Specific ion effects of H+-base cation coupling on permanently charged soil aggregation

The accumulation of excessive H⁺ can cause soil acidification and then affect the aggregation and dispersion of soil particles through changes in pH as well as electrolyte type and concentration. In this study, dynamic light scattering (DLS) technology was employed to investigate the aggregation kinetics of soil particles in several base cation solutions at different pHs. The results showed that, (1) specific ion effects of base cations were observed in aggregation rates, critical coagulation concentrations (CCCs) and activation energies for soil particle aggregation at different pHs; (2) H⁺ enhanced the aggregation rate, but reduced the CCC values and activation energies of the base cations, and then greatly promoted soil particle aggregation; (3) H⁺ strongly decreased specific ion effects of base cations on the aggregation rates, CCCs and activation energies for soil particle aggregation. The analyses of those differences related to soil aggregation kinetics in different base cation solutions at different pHs revealed that, the lower the pH, the weaker the electric field strength, and therefore the weaker the polarization of base cations and surface O-atoms would be. Moreover, H⁺ reduced the charge density for soil particle aggregation, which was the main source for decreasing the electrostatic repulsive energy for soil particle aggregation at different pHs. The study improves our understanding of soil acidification effects on soil particle aggregation and aggregate stability.