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.