Ferric iron geometry and coordination during hydrolysis and ferrihydrite precipitation

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Mineralogical Society of Great Britain & Ireland
Definitive structural characterisation of ferrihydrite has challenged scientists primarily due to its nanosized particles and inherent long-range structural disorder which challenges analytical methodology (and modelling) typically employed to determine the structure of minerals. Here we report on the application of a synchrotron quick-scanning X-ray absorption spectroscopy (XAS) approach, which allows the collection of Extended X-ray Absorption Fine Structure (EXAFS) spectral data to k = 15 Å-1 in < 1 minute, to obtain unparalleled iron Kedge data on the hydrolysis of FeIII(H2O)6 and ferrihydrite precipitation. Modelling of the pre-edge and EXAFS data: 1) supports theoretical studies which have suggested the existence of a monomeric penta-coordinated FeIII hydrolysis species and; 2) corroborates recently proposed structural models of ferrihydrite that contain tetrahedral FeIII. Modelling results indicate that ferrihydrite consists of 15 to 25 % tetrahedral FeIII and suggest that this geometry must be included in any comprehensive structural model of ferrihydrite and, furthermore, should be considered when evaluating the reactivity, stability and other structure-property relationships of this mineral. © 2011 The Authors.
Iron compounds, Ferrites, Geometry, Precipitation, Nanostructures, Minerals, Absorption spectroscopy, Simulation
Collins, R. N., Rose, A. L., Glover, C. J., Boland, D. D., Payne. T. E., & Waite, T. D. (2011). Ferric iron geometry and coordination during hydrolysis and ferrihydrite precipitation. Abstract presented to Goldschmidt 2011, Prague, Czech Republic, 14 August 2011 - 19 August 2011.