
%0 Journal Article
%A Escudey, M. 
%A Diaz, P. 
%A Foerster, J. E. 
%A Galindo, G. 
%T Adsorbed ion activity coefficients in K&#8211;Ca exchange on soil fractions derived from volcanic materials
%J Soil Research
%D 1997/01/08
%V 35
%N 1
%P 123-130
%K allophanic soils, cation exchange, thermodynamics.
%R https://doi.org/10.1071/S96051
%U https://www.publish.csiro.au/paper/S96051 
%X The effects of temperature and iron oxide coatings on the adsorbed ion activity coefficients obtained by the Gaines&#8211;Thomas treatment for the K&#8211;Ca exchange equilibria on clay fractions of 3 Chilean Andisols were studied. The comparison with the values calculated through the Vanselow approach, using conversion equations, was also considered. Adsorbed Ca activity coefficient curves present a similar shape for the Gaines&#8211;Thomas and Vanselow approaches; for K, maxima were observed only when the Gaines&#8211;Thomas treatment was used. Iron oxide coated samples showed higher adsorbed ion activity coefficients than allophanic samples. The adsorbed K activity coefficients increased when temperature increased from 4&#176;C to 26&#183;5&#176;C, but only a slight effect on Ca ions was observed. In both types of samples, the presence of 3 possible selective sites was detected: K-selective sites, Ca-selective sites, and sites where K&#8211;Ca competition occurs. 
