Philippe de Donato

Channel occupancy in an alkali-poor beryl from Serra Branca (Goias, Brazil): Spectroscopic characterization

Abstract Spectroscopic (micro FTIR, Raman, MAS NMR) and mass spectroscopic techniques have been used to examine, on both single-crystal and powder samples, the behavior of H2O and CO2 molecules in the structural channels of an alkali-poor, volatile-rich beryl from Brazil. Polarized single-crystal FTIR and Raman spectra were obtained on oriented wafers of isolated crystals. Location and orientation of H2O and CO2 molecules were determined from IR spectra. The proton-proton vectors of type-I and type-II H2O are parallel and perpendicular to the c axis, respectively; the molecular axis of the CO2 molecule is perpendicular to the c axis. Relative proportions of both types of H2O were determined from their respective IR absorption-band intensities and were found to be nearly equivalent. There is, contrary to what is generally claimed in the literature, no relation between alkali and type-II H2O contents. Absorptivity coefficients for H2O and CO2 were computed for every specific orientation. A 1H MAS NMR spectrum resolved as a “Pake” doublet seems to confirm the absence of any anisotropic movement of the H2O molecules from one orientation to the other on the NMR time scale. Mass discrimination of volatiles released by pyrolysis under vacuum confirms the weak mobility of H2O and CO2 molecules in the channel sites, although the plugging effect of alkalis in the channels can be neglected for such an alkali-poor beryl. The volatile vs. alkali content ratio in beryl could possibly be used as an environmental indicator.

Study of tropaeolin degradation by iron—proposition of a reaction mechanism

The degradation of tropaeolin by iron was studied under oxidizing and inert atmospheres. The products were identified by various chromatographic and spectroscopic methods. Under inert atmosphere, the proposed model of mechanism is based on the adsorption of tropaeolin by the sulfonate function on the solid iron, followed by a reduction of the [bond]Nz[double bond]N[bond] bond with formation of 1-amino-2-naphthol and sulfanilic acid. These two intermediaries were reduced to 1,2-dihydroxynaphthalene and benzene with NH(4)(+) and HSO(3)(-) liberation. Under oxidizing atmosphere, besides the reductions of tropaeolin, water and ferric ions, the existence of a homogeneous degradation was found. This process was explained (on the basis of surface iron potential monitoring) by a stepwise reduction of oxygen giving hydrogen peroxide. The initial stages of the mechanism were similar to those under inert atmosphere, but the degradation of the 1,2-dihydroxynaphthalene continued giving 1,2-naphthalenedione, then various polar monocyclic compounds leading to three unidentified volatile final products.

A 'dry' condensation origin for circumstellar carbonates.

The signature of carbonate minerals has long been suspected in the mid-infrared spectra of various astrophysical environments such as protostars. Abiogenic carbonates are considered as indicators of aqueous mineral alteration in the presence of CO2-rich liquid water. The recent claimed detection of calcite associated with amorphous silicates in two planetary nebulae and protostars devoid of planetary bodies questions the relevance of this indicator; but in the absence of an alternative mode of formation under circumstellar conditions, this detection remains controversial. The main dust component observed in circumstellar envelopes is amorphous silicates, which are thought to have formed by non-equilibrium condensation. Here we report experiments demonstrating that carbonates can be formed with amorphous silicates during the non-equilibrium condensation of a silicate gas in a H2O-CO2-rich vapour. We propose that the observed astrophysical carbonates have condensed in H2O(g)-CO2(g)-rich, high-temperature and high-density regions such as evolved stellar winds, or those induced by grain sputtering upon shocks in protostellar outflows.

Evidence of bacterial activity from micrometer-scale layer analyses of black-smoker sulfide structures (Pito Seamount Site, Easter microplate)

Abstract We report the observation of an external layer, less than 20 μm thick, attached to hydrothermal chimney fragments of black smokers collected from the Pito Seamount site on the Easter microplate. Scanning electron microscope observations revealed bacterial imprints located on and within the layer, which was associated with underlying layers of thin jarosite deposits and iron sulfides displaying corrosion features. X-ray, electron microprobe, DRIFT and HPLC measurements were used to determine the precise chemical composition and nature of compounds in the layer. The external layer was composed mainly of a combination of hydrated ferric sulfate, ferrous sulfate, iron oxi-hydroxide and elemental sulfur species. A jarosite-like mineral was found deeper in the layer. We suggest that this layer may not be the result of an abiotic thermochemical precipitation, but instead, was formed chemically by bacterial processes. These processes were (1) elemental sulfur oxidation which represents major energetic exchanges within the external layer and (2) bioleaching processes inducing iron oxidation. Originally, elemental sulfur probably resulted from thermochemical precipitation. The results of this study give new insight on the possible role and impact of related acidophilic microorganisms living in hot vent environments of the deep sea.

Infrared spectroscopy of OD vibrators in minerals at natural dilution: hydroxyl groups in talc and kaolinite, and structural water in beryl and emerald.

An infrared (IR) study of natural deuteration is conducted on minerals containing hydroxyl groups (talc and kaolinite) and channel-water-bearing minerals (beryl and emerald). In talc, the OD valence vibration is located at 2710 cm−1, corresponding to OD groups surrounded by 3 Mg atoms. In kaolinite, the OD valence vibrations are located at 2671 cm−1 (inner OD group), 2712, 2706, and 2700 cm−1 (three inner-surface OD groups). In beryl and emerald, natural deuteration of channel water is observed for the first time by infrared microspectroscopy. In beryl from Minas Gerais (Brazil), the OD profiles are characterized by four bands at 2735, 2686, 2672, and 2641 cm−1. In emeralds from Colombia and Brazil, the OD profiles are characterized by five or four bands, respectively, at 2816, 2737, 2685, 2673, and 2641 cm−1 (Colombia) and 2730, 2684, 2672, and 2640 cm−1 (Brazil). The band at 2816 cm−1 can be assigned to –OD or OD−, and bands at 2686–2684, 2673–2672, and 2641–2640 cm−1 can be assigned to type-I and type-II HOD molecules. The band at 2737–2730 cm−1 is partially disturbed by combination bands of the mineral. Such OD profiles are different from those obtained by artificial deuteration at higher OD dilution.

FT-IR metrology aspects for on-line monitoring of CO2 and CH4 in underground laboratory conditions

The French National Radioactive Waste Management Agency (ANDRA) has recently developed a new experimental set-up which allows sampling water from marl rock formations, together with an in situ characterisation of the composition and migration mechanisms of the gases dissolved in the marl porewater. Gases and liquids are collected from vertical borehole drillings in underground laboratories. The analytical design, Fourier transformed infrared spectroscopy based, allows powerful and long term on-line monitoring of gases released by low-permeability media. The IR system is designed to cope with the unfavourable measurement conditions occurring in an experimental underground laboratory (moisture, dust, etc.). Because the working conditions in such an underground laboratory make complete purging of the IR spectrometer difficult, the IR spectra of geological gases are often perturbed by contributions from atmospheric CO2 and water vapour. The metrology aspect is based on an IR low resolution sensor equipped with two measurement compartments. In the internal compartment linked to the borehole layout, gases are monitored on-line through a cell with a variable optical path, whereas in the external compartment, atmospheric CO2 is measured through a short open path configuration. The experimental method and data processing procedure used to determine the real partial pressure of CO2 arising from the marl rock formation are described in this paper. Results of the on-line gas (CO2 and CH4) monitoring conducted in the Mont Terri underground laboratory are presented and compared with punctual gas chromatography analyses.

In situ gas monitoring in clay rocks: mathematical developments for CO2 and CH4 partial pressure determination under non-controlled pressure conditions using FT-IR spectrometry

The quantification of dissolved gases in water at equilibrium with rock assemblages is very important for modelling the long-term behaviour of radioactive wastes and other materials in a deep geological disposal. This paper presents the mathematical development allowing to quantify the partial pressures of evolved gases from the rock that were collected from a borehole and transferred to a gas cell coupled to a low resolution FT-IR spectrometer. The areas of the different ν3 bands of CO2 between 2400 and 2220 cm−1 and the CH4 Q-branch between 3022 and 3002 cm−1 have been calculated using a peak integration method. It has been shown that the equation between the integrated area and the partial pressure for CH4 and CO2 for a spectral resolution of 1 cm−1 does not follow Beer–Lambert law and is dependent on the bulk pressure. A non-linear continuous calibration model has been developed for a range of bulk pressures from 0.9 to 1.4 bar, giving, for each gas, a relation between partial pressure and both integrated area and bulk pressure. Explored partial pressure ranges are between 0.3 and 4 mbar for CO2, and 0.3 and 12 mbar for CH4 with an equivalent optical path of 1 m. The relative root mean squared error of the prediction of the models is included between 1 and 3% in the explored pressure ranges for each gas.

On the use of electrokinetic phenomena of the second kind for probing electrode kinetic properties of modified electron-conducting surfaces

The electrokinetic features of electron-conducting substrates, as measured in a conventional thin-layer electrokinetic cell, strongly depend on the extent of bipolar faradaic depolarisation of the interface formed with the adjacent electrolytic solution. Streaming potential versus applied pressure data obtained for metallic substrates must generally be interpreted on the basis of a modified Helmholtz-Smoluchowski equation corrected by an electronic conduction term-non linear with respect to the lateral potential and applied pressure gradient-that stems from the bipolar electrodic behavior of the metallic surface. In the current study, streaming potential measurements have been performed in KNO(3) solutions on porous plugs made of electron-conducting grains of pyrite (FeS(2)) covered by humic acids. For zero coverage, the extensive bipolar electronic conduction taking place in the plug-depolarized by concomitant and spatially distributed oxidation and reduction reactions of Fe(2+) and Fe(3+) species-leads to the complete extinction of the streaming potential over the entire range of applied pressure examined. For low to intermediate coverage, the local electron-transfer kinetics on the covered regions of the plug becomes more sluggish. The overall bipolar electronic conduction is then diminished which leads to an increase in the streaming potential with a non-linear dependence on the pressure. For significant coverage, a linear response is observed which basically reflects the interfacial double layer properties of the humics surface layer. A tractable, semi-analytical model is presented that reproduces the electrokinetic peculiarities of the complex and composite system FeS(2)/humics investigated. The study demonstrates that the streaming potential technique is a fast and valuable tool for establishing how well the electron transfer kinetics at a partially or completely depolarised bare electron-conducting substrate/electrolyte solution interface is either promoted (catalysis) or blocked (passivation) by the presence of a discontinuous surface layer.

Use of Treated Bark for the Removal of Lipids from Water

Abstract Raw, biologically treated bark and bark impregnated with transition metal ions were used to retain the lipids from synthetic emulsions. Several experimental parameters affecting the lipid removal efficiency (RE) were studied (initial concentration of lipids, temperature, time, pH, carboxylic acid chain length, etc.). Saturated bark was characterized using Fourier transform infrared (FTIR) spec-troscopy and light microscopy, and the treated bark wetting index was determined. Results show that lipid removal can exceed 95% of the initial concentration at a pH lower than 7. The uptake of lipids by these sorbents varied from 0.2 to 2.5 g/g of dry bark. Trials for regenerating the sorbent saturated by lipids allowed the recovery of ~95% of lipids. The calorific value of the saturated bark was ~79% that of domestic fuel and can be considered as an energy source, thus avoiding its waste disposal. These results may upgrade the treatment of wastewater generated by several industrial sectors, such as the food industry, surface treatment, and so on.

Near Real-Time Ground-to-Ground Infrared Remote-Sensing Combination and Inexpensive Visible Camera Observations Applied to Tomographic Stack Emission Measurements

Evaluation of the environmental impact of gas plumes from stack emissions at the local level requires precise knowledge of the spatial development of the cloud, its evolution over time, and quantitative analysis of each gaseous component. With extensive developments, remote-sensing ground-based technologies are becoming increasingly relevant to such an application. The difficulty of determining the exact 3-D thickness of the gas plume in real time has meant that the various gas components are mainly expressed using correlation coefficients of gas occurrences and path concentration (ppm.m). This paper focuses on a synchronous and non-expensive multi-angled approach combining three high-resolution visible cameras (GoPro-Hero3) and a scanning infrared (IR) gas system (SIGIS, Bruker). Measurements are performed at a NH3 emissive industrial site (NOVACARB Society, Laneuveville-devant-Nancy, France). Visible data images were processed by a first geometrical reconstruction gOcad® protocol to build a 3-D envelope of the gas plume which allows estimation of the plume’s thickness corresponding to the 2-D infrared grid measurements. NH3 concentration data could thereby be expressed in ppm and have been interpolated using a second gOcad® interpolation algorithm allowing a precise volume visualization of the NH3 distribution in the flue gas steam.