Increase in cation adsorption induced by surface complexation of sulfate on andisols and prediction by “four-plane model”

Abstract

The “Four-plane model” is one of the surface complexation models developed for analyzing the electrostatic charge of synthetic oxides. This model which was applied to the B horizon of Andisols, was equilibrated with an electrolyte solution containing KCl, KNO3, K2SO4 in the concentration range of 0.0033, 0.01, 0.033, 0.1 M, and pH range of 2 to 11. The amounts of NO3−, Cl−, SO42−, and K+ adsorbed were determined from the products remaining in the liquid phase. The increase in the pH value results in the increase of K+ adsorption, and decrease of anion adsorption. The increase in the equilibrium concentration increased both K+ and anion adsorption. The parameters of the model were determined by measurements and the iterative method. The model have a good agreement between calculated and measured values of cation and anion adsorption. Among the anion species, the amount of adsorbed anions was in the order of SO42−≫Cl−