An analytical approach to estimating electrostatic repulsion between soil particles

Abstract

The electrostatic repulsion between soil particles has an important effect on the stability of soil aggregates and soil water movement. However, the electrostatic repulsive pressure is traditionally quantified through a complicated numerical method. In this study, the analytical expressions for calculating the midplane potential between soil particles in 1:1 and 2:1 electrolytes were derived respectively, consequently an analytical method for estimating the electrostatic repulsive pressure was obtained. The theoretical solutions of midplane potential between particles and electrostatic repulsive pressure are in good agreement with the numerical ones, and correctly predict the swelling pressure of montmorillonite. The surface potential, midplane potential and electrostatic repulsive pressure between soil particles calculated by the analytical method increase with increasing charge density, which depends on ionic polarization or/and polarization-induced covalent bond. For example, electrostatic repulsive pressure is the highest in non-polarized Li+, decreases in polarized Na+, and the lowest in K+ solution due to potassium’s relatively high polarization and polarization-induced covalent bond. The percentage of large soil pores (> 1 mm) and electrostatic repulsive pressure appear in a negative correlation, which is consistent with changes in the soil water infiltration rate, whereas the percentage of small soil pores (< 0.5 mm) has a positive relationship to electrostatic repulsive pressure. The ion polarization or/and polarization-induced covalent bond affect soil pore distribution and control soil water infiltration through significantly affecting the electrostatic repulsive pressure between soil particles. The analytical estimation of electrostatic repulsion is of great significance for understanding the physical/chemical processes in soils and quantifying the relations between mesoscopic processes and macroscopic phenomena.