Thermodynamic treatment of hydrates.

The thermodynamic properties of the hydration water of hydrated minerals co ntribute to the variations of the solubility products and cation selectivit y constants. This is illustrated here as an example taken from series of hy drated magnesium and strontium chlorides. Such variations are a function of temperature, pressure, or activity of water. The proposed method, applicab le to clay minerals, allows hydration processes to be taken into account fo r calculating solubility products when only the thermodynamic properties ei ther of the dehydrated or hydrated mineral phase, the hydration isotherm of the mineral and the thermodynamic properties of the hydration water are es tablished. (C) 2000 Academie des sciences / Editions scientifiques et medic ales Elsevier SAS.