In this study, the mechanism of reduction of hematite-magnetite concentrate (HMC) by graphite-calcium carbonate reductant mixture at about 1000 °C was investigated. The initial and middle stages of the reduction process (up to 63 pct) were mainly affected by the heat transfer inside the crucible. It was concluded that in the middle to final stages of the reduction process, the gaseous diffusion of reducing gas to the FeO-Fe reaction interface and the carbon gasification are the mixed controlling mechanism. The reduction rate was relatively slow below the carbon gasification temperature. According to X-ray diffractometer (XRD) analysis, the formation of the metallic iron was not observed before the carbon gasification. The scanning electron micrographs showed the formation of iron whiskers in the outer layer of the sample, which resulted in swelling of the sample. The observation of the reduced samples’ sections showed that the reduction progress was topochemical. The progress of the reduction from the inner surface of the sample was insignificant compared to the reduction from the outer.

中文翻译：

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石墨-碳酸钙混合物还原赤铁矿-磁铁矿空心圆柱丸的机理

在这项研究中，研究了石墨-碳酸钙还原剂混合物在 1000 °C 左右还原赤铁矿-磁铁矿精矿 (HMC) 的机理。还原过程的初始和中间阶段（最多 63 pct）主要受坩埚内传热的影响。结果表明，在还原过程的中后期，还原气体向FeO-Fe反应界面的气态扩散和碳气化是混合控制机制。在碳气化温度以下还原速率相对较慢。根据 X 射线衍射仪 (XRD) 分析，在碳气化之前未观察到金属铁的形成。扫描电子显微照片显示在样品的外层形成了铁晶须，导致样品膨胀。对还原样品切片的观察表明，还原过程是拓扑化学的。与从外表面的还原相比，从样品的内表面还原的进展是微不足道的。