Modeling of the kinetics of internal-diffusion binary exchanges of ions with different charges in nonlinear selective systemsстатья
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Дата последнего поиска статьи во внешних источниках: 10 августа 2018 г.
Местоположение издательства:Road Town, United Kingdom
Первая страница:399
Последняя страница:411
Аннотация:A previously developed model based on the postulate that ion exchange in ionite grains involves the association reaction RA + B ⇄ RB + A of fixed groups with counterions B and A that can exist in a free state and a bound state is discussed. Counterions i are immobile in the bound state (Ri) and can diffuse in the free state. The model is based on equations of mass balance for the ions, including coion Y; in these equations, the fluxes of the species are described by the Nernst-Planck relation. The model is extended to the case of ion exchange between ions with different charges. Computer simulations of the influence of the diffusion coefficients of the counterions DA and DB, the association constants KRA and KRB, and the ratio between the charges zi on the characteristics of propagation of concentration waves of the diffusing species and on the rate of the internal-diffusion kinetic process in the ionite grain. The calculation results are presented in the three-dimensional coordinates formed by the concentration, current grain radius, and time, which make it possible to graphically present complicated ion-exchange processes over the entire time interval. The differences in the profiles of the concentration waves for the direct and reverse exchanges of ions with different charges are determined not only by the ratios between the diffusion coefficients and association constants, but largely by the charge factor zA/zB.