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Modeling Potassium‐Calcium Exchange Isotherms in Soils
Author(s) -
Dufey Joseph E.,
Delvaux Bruno
Publication year - 1989
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1989.03615995005300040051x
Subject(s) - ion exchange , chemistry , selectivity , affinities , potassium , activity coefficient , soil water , cation exchange capacity , ion , thermodynamics , mineralogy , analytical chemistry (journal) , soil science , chromatography , geology , stereochemistry , physics , organic chemistry , aqueous solution , catalysis
Ion exchange equilibria involving K cannot be described by a constant selectivity coefficient for all surface compositions. The main reason is that the soil exchanger contains various types of sites with different affinities for K ions. This paper makes use of a multi‐site model, the main assumption of which is that the exchange reaction is governed by single values of the Vanselow selectivity coefficient, K v , for each type of site. The simplest model—i.e., the two‐site model—is tested. Three parameters must be adjusted: the proportion of high and low selective sites, and the K v 's for these two classes of sites. Simulated K‐Ca exchange isotherms are shown, with various combinations of the parameters. The model has been adjusted to experimental K‐Ca exchange data, using a non‐linear regression procedure. A fair agreement between the experimental and calculated curves is obtained. As a consequence, this simple model proves to be a powerful tool for a quantitative description of exchange data involving K ions.