Oxidation Behavior of High FeO Ferrous Spinels and Its Impacts on the Induration Characteristics of Oxidized Pellets

The oxidation behavior and induration characteristics of typical ferrous spinel concentrates including low-Mg (OM) and high-Mg magnetite (MM), titanomagnetite (TM), and chromite (CM) was investigated. An insight into the thermodynamics, phase and microstructure transformation, element migration mechanism of the oxidation of different types of ferrous spinel was taken using thermogravimetry–differential scanning calorimetry (TG–DSC), X-ray diffraction (XRD), scanning electron microscopy-energy and energy dispersive X-ray spectroscopy (SEM–EDS), and X-ray photoelectron spectroscopy (XPS) at temperatures ranging from room temperature to 1273 K. The results indicate that OM, MM, and TM start to oxidize and form hematite at a similar temperature of approximately 673 K, while oxidation of CM begins at a higher temperature of around 873 K. Among them, OM exhibits superior oxidizability. For MM, the incorporation of magnesium ions into the octahedral crystal sites of magnetite tends to stabilize the crystal structure of magnetite and presents some negative influence on its oxidizability. TM has more complex chemical and phase compositions, dominantly consisting of titanomagnetite (Fe_2.75Ti_0.25O₄) with good oxidizability, whereas the presence of a small quantity of ilmenite (FeTiO₃) reduces the final oxidation degree. Compared with OM, MM, and TM, CM exhibits inferior oxidizability due to its complex chemical compositions and phase transformation. The induration characteristics of pellets prepared by four kinds of spinel also shows significant differences. Under the conditions of 1553 K, the induration characteristics are best with OM, followed by CM and TM, while MM exhibits the best induration performance at 1473 K.