Bernard Humbert

Sorption of selenium oxyanions on TiO2 (rutile) studied by batch or column experiments and spectroscopic methods

Selenium is a known toxic element released in the environment by anthropogenic activities. The present study is devoted to the aqueous sorption behaviour of selenium oxyanions (selenate and selenite) on a reference oxide surface, namely rutile TiO(2). Batch sorption kinetics and isotherms have been studied using different physico-chemical conditions of the solution (changes of pH and ionic strength). The sorption was favoured for both anions in acidic conditions, in agreement with a surface complexation mechanism and CD-MUSIC predictions. Spectroscopic investigations of the sorbed rutile powder were also consistent with such a mechanism. EXAFS spectra confirmed that for selenite anions, an inner-sphere mechanism was the most probable process observed. Dynamic sorption experiments using a column filled with rutile powder also substantiated that a part of the surface complexes follows the inner-sphere mechanism, but also evidenced that an outer-sphere mechanism cannot be excluded, especially for selenate anions.

A vibrational study of the nature of hydroxyl groups chemical bonding in two aluminium hydroxides.

Lengths, strengths and valences of OH bonds in the two aluminium hydroxides gibbsite and bayerite were determined on the basis of vibrational spectral data. The uncoupled OD stretching modes in the range 2400-2800cm(-1) were recorded by means of infrared diffuse reflectance, thereby avoiding effects of surface, vibrational coupling or particle shape. The assignment of the corresponding Raman spectra resulted in the determination of harmonic wavenumbers, force constants and anharmonicity coefficients of bulk OH groups in the two minerals. OH bond lengths deduced from these data varied from 0.964A to 0.975A in gibbsite and 0.962A to 0.973A in bayerite. These lengths appear to correspond to weak H-bonds contrary to previously recognized data from X-ray diffraction and neutron diffraction studies. Finally, bond valences were calculated on the basis of these new bond lengths and discussed as a function of crystallographic structures and the nature of hydrogen bonding in these two structures.

Perforative Corrosion of Pyrite Enhanced by Direct Attachment of Acidithiobacillus ferrooxidans

This study aimed to determine the relationship between cell adhesion and pyrite corrosion. In order to determine cell adhesion rates, a new in vivo imaging procedure was developed with CLSM. Total bacteria coverage rates remained low (< 14%). Adsorption isotherms pointed out two types of cell adhesion sites. Bacteria adhered mainly to corrosion pittings walls with a higher affinity. They favour the formation of deep corrosion pits by maintaining short-range electronic circulations and they avoid surface passivation. This study completes the common model of bio-corrosion of pyrite and we propose to refine the direct/indirect model by proximal and distal approaches.

Accurate μRaman characterization of reaction products at the surface of (bio)oxidized pyrite

Abstract Biotic and abiotic oxidation experiments were performed on ground pyrite grains. MicroRaman (μRaman) spectroscopy was used to characterize and statistically analyze the reaction products formed at the pyrite surface. Reaction compounds consist of iron and sulfur-oxy species for all experiments including various amounts of sulfates, iron oxi-hydroxides, polysulfides, and elemental sulfur as well as scarce amounts of thiosulfate. These compounds are distributed as micrometric to submicrometric bumps. μRaman spectroscopy allowed for clear recognition of four phases of iron oxi-hydroxides and, without any correlation, four molecular structures of sulfate groups. Peaks associated with the oxidation products were assigned and are discussed according to hydration and to most probable chemical bonds with pyrite surfaces. Sulfates formed in solution (Td local symmetry) are distinguished from anhydrous sulfates (C3v to 0 local symmetries) formed directly at the surface of pyrite grains. Proposed structures are related to the surrounding chemical properties (e.g., local acidity) and to the heterogeneous electronic properties of pyrite grains. The distribution and combination of oxidation compounds at the surface of pyrite grains provide clues that distinguish bio-oxidized from chemically oxidized pyrite surfaces. Bio-oxidized surfaces are characterized by the exclusive presence of C3v sulfates that reflect active electronic circulations within the pyrite lattice. In contrast, air-oxidized pyrite surfaces exhibit a high proportion of 0 symmetry sulfates adsorbed on hematite bumps indicating a strong passivation of the mineral surface.

On the modeling and processing of polarization in Raman spectroscopy

The use of polarized lasers for Raman spectroscopy provides a powerful tool in chemical physics as it allows a precise differentiation of the vibration modes of the crystals according to their crystallographic symmetry and local spatial orientation. In this paper we analyze the possibility of efficiently using the polarization information in Raman spectroscopy by taking into account the relationships between the two polarized spectra (parallel and orthogonal). New signal processing models for the polarized Raman spectroscopy data are introduced and algorithmic solutions are proposed.