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 degrees C/min to 233.0 degrees 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.