Kinetic modeling of the hematite to magnetite reduction with starch

The kinetic parameters (the activation energy and the reaction rate constants) for the process of hematite to magnetite transformation with starch have been determined. Based on the saturation magnetization of transformed samples, the conversion fraction of each sample was estimated. The conversion fraction increased up to 0.5 at 600 °C with rising time. In addition, two stages of the reaction were clearly distinguished. The first stage (acceleration process) involves the rapid nucleation and growth of magnetite on hematite particles. The second (deceleration process) is attributed to the reaction interface progress towards the center of the hematite grain. Kinetic analysis showed that the first stage is best-described by Avrami-Erofeev Reaction Model which involves the restrictions on nuclei growth. The second stage corresponds to the Jander Reaction Model in which hte diffusion is the restriction factor. The reaction rate constants of hematite to magnetite transformation increased 30 times for the first stage of the reaction and only 4 times for the second stage with increasing temperature. The activation energy of acceleration process was 84 kJ/mol; the activation energy of deceleration process was 33 kJ/mol. The results of this work are important for the development of beneficiation technologies of iron ore by magnetizing roasting.