Redution kinetics of hematite and magnetite pellets containing coal char.

The rate of reduction of hematite and magnetite pellets containing coal char in a nitrogen atmosphere and at the temperatures between 800°C and 1200°C was investigated. The reduction rate was found to increase with increasing temperatures, and increasing calcium oxide content of the pellets. The reduction was not stepwise. That is, iron, hematite, magnetite and wustite were detected by X-ray analysis as coexisting phases during early stages of the reduction process. Large temperature differences were found between the core and surface of the pellets, indicating that the reduction process occurred under non-isothermal conditions.Calculated values for the apparent activation energy ranged between 38kcal/mol to 51kcal/mol. These values are lower than those reported by previous workers, but still within the accepted range for chemically controlled processes. The rate of the carbon gasification reaction and the rate of heat transfer from the furnace wall to the reacting pellet were found to exert the strongest influence on the overall rate of the process. Considering the observed non-isothermal conditions, the highly endotermic nature of the carbon gasification reaction and the large increase in the reduction rate with increasing temperature, it appeared that the overall process was heat transfer controlled.