Reduction Kinetics of Iron Oxide Pellets with Hydrogen at Lower Temperatures

Abstract

Some investigators^(5)∼(11) have proposed that two steps should be considered with regard to the reduction kinetics of the iron oxide pellet. One is the chemical reaction at the interface between the reduced and unreduced layers and the other is the gaseous diffusion through the reduced layer. A new method of analysis of the experimental data in the mixed-control mechanism of the above two steps was devised. The hypothesis that the reaction proceeds topochemically is adopted and the time required for 87.5% reduction which is one-half of complete reduction and the time for 50% reduction are utilized in this new method. By using the above two time values obtained experimentally, the chemical reaction constants and the intraparticle diffusion coefficients are briefly calculated by Eqs. (8)∼(12). Especially, in the case where the produced gas retards the reaction by its adsorption on the reacting surface, the analysis is possible by use of such a counting chart as Fig. 3 which is made out from the numerical calculation employing the retarding function.
Hematite and magnetite pellets prepared from the Brazillian ore were reduced with hydrogen at low temperatures (500°, 550°C) and the decreases in the weight were measured by a thermobalance. The results are listed in Table 2. This method is simpler than the previous ones.