Evaluation of exchange equilibria on strongly acidic ion exchangers with gel-type, macroporous and macronet structure

The effects of the structure of sulfonated polystyrenic resins of type gel, macroporous and macronet (hyper-crosslinked) on H+/Cu+, Zn2+, and Cd2+ binary ion exchange equilibria were investigated. The ion exchange isotherms were measured at 298 K and 0.01 total equivalent concentration of the aqueous external solution using the atomic absorption spectrometry. Many equations were fitted to the experimental isotherms in order to investigate the energetic heterogeneity of the resin surface for the selected ions. The Langmuir isotherm seems to be a good approximation for all considered systems, within the experimental errors. It was shown that the fitted Langmuir isotherm could be used to determine the ion exchange equilibrium constants in the surface complexation model. The sorption constants and the ion exchange equilibrium constants of the surface complexation model give the same series of selectivity and affinity. For gel and macronet resins, the selectivity series is Cd2+ > Zn2+ > Cu2+, and for macroporous resin is Cu2+ > Cd2+ > Zn2+. The affinity of the macronet strong acid polystyrenic resin is higher than the affinity of the gel strong acid polystyrenic resin, for each investigated ion. The affinity of the macroporous strong acid resin compared with the gel and macronet is the highest for Cu2+, and the lowest for Cd2+. The ion exchange equilibrium constants for the selected counter-ions on the macronet resin present a notable variation, favoring a better separation, than on gel or macroporous resins.