Models and physical reality in ion-exchange kinetics

✍ Scribed by Friedrich G. Helfferich

• Publisher: Elsevier Science
• Year: 1990
• Weight: 273 KB
• Volume: 13
• Category: Article
• ISSN: 0923-1137
• DOI: 10.1016/0923-1137(90)90053-7

✦ Synopsis

Four cases of ion-exchange kinetics are pointed out in which premises of a mathematical model are incompatible with facets of physical reality. The cases are (1) calculation of nonlinear gradients in an unstirred Nernst "'film'" (2) shell-core models in the absence of a mechanism that can produce shell-core behavior, (3) reaction-controlled shell-core models, and ( 4) models for macroporous beads in which the wrong diffusion step becomes rate-controlling. Ion-exchange kinetics offers a great variety of combinations of diffusion, convection, electric transference, and chemical reaction. This variety can make it difficult to ensure that, under the prevailing conditions, the kinetic model chosen is not at odds with any facet of physical reality. My experience as editor of this journal and reviewer for several others prompts me to point out four fairly common pitfalls.