Title

Iron Ore Concentrates – Oxidation and Reduction

Authorship

MONSEN, DR. ING. BODIL E.; OLSEN, PROFESSOR SVERRE E.; KOLBEINSEN, DR. ING. LEIV

MONSEN, DR. ING. BODIL E.

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OLSEN, PROFESSOR SVERRE E.

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KOLBEINSEN, DR. ING. LEIV

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DOI

10.5151/2594-5327-49v7-373-388

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Abstract

Different prereduction rates of oxidized magnetite concentrates are explained by characterization of the preoxidized materials. Oxidation of magnetite: Some Sydvaranger super magnetite (63–90 µm) was completely oxidized at constant temperatures ranging from 800–1250°C to produce material for subsequent reduction experiments. Individually oriented hematite crystals formed in each grain. Substructures were characterized using mean SBA values (ratio of total subgrain boundary length to grain section area), which decreased with increasing oxidation temperature, approaching zero at 1250°C. Prereduction of hematite: Hematite concentrates (63–90 µm) were isothermally reduced at 700–850°C for up to 60 seconds in gas mixtures of CO, CO₂, H₂, and H₂O. Reduction to magnetite occurred mainly through subgrain boundaries. Iron began forming in magnetite pores before full hematite conversion. Metallization proceeded uniformly. Conclusion: Prereduction of Sydvaranger magnetite was more efficient after preoxidation at lower temperatures (<1050°C), due to easier iron nucleation along subgrain boundaries caused by numerous active sites such as tiny cracks or foreign ions.

Keywords

Iron ore, Magnetite, Hematite, Oxidation, Prereduction