From the analysis of fossils, using the cathodoluminescence technique, it is seen that there is a pattern to the luminescence colours exhibited by dolomite, calcite and quartz, depending on the amount of the trace element Mn2+ present in the structure of the minerals. In the experiment dolomite luminesces turquoise blue, calcite luminesces pale pink & bright red, & quartz luminesces sea blue. The calcite and quartz colours agree well with the observation of both Agrell et al. (1965) and Sippel et al. (1965). However, the dolomite luminescence colour definitely agrees better with the colour described by Agrell et al. than with that observed by Sippel et al. Selective replacement of material occurs in Rugosa corals of the Devonian Onondaga formation of Southern Ontario. Quartz replacing material in the cavities of fossils is common, with the fringe wall of the fossil being of calcite as was previously observed by Middleton (1958). The matrix around the fossils consists mainly of quartz and calcite with minor dolomite. A systematic difference in style of replacement (with respect to the various heights from which the fossils came in the section) occurred when considering replacement of the fossils by quartz. Replacement of calcite by quartz followed by slight dolomitization of the matrix in the Onondaga is suggested by luminescence observation. Also suggested by luminescence observations is: 1) Dolomitization by a downward influx of Mg2+ ions, and 2) Homogenous and heterogenous micritic mud fillings in Rugosa corals' cavities. / Thesis / Bachelor of Science (BSc)

<p> A simplistic equilibrium, computer model was devised to simulate the removal of orthophosphates from wastewater. The components of the model were calcium, magnesium, carbonate and orthophosphate present as simple hydrated ions, ligands, acid-base dissociation products, ion pairs, ion pair complexes, ion complexes and precipitates. Data from laboratory experiments were tested in the model to determine the apparent activity products of calcite, hydroxyapatite, tricalcium phosphate and brucite. The results indicated a degree of supersaturation of hydroxyapatite between 15 to 20 orders of magnitude dependent on the aqueous species included in the calculations. The apparent pKsp values for different sets of data showed the mean ranging from 95 to 102.5 with standard deviations 2 to 5. The inclusion of the aqueous ion complexes Ca2·HPO4·CO^o 3 and Ca2·PO4·CO- 3 when calculating the apparent activity products results in a pKsp of 102.5 which varies little with pH or the presence of magnesium. The solubility of tricalcium phosphate varies more with pH than hydroxyapatite, a mean pKsp of 26.8 was calculated which compares favourably with the pKsp of 27.0 quoted in the literature. The apparent activity product of brucite was strongly dependent on pH while that of calcite was extremely variable. When hydroxyapatite precipitated, there was a minimum residual phosphate between pH 8.5 - 9.0, followed by an increase of phosphates in solution due to calcium being removed by the precipitation of calcite. Beyond pH 10, the phosphate concentration in solution decreased rapidly as there was an increase in the precipitation of hydroxyapatite coupled with a decrease of calcite. Under identical initial conditions, the precipitation of tricalcium phosphate compared to hydroxyapatite resulted in similar orthophosphate residuals. The use of the apparent activity products compared to literature solubility products results in 2 to 3 orders of magnitude greater phosphate residuals in solution.</p> / Thesis / Master of Science (MSc)

No description available.

On surfaces and within interfaces occur some of the most important reactions in chemistry, from world changing industrial reactions to critical environmental processes. It is even hypothesized that the chiral nature of life arose from reactions occurring on chiral mineral surfaces. In any case adsorption typically plays a key role. Adsorption can occur on rapid time scales, particularly in catalytic systems, and it can be the precursor to highly stable surface interaction mechanisms such as surface precipitation. Surface adsorption can have a dramatic affect on the resulting surface increasing or decreasing the propensity for further reactivity or adsorption. In order to understand the processes occurring on a surface both the surface and the adsorbate must be understood. This includes a surface with any prior adsorbates. This is why many catalytic studies are done in UHV environments where clean surfaces are prepared for each experiment. The same is true with environmental surfaces, but obtaining pristine surfaces can be problematic, and systems are often extremely complicated involving organic, inorganic, and biological components. Often research is focused on just one component. A significant portion of this dissertation is focused on the adsorption of organic and inorganic species on pristine mineral surfaces. While there is significant research done on environmental surfaces, often times the surface used in studies is not well characterized. In essence lesser attention is paid to the substrate then the adsorbate. This is particularly true of infrared studies similar to the type presented in chapter 5 where carbonate is shown to exist in significant quantity on all ferrihydrite surfaces. Furthermore, chapter 4 highlights the potential for ion mobility on calcite surfaces under ambient conditions and the effect the adsorbates in chapter 3 have on the mobility process. The principal of this dissertation is to characterize fundamental surface processes which occur on calcite and ferrihydrite surfaces under ambient conditions. The hope is that this can lay the ground work for future studies where native adsorption and restructuring is taken into account on mineral surfaces during experimental studies. / Chemistry

The scientific community is undergoing a paradigm shift with the realization that the formation of carbonate minerals with diverse compositions and textures can be understood within the framework of multiple pathways to mineralization. A variety of common minerals can form via an amorphous pathway, where molecules or clusters aggregate to form a metastable amorphous phase that later transforms to one or more crystalline polymorphs. Amorphous calcium carbonate (ACC) is now recognized in a wide variety of natural environments. Recent studies indicate the chemical signatures and properties of the carbonate polymorphs that transform from an ACC pathway may obey a different set of dependencies than those established for the "classical" step-growth process. The Mg content of ACC and calcite is of particular interest as a minor element that is frequently found in ACC and the final crystalline products of calcified skeletons or sediments at significant concentrations. Previous studies of ACC have provided important insights into ACC properties, but a quantitative understanding of the controls on ACC composition and the effect of mineralization pathway on Mg signatures in calcite has not been established. This study utilized a new mixed-flow reactor (MFR) procedure to synthesize ACC from well-characterized solutions that maintain a constant supersaturation. The experimental design controlled the input solution Mg/Ca ratio, total carbonate concentration, and pH to produce ACC with systematic chemical compositions. Results show that ACC composition is regulated by the interplay of three factors at steady state conditions: 1) Mg/Ca ratio, 2) total carbonate concentration, and 3) solution pH. Findings from transformation experiments show a systematic and predictable chemical framework for understanding polymorph selection during ACC transformation. Furthermore, results suggest a chemical basis for a broad range of Mg contents in calcite, including high Mg calcite. We find that the final calcite produced from ACC is similar to the composition of the initial ACC phase, suggesting that calcite composition reflects local conditions of formation, regardless of the pathway to mineralization. The findings from this study provide a chemical road map to future studies on ACC composition, ACC transformation, polymorph selection, and impurities in calcite. / Ph. D.

Respirable coal mine dust (RCMD) has long been recognized as an occupational health hazard. In addition to coal, RCMD can contain minerals such as crystalline silica (i.e., most often present as quartz). There has been a resurgence of lung diseases among US coal miners since the late-1990s which has emphasized the need for better quartz monitoring, and better dust characterization in general. Quartz monitoring in coal mines has traditionally used infrared (IR) spectroscopy-based analytical methods such as the MSHA Method P7 that require significant sample preparation and must be performed in a centralized lab. There are generally thus days to weeks between dust sample collection and reporting of results, which can prevent the prompt mitigation efforts to better control dust and reduce exposures. Recently, a rapid analysis method for quartz has been developed by the US National Institute for Occupational Safety and Health (NIOSH) using direct-on-filter (DOF) Fourier Transform Infrared (FTIR) spectroscopy. The method has been demonstrated in a number of NIOSH-led studies using both laboratory and field samples, and the results show very good accuracy relative to the Method P7 reference. However, it has heretofore not been widely used by others or compared to results from other non-IR analytical methods. Moreover, while FTIR can allow the measurement of additional analytes, this has not yet been a focus of DOF FTIR for RCMD analysis. Analytes such as kaolinite and calcite could be of particular interest in the context of RCMD source apportionment. In this thesis, the DOF FTIR method is used to estimate silica, kaolinite, and calcite mineral fraction in RCMD samples collected in 16 coal mines, and in the laboratory using dust source materials from those same mines. The results are compared to results from other dust characterization methods such as mass-based thermogravimetric analysis (TGA) and particle-based scanning electron microscopy with energy dispersive X-ray (SEM-EDX). Results indicate the usefulness of the DOF FTIR method, and comparison suggests the presence of significant non-carbonate minerals other than silica and kaolinite in the coal mine dust. The results also show that SEM-EDX frequently indicates more mineral content (primarily other aluminosilicates), than that is predicted by either FTIR or the TGA. Additionally, by focusing mainly on calcite (generally sourced from limestone-based rock dust used in coal mines to prevent coal dust explosion), the second part of this study explores basic source apportionment by analyzing mine samples and samples of major dust source materials (such as run-of-mine coal, rock strata, and rock dust products). Results show that calcite can serve as a suitable proxy for rock dust in coal mine dust, and the results are consistent with expectations surrounding the contribution of dust from different mine locations and sample sources. Additionally, the DOF FTIR also showed good agreement with the TGA and SEM-EDX. / Master of Science / Respirable dust generated in coal mines has long been recognized as an occupational health hazard. In addition to coal, coal mine dust can contain minerals such as crystalline silica, which is particularly hazardous. Since the mid-1990s, there has been an alarming and unexpected increase in lung diseases in coal miners. Respirable crystalline silica is assumed to be a likely causal factor for this resurgence of lung diseases, and this has emphasized the need for better respirable crystalline silica monitoring and to better understand coal mine dust composition. The standard method of measurement of silica (called the MSHA Method P7) generally takes days to weeks between dust sample collection and reporting of results, which can prevent the mine from taking prompt mitigative efforts to better control dust and reduce exposures. Recently, a rapid analysis method for silica has been developed by the US National Institute for Occupational Safety and Health (NIOSH) called the DOF FTIR (direct-on-filter Fourier Transform Infrared Spectroscopy). This method has been shown to have very good accuracy relative to the standard method (MSHA P7). However, it has heretofore not been widely used by others or compared to results from other analytical methods. Moreover, DOF FTIR can also be used to estimate other minerals of interest such as kaolinite and calcite, which can be important in the context of understanding coal mine dust sources. In this thesis, the DOF FTIR method is used to estimate silica, kaolinite, and calcite mineral fraction in coal mine dust samples collected in 16 coal mines, and in the laboratory using dust source materials from those same mines. The results are compared to results from other dust analysis methods such as mass-based TGA (thermogravimetric analysis) and particle-based SEM-EDX (scanning electron microscopy with energy dispersive X-ray). Results indicate the usefulness of the DOF FTIR method, and comparison suggests the presence of significant non-carbonate minerals other than silica and kaolinite in the coal mine dust. The results also show that SEM-EDX frequently indicates more mineral content than that is predicted by either FTIR or the TGA. Additionally, by focusing mainly on calcite—which is generally sourced from limestone-based rock dust used in coal mines to prevent coal dust explosion—the second part of this study explores the sources of the dust by analysing samples collected in mines, and samples generated in lab from major dust source materials (such as the raw coal, rock strata, and rock dust products obtained from the mines). Results show that calcite can be representative of rock dust in coal mine dust, and the results are consistent with expectations surrounding the contribution of dust from different mine locations and sample sources. Additionally, the DOF FTIR also showed good agreement with the TGA and SEM-EDX.

Yes / Archaeological burial contexts may include a variety of white substances, but few analyses have been published. This study reports on the physico‐chemical characterization of such residues from seven archaeological sites. It is often assumed that white materials from burial contexts are lime. Our findings demonstrate that they can be gypsum, calcite (chalk), aragonite, brushite, degraded metal, natural (gum) resins or synthetic polymer–based products. These may be present as the result of diagenetic processes, funerary practices or modern contamination. This paper provides an analytical approach for the holistic investigation of white materials encountered in burial contexts. / Investments for the future’ (IdEx Bordeaux ANR‐10‐IDEX‐03‐02). Grant Number: ANR‐10‐IDEX‐03‐02; Collaborative Projects of the France‐Stanford Center for Interdisciplinary Studies; Collaborative Projects of the France–Stanford Center; French State. Grant Number: IdEx Bordeaux ANR‐10‐IDEX‐03‐02; Northern Archaeological Associates Ltd; PACEA; Wessex Archaeology; INRAP; Mersea Island Museum Trust; Vatican's Pontifical Commission for Sacred Archaeology; University of Reading; IRAMAT-CRP2A; University of Bradford; CEREGE

Il est indispensable pour comprendre la diagenèse, i.e., la formation des roches sédimentaires, le durcissement des matériaux de construction hydrauliques comme le ciment ou le plâtre, ou la biominéralisation, d'identifier les mécanismes élémentaires de la cristallisation minérale. Le taux de réaction macroscopique des minéraux est généralement déduit de mesures de chimie des solutions. A côté de ces mesures macroscopiques, l'étude de la réactivité des minéraux inclut maintenant l'analyse des mécanismes atomiques a l'origine des réactions chimiques. Cela a été rendu possible depuis deux décennies par l'apparition d'outils capables d'observer des surfaces avec une résolution nanométrique, tels que la microscopie à force atomique et l'interférométrie à balayage vertical. Le gypse et la calcite font partie des minéraux dits mous. Ce sont des minéraux extrêmement répandus, que l'on peut trouver autant dans la nature sous forme de roches sédimentaires que dans le monde industriel. Le gypse (CaSO4,2H2O) est une évaporite dont les applications incluent la fabrication des plaques de plâtre, l'ajout au ciment Portland comme retardateur, l'élaboration du plâtre de Paris et l'amendement des sols. La sélénite ou l'albâtre sont des variétés de gypse utilisés comme matériaux pour l'ornement, mais leur faible dureté limite leur durabilité. La calcite, forme la plus stable de CaCO3, est un des principaux biominéraux, et un des constituants majeurs des roches des réservoirs carbonates, stockant naturellement de l'eau, du pétrole ou du gaz naturel. Quand les organismes biologiques font croitre leur coquille, ils contrôlent la morphologie, la taille, l'orientation et même la phase des cristaux de carbonates de calcium qui la constituent. Cela conduit à des biomatériaux présentant des propriétés physiques et chimiques qui diffèrent significativement de ceux de la calcite inorganique. Une connaissance plus approfondie des mécanismes sous-jacents à la réactivité de surface de la calcite et de l'effet des impuretés sur celle-ci permettra de nous rapprocher de la possibilité de synthétiser des minéraux biomimétiques, aux propriétés comparables à celles de la calcite biogénique. Dans ce contexte, ma thèse s'est développée dans trois directions. Dans la première, j'ai étudié l'influence d'une contrainte mécanique sur les mécanismes de dissolution. Mon objectif dans cette partie a été de tacher de déduire le taux de dissolution macroscopique à partir de la cinétique des mécanismes atomiques. La seconde partie de la thèse, la plus conséquente, a consisté à étudier l'influence d'une contrainte mécanique sur la croissance de la calcite, et à sonder le rôle d'un additif organique lors de cette croissance sous contrainte. Dans la troisième partie, je me suis penchée sur la dissolution de cristaux de calcite à l'aide de mesures topographiques quantitatives sur des aires relativement étendues de la surface des cristaux, dans une large gamme de pH. J'ai en particulier étudié l'influence d'un additif organique sur la dissolution et la cinétique de réaction à grande échelle. Les taux de dissolution macroscopique et microscopique, c'est-à-dire déduits de la dynamique d'évènements moléculaires (croissance de piqure d'attaque, migration de marche atomique), ne sont presque jamais en accord, même qualitativement, et l'élaboration d'une théorie générale liant la cinétique du phénomène aux deux échelles est encore en cours. Je présente ici des taux de dissolution microscopique du gypse, mesures par microscopie par force atomique (AFM), en accord quantitatif avec les taux de dissolution macroscopiques. Cet accord inédit a été obtenu en prenant soin de neutraliser le biais induit par le fait que la pointe AFM applique une force sur la surface qu'elle sonde, et en identifiant avec soin les mécanismes moléculaires majeurs à l'œuvre lors de la dissolution...[etc] / Identifying reaction mechanisms of minerals is fundamental to understand diagenesis, i.e, sedimentary rock formation, construction material, like cement or gypsum, hardening, and biomineralization. The macroscopic reaction rates of minerals are generally deduced from solution chemistry measurements. Beside the measurement of macroscopic reaction rates, the study of the reactivity of minerals includes now the investigation of the atomic mechanisms involved in the reactions. This has been made possible for two decades by the use of tools resolving nanometric objects, such as vertical scanning interferometry (VSI) and atomic force microscopy (AFM). Gypsum and calcite are among soft minerals. They are extremely widespread mineral that can be found naturally in sedimentary rocks. They are also used in many industrial fields. Gypsum (CaSO4,2H2O) is an evaporate mineral. Gypsum uses include: manufacture of wallboards, plaster of Paris, soil conditioning, and hardening retarder in Portland cement. Varieties of gypsum known as "satin spar" and "alabaster" are used for a variety of ornamental purposes; however, their low hardness limits their durability. Calcite, the most stable crystalline form of CaCO3, is moreover important as a bio-mineral and a major constituent of host rock in carbonate reservoirs, which host drinking water and natural oil and gas. When biological organisms grow their shells, they control the crystal morphology, size, orientation and even the crystal phase of precipitated calcium carbonate. This results in materials with physical and chemical properties that differ significantly from those of inorganically precipitated calcite. Gaining more insight into the surface reactivity of calcite and the effect of surface impurities will bring us one step closer to being able to synthesize biomimetic material, which mimic the properties of biogenic calcite. In this thesis, I had three main focus points. In the first part I studied the effect of stress on the dissolution mechanisms. I investigated to deduce the dissolution rate from the atomic kinetics. The second and the most extensive was the study of the influence of stress on the calcite growth and probing the role of an organic additive on the dynamics of calcite growth while applying stress. In the third part I emphasised on quantitative topographic measurements of dissolving calcite crystal over a relatively large and fixed view at vast range of pH. I considered the influence of an organic additive on the dissolution and surface reaction kinetics at this larger scale. Both macroscopic and microscopic dissolution rates can also be deduced from the dynamics of molecular events (etch pit growth, atomic step migration), but they hardly ever agree, even qualitatively, and the elaboration of a general theory linking the kinetics at the two scales is still in progress. I presented here microscopic dissolution rates of gypsum, measured by atomic force microscopy (AFM), in quantitative agreement with macroscopic rates. This agreement has been obtained in taking care to neutralize the bias induced by the force applied by the AFM tip on the surface, and to identify clearly the driving molecular mechanism. The force applied by the AFM tip on the surface has been seen to increase the solubility of the mineral, thereby introducing a bias, so I have always worked with a constant and low applied force. This result shows that the determination, among the topographic changes during the dissolution of a mineral, of the dominant one, and the measurement of its dynamics, may permit deducing from AFM experiments a reliable macroscopic dissolution rate. The transformation of loose grains into a cohesive solid requires the crystallites to grow eventually constrained by the surrounding grains. Whereas never measured, this confinement and the associated stress is expected to influence noticeably the growth, and the final properties of the material… [etc]

La datation des carbonates est un enjeu important en géosciences car ces minéraux sont présents dans tous les grands cycles superficiels terrestres. Actuellement, l’âge de formation des cristaux de calcite de failles peut être déterminé par la méthode de déséquilibre U-Th ou par la méthode U-Pb. La potentialité de la méthode (U-Th-Sm)/He a été envisagée à partir des premiers résultats de diffusion de l’hélium dans les carbonates (Copeland et al. 2007) qui montrent que l’hélium est rétentif à basse température, inférieure à 70°C. Le développement de cette méthode nécessite une identification des propriétés cristallochimiques et du comportement de la calcite afin de discuter la validité des âges obtenus. Une zone de déformation au contact d’une faille normale du fossé d’effondrement de Gondrecourt à Augeville (Est du bassin de Paris) et des cristaux de calcite géodique des argilites de Tournemire (Aveyron) ont été étudiés. Une étude pétrographique et géochimique (analyse des isotopes stables δ18O et δ13C et des éléments mineurs et traces) a permis d’identifier les phases de remplissage de la zone de déformation d’Augeville. Sur les phases de remplissages une étude cristallographique par DRX (diffraction des rayons X) et ATG (analyse thermogravimétrique) a permis d’identifier les propriétés mécaniques de la calcite à différentes températures. Des expériences de diffusion de l’hélium ont été conduites selon un protocole différent de celui de Copeland et al. (2007) : temps de chauffage inférieur à 12 heures au lieu de paliers de chauffage de plusieurs heures à semaines. Des datations (U-Th-Sm)/He ont été réalisées sur toutes les phases de remplissage de la zone de déformation ainsi que sur les cristaux géodiques de Tournemire. Les résultats pour Gondrecourt mettent en évidence une zone de déformation à remplissage calcitique pluriphasée qui marque chaque étape de l’évolution tectonique de la zone. Il s’agit majoritairement de remplissages de brèches hydrauliques à brèches chaotiques avec, pour finir, la mise en place de filons. Sur ces minéralisations les résultats cristallochimiques montrent que lorsqu’ils sont soumis à une température croissante, de température ambiante à 400°C, ou sur le long terme à 200°C, il y a un accroissement du nombre de microfissures qui aboutit à la formation de clivage. L’évolution cristallochimique sous l’effet de la température présente des modifications structurales pour chacune des phases étudiées. Les expériences de diffusion dépendent de ces microfissures et de cette évolution microstructurale. Ces résultats mettent en évidence les mécanismes de diffusion de l’hélium dans la calcite à travers de multiples domaines de diffusion différents de la taille du grain. Ces domaines de diffusion dépendent de l’état microstructural de l’échantillon. Les résultats de datation (U-Th-Sm)/He présentent une large dispersion de 0,1 Ma à 35 Ma pour la zone de déformation de Gondrecourt et de 0,4 Ma à 20 Ma pour les cristaux géodiques de Tournemire. La variation des âges est en partie liée à la position des cristaux de calcite dans la succession paragénétique qui entraine un continuum de fracturation qui génère de multiples domaines de diffusion dans les cristaux de calcite. / Carbonate dating is a major issue in geosciences due to their widespread terrestrial environments presence . Precipitation ages determination are actually provide by U-Th disequilibrium series for young <1 Ma carbonates crystal and/or U-Pb method for older samples. In addition, Copeland et al. (2007) have proposed the development of (U-Th-Sm)/He dating method based on retentive helium behavior at surface temperature, conclusion issue of their first diffusion coefficients determined on carbonates samples. In this thesis work, the intention was to get an identification of crystallo-chemical properties and behavior of helium in calcite to date samples by (U-Th-Sm)/He and finally discuss the validity of this method. Deformation zones in contact to the normal fault of the Gondrecourt trench close to Augeville (eastern side of Basin of Paris) and calcite crystals geodic Tournemire argillites (Aveyron) were studied. Petrographic and geochemical couples studies (analysis of stable isotopes δ18O and δ13C and minor and trace elements) have allow the filling phases identification of the Augeville deformation zone. Based on the filling phases results, a crystallographic study by XRD (X-ray diffraction) and TGA (Thermogravimetric analysis) have been performed to identify the mechanical properties of calcite at different temperatures. Then, diffusion experiments on natural helium were conducted using a protocol differing than Copeland et al. (2007): heating time less than 12 hours instead of heating stages from hours to weeks. (U-Th-Sm)/He analyses were performed on all filling phases of the deformation zone and on the crystal geodes of Tournemire. Results for Gondrecourt samples show a deformation zone that marks several calcitic fillings corresponding to each stage of the tectonic evolution of the area. Calcite filling mainly corresponds to breccia and/or vein fillings which have precipitated approximatively in the same time. Crystallochemical results of these samples, show an increased number of microcracks leading to the formation of cleavage when samples are subjected to temperature increasing, from room temperature to 400 °C, or several days the long term at 200 °C. The crystallochemical evolution under the effect of temperature exhibits structural modifications for each studied phase. Diffusion experiments depend on these microcracks abundance and the microstructural evolution. These results emphasize the mechanisms of helium diffusion in calcite across multiple diffusion domains at different grain size. These multiple diffusion domains are linked to microstructural state of the sample. The results of dating (U-Th-Sm)/He ages show a wide dispersion of 0.1 to 35 Ma for the deformation zone Gondrecourt and from 0.4 to 20 Ma for Tournemire crystal geodes. Ages variation are partly related to the calcite crystals position in the paragenetic sequence. When a mineral undergoes deformations it becomes less retentive.

Ces travaux de recherche s’inscrivent dans le cadre des études de faisabilité du stockage du dioxyde de carbone en couches géologiques profondes, et portent plus particulièrement sur l’évolution des propriétés de confinement de roches-couvertures de type argilite, soumises à des fluides enrichis en CO2. Pour ce faire, les argilites de Tournemire (Aveyron, France) ont été utilisées comme roches analogues, après avoir identifié leurs possible points de faiblesse vis-à-vis du stockage, à savoir leur minéralogie, la présence de fissures naturelles remplies de calcite et la présence d’interfaces ciment/argilite attendues au niveau des puits d’injection rebouchés. Le montage expérimental de type « diffusion à travers » a été adapté pour permettre d’estimer (i) la possible modification des paramètres de transport diffusif enregistrés, avant et après attaque acide, pour les différents traceurs radioactifs (tritium et chlore-36) et non-radioactifs (deutérium et bromure) utilisés pour caractériser les échantillons d’argilite de Tournemire et de pâte de ciment et (ii) l’évolution des compositions chimiques des solutions contenues dans les réservoirs amont et aval des cellules de diffusion au cours des attaques acides. Enfin, l’analyse des solides a été réalisée pour partie par MEB-EDS, µTomographie-X et DRX. Tout d’abord, pour l’ensemble des échantillons étudiés, les valeurs des paramètres de transport déterminées avant attaque acide (coefficient de diffusion effectif et porosité) sont cohérentes avec celles de la littérature. En outre, il apparaît que tous les matériaux ont fortement réagi aux attaques acides. Ainsi, les argilites ont vu leurs paramètres de diffusion augmenter jusqu’à un facteur deux, notamment pour les traceurs anioniques, et ce, quelque soit la proportion de minéraux carbonatées présents initialement dans les échantillons d’argilite. Les observations post-mortem ont permis l’identification d’une zone de dissolution des minéraux carbonatés en leur au sein, mais dont l’extension (400 µm au maximum) ne peut à elle seule expliquer cette importante dégradation des propriétés de confinement. Seuls des phénomènes non observables à l’échelle d’investigation, tels des effets de digitation au sein du réseau poreux pourraient en être à l’origine. Par ailleurs, les échantillons d’argilites recoupés par des fissures naturelles ont systématiquement développé des courts-circuits hydrauliques, qui s’expliquent par la mise en place d’un processus de chenalisation préférentielle au sein même de la fissure, observé au MEB-EDS et par µTomographie X. De plus, les matériaux cimentaires ont vu leurs propriétés de confinement améliorées, et ce, plus le fluide d’attaque était proche de la neutralité. Ceci est lié à l’apparition d‘une croûte de calcite d’environ 30 µm d’épaisseur, situé à l’avant d’une zone de dissolution, dont l’épaisseur est proportionnelle à la quantité d’acide en solution. Cette croûte imperméable, obstruant la porosité, serait responsable de la diminution des paramètres de diffusion, observée à l’échelle de l’échantillon, ainsi que le reproduisent les simulations numériques. Enfin, les interfaces ciment/argilites n’ont pas révélé de changement de leurs propriétés de confinement à l’échelle globale, la dégradation des argilites étant compensé par l’aggradation du ciment via la formation de cette croûte de calcite. / This research is part of the studies of feasibility of CO2 storage in deep geological strata, focusing more particularly on the evolution of the confinement properties of cap-rocks type argillite subjected to CO2 enriched fluids. The argillite of Tournemire (Aveyron, France) were used as analog rocks, having identified what their weak points could be face to storage, namely their mineralogy, natural fractures filled with calcite and the presence of interfaces cement / argillite expected in filled injection wells. The "through diffusion" experimental setup has been adapted to estimate (i) the possible modification of diffusive transport parameters recorded before and after acid attack for different radioactive tracers (tritium and chlorine-36) and non-radioactive tracers (deuterium and bromide) used to characterize samples of argillite of Tournemire and cement paste and (ii) the evolution of the chemical compositions of the solutions in the upstream and downstream reservoirs of diffusion cells during acid attacks. Finally, the analysis of solids was carried out in part by SEM-EDS, XRD and X-μTomographie. Firstly, for all the samples studied, the values of the transport parameters determined before acid attack (effective diffusion coefficient and porosity) are consistent with those of the literature. In addition, it appears that all materials have reacted strongly to acid attacks. Thus, argillites saw their diffusion parameters increase up to a factor of two, especially for anionic tracers, and, whatever the proportion of carbonate minerals initially present in samples of argillite. The post-mortem observations have led to the identification of a zone of dissolution of carbonate minerals in them, but whose extension (400 microns or less) can not alone explain the significant degradation of the containment properties. Only unobservable phenomena during investigation scale, such as wormhole effects in porous network could be the cause. In addition, the samples of argillite intruded by natural fractures have systematically developed hydraulic short circuits, which can be explained by the introduction of a process of preferential channeling within the fracture observed by SEM-EDS and X. μTomographie In addition, the more close to neutral was the fluid attack the more cementitious materials saw their confinement properties improved. This is related to the appearance of a crust of calcite about 30 microns thick on the front of a dissolution zone, the thickness of which is proportional to the amount of acid in solution. This waterproof crust, clogging the pores, would be responsible for the decrease in diffusion parameters observed across the sample, and as numerical simulations reproduce it. Finally, the interface cement / claystone showed no change in their confinement properties on a global scale, the degradation of clays being offset by aggradation cement via the formation of the crust of calcite.