European Journal of Soil Science
Xu, C-Y.Li, H.Hu, F-N.Li, S.Liu, X-M.Li, Y.
The stability of soil aggregates is closely connected with particle interaction determined by the combination of the van der Waals attractive force and electric repulsive force according to Derjaguin-Landau-Verwey-Overbeek (DVLO) theory. Recently, hydration force and dispersion force were put forward to explain the different behaviours of cations or anions of the same valence at the ion-surface interface, namely the specific ion effect, where the application of classical DLVO theory had failed. Here, we employed two cation species, potassium and sodium (K+ and Na+), to discover how the specific ion effect would influence clay aggregate stability. The stability of K+- and Na+-montmorillonite aggregates was determined under different electrolyte concentrations, indicated by the mass percentages of particles with diameters of & lt; 10, & lt; 5 and & lt; 2 mu m released after aggregate breakdown. There were large differences in the stability of the K+- and Na+- aggregates, and strong specific ion effects were shown. These effects could not be explained by the differences in ionic size, hydration and ion-surface dispersion forces between K+ and Na+. We have proved that the difference in polarization between the K+ and Na+ at the charged clay surface was responsible for the specific ion effects. The difference in polarization observed between the adsorbed K+ and Na+ was hundreds to thousands of times larger than classical values; these results were also verified independently with different methods. The strong non-classical polarization of the adsorbed cation decreased the electric field and the electrostatic repulsion between adjacent particles in the aggregates, and thus strongly increased the aggregate stability.
