydrogen. In-depth reduction studies were carried out using zinc-rich (17 wt.%), iron-poor (35 wt.%) ZBD; coke oven battery dry quenching dust (CDQD) was used as reductant. Briquettes were prepared by mixing ZBD and CDQD powders in a range of proportions; heat treatments were carried out in flowing H₂ gas at 700 °C–900 °C for 4 h. The reduced products were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and inductively coupled plasma (ICP). The Fe content of the reduced briquettes showed increases between 50 and 150%, depending on composition and reduction temperature; Zn, Pb, Cl, Na, K and S were completely absent. The gaseous elements were collected in cooled traps at the furnace outlet to recover metallic zinc and other phases. The volatile products collected at the outlet (900 °C) contained more than 70% zinc and 6% lead; small amounts of zinc were also present in the metallic phase. The processing temperatures were significantly lower in the combined approach as compared to 100% carbothermal reduction. While reducing energy consumption and limiting the generation of greenhouse gases, this approach has the potential for enhancing the reutilization of hazardous industrial wastes, resource recovery, and economic and environmental sustainability. Full article

Aiming at the problems of low utilization rate of spodumene resources and serious environmental pollution, our team proposes a clean process to produce manganese-silicon alloy for lithium enrichment by carbothermal reduction of spodumene. In this process, the melting point and viscosity of the slag phase are very high, which affects the slag discharge and slag–metal separation. Therefore, this experiment considers the addition of CaO as a slagging agent based on the previous process and tests and analyzes the slag phase under different CaO contents. When the CaO content is 30%, the slag phase is mainly Ca₂Al₂SiO₇; the reduction rate of lithium is 99.02%; the direct yield of the alloy is 89.12%; and the melting point of the slag is 1260 °C. It can melt and wrap the alloy before removing the alloy, which has heat preservation and oxidation resistance. The viscosity of the slag at 1360 °C is 0.11 Pa·s, which is within the optimum viscosity range of the slag in actual industrial production. Experiments show that the addition of CaO is beneficial to the removal of lithium and the separation of slag and metal, which lays a good foundation for the industrialization development of the previous process and improves the economic benefits of the whole process. Full article

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. Full article

Ilmenite concentrate has emerged as the key titanium raw material for exploitation and utilization, playing a crucial role in the preparation of metallic titanium and titanium dioxide. However, the presence of impurities such as Fe, Ca, and Mg in ilmenite concentrate severely restricts its economic utilization and environmentally friendly applications. In our previous research, a novel process was proposed to prepare TiCl₄ from high-Ca- and Mg-containing ilmenite through carbothermal reduction and boiling chlorination. Nevertheless, the employment of graphite as a reducing agent and hydrochloric acid for metallic iron separation led to elevated production costs. The aim of this study was to explore an alternative and more cost-effective method. Petroleum-derived coke was used as the reducing agent to investigate the feasibility of producing titanium oxycarbide from ilmenite concentrate via carbothermal reduction and magnetic separation. The results showed that petroleum-derived coke is capable of reducing ilmenite concentrate to coral-shaped TiC_xO_y under high-temperature conditions. However, an approximate 100 °C increment in temperature is required to reach an equivalent reduction efficiency compared with graphite. The X-ray diffraction (XRD) analysis results of the reduced products reveal that complete reduction of ilmenite concentrate by petroleum-derived coke can only be achieved when the reduction process is conducted at 1600 °C for 3 h or at 1500 °C for 5 h. The reduced product obtained at 1600 °C, characterized by a substantial presence of dense Ti₂O₃, exhibits a significantly coarser particle size after 30 minutes of ball milling in contrast to the reduced product obtained at 1200 °C, which is rich in M₃O₅ anosovite. Magnetic separation results showed that the reduction product at 1200 °C could not have metallic iron removed by magnetic separation at 1.2 T, while the reduction product at 1600 °C could yield a non-magnetic charge rich in Ti₂O₃ and TiC_xO_y with an iron content as low as 2 ± 0.03 wt.%, which fully meets the requirements for producing TiCl₄ by boiling chlorination. Overall, these research results offer a new approach for the low-cost production of TiCl₄ from ilmenite concentrate with high levels of Ca and Mg impurities through boiling chlorination. Full article

Submicron-sized TiB₂ powders (300 nm–1 μm) were prepared by the reaction of TiC, B₄C, and Ca assisted by molten CaCl₂. The optimal reaction procedure (1200 °C and 25 wt.% CaCl₂ + 25 wt.% Ca) was obtained by exploring the effects of the boronization reaction temperature and the addition of an amount of CaCl₂. It was found that the introduction of CaCl₂ not only promoted the reaction but also effectively inhibited the volatilization of excess Ca. Furthermore, SEM images of the products showed that the morphology and particle size of TiB₂ were inherited from the carbothermal reduction product TiC, which was dominated by the “template/growth” mechanism. The process of the boronization reaction was that B atoms migrated from B₄C and replaced the C atoms in the lattice of TiC. Full article

Carbon dioxide is emitted in several industrial processes and contributes to global warming. One of the industries that is considered a significant emitter is metallurgy. Therefore, it is necessary to search for and implement methods to reduce its emissions from metallurgical processes. An alternative option to the use of conventional coke, which is produced solely from fossil coal, is the utilization of bio-coke. The production of bio-coke involves the use of coking coal and the incorporation of biomass-derived substances such as biochar (charcoal). The article presents the results of the research on the influence of the biochar addition on the structural, textural, and technological properties of produced bio-coke. Research on the production and analysis of the properties of the obtained bio-coke aimed at assessing the potential possibilities of applying it in the process of a carbothermal reduction of manganese ore in order to smelt ferroalloys. Studies have shown that biochar addition to the coking blend in an amount of up to 20% allows a bio-coke characterized by properties enabling the mentioned use to be obtained. Bio-coke was characterized by higher CO₂ reactivity index (CRI), lower post-reaction strength (CSR), and higher reactivity to synthetic manganese ore than regular metallurgical coke. In the context of industrial applications of bio-coke, it is necessary to verify its production and use on a pilot and industrial scale. Full article

This study presents a comparative analysis of titanium leaching from tionite (a byproduct of the titanium dioxide production process) and carbothermally reduced red mud (derived from aluminum residues). Tionites from the sulfate process and red mud residue are known for their environmental impacts due to their metal content and acidic/basic nature. This study explored leaching as a method to recover titanium and other metals under high-pressure and high-temperature conditions using sulfuric acid. Experiments were conducted in an autoclave with different parameter changes, like varying oxygen pressure, temperature, and reaction time to optimize metal extraction. The leaching efficiency of titanium was found to be higher in the carbothermal-reduced slag compared to tionite due to the altered mineral phases in the reduced material. XRD and SEM-EDS analyses confirmed the differing leaching behaviors, with titanium compounds in tionite showing greater resistance to dissolution. These findings highlight the importance of thermal pre-treatment for optimizing metal recovery from industrial residues. The main aim of this study is to contribute to the development of sustainable waste management solutions for tionites and red mud, emphasizing the potential of hydrometallurgical methods for metal recovery. The results are expected to inform future research and industrial applications, advancing the recovery of valuable metals while reducing the environmental footprint of titanium and aluminum residue disposal. Full article

Piezocatalytic materials have attracted widespread attention in the fields of clean energy and water treatment because of their ability to convert mechanical energy directly into chemical energy. In this study, γ-AlON particles synthesised using carbothermal reduction and nitridation (CRN) were used for the first time as a novel piezocatalytic material to degrade dye solutions under ultrasonic vibration. The γ-AlON particles exhibited good performance as a piezocatalytic material for the degradation of organic pollutants. After 120 min under ultrasonic vibration, 40 mg portions of γ-AlON particles in 50 mL dye solutions (10 mg/L) achieved 78.06%, 67.74%, 74.29% and 64.62% decomposition rates for rhodamine B (RhB), methyl orange (MO), methylene blue (MB) and crystal violet (CV) solutions, respectively; the fitted k values were 13.35 × 10⁻³, 10.79 × 10⁻³, 12.09 × 10⁻³ and 8.00 × 10⁻³ min⁻¹, respectively. The piezocatalytic mechanism of γ-AlON particles in the selective degradation of MO was further analysed in free-radical scavenging activity experiments. Hydroxyl radicals (•OH), superoxide radicals (•O₂⁻), holes (h⁺) and electrons (e⁻) were found to be the main active substances in the degradation process. Therefore, γ-AlON particles are an efficient and promising piezocatalytic material for the treatment of dye pollutants. Full article

The smelting of chromite to produce ferrochrome (FeCr) and subsequently, stainless steel, is an energy-intensive carbothermic process. Various countries apply the Outotec FeCr process, which employs oxidative sintering in air to produce mechanically strong chromite pellets. During this process, iron (Fe) is liberated from the chromite spinel due to the elevated temperatures and oxidative nature of the process. It is well understood that oxidatively altered chromite requires less energy to be smelted when compared to non-oxidized chromite. This study showed that sintered pellets obtained from five South African pellet sintering plants had vastly different oxidative alteration penetrations. Additionally, sintered pellets from the same plant may also vary significantly. It was further shown that ores mined from various locations in South Africa had dissimilar sintering behaviors, suggesting that sintered pellets should be characterized before smelting to determine the extent of oxidative alteration. The benefit of a smelter consuming oxidized ore was also demonstrated by comparing the interaction between oxidized and non-oxidized chromite with a carbon (C) source. Full article