Mechanism of Reduction of Hematite-Magnetite Hollow Cylindrical Pellet by Graphite-Calcium Carbonate Mixture

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Vol. 51; no. 4; pp. 1460 - 1468
• Main Authors: Haghi, S. M. A., Zabett, A., Mirjalili, M.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.08.2020; Springer Nature B.V
• Subjects: Calcium carbonate; Carbon; Characterization and Evaluation of Materials; Chemistry and Materials Science; Crucibles; Electron micrographs; Gaseous diffusion; Gasification; Graphite; Hematite; Iron; Magnetite; Materials Science; Metallic Materials; Nanotechnology; Structural Materials; Surfaces and Interfaces; Thin Films; Whiskers (metals)
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-020-01852-6

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.