Application of ToF-SIMS for sulfur isotopic fractionation in sulfide phases of iron corrosion layers: determination of bacterial impact on the formation of these phases

International audienceTo a better understanding of the iron corrosion mechanisms, it is crucial to elucidate the role of bacteria. Thus, in order to have a diagnosis of the action of bacteria in the iron corrosion, the objective of this study is to determine by ToF-SIMS the isotopic sulfur fractionation δ 34 S in iron sulfides of (sub)micrometric size located in the corrosion product layers of the ferrous objects corroded in anoxic soils and marine environment. These iron sulfides may have two origins: an abiotic origin resulting in the dissolution/reprecipitation of sulfides from the surrounding medium (for example from pyrite in a soil) or a biotic origin by the action of the sulfate-reducing bacteria that reduce sulfate ions into sulfides leading to the formation of iron sulfides with ferrous ions issued from the aqueous dissolution of metal iron. A difference in the isotopic sulfur fractionation δ 34 S in the sulfur phases according to the abiotic or biotic origin of these phases is reported in the literature. Thus in this study, the isotopic sulfur fractionation δ 34 S in the iron sulfides formed in the corrosion product layers of iron was determined to identify the formation origin of these phases and the role of bacteria in the iron corrosion. After characterization of the distribution of the different iron sulfides within the layers (optical microscopy, SEM-EDS, μRaman spectroscopy), the local isotopic fractionation of sulfur is measured by the imaging and spectroscopy ToF-SIMS technique. Some important results have been obtained. First of all, the reproducibility and the accuracy of the method were established by the choice and the validation of a hydrothermal pyrite sample calibrated relatively to the international sulfur isotopic standard Canon Diablo Troilite. Secondly, it was observed that there was no or little variation in the isotopic sulfur fractionation δ 34 S with the degree of oxidation of sulfur. Finally, a noticeable difference in the isotopic sulfur fractionation δ 34 S between iron sulfides formed in laboratory under abiotic or biotic conditions was evidenced: δ 34 S is close to 0 in abiotic conditions whereas in biotic conditions it is shifted from 0 with values up to up to some tens per mil. These first results being promising, the study is actually in progress to determine the formation origin (abiotic/biotic) of the Fe-S present in the corrosion product layers of natural systems of iron corrosion, from soils, subaquatic and marine environments

Les sulfures dans la corrosion anoxique du fer. Rôle , identification et origine de la formation : approche multi-techniques du micro au nano

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Suivi de la fusion expérimentale de la galène de Melle (79) par microspectroscopie Raman

International audienceThis paper focuses on the study (macroscopic and microscopic) of the transformation of classic silver ore (galena: PbS) and its evolution from a repository produced experimentally in a muffle furnace operating at charcoal. While the chemical reaction that leads from the sulfide lead bullion is identified for a long time, its reproduction in a reactor bottom furnace remains unsatisfactory and attempts to understand the transformation processes of the galena remain largely unsuccessful. This lack of mastery of the process blocks possible reflections on material balances and weight mining in ancient economies including matters related to the circulation of lead. Thus two great moments in this production line must be better understood: the roasting phase of galena and the reduction into lead. To reach these objectives, µRaman spectroscopy provides a complementary view of the macroscopy approach to processing the silver galena especially to identify the various chemical species of lead (oxides, sulfates, oxysulfates, carbonates) formed during the transformation of galena. The transformation of the mineral occurs in the following steps: appearance of elemental sulfur and sulfates in the first minutes; reduction of sulfates in favor of the emergence of lead oxides; further reduction of sulfates with the appearance of cerusite

Sorption de l'ion uranyle sur la silice en présence d'acides carboxyliques à courte chaine

Ce travail s inscrit dans le cadre de la migration des éléments radiotoxiques dans la géosphère, en contexte de stockage géologique futur de déchets nucléaire. Pour mieux comprendre les phénomènes de rétention, nous avons choisi d étudier la spéciation de l ion uranyle (modèle d un ion radiotoxique mobile) sur la silice (modèle d oxyde) en présence d acides monocarboxyliques à courte chaîne (un des modèles des matières organiques naturelles et surtout caractéristiques des produits de dégradation de la cellulose contenue dans les déchets technologiques). La démarche adoptée consiste à associer une étude macroscopique et une analyse structurale, afin d accéder par modélisation, aux valeurs des constantes associées des équilibres de rétention mis en jeu.Les courbes de sorption réalisées en fonction du pH en présence d acides organiques nous montrent une relation compétitive pour complexer l ion uranyle entre les ligands organiques et des sites de surface de la silice. D ailleurs, plus longue est la chaîne carbonée, plus évidente est cet effet de compétition.La caractérisation structurale des complexes de surface formés a été réalisée par ATR FTIR et par SLRT. Ces deux techniques montrent que la présence d acides organiques change l environnement de l uranyle sorbé par rapport au système uranyle/silice, ainsi un complexe ternaire de surface silice-uranyle-organique ne se sorbe qu en présence d acide acétique ou propanoïque. La coordination chelating-bidentate entre l uranyle et le carboxylate, est mise en évidence par spectroscopie Infrarouge. L ensemble de ces données expérimentales permet de simuler de manière très cohérente des courbes de sorption en utilisant le modèle de complexation de surface à capacité constante.Understanding the migration behaviour of radionuclides is essential for a reliable long-term safety assessment of nuclear waste disposal sites. In this study, we focus on the sorption behaviour of uranyl ion (model of hexavalent actinides) on silica gel (reference oxide presents in soils) in the presence of the simplest monocarboxylic acids (to model the organic matters or to be degradation products of cellulose issued from nuclear industry). Moreover, no investigation has been reported on their interactions in previous studies, while the main part of studies on ternary systems concerns the effect of humic or fulvic substances. In this work, the studies of uranyl ion and acids uptake in sorption systems have been performed by combining the macroscopic sorption data and the spectroscopic informations of the surface complexes. The sorption edges as function of pH for different systems indicate that the increase of organics concentration results in a decrease of uranyl ion retention in the following order: propionate > acetate > formate, which can be interpreted as their complexing capacity with uranyl ion in solution. ATR FTIR and TRLFS are applied to carry out the structural information of sorbed uranyl ion and carboxylic acids at the silica/electolyte interface. Both techniques show a good agreement that the presence of acids changes the environments of sorbed uranyl and suggest the existence of silica-uranyl-organic ternary surface complexe when acetic or propionic acid presents. Infrared spectroscopy shows also that the coordination between uranyl ion and carboxylate group is chelating-bidentate coordination type. Based on these structural investigations, the sorption edges are simulated effectively and the reaction constants are then obtained by using the constant capacitance surface complexation model.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Capillary zone electrophoresis for U(VI) and short chain carboxylic acid sorption studies on silica and rutile

Capillary zone electrophoresis was used to study the uranyl and short chain carboxylic acid sorption on silica and rutile. The separation and the simultaneous determination (in a single run) of a number of short chain carboxylic acids (oxalic, formic, acetic and propionic) and U(VI) with direct UV detection is developed for the analysis of solutions after the sorption experiments. The reverse polarity mode is used (the injection is performed at the negative end). The matrix effect of Si(IV) (possible silica dissolution product) and perchlorate (added for constant ionic strength in sorption experiments) on the separation of U(VI) and organic acids is investigated. The influence of methanol addition in carrier electrolyte on the separation selectivity of given analytes is also studied. Under the chosen conditions (carbonate buffer (ionic strength of 0.1 M), pH 9.8, 0.15 mM of tetradecyltrimethylammonium bromide, 25% (v/v) of methanol) the calibration curves are plotted. They are linear in two ranges of concentration from not, vert, similar1 × 10−5 to not, vert, similar1 × 10−3 M for oxalate, acetate, propionate, U(VI) and not, vert, similar1 × 10−4 to not, vert, similar1 × 10−3 for formate. The accuracy of the procedure is checked by the “added-found” method in simulation solutions. The relative standard deviations of the concentrations found are within the range of 1–10% and the recovery is in the range of 90–115%. This method is applied for the analysis of aqueous samples issued from sorption experiments on silica and rutile. The obtained results indicate that the given organic acids decrease uranium sorption both on silica and rutile. These experiments demonstrate that short chain carboxylic acids can influence the mobility and the chemistry of U(VI) in the environment

Effect of short chain aliphatic carboxylic acids for sorption of uranyl on rutile Zeta potential and in situ ATR-FTIR studies

International audienceMigration of radionuclides in aqueous system is a matter of great environmental concern due to their acute and long-term toxicity. This study seeks to address the sorption of uranyl on rutile in presence of short-chain aliphatic carboxylic acids by zeta potential analysis and in situ ATR-IR spectroscopy. Point of zero charge of rutile was significantly shifted with the addition of carboxylic acids/uranyl ions separately in solution but it was negligible when organics and uranyl ions were added in the suspension. In situ ATR-IR data for uranyl sorption was evidenced by an absorption band of uranyl as(UO2) at 915 cm−1

Temperature effects on the surface acidity properties of zirconium diphosphate

As part of the temperature effects study on the sorption of metallic cations onto zirconium diphosphate, we have first investigated the intrinsic surface properties of this synthetic compound for different temperatures (25, 50, 75 and 90 °C). A physico-chemical study (IR, XRD) assessed its purity, and the measured N2-BET specific area was Click to view the MathML source. Mass and potentiometric titrations showed that the experimental point of zero charge (pHpzc=2.6±0.2) and the surface site density remained constant between 25 and 90 °C. The potentiometric titration data were simulated with the constant capacitance model, considering two reactive surface sites, with a total surface site density equal to Click to view the MathML source. The intrinsic protonation and deprotonation constants were found to increase with the temperature, as well as the calculated apparent constants. The simulation results showed that the capacitance increased with the temperature. The proportions of the neutral, protonated and deprotonated forms for each site type were quantified thermodynamically by application of the Van't Hoff relation

Electronic properties at the nanometer scale of iron anoxic corrosion product layers

International audienceIn the double context of the in situ preservation of archaeological objects and nuclear waste disposal in deep geological media, the corrosion of iron metal buried in anoxic carbonated soils has to be studied. The iron corrosion rate is conditioned by the characteristics of the corrosion anodic and cathodic reactions. Therefore, for a better understanding of the corrosion mechanisms, the limiting steps both for the anodic and for the cathodic reactions need to be identified. As far as the corrosion mechanisms of iron are considered, the major part of publications concerns the anodic reaction study and there is a serious lack of data linked to the corrosion cathodic reaction. The limiting steps of this latter can be: transport inside the corrosion product layer (CPL) of the electrolyte, of the chemical species (such as H 2) or electrons issued from the iron anodic dissolution. Therefore we investigated the corrosion cathodic reaction for iron corroded in anoxic medium by studying iron nails corroded from the 16 th century in anoxic carbonated soils (archaeological site of Glinet Seine-Maritime, France). We intend to identify the limiting step and the location of the corrosion cathodic reaction by measuring local conductivity of the CPL. The description of the crystalline nature of the iron CPL, distribution, electronic properties and porosity at the different scales from global to the nanometer scale are important to have a complete knowledge of the corrosion mechanisms. Indeed the electrical properties of the CPL were probed by Conductive Atomic Force Microscopy (C-AFM) which provides measurements within the range of nanometers. In addition the corrosion product layers was characterized by μRaman spectroscopy for the determination of the crystalline nature of the corrosion products and by Field Emission Scanning Electron Microscopy (FESEM) for the distribution phases from metal to the metal/soil interface. Different patterns representative of the anoxic CPL of the 400 years old iron archaeological nails were identified: CPL constituted of only ferrous carbonates such as siderite FeCO3 and chukanovite Fe2(OH)2CO3, CPL composed of mainly ferrous carbonates but with the minor presence of magnetite Fe3O4 under strips or under nodules inside the ferrous carbonates matrix, or showing locally iron sulfides borders

Electronic properties at the nanometer scale of iron anoxic corrosion product layers

International audienceIn the double context of the in situ preservation of archaeological objects and nuclear waste disposal in deep geological media, the corrosion of iron metal buried in anoxic carbonated soils has to be studied. The iron corrosion rate is conditioned by the characteristics of the corrosion anodic and cathodic reactions. Therefore, for a better understanding of the corrosion mechanisms, the limiting steps both for the anodic and for the cathodic reactions need to be identified. As far as the corrosion mechanisms of iron are considered, the major part of publications concerns the anodic reaction study and there is a serious lack of data linked to the corrosion cathodic reaction. The limiting steps of this latter can be: transport inside the corrosion product layer (CPL) of the electrolyte, of the chemical species (such as H 2) or electrons issued from the iron anodic dissolution. Therefore we investigated the corrosion cathodic reaction for iron corroded in anoxic medium by studying iron nails corroded from the 16 th century in anoxic carbonated soils (archaeological site of Glinet Seine-Maritime, France). We intend to identify the limiting step and the location of the corrosion cathodic reaction by measuring local conductivity of the CPL. The description of the crystalline nature of the iron CPL, distribution, electronic properties and porosity at the different scales from global to the nanometer scale are important to have a complete knowledge of the corrosion mechanisms. Indeed the electrical properties of the CPL were probed by Conductive Atomic Force Microscopy (C-AFM) which provides measurements within the range of nanometers. In addition the corrosion product layers was characterized by μRaman spectroscopy for the determination of the crystalline nature of the corrosion products and by Field Emission Scanning Electron Microscopy (FESEM) for the distribution phases from metal to the metal/soil interface. Different patterns representative of the anoxic CPL of the 400 years old iron archaeological nails were identified: CPL constituted of only ferrous carbonates such as siderite FeCO3 and chukanovite Fe2(OH)2CO3, CPL composed of mainly ferrous carbonates but with the minor presence of magnetite Fe3O4 under strips or under nodules inside the ferrous carbonates matrix, or showing locally iron sulfides borders

Role of acetic acid on U(VI) sorption on silica

International audienceThe influence of acetate on U(VI) sorption on silica from aqueous solutions was studied at pH 2–7 by complementary experimental methods of macroscopic measurement, spectroscopic investigation and thermodynamic calculation. Sorption percentage of U(VI) in the absence and in the presence of different acetate concentrations was determined by batch sorption procedures. Attenuated total reflection Fourier transform infra-red spec-troscopy (ATR-FTIR) was used to elucidate the mechanisms of uranyl sorption on silica in the presence of acetate, by investigating, in-situ, the changes in the U(VI) sorption on silica surface in presence of ligand: the absorption bands of carboxylate ν(COO) in the range 1300–1700 cm −1 and those around 850–950 cm −1 of uranyl species νas(UO 2) are followed. The decrease of U(VI) sorption with increasing acetate concentration was observed. Sorption of U(VI)-acetate (U-Ac) species on silica surface was demonstrated for the first time. ATR-FTIR investigations clearly evidenced the absorption bands characteristic of sorbed U-Ac complexes both from the acetate and uranyl spectral regions those the wavenumbers correspond to sorbed species. No sequence effect of acetate and uranyl on the sorption on silica in ternary systems U(VI)-acetate-silica was observed from the sorption data. From the ATR-FTIR investigations, we can induce that the sorption of U-Ac leads to chemical equilibria and makes possible the modeling of sorption isotherms by surface complexation models. The related thermodynamic constants were modeled using CCM surface complexation modeling