Mössbauer spectroscopic and magnetokinetic studies on the oxidation of pyrite (FeS2)

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Abstract
In an earlier publication 1 we reported aspects of magnetokinetic studies on the oxidation of FeS2 carried out as a function of its particle size (90 to 250μm) and temperature (400–500 °C); in this study we considered mostly the formation of α and γ Fe2O3. In the present paper we have considered the formation of other oxidation products such as (a) Fe2 (SO4)3, and (b) superparamagnetic particles of α Fe2O3. Mössbauer spectroscopy has confirmed the presence of (a) and, coupled with X‐ray line broadening studies has shown the absence of (b). The yield of Fe2 (SO4), is found to increase with decreasing starting particle size of FeS2. Using our earlier results 1 we have obtained values of (dM/dt) from the initial slopes of the magnetization (M) vs. time curves for particle sizes (180 to 250 μm). From plots of ln (dM/dt) versus 1/T an activation energy of ∼7 Kcal/mole has been obtained for the following predominant reaction: FeS+(11/4)O2→ (1/2) αFe2O3+2SO2. This value compares favorably with values reported by other workers2 who used classical thermogravimetric analysis.