Study of a mechanochemical transformation in iron pyrite

Abstract The observation of a phase transformation from pyrite FeS 2 (Fe 2+ in a low-spin state) to szomolnokite FeSO 4 ·H 2 O (Fe 2+ in a high-spin state) by the mechanical action of ball-milling in air is reported. 57 Fe Mossbauer spectroscopy, X-ray diffraction and scanning electron microscopy were used to identify changes produced by mechanical activation. The pyrite structure can be sufficiently destabilized locally in the core of the powder particles, so that it may partly transform into szomolnokite during the milling process itself. After a long relaxation period in ambient air following sample grinding, the transformation process is shown to extend to the grain periphery without further mechanical activation.