Hydration energies and clay mineral thermodynamic stability. I. A fictitious averaged clay mineral.

By averaging large number of experimental dehydration isotherm propel-ties of various dioctahedral (Al3+ Fe3+) or trioctahedral (Mg2+, Fe2+) smectites (low interlayer charges) and verniculites (high interlayer charges) satura ted by Li+, Na+, K+, Mg2+ or Ca2+, one may define a fictitious interstratif ied solid solution of hydrated layers. As an example of thermodynamic treat ment, have been calculated as a function of water activity: water content, hydration energy, Gibbs free energies of formation, true and apparent solub ility products. (C) 2001 Academie des sciences / Editions scientifiques: et medicales Elsevier SAS.