Effect of Oxides and Carbonate on the Reaction of Hematite and Graphite Mixture Obtained by the Mechanical Milling

Abstract

Effects of oxides (SiO₂ and Al₂O₃) and Carbonate (CaCO₃) on the reaction of hematite and carbon obtained by the mechanical milling were studied. The content of the additives were 3 mass%. The hematite contained the oxide or carbonate was mixed with graphite, and the ratio of hematite to carbon was 80 to 20. Ball milling (alumina ball and vessel) was carried out for 24 h under an argon atmosphere. The reaction rates were measured by TG–DTA and examined the effects of oxides and carbonate on the reaction rate.
The main peak of reaction rate, which corresponds to the successive reaction of Fe₃O₄–FeO–Fe reduction, was located at 850°C for no-addition sample. When 3 mass% Al₂O₃ was added to the mixture of hematite and carbon, the temperature of main peak did not change. It was considered that since the vessel and balls were also made of alumina, the effect of alumina already existed in the no-addition sample. When 3 mass% SiO₂ (reagent grade) was added to the mixture, the temperature of main peak was 1000°C, which meant the retardation effect on the hematite and carbon reaction. On the other hand, 3 mass% CaCO₃ addition promoted the reaction and the main peak was 790°C, which was about 60°C lower than that of no-addition. Using the results of quartz and CaO addition, the reaction mechanisms for the retardation effect of SiO₂ and the acceleration effect of CaCO₃ were considered.