THERMOGRAVIMETRIC ANALYSIS OF A TALC MIXTURE

A commercial talc also containing chlorite. dolomite and magnesite was subjected to thermogravimetric analysis to determine its mineral composition. Knowledge of the reactions and the decomposition temperatures, as well as the crystallochemical formulae of the phases present, has permitted the application of a system of equations that has provided mineral composition results in good agreement with standard analysis obtained via elemental chemical analysis

Indirect estimation of the clay content of clay-rocks using acoustic measurements: New insights from the Montiers-sur-Saulx deep borehole (Meuse, France)

International audienceThis work benefited from a comprehensive set of logging and mineralogical data that was acquired from the 2-km-deep EST433 borehole of Montiers-sur-Saulx (Meuse, France). A multiple linear regression analysis was performed on three sets of data: (a) sonic data (P- and S-wave velocities), (b) total combinable magnetic resonance (TCMR) porosity data, and (c) X-ray diffraction (XRD) data. The analysis was performed to estimate the clay content in the Callovo-Oxfordian (COx) claystone and other clay-rocks of the stratigraphic column. The inferred statistical relationships were compared to results obtained from a conventional spectral gamma ray (GR) approach.The results indicate that simple linear regressions using only elastic wave velocities (a) accounted for more than 81% of the vertical variability of the clay content in the COx formation (i.e., coefficient regression R-2 values greater than 81%) and (b) enable the estimation of clay content with the same accuracy as the spectral GR approach. Both approaches, our acoustic regressions and spectral GR methodology, provide estimate errors that are within the range of uncertainties associated with the XRD analysis applied. Moreover, using the whole set of XRD data showed that the elastic wave velocities and the TCMR porosity as explanatory variables are better predictors of total clay content than swelling clay mineral content.Blind estimations of clay content were performed using data acquired in clay-rocks from the same stratigraphic column and in the COx formation located a few kilometers distant in the EST423 borehole. The results demonstrated that the established regressions must be used with caution when vertically and horizontally extrapolating the estimated clay content. This difficulty is partly explained by the influence of the microstructure of the studied clayrocks, which was insufficiently taken into account via the petrophysical variables considered in this work

Experimental study of the transformation of smectite at 80 and 300°C in the presence of Fe oxides

International audienceThe alteration and transformation behaviour of montmorillonite (Wyoming bentonite) was studied experimentally to simulate the mineralogical and chemical reaction of clays in contact with steel in a nuclear waste repository. Batch experiments were conducted at 80 and 300ºC, in low-salinity solutions (NaCl, CaCl 2) and in the presence or otherwise of magnetite and hematite, over a period of 9 months. The mineralogical and chemical evolution of the clays was studied by XRD, SEM, transmission Mössbauer spectroscopy and EDS-TEM. Experimental solutions were characterized by ICP-AES and ICP-MS. The main results are that no significant change in the crystal chemistry of the montmorillonite occurred at 80ºC, while at 300ºC, the presence of Fe oxides leads to a partial replacement of montmorillonite by high-charge trioctahedral Fe 2+-rich smectite (saponite-like) together with the formation of feldspars, quartz and zeolites