Hydrogen-rich reduction behavior and performance regulation of high-purity iron concentrate pellets with different basicities

To investigate the hydrogen-rich reduction behavior of high-purity iron concentrate pellets with different basicities and to reveal the influence mechanism of liquid phase properties on reduction swelling, this study combined microstructural characterization with quantitative analysis to systematically examine the microstructure evolution and hydrogen-rich reduction behavior of high-purity iron concentrate pellets at different basicities （R=0.07-1.0）. The mechanism by which liquid phase properties affect the reduction swelling performance of pellets with different basicities was emphatically revealed. The results show that as the pellet basicity increases, the amount of liquid phase within the pellets gradually increases, and the contents of Ca and Fe components in the liquid phase rise. Under simulated HYL（Hojalata Y Lamina） hydrogen-rich gas conditions, the reducibility index of different pellets first decreases and then increases, while the reduction swelling index shows the opposite trend. Abnormal swelling occurs during the reduction of roasted pellets in the basicity range of 0.4-0.8. At low basicity （R=0.07）, the amount of liquid phase formed in the roasted pellets is small, and under reducing conditions, metallic iron primarily grows in a dense layered manner. At medium basicity （R=0.60）, the dynamic "dissolution-precipitation" behavior occurred between the glass phase and iron oxides during reduction induces the formation of a porous structure and mound-like iron morphology, leading to abnormal swelling. At high basicity （R=1.00）, the amount of liquid phase in the pellets increases significantly, forming a continuous glass phase skeleton after cooling, which effectively suppresses the reduction swelling of pellets. Under the condition of basicity of 0.6, by appropriately increasing the SiO₂ and CaO contents in the pellets, the reduction swelling index significantly decreases from 48.92% to 7.38%. By controlling the composition and content of the liquid phase in iron ore pellets with different basicities, the reduction swelling performance of pellets can be significantly improved, providing a theoretical and technical basis for the preparation of high-performance iron oxide pellets.