Surface Of Soil Particles Research Articles

The Variation Mechanism of Thermal Properties of Loess with Different Water Contents during Freezing

The thermal properties of soils are affected by many factors, such as temperature, water content, and structure. Based on the transient plane source method of thermal physics, the thermal properties of loess with different water content during the freezing process were tested. We analyzed the variation mechanism of thermal properties from the perspective of phase change. Based on the Pore/Particle and Crack Analysis System (PCAS) and theory of heat transfer, we then analyzed the microstructure and heat conduction process of loess. And a calculation model of volumetric heat capacity of frozen soil was presented. The results show that, in the major phase transition zone, the variation of the thermal properties of loess with temperature is the most significant. And the thermal diffusivity increases sharply with the significant increase of thermal conductivity and the rapid decrease of volumetric heat capacity. Moisture content not only increases the thermal conductivity and volume heat capacity of loess but also makes the influence of temperature on the thermophysical parameters more significant. The effect of temperature on thermal properties is mainly due to the change of heat transfer media caused by phase transition of water-ice, followed by the change of thermal properties of heat transfer media such as soil particles, water, ice, and air with temperature. Increasing the water content reduces the contact thermal resistance between soil particles because of the increase in the thickness of the water film on the surface of soil particles and the thermal conductivity of the heat transfer medium between particles, thus changing the thermal properties of soils.

Coupling of Hofmeister effect, electrolyte concentration, and mechanical composition in soil loss: Runoff simulation study

Electrostatic repulsive forces among soil particles control the intensity of soil loss in runoff and are controlled by the coupling of cation surface reactions (e.g., the Hofmeister effect), electrolyte concentration, and soil particle size composition. In this study, we used different concentrations of Li+, K+, and Cs+ to adjust the cation surface reaction or Hofmeister effect and electrolyte concentration of a neutral purple soil (Entisol). The mechanical composition of the soil was adjusted by adding 0.55–1 mm diameter quartz particles, and the mean surface potential of the soil particles was used to indirectly express the electrostatic repulsive force between particles. The results show that the Hofmeister effect, electrolyte concentration, and mechanical composition are strongly coupled during soil loss, of which the Hofmeister effect plays the most critical role. The physical mechanisms of the coupling effects can be summarized as follows. The electrostatic repulsive force among soil particles depends on the coupling of the Hofmeister effect and electrolyte concentration. Breaking intensity of the soil aggregate, which influences soil loss intensity in runoff, is determined by the electrostatic repulsive force and the production rate of the electrostatic repulsive force-which is controlled by the soil mechanical composition. We conclude that: (1) soil cation surface reactions are a key factor for determining the electrostatic repulsive forces and thus soil loss intensity in runoff; (2) for a given soil, the mechanical composition provides the basic factors that determine the production rate of the electrostatic repulsive force to break soil aggregates; and (3) increasing the soil’s large particle content enhances soil loss intensity but not necessarily soil loss quantity.

Beryllium-7 interception by cultivated plants on the slopes of the Yangtze river delta

The radionuclide, beryllium-7 (7Be) has been widely used as a nuclear trace element to study surface soil particle migration and identify sediment sources in short-term processes. In this study, we measured 7Be concentration in vegetation and its interception (7Be deposition intercepted by vegetation) and absorption from the atmosphere on the slopes of the Yangtze river delta. We report the concentrations of 7Be were highest in dry plants and lower in cultivated crops. 7Be interception amounts varied greatly among different plant species, with an average interception ratio of 7Be plant inventories to soil deposition of 13 ± 8%. There is a significant positive correlation between biomass and 7Be interception in natural and wild plants. The depositional 7Be was redistributed by the covering vegetation. This study provides an important basis for using 7Be as a tracer for soil erosion under vegetation cover.

The Influence Mechanism of Ettringite Crystals and Microstructure Characteristics on the Strength of Calcium-Based Stabilized Soil.

To reveal the influence mechanism of ettringite (AFt) crystals and microstructure characteristics on the strength of calcium-based stabilized soil, the strengths and microscopic properties of seven groups of stabilized soil samples were studied systematically through unconfined compressive strength, scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetry (TG), and Fourier transform infrared spectroscopy (FTIR) testing methods. The results indicate that the strength of the cement-stabilized soil is relatively high because abundant calcium silicate hydrate (CSH) gels coat the outer surface of soil particles to cement together. For the cement–gypsum-stabilized soil, superabundant thick and long AFt crystals make the pores in soil particles larger, and the sample becomes looser, resulting in lower strength than that of the cement-stabilized soil. However, the strength of the cement–gypsum–lime-stabilized soil is slightly stronger than that of the cement-stabilized soil, for the reason that the appropriate amount of fine AFt crystals fill the macropores between soil particles to form a network space structure and sufficient CSH gels cement the soil particles and the AFt crystals network space structure tightly together. It could be suggested that the components of calcium-based stabilizer should consider the optimal production balance between CSH gels and fine AFt crystals.

Sorption Mechanisms of Chemicals in Soils

Sorption of chemicals onto soil particle surfaces is an important process controlling their availability for uptake by organisms and loss from soils to ground and surface waters. The mechanisms of chemical sorption are inner- and outer-sphere adsorption and precipitation onto mineral surfaces. Factors that determine the sorption behavior are properties of soil mineral and organic matter surfaces and properties of the sorbing chemicals (including valence, electron configuration, and hydrophobicity). Because soils are complex heterogeneous mixtures, measuring sorption mechanisms is challenging; however, advancements analytical methods have made direct determination of sorption mechanisms possible. In this review, historical and modern research that supports the mechanistic understanding of sorption mechanisms in soils is discussed. Sorption mechanisms covered include cation exchange, outer-sphere adsorption, inner-sphere adsorption, surface precipitation, and ternary adsorption complexes.

Water infiltration into subcritical water-repellent soils with time-dependent contact angle

Soil water repellency, defined as the situation in which the affinity of soils to water is reduced, has been reported for many natural and agricultural soils worldwide. Soil water repellency has significant impacts on hydrology and geomorphology. It has been widely observed that the contact angle (CA) of a sessile water drop placed on a single-layer surface of water-repellent soil particles decreases in an exponential manner with time. This time-dependent CA has a substantial effect on flow in water-repellent soils. However, mathematical models aimed at modeling water flow in water-repellent soils disregard the time-dependent CA's effect. The current study aims to correct this omission. Using capillary rise of water with a time-dependent CA in a capillary tube, a model for water infiltration into subcritical water-repellent soils (CA < 90°) was developed. This model was successfully verified by performing infiltration experiments into (packed) coated glass beads. The CA at the wetting front during infiltration decreased exponentially to equilibrium, and the time to equilibrium was similar to that measured for a reference single layer of coated glass beads. Simulations for subcritical water-repellent soils with time-dependent CA yielded an infiltration rate that is either increasing with time (noted as concave) or initially increases and afterward decreases (noted as a concave-convex pattern).

Quantitative Analysis of Generalized Suction on the Shear Strength of Unsaturated Soils

Taking the shear strength as the characteristic index to measure the strength of the soil, a characteristic parameter is established that can describe the contact distance between the surface of soil particles—the mean value of particle contact density. Using the indoor direct shear test of the preset scheme, the first-hand test data that three different factors such as moisture content, dry density and grain size quantitatively affect the shear strength of soil are obtained. Through the establishment of the quantitative relationship between the mean value of particle contact density and the shear strength, the theoretical description of the influence law that several key elements such as moisture content, void ratio, gradation, and particle size on the shear strength of unsaturated soil is realized, and the theoretical description and quantitative analysis of the influence of generalized suction on the shear strength of unsaturated soils are also completed.

Efficient simultaneous removal of heavy metals and polychlorobiphenyls from a polluted industrial site by washing the soil with natural humic surfactants

We evaluated the effectiveness of natural organic surfactants such as humic acids (HA) from lignite to simultaneously wash heavy metals (HM) and polychlorobiphenyls (PCB) from a heavily contaminated industrial soil of northern Italy. Supramolecular HA promote in solution a micelle-like structure, where recalcitrant apolar organic xenobiotics are repartitioned from surfaces of soil particles during soil washing process. Concomitantly, the HA acidic functional groups enable a simultaneous complexation of HM. A single soil washing with HA removed 68 and 75% of PCB congeners for 1:1 and 10:1 solution/soil ratios, respectively. The same HA washing simultaneously and efficiently removed a cumulative average of 47% of total HM, with a maximum of 57 and 67% for Hg and Cu, respectively. We showed that washing a highly polluted soil with HA solution not only is an effective and rapid soil remediation technique but also simultaneously removes both HM and persistent organic pollutants (POP). Soil washing by humic biosurfactants is also a sustainable and eco-friendly technology, since, contrary to synthetic surfactants and solvents used in conventional washing techniques, it preserves soil biodiversity, promotes natural attenuation of unextracted POP, and accelerates further soil reclamation techniques such as bio- or phytoremediation.

Effects of Different Types of Fibers on the Physical and Mechanical Properties of MICP-Treated Calcareous Sand.

Microbial-induced calcite precipitation (MICP) has been a promising method to improve geotechnical engineering properties through the precipitation of calcium carbonate (CaCO3) on the contact and surface of soil particles in recent years. In the present experiment, water absorption and unconfined compressive strength (UCS) tests were carried out to investigate the effects of three different fiber types (glass fiber, polyester fiber, and hemp fiber) on the physical and mechanical properties of MICP-treated calcareous sand. The fibers used were at 0%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, and 0.40% relative to the weight of the sand. The results showed that the failure strain and ductility of the samples could be improved by adding fibers. Compared to biocemented sand (BS), the water absorption of these three fiber-reinforced biocemented sands were, respectively, decreased by 11.60%, 21.18%, and 7.29%. UCS was, respectively, increased by 24.20%, 60.76%, and 6.40%. Polyester fiber produced the best effect, followed by glass fiber and hemp fiber. The optimum contents of glass fiber and polyester fiber were 0.20% and 0.25%, respectively. The optimum content of hemp fiber was within the range of 0.20–0.25%. Light-emitting diode (LED) microscope and scanning electron microscope (SEM) images lead to the conclusion that only a little calcite precipitation had occurred around the hemp fiber, leading to a poor bonding effect compared to the glass and polyester fibers. It was therefore suggested that polyester fiber should be used to improve the properties of biocemented sand.

Adsorption of double-stranded ribonucleic acids (dsRNA) to iron (oxyhydr-)oxide surfaces: comparative analysis of model dsRNA molecules and deoxyribonucleic acids (DNA).

Double-stranded ribonucleic acid (dsRNA) molecules are novel plant-incorporated protectants expressed in genetically modified RNA interference (RNAi) crops. Ecological risk assessment (ERA) of RNAi crops requires a heretofore-missing detailed understanding of dsRNA adsorption in soils, a key fate process. Herein, we systematically study the adsorption of a model dsRNA molecule and of two double-stranded deoxyribonucleic acid (DNA) molecules of varying lengths to three soil iron (oxyhydr-)oxides - goethite, lepidocrocite, and hematite - over a range of solution pH (4.5-10), ionic strength (I = 10-100 mM NaCl) and composition (0.5, 1, and 3 mM MgCl2) and in the absence and presence of phosphate (0.05-5 mM) as co-adsorbate. We hypothesized comparable adsorption characteristics of dsRNA and DNA based on their structural similarities. Consistently, the three nucleic acids (NAs) showed high adsorption affinities to the iron (oxyhydr-)oxides with decreasing adsorption in the order goethite, lepidocrocite, and hematite, likely reflecting a decrease in the hydroxyl group density and positive charges of the oxide surfaces in the same order. NA adsorption also decreased with increasing solution pH, consistent with weakening of NA electrostatic attraction to and inner-sphere complex formation with the iron (oxyhydr-)oxides surfaces as pH increased. Adsorbed NA concentrations increased with increasing I and in the presence of Mg2+, consistent with adsorbed NA molecules adopting more compact conformations. Strong NA-phosphate adsorption competition demonstrates that co-adsorbates need consideration in assessing dsRNA fate in soils. Comparable adsorption characteristics of dsRNA and DNA molecules to iron (oxyhydr-)oxides imply that information on DNA adsorption to soil particle surfaces can inform dsRNA ERA.

十字槽开沟器横刀后掠角对土壤扰动的影响

The cross-slot opener is a new type of seeding opener. The sweep angle, which is a key structural parameter of the cross knife, has an important influence on soil disturbance. In this paper, discrete element method and tracer method are used to study the conditions of working speed of 0.83m/s and ditching depth of 130mm, the sweep angles of the transverse knife are 0°, 10°, 20°, 30°, 40°, respectively. The influence of time opener on soil disturbance and working resistance. The simulation analysis of the operation process of the cross groove opener shows that the trenching process under different sweep angles of the transverse knife is basically the same, and the standing knife is the main cause of soil disturbance; both the tracer method and the simulation results show the surface and shallow soil particle disturbance. The proportional and horizontal working resistance first decrease and then increase with the increase of the sweep angle of the cross-slot opener. When the sweep angle of the cross-slot opener is 20°, the micro-disturbance of soil particles and the horizontal work resistance are the least; The relative error of the soil disturbance ratio obtained by the tracer method and the discrete element method are both within 15%, and the relative error of the horizontal working resistance is 6.5%. The established discrete element simulation model can more accurately simulate the soil disturbance process of the cross-slot opener.

Possibility of impervious coating for the geotechnical reuse of soil and solid waste

Impervious coating treatment is an original technology which consists of coating of soil and solid waste by particle units with an impervious coating material (a sealing material) containing water-absorbent polymers. The elution of attached substances, such as heavy metals, from the surface of soil particles is suppressed. This is because each particle is uniformly coated with the sealing material. Furthermore, because the sealing material swells, due to the absorption of pore water, and fills the void spaces of the soil and solid waste, the water interception performance of the treated soil can be expected to improve. Through laboratory experiments, this study evaluated the basic characteristics, such as the elution of heavy metals and hydraulic conductivity, of soil and solid waste that have been treated with an impervious coating in order to investigate their reutilisation.

Exothermic adsorption of chromate by goethite

Goethite is a common Fe oxyhydroxide coating soil particle surfaces, which has a high Cr(VI) adsorption capacity under acidic pH conditions. Batch equilibrium adsorption experiments with chromate concentrations of 0.1, 0.2, and 0.3 mM were performed using solutions with ionic strengths of 0.1, 0.05, and 0.01 M and pH values of 3–11 and at four temperatures between 10 and 75 °C. The results of these experiments show that the amount of chromate adsorbed decreases as the pH increases towards the zero-point-of-surface-charge of goethite (pHPZC 9.1), which is typical for anions. The chromate adsorption efficiency also depends on the ionic strength of the solution. The amount of chromate adsorbed decreases as the ionic strength increases, indicating that outer-sphere surface complexation affects the adsorption process. The data were interpreted using the charge distribution multisite surface complexation (CD-MUSIC) model framework. Variations in the complexation constants with temperature were fitted using the two-term van't Hoff equation to give partial molar enthalpy and entropy constants. The enthalpies were negative, indicating that chromate adsorption is exothermic, whereby outer-sphere binding was found to be less exothermic (ΔrGOS,298 −62.19 kJ mol−1) than inner-sphere binding (ΔrGIS,298 −112.25 kJ mol−1). The adsorption strength, therefore, decreases as the temperature increases because of the exothermic nature of surface complexation.

The influence of sample preparation techniques on results of extraction of heavy metals from soil

A study of the composition of mobile compounds of heavy metals (HM) in the area of aerosol contamination by a heat supply company showed an increase in the number of these compounds near the source of contamination. In the group of loosely bound compounds, the largest part is represented by specifically sorbed compounds. Sample preparation (the degree of sample grinding) had a noticeable effect on the extractability of Zn, Cu, and Pb from the soil. During the sifting of a soil sample through a 0.25 mm sieve, the extraction of mobile forms of HM increases significantly (by 7–16 %). Thus, with an increase in the specific surface of soil particles, the extracting ability of the reagents increases. It is necessary to take into account the sample preparation used in each fractionation method to evaluate the results and compare them.

Electrical double layer interactions between soil colloidal particles: Polarization of water molecule and counterion

The electrical double layer (EDL) interactions strongly affect aggregation and dispersion of soil colloidal particles. In this research a modified model taking the polarization of water molecule and counterion into account was proposed based on nonlinear Poisson-Boltzmann theory to describe electrostatic interaction. The polarizations of both the counterion and the water molecule can increase the interaction between ion/water and soil particle surface, and then decrease the surface potential. Particle surface potential also depends on the surface separation when the EDL overlaps. The midpoint potential between colloidal particles decreases with increase of ion polarization but increases in the presence of water polarization through the change of the double layer thickness. Both the electrostatic repulsive pressure between soil particles and its force range increase markedly in the presence of the polarization of water molecules, but decrease with increase of counterion polarization. The water molecule polarization, rather than the counterion polarization, contributes more to EDL interactions. The counterion polarization is the origin of Hofmeister effects of the EDL interactions, which is affected by water polarization. The theoretical predicted force curve between clay particles by the modified model was verified by the experimental determination of surface force. In addition, the hydration force, fitted to a double exponential decay function, can be estimated by subtraction of the electrostatic interaction force based on DLVO theory from that based on the present model.

Selectivity of aggregate fractions for loess soils under different raindrop diameters

Raindrop impact causes splash erosion, the initial form of water erosion, which splashes and disperses surface soil particles. To date, there have been several wide-ranging studies of the Loess Plateau; however, a single soil type was generally studied. This meant that the large differences in the characteristics of different soil types because of variation in topography and soil-forming conditions were disregarded. The objectives of this research were to clarify the soil aggregate splash characteristics of different soil types under different rainfall conditions on the Loess Plateau. This study analysed the soil aggregate mass and distribution of aggregate fractions from splash erosion under six rainfall conditions (raindrop size: 2.67–5.45 mm) at five splash distances (0–10, 10–20, 20–30, 30–40 and 40–50 cm). Five types of soil on the Loess Plateau were selected for this research. The results showed that soil properties had a greater effect on aggregate distribution in splash. With the increase in raindrop diameter, the mass from splash erosion of Lou, Linnamon and Dark loessial soils increased. The mass from splash erosion of Loessial and Aeolian sandy soils, however, showed a variable trend as the raindrop diameter increased to a peak at a diameter of 4.05 mm. Soil types with smaller clay contents were more likely to be transported under high rainfall intensity, and increasing raindrop diameter can transport more soil and also break down aggregates. For the same soil type, the distribution of splash aggregate fractions was similar at different splash distances, and the splash mass decreased exponentially as the splash distance increased (P < 0.001). The Aeolian sandy soil had the largest splash mass for each splash distance, and its resistance to soil erosion was poor. A model was developed to predict the splash mass using the soil erodibility factor, splash distance, raindrop diameter and raindrop intensity. Our findings indicated that compared with rainfall conditions, soil properties had a greater effect on aggregate distribution from splash, indicating that improved soil structure is the main factor that can reduce the water erosion damage.

Desiccation Cracking Behavior of Clayey Soils Treated with Biocement and Bottom Ash Admixture during Wetting–Drying Cycles

Desiccation cracking considerably impairs the hydraulic and mechanical properties of clayey soils that are critical to the long-term performance of infrastructure foundations and earth structures. Typical crack remediation methods are associated with high labor and maintenance costs or the use of environmentally unfriendly chemicals. Recycling waste materials and developing biomediated techniques have emerged as green, sustainable soil stabilization solutions. The objective of this study was to investigate the feasibility of soil crack remediation through use of bottom ash admixtures and microbial-induced calcite precipitation (MICP). We carried out cyclic wetting–drying tests to characterize the effects of bottom ash and MICP on the desiccation cracking behaviors of bentonite soils. Two groups of soil samples that contained different percentages of bottom ash (0%, 20%, 40% by weight) were prepared for cyclic water and MICP treatments, respectively. The desiccation cracking patterns captured by a high-resolution camera were quantified using image processing. We also employed scanning electron microscopy for microstructural characterizations. Experimental results revealed that cyclic water treatment resulted in more cracking, whereas cyclic MICP treatment improved soil strength owing to the precipitation of calcite crystals on the soil particle surface and inside the interparticle pores. Adding bottom ash to bentonite reduced the plasticity of the mixture, promoted the flocculation of clay particles by cation exchange, and also provided soluble calcium to enhance calcite precipitation. This study demonstrates the potential of bottom ash and MICP for crack remediation and brings new insights into the design and assessment of sustainable infrastructures under climate changes.

Mineralogy and microstructure effects on the stiffness of activated slag treated alluvium

Alkali-activated alumino-silicate-based industrial waste products have recently proven to be beneficial as low-carbon alternatives to ordinary Portland cement binders for strengthening soft soils. This paper examines the small-strain stiffness behaviour of a UK silty alluvial soil in its natural state and artificially cemented using sodium hydroxide-activated ground-granulated blast-furnace slag (GGBS). Undrained triaxial testing with bender element measurements revealed that the initial small strain shear stiffness (Gmax), shear strength and hydraulic conductivity of the alluvium were all significantly enhanced after 28 d curing. Microstructural and mineralogical analyses were carried out on stabilised soil to understand the mechanisms better through which the enhanced engineering performances were achieved. Through hydration and pozzolanic reactions, a significant proportion of the clay minerals within the original soil had been converted into new cementitious hydrates. These were observed to infill pore spaces, coating soil and GGBS particle surfaces and increased interparticle bonding throughout the matrix of the material. The outcomes from this study have the potential to contribute towards improving current practices for modelling cemented soils and ultimately making geotechnical designs involving deep soil mixing less conservative.

Evaluating a new injection method of liquid/gas mixture spray injection via performing long-term in situ bioremediation tests

During in situ bioremediation, continuous injection of growth substrates such as carbon sources, electron donors, or electron acceptors inevitably results in microbial growth, resulting in biological clogging in an aquifer. Therefore, for successful bioremediation, development of a new injection method is needed to reduce or alleviate this clogging problem. In this study, we carried out field tracer tests using single-well push-pull tests (SWPPTs), single-well natural gradient drift tests (SWNGDTs), and long-term in situ well-to-well tests to develop and evaluate a new method of liquid/gas mixture spray injection. The effectiveness of the new method was evaluated by estimating the factors as follow: longitudinal dispersivity (αL), radius of influence (RI), shear stress on the surface of aquifer particles (σ), biofilm-shear-loss rate (Rs), and the ratio of volume occupied by cells grown to the original pore volume. At the tested site, the liquid/gas mixture spray injection method turned out to have several advantages compared to the traditional solution injection method: 1) transport of solute to a larger proportion of an aquifer by a factor of 1.3–1.7, 2) application of higher shear stress onto the surface of soil particles by a factor of 4.2–5.0, 3) faster biofilm sloughing rates by a factor of 2.3–2.6, 4) reduction in the ratio of the volume occupied by microorganisms to total pore volume (Volmicrobes/Volpore), and 5) efficient trichloroethylene (TCE) dechlorination for a period of 550 days without any injection problems. This new injection method showed positive effects on the hydrogeological and physical characteristics of the system, thus alleviating the biological clogging problem.

Soil organic matter and silt contents determine soil particle surface electrochemical properties across a long-term natural restoration grassland

Vegetation restoration is an effective way to rebuild degraded ecosystems and restore soil function. Soil surface electrochemical properties, including specific surface area, cation exchange capacity, surface charge density, surface electric field strength, and surface potential, are often used as indicators to evaluate agricultural soil quality and fertility. However, little attention has been payed to the effect of natural revegetation on soil surface electrochemical properties. In this work, we selected a grassland restoration chronosequence (slope cropland, 0 years; natural grasslands restored for 3, 8, 22 and 24 years, i.e. NR3, NR8, NR22 and NR24, respectively) to investigate the changes of soil surface electrochemical properties along with vegetative restoration. Our results showed that surface charge density and surface potential for restored grassland ranged from 0.16 to 0.20 C m−2 and from −94 to −109 mV, with an average of 0.18 C m−2 and −101 mV, respectively. The value of surface electric field strength could reach to the order of magnitude of −107 V m−1 and showed a decreasing trend with increasing period of natural vegetation recovery. Cation exchange capacity and specific surface area significantly increased with the extension of natural restoration period except for NR3 (P < 0.05). It was found that soil organic matter (SOM) and silt content were the main factors to determine cation exchange capacity and specific surface area. Both cation exchange capacity and specific surface area were closely related to silt content but weakly related to clay content, possibly due to the high silt content in our studied soils. Moreover, cation exchange capacity and specific surface area showed a significant linear relationship with SOM, which may be ascribed to the diversity in cation substitution sites and high specific surface area of SOM. Our results indicated that the long-term natural restoration of grassland contributed to the improvement of cation exchange capacity and specific surface area.