Abstract
Smectites are widespread minerals of soils, weathering formations and sediments. They possess an important surface reactivity which allows them to dominate many of the physicochemical properties of the na~tral systems in which they are present. Owing to this widespread occurrence and importance, the properties of the smectite-water interface, and specifically the smectite surface stability and sorption properties, deserve a particular interest. The high surface reactivity of smectites is a consequence of their lamellar and defective structure. Smectites are built of layers made by the condensation of one central (Mg, Li, A1) octahedral sheet and two (Si, A1) tetrahedral sheets. Heteroionic cationic substitutions in these layers impart to smectites a negative structural charge, which results in cation exchange properties. Truncation of the bulk structure at the layer edges leads to unsaturation of surface oxygens, which can promote both pH-dependent sorption or surface dissolution. However, no definite evidence for the adsorption of cations on layer edges has been reported today. Furthermore, whereas it has been observed that the dissolution rate of smectites decreases in presence of metal cations, the exact
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