Simulation of the internal diffusion process for the ternary exchange of equally charged counterionsстатья
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Дата последнего поиска статьи во внешних источниках: 10 августа 2018 г.
Местоположение издательства:Road Town, United Kingdom
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Аннотация:The kinetic model previously developed for binary exchange was extended to ternary selective systems. The ternary exchange processes of equally charged counterfoils of type (B + E)/ℛA ("sorption") and of type A/(ℛB + ℛE) ("regeneration") were considered. The basic assumption of the model was that, during the exchange process within the grains of a selective ion exchanger, counterions i. are immobile in the bound state (ℛi) and diffuse in the free stale. The model involves mass balance equations for all ions, including the colon (Y); the ionic fluxes are expressed by Nernst-Planek relations. The influence of the association constants KRA, KRB, and KRE on concentration waves of the diffusing components B, E, A, and Y and on the rate of the internal diffusion selective kinetic process in the grains at identical values of the diffusion coefficient for the three counlerions (DA = DB = DE) was considered on the basis of a theoretical analysis of computer simulation results. The effects of the main factors on the characteristics of concentration waves in the kinetic process were represented in the concentration-radius-time pseudo-three-dimensional space. A maximum in the sorption-inter-mittent desorption kinetic curve was found. This unusual effect was observed only for the exchange (sorption) branch of the curve only for one of the two entering counterions (B and E), namely, for the counterion with lower selectivity. In this case, early in the process, the concentration front of the least selective entering counterion was displaced toward the grain center by the wave of the more selective counterion.