FeII induced mineralogical transformations of ferric oxyhydroxides into magnetite of variable stoichiometry and morphology

Muhammad Usman (1) , Mustapha Abdelmoula (1) , Khalil Hanna (1) , Brian Grégoire (1) , Pierre Faure (2) , Christian Ruby (1)

1 LCPME - Laboratoire de Chimie Physique et Microbiologie pour l'Environnement
2 LIEC - Laboratoire Interdisciplinaire des Environnements Continentaux

The Mössbauer spectroscopy was used to monitor the mineralogical transformations of ferrihydrite (F), lepidocrocite (L) and goethite (G) into magnetite as a function of aging time. Ferric oxyhydroxides were reacted with soluble FeII and OH- in stoichiometric amounts to form magnetite at an initial pH of  9.7. Observed transformation extent into magnetite followed the order: F > L > G with almost 30 % of untransformed G after 1 month. The departure from stoichiometry, δ, of magnetite (Fe3-δO4) generated from F (δ ~ 0.04) and L (δ ~ 0.05) was relatively low as compared to that in magnetite from G (δ ~ 0.08). The analysis by transmission electron microscopy and BET revealed that generated magnetite was also different in terms of morphology, particle size and surface area depending on the nature of initial ferric oxyhydroxide. This method of preparation is a possible way to form nano-sized magnetite.

Mots clés: ferrihydrite; lepidocrocite; goethite; magnetite; Mössbauer

Domaines: Chimie-Physique [physics.chem-ph]

Muhammad Usman, Mustapha Abdelmoula, Khalil Hanna, Brian Grégoire, Pierre Faure, et al.. FeII induced mineralogical transformations of ferric oxyhydroxides into magnetite of variable stoichiometry and morphology. Journal of Solid State Chemistry, 2012, 194, pp.328-335. ⟨10.1016/j.jssc.2012.05.022⟩. ⟨hal-00845705⟩