pH Dependence of Sorption Processes from Aqueous Solution.

The adsorption of weak electrolytes from aqueous solutions onto solid surfaces is strongly influenced by the pH of the liquid phase due to shifts of dissociation equilibria as well as changes in the surface charge density. Satisfactory agreement with experimental adsorption data is obtained for computed values based on an IAS treatment of Langmuir- or Freundlich-type isotherm equations for the conjugated acid-base system. Results of kinetic investigations confirm previous findings that surface diffusion coefficients exhibit maximum values near the zero point of charge pH level, and pH dependent breakthrough curves can be predicted.