Synergistic effect of alkali metals and fluorine on the reduction swelling properties of pellet ores: Influence of basicity

Abstract

Bayan Obo iron ore concentrate is a crucial raw material in steel production, but its high content of harmful elements like alkali metals and fluorine (F) affects the reduction swelling properties of pellet ores. This study aimed to clarify these effects at different basicity by simulating Bayan Obo iron ore concentrate using synthetic reagents. Comprehensive investigations were conducted using a high-temperature deformation analyzer, X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and thermogravimetric analysis to explore the reduction swelling process, phase crystal structure, microstructure, and kinetic behavior during reduction. The results showed that under the different basicity and reduction conditions, pellet ores containing Na and F exhibited a higher reduction swelling index than those pellet ores containing K and F. The maximum total reduction swelling index for both types of pellet ores occurred at a basicity of 0.8, with values of 50.6 % and 96.5 %, respectively. Additionally, a detrimental synergistic effect between Na and F was observed, which promoted the incorporation of alkali metals into the iron oxide lattice, leading to higher lattice constants, residual stresses, and distortion. The iron whiskers in the pellet ores containing Na and F formed a coarse reticular structure, indicating a synergistic effect of Na and F in promoting the growth of iron whiskers. Thermogravimetric and kinetic analysis indicated that the synergistic interaction between Na and F decreased the initial and final reaction temperatures of the pellet ores, reduced the energy required for the reduction reaction, and accelerated the reaction process, which was a key factor in exacerbating the reduction swelling of the pellet ores.