APPLICATION OF THE SURFACE COMPLEX-FORMATION MODEL TO EXCHANGE EQUILIBRIA ON ION-EXCHANGE RESINS .1. WEAK-ACID RESINS

Ion exchange equilibria on weak-acid resins are described by means of a theoretical approach, in which fixed sites and counterions are assumed to form so-called surface complexes. The electric charges of the fixed sites generate an electric field normal to the resin surface. Counterions are located in individual sorption layers which have a certain charge density. Due to the existence of one layer for each kind of counterions, the entire resin phase can be considered as a series of electric capacitors. For the exchange of protons against metal counterion a set of always two characteristic quantities has to be derived from experiments. By means of this set of constants, the equilibrium can be calculated for a broad range of initial conditions. If relationships about the capacitances in a series of electric capacitors are applied, multicomponent equilibria can be predicted using the sets of binary exchange parameters. The assumption that all counterions are located in their characteristic layers leads to a simplified mathematical method. As supported by a large number of results the surface complex formation model provides an excellent agreement between experimental data and predicted equilibria. © 1990.