V oxidation state in Fe–Ti oxides by high-energy resolution fluorescence-detected X-ray absorption spectroscopy

• Published in: Physics and chemistry of minerals Vol. 38; no. 6; pp. 449 - 458
• Main Authors: Bordage, Amélie, Balan, Etienne, de Villiers, Johan P. R., Cromarty, Robert, Juhin, Amélie, Carvallo, Claire, Calas, Georges, Sunder Raju, P. V., Glatzel, Pieter
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.06.2011; Springer Nature B.V
• Subjects: Absorption spectroscopy; Bearing; Boreholes; Crystallization; Crystallography and Scattering Methods; Earth and Environmental Science; Earth Sciences; Energy resolution; Fluorescence; Geochemistry; Hematite; Iron; Magnetite; Mineral Resources; Mineralogy; Original Paper; Oxidation; Oxides; Radiation; Spectroscopy; Spectrum analysis; Synchrotron radiation; Titanium; Valence; Vanadium; X ray absorption; X-ray spectroscopy; India; edge HERFD-XAS; Fe–Ti oxides; Impurity; Oxidation state; V; Vanadium
• ISSN: 0342-1791; 1432-2021
• DOI: 10.1007/s00269-011-0418-3

The oxidation state of vanadium in natural and synthetic Fe–Ti oxides is determined using high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS). Eleven natural magnetite-bearing samples from a borehole of the Main Magnetite Layer of the Bushveld Complex (South Africa), five synthetic Fe oxide samples, and three natural hematite-bearing samples from Dharwar supergroup (India) are investigated. V  K edge spectra were recorded on the ID26 beamline at the European Synchrotron Radiation Facility (Grenoble, France), and the pre-edge features were used to determine the local environment and oxidation state of vanadium. In the case of the magnetite samples (natural and synthetic), we show that vanadium is incorporated in the octahedral site of the spinel structure under two oxidation states: +III and +IV. The variations of the pre-edge area are interpreted as various proportions in V 3+ and V 4+ (between 9.5 and 16.3% of V 4+ ), V 3+ being the main oxidation state. In particular, the variations of the V 4+ /V 3+ ratio along the profile of the Main Magnetite Layer seem to follow the crystallization sequence of the layer. In the case of the hematite samples from India, the pre-edge features indicate that vanadium is substituted to Fe and mainly incorporated as V 4+ (between 40 and 72% of V 4+ ). We also demonstrate the potentiality of HERFD-XAS for mineralogical studies, since it can filter out the unwanted fluorescence and give better resolved spectra than conventional XAS.