ABSTRACT
The surface chemistry of clay minerals is typically a great deal more complex than that of oxides and hydroxides, in part because there are a seemingly infinite number of clay stoichiometries. In short, the surface reactivity of clays arises from two distinct causes: exchangable cations on interlayer sites that are incorporated to maintain an overall neutral charge on the crystal lattice, and the broken bonds that exist on the edges when the periodic arrangement of atoms is terminated. One consequence of the constant-charge rule is that the ion exchange sites on clays in contact with low ionic strength groundwaters typically contain a greater proportion of divalent cations. The changes in clay bulk composition that are caused by ion exchange and edge adsorption at low temperatures are dwarfed by the significantly greater changes that occur when clays are exposed to greater temperatures and salinity during geological burial.
