ION-EXCHANGE ON RESINS WITH TEMPERATURE-RESPONSIVE SELECTIVITY - II -THERMOINDUCED CONCENTRATION WAVES IN ION-EXCHANGE COLUMN

The kinetics of H+-Cu2+, H+-Zn2+, Zn2+-Cu2+, and Cu2+-Zn2+ exchanges o n iminodiacetic resin Lewatit TP-207 at 293 K has been studied. The ef fective diffusion coefficients of Cu2+ and Zn2+ have been determined t o be 2.6X10(-8) and 1.4X10(-7) cm(2)/s, respectively, for the given co nditions. The kinetics of Cu2+ and Zn2+ thermostripping from the resin preequilibrated a with a mixture of zinc and copper sulfates at pH 1. 8 have been shown to be influenced by the different metal ion diffusiv ities and by the presence of a third component (H+) in the system so t hat an oscillation of ion concentration is observed. This phenomenon i s observed more clearly with the increase of resin beds when studying the dynamics of the column thermostripping process. Formation of a con centration wave results in the enrichment of the first halfwave with Z n2+ while the second halfwave appears to be enriched with Cu2+. A math ematical model of ion-exchange dynamics of components with dissimilar diffusivities has been developed. The phenomenon of formation of conce ntration waves is interpreted within the model as a result of the infl uence of a local electrical field, arising in the resin phase, from th e difference on fluxes of exchanging ions. The results of computer sim ulation of the thermostripping process within the frame of the model p roposed are in a good agreement with those obtained in thermostripping experiments. (C) 1998 Elsevier Science B.V.