Quantitative Characterization of Non-Classic Polarization of Cations on Clay Aggregate Stability

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.

Sewage Sludge Amendment Combined with Green Manuring to a Coastal Mudflat Salt-Soil in Eastern China: Effects on Soil Physicochemical Properties and Maize Yield

“…The similar negative effects of ESP on soil aggregation were found by other studies [45][46][47]. This might be attributed to that sodium causes swelling and dispersion of soil mineral particles and slaking of unstable aggregates [45,48]. In addition, high ESP value can reduce microbial biomass and activity, which may also contribute to the decrease in aggregation [49].…”

EFFECT OF NONCLASSICAL POLARIZATION OF Na+ AND K+ ON THE STABILITY OF SOIL COLLOIDAL PARTICLES IN SUSPENSION

“…E®ect of Nonclassical Polarization of Na þ and K Therefore, the nonclassical polarization of ions has to be included in the surface potential 12,15 :…”

“…Tian et al 3 found that Li þ , Na þ , K þ , Rb þ and Cs þ exhibit substantially di®erent e®ects on the colloidal aggregation of inorganic clay minerals. Hu et al, 12 Xu et al, 13 and Li et al 14 found that Li þ , Na þ , K þ , and Cs þ are also signi¯cantly di®erent in terms of their involvements in soil aggregate stability and soil erosion processes. These researchers concluded that the interactions between soil particles and macroscopic phenomena result from ion-speci¯c e®ects induced by the interactions between ions and the electric¯eld on the particle surface.…”

Specific ion effects on soil water movement

“…Tian et al (2015) demonstrated that specific ion effects strongly influenced soil particle aggregation. Hu et al (2015b) and Xu et al (2015) further demonstrated that clay aggregate stability was strongly influenced by specific ion effects, which they found to have originated from ionic polarization in the soil electric field. The strength of the observed polarization was observed to be hundreds to thousands of times higher than that of classical polarization.…”

“…Recent studies have also shown that, in addition to the electrostatic (Coulombic) effects mentioned above, specific ion effects play an important role in particle interactions in aqueous solutions (Tian et al, 2014(Tian et al, , 2015, which will therefore strongly influence soil aggregate stability (Hu et al, 2015a(Hu et al, , 2015bXu et al, 2015), soil porous state, and thus soil water movement. Specific ion effects are also referred to as Hofmeister effects, which were first observed as far back as 120 years ago by Hofmeister through his study of protein aggregation (Kunz et al, 2004a(Kunz et al, , 2004b.…”