A selection of thermodynamic properties for zeolites: application to the cement/clay interactions

Deep disposal concepts are usually based on a multibarrier concept that may involve a physical contact between clayey and cementitious materials. In such context, zeolites are a group of important phases, which group most of the transition phases between cement and the clayey barrier since zeolites have been shown to form readily after the weathering of clays in a hyperalkaline environment [1]. Thermodynamic properties can be found in the literature for some of the zeolites of interest in deep disposal contexts. However, there is still a lack of consistency among the available thermodynamics datasets. A first task realized in the present work consists in a critical selection of the thermodynamic datasets published so far. The selection could be achieved with some confidence for a rather large list of minerals. Some questions and uncertainties still remain for phases like phillipsite, chabazite or gismondine. Cases from the previous critical selection indicate the role of kinetics in the precipitation of zeolites, which can help in moderating the phase relations indicated by thermodynamics and can be related to field observations or experimental results. In addition, the concept of rock acidity can applied with success in order to investigate the phase relations between cements, zeolites and clayey materials

Thermodynamics of hydration of MX80-Na: an experimental study of the hydration energies

Hydration properties of swelling clay minerals may be very variable depending on the chemical composition of the clay, on the nature of the interlayer cations and on the interlayer charge (Berend et al., 1995; Vieillard et al., 2011). The Wyoming smectite has been largely studied, notably for assessing its hydration behavior as a function of the interlayer cations, in connection with its structural characteristics (Ferrage et al., 2005; Salles et al., 2007). In the present work, carried out as part of a collaborative Andra/BRGM/HydrASA research program for ThermoChimie project, we propose an original experimental study, based on adsorption and desorption isotherms performed on MX80 clay samples. The goal is to determine energetic contributions to the reactions of hydration, which have been revealed to be non-negligible with respect to the stability of the clay minerals (Gailhanou et al., submitted). In particular, the present work addresses the problems of the hysteresis loop between adsorption and desorption isotherms and of the irreversibility of hydration reactions. This is directly related to the application of classical thermodynamics to the hydration reactions of clay minerals. In a first stage, an experimental study is dedicated to better understand the origin of the hysteresis loop which is systematically observed for the adsorption-desorption isotherms at 25°C. The development of the hysteresis loop has been studied by considering several kinetically related parameters: stabilization periods, temperatures (from 25°C to 60°C) and hydration steps (Figure 1). No sensible change was observed in the hysteresis loop. Therefore, the amount of adsorbed water depends on the followed reaction pathway (adsorption or desorption). The variations in microstructures and in the distribution of hydration layers (0/1/2 water layers; Ferrage et al., 2005) as a function of relative humidity (RH) could provide a possible explanation for this phenomenon

Extending the prediction of the thermodynamic properties of clay minerals to the trapping of trace elements

The thermodynamic properties of clay minerals, which control the stability of these minerals in solution, are still a matter of debate in spite of recent advances (Gailhanou et al., submitted). This is especially the case for the minerals that may structurally include trace elements and potential radionuclides such like Ni, Cd, Co, Cr, Mn, Pb, ... The usual methods developed in order to predict thermodynamic properties are parameterised using a given set of minerals. For clay minerals, the latter are mainly composed by Si, Al, Fe and Mg, apart from the alkalis elements (Chermak and Rimstidt, 1989), which means that predictions are limited to minerals whose layers are composed by Si, Al, Fe and Mg. At the vicinity of H&ILW disposal cells, the possible interactions between clay rock or engineered barrier and waste degradation products can result in the appearance of clay minerals that may structurally include radionuclides within an irreversible trapping process. This work aims at proposing a method for predicting the thermodynamic properties of such minerals. Theoretical principle and selection of calibration phases Vieillard (1994) has developed a methodology of estimation based on the difference of electronegativity by considering three scales of values of the parameter HO=(Mz+clay) in the three sites of phyllosilicates. We have considered the work of Vieillard (1994) that originally applies to the estimate of H0f and extended it to the estimate of Cp(T), S0 and V. Some popular estimate methods (Chermak and Rimstidt, 1989) are based on the hypothesis that the thermodynamic property of a mineral can be obtained by combining the properties of its components. An improvement of this principle had consisted in decomposing minerals into their polyhedral components (Chermak and Rimstidt, 1989). Now, we can write the fictive solution equilibrium with a basic polyhedral component MxOy as: and assumming the entropy of this fictive reaction is zero, we can define a SO= parameter as: . The value for the oxide analog of the polyhedral unit is obtained by implementing S0 of the oxide in the S0(MxOy) term. We have also defined, from the same reasoning, similar parameters for heat capacity and volume of the basic polyhedral components: ; . Results and discussion On Figure 1, we have displayed, for entropy, the correlation obtained between calculated values of SO= for the polyhedral unit and for the oxide analog. A straight line and a second-order function are obtained, for the interlayer and octahedral cations, respectively, with a good correlation coefficient. Fig. 1 - Development of predictive capacity for entropy estimates The implementation of the derived semi-empirical, first or second order relations allows to estimate the thermodynamic properties of a clay mineral, MX80 (Na0.409K0.024Ca0.009(Si3.738Al0.262)(Al1.598Mg0.214Fe3+0.173Fe2+0.035)O10(OH)2) in the present case, loaded by 6 radionuclides and to compare the values with the results obtained by Gailhanou et al. (submitted).The results can be expressed in terms of the concentrations for the elements Ni, Cd, Co, Cr, Mn and Pb and in terms of energetic potential with respect to the measurements performed by Gailhanou et al. (submitted)

Détermination expérimentale des propriétés thermodynamiques et étude des nanostructures de minéraux argileux

Les minéraux argileux sont très étudiés pour le confinement de déchets industriels ou radioactifs, mais leurs propriétés thermodynamiques, essentielles pour connaître leur comportement géochimique à long terme, sont rares et peu fiables. Nous déterminons, pour la première fois, l'ensemble des fonctions thermodynamiques de minéraux argileux, de référence internationale, du type illite, smectite et interstratifiés illite-smectite. L'étude des nanostructures, par METHR-EDX, révèle des résultats très originaux (présence d'illite trioctaédrique) et conduit à redéfinir précisément ces minéraux. Les enthalpies de formation, de mélange et d'hydratation, les capacités calorifiques, les entropies, les enthalpies libres de formation, entre 0 et 500K, sont obtenues pour les minéraux anhydres et hydratés, à l'aide de plusieurs méthodes calorimétriques (calorimétrie de dissolution, calorimétrie adiabatique, DSC). Des études d'équilibre en solution sont confrontées aux résultats calorimétriques.AIX-MARSEILLE3-BU Sc.St Jérô (130552102) / SudocSudocFranceF

Thermodynamics of hydration of MX80 smectite derived from hydration isotherms

Hydration energies contribute significantly to the stability of hydrated clay minerals. However, thermodynamic data of hydration for clay minerals are still poorly known. The present study aims to improve our comprehension of the hydration processes of sodic smectite MX80, and to implement a new methodology for extracting thermodynamic data of hydration of the smectite

Hydration thermodynamics of the SWy-1 montmorillonite saturated with alkali and alkaline-earth cations: A predictive model.

International audienceThe aim of the present work was to study the thermodynamic equilibria between water and a homo-ionic montmorillonite SWy-1 saturated by different cations. The choice of this smectite is justified by the large set of experimental data available from the literature for eight different interlayer cations: Na(+), K(+), Rb(+), Cs(+), Mg(2+), Ca(2+), Sr(2+), and Ba(2+). In particular, studies by Cases et al. (1992, 1997) and Berend et al. (1995) are providing heat of adsorption data, pairs of desorption-adsorption isotherms, and information about the partition of adsorption-desorption water molecules between external surfaces and internal spaces. By calculating the effective amount of hydration water as the difference between the so-called gravimetric water and the surface covering water, a thermodynamic model was then developed, based on the concept of Ransom and Helgeson (1994) considering an asymmetric subregular binary solid solution between a fully hydrated and a anhydrous smectite. A set of six thermodynamic parameters (Delta H degrees(hyd), S degrees(hyd) and four Margules parameters) was extracted by a least square method from measurements of enthalpies of adsorption and paired adsorption-desorption isotherms for each interlayer cation. These six initial parameters were then used to determine a complete set of standard thermodynamic hydration parameters (Delta H degrees(hyd), Delta G degrees(hyd), Delta S degrees(hyd), heat capacity, molar volume, and number of interlayer H(2)O) and quantify, for each cation, the number of moles of hydration water molecules as a function of relative humidity and temperature. The validation of the standard state thermodynamic properties of hydration for each end member was carried out using three approaches: (1) a comparison with experimental isotherms obtained on hetero-ionic and homo-ionic SWy-1 smectite at different temperatures; (2) a comparison with the experimental integral enthalpy and entropy of hydration of the SWy-1 smectite; and (3) a comparison with experimental isotherms acquired on various smectites (Upton, MX80, Arizona) with different layer charges. Eventually, the present work demonstrates that, from a limited number of measurements, it is possible to provide the hydration thermodynamic parameters for hydrated smectites with different compositions and under different conditions of temperature and relative humidity, using the newly developed predictive model

Carbonates reactivity in temperature and interactions with Fe- minerals

International audienceThe carbonate system is the one of most reactive in the mineralogical assemblages of clay-rocks. Consequently, pristine clay-rocks pore water compositions are expected to be at equilibrium with carbonate minerals. However, it is difficult to fully reconcile the concentration data obtained from seepage water sampled in equipped in situ boreholeswith the equilibrium concentrations obtained from pore water modeling (Pearson et al., 2011). It is especially true for dolomite whose solubility spans a large range of values in thermodynamic database as a function of crystallinity considerations, and for siderite/ankerite or other Fe-bearing carbonates whose compositions influence their solubility. The understanding of the carbonate system in clay-rock is necessary for a number of predictions including the effect of an increase of temperature on the pore water chemistry. In this respect, experiments were conducted to study the kinetics of equilibration of carbonate mineral assemblages as a function of temperature (25-80°C) in chemical conditions otherwise similar to those encountered in the Callovian-Oxfordian clay-rock

A predictive model of thermodynamic entities of hydration for smectites: Application to the formation properties of smectites

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Avancées dans le domaine de la thermodynamique des minéraux argileux

La connaissance des propriétés thermodynamiques des minéraux argileux représente un enjeu important pour la mise en oeuvre et la sécurité à long terme des installations de stockage sous-terrain, pour le stockage de déchets nucléaire, de CO2 ou de toute autre substance dangereuse. Ces propriétés, issues pour la plupart d'expériences de mise à l'équilibre plus ou moins bien contrôlées ou de méthodes d'estimation souffrant d'un déficit de données pour leur calibration, étaient considérées comme mal définies. Afin de répondre à ce manque de connaissance, un programme spécifique a été mis en place. Ce programme, baptisé Thermochimie, a été initié et conduit avec le soutien de l'ANDRA. Il vise à compléter les bases de données thermodynamiques nécessaires aux calculs géochimiques, vis-à-vis des propriétés de ces minéraux argileux

Equilibrium Partial Pressure of CO2 in the Callovo-Oxfordian Argillite as a Function of Relative Humidity.

International audienceUnderstanding the behavior of a clay mineral-rich rock submitted to different physical-chemical perturbations is important for assessing the safety of nuclear waste disposal facilities in the corresponding geological formations. In this work we studied the effect of rock desaturation on the CO2 partial pressure signature of the Callovo-Oxfordian argillite. This integrated study, which combines experiments and geochemical modeling, points out the primary role of capillary forces on the chemical equilibria. In particular, it was possible to model, without any fitting parameters, the experimental decrease of pCO2 as a function of decreasing water content in the argillite. Moreover, this application to a complex natural system is an example of confirmation of the theoretical concepts of geochemistry in capillary contexts and is promising for dealing with other natural and industrial systems