Ion exchange on resins with temperature-responsive selectivity II. Thermo-induced concentration waves in ion-exchange column

The kinetics of H+-Cu2+, H+-Zn2+, Zn2+-Cu2+, and Cu2+- Zn2+ exchanges on iminodiacetic resin Lewatit TP-207 at 293 K has been studied. The effective diffusion coefficients of Cu2+ and Zn2+ have been determined to be 2.6x10-8 and 1.4x10-7 cm2/s, respectively, for the given conditions. The kinetics of Cu2+ and Zn2+ thermostripping from the resin preequilibrated with a mixture of zinc and copper sulfates at pH 1.8 have been shown to be influenced by the different metal ion diffusivities and by the presence of a third component (H+) in the system so that an oscillation of ion concentration is observed. This phenomenon is observed more clearly with the increase of resin beds when studying the dynamics of the column thermostripping process. Formation of a concentration wave results in the enrichment of the first halfwave with Zn2+ while the second halfwave appears to be enriched with Cu2+. A mathematical model of ion-exchange dynamics of components with dissimilar diffusivities has been developed. The phenomenon of formation of concentration waves is interpreted within the model as a result of the influence of a local electrical field, arising in the resin phase, from the difference on fluxes of exchanging ions. The results of computer simulation of the thermostripping process within the frame of the model proposed are in a good agreement with those obtained in thermostripping experiments.