Study of a mechanochemical transformation in iron pyrite

The observation of a phase transformation from pyrite FeS2 (Fe2+ in a low-spin state) to szomolnokite FeSO4. H2O (Fe2+ a high-spin state) by the mechanical action of ball-milling in air is reported. Fe-57 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. (C) 2000 Published by Elsevier Science S.A. All rights reserved.