Exploring Microwave Roasting Characteristics of Magnetite Pellets: A Focus on Hematite Formation and Elemental Migration

The microwave roasting characteristics of magnetite pellets were investigated by varying microwave roasting power (1300–1700 W) and time (7–11 min) to produce high-quality oxidized pellets for ironmaking. It was found that along with the continuous increase in oxidation fraction, the compressive strength of the pellets increased linearly with the power and time. The variations were also attributed to the decrease in porosity and changes in hematite particles of the pellets. As microwave roasting power and time increased, the hematite particle average size and connectivity number, which denotes the quantity of adjacent particles for a target particle, increased from 4.09 µm and 2.07 to 7.01 µm and 2.98, respectively. The results demonstrated that microwave radiation had an evident promoting effect on the development of hematite configuration, with the power being more influential than the time. This effect was even pronounced in the pellet shell due to its higher density with stronger microwave absorption. Increasing the power and time contributed to a more uniform distribution of hematite particles despite variations in particle size, as confirmed by the much lower relative standard deviation (RSD) of connectivity number of hematite particles. It also facilitated the migration of aluminum and magnesium from silicate to hematite in the pellets.