DIFFUSION OF IONS IN VARIABLE-CHARGE SOILS

Diffusion coefficients of Cl−, NO3−, K+. and Ca2+ in variable-charge soils from diffusing sources consisting of mixed salts were determined. The effects of diffusing ion species, soil surface charge, and other ions on diffusion coefficients were similar to those in single-salt systems. However, the diffusion coefficients were larger for anions when soil pH was low and for cations. The difference in diffusion coefficient between anion species was larger and that between cation species was smaller than when a single salt diffused alone. These differences were interpreted in terms of the interactions between ions and soil surface charges and among ions during diffusion.