Odile Barres

Fe, Mg and Al distribution in the octahedral sheet of montmorillonites. An infrared study in the OH-bending region

Abstract Ten montmorillonites of different origins with variable Fe contents were analysed using transmission IR spectroscopy. Special attention was devoted to the OH-bending region to obtain information about the distribution of octahedral cations. For low to medium Fe contents (≤ 0.56 per Si8 formula unit), a linear relationship between the position of the δAlFeOH band and Fe content was observed. Such correlation might be explained by changes in the cis-trans occupancy of Fe in the octahedral sheet. Deconvolution of the OH-bending domain allows us to discriminate three components (δAlAlOH, δAlMgOH and δAlFeOH) which are correlated with cation abundances derived from chemical analysis. The relative area of each band can then be compared with theoretical areas calculated assuming a fully random distribution of cations in the octahedral sheet. Using such treatment, eight of the 10 montmorillonites studied presented a nearly randomized octahedral distribution. The two samples from Wyoming were clearly different as they exhibited a strong ordering tendency.

FTIR reflectance vs. EPR studies of structural iron in kaolinites

The substitution of Fe3+ in the kaolinite structure is studied by EPR spectrometry and by FTIR spectrometry on a large set of kaolins from different origins (sedimentary and primary ores, soil kaolins). The IR bands at 3598 and 875 cm−1, observed in the literature only in the case of disordered kaolins or in Fe-rich environments (synthetic, lateritic), are revealed by high-resolution IR analysis, whatever the origin and the total Fe content of the samples. The EPR bands corresponding to Fe3+ substituted in sites II of the octahedral sheet increase when the IR absorbance near 3600 cm−1 increases. Two IR absorption bands near 4465 cm−1 and 7025 cm−1 are observed for the first time, both in transmission and diffuse reflectance on all samples. These bands are assigned to the combination of the 3598 and 875 cm−1 bands and to the first harmonic of the band at 3598 cm−1, respectively. The area of the band at 4465 cm−1 in diffuse reflectance is quantitatively correlated to the abundance of Fe3+ located in centers II as measured by ESR. This directly confirms the assignment of the two IR bands at 3598 and 875 cm−1 to OH stretching and deformation vibration bands in octahedral FE3+ environment in the kaolinite structure, respectively. Effects due to the size of particles and to the main kaolins impurities on the near infrared spectra, are also discussed.

Composition, structure and size distribution of suspended particulates from the Rhine River

Fluvial suspended particulates collected from the Rhine River were investigated in terms of composition, structure and size distribution. Elemental analysis and Diffuse Reflectance Infrared Spectroscopy reveal that most particulate organic matter is formed from material derived from microorganisms. Transmission Electron Microscopy observations on resin-embedded samples and structural characterization from break-up experiments, show that fluvial particulate matter should be viewed as fractal aggregates organized by bacterial exopolymeric substances. The shape of particulate size distribution suggests that the formation and dynamics of suspended particulate matter are controlled mainly by physical processes. Finally, particulate growth and structure are consistent with a cluster-cluster aggregation scheme.

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.

Separation of hydrocarbons and lipid from water using treated bark

This paper explores the possibility of using treated bark to remove oily compounds from water. Bark was first biologically or chemically treated and saturated with transition metal ions (TMI) to avoid the release of soluble organic compounds from the bark in the treated effluents. Several experimental parameters affecting the oil removal efficiency (RE) were studied (initial oil concentration, temperature, time, etc.). Saturated bark was characterized using Fourier transform infrared (FTIR) spectroscopy and bark wetting index was determined. Results of the retention of lipids suggested that their removal could exceed 95% of initial oil concentration. The uptake of lipid by treated bark varied from 0.2 to 2.0 g of organic oil/g of dry sorbent. No significant chemical modifications of saturated bark were observed in infrared spectroscopy after the sorption of oleic acid on bark treated with transition metal ions. The structure of adsorbed tridimensional layer of oleic acid molecules seemed to take place through the double bond. The hydrocarbon RE exceeded 95% using oil-water mixture with a hydrocarbon/bark ratio of one. The sorption reaction of hydrocarbons and lipids was quasi-instantaneous and seemed to be influenced by the temperature. This indicated that the retention mechanism was related to the capillary action. Results of FTIR spectroscopy suggested that no chemical bonds between barks and oily compounds were established.

Application of Micro-FT-IR Spectroscopy to Individual Hydrocarbon Fluid Inclusion Analysis

Infrared spectra of fluid inclusions are obtained with a Fourier transform infrared miscrospectrometer. The experimental conditions and the analytical use are discussed. Interferograms are recorded in the transmission mode. The quality of spectra is good for fluid inclusions with diameters larger than 30 μm, the spectral resolution being 4 cm−1 and the recording time 200 s. Interferograms made of inclusions with diameters of less than 20 μm are reached in the same amount of time, but with worse spectral resolution. Infrared spectra are usually only suitable above 2000 cm−1, because of the absorption of most of the inclusion-bearing host minerals, the thickness of which should never exceed 1 mm. This fact further limits their interpretation, as the inclusion composition is complex. However, complementary information can be obtained in the 4600–4000-cm−1 range for hydrocarbon inclusions with a thickness that is larger than some tens of micrometers. This shows that it is necessary to use a detector which is as sensitive as possible towards high frequencies. A comparison of the current performances of infrared and Raman spectroscopies as analytical methods for investigating fluid inclusions is presented. The important improvement of better spatial resolution and the corresponding possibility of being able to characterize heterogeneities, in comparison to limitations with classical dispersive infrared spectrometry, are discussed. Methane, carbon dioxide, liquid water, aromatic ester, and linear or branched alkanes are identified in several samples. It is also possible to estimate the mean ratio of alkane CH2/CH3 groups. In some cases, the intensity of the absorptions indicates the inclusion effective thickness and the mole fraction ratio.

Semi-quantitative FT-IR microanalysis limits: Evidence from synthetic hydrocarbon fluid inclusions in sylvite☆

Infrared microspectrometry is an essential technique for the in situ analysis of individual fluorescent hydrocarbon inclusions. In order to calibrate this technique alkane and benzene inclusions have been synthesized in sylvite crystals below 100°C at atmospheric pressure. We show that the infrared spectra obtained on pure alkane synthetic inclusions differ from equivalent composition standards. The n-alkane and cyclohexane inclusions exhibit an intense spectral deformation characterized by a broadening, a flattening, and a waving of the peak. This spectral deformation takes place in the C-H stretching and bending infrared regions and affects the CH2CH3 peak area ratio measurements. No spectral deformation occurs for benzene inclusions in the C-H stretching region. Raman analysis confirms that no change in composition occurs during trapping. When the dilution of alkanes in a solvent increases, the infrared spectral deformation observed for the inclusions disappears. This dilution effect is not observed for pure alkane standards. It is possible to approximate the alkyl chain carbon number (X) which is between the pure n-alkane standard value and the synthetic inclusion value: (AREA [∑CH2]/AREA [∑CH3] + 0.1)/0.27 < X < (AREA [∑CH2]/AREA [∑CH3] − 0.8)/0.09. These results can be applied to the natural environments taking into account the limits of the FT-IR (Fourier Transform-Infra Red) microanalysis of fluid inclusions.

EFFECTS OF TEMPERATURE, pH, AND IRON/CLAY AND LIQUID/CLAY RATIOS ON EXPERIMENTAL CONVERSION OF DIOCTAHEDRAL SMECTITE TO BERTHIERINE, CHLORITE, VERMICULITE, OR SAPONITE

AbstractIn deep geological repositories for high-level nuclear wastes, interactions between steel canisters and clay-rich materials may lead to mineralogical transformations with a loss of the confining properties of the clays. Experiments simulating the conversion of smectite to Fe-rich clay phases in contact with Fe metal have been carried out to evaluate such a possibility by taking into account the effects of a series of critical parameters, including temperature, pH, and Fe/clay (Fe/C) and liquid/clay (L/C) ratios. The mineralogical and chemical transformations observed in these experiments have been compared with data from the literature, and subsequently used to propose a conceptual model for the main mineralogical transformations which can be expected in clay formations surrounding high-level nuclear waste repositories. In the presence of Fe metal and under low oxygen fugacity (<-40) the main mineralogical sequences are as follows: (1)up to 150°C, under neutral pH, and L/C > 5: dioctahedral smectite (di-sm) → 7 Å Fe-rich phase (berthierine, odinite-cronstedtite) for large Fe/C ratios (>0.5), or di-sm → Fe-rich di-sm + Fe-rich trioctahedral smectite (tri-sm) for small Fe/C ratios (0.1)(2)up to 150°C, under alkaline pH (10–12), and L/C > 5: di-sm → Fe di-sm (±palygorskite) for a small Fe/C ratio (0.1)(3)at 300°C, Fe/C = 0.1, and L/C > 5: di-sm → Fe-rich saponite → trioctahedral chlorite + feldspar + zeolite (near-neutral pH); di-sm → Fe-rich vermiculite + mordenite (pH 10–12). Low temperatures (<150°C) and large L/C and Fe/C ratios seem to favor the crystallization of the serpentine group minerals instead of Fe-rich trioctahedral smectites or chlorites, the latter being favored by higher temperatures. The role of L/C and Fe/C ratios and the competition between them at different temperatures is a crucial point in understanding the transformation of smectite in contact with Fe metal.

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.

Adsorption of polyamine on clay minerals.

This work aims at a better understanding of the interaction between a polycationic quaternary amine polymer (F25) and three different clay minerals: montmorillonite, illite, and kaolinite. For this, adsorption isotherms of F25 on the clay surfaces were measured together with the evolution of the CEC along the isotherm, which revealed that cation exchange plays an important role in the adsorption process. These first results were confirmed by XRD measurements on dried powders that are evidence in the case of montmorillonite of the presence of polymer in the interlayer spaces. In addition, the evolution of the short range structure of clay minerals suspensions on polymer adsorption was followed by WAXS experiments. Polymer intercalation was observed while the structure of the resulting stacking appeared to change slightly along the polymer adsorption isotherm. Diffuse reflectance infrared measurements revealed that significant conformational changes occur on polymer adsorption onto montmorillonite surfaces. Furthermore, adsorption above the CEC is observed which involves a charge reversal of clay mineral surfaces, the zero charge being reached for an adsorbed amount corresponding to the CEC. Finally, flocculation was discussed compared to adsorption amounts and zeta potential measurements, confirming that optimum flocculation concentration is reached for noncharged particles.