Yves Tardy

Thermochemical Properties of Phosphates

This chapter summarizes the thermochemical data of phosphate ions, aqueous complex species as well as minerals occurring in natural environments. The data are presented in such a way as to express all equilibrium reactions as a function of a set of reference aqueous ions. The sources of these data were selected, as far as possible, according to their internal consistency and the newness of the corresponding experimental works.

Le concept d'eau ice-like: hydratation-déshydratation des sels, hydroxydes, zeolites, argiles et matières organiques vivantes ou inertes

Abstract The concept of ice-like water is applied to the prediction of hydration-dehydration reactions among clay minerals, hydroxides, hydrated salts, and living or inert organic matter, which appear to be very sensitive indicators of the climate of soil genesis and conditions o bunal diagenesis Adsorption-desorption under temperature or pressure depends on the thermodynamic properties (entropy, heal capacity and volume) of structural water retained in organic or mineral compounds, which are similar to those of the dense ice polymorphs.

Thermodynamique des hydrates

Abstract The thermodynamic properties of the hydration water of hydrated minerals contribute to the variations of the solubility products and cation selectivity constants. This is illustrated here as an example taken from series of hydrated magnesium and strontium chlorides. Such variations are a function of temperature, pressure, or activity of water. The proposed method, applicable to clay minerals, allows hydration processes to be taken into account for calculating solubility products when only the thermodynamic properties either of the dehydrated or hydrated mineral phase, the hydration isotherm of the mineral and the thermodynamic properties of the hydration water are established.

Érosion chimique et mécanique sur les bassins du Niger et de l'Amazone. Évolution climatique et paléoclimatique des paysages tropicaux

Abstract The annual hydrograph separation of the upper Niger basin at Bamako, determined from the TDS and TSS concentration variations in the river waters during the dry period 1990–1992, has been extrapolated to climatic cycles from arid to perhumid. A dilution factor (F = rainfall/runoff) is introduced, so that the extrapolation from the Niger basin data corresponds to the weathering parameters which characterize, in very humid environments, three tributaries of the Amazon. The erosion rates of tropical landscapes submitted for 150 Myr are finally reconstituted to major paleoclimatic oscillations.

Énergies d'hydratation et stabilité thermodynamique des minéraux argileux. I. Cas d'une argile fictive moyenne

Abstract By averaging a large number of experimental dehydration isotherm properties of various dioctahedral (Al3+, Fe3+) or trioctahedral (Mg2+, Fe2+) smectites (low interlayer charges) and vermiculites (high interlayer charges) saturated by Li+, Na+, K+, Mg2+ or Ca2+, one may define a fictitious interstratified solid solution of hydrated layers. As an example of thermodynamic treatment, have been calculated as a function of water activity: water content, hydration energy, Gibbs free energies of formation, true and apparent solubility products.

Refinements in the use of Chemical Geothermometers Application to the Plombieres System (France)

Classical and new geochemical thermometers were tested in the thermal waters of the Plombieres system. Twenty five springs, coming out of the cracks of a granitic body at different temperatures, were sampled and analyzed during three years. These waters are of surface origin and are mixed from three reservoirs: (i) a surface reservoir, cold, not polluted, (ii) a surface reservoir, cold and slightly polluted and (iii) a deep and hot reservoir. The direct use of the different geochemical thermometers fails and geochemistry of the system should be interpreted in terms of a mixing model. With the aid of this model, the temperature of the hot reservoir is estimated to be 140°C.