Intensive Improvement of Reduction Rate of Hematite-Graphite Mixture by Mechanical Milling

The effect of ball milling of raw materials on the reaction behavior of composite mixture of hematite and graphite have been studied. Hematite was mixed with 19.84 wt% graphite (C/O ratio was 1.1 in composite mixture) and subjected to ball milling. The milling time was changed from 6 to 100 hr with the hematite–graphite mixture. On the other hand, graphite or hematite was milled alone and then mixed with non-milled hematite or graphite, respectively. The effect of milling time on reduction process in an Ar atmosphere was studied by TG-DTA. The samples were heated by a constant heating rate of 10°C/min from room temperature up to 1100°C and maintained for 30 min at this temperature. The rate of reaction (RTG) was obtained by the differentiation of weight loss curve. It was found that the RTG curve consisted of three reaction curves which were hematite–magnetite (HM), magnetite–wustite (MW) and wustite–metallic iron (WF) reductions. The curve corresponding to the HM reduction located in low temperature range and stood alone from other two reduction curves ( MW and WF reductions). The curves of MW and WF reductions were overlapped. The pulse-like reduction curve corresponding to WF reduction was observed in the longer milling time, which meant extremely high rate of reduction. The temperatures decreased and the reaction degrees at each peaks increased with increasing milling time. The kinetic analysis applying the single and consecutive reaction was carried out. The calculated reaction curves were in good agreement with the observations which showed that the reaction mainly occurred in this system was the solid oxide–solid carbon reaction. The variation of parameters of rate constant presented the different mechanism of reaction between shorter and longer milling time at the border of 24 hr