The properties of this ion are strongly related to the surface potential present on a corresponding solid.
In a colloidal dispersed system, ion dissolution arises, where the dispersed particles exist in equilibrium with their saturated counterpart, for example: The behavior of this system is characterised by the components activity coefficients and solubility product: In clay-aqueous systems the potential of the surface is determined by the activity of ions which react with the mineral surface.
Frequently this is the hydrogen ion H+ in which case the important activity is determined by pH.
The simultaneous adsorption of protons and hydroxyls as well as other potential determining cations and anions, leads to the concept of point of zero charge or PZC, where the total charge from the cations and anions at the surface is equal to zero.
The charge must be zero, and this does not necessarily mean the number of cations versus anions in the solution are equal.