Identification and Quantification of Carbonate Species Using Rock-Eval Pyrolysis

Abstract

Résumé -Détermination et quantification des carbonates par pyrolyse Rock-Eval -Cet article présente une nouvelle méthode fiable et rapide pour caractériser et quantifier les carbonates dans tout type d'échantillon solide. La méthode est basée sur la quantification du flux de CO 2 émis lors de la décomposition thermique progressive des carbonates au cours d'un chauffage programmé. Les différents pics de déstabilisation permettent la détermination des différents types de carbonates présents dans l'échantillon analysé. La quantification de chaque pic donne les proportions respectives de ces différents types de carbonate présents dans l'échantillon. La procédure qui a été choisie dans ce travail utilise un pyrolyseur Rock-Eval 6 standard en mode oxydation. Des profils caractéristiques d'échantillons de références sont présentés pour les carbonates naturels les plus courants. Cette méthode devrait permettre différents types d'application dans des disciplines diverses et dans des domaines à la fois académiques et industriels. Abstract -Identification and Quantification of Carbonate Species Using Rock-Eval Pyrolysis

Guidelines for Rock–Eval analysis of recent marine sediments

“…In most sedimentary rocks, the natural mixture of carbonate minerals of different origin does not display the simple and unequivocal series of thermal destabilization obtained with pure products. This is particularly apparent for recent sediments in which the carbonate minerals are usually poorly crystallized and may then show thermal destabilization at a temperature lower than demonstrated by Pillot et al (2013).…”

“…Although this phenomenon is moderate for most carbonates, small calcite minerals are destabilized more easily than large calcite minerals. For instance, chalk is destabilized at a lower temperature than marble, but the difference is only 2 to 4 °C, with the destabilization temperature always ≥ 775 °C (see Table 1 in Pillot et al, 2013). It should be noted that these authors used pure carbonate fractions for their experiments and did not show curves for natural samples having a complex mineralogy.…”

“…It is then possible to deduce the nature of the carbonate from its specific decomposition temperature. Pillot et al (2013) mention, however, that the size of some carbonate minerals has an effect in terms of thermal destabilization. Although this phenomenon is moderate for most carbonates, small calcite minerals are destabilized more easily than large calcite minerals.…”

“…Our own experience in analyzing sedimentary rocks using Rock-Eval pyrolysis led us to modulate the extrapolation made by Pillot et al (2013). In most sedimentary rocks, the natural mixture of carbonate minerals of different origin does not display the simple and unequivocal series of thermal destabilization obtained with pure products.…”

“…1 and refer to Behar et al (2001) for further explanation]. Recently, Pillot et al (2013) promoted the Rock-Eval analysis as a rapid method for determining the nature and amount of carbonate in sediments based on the CO 2 flux produced during the oxidation phase of the analysis. Depending on the type of carbonate mineral (azurite, malachite, siderite, rhodochrosite, magnesite, dolomite, aragonite or calcite), the thermal destabilization produced a peak characterized by both its shape and the temperature of maximum production of CO 2 .…”