Soil Particle Interaction Research Articles

Influence of soil hysteretic damping on lateral response of offshore wind turbine monopile in sandy soil

Damping plays an important role in the design of offshore wind turbine structures. The hysteretic damping of the seabed soil represents the energy dissipation caused by the soil-particle interaction and the nonlinear behavior of the soil under cyclic loading. However, the effect of sand damping on the lateral response of the monopile foundation of an offshore wind turbine is still unclear. In this paper, the effect of soil hysteretic damping on the lateral dynamic response of a monopile foundation in a sandy seabed is investigated using a subplastic soil constitutive model. The constitutive model response at the foundation level is verified by comparing the monotonic and cyclic responses of the monopile with the results of the 1g model test. The results show that when soil hysteretic damping is present in the monopile-soil system, the energy dissipation in the soil reduces the stress accumulation in the soil, resulting in a reduction in the bending moment and horizontal displacement of the monopile, compared with the case without soil hysteretic damping. The results are crucial for optimizing the monolithic design of offshore wind turbine structures.

Calibration and Testing of Discrete Element Simulation Parameters for Ultrasonic Vibration-Cutter-Soil Interaction Model

This paper established an accurate discrete element for ultrasonic vibration-cutter-soil interaction model to study the interaction mechanism between the soil-engaging component and the soil. In order to reduce the interaction between calibration parameters and improve the calibration accuracy, it is proposed that the soil constitutive, contact parameters, and bonding parameters be calibrated by combining the soil repose angle experiment and the soil resistance experiment of ultrasonic vibration cutting. The study adopts the Hertz-Mindlin (no slip) contact model used in EDEM, to explore soil particle interactions. The central composite design is used to achieve systematic investigation. 3-factor 3-level orthogonal design experiment was employed using the coefficient of restitution, the coefficient of static friction, and the coefficient of rolling friction as key test factors and soil’s repose angle as the response index. Based on the Hertz-Mindlin with bonding contact model, Design-Expert 13.0 software was used to design the Plackett-Burman experiment, the steepest ascent, and the Box-Behnken experiment. With the maximum soil cutting resistance in ultrasonic vibration cutting experiment used as the response value, the adhesion parameters were optimized, and the optimal solution combination was obtained as: Normal Stiffness = 4.635 × 106 N/m, Shear Stiffness = 3.401 × 106 N/m, and Bonded Disk Radius = 2.57 mm. The optimal parameter combinations obtained from the calibration experiments were verified in two ways: ultrasonic vibration cutting and non-ultrasonic vibration cutting. The results showed that the errors between the simulation values and the actual values of the two comparative experiments were less than 5%, and the model calibrated for the three parameters can be used to study the drag reduction mechanism of ultrasonic vibration cutting in soil.

Internal Force Mechanism of Pisha Sandstone as a Soil Amendment to Improve Sandy Soil Structural Stability in Mu Us Sandy Land

Compounding Pisha sandstone (PSS) with sandy soil in Mu Us Sandy Land is a viable agronomical measure to effectively reduce soil erosion and improve soil quality due to the complementary characters and structures of the two materials. Aggregate stability is an important indicator to assess sandy soil erosion resistance and quality, which could be largely affected by soil surface electrochemical properties and particle interaction forces. However, the effect of the compound ratio and particle interaction forces on the aggregate stability of compound soils with Pisha sandstone and sandy soil is still unclear. Therefore, in this study, the electrochemical properties, particle interaction forces, and their effects on the aggregate stability of PSS and sandy soil at five volume ratios (0:1, 1:5, 1:2, 1:1, and 1:0) were determined to clarify the internal force mechanism of PSS to increase sandy soil structural stability in a 10-year field experiment. Experiments were measured by a combined method for the determination of surface properties and aggregate water stability. A ten-year field study revealed that the incorporation of Pisha sandstone significantly enhanced the soil organic carbon (SOC) and cation exchange capacity (CEC) (p < 0.05), while the CEC value notably increased from 4.68 to 13.76 cmol·kg−1 (p < 0.05). The soil surface potential (absolute value) and the electric field intensity gradually decreased with the increase in the Pisha sandstone content. For the compound soil particle interaction force, the addition of Pisha sandstone enhanced the van der Waals attraction force, reduced the net repulsive force between compound soil particles, and promoted the agglomeration of aeolian sandy soil. The overall trend of the aggregate breaking strength of compound soils under different addition ratios of PSS was 1:0 > 1:1 > 0:1 > 1:5 > 1:2. When the Pisha sandstone content in the compound soils was <50%, the aggregate stability was mainly influenced by compound soil particle interaction forces, and the interaction force increase was the key reason for the aggregate breakdown. When the Pisha sandstone content in the compound soils was ≥50%, the aggregate stability was affected by the combined effects of the compound soil particle composition and particle interaction forces. These results indicate that PSS addition ratios and particle interaction force are important factors affecting the structural stability of compound soils, in which the volume ratio of PSS to sandy soil of 1:2 is the appropriate ratio. Our study provides some theoretical references for further understanding of the compound soil structure improvement and sandy soil erosion control in Mu Us Sandy Land.

Interaction force mechanism for the improvement of reclaimed soil aggregate stability in abandoned homestead by different organic-inorganic soil conditioners

Reasonable application of organic-inorganic soil conditioners can effectively improve the structure and fertility of reclaimed soil in abandoned homestead. Aggregate stability is an important indicator to evaluate soil structure and fertility, and is largely influenced by soil internal forces (van der Waals attractive force, electrostatic repulsive force, hydration repulsive force) and particle surface properties. However, there are few studies on the influence of different soil conditioners on the reclaimed soil internal forces and its relationship with the aggregate stability. Therefore, we selected six different treatments of organic fertilizer (TO), fly ash (TF), maturing agent (TM), maturing agent + organic fertilizer (TMO), fly ash + organic fertilizer (TFO) and control (CK) to conduct a 5-year field experiment to study the effects of reclaimed soil particle interaction forces and surface characteristics on aggregate stability under the treatment of different soil conditioners. The results showed that with the application of soil conditioners, the soil organic matter (SOM), specific surface area (SSA), surface charge (σ0), cation exchange capacity (CEC), aggregate mean weight diameter (MWD) and Hamaker constant increased gradually, while the pH value decreased slightly. In particular, the MWD under the treatments of TFO and TMO increased by 150.3% and 65.6% respectively compared with that under the CK treatment. With the increasing application of soil conditioners, the electrostatic repulsive force and van der Waals attractive force between reclaimed soil particles increased constantly, but the net resultant force between particles decreased and the net attractive force increased continuously, thus improving the aggregate stability. Therefore, there is a significant negative correlation between the net resultant force among reclaimed soil particles and MWD and CEC. In addition, 10−2 mol L-1 is the critical concentration that affects the reclaimed soil internal force, and the organic-inorganic treatments of TFO and TMO can improve the net resultant force better. In a word, the particle interaction forces are important factors affecting the reclaimed soil structural stability, and this study provides a scientific reference for the rational selection of soil conditioners and its interaction force mechanism in the reclaimed soil improvement.

Impact of soil surface properties on soil swelling of different soil layers in collapsing wall of Benggang.

Benggang is one of the most serious soil erosion problems in tropical and subtropical areas in southern China. Little work has been reported on the surface properties of soil colloidal particle and its influence on soil swelling of different soil layers in collapsing wall of Benggang. In this present work, the effects of sodium concentration on soil swelling, and the correlations between soil swelling rates and soil colloidal surface properties were comprehensively evaluated by carefully examining soil physicochemical properties and soil colloidal surface properties of red, sandy and detritus soil layers from a collapsing wall. Our results showed that the soil swelling rates of red, sandy and detritus soil layers all exponentially decreased with increasing initial water contents. The relationship between soil swelling rate and the thickness of shear plane showed an extremely significant negative correlation for red soil layer and no correlation for sandy and detritus soil layers. Moreover, the elevating sodium concentrations reduced the thickness of shear plane from 39.69 to 0.76 nm for red soil layer, followed from 22.56 to 0.79 nm for sandy soil layer and from 18.61 to 0.64 nm for detritus soil layer. These findings indicated that the soil particle interactions played a crucial role in the development and occurrence of Benggang. This work will be helpful in understanding the mechanisms of soil mass loss on the gully head and collapsing wall of Benggang.

Polarisation‐induced covalent interactions between H+ and surface O atoms promote clay aggregation

AbstractAccumulation 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.

Coupling effects of humus and 2:1 type electrolyte on soil water movement

Recent studies have shown that, soil particle interaction forces strongly affect soil water movement. Classically, humus could increase the attractive forces through the complex interactions between humus and clay particles, but in the meanwhile humus could increase soil electric field and thus increase electrostatic repulsive forces due to surface charges of humus. On the other hand, electrolyte concentrations could affect soil particle interactions through the influence on soil electric field and osmotic pressure. Therefore, the effect of humus and electrolyte concentration would be coupled in soil water movement. In this study, the coupling effects were explored with a purple soil under different humus contents and MgCl2 concentrations. The results showed that: (i) the total repulsive energies among soil particles would increase with increasing humus content, and soil aggregate stability as well as the soil water transportation and infiltration would correspondingly decrease; (ii) a critical MgCl2 concentration was observed, and at the critical concentration the total repulsive energy was the lowest, while both the soil aggregate stability and soil water movement were the highest; (iii) humus content did not significantly change the critical concentrations. The analysis of water movement changing with soil particle interaction energy showed that, both of them decreased linearly with increasing total repulsive energies between soil particles, and different humus contents obeyed the same linear relationship for water movement. We concluded that, (i) the total repulsive energies between soil particles control soil water movement through their effect on soil aggregate stability; (ii) humus affected soil water movement mainly through its effect on the total repulsive energy between soil particles; (iii) the total repulsive energy was mainly from the electrostatic repulsive force among soil particles as MgCl2 concentration was lower than the critical concentration, while it was mainly from the osmotic pressure when the MgCl2 concentration was higher than the critical concentration.

Importance of soil interparticle forces and organic matter for aggregate stability in a temperate soil and a subtropical soil

Soil organic matter (SOM) and interparticle forces, including the electrostatic repulsive force (ERF), surface-hydration repulsive force (SHRF) and van der Waals attractive force (vDWAF), play crucial roles in aggregate stability. However, few studies investigated their coupled effects on aggregate stability in variably charged soils, in which soil particle interactions are more complex than in permanently charged soils due to the coexistence of positive and negative charges and the variable surface charge characteristics. Therefore, this study aims to: 1) investigate the combined effects of soil solution pH and the overlapping of electric double layers (EDLs) between positively charged Fe/Al (hydro)oxides and negatively charged SOM on the ERF and aggregate stability before (control) and after SOM removal and after straw incubation for 240 days; and 2) evaluate the importance of soil interparticle forces and SOM for aggregate stability in a permanently charged temperate soil (Vertisol) and a variably charged subtropical soil (Ultisol). Soil aggregate stability was determined by measuring the release of small particles (w(<d)%) after aggregate breakdown at different KCl concentrations (10−1 to 10−5 mol L−1). Soil solution pH was adjusted by varying KCl concentration. In both soils, the w(<d)% increased exponentially with the net force of the soil interparticle forces. However, in contrast to the Vertisol, the w(<d)% of the differently treated Ultisol showed almost no change before the KCl concentration decreased to 10−2 mol L−1 and continuous changes after the KCl concentration decreased to 10−2 mol L−1. In addition, the differences in the w(<d)% between the SOM removal treatment and the control and straw incubation treatments were much larger in the Ultisol than in the Vertisol. In the Ultisol, the ERF did exhibit little and continuous increase over the whole range of tested pH. When considering the impact of the overlapping of oppositely charged EDLs between Fe/Al (hydro)oxides and SOM, a much stronger reduction in ERF was observed in the control and straw incubation treatments and at lower KCl concentrations. Consequently, in both the Vertisol and Ultisol, aggregate stability is essentially controlled by the soil interparticle forces, whereas the effects of soil solution pH and the overlapping of oppositely charged EDLs between SOM and Fe/Al (hydro)oxides on the ERF must be considered in variably charged soils (i.e. Ultisol). Moreover, SOM can play a more important role in aggregate stability in subtropical soil than in temperate soil.

Effects of interactions between soil particles and electrolytes on saturated hydraulic conductivity

AbstractInteractions between soil particles can strongly affect water movement in soil. In this study, a model to predict soil saturated hydraulic conductivity based on interactions between soil particles was proposed. Firstly, a model of ion−soil particle interactions at the soil/water interface was established taking specific ion effects into account. Based on the ion–soil interaction model, the theoretical relationship between the sodium adsorption ratio and the surface potential was derived, and the surface potentials were calculated at different sodium adsorption ratios and electrolyte concentrations. Secondly, a theoretical expression of midpoint potential between two adjacent soil particles in a mixed 1:1 + 2:1 electrolyte solution (e.g., NaCl + CaCl2) was derived. The midpoint potential was estimated based on the calculated surface potential. Thirdly, the interaction pressure (repulsive pressure) between soil particles was quantified based on the obtained midpoint potential. Finally, an empirical model of the relationship between measured saturated hydraulic conductivity and maximum net repulsive pressure was proposed. The surface potential, electrostatic repulsive pressure and net pressure between soil particles in the presence of Na+ is higher than that of Ca2+ because the effective charge of the former (1.18) is smaller than that of the latter (1.98). Although the soil saturated hydraulic conductivities were substantially different in Na+ and Ca2+ solutions, they can be described as a function of maximum repulsive pressure between soil particles. Employing this empirical relationship, saturated hydraulic conductivities might be predicted in other soils at different sodium adsorption ratios. This work implies that the sodium adsorption ratio and electrolyte concentration control saturated hydraulic conductivity through affecting the electrostatic repulsive pressure between soil particles.Highlights A model of ion–soil particle interactions was established considering specific ion effects. The theoretical relationship between sodium adsorption ratio and surface potential was derived. The interaction pressure between soil particles in mixed electrolytes was quantified. An empirical model of the relationship between saturated hydraulic conductivity and net repulsive pressure was proposed.

Phosphorus transportation in runoff as influenced by cationic non-classic polarization: a simulation study

Phosphorus (P) transportation from agricultural soil to surface water is a major contributor to P pollution in the environment, and particle phosphorus (PP) transportation is the major contributor to the total P transportation. The intensity of soil particle interaction and transportation is strongly influenced by ion-surface reactions; however, quantitative study regarding the influence of soil particle interactions on P transportation during runoff is still lacking. A simulation study on P transportation of an Entisol during runoff was conducted in this study. To quantitatively characterize the non-classic polarizability of cations on P transport in runoff, the soil was first saturated with Li+, Na+, and K+. The saturated soil layer (5 cm × 5 cm area, 3-cm thickness) was packed in a synthetic glass tray for each experiment, and the slope of the soil surface was set as 30°. The runoff water was replaced by electrolyte solutions of KNO3, NaNO3, and LiNO3 with concentrations of 0.0001, 0.001, 0.01, and 0.1 mol/L, respectively, and the solution temperature was set as 298 K. The height of water dropping was set to 3 cm. Each runoff simulation experiment lasted for 90 min. Runoff and sediment were collected by time, and the solids and solution in the collected suspensions were separated by a high-speed centrifuge. The dissolved P (DP) in the supernatant and the PP in the sediment were measured. The amount of PP transportation for the K+ treatment was 45 or 69 times smaller than that for the Na+ and Li+ treatment. The amount of DP transportation for the K+ treatment was 1.7 times higher than that for the Na+ and Li+ treatment. Additionally, increasing soil electrolyte concentration decreased both PP and DP transportation from soil to surface water. Cationic non-classic polarization could quantitatively explain the observed experimental results in PP transportation. Soil could strongly enhance the polarizability of cations; the observed polarizabilities of K+, Na+, and Li+ reached 507, 124, and 45.8 A3, respectively, but their classic values are only 0.814, 0.139, and 0.0285 A3, respectively. K+ could strongly decrease PP transportation because K+ had the strongest polarizability. The cationic non-classic polarization strongly decreased the electric field around soil particles, thus strongly decreasing the electrostatic repulsive forces between adjacent soil particles in aggregate, which decreased PP transportation in runoff. K+ cation with larger non-classic polarizability, relative to Na+ and Li+, decreased the PP transportation. The soil electric field and specific ion effects were found to play an important role in DP transportation.

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

SummaryParticle 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 effects of NO3− and Cl− on negatively charged clay aggregation

Farmer’s experiences told us that, NO3− could strongly decrease soil aggregate stability and compact the soil, thus increase tillage difficulty and decrease tillage quality, but Cl− could not. It implies that, even though soil particles are often with net negative charges, NO3− and Cl− could cause different effects on soil particle interactions. The purpose of present study is to examine whether and how those two anions could influence the negatively charged clay particles interaction. In this study, the technique of multi-angle dynamic light scattering was used to study the aggregation kinetics of montmorillonite for the presence of NO3− and Cl− respectively. The results showed that, the aggregation rate of montmorillonite particles in NO3− solution was much lower than that in Cl− solution, and correspondingly the critical coagulation concentration and the activation energy for the presence of NO3− was much higher than that for the presence of Cl−. Zeta potential measurements implied that, the electrostatic repulsive force among the montmorillonite particles for the presence of NO3− would be much higher than that for the presence of Cl−, because the zeta potential of montmorillonite in NO3− solution was much higher than that in Cl− solution. Further measurements for the anion adsorption quantities showed that, under given solution conditions the adsorption quantity of NO3− was much higher than Cl−. We speculate that, the non-classic polarization of anion might be a possible explanation for those observations. Our study might give a reasonable explanation that NO3− could strongly decrease soil aggregate stability and tillage quality.

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

SummarySoil 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.

Effects of DLVO, hydration and osmotic forces among soil particles on water infiltration

SummarySoil water infiltration is closely associated with the transport of nutrients and contaminants in soil. The physical mechanism by which electrolyte concentration influences water infiltration is not clear, however. Recent studies have shown that interaction forces between soil particles play a crucial role in the stability of soil aggregates and pores, which further affects soil water infiltration. In this research, column experiments were used to elucidate the effects of soil particle interaction forces on water infiltration in a permanently charged and a variably charged soil using different concentrations of KNO3 solutions (0.0001, 0.001, 0.01 and 0.1 mol l−1), and some interesting results on soil water infiltration were discovered. They indicated that: (i) four forces in soil (long‐range van der Waals attractive, electrostatic repulsive, hydration and osmotic repulsive forces) co‐determined the rate of soil water infiltration for both soil types tested, (ii) at smaller soil water content (large electrolyte concentration) the osmotic repulsive force became more important in soil water infiltration, and yet with a larger water content (small electrolyte concentration) the electrostatic repulsive force became more important, and (iii) the osmotic force affected water infiltration through its effect on particle interaction forces rather than its influence on the osmotic potential of water. This paper presents a quantitative description of how particle interaction forces affect water infiltration into soil.HighlightsElucidation of physical mechanisms of effects of clay charge and electrolyte concentration on soil water infiltration. Quantified effects of interaction forces of soil particles on soil water infiltration. Electrostatic repulsive and osmotic forces play a critical role in water infiltration. DLVO, hydration and osmotic forces among soil particles co‐determined soil water infiltration rate.

Quantitative characterization of non-classic polarization of cations on clay aggregate stability.

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.

Particle Interaction Forces Induce Soil Particle Transport during Rainfall

Soil particle transport causes serious environmental problems, and particle interaction forces will be the controlling force for soil transport during rainfall. However, few reports can be found in literature concerning the quantitative evaluation of particle interaction forces on soil particle transport. In this study, purple soil was adopted to study soil particle transport under different force strength conditions of particle interaction during rainfall simulation with precipitation intensity of 150 mm h–1 for 110 min. We first analyzed soil particle interaction forces quantitatively under different KNO3 and Ca(NO3)2 concentrations (0.0001, 0.001, 0.005, 0.01, 0.05, 0.1, and 1 mol L–1) which adjusted surface potential of soil particle from –323 to –50 mV. The results indicated that the net Derjaguin–Landau–Verwey–Overbeek (DLVO) force could not solely cause soil particle transport during rainfall. The hydration repulsive force, which was much stronger than the DLVO force, played a crucial role in soil particle transport. During rainfall, soil particle in aggregate was separated to a distance of 1.5 to 2 nm by the strong hydration repulsive force (swelling process). Then aggregate was thoroughly broken by the electrostatic repulsive force. The hydration repulsive force dominated aggregate swelling, and the electrostatic force determined the transport intensity. We found that, at surface potentials lower than –100 mV, soil transport did not occur even precipitation intensity reaching 150 mm h–1; and –200 mV of surface potential was the critical potential for soil particle transport. We conclude that the surface hydration force and electrostatic repulsive force were the controlling force for soil particle transport during rainfall.

Heavy metal soil remediation: The effects of attrition scrubbing on a wet gravity concentration process

AbstractThe US military has historically conducted activities which have either directly or indirectly contributed to environmental contamination. Metal contaminated soil at military sites has resulted from operations such as weapons production, small arms training activities, metal cleaning, and metal plating activities.Soil washing is an effective approach to the treatment of contaminated soils employing both physical and chemical separation techniques. Physical separation methods encompass many different unit operations including screening, grinding, flotation, hydroclassification, attrition scrubbing and gravity concentration such as tabling and spiraling. The primary focus of this paper will be to address the effects of attrition scrubbing (an abrasive soil particle to soil particle interaction in a high solids environment), on a gravity concentration process.Soil from an Army small arms training range with lead contamination in the bulk soil at approximately 40,000 mg/kg, was evaluated using a WEMCO® Laboratory Attrition Scrubber in conjunction with a Wilfley® Laboratory Wet Shaking Table. Results indicate attrition scrubbing enhanced the physical separation process on the wet shaker table by liberating the Pb contamination from the bulk soil, which resulted in a large volume of clean soil while simultaneously producing a small volume of Pb concentrated soil. Laboratory tests indicate over 96% of the contamination could be concentrated on 20% of the original soil mass.