Search Results (16)

Against the background of blast furnace burden optimization and the low-carbon transition of the steel industry, the development of high-quality Mg-bearing fluxed pellets is of great significance for the efficient utilization of medium-high silica iron ore concentrates. In this study, Mg-bearing medium-high silica fluxed pellets with a fixed SiO₂ content of 5.5% were prepared, and the effect of basicity in the range of R = 1.0–1.4 on compressive strength, liquid phase behavior, slag phase composition, and pore structure evolution was systematically investigated. The results showed that the compressive strength of the pellets decreased from 2527 N/pellet to 2079 N/pellet as the basicity increased from 1.0 to 1.4. At 1250 °C, the liquid phase content first decreased from 2.66% to 1.30% and then increased to 7.38%, while the liquid phase viscosity decreased continuously. Meanwhile, the liquid phase composition evolved from a SiO₂-rich calcium–iron silicate system to a Fe₂O₃⁻ and CaO-rich system. XRD results indicated that Fe₂O₃ was the dominant crystalline phase in the pellets, accompanied by a small amount of Fe₃O₄, whereas no distinct highly crystalline slag phase was detected. The slag phase was mainly a Fe-Ca-Si composite slag, in which the Fe₂O₃ content increased and the SiO₂ content decreased with increasing basicity. At higher basicity, the number and size of pores increased, and the pore morphology evolved from dispersed fine pores to irregular large pores and locally connected pores. Meanwhile, the slag phase became more widely distributed and locally enriched, weakening the continuity of the iron oxide load-bearing skeleton, which was the main reason for the decrease in compressive strength. This study provides a theoretical basis for preparing high-quality Mg-bearing fluxed pellets from medium-high silica iron ore concentrates. Full article

Against the backdrop of global climate warming and energy shortages, China proposed the “dual-carbon strategy” in 2020 to address climate change and promote ecological civilization. As a high-carbon emission industry, the iron and steel sector faces an urgent need to accelerate low-carbon transformation. In 2024, China’s crude steel production accounted for over 50% of the total global crude steel production, with the blast furnace–basic oxygen furnace route remaining the dominant process. As a natural iron-bearing raw material, lump ore features high iron grade and low cost, eliminating the requirements of high-temperature processing steps such as sintering or pelletizing. Therefore, increasing the proportion of lump ore in the blast furnace burden represents an effective approach to achieving energy conservation and emission reduction. However, constrained by technical constraints, the current utilization rate of natural lump ore in Chinese steel enterprises remains generally low. Research indicates that despite their higher iron content, lump ores exhibit deficiencies in metallurgical properties such as thermal shock resistance and softening–melting drip characteristics, limiting their large-scale application. Therefore, it is typically necessary to perform pre-treatment such as preheating before charging into the furnace. In actual blast furnace burden design, it is essential to balance metallurgical performance and economic considerations by appropriately combining lump ore with high-basicity sinter and pellets. This approach leverages high-temperature interactions among the burden materials to optimize the overall softening and melting behavior of the mixed charge, thereby ensuring smooth furnace operation while simultaneously advancing the low-carbon transition of the iron and steel industry. Full article

Pelletizing is an effective way of converting abundant phosphate ore fines into usable feedstocks for yellow-phosphorus production. In this work, the oxidation-roasting behavior of siliceous–calcareous phosphate ore pellets and siliceous phosphate ore pellets was evaluated in a laboratory tube furnace. The consolidation mechanisms were revealed using optical microscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The results indicate that siliceous phosphate ore pellets exhibit superior oxidation-roasting performance relative to siliceous–calcareous phosphate ore pellets. After roasting, oxidized siliceous–calcareous phosphate ore pellets show a loose and porous framework with large pores, thin walls, and occasional surface cracking. The consolidation of siliceous–calcareous phosphate ore pellets is mainly governed by the recrystallization bonding of silicon–magnesium-bearing fluorapatite. In contrast, oxidized siliceous phosphate ore pellets display a denser microstructure and stronger intergranular bonding. The dominant bonding forms are the recrystallization bonding of silicon-bearing fluorapatite and solid-state bonding between silicon-bearing fluorapatite particles and quartz particles. Furthermore, carbonate gangue minerals are detrimental to strength development because CO₂ release during roasting promotes the development of interconnected porosity and defects, thereby reducing the compressive strength of oxidized phosphate ore pellets. Full article

High-iron red mud presents a major obstacle to comprehensive resource utilization, as iron and aluminum minerals form tightly interwoven and encapsulated structures that resist conventional separation, hindering efficient co-recovery of these valuable elements. This study aimed to address this bottleneck by developing an effective strategy for iron–aluminum separation and synergistic recovery. A reduction smelting process was conducted in a sealed electric furnace using internally carbon-containing red mud pellets, enabling phase reconstruction to regulate aluminum-bearing phases while achieving iron–aluminum separation. XRD and SEM analysis verified that iron oxides were reduced to metallic iron with recovery exceeding 98%, and aluminum-bearing phases were selectively converted into active α-Al₂O₃ and mainly dodecacalcium hepta-aluminate (Ca₁₂Al₁₄O₃₃) in the slag. Under optimized Bayer leaching conditions (150 g/L NaOH, 240 °C, 90 min, liquid-to-solid ratio 6:1), aluminum extraction exceeded 60%, comparable to conventional red mud processing. This work overcomes the technical barrier of iron–aluminum co-recovery from high-iron red mud, offering a practical and efficient route for its sustainable valorization. Full article

The present study explores the production of metallized titanomagnetite briquettes, with a view to addressing two key issues. Firstly, it seeks to address the growing shortage of high-quality iron-bearing raw materials. Secondly, it looks at how to meet the increasingly stringent environmental constraints. The conventional blast-furnace treatment of titanomagnetite is hindered by the formation of refractory Ti-rich slags. It is hereby proposed that a single-cycle briquetting process in conjunction with a thermal reduction route should be utilized. This approach enables precise regulation of the Fe/flux ratio. Experiments were conducted on a low-grade titanomagnetite concentrate (68.5% Fe) from the Pervouralsk deposit (Russia). Cylindrical briquettes (D 15–20 mm, h 8–10 mm) were subjected to a pressure of 300 MPa during the pressing process, with the utilization of diverse binders comprising rubber cement, CaO, graphite + water, and basic oxygen-furnace (BOF) slag + sodium silicate. Following an oxidative pre-heating process at 1300 °C for two hours, followed by a gas-based reduction process at 1050 °C for three hours, with a CO/N₂ ratio of 90/10, the products demonstrated an oxidation rate of 85–95% and a cold compression strength of 16–80 MPa. The highest observed strength (80 MPa) was obtained with a binder comprising CaO·MgO·2SiO₂ (diopside/merwinite), which forms a low-viscosity melt, fills 90% of pores and crystallizes as acicular Mg-SFCA-I during cooling. Conversely, the CaO·TiO₂ and FeO·TiO₂ + Fe₃C associations yield brittle structures and a maximum strength of 16 MPa. The optimum briquette (0.55% CaO, D/H = 20/10 mm) exhibited a 95.7% metallization degree, a compressive strength of 48.9 MPa, and dimensional changes within acceptable limits, thus fulfilling the requirements for electric arc furnace feedstock. Further research is required in the form of a full Life Cycle Assessment and pilot-scale testing. However, the results obtained thus far confirm that titanomagnetite briquettes with a binder consisting of CaO, MgO and SiO₂ are a promising alternative to pellets for low-carbon steelmaking. Full article

Against the backdrop of escalating global carbon emissions, the steel industry urgently requires a transition toward green and low-carbon practices. As a conditionally carbon-neutral renewable energy source, biochar holds potential for replacing traditional fossil-based reducing agents. This study aims to investigate the mechanism and performance differences between biochar (wood char, bamboo char) and conventional reducing agents (semi-coke, coke powder, anthracite) in the direct reduction process of carbon-bearing briquettes. Through reduction experiments simulating rotary kiln conditions, combined with analysis of reducing agent gasification characteristics, carbon-to-oxygen (C/O) molar ratio control, X-ray diffraction (XRD), and microstructural examination, the high-temperature behavior of different reducing agents was systematically evaluated. Results indicate that biochar exhibits superior gasification reactivity due to its high specific surface area and developed pore structure: wood char and bamboo char show significantly enhanced reaction rates above 1073 K, approaching complete conversion at 1173 K. In contrast, anthracite and coke powder, characterized by dense structures and low specific surface areas, failed to achieve complete gasification even at 1273 K. Pellets containing bamboo char achieved the highest metallization rate (90.16%) after calcination at 1373 K. The compressive strength of the pellets first decreased and then increased with rising temperature, consistent with the trend in metallization rate. The mechanism analysis indicates that the high reactivity and porous structure of biochar promote rapid CO diffusion and synergistic gas–solid reactions, significantly accelerating the reduction of iron oxides and the formation of metallic iron. Full article

A technology was developed for managing Zn-bearing dust, facilitating the recycling of hazardous solid waste and the production of porous carbon materials. In the one-step process, Zn-bearing dusts were employed not only as raw materials to prepare reduced Zn-bearing dust pellets but also as activators to prepare K, Na-embedded activated carbon. In the process, the Fe, C, Zn, K, and Na in the dusts were rationally utilized. Under optimal conditions, the reduced pellets and porous carbon materials were simultaneously produced and characterized using XRD, SEM/EDS, FTIR, and adsorption of nitrogen techniques. The results indicated that the reduced pellets, with low levels of harmful elements and high iron grade and strength, could be directly used as burden for enhancing blast furnace operation without additional agglomeration. Meanwhile, the K and Na-embedded porous carbon material demonstrated superior SO₂ and NO adsorption capacities compared to the commercial activated carbon, making it suitable for purifying SO₂ and NO-bearing flue gas. The hazardous solid wastes were effectively used to treat flue gases through this technology. The mechanism in the synergistic reduction and activation process was elucidated. The coupling effect between the reduction reactions of Fe₂O₃, Fe₃O₄, FeO, MgFe₂O₄, CaFe₂O₄, ZnFe₂O₄, KFeO₂, and NaFeO₂ in the dusts and activation reaction of C in the coal promoted the synchronous reduction and activation process. Full article

The authors of this study focused on the energy and material assessment of processes for processing pellets from metal-bearing waste, specifically Fe concentrate. A mathematical model was created for process evaluation, with which thermotechnical calculations of parameters in the processing of metallized pellets were carried out. Thermodynamic calculations were performed to determine the enthalpy of the charge in individual devices (drying chamber, rotary kiln, cooler). For the reduction of Fe oxides, carbon from coke (with Fe oxide reductions of 50%, 61%, and 92%) and lignite (with Fe oxide reductions of 69% and 92%) were considered as part of the pellets. The degree of reduction of iron oxides was a determining parameter, and the consumption of the reducing agent corresponded to the direct reduction of Fe oxides by carbon with a coefficient of 1.5. Another determining parameter was the input and output temperature in individual devices. For a more precise description of the processes in individual devices, calculations were carried out zonally. The results of the calculations are analyses and recommendations for feasible alternatives for the reducing agent and associated processes. Full article

Short carbon fiber (sCF)-based polymer composite parts enable one to increase in the material property range for additive manufacturing (AM) applications. However, room for technical and material improvement is still possible, bearing in mind that the commonly used fused filament fabrication (FFF) technique is prone to an extra filament-making step. Here, we compare FFF with direct pellet additive manufacturing (DPAM) for sCF-based composites, taking into account degradation reactions, print quality, and energy usage. On top of that, the matrix is based on industrial waste polymers (recycled polycarbonate blended with acrylonitrile butadiene styrene polymer and recycled propylene), additives are explored, and the printing settings are optimized, benefiting from molecular, rheological, thermal, morphological, and material property analyses. Despite this, DPAM resulted in a rougher surface finish compared to FFF and can be seen as a faster printing technique that reduces energy consumption and molecular degradation. The findings help formulate guidelines for the successful DPAM and FFF of sCF-based composite materials in view of better market appreciation. Full article

As a renewable, carbon-neutral raw material, the application of biomass in steel production is conducive to reducing greenhouse gas emissions and achieving green and sustainable development in the steel industry. The heating and reduction process of a rotary hearth furnace was simulated under laboratory conditions to roast and reduce biochar carbon-bearing pellets with coke powder and anthracite carbon-bearing pellets as a comparison. This was conducted to investigate the impact of biochar as a reducing agent on the direct reduction in carbon-bearing pellets. Under various reduction temperatures, carbon/oxygen ratios, and reduction times, tests were conducted on the compressive strength and metallization rate of carbon-bearing pellets made using typical binder bentonite. Results show that with the increase in reduction temperature, the metallization rate of pellets increases, while the compressive strength initially decreases and then increases, reaching the lowest point at 900 °C and 1000 °C. When the ratio of carbon to oxygen is between 0.7 and 0.9 and the reduction time is between 15 and 25 min, carbon-bearing pellets meet the requirements of both the metallization rate and the strength, with the metallization rate above 80%. However, severe volume swelling and low strength were observed in biochar carbon-bearing pellets at 900 °C and 1000 °C, which negatively impacted multi-layered charging and heat transfer efficiency in the blast furnace. Therefore, a novel laboratory-prepared binder was introduced in the preparation process of biochar carbon-bearing pellets at an appropriate addition ratio of 5–8%. Without producing any swelling concerns, the inclusion of this binder considerably improved the compression strength and metallization rate of the pellets, enabling them to fulfill the standards for raw materials in the blast furnace. Full article

In order to pursue the goal of low-carbon ironmaking, a new type of humic acid (HA)-based binder was applied to the preparation of oxidized pellets from vanadium-bearing titanomagnetite (VTM) in this work. Effects of the HA binder (or with limestone) on the balling, preheating, and roasting behaviors of VTM were comparatively studied with bentonite. The embedded features of each mineral phase in sintered pellets, especially the crystallization and growth state of hematite grains, were deeply investigated by XRD, optical microscopy, and SEM–EDS measures. The binder dosage can be cut down by 50% when HA was used instead of bentonite. Fine hematite grains in HA pellets evolved into plump interlocking grains with ~5% of limestone addition. Pseudobrookite and magnesioferrite spinel phase formed at the optimal sintering temperature of 1250 °C, which could hinder the crystallization of hematite and affect the strength of final pellets. Full article

Zinc ash is a by-product of the hot-dip galvanizing process and the electrolytic zinc process, which is classified as a hazardous waste consisting predominately of zinc oxide that could be recovered as the useful main resource for ZnO preparation. In this work, in order to reduce the energy consumption of the direct reduction process and improve the resource-recovery rate. A new technology for zinc oxide production, by a carbothermal reduction of zinc ash, is proposed. This process includes two steps: high-temperature roasting of zinc ash for dechlorination and a carbothermal reduction of dechlorination ash. Zn in zinc ash is mainly presented in the form of zinc oxide (ZnO), basic zinc chloride (Zn₅(OH)₈Cl₂H₂O), and metallic zinc (Zn). Basic zinc chloride can be roasted and decomposed to reduce the chlorine content in zinc ash. The results of a chloride ion removal test show that the optimal roasting temperature is 1000 °C, with a holding time of 60 min. Under the modified conditions, the chloride content in the roasted zinc ash is reduced to 0.021 wt.%, and the dechlorination rate is more than 99.5%, which can meet the requirements of zinc oxide production. The best process conditions for zinc oxide production by carbothermic reduction are as follows: reduction temperature of 1250 °C, reduction time of 60 min, and reduction agent addition of 22 wt.%. Under the best reduction process, the purity of zinc oxide product is 99.5%, and the recovery of zinc is more than 99.25%. Needle-like zinc oxide obtained by carbothermic reduction has high purity and can replace zinc oxide produced by an indirect process. Full article

The isothermal reduction of iron oxide pellet fines–carbon composites was investigated at temperatures of 900–1100 °C. The reduction reactions were monitored using the thermogravimetric (TG) technique. Alternatively, a Quadruple Mass Spectrometer (QMS) analyzed the CO and CO₂ gases evolved from the reduction reactions. The effect of temperature, carbon source, and reaction time on the rate of reduction was extensively studied. The phase composition and the morphological structure of the reduced composites were identified by X-ray diffraction (XRD) and a scanning electron microscope (SEM). The results showed that the reduction rate was affected by the temperature and source of carbon. For all composite compacts, the reduction rate, as well as the conversion degree (α) increased with increasing temperature. Under the same temperature, the conversion degree and the reduction rate of composites were greater according to using the following carbon sources order: Activated charcoal > charcoal > coal. The reduction of the different composites was shown to occur stepwise from hematite to metallic iron. The reduction, either by activated charcoal or charcoal, is characterized by two behaviors. During the initial stage, the chemical reaction model (1 − α)⁻² controls the reduction process whereas the final stage is controlled by gas diffusion [1 − (1 − α)^1/2]². In the case of reduction with coal, the reduction mechanism is regulated by the Avrami–Erofeev model [−ln (1−α)²] at the initial stage. The rate-controlling mechanism is the 3-D diffusion model (Z-L-T), namely [(1−α)^−1/3−1]² at the latter stage. The results indicated that using biomass carbon sources is favorable to replace fossil-origin carbon-bearing materials for the reduction of iron oxide pellet fines. Full article

In the processing of waste materials, attention must be given to the efficient use of energy. The pelletization of dry ice is a good example of such processes. A literature review shows that in the pelletizers available on the market, the force applied in the process is excessive. As a result, the efficiency of the utilization of inputs, including electricity and carbon dioxide, is at a very low level. This article presents the results of experimental research on the effect of the degree of dry ice compression on the value of the Poisson ratio. The first part of this article presents the research methodology and a description of the test stand, developed specifically for this research, bearing in mind the unique properties of carbon dioxide in the solid state. The results presented show the behavior of dry ice during compression in a rectangular chamber for different final densities of the finished product. As a result, it is possible to determine the values of the Poisson ratio as a function of density, using for this purpose four mathematical models. The findings of this research may be useful for research work focused on the further development of this process, such as by using the Drucker–Prager/Cap numerical model to optimize the geometric parameters of the parts and components of the main unit of the machine used in the extrusion process of dry ice. Full article

To release the environmental pressure from the massive discharge of bauxite residue (red mud), a novel recycling method of red mud in steel making process was investigated through high-temperature experiments and thermodynamic analysis. The results showed that after the reduction roasting of the carbon-bearing red mud pellets at 1100–1200 °C for 12–20 min, the metallic pellets were obtained with the metallization ratio of ≥88%. Then, the separation of slag and iron achieved from the metallic pellets at 1550 °C, after composition adjustment targeting the primary crystal region of the 12CaO·7Al₂O₃ phase. After iron removal and composition adjustment, the smelting-separation slag had good smelting performance and desulfurization capability, which meets the demand of sulfurization flux in steel making process. The pig iron quality meets the requirements of the high-quality raw material for steel making. In virtue of the huge scale and output of steel industry, the large-scale consumption and zero-waste recycling method of red mud was proposed, which comprised of the carbon-bearing red mud pellets roasting in the rotary hearth furnace and smelting separation in the electric arc furnace after composition adjustment. Full article