hal-00701813
https://brgm.hal.science/hal-00701813
https://brgm.hal.science/hal-00701813/document
https://brgm.hal.science/hal-00701813/file/Blanc_Montpellier12r2.pdf
[SDE] Sciences De l'Environnement
[INSU] INSU - Institut National des Sciences de l'Univers
[BRGM] Bureau de Recherches Géologiques et Minières
[CNRS] CNRS - Centre national de la recherche scientifique
[UNIV-POITIERS] Université de Poitiers
[ANDRA] Agence Nationale pour la gestion des Déchets RAdioactifs
[IC2MP] INSTITUT DE CHIMIE DES MILIEUX ET MATERIAUX DE POITIERS
[GIP-BE] GIP Bretagne Environnement
[FRANTIQ] FRANTIQ Fédération et ressources sur l’Antiquité
[INC-CNRS] Institut de Chimie du CNRS
[TEST2-HALCNRS] TEST2-HALCNRS
Extending the prediction of the thermodynamic properties of clay minerals to the trapping of trace elements
Blanc, Philippe
Vieillard, Philippe
Gailhanou, Hélène
Gaboreau, Stéphane
Lassin, Arnault
Gaucher, Eric C.
Fialips, C.I.
Giffaut, Eric
[SDE.ES] Environmental Sciences/Environmental and Society
[SDU.STU.GC] Sciences of the Universe [physics]/Earth Sciences/Geochemistry
[SDE.MCG] Environmental Sciences/Global Changes
COMM
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).
2012-10-22
2012-05-26
en
International meeting "Clays in Natural and Engineered Barriers for Radioactive Waste Confinement"
Montpellier, France