Utilisation de carrières souterraines de la région parisienne pour stockage intersaisonnier d'énergie solaire pour l'habitat

La ville de Paris et sa banlieue comportent de nombreuses anciennes carrières souterraines qui posent des problèmes de stabilité du sol. On peut chercher à les consolider tout en les utilisant pour stocker de l'eau chauffée par des capteurs solaires en vue du chauffage de bâtiments. Dans le cadre d'un projet de construction d'une école maternelle à Sèvres (Hauts-de-Seine), une étude fine, à l'aide d'un modèle par différences finies, des transferts thermiques dans le stock d'eau non isolé et le massif rocheux encaissant, met en évidence la participation de celui-ci à la fonction de stockage. Un tel projet semble faisable à condition d'exploiter le stock à un bas niveau thermique

Adsorption mechanisms of trivalent gold on iron- and aluminum-(oxy)hydroxides. Part 1: X-ray absorption and Raman scattering spectroscopic studies of Au(III) adsorbed on ferrihydrite, goethite, and boehmite

International audienceGold adsorption products on powdered ferrihydrite, goethite, and boehmite samples, prepared by reacting Au(III)-Cl solutions ([Au] = 4.2 x 10(-5)-9.0 x 10(-3) M; [Cl] = 0.017-0.6 M) with these adsorbents at pH Values of 4 to 9 and Au adsorption densities ranging from 0.046 to 1.53 mumol/m(2) were characterized using Au-L-III XAFS spectroscopy. The solutions (before and after uptake) were investigated by Raman scattering to determine speciation and by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) to determine solution composition. We present an analysis of several effects that are observed in the Au L-III-edge XAFS spectra, including X-ray beam.-induced photo-reduction, multi-electronic excitations, disorder effects. and multiple scattering, that would complicate interpretation of the spectra if not accounted for. A combination of methods (spectral deconvolution, principal component analysis, spectral inversion, and wavelet analysis) was used to identify and quantify these effects, to characterize the nature of mixed ligands around gold, and to distinguish between multiple-scattering features and features due to next-nearest neighbors in the XAFS spectra. Analysis of the Au-L-III XAFS spectra showed that Au(III) is present as square-planar Au(III)(O,Cl)(4) complexes in the aqueous solutions and on the surfaces of the Al/Fe-(oxy)hydroxide adsorption samples with dominantly 0 ligands at pH > 6 and mixed O/Cl ligands at lower pH values. The EXAFS-derived Au-O and Au-Cl distances are 2.00(2) and 2.28(2) Angstrom, respectively, and the magnitudes of the Debye-Waller factors and third cumulants from anharmonic analyses indicate very little thermal or positional disorder around Au(III) in the adsorption samples. Iron second neighbors are present around An in the Au(III)/ferrihydrite and Au(III)/ Goethite adsorption samples, with Au-Fe distances of 3.1(1) and 3.3(1) Angstrom. In boehmite, two sets of Au-Al distances were detected at 3.0(1) and 3.2(1) Angstrom. A reverse Monte Carlo study of the XAFS spectroscopic data suggests the presence of a continuum of edge-shared AuO4-FeO6 distances, which cannot be described correctly by a classical model of these data in which only a mean distance (although severely under-estimated) is derived. Copyright (C) 2004 Elsevier Ltd