Ferrite grade iron oxides from ore rejects

Iron oxyhydroxides and hydroxides were synthesized from chemically beneficiated high SiO₂/Al₂O₃ low-grade iron ore (57.49% Fe₂O₃) rejects and heated to get iron oxides of 96–99.73% purity. The infrared band positions, isothermal weight loss and thermogravimetric and chemical analysis established the chemical formulas of iron-oxyhydroxides as γ-FeOOH.0.3H₂O; α-FeOOH.0.2H₂O and amorphous FeOOH. The thermal products of all these were α-Fe₂O₃ excepting that of γ-FeOOH.0.3H₂O which gave mainly γ-Fe₂O₃ and some admixture of α-Fe₂O₃. The hydrazinated iron hydroxides and oxyhydroxides, on the other hand, decomposed autocatalytically to mainly γ-Fe₂O₃. Hydrazine method modifies the thermal decomposition path of the hydroxides. The saturation magnetization,J _s, values were found to be in the range 60–71 emu g⁻¹ which are close to the reported values for γ-Fe₂O₃. Mechanism of the γ-Fe₂O₃ formation by hydrazine method is discussed.