International audienceA specific methodology was developed to collate the interlayer configurations resulting from Grand-Canonical Monte Carlo (GCMC) simulations with experimental X-ray and neutron diffraction data for two synthetic Na-saturated saponites having contrasting layer charge. Numerical simulations were performed assuming different existing sets of atomic partial charge and Lennard-Jones parameters for clay and water. For each parameter set and for the two samples in both the mono- and bihydrated states, the water contents resulting from GCMC simulations were first compared to water vapor desorption gravimetry data. The density distributions of interlayer species were then used to generate 00l intensities that were compared to X-ray and neutron diffraction data, the latter being recorded on both hydrogenated and deuterated specimens. The CLAYFF model [Cygan et al. J. Phys. Chem. B2004, 108, 1255] is shown to better account for water content and organization compared to the model developed by Skipper et al. (Clays Clay Miner.1995, 43, 285) and modified by Smith (Langmuir1998, 14, 5959). However, diffraction patterns calculated for bihydrated samples from CLAYFF simulations did not match satisfactorily the diffraction data. Lennard-Jones parameters were thus modified for oxygen atoms from the clay layer. When combined with the SPC/E water model, this modified version of CLAYFF allows matching experimental water contents and fitting the complete set of diffraction data. Relevant information may thus be derived on the influence of layer charge on the orientational properties of interlayer water molecules which differs for the different clay models. Finally, the approach used in the present study proved powerful for assessing atomic interaction parameters considered for computational simulations

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Submerged sediment cores were collected upstream of a dam in the Orne River, northeastern France. This dam was built in the context of steelmaking to constitute a water reservoir for blast furnace cooling and wet cleaning of furnace smokes. The dam also enhanced sediment deposition in the upstream zone. This study was performed to unravel the contamination status of sediments and to evidence possible contribution sources. The sediment layers were analyzed for water content, grain size, chemical composition, crystalline phases at a bulk scale and poorly crystalline and amorphous phases at a sub-micrometer scale. Visual aspect, texture, color, and chemical and mineralogical analyses showed that the settled sediments were mainly composed of fine black matter, certainly comprising steelmaking by-products. Those materials were highly enriched with Fe, Zn, Pb and other trace metals, except for a relatively thin layer of surficial sediments that had settled more recently. Bulk mineralogy revealed crystalline iron minerals, such as magnetite, goethite, wuestite and pyrite, in the deep layers of the sediment cores. Furthermore, microscopic investigations evidenced the presence of ferrospheres, goethite nanoparticles and newly formed Fe-aluminosilicates; all originating from the former steelmaking facilities. The variation of iron mineralogy, combined with specific chemical profiles and other sediment features, demonstrate the different contributions that constitute the sediment deposit. Furthermore, chemical and mineralogical features of goethite and Fe-aluminosilicates could be used as a fingerprint for such contaminated sediments.