Effect of Silica on Reduction Behaviors of Hematite-carbon Composite Compact at 1223–1373 K

Abstract

The influence of compositional changes in the SiO2–Fe2O3 binary oxide system on the reduction behavior of carbon-bearing compact was investigated at 1223–1373 K. Density functional theory (DFT) calculations were employed to investigate the adsorption behaviors of O–Si–O on various FeO surfaces in order to explore the mechanism of the conversion of FeO to Fe–Si–O phase. Chemical analysis, SEM-EDX, and XRD were carried to characterize the conversion mechanisms. According to experimental results, silica causes the decrease of the metallization ratio by hindering the reduction of FeO to Fe and facilitating the reaction of FeO to Fe–Si–O phases. The size of metallic iron granules diminishes gradually and the boundary between the iron phase and the slag phase becomes less obvious with increasing silica content, which greatly increases the contact probability of SiO2/liquid phases and FeO. For the three adsorption sites, the adsorption energies of Si atoms onto FeO surfaces are all obviously larger than that of the reducing gases, making it extremely difficult for the reducing gases to remove O atoms from FeO surfaces, as the DFT results show. Moreover, it is easier to form the Fe–O–Si phase on the FeO (110) surface since the adsorption energy of O–Si–O onto this surface is greater than that onto the FeO (100) and FeO (111) surfaces. Additionally, the charge of the O (FeO) 2p orbital, the Si 3p orbital, as well as the 3s, 3p, and 3d orbitals of the Fe atom take charge of the formation of Si–O–Fe bond.