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• The distribution characteristics of CaS in the radial direction of the hearth were analyzed. • The formation mechanism and migration process of CaS in the hearth were analyzed. • The interface reaction between slag and coke is the main source of CaS formation in the furnace hearth. As the main occurrence form of sulfur element in blast furnace hearth, high content of CaS within the blast furnace hearth have a certain impact on low-carbon smelting of blast furnace. In this paper, the micro-morphology and distribution of CaS in the hearth area are studied by scanning electron microscopy and industrial CT, and the formation process of CaS in the deadman is clarified by drilling core samples of residual iron in the hearth of 3200 m3 blast furnace in China. The research results indicate that CaS in the hearth is mainly formed by slag-coke interface reaction and slag-iron interface reaction. Based on an analysis of the relative difficulty of these two pathways, it was observed that CaS is more readily generated through the slag-coke interface reaction. Based on the analysis of the difficulty of the two generation paths, it is found that CaS in the blast furnace hearth is more easily generated through slag coke interface reaction. The CaS particles generated in the hearth take the slag as the growth matrix, and with the flow of slag and iron and the renewal of the deadman coke, they are finally enriched and precipitated in the edge area of the deadman in the form of agglomerates. Based on the formation mechanism of CaS in the hearth, it is analyzed that the formation of CaS aggregates in the hearth is mainly affected by three factors: sulfur load, slag basicity and hearth temperature. This study provides a certain theoretical reference and guidance for steel enterprises aiming to reduce fuel consumption and achieve green production practices. [ABSTRACT FROM AUTHOR]

• The temperature field in the bird's nest area of blast furnace tuyere is characterized. • The phase composition of coal-coke-slag is quantitatively characterized. • The radial physicochemical properties of coal-coke-slag are analyzed. • Modification suggestions of coal-coke-slag are proposed. Understanding the occurrence of phases and the evolution of physicochemical properties in coal-coke-slag powder within the blast furnace tuyere's bird's nest area is crucial for reducing carbon emissions and energy consumption in the blast furnace. By dissecting a 2200 m3 blast furnace in China, the temperature field and high-temperature physicochemical properties of coal-coke-slag powder in the tuyere bird's nest area along the radial direction were determined. Firstly, the temperature range in the tuyere bird's nest area spanned from 1523 °C to 1709 °C, with the maximum temperature near the end of the bird's nest area. Secondly, the mass proportions of coal, coke and slag in coal-coke-slag powder were 42.16 %, 25.90 % and 31.94 %, respectively. Along the radial direction of the blast furnace, the degree of graphitization of carbon components of coal-coke-slag increased gradually, and the melting temperature and viscosity of the slag phase also exhibited a gradual increase. Finally, the modification suggestions of the physicochemical properties of coal-coke-slag were put forward, with a focus on three factors: fuel, slag, and temperature. By employing tuyere injection operations with Ca-Fe flux, and using fuel with low ash content, larger particle size, fewer harmful elements, and excellent combustion performance, more heat input was provided to the front of the bird's nest area, which contributed to improved furnace efficiency and performance. [ABSTRACT FROM AUTHOR]

• Occurrence state of cinder multiphase components in the bird's nest area is reviewed. • Formation mechanism of tuyere cinder is proposed. • Modification methods of tuyere cinder are reviewed. • Future research directions of tuyere cinder are proposed. The presence of cinder in the tuyere bird's nest region poses a significant obstacle to the energy-saving production of blast furnaces by impeding the penetration of high-temperature gas into the charge column. This paper provides a comprehensive review of the multiphase occurrence state, formation mechanism, and modification methods of cinder. Firstly, the phase composition and high-temperature performance of cinder are investigated from various perspectives, including tuyere coke, tuyere slag, coal ash slag, and the interaction between residual carbon and coal ash slag. These aspects shed light on the characterization of cinder and its behavior at elevated temperatures. Secondly, the formation mechanism of cinder is explored, aiming to unravel the factors contributing to its generation. Understanding the underlying mechanisms is crucial for devising effective strategies to mitigate or modify its formation. Thirdly, the paper examines the modification methods of cinder from three aspects: tuyere flux injection technology, tuyere hydrogen-rich injection technology, and tuyere sequence impulse injection technology. These approaches offer potential means to alter the characteristics and behavior of cinder. Finally, future research on cinder can focus on the characterization and performance analysis, depth analysis of formation mechanisms, and exploration of the modification mechanisms. [ABSTRACT FROM AUTHOR]

High-alumina fly ash microbeads and steel slag were used as main raw materials to synthesize feldspar porous ceramics via high-temperature solid phase sintering by adding pulverized coal as a pore-forming agent. The effects of the steel slag and pore-forming agent on the apparent porosity and flexural strength of porous ceramics were investigated. The phase composition and microstructure of porous ceramics were characterized using X-ray diffraction and scanning electron microscopy, and the results indicated that the added amount of steel slag was only related to the amount of liquid phase formed in porous ceramics. The higher the amount of steel slag added, the more the liquid phase formed. At the same sintering temperature, the higher the pore former content, the higher the porosity of the porous ceramics and the lower the bending strength. When porous ceramics were sintered at 1160 °C steel slag melted and fly ash microsphere structures were formed. When the porous ceramics were sintered at 1190 °C, the fly ash microsphere structure disappeared. After the internal liquid phase of the ceramic was formed, the lower the sintering temperature, the larger the porous ceramic structure factor, the more sensitive the flexural strength to changes in porosity and the higher the theoretical strength of ceramic densification. Moreover, as the sintering temperature decreased, the network structure formed during the reaction of fly ash microbeads with CaO greatly increased the flexural strength of fly ash ceramics. When the sintering temperature, sintering time and pore former content were 1170 °C, 120 min, and 10%, respectively, the obtained porous ceramics presented superior apparent porosity and flexural strength (49.21% and 12.88 MPa, respectively), and the main crystalline phase of porous ceramics was anorthite featuring pore size ranging from 5 to 50 μm. [ABSTRACT FROM AUTHOR]

Red mud is a kind of by-product generated in alumina production and typically contains some rare metals like Sc and Ga. In this study, Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) and Electron Probe Micro-Analysis (EPMA) were used to investigate the affinities of Sc and Ga with the major elements including Fe, Al, Si, Ti and Ca existed in red mud. Combined the mapping analyses of high mass resolution of ToF-SIMS with individual spot and mapping analyses of EPMA, the substitution of scandium and gallium for these major elements should follow the order of Ti > Fe > Al > Si and Fe > Al > Ti > Ca > Si, respectively. Scandium has an apparent enrichment in the mineral phases of anatase, hematite and goethite. The hetero-valent isomorphism of 4Sc 3+  → 3Ti 4+ plays a critical role in substitution of Sc 3+ into the anatase structure and is different from that of Sc 3+  → Fe 3+ occurred in hematite or goethite. Part of scandium is also found to be existed in silicon-rich minerals of quartz or zeolite. Gallium is closely coordinated with ferrum and aluminum, suggesting that it can proxy for these elements in the crystal lattices of hematite, goethite and gibbsite. All the observations are fundamental clues to the extraction technology of scandium and gallium from red mud. [ABSTRACT FROM AUTHOR]

The iron rich glass–ceramics were prepared by cold pressing sintering method under various atmospheres. Microstructure evolution and crystalline phase transition of glass ceramics were investigated by field emission scanning electron microscopy and X-ray diffraction. The influence of sintering atmosphere on crystallization behaviour was carried out by differential thermal analysis experiment. The results indicate that the akermanite and gehlenite, in the form of spherical or granular, uniformly distribute in the glass matrix as samples sintered in N 2 and CO (10 vol% CO, 90 vol% N 2 , 60 mL/min) atmospheres. The corresponding nucleation and crystallization temperatures are both reduced by ~20 °C. Moreover, the main mechanical properties of glass samples sintered in CO and N 2 atmospheres are improved as compared with air ones, and the performance of samples sintered in CO (Bending strength 55 MPa, micro-hardness 3.6 GPa) is much better. This research is of special interest for the utilization of steel slag and energy saving. [ABSTRACT FROM AUTHOR]

• The physicochemical properties of cinder slag in the birdnest region are characterized. • The modification effects of Ca2+, Mg2+ and Fe2+ on the cinder slag are analyzed. • The interaction modification of Ca2+ and Fe2+ is more strongly. • The injection content of alkaline flux from the tuyere is clarified. An important factor in increasing gas utilization and lowering carbon emissions is the removal of cinder from the tuyere birdnest region of the blast furnace. Based on a 2200 m3 blast furnace in China, the physicochemical characteristics of cinder are investigated in this paper. Alkaline flux's chemical modification and flux injection content are examined to alter the fluidity of cinder slag. Firstly, the basicity and aluminum content of cinder slag are 0.80 and 40.33%, respectively. The melting characteristic of cinder slag is high and the liquid phase fluidity is poor. Secondly, as the content of CaO, MgO, and FeO grow while the viscosity keeps declining, the melting temperature of the cinder first decreases and then rises, rises, and decreases. Compared to Mg2+, Ca2+ and Fe2+ have higher diffusion rates and a stronger interaction modification impact. The potential of flux modification is CaO + FeO > CaO + MgO > CaO > FeO > MgO. Finally, the optimum chemical modification occurs when the basicity of cinder slag is 1.05 and the FeO content is 0.40%. During regular blast furnace operation, 1.62 kg/tHM of limestone and 5.92 kg/tHM of basic oxygen furnace (BOF) slag are injected into the tuyere. [ABSTRACT FROM AUTHOR]

• Systematic classification of concepts in the oxygen blast furnace. • Reported the recent advancements in industrial oxygen blast furnaces. • Explored future development directions for oxygen blast furnace based on practices. • Analyzed the smelting of vanadium-titanium magnetite in the oxygen blast furnace. Climate change poses a shared global challenge. Given its substantial contribution to CO 2 emissions, the steel industry must shoulder a significant responsibility for the carbon neutrality goal. Achieving carbon neutrality in the iron and steel industry is a complex and gradual endeavor, requiring sustained efforts rather than offering a swift resolution in practical terms. Despite the ambitious development of numerous non-blast furnace processes, the traditional blast furnace (TBF) is poised to persist as the dominant ironmaking process in the upcoming decades. Conversely, the oxygen blast furnace (OBF) process, distinguished by its exceptional emission reduction potential and low retrofit costs, emerges as one of the most promising ironmaking technologies for the future. Therefore, this review comprehensively explores the origin and evolution of the OBF process, elucidating technological advancements across various historical periods. Furthermore, the review puts forth a comprehensive analysis of the feasibility of employing the OBF process for smelting vanadium-titanium magnetite (VTM), considering the benefits of the OBF and the challenges it encounters. Looking ahead, the advancement of the OBF should concentrate on pivotal domains like enhancing furnace condition control technology, exploring and innovating coke substitutes, and developing new materials with high-temperature and oxidation resistance. Concurrently, the Carbon Capture, Utilization, and Storage (CCUS) technologies are vigorously developed to further enhance the carbon reduction potential of OBF. This review aims to ignite readers' research curiosity regarding the OBF process and its application in smelting VTM. It also endeavors to propel the industrialization process and foster the sustainable development of the OBF. [ABSTRACT FROM AUTHOR]

Reasonable slag fluidity is essential for stable HIsmelt process operation. During the slag-tapping process, crystallization will cause the slag viscosity to rise sharply, which is not conducive to stable slag-tapping operation, especially for smelting high-titanium slag. In this paper, the viscosity of the CaO-MgO-Al 2 O 3 -SiO 2 -TiO 2 -FeO slag with varying 10–50% TiO 2 content was studied in the laboratory. The crystalline phases of water quenched slag samples at different temperatures were determined by XRD, and it was verified with the results of Factsage thermodynamic calculations. In addition, the effects of crystalline phase, crystalline morphology and crystal size on the critical viscosity of slag were discussed through SEM-EDS analysis. The results show that the proper TiO 2 content in the slag is below 40%, the temperature of critical viscosity (T cv) of the slag is between 1336 °C and 1360 °C, and the T cv of the slag with a TiO 2 content of 50% increases to 1500 °C. The sudden increase in viscosity is related to the crystallization behavior of the slag. With the increase of TiO 2 content, the main precipitated titanium-rich phase in the slag changed from dendritic perovskite to plate-shaped pseudobrookite. Among them, when the TiO 2 content is 10%, the sharp increase in viscosity of the slag is mainly determined by the precipitation amount of melilite. The amount of crystals in the slag between 20% and 43% causes the viscosity of the slag to rise rapidly, which is mainly due to the fact that the granular crystals have a greater influence on the viscosity than the plate crystals. Compared with the experimental results, it is found that Factsage software cannot accurately calculate the phase equilibrium of slag with a TiO 2 content of 40–50%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Structure of liquid Fe-C alloy consists of medium-range order clusters, short-range order cores and free volume. • Iron atoms act in three coordination states, while the carbon atoms stay in the short-range cores and medium-range order clusters. • Medium-range order clusters in Fe-C melt are unstable. • Effects of the temperature and composition on melt order degree are inconsistent, so as to the change of viscosity. A comprehensive investigation on liquid structure and viscosity of Fe-C melts were performed. The result shows that there is actually a medium-range ordered cluster structure in molten iron, which is unstable and will change due to the existence of free volume. Carbon atoms exist in an ordered structure inside the melt, while iron atoms have three coordination states. The reduction of carbon content and the increase of temperature contribute to a low viscosity of molten iron. Meanwhile, the number and size of clusters in the Fe-C melt increase accordingly, but the mechanisms affected by temperature and composition are different. [ABSTRACT FROM AUTHOR]

The slag, iron and coke in the deadman are extremely difficult to obtain in regular production. In this study, a commercial blast furnace was shut down and the samples were adopted systematically through a dissection study. The image processing method was also involved to clarify the macroscopic morphology of the deadman coke and the coke size distribution as well as the variation of the deadman voidage. It was found that the average size of coke was distributed in "M-shape" and voidage of deadman decreased with the increase of distance to the hearth wall in the horizontal direction. The voidage in the middle and lower of the vertical deadman was the largest and the average size of coke decreased with the increase of the distance to the taphole centerline in the height direction. In addition, the formation mechanism was analyzed, including carburization with hot metal, coke graphitization, the erosion of slag, hot metal, gas flow, etc., which provided an important reference for the high efficiency and low carbon smelting of the blast furnace. • Coke size decreased gradually and the deadman voidage increased in the height direction of the hearth. • Coke size distributes in "M-shape" while voidage in "V-shape" in the horizontal direction. • Main ways of coke consumption are carburization reaction and consumption in the raceway zone, followed by graphitization and the washing of hot metal. • The consumed coke was replaced by the "new" coke falling from the upper loose coke zone to update the deadman. [ABSTRACT FROM AUTHOR]