Abstract
Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10−5 to 10−1 mol L−1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation–surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability.
Highlights
Aggregate stability is important because it affects many properties and processes of soil, but is related to environmental problems
We found that the strong electric field from surface charges increased with decreasing electrolyte concentration, which determined the manner of soil aggregate swelling, dispersion, and explosion [16]
This study showed that it was not ion size, hydration, or dispersion forces in the cation–surface interactions but strong non-classic polarization of the adsorbed cations that resulted in the specific ion effects
Summary
Aggregate stability is important because it affects many properties and processes of soil, but is related to environmental problems. The liquid soil phase, which mainly contains water, and the chemical composition can greatly affect aggregate stability. Some studies have reported that increasing the electrolyte concentration of the bulk solution and/or adding high-valence ions to the bulk solution can decrease the electric field and improve the stability of aggregates [16,17]. These conclusions can be well understood by Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Levy and Van Der Watt [19] observed that ions had different abilities to maintain the aggregate stability, and followed the sequence Ca2+>K+>Na+. What happened about Hofmeister effects on aggregates stability does pay little attention to soil science hitherto
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
