Effect of Magnetite (Fe²⁺ source) on initial liquid formation in sintering process

A situation of sintering raw materials becomes more severe in this century. In the sintering process, magnetite iron ore is expected as high grade and condensation raw materials. However, there are not sufficient researches on the solid-solid reactions between magnetite and CaO in the sintering process. Therefore, purpose of this study is to clarify the initial liquid formation behavior by investigating the solid-solid reactions between magnetite and CaO under Ar or air atmosphere. In order to simply simulate the sintering raw materials, mixture samples of iron oxide and CaO were prepared. Reagent magnetite and reagent hematite were prepared as iron oxide. The mixtures, which have the weight ratio of iron oxide/CaO=80/20, 85/15 and 90/10, were pressed into tablet shape and used as experimental samples. "In-situ" observations of the initial liquid formation behavior in the samples were carried out by a laser microscope combined with infra-red furnace. The samples were heated at 50°C/min under Ar or air atmosphere. The initial liquid formation temperatures were decided from this observation. In the case under Ar atmosphere, the initial liquid formation temperature of magnetite-CaO mixture samples became higher than that of hematite-CaO mixture samples. This difference was caused from CaO·FeO·Fe₂O₃ formation before liquid formation between magnetite and CaO. In the case under air atmosphere, the initial liquid formation temperature of magnetite-CaO mixture samples became lower than that of hematite-CaO mixture samples, and the temperatures were decreased with the increasing of magnetite. This reason was because 4CaO·FeO·8Fe₂O₃ was formed by the solid-solid reactions between magnetite and CaO. It was found that the sintering atmosphere and magnetite blending ratio to raw materials have the influence on the initial liquid formation temperature when the magnetite iron ore is used in the sintering process.