Gaines–thomas and rothmund–kornfeld descriptions of potassium–calcium exchange on variable surface charge soils

Abstract

ABSTRACT The empirical Rothmund–Kornfeld power function approach (in terms of equivalent fractions) was applied to potassium–calcium (K–Ca) exchange equilibrium carried out at 25°C and 0.05 M ionic strength on 4 soils derived from volcanic materials in southern Chile. Results were compared with those obtained by the Gaines–Thomas approach, where a K preference was observed in all samples, with equilibrium constant values ranging from 0.097 to 0.492. The equivalent fraction form of Rothmund–Kornfeld fit the exchange isotherm curves obtained by the Gaines–Thomas convention and provides a good description of experimental exchange data. The exchange equilibrium constants and adsorbed ion activity coefficients calculated with Rothmund–Kornfeld parameters are comparable with those obtained by the Gaines–Thomas approach.