Fe ^II induced mineralogical transformations of ferric oxyhydroxides into magnetite of variable stoichiometry and morphology

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 Fe ^II 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 (Fe _3-δO ₄) 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.