An EPR, HFEPR and XAS study of volcanic ashes from Mt. Etna, Catania (Italy)

The surfaces of the volcanic ashes are widely modified during explosive eruption by the interaction with the gas/areosol occurring in the plume. The mineralogical and compositional changes have important consequences for the impact on the environment and human health. In this context, the behaviour of the iron is largely unpublished. In particular, the oxidation state and the formations of new phases due to the S, Cl and F present in the plume are key points for the analysis of the consequences that these products may have on human health. In this study, we report the data collected on volcanic tefra of the Mt. Etna eruptions occurred in numerous explosive episodes which occurred during 2013. The tefra samples were investigated by a wide multianalytical study, which included conventional EPR, HFEPR and XAS, this latter performed at the Fe K edge. The three techniques were chosen in order to get the closest information onto the Fe valence state and coordination, as being highly element selective. The preliminary results, presented here, highlight, from the pre-edge and the XANES regions, the coexistence of Fe(II) and Fe(III) species in an almost constant ratio. Fe(III), in turn, is distributed over at least two different phases, most of it being included in the volcanic glass, and the remaining hosted in an own, magnetic, phase, probably an Fe oxide. The two phases were clearly isolated by means of the coupled study through EPR and HFEPR. Moreover, information on the spectral behavior of samples differing in granulometric distribution or as a function of progressive leaching under laboratory conditions is discussed.