Deqing Zhu,Yuxiao Xue,Jian Pan,Congcong Yang,Zhengqi Guo,Hongyu Tian,Dingzheng Wang,Yue Shi
The alumina content of iron ores for sintering is gradually increasing with the growing depletion of high-grade iron ores, which is harmful to the sintering process. Therefore, it is essential to reveal the action mechanism of alumina on sinter quality. In this paper, the aluminum occurrence of various iron ores was determined by applying X-ray diffraction (XRD), optical microscopy, scanning electron microscopy and energy dispersive spectrum analysis (SEM-EDS). Then, the effects of iron ore type, aluminum occurrence (free alumina, gibbsite, diaspore, alumogoethite and kaolinite) and alumina content on formation characteristics of SFCA bonding phases as well as sinter matrix strength were investigated based on laboratory compact sintering tests. The results show that the discrepancy of aluminum occurrence contributes to different SFCA formation characteristics and then sinter matrix strength, due to different reactivity of various aluminum-containing minerals with iron oxides and fluxes. Increasing alumina content generally results in an increase in the porosity of sinters and deterioration of sinter matrix strength for all aluminum occurrence. Aluminum in the form of kaolinite is more conducive to form dendritic or acicular SFCA with superior sinter matrix strength compared with other aluminum occurrences. In contrast, aluminum occurring in free alumina presents greatest adverse impacts on sinter matrix strength due to its poor reactivity and high porosity of resultant sinters.
Yuxiao Xue,Jian Pan,Deqing Zhu,Zhengqi Guo,Hongyu Tian,Yue Shi,Shenghu Lu
Iron ores always contain several forms of alumina, which may have different effect on sintering performance. In this paper, sinter pot tests were systematically conducted with various alumina types and contents by means of alumina additives substituting for the corresponding types of alumina, and the relevant action mechanism on sintering performance was clarified by the mineralogy of product sinter. The results show that kaolinite is beneficial to the granulation process rather than other three alumina types. In addition, it contributes to relatively better sintering performance while aluminous goethite ranks the only next, followed by gibbsite and free alumina. Mechanism analysis indicates that kaolinite and aluminous goethite are preferable to achieve relatively lower sinter porosity and higher amount of silico-ferrite of calcium and alumina (SFCA) compared with gibbsite and free alumina. Besides, the former two alumina types are apt to promote the formation of higher strength SFCA such as dendritic and acicular SFCA. Furthermore, much tighter interlocking texture in product sinter is formed as alumina occurs in kaolinite or aluminous goethite. Kaolinite and aluminous goethite are the preferably desirable alumina types for sintering rather than free alumina and gibbsite.
Increasing Fe/Al molar ratio promoting better assimilation of iron ore powder. • The inter-particle bonding ability of SFCA can be evaluated by osmotic pressure. • Lower Fe/Al ratios coupled with slower cooling promote dendritic SFCA formation. • Higher crystallization rate enhances hardness but reduces elastic modulus of SFCA. • Optimizing SFCA micromechanical properties through Fe/Al ratio and cooling rate. Iron ore sintering represents a critical agglomeration process wherein the silico-ferrite of calcium and aluminum (SFCA) phase governs the consolidation behavior and final product quality. In this study, the effects of Fe/Al molar ratio (4.53 to 12.27) and cooling rate (50 to 200 °C/min) on SFCA characteristics in Fe 2 O 3 -CaO-SiO 2 -Al 2 O 3 systems were systematically investigated by using X-ray diffraction, in situ thermal analysis platform, Raman spectroscopy, Scanning electron microscope (SEM) and nanoindentation. Increasing Fe/Al ratio could reduce the liquid phase formation temperature and enhance the melt fluidity, promoting better assimilation of iron ore powder. Meanwhile, optimal inter-particle bonding occurred with optimal osmotic pressure achieved at 300 to 350 s of high-temperature maintenance. Higher cooling rates significantly accelerated crystallization kinetics, leading to refined microstructures with dispersed crystalline phases. Notably, lower Fe/Al ratios coupled with slower cooling promoted dendritic SFCA formation, while accelerated crystallization enhanced hardness but compromised elastic modulus. The influence of slower cooling rates on crystallization rate and micromechanical properties was more pronounced in sintered liquid phases with lower Fe/Al molar ratios. These findings provide crucial insights into the fundamental mechanisms governing SFCA formation in iron ore sintering, offering practical strategies for optimizing sintering parameters through precise regulation of chemical composition and thermal conditions. Download: Download high-res image (126KB) Download: Download full-size image
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