Characterisation of iron ore sinter products with varying binary basicity (CaO/SiO 2 ) from 1.5 to 2.7

Iron ore sinter is one of most extensively utilised ferrous burdens for blast furnace (BF) worldwide. The sinter quality greatly depends on the microstructure and chemical compositions of calcium ferrites which is significantly affected by sinter basicity (mass ratio of CaO to SiO₂). The characterisation of iron ore sinter products with varying binary basicity (CaO/SiO2) from 1.5 to 2.7 was studied by using optical microscopy and scanning electron microscopy-energy spectrometer (SEM-EDS). The results show that the change of sinter basicity changes the microstructure and composition of silico-ferrite of calcium and aluminium (SFCA), and more dendritic shape composite calcium ferrite (SFCA) with Fe-rich/low-Si is generated. Under the optical microscope, statistical results of the sinter reveal that with the increase in basicity, the aspect ratio of calcium ferrite increases from 2.35 to 7.69, indicating a gradual refinement of the crystals. Moreover, the distribution of crystals becomes more uniform, and the size of pores between crystals also decreases gradually, thereby the mechanical properties of the sinter from a microscopic structural perspective being enhanced. SEM-EDS analysis studies have found a certain linear relationship between the aspect ratio of SFCA and its iron content, where higher iron content in SFCA leads to finer and narrower SFCA formations. Additionally, an increase in basicity favours the generation of more composite calcium ferrite (SFCA) with Fe-rich/low-Si characteristics, which significantly improves the reducibility of the sinter. Moreover, what is even more interesting is that the iron content in SFCA shows an inverse relationship with the content of silicon, calcium and aluminium elements, yet it is directly proportional to the quaternary basicity [(CaO + MgO)/(SiO₂+ Al₂O₃)] in SFCA.