The role of the activity coefficients of surface groups in the formation of surface charge of oxides. Part II: Ion exchange and ζ potentials

Abstract

A new method is developed to calculate the surface charge densities and ζ potentials of oxides in contact with electrolyte solution as functions of pH and ionic strength. For low ionic strength and not too far from p.z.c. (up to 3 pH units for 10⁻³ mol dm⁻³ NaCl) the previous model (Kosmulski, 1992) neglecting the ion exchange can be used but farther from p.z.c., correction for the ion exchange is necessary for some systems. This correction leads to increase of the calculated titration charge (that is not necessarily equal to the surface charge), but does not affect the diffuse charge and ζ potential.