More and more studies carried out on the Geosphere-Biosphere interactions show how the Biosphere can influence, involve, slow down or speed up the inorganic processes. CO2-atmospheric sequestration is an important process that spontaneously occurs in the carbonated serpentinites at Montecastelli site (Tuscany, Italy). In the studied area, carbonate precipitates, mainly hydrated Mg-carbonates, are present in form of crusts, coating and spherules on exposed surfaces, in rock fractures and on tailings in a small mine dump. Selected serpentinites sample, associated with hydrated Mg-carbonates, have been collected and analyzed to investigate the serpentinites alteration and the related carbonate products, the presence of biological activity and its influence on the overall process. Thin sections of unaltered and carbonated serpentinites and carbonate precipitates have been prepared for petrographic and SEM-EDS observations. Their study revealed that Montecastelli serpentinites are mostly unaltered with respect to the carbonation process; samples preserve their original pseudomorphic mesh to hourglass texture of the serpentine after olivine, with magnetite-rich mesh rims and relicts of primary spinel. Hydrated Mg-carbonate precipitation is restricted to pre-existing veins or, more commonly, to the rock surface. They form whitish thin crust with laminar or bubble-like appearance, white small spherules over the crust or just on the rock surface, or mixing between them. The different precipitated types have been selected under binocular microscope for XRD analyses performed at the Dipartimento di Scienze della Terra (University of Pisa, Italy): precipitated minerals which can be traced are hydromagnesite, nesquehonite, manasseite, pyroaurite, brugnatellite, often associated with aragonite. Detailed analyses using Confocal Raman microspectroscopy and electron microscopy have been performed at the Institut de Physique du Globe de Paris (IPGP, France). The spectra Raman can provide evidence of the presence of organic compounds, such as aliphatic and aromatic mixtures. The presence of active microbial communities in hydrated Mg-carbonates could promote and/or enhance the acid-base reaction, through which the serpentine, reacting with the carbon dioxide, transforms into hydromagnesite or in other metastable hydrated Mg-carbonates. In nature, the considered acid-base reaction occurs very slowly, so that bacteria can behave like catalysts, increasing the reaction rate and promoting this key reaction to occur in a relatively short time. Our study would increase the knowledge about the key parameters affecting and enhancing the natural process of CO2 mineral sequestration, throughout carbonation of silicate minerals. This process could be simulated on industrial scale to reduce the greenhouse gas content of the atmosphere.
Interaction between Geosphere and Biosphere in CO2-mineral sequestration environment
BEDINI, FEDERICA;PERCHIAZZI, NATALE;ZANCHETTA, GIOVANNI
2013-01-01
Abstract
More and more studies carried out on the Geosphere-Biosphere interactions show how the Biosphere can influence, involve, slow down or speed up the inorganic processes. CO2-atmospheric sequestration is an important process that spontaneously occurs in the carbonated serpentinites at Montecastelli site (Tuscany, Italy). In the studied area, carbonate precipitates, mainly hydrated Mg-carbonates, are present in form of crusts, coating and spherules on exposed surfaces, in rock fractures and on tailings in a small mine dump. Selected serpentinites sample, associated with hydrated Mg-carbonates, have been collected and analyzed to investigate the serpentinites alteration and the related carbonate products, the presence of biological activity and its influence on the overall process. Thin sections of unaltered and carbonated serpentinites and carbonate precipitates have been prepared for petrographic and SEM-EDS observations. Their study revealed that Montecastelli serpentinites are mostly unaltered with respect to the carbonation process; samples preserve their original pseudomorphic mesh to hourglass texture of the serpentine after olivine, with magnetite-rich mesh rims and relicts of primary spinel. Hydrated Mg-carbonate precipitation is restricted to pre-existing veins or, more commonly, to the rock surface. They form whitish thin crust with laminar or bubble-like appearance, white small spherules over the crust or just on the rock surface, or mixing between them. The different precipitated types have been selected under binocular microscope for XRD analyses performed at the Dipartimento di Scienze della Terra (University of Pisa, Italy): precipitated minerals which can be traced are hydromagnesite, nesquehonite, manasseite, pyroaurite, brugnatellite, often associated with aragonite. Detailed analyses using Confocal Raman microspectroscopy and electron microscopy have been performed at the Institut de Physique du Globe de Paris (IPGP, France). The spectra Raman can provide evidence of the presence of organic compounds, such as aliphatic and aromatic mixtures. The presence of active microbial communities in hydrated Mg-carbonates could promote and/or enhance the acid-base reaction, through which the serpentine, reacting with the carbon dioxide, transforms into hydromagnesite or in other metastable hydrated Mg-carbonates. In nature, the considered acid-base reaction occurs very slowly, so that bacteria can behave like catalysts, increasing the reaction rate and promoting this key reaction to occur in a relatively short time. Our study would increase the knowledge about the key parameters affecting and enhancing the natural process of CO2 mineral sequestration, throughout carbonation of silicate minerals. This process could be simulated on industrial scale to reduce the greenhouse gas content of the atmosphere.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
