Application of High-Alumina Type Calcium Ferrite: a new strategy of mineral phase regulation instead of chemical composition regulation in iron ore sintering

High-alumina iron ores (Al₂O₃ content >3.0%) 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. To address the decline in ore quality, the steel industry has adopted complex, low-grade ores such as high-alumina ores as alternative raw materials. However, the metallurgical performance constraints of high-alumina ores limit their widespread use. 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 30%, 50%, and 100% replacement ratios of Al₂O₃. Previous work developed two types of high-alumina SFCAs (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 (CaAl_xFe_2-xO₄). SEM and mineralogical analyses reveal that sinter substituted with A-type SFCA primarily consists of SFCA and 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 100% substitution, the reducibility reaches 0.85, a 0.33 increase over the baseline (A-type and B-type SFCA are not added). Future applications could involve prefabricating SFCA to significantly enhance the liquid phase ratio without altering the yield, thus reducing the required carbon ratio. 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. Overall, 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.