Key Takeaways & Executive Findings
- •• Substituting Al2O3 with A-type high-alumina calcium ferrite (SFCA) in sintering enhances sinter compressive strength by 6.76 MPa and reducibility by 0.33, achieving 22.57 MPa and 0.85, respectively. • Increasing A-type SFCA proportion raises calcium ferrite and composite calcium ferrite contents while reducing Al2O3, CaO, SiO2, and silicate phases, improving sinter mineralogy and reducing porosity. • A cost-effective SFCA production method using high-alumina ores, hazardous waste, and iron-calcium-based solid waste promotes industrial solid waste recycling and lowers production costs. • A-type SFCA demonstrates superior mechanical properties, reducibility, and melting characteristics, offering a promising strategy for optimizing sinter performance and reducing carbon emissions in ironmaking.
Abstract
High-alumina iron ores (Al2O3 content > 3.0wt%) are widely utilized in sinter production due to their economic benefits, yet their high alumina content challenges the performance of sinter and the stability of blast furnaces. This study focuses on the application of high-alumina composite calcium ferrites (SFCA) in the sintering of high-alumina iron ores. By prefabricating calcium ferrites, we aimed to substitute phase adjustment for compositional tuning, particularly examining its effects on enhancing sinter quality at 30wt%, 50wt%, and 100wt% replacement ratios of Al2O3. Previous work developed two types of high-alumina SFCA (A-type and B-type), with A-type demonstrating superior experimental performance. Our results indicate that increasing the proportion of A-type SFCA in the raw materials leads to higher calcium ferrite and composite calcium ferrite contents, while decreasing the proportions of Al2O3, CaO, SiO2, calcium silicate, and calcium alumino-ferrite (CaAlxFe2–xO4). Scanning electron microscopy (SEM) and mineralogical analyses reveal that sinter substituted with A-type SFCA primarily consists of SFCA and calcium ferraluminate (CFA), with increasing calcium ferrite content and decreasing porosity and silicate content as the substitution ratio increases. Complete substitution of Al2O3 with A-type SFCA enhances the compressive strength of the sinters to 22.57 MPa, a 6.76 MPa improvement over traditional methods. With 100wt% substitution, the reducibility reaches 0.85, a 0.33 increase over the baseline (A-type and B-type SFCA are not added). A cost-effective method for SFCA production using high-alumina ores, hazardous waste, and iron-calcium-based solid waste is proposed to lower production costs and promote the recycling of industrial solid waste. A-type SFCA exhibits significant advantages in mechanical properties, reducibility, and melting characteristics, validating its potential in optimizing sinter performance and reducing carbon emissions, thereby laying a theoretical and practical foundation for the industrial application of high-alumina SFCA.
1. Introduction
High-alumina iron ores (Al2O3 content > 3.0wt%) have gained prominence in sintering processes due to their economic viability, particularly exemplified by Australian imports such as Jimba and SP10 ores, which achieved a 20wt% blending ratio in domestic steel mills by 2020 [1–4]. While these ores enhance sinter cohesion and mechanical strength through their aluminous composition [5–8], their escalating utilization presents a critical paradox in ironmaking metallurgy [9–11]. The technical challenges emerge systematically across production stages. During sintering, alumina-rich ores demand 70–90 kg/t solid fuel consumption, exceeding conventional ores by 40%–60%, primarily due to elevated liquid-phase viscosity impeding permeability [12–15]. This viscosity escalation correlates directly with Al2O3 concentration, as demonstrated by Wen Tao’s phase analysis showing calcium ferrite morphology transition from acicular to platy structures when Al2O3 exceeds 2.0wt% [16]. Field trials by Wu Yi further quantify operational trade-offs: maintaining sinter yield above 3.5wt% Al2O3 necessitates increased raw material inputs, paradoxically reducing drum strength by 8%–12% [17]. Mežibrický et al. [18] synthesized high alumina composite calcium ferrite (SFCA) crystals at high temperatures using alumina crucibles and found that the Al3+ provided by the crucible made the material composition and mechanical properties (elastic modulus 225.1 GPa, hardness 27.2 GPa) highly stable, indicating that the high alumina core of sintered particles can shield the influence of external compositional differences.
Blast furnace operations confront compounded effects. Slag viscosity increases 30wt%–45wt% when Al2O3 rises from baseline 12wt%–15wt% to 20wt%, critically impairing slag–iron separation efficiency [19–24]. Additionally, the high alumina content in these ores raises the melting point, leading to increased energy consumption during ironmaking, as higher temperatures are required for complete melting [25–27]. From the perspective of metallurgical economy, high alumina iron ore has significant cost advantages compared to high-grade iron ore, and it is expected that its proportion in the sintering raw material structure will show an increasing trend. However, with the increase of Al2O3 content, the above challenges intensify, necessitating innovative approaches to mitigate the adverse effects on sinter quality and blast furnace performance.
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Rende Chang, Chengyi Ding, Feng Jiang, Hongming Long, Xuewei Lv, Gang Li, Peng Yuan, Changyou Yu, Mengbo Dai, Tiejun Chun (2025). Application of high-alumina type calcium ferrite: A new strategy of mineral phase regulation instead of chemical composition regulation in iron ore sintering. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3128-4
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Frequently Asked Questions
What is the main objective of the study on high-alumina calcium ferrite in iron ore sintering?
The study aims to replace traditional chemical composition regulation with mineral phase regulation by prefabricating high-alumina composite calcium ferrites (SFCA) to enhance sinter quality and reduce carbon emissions in ironmaking.
How does substituting Al2O3 with A-type SFCA affect sinter properties?
Substituting Al2O3 with A-type SFCA increases calcium ferrite content, reduces porosity and silicate content, and improves compressive strength (up to 22.57 MPa) and reducibility (up to 0.85) compared to conventional methods.
What are the environmental benefits of using A-type SFCA in sintering?
The proposed cost-effective production method utilizes high-alumina ores, hazardous waste, and iron-calcium-based solid waste, promoting industrial solid waste recycling and lowering production costs while reducing carbon emissions.
What is the significance of the A-type SFCA compared to B-type?
A-type SFCA demonstrates superior experimental performance in mechanical properties, reducibility, and melting characteristics, making it more effective for optimizing sinter performance and reducing carbon footprint.
How does the study address the challenges of high-alumina iron ores in blast furnaces?
By using A-type SFCA to regulate mineral phases, the study mitigates issues like increased slag viscosity and higher melting points, improving slag-iron separation and reducing energy consumption in blast furnace operations.
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