The kinetics of simultaneous loading of cobalt and copper onto an iminodiacetic-type resin is investigated here. This process is characterized by the appearance of a maximum of metal load for the cation with less affinity for the functional group. In our case cobalt load shows a maximum over time. When a semireacted bead is analyzed under the microscope, two different colored layers surrounding the central core are observed. The diffusional model proposed here takes into account the mobility of the cations through the two phases of the macroporous ion exchanger. The numerical solution of the system of differential equations yields solid-phase concentration profiles and metal load over time. Model parameters are adjusted to fit the estimated metal load from reacted layer motion.