The internal porosity and swelling/shrinking of a chelating iminodiacetic type ion exchange resin have been experimentally studied during the uptake of copper onto it. The swelling of the particle could be analyzed with a modified model on th basis of the unreacted core model (UCM), including the influence of chemical equilibrium. The ion exchange kinetic results in batch experiments are used with the UCM to calculate the effect of pH on the internal diffusion coefficients. Results from shallow bed experiments with mixed internal and external diffusion controls have shown the applicability of the above model to analyze ion exchange with low external velocities.