Approach to theoretical estimation of the activation energy of particle aggregation taking ionic nonclassic polarization into account

It is well known that humus markedly increases soil aggregate stability, but at the same time strongly decreases the flocculation of clay particles in suspension. These seemingly inconsistent observations suggest the need for a deeper understanding of the physical mechanisms that govern clay–humus interactions. In this research, soil samples from an Entisol were used to explore the role of cationic polarization in humus‐increased soil aggregate stability and sodium (Na+) and potassium (K+) ions were used to characterize weak and strong polarization, respectively. The results showed that strong cationic polarization has a critical role in increased soil aggregate stability in the presence of humus. We concluded that, without cationic polarization, the effects of humus alone on soil aggregate stability were weak in the presence of monovalent metal cations. When we compared the individual contributions of humus and strong cationic polarization, the latter proved much more important than humus in increasing soil aggregate stability. The strongest increase in soil aggregate stability occurred when strong cationic polarization was coupled with humus. The combined analysis of activation energy of soil flocculation in suspension and soil aggregate stability in the presence of humus indicated that humus increased the long‐range electrostatic repulsive force of soil particles, and increased the short‐range attractive force of soil particles. Consequently, humus decreased the flocculation of soil particles in suspension but increased soil aggregate stability; all effects were adjusted by the strength of cationic polarization. Highlights Elucidation of physical mechanisms of cation–surface interactions that determine clay–humus interactions. Cations at the particle surface of the clay–humus complex are strongly polarized. Cationic polarization has a critical role in humus‐increased soil aggregate stability. Without cationic polarization, the effect of humus alone on soil aggregate stability was weak.

Section: Theory For Calculating Surface Potential Of Soil Particles Tmentioning

confidence: 99%

Role of cationic polarization in humus‐increased soil aggregate stability

Huang

et al. 2016

“…We characterized the rate of aggregation using the rate of total average aggregation (TAA) (Jia et al, ), which is defined by the equation given below (Jia et al, ; Tian et al, , ; Li et al, ):

{\overset{v}{true}}_{T} (f_{0}) = \frac{1}{t_{0}} \int_{0}^{t_{0}} \overset{true˜}{ν} (t, f_{0}) d t = \frac{1}{t_{0}} \int_{0}^{t_{0}} \frac{D (t) - D_{0}}{t} d t,

where

\overset{true˜}{ν}

T ( f 0 ) (nm minute −1 ) is the TAA rate, D ( t ) is the mean hydrodynamic diameter of clusters at time t (as shown in Figure ), D 0 is the initial mean hydrodynamic diameter of soil particles at t = 0 and t 0 is equal to 60 minutes in this study.…”

Section: Resultsmentioning

confidence: 99%

“…Repulsive electrostatic energy can be defined as the work required for a particle with a head area S (nm 2 ) to move from λ = b to λ = a in a repulsive space with the pressure distribution P E ( λ ) (Li et al ., ). Therefore, the repulsive electrostatic energy can be calculated with Equation :

E (c_{0}) = 101 S \int_{a}^{b} P_{normalE} (λ) d λ = 101 S \times A

where E ( c 0 ) is the repulsive electrostatic energy (J mol −1 ); a = 2 nm, b = 10 nm.…”

Section: Discussionmentioning

confidence: 97%

See 1 more Smart Citation

Effect of soil particle interaction forces in a clay‐rich soil on aggregate breakdown and particle aggregation

et al. 2018

Summary Particle aggregation and aggregate breakdown are important processes that frequently occur in soil under natural conditions. However, how these two opposing processes are affected by the forces that govern soil particle interaction remains unclear. Thus, in this research, we aimed to: (i) investigate the relation between particle aggregation and aggregate breakdown and (ii) probe the mechanism underlying particle aggregation and aggregate breakdown under the influences of soil particle interaction forces. Specifically, we investigated particle aggregation and aggregate breakdown in a permanently charged clay‐rich soil in solutions with different electrolyte (NaNO3 and Mg(NO3)2) concentrations. We used the fast wetting method in aggregate breakdown experiments and the dynamic light‐scattering method in aggregation experiments. For soils in either NaNO3 or Mg(NO3)2 solution, the critical coagulation concentration obtained through particle aggregation experiments was equal to the critical breakdown concentration from aggregate breakdown experiments. This result indicated that the net force, which is defined as the sum of the van der Waals, electrostatic and surface hydration forces, is attractive for aggregation but is repulsive for aggregate breakdown. Although several interaction forces were involved in soil particle interactions, we found that the repulsive electrostatic force solely determines whether the net force is attractive or repulsive and thus determines whether aggregation or breakdown would occur. For a given soil, non‐classical cationic polarization in cation–surface interactions strongly influenced the repulsive electrostatic potential energy of soil particles, thus influencing the occurrence of aggregation or breakdown. Our results suggested that adjusting soil internal forces is a feasible approach to regulate particle aggregation and promote aggregate stability. Highlights The process of soil aggregate breakdown and particle aggregation were evaluated quantitatively. There was equality in the opposing forces for particle aggregation and aggregate breakdown. Electrostatic repulsive force between soil particles controlled processes of aggregation and aggregate breakdown Cationic non‐classic polarization in cation–surface interactions has an important effect on aggregation and aggregate breakdown.

“…(), the charge number of cation Z in the equations can be replaced by γZ (Li et al . ), and the surface potentials of the two soils under different electrolyte concentrations could be estimated; the results are given in Table . On the other hand, to calculate the long‐range van der Waals attractive force, the Hamaker constant must also be given; for soil we take the Hamaker constant to be 7.8 × 10 −20 J (Yu et al ., ).…”

Section: Discussionmentioning

confidence: 99%

Coupling effects of surface charges, adsorbed counterions and particle‐size distribution on soil water infiltration and transport

Gong

Tian

2018

Summary Soil pores are the channels for water transport. The surface charges, the non‐classic polarizabilities and concentrations of the adsorbed counterions in a soil determine soil particle interaction forces that affect soil pore status. Particle‐size distribution is another important factor that affects soil pore status. Therefore, surface charges, adsorbed counterions and particle‐size distribution would probably be coupled in soil water transport. In this study, two soils with different surface charge densities, different adsorbed counterions and different particle‐size distributions were used to study their coupling effects on soil water movement. The results showed that these factors were strongly coupled in soil water movement. When the soil electric field strength was strong (depending on surface charges, adsorbed counterion polarizabilities and concentrations), the net interaction forces of soil particles was repulsive, thus soil aggregates could be broken. The degree of aggregate breakdown coupled with particle‐size distribution determined soil water movement. For this case we found that (i) increasing attractive forces of soil particles could greatly improve soil water movement and (ii) water movement was slow when the soil had large clay or small silt or sand contents. When the soil electric field was weak, the net interaction force of soil particles was attractive, thus aggregates could not be broken. For this case we found that (i) further increasing the attractive forces of soil particles could not improve soil water movement and (ii) water movement was fast when the soil had large clay or small silt or sand contents. Highlights Coupling effects of particle size and particle interactions on soil water movement are not clear. Large clay contents can decrease or increase soil water movement depending on soil particle interaction forces. Fast water movement occurred in soil with strongly polarized cations and large clay content. Particle interaction forces and particle‐size distribution were strongly coupled in soil water movement.