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.

The kinetics of heavy metal uptakecopper and cobalt against sodiumby chelating resins was analyzed experimentally by measuring the internal concentration profiles inside a single bead. Metal concentration profiles inside the particles at different reaction times were measured using an energy dispersive X-ray (SEM-EDX) coupled to a scanning electron microscope. This technique provided a line scan along diametrical positions, yielding the metal concentration profiles needed in order to build mathematical models for the simultaneous uptake of copper and cobalt. This process is described by means of a mathematical model which uses the Nernst−Planck equation for diffusion and takes into account relevant physical and chemical effects. The diffusion model proposed here takes into account the mobility of ions through the macroporous ion exchanger and the corresponding electric field generated by the diffusion of ions with dissimilar diffusivities. The estimated diffusion coefficients are discussed in terms of the mobility of a single metal and the contribution of its co-ion. The dynamic behavior of a system composed of two intraparticular phases is correctly described by this diffusion model, including the nonmonotonous tendencies which are not associated with the different values of the diffusion coefficient.