7 Matching Results

Search Results

Advanced search parameters have been applied.

in creator/contributor: "Farges, Francois"

open access

Adsorption Mechanisms of Trivalent Gold onto Iron Oxy-Hydroxides: From the Molecular Scale to the Model

Gold is a highly valuable metal that can concentrate in iron-rich exogenetic horizons such as laterites. An improved knowledge of the retention mechanisms of gold onto highly reactive soil components such as iron oxyhydroxides is therefore needed to better understand and predict the geochemical behavior of this element. In this study, we use EXAFS information and titration experiments to provide a realistic thermochemical description of the sorption of trivalent gold onto iron oxy-hydroxides. A… more

Date: December 13, 2006

Creator: Cances, Benjamin; Benedetti, Marc; Farges, Francois; Brown, Gordon E., Jr. & /Stanford U., Geo. Environ. Sci. /SLAC, SSRL

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Coordination Environments of Highly Charged Cations (Ti, Cr, and Light REE's) in Borosilicate Glass/Melts to 1120C

The local environments around Ti, Cr, and several light rare-earth elements (La, Ce, and Nd) were investigated by in-situ XANES spectroscopy in a number of complex borosilicate glasses and melts (to 1120 C) that are used for nuclear waste storage. Examination of the high-resolution XANES spectra at the Ti K-edge shows that the average coordination of Ti changes from {approx}5 to {approx}4.5. Cr is dominantly trivalent in the melts studied. However, its average coordination is probably lower in … more

Date: January 2, 2007

Creator: Farges, Francois; /Museum Natl. Hist. Natur. /Stanford U., Geo. Environ. Sci.; Brown, Gordon E., Jr. & /Stanford U., Geo. Environ Sci. /SLAC, SSRL

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Adsorption and Precipitation of Aqueous Zn(II) on Hematite Nano- and Microparticles

As part of a study of the effect of particle size on reactivity of hematite to aqueous metal ions, the sorption of Zn(II) on hematite nanoparticles and microparticles was examined over a wide range of Zn(II) concentrations using Zn K-edge EXAFS. When reacted with nanoparticles at pH 5.5 and low Zn(II) sorption densities (0.04 {le} {Lambda} < 2.76 imol/m{sup 2}), Zn(II) formed five-coordinated or a mixture of four- and six-coordinated surface complexes with an average Zn-O distance of 2.04({+… more

Date: December 13, 2006

Creator: Ha, Juyong; /Stanford U., Geo. Environ. Sci.; Farges, Francois; /Stanford U., Geo. Environ. Sci. /Museum Nat. Hist., Paris; Brown, Gordon E., Jr. & /SLAC, SSRL

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Chrysolcolla Redefined as Spertiniite

XAFS and {mu}-XAFS spectra were collected at the Cu K-edge for seven chrysocolla samples (Peru, USA, and Congo). The results suggest that the local structure around Cu is similar to that in Cu(OH){sub 2} (spertiniite). Cu-L{sub 3} STXM imaging and spectroscopy confirm that the chrysocolla samples examined here consist of mesoscopic Cu(II)-rich domains surrounded by Si-rich domains (in agreement with results from infra-red spectroscopy). Hence, we suggest that chrysocolla, which is generally con… more

Date: December 13, 2006

Creator: Farges, Francois; /Museum Nat. Hist., Paris /Stanford U., Geo. Environ. Sci.; Benzerara, Karim; /Paris U., VI-VII, LMCP; Brown, Gordon E., Jr. & /Stanford U., Geo. Environ. Sci. /SLAC, SSRL

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Selenium Speciation in Biofilms from Granular Sludge Bed Reactors Used for Wastewater Treatment

Se K-edge XAFS spectra were collected for various model compounds of Se as well as for 3 biofilm samples from bioreactors used for Se-contaminated wastewater treatment. In the biofilm samples, Se is dominantly as Se(0) despite Se K-edge XANES spectroscopy cannot easily distinguish between elemental Se and Se(-I)-bearing selenides. EXAFS spectra indicate that Se is located within aperiodic domains, markedly different to these known in monoclinic red selenium. However, Se can well occur within na… more

Date: December 13, 2006

Creator: van Hullenbusch, Eric; U., /Marne la Vallee; Farges, Francois; /Stanford U., Geo. Environ. Sci. /Museum Natl. Hist. Natur., Paris; Lenz, Markus; Lens, Piet et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Durability of Silicate Glasses: An Historical Approach

We present a short review of current theories of glass weathering, including glass dissolution, and hydrolysis of nuclear waste glasses, and leaching of historical glasses from an XAFS perspective. The results of various laboratory leaching experiments at different timescales (30 days to 12 years) are compared with results for historical glasses that were weathered by atmospheric gases and soil waters over 500 to 3000 years. Good agreement is found between laboratory experiments and slowly leac… more

Date: January 2, 2007

Creator: Farges, Francois; /Museum Natl. Hist. Natur. /Stanford U., Geo. Environ. Sci.; Etcheverry, Marie-Pierre; U., /Marne la Vallee; Haddi, Amine; U., /Marne la Valle et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

On the Coordination of Actinides and Fission Products in Silicate Glasses

The local structure around Th, U, Ce and Nd in leached silicate glasses was examined using XAFS spectroscopy at their L3 edges and also at the K edge of Fe, Co, Ni, Zr and Mo. Pellets of inactive borosilicate glasses with a simplified or a complex composition were leached statically at 90 C, at pH buffered to 0 or 6 for 28 days (surface/volume, S/V, ratios of 0.1 cm{sup -1}). These glasses are compared to another SON68 sample (denoted ''SP1'' in this paper) that was statically leached for 12 ye… more

Date: December 13, 2006

Creator: Haddi, Anne; U., /Marne la Vallee; Farges, Francois; /Marne la Vallee U. /Museum Nat. Hist., Paris /Stanford U., Geo. Environ. Sci.; Trocellier, Patrick; /Saclay et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department