Abstract
Silico-ferrite of calcium and aluminum (SFCA) is one of the most commonly-produced phases in fluxed iron-ore sintering, and has long been regarded as an important bonding phase in industrial sinters. It is thus considered to have a significant effect on sinter quality. In this study, a solid solution model and database has been developed for the SFCA phase, and has been incorporated into the thermodynamic software, Multi-Phase Equilibrium (MPE). MPE calculations were compared with the in situ X-ray powder diffraction (XRD) observations of the formation of SFCA phase during sintering. The effects of the raw material composition, temperature and the oxygen partial pressure on the formation of mineral phases in the sinter, as well as the viscosity of the melt formed during sintering under equilibrium conditions, were modelled using MPE. The results show that the formation of SFCA phase can be promoted by increasing oxygen partial pressure and basicity of the raw material. Increases of Al2O3 and MgO content have no significant effect on the SFCA formation under equilibrium condition. The increase of oxygen partial pressure (10−3 atm or above) and basicity also leads to a decrease in melt viscosity, which enhances the fluidity of the melt, and hence, the assimilation of the sinter. However, increases of Al2O3 and MgO result in the increase of melt viscosity.
Highlights
During the iron ore sintering process, the loose raw materials, mixtures of fine ore, limestone flux and coke breeze, are converted into a porous but physically strong cake, which is generally composed of four main phases: iron oxides, ferrites, most of which are a complex silico-ferrite of calcium and aluminum (SFCA), glasses and dicalcium silicate
It was reported that the number of phases in final sinter for ores containing 1.4 and 2.2 mass% Al2 O3 was almost the same, but that the composition and morphology of the phases were markedly different [26].The modelling results reveals that the Al2 O3 solubility in the SFCA phase increases from 7 to 17 mass% with Al2 O3 content in the raw material increases from 1 to 7 mass%, while the SFCA phase quantity remains almost constant under equilibrium condition
Multi-Phase Equilibrium (MPE) calculation was compared with the data from the in situ X-ray powder diffraction (XRD) observation on the formation of SFCA phase during sintering
Summary
During the iron ore sintering process, the loose raw materials, mixtures of fine ore, limestone flux and coke breeze, are converted into a porous but physically strong cake, which is generally composed of four main phases: iron oxides, ferrites, most of which are a complex silico-ferrite of calcium and aluminum (SFCA), glasses and dicalcium silicate. Minerals 2019, 9, 361 the raw material composition have significant impact on the composition and quantity of the mineral phases present in the sinter [7,8,9,10] Webster and his coworkers [11,12,13,14,15,16] investigated the SFCA and SFCA-I dynamic formation during heating and cooling of sinter with various compositions under various oxygen partial pressure using the in situ XRD technique. The effects of the composition of the raw material, temperature and the oxygen partial pressure on the formation of the mineral phases in the iron ore sinter, as well as the viscosity of the melt formed during sintering, have been modelled
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