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CaO-(0-20 mass%) and SiO2-containing (0-30 mass%) wüstite ('FeO') compacts were isothermally reduced at 1 273 K under CO and H2 gas. Prior to reduction, the phase of dicalcium ferrite (Ca2Fe2O5) and fayalite (Fe2SiO4) was equilibrated with 'FeO' at 1 273 K under 50%CO/50%CO2 and identified using X-ray diffraction and scanning electron microscopy. The rate of reduction for CaO-containing 'FeO' compacts under both H2 and CO increased up to the vicinity of 2.5 mass% CaO, and then decreased with higher CaO dependent on the formation of an intermediate phase of dicalcium ferrite. For SiO2-containing 'FeO', the rate decreased with SiO2 additions. When the dense fayalite is present reduction using CO was limited, while considerable reduction was observed using H2. The reduction was affected by three distinct reduction mechanisms of interfacial chemical reaction, gaseous mass transport, solid state diffusion of oxygen or a combination of these individual mechanisms termed the mixed control. The contribution of each mechanism with the content of CaO or SiO2 affecting the reduction behavior was determined. The compact porosity increased when CaO was added to approximately 2.5 mass% and subsequently decreased with higher CaO, but continuously decreased with SiO2 additions. The ratio of the effective diffusivity (De) to molecular interdiffusivity (D) was highest at the vicinity of 2.5 mass% CaO and thus the maximum reduction rate was obtained when the porosity was highest.

This study aims to utilize the high Al2O3 pisolitic ore in sintering process by designing the quasi-particle where the pisolitic ore is used as nuclei and ultra-fine hematite and magnetite ores are employed as adhering fines. The assimilation behavior between nuclei and adhering fines was investigated through microstructure analysis and it was correlated to sinter quality. When ultra-fine hematite ore was used as adhering fines, the low viscous melt of CaO·Fe2O3 was formed in the assimilation. Since this results in the low extent of Al2O3 localization and the porous structure, the detrimental effect of Al2O3 on the strength was not fully controlled. On the other hand, for the ultra-fine magnetite ore, 3CaO·Fe2O3·3SiO2 melt with high viscosity was predominantly participated in the assimilation. The assimilation was suppressed by the formation of 'interfacial layer'. Due to the dense structure and high extent of Al2O3 localization, the detrimental effect of Al2O3 on strength was reasonably controlled. The quasi-particle comprising high Al2O3 pisolitic ore and ultra-fine magnetite ore showed the equivalent sinter quality to the quasi-particle sample consisting of nuclei of dense hematite and adhering fines of ultra-fine hematite resulting in the high sinter quality.

The effects of basicity and Al 2 O 3 content on the chemistry of phases in iron ore sinter containing ZnO were investigated by Rietveld analysis of the X-ray diffraction (XRD) patterns. Bulk composition analysis was carried out using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and wet-chemical analysis. The composition of each phase was investigated using a scanning electron microscope-energy dispersive X-ray analyzer (SEM-EDX). It was found that ZnO exists in the franklinite and the silicoferrite of calcium and aluminum (SFCA) phases. With increasing ZnO content, the phase fraction of the franklinite increased, while the fraction of SFCA slightly increased. When ZnO content was fixed at 1 wt pct and basicity increased, the fraction of franklinite decreased and that of SFCA increased. Here, the solubility of ZnO in the SFCA increased. As the Al 2 O 3 content increased, the fraction of franklinite decreased and that of SFCA increased, while ZnO content in the SFCA did not change significantly.