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The reductive immobilization of Se(IV) by micrometer-sized (100-200 μm) calcite containing sorbed or coprecipitated Fe(II) was investigated at pH 7 under anoxic conditions (O2 < 1 ppmv) using X-ray absorption near-edge structure (XANES) spectroscopy. The Se(IV) sorption on calcite increased in the presence of sorbed Fe(II) compared to that of Fe-free pure calcite. XANES spectra of Se K-edge shows that nearly half of the total sorbed Se(IV) is reduced to Se(0) by Fe(II) sorbed on calcite within 24 h. The extent of reduction decreases with increasing equilibration time of calcite with Fe(II) solution before Se(IV) addition. The combined results of field emission scanning electron microscopy and X-ray diffraction have shown that needle-shaped red monoclinic elemental Se with diameters of 30-50 nm and lengths of up to 100 nm is precipitated on the calcite surface. Fe(II) coprecipitated calcite does not contribute to Se(IV) reduction within 72 h. Therefore, the reduction capacity of Fe(II) linked to calcite critically depends on its location (either on the surface or in the bulk solid), and less extensively on the pre-equilibration time of calcite with Fe(II) solution. Such understanding is important to predict the transport, transformation, and attenuation of Se in subsurface and in nuclear waste repositories. [ABSTRACT FROM AUTHOR]

The appropriate selection of representative pure compounds to be used as reference is a crucial step for successful analysis of X-ray absorption near edge spectroscopy (XANES) data, and it is often not a trivial task. This is particularly true when complex environmental matrices are investigated, being their elemental speciation a priori unknown. In this paper, an investigation on the speciation of Cu, Zn, and Sb based on the use of conventional (stoichiometric compounds) and non-conventional (environmental samples or relevant certified materials) references is explored. This method can be useful in when the effectiveness of XANES analysis is limited because of the difficulty in obtaining a set of references sufficiently representative of the investigated samples. Road dust samples collected along the bridge connecting Venice to the mainland were used to show the potentialities and the limits of this approach. [ABSTRACT FROM AUTHOR]

Aqua Traiana is an ancient Roman aqueduct, built to supply water to the ancient city of Rome and still working nowadays. This work is focused on the characterization of its mortars, and in particular the binders, to identify the reasons of such a durable resistance. Samples collected inside the aqueduct were analysed by Optical Microscopy (OM) in thin sections, X-ray Powder Diffraction (XRPD), Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDS), High Resolution Field Emission Scanning Electron Microscopy (HR-FESEM-EDS), Electron Microprobe (EMPA), Differential Scanning Calorimetry coupled with Thermogravimetric Analysis (DSC-TGA), Fourier-Transform Infrared spectroscopy (FTIR), X-ray Absorption Near Edge Structure (XANES) spectroscopy and N 2 adsorption/desorption measurements. The presence of an amorphous gel-like C-(N,K)-A-S-H binder and the complete absence of calcite in Trajan Age samples constitute a unique case, and may be the reason of the high hydraulicity of the mortar. Establishing how these features were produced could allow them to be replicated in high-durability and high-compatibility restoration mortars. • Ancient mortars from Aqua Traiana are characterised by a multi-analytical approach. • Trajan mortars have pozzolanic aggregate, amorphous gel-like binder without calcite. • The absence of calcite in Trajan samples constitutes a unique case in history. • The amorphous binder gives better hydraulicity and mechanical strength. • High-durability and green mortars could be produced from ancient recipes. [ABSTRACT FROM AUTHOR]