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Potassium‐Calcium Exchange in a Multireactive Soil System: I. Kinetics
Author(s) -
Jardine P. M.,
Sparks D. L.
Publication year - 1984
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/sssaj1984.03615995004800010007x
Subject(s) - desorption , chemistry , ion exchange , diffusion , kinetics , adsorption , inorganic chemistry , rate determining step , bromide , ion , thermodynamics , organic chemistry , catalysis , physics , quantum mechanics
The kinetics of K exchange were investigated in Ca‐saturated samples from the Ap horizon of an Evesboro soil from Delaware. Biphasic kinetics characterized the first‐order plots for K adsorption and desorption at 283 and 298K with the two simultaneous reactions being attributed to exchange sites with varying reactivity for K and Ca ions. The rapid reaction was ascribed to exchange sites of the soil that are readily accessible to cation exchange reactions, whereas the slow reaction was attributed to exchange sites that are difficultly accessible to cation exchange reactions. Confirmation of the hiphasic kinetics was achieved through the use of cetyltrimethylammonium bromide (CTAB). Parabolic diffusion plots for K adsorption and desorption at 283 and 298 K indicated that an intraparticle diffusion process may be rate limiting for the difficultly accessible sites of the soil. The initial deviation from linearity of the parabolic plots for K desorption suggested that film diffusion may be rate limiting for desorption on readily accessible sites of the soil that form strong bonds with Ca ions. At 313 K the initial rapid kinetics of exchange was no longer present, and the exchange process was described by a single first‐order reaction. The parabolic plots at 313 K suggested that this phenomenon could possibly be attributed to the finite rate at which the polymer structure of soil organic matter changes in response to the adsorption and desorption of the two reacting cations.