Multi-component calcium ferrites represented by silico-ferrite of calcium and aluminum (SFCA: Ca2(Ca,Fe,Al)6(Fe,Al,Si)6O20) or SFCA-I(Ca3(Ca,Fe)(Fe,Al)16O28) are key mineral phases for exhibiting sinter ore properties. They are formed from calcium ferrite melt during the cooling process in the sintering reaction, which is a short period and non-equilibrium. Highly accurate quantification of SFCA and SFCA-I by conventional X-ray diffraction (XRD) analysis is difficult because their XRD patterns are similar and complicated. However, the determination precision could be improved by using Rietveld analysis, which is a pattern-fitting technique using the crystallographic parameters of existing phases and profile parameters. The aim of this study is to research the forming conditions of multi-component calcium ferrites and other phases by quantitative analysis of sintered tablet samples formed in non-equilibrium reaction to understand the sinter microtexture and improve the sinter ore quality. Mixtures of iron ore and reagent grade powder of CaCO3, SiO2, Al2O3 (CaO content of 0.91 mass%) were pressed into tablets
and heated up to 1573 K with a heating rate of 200 K/min then cooled with a cooling rate of -66.7 K/min under air atmosphere. The compositional ratio of Al2O3 (0.33-2.33 mass%) and SiO2 (2.36-4.36 mass%) was varied. Products were identified and quantified by powder XRD and Rietveld analysis. The cross-sections of tablet samples were studied using an optical microscope to see the morphology of calcium ferrites. The SFCA fraction in products increased with increasing the concentration of Al2O3 (In case SiO2 was a constant of 2.36 mass%). However, SFCA-I fraction slightly decreased. SFCA-I fraction also decreased with the addition of silicon oxide. These results were consistent with the compositional ranges of SFCA and SFCA-I. Gangue minerals solution especially silicon oxide in the calcium ferrite melt is important for the formation of SFCA or SFCA-I. Acicular calcium ferrite was not observed in tablet samples with low Al2O3 and SiO2 concentration and high SFCA-I mass fraction. Acicular calcium ferrite was observed in the sample with high Al2O3 and SiO2 concentration whose calcium ferrite phase was mostly occupied with the SFCA phase. Although the relation of acicular morphology and SFCA-I or SFCA species has not clarified yet, multi-component calcium ferrites (SFCA-I and SFCA phases) affect the formation of acicular morphology.
CITATION:Takayama, T, Higuchi, K and Okazaki, J, 2019. Study on multi-component calcium ferrites formation by using XRD-Rietveld analysis, in Proceedings Iron Ore 2019, pp 166175 (The Australasian Institute of Mining and Metallurgy: Melbourne).