Polarization‐induced covalent interaction between H ⁺ and surface O atom promoting clay aggregation

Accumulation of H + can cause soil acidification, affect soil particle interactions, and alter soil processes. In this study, aggregation kinetics of montmorillonite colloids induced by monovalent ions of Li + and H + were determined by dynamic light scattering. The experimental results indicated that the critical coagulation concentration ( CCC ) value of Li + was 4.5 times that of H + , indicating that H + can strongly promote montmorillonite colloids aggregation. Joint analysis of the adsorption force type and energy of Li + and H + as well as the infrared spectroscopy of Li + and H + montmorillonite indicated that there was only electrostatic adsorption for Li + , while there was not only electrostatic adsorption but also a new type of covalent adsorption for H + : polarisation‐induced covalent adsorption. The total adsorption energy of H + is thus much higher than that of Li + on montmorillonite surfaces. Moreover, the polarisation‐induced covalent adsorption energy of H + increased linearly with increasing electric field strength, which is consistent with the quantum mechanical analysis of the asymmetric orbital hybridisation of surface O atoms on montmorillonite. On this basis, the polarisation‐induced covalent adsorption energy of H + was employed to predict the CCC value of H + induced montmorillonite aggregation, and it was 7.40 mmol L −1 . The high agreement with experimental results (7.26 mmol L −1 ) proved that the polarisation‐induced covalent interactions between H + and surface O atoms promotes montmorillonite aggregation. This polarisation induced covalent effect between H + and surface O atoms might further affect the formation and stability of soil aggregates and the pore status of soil structure, especially as soil acidification is currently becoming a global issue. The discovery from this study will improve our understanding of the effects of soil acidification on soil properties and processes. Highlights H + greatly promoted clay aggregation. Polarization‐induced covalent between H + and surface O presented at clay surface. Polarization‐induced covalent bonding energy increase with increasing electric field. Electrostatic and covalent bonding forces jointly determined clay aggregation.