Preheating Characteristics of Magnetite Pellets Under Microwave Irradiation

The microwave preheating characteristics of magnetite pellets were investigated based on the microwave absorption capability analysis. With increasing microwave power from 1100 W to 1500 W, the initial heating rate of the pellets increased from 134.9°C/min to 233.0°C/min and then decreased because of the decrease in microwave magnetic loss induced by the oxidation of Fe₃O₄ to Fe₂O₃ and more heat loss from the pellets to the surroundings. With the same terminal temperature, the pellets after microwave preheating (MP pellets) obtained higher oxidation fraction and compressive strength and lower porosity than those produced by conventional preheating (CP pellets), associated with the variations of content and crystallite size of Fe₂O₃. Moreover, MP pellets had larger and more concentrated Fe₂O₃ particles in their cores than their shells and the corresponding areas in CP pellets, demonstrating the advantages of microwave which intensified the oxidation of the pellets in the preheating process.