Kinetic model for the carbothermic reduction of manganese dioxide
Mixtures of MnO2 and graphite were reacted under argon at different constant temperatures, and the loss in mass was recorded continuously. The reduction path was assumed to be MnO2 → Mn3O4 → MnO → Ma5C2 or Mn. Chemical conditions determine the ratio of Mn5C2/Mn formed in the reduction product. A multi-step shrinking-core model was proposed to describe the kinetics of reduction. Parameters in this model were estimated by performing a least-squares regression on the experimental data. Acceptable correspondence was obtained between predicted and experimental kinetic curves. The activation energy for the reduction of MnO2 to Mn3C4 was only 71.3 kJ mol-1, which indicated a weak dependence on temperature. Further reduction steps revealed activation energies of about 207 kJ mol-1, and were of the same order of magnitude as the activation energy for the Boudouard reaction. The distribution of species at any point in time, which depended on the MnO2/carbon ratio and the temperature, could be calculated by means of this proposed model. © 1988.