Surface Of Soil Particles Research Articles

Effects of Isopropanol/Ammonia Extraction on Soil Water Repellency as Determined by Atomic Force Microscopy

Extraction of soil with solvents is commonly used to isolate fractions of soil organic matter (SOM) thought to cause soil water repellency. Previous studies have assessed the efficiency of extraction procedures by determining sample water repellency and SOM content, before and after extraction, and the ability of extracts to render wettable materials repellent. Here we use atomic force microscopy (AFM) for the direct, high‐resolution examination of the effects of the most commonly used solvent (isopropanol/ammonia) on physicochemical properties of soil particle surfaces. Particles, from three pairs of wettable and water repellent sandy soils, were examined before and after Soxhlet extraction and following extract application to extracted soil material. Complementary evidence was provided by comparison with the effects of exposing clean sand to organic compounds of known composition. The extraction rendered all soils wettable and resulted in a reduction in particle surface area covered by SOM. Subsequent exposure of these wettable particles to extracts (i) re‐introduced some level of water repellency despite achieving only a minimal increase in SOM; (ii) led to a more uniform scatter of soft regions, indicative of SOM; but (iii) did not consistently recreate original surface features. The outcomes suggest that (i) although isopropanol/ammonia extraction may be able to isolate key compounds involved in causing water repellency, these compounds appear to be obtained in a form with little affinity for clean mineral surfaces; (ii) the extent and distribution of SOM on soil particle surfaces appears to be a critical factor in the expression of water repellency.

Dissolved organic matter release and retention in an alkaline soil from the Nile River Delta in relation to surface charge and electrolyte type

The sorption of dissolved organic matter (DOM) on surfaces of soil particles strongly depends on surface charge (SC). As anions and cations in soil solution affect SC, the sorption properties can also be modified by electrolytes. This issue is particularly important in alkaline soils. In order to describe the effect of electrolyte type on SC properties and DOM sorption we comparatively investigated in column and batch experiments the release and retention behaviors of DOM of a Vertisol from the Nile River Delta. As electrolytes we have chosen NaCl, Na 2SO 4, and CaCl 2, which are commonly found in soil solution. CaSO 4 was included to investigate the effect of gypsum application to the soil on the tested factors. The SC of the clay fraction was quantified at the initial soil pH of 8.3 at electrolyte concentrations of 0–10 mmol c l − 1 and a DOM application between 0 and 25 mg DOC l − 1 . The kind of anion had strong effects on SC of the clay fraction. At 10 mmol c L − 1 the SC was − 2.6 and − 4.1 mmol c kg − 1 for NaCl and Na 2SO 4, respectively. Strong negative SC at presence of Na 2SO 4 led to repulsive forces, which hindered the sorption of DOM on clay particles and induced high DOM release in column experiments. At 10 mmol c l − 1 concentration of CaCl 2 and CaSO 4, the values of SC were −0.9 and −0.7 mmol c kg − 1, respectively, indicating that Ca 2+ is much stronger adsorbed than SO 4 2 − under the alkaline conditions. In the DOM-clay system, most negative SC values were obtained in deionized water as compared to the electrolyte solutions, indicating that in the absence of electrolytes the strongest repulsive forces hindered the sorption of DOM on clay particles. The sorbed amounts of DOM on fine soil were large not only for both CaCl 2 and CaSO 4 electrolytes, but also for NaCl electrolyte with almost the same values. The fact that NaCl increased DOM sorption can be explained by soluble Ca 2+ and ion exchange as distinct amounts of Ca 2+ were released during percolation from the sample which stabilize DOM by Ca 2+ bridging. Despite some negative impact of applied SO 4 2 − on stable aggregation and DOM leaching, for agricultural practice the application of CaSO 4 is superior to that of CaCl 2, since the former removes Na + more efficiently.

Comparative analysis of mono- and polyelement adsorption of copper, lead, and zinc by an ordinary chernozem from nitrate and acetate solutions

Isotherms of mono- and polyelement adsorption of Cu2+, Pb2+, and Zn2+ by an ordinary chernozem were described by the Langmuir equation. The values of the adsorption constant k decreased in the range Cu2+ > Pb2+ ≫ Zn2+ for the monoelement adsorption from nitrate and acetate salt solutions, Cu2+ > Pb2+ > Zn2+ for the polyelement adsorption from nitrate solutions, and Pb2+ > Cu2+ ≫ Zn2+ for the polyelement adsorption from acetate solutions. The maximum adsorption (Cmax, ∞) of individual cations at the polyelement contamination was always lower than at the monoelement contamination because of the mutual competition. At the same time, the values of k for the polyelement adsorption were higher than those for the monoelement adsorption because heavy metals (HMs) interact with most of the specific adsorption centers. It was shown that the ratio between the content of exchangeable cations displaced from the soil exchangeable complex (SEC) into the solution and the content of adsorbed HMs decreased with the increasing concentration of adsorbed HMs. These values could be higher (for Cu2+), equal, or lower than 1 (for Pb2+ and Zn2+). In the former case, this was due to the dissolution of readily soluble salts at low HM concentrations in the SEC. In the latter case, this was related to the adsorption of associated HMs and the formation of new phases localized on the surface of soil particles at high HM concentrations in the SEC.

Influence of Electrostatic Field from Soil Particle Surfaces on Ion Adsorption–Diffusion

Despite the fact that soil is electrically neutral at a macroscopic scale, the potential gradient in the electric double layer (EDL) adjacent to the solid–liquid interface is not zero. The driving forces, therefore, must include the concentration gradient as well as the potential gradient for the adsorption or diffusion of charged ions in the soil. The purpose of this study was to theoretically and experimentally demonstrate that the electrostatic field in the EDL originating from surface charges will strongly influence cation adsorption and diffusion. The generalized linear theory for describing nonlinear diffusion was applied to a miscible displacement experiment in this study. Both theoretical analysis and experimental data showed that the electric field in the EDL exerted a significant influence on ion adsorption and diffusion. Calculation based on the generalized linear theory clearly demonstrated how the electric field from surface charges of soil particles affected the kinetics of adsorption. The experimental results of Mg2+ adsorption in soil and pure clay samples showed that the experimental data can be well represented by the new diffusion model that accounts for the influence of the electrostatic field from a charged soil particle surface. In contrast, the models established based on Fick's diffusion laws failed to give a theoretical interpretation for why ion distribution in the soil should obey Boltzmann distribution when equilibrium is reached and why a great discrepancy existed between Fick's laws and the experimental data. This study indicated that the exchange and diffusion processes occurring in the external electric field of the EDL are essentially the same process.

Proton Nuclear Magnetic Resonance (NMR) Relaxometry in Soil Science Applications

Proton NMR relaxometry is a very powerful tool for investigating porous media and their interaction with wa- ter or other liquids and the mobility and interaction of organic molecules in solution. It is commonly used in material sci- ence or earth science. However, it is only scarcely applied in soil science although it shows great potential for helping to understand water uptake into the soil matrix and processes occurring at the solid-liquid interface at soil particle surfaces. This review introduces proton NMR relaxometry in the context of soil science and discusses the most important applica- tions of the method in this field. Relevant results from different applications of NMR relaxometry in soils are described and research gaps identified. Some original data is presented concerning biofilm formation in soils, which was investi- gated using proton NMR relaxometry. NMR relaxometry is a sensitive, informative and promising method to study pore size distribution in soils as well as many kinds of soil physicochemical processes, among which are wetting, swelling or changes in macromolecular status. It is further a very helpful method to study interactions between molecules in soil or- ganic matter and can serve to study the state of binding of water or organic chemicals to soil organic matter. Relaxation times determined by NMR relaxometry are sensitive to various factors that play a role in soil-water interaction which is both an advantage and shortcoming of the method: NMR relaxometry can be applied to numerous investigations in soil science, but at the same time interpretation of the results may be very difficult in such complex and heterogeneous sys- tems like soils.

인공강우기에 의한 밭에서의 영양물질 배출특성 모의 - 시비량 및 경사도 변화 -

Various fundamental and practical theories and technologies are needed for the development of Best Management Practices (BMPs) to manage the problems. The objectives of this paper was to investigate the effect of fertilizer and Non-point suource (NPS) pollution discharges from the field. The effect of fertilizer application was measured with respect to 10 % and 20 % slopes, respectively, using artificial rainfall simulator. The effect of fertilizer application on runoff was not significant because the effect of slope and rainfall intensity were overwhelmed. Runoff from 20 % plots was 21 % larger than that from 10 % plots. While groundwater discharge from 10 % plots was about 70 % larger than that from 20 % plots. It was concluded that runoff and groundwater discharge were largely affected by slope. T-N concentration in groundwater was much higher than that in runoff for both 10 % and 20 % plots. While T-P concentration in groundwater was lower than that in runoff. It explained that T-N moved well through soil pores without adsorption and other chemical reactions but T-P was well adsorbed on the surface of soil particles.

Binding energies of monovalent anions with Fe/Al oxides based on ion activity and suspension Wien effect methods

Purpose Adsorption is one of the most important chemical processes at the interface between soil particles and water. It determines the quantities of plant nutrients and pollutants which can be retained on the surfaces of soil particles, and therefore, it is one of the primary processes that affect transport of nutrients and contaminants in soils. The Wien effect, i.e., the dependence of the electrical conductivity of soil suspensions on electrical field strength, has recently been proposed as the basis of a novel method to characterize energy relationships between cations and soil particles, but little attention has been paid to the binding energies of anions with soil particles. The aim of this study was to examine the Wien effect of three anions F−, Cl−, and NO 3 − in Fe/Al oxide suspensions and to investigate their binding energies with ion activity and Wien effect methods for comparison.

Greywater reuse for irrigation: Effect on soil properties

A controlled study of the effect of greywater (GW) irrigation on soil properties was conducted. Containers of sand, loam and loess soils were planted with lettuce, and irrigated with fresh water, raw artificial GW or treated artificial GW. Greywater was treated using a recirculating vertical-flow constructed wetland. Soil samples were collected every 10 days for the 40-day duration of the study, and plant growth was measured. Soils were analysed for physicochemical and biological parameters to determine changes caused by the different treatments. It was demonstrated that raw artificial GW significantly increased the development of hydrophobicity in the sand and loam soils, as determined by water droplet penetration time. No significant changes were observed for the loess soil under all treatments. Observed hydrophobicity was correlated with increased oil and grease and surfactant concentrations in the soil. Zeta (ζ) potential of the soils was measured to determine changes in the soil particle surface properties as a result of GW irrigation. A significant change in ζ-potential (less negative) was observed in the raw artificial GW-irrigated sand, whereas no difference was observed in the loam or loess. Soils irrigated with fresh water or treated GW exhibited no increase in hydrophobicity. Fecal coliform bacteria were absent or < 10 CFU g − 1 in soils irrigated with fresh water or treated GW, but at least 1 order of magnitude higher in raw artificial GW irrigated soils. Only in the last sampling event and only for the loess soil was plant growth significantly higher for fresh water irrigated vs. raw or treated GW irrigated soils. This study demonstrates that treated GW can be effectively irrigated without detrimental effects on soil or plant growth; however, raw GW may significantly change soil properties that can impact the movement of water in soil and the transport of contaminants in the vadose zone.

Phosphate affects the adsorption of tetracycline on two soils with different characteristics

Tetracyclines (TCs) have been widely used as feed additives in intensive livestock production, and are often detected in animal manure and agricultural soils. Their fate in the environment, e.g., adsorption, leaching and degradation, is influenced by soil characteristics. This study evaluated the adsorption of tetracycline (TC; H 3L) on two soils as affected by phosphate (P). Freundlich equations fit the adsorption data of TC on the soils well with high correlation coefficients (0.994–0.999). Compared with the control (without P addition), the K f values of TC after addition of 31 mg P l − 1 decreased from 9210 to 5700 on the Red soil (RS, Udic Ferrosols, with lower pH and organic matter), and from 3730 to 2470 on the Wushan soil (WS, Anthrosol, with higher pH and organic matter). Solution pH strongly affected TC adsorption on the soils with and without P. Addition of 31 mg P l − 1 as orthophosphate increased TC adsorption on the RS at pH < 4 and then decreased with further increasing pH. However, no significant influence of P on TC adsorption was observed on the WS in a wide pH range. Phosphate is known to convey negative charges to soil particle surface, which will decrease the zeta potential of the soils, and consequently affect TC adsorption on the soils. The adsorption model, in which species-specific sorption coefficients ( K di) were weighted by pH-dependent fractions of each species, fits the experimental data very well. The addition of P increased the sorption coefficients of H 3L + 00 about 123% and 14.1% on the RS and WS, respectively, while decreased the sorption coefficients of H 2L +−0 and HL +−−. Our results suggest that application of high rate of P fertilizer may enhance TC leaching, especially from the soils with variable charges.

디젤오염토양 복원 효율 증진을 위한 음이온/비이온 계면활성제 토양세척공정에 초음파 적용 영향

Ultrasound and Surfactant aided soil washing process has been shown to be an effective method to remove diesel from soils. The use of surfactants can improve the mobility of diesel in soil-water systems by increasing solubility of adsorbed diesel into surfactant micelles. However, a large amount of surfactant is required for treatment. In addition, synthetic surfactants, specially anionic, are more toxic and the surfactant wastewater is hard to treat by conventional wastewater treatments even by AOPs. Ultrasound improves desorption of the diesel adsorbed on to soil. The mechanisms are based on physical breakage of bonds by hot spot, directly impact onto soil particle surface, the fragmentation of long-chain hydrocarbons by micro-jet and microstreaming in the soil pores. The use of ultrasound as an enhancement method in both anionic and nonionic surfactant aided soil-washing processes were studied. And all experiments were examined proceeded under CMC surfactant concentration, frequency 35 khz, power 400 W, Soil-water ratio 1:3(wt%), particle size 0.24 ~ 2mm and initial diesel concentration. 20,000 mg/kg. Combination with ultrasound showed significant enhancements on all the processes. Especially, nonionic surfactant Triton-X100 with ultrasound showed remarkable enhancements and diesel removal rate enhanced by ultrasound helps desorpting of surfactant adsorbed onto soils which prevented decreasing surfactant activity.

Comparison Study between Mg&lt;sup&gt;2+&lt;/sup&gt;-K&lt;sup&gt;+&lt;/sup&gt; and Ca&lt;sup&gt;2+&lt;/sup&gt;-K&lt;sup&gt;+&lt;/sup&gt; Exchange Kinetics under Electric Fields at the Solid-Liquid Interface of Soil

Comparison study between Mg2+ and Ca2+ adsorption kinetics,as influenced by different particle surface potentials,was investigated by the miscible displacement technique.In this study,important new features of ion adsorption were discovered.(1) The initial stage of experiment the adsorption process had zero-order kinetics because of strong adsorption.First-order kinetics then resulted because of weak adsorption and the transition point from zeroorder to first-order kinetics was very sharp for each system.(2) At equivalent supporting electrolyte concentrations,the adsorption rate of Ca2+ is obviously faster than that of Mg2+,and the equilibrium adsorption capacity of Ca2+ is more than that of Mg2+.The coverage of Ca2+ on the solid soil particle's surface is also higher than that of Mg2+.(3) The differences between the relative effective charge coefficient and the surface electrochemical properties are the reason why the Ca2+,Mg2+ adsorption kinetics are different.(4) We also determined some important properties of the adsorbed ions such as the rate coefficients,the adsorption quantities,the surface coverage of the adsorbed ions and the distributed space in the fixed liquid film of the adsorbed ions.These parameters allow a future quantitative evaluation of the effects of different colloid surface potentials on the ion diffusion/adsorption kinetics.

Derivation of a Macroscopic Model for Transport of Strongly Sorbed Solutes in the Soil Using Homogenization Theory

In this paper we derive a model for the diffusion of strongly sorbed solutes in soil taking into account diffusion within both the soil fluid phase and the soil particles. The model takes into account the effect of solutes being bound to soil particle surfaces by a reversible nonlinear reaction. Effective macroscale equations for the solute movement in the soil are derived using homogenization theory. In particular, we use the unfolding method to prove the convergence of nonlinear reaction terms in our system. We use the final, homogenized model to estimate the effect of solute dynamics within soil particles on plant phosphate uptake by comparing our double-porosity model to the more commonly used single-porosity model. We find that there are significant qualitative and quantitative differences in the predictions of the models. This highlights the need for careful experimental and theoretical treatment of plant-soil interaction when trying to understand solute losses from the soil.

Interaction of phytases with minerals and availability of substrate affect the hydrolysis of inositol phosphates

The stability and activity of phytases in the soil environment may be affected by their sorption on soil particle surfaces and by substrate availability with important consequences for P cycling and nutrient bioavailability. This work evaluated the interaction of phytases with goethite, haematite, kaolinite, montmorillonite and two oxisol clays and investigated how this interaction is affected when myo-inositol hexakisphosphate (Ins P 6) was sorbed on the mineral surfaces. phyA histidine acid phosphatases of fungal origin were used and their ability to release orthophosphate from the Ins P 6-saturated minerals was evaluated. The phytases showed a high affinity for the mineral surfaces, with a loss of enzyme activity generally being observed over 24 h (up to 95% of the initially added activity). The loss of phytase activity was dependent on the type of mineral, with kaolinite and montmorillonite showing the greatest effect. Retention of enzyme activity was higher with the two oxisol clays, suggesting that the heterogeneous nature of clay surfaces and the presence of endogenous organic matter may limit the inhibition caused by interaction with minerals. In the presence of mineral surfaces saturated with Ins P 6, the partitioning of enzyme activity between the solution and the solid phase was shifted more towards the solution phase, presumably due to the mineral surfaces being occupied by the substrate. However, phytases were not able to release any orthophosphate directly from Ins P 6-saturated goethite and haematite, and hydrolysed Ins P 6 that was desorbed from haematite. Conversely, in the case of kaolinite and of the oxisol clays, where desorption was limited, phytases appeared to be able to hydrolyse a small fraction of the Ins P 6 adsorbed on the surfaces. These findings suggest that the bioavailability of P from inositol phosphates is governed to a large extent by the mineral composition of soil and by competitive effects for sorption on reactive surfaces among inositol phosphates and phytases.

Adsorption of dissolved nitrogen by forest mineral soils

Dissolved nitrogen (N) species, including ammonium (NH4+-N), nitrate (NO3–-N), and dissolved organic nitrogen (DON), are important nutrient sources in soils. The mobility of DON and NH4+-N in soil solutions is influenced by abiotic adsorption to mineral soil particle surfaces. We determined relationships between soil properties and their ability to adsorb NH4+-N, NO3–-N, and DON, using batch experiments. A range of 41 mineral horizons was collected from across Canada, including Podzols, Brunisols, Luvisols, Gleysols, and an organic soil. The adsorption of DON and dissolved organic carbon (DOC) were positively correlated (R2= 0.86), and both were best explained by the amount of iron and aluminum associated with poorly crystalline phases. Adsorption of NH4+-N was strongest in Gleysols and Luvisols, while adsorption of NO3–-N was weak in all soils. A reduction in the DOC:DON ratio was observed for most mineral horizons (89%) after equilibration from an original ratio of 35:1. Mineral horizons with a net desorption of DON had a significantly greater reduction in the final DOC:DON ratios than horizons with a net adsorption of DON. The results from this study found that while similar soil properties could predict DOC and DON adsorption, DON was slightly more mobile than DOC.

Wind erosion and soil carbon dynamics in south-western Australia

The incidence of wind erosion and its affect on soil organic carbon content was assessed in a dryland farming system near Jerramungup, Western Australia, using remote sensing, ground observations and soil analysis. Relationships were found between the patterns of wind erosion, past geomorphic processes and an array of soil attributes. These associations can be used to identify those soils that are most susceptible to erosion and thus soil carbon loss. Despite strong evidence of relict aeolian activity associated with a previous more arid climate, the incidence of contemporary wind erosion was only partly related to past geomorphological processes. Quartzose dune sands were particularly susceptible to erosion (47% of total area eroded), whereas texture contrast soils formed on clayey, wind-formed lunettes (16%) and deeply weathered regolith were less eroded (34%). Soils formed on stripped regolith and on loamy surfaced lunettes and swales were not eroded. Wind erosion was strongly related to soil particle size distribution and surface horizon depth, only occurring on sandy surfaced soils, with 50 cm deep. The incidence of erosion markedly increased with small decreases in clay and silt contents below these thresholds. Wind erosion resulted in the loss of ∼3% of the total stock of carbon to 1 m depth or 3.6 t C ha-1 for the eroded soils. The consideration of wind erosion induced carbon loss, both from the standpoint of sustaining farmland productivity and also in producing accurate national carbon accounts, at both the project and national scales, requires resolution.

Investigating the Fate of Nitroaromatic (TNT) and Nitramine (RDX and HMX) Explosives in Fractured and Pristine Soils

Explosives compounds, known toxins, are loaded to soils on military training ranges predominantly during explosives detonation events that likely fracture soil particles. This study was conducted to investigate the fate of explosives compounds in aqueous slurries containing fractured and pristine soil particles. Three soils were crushed with a piston to emulate detonation-induced fracturing. X-ray diffraction, energy-dispersive X-ray spectrometry, gas adsorption surface area measurements, and scanning electron microscopy were used to quantify and image pristine and fractured soil particles. Aqueous batches were prepared by spiking soils with solutions containing 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 2,4-dinitrotoluene (2,4-DNT). Samples were collected over 92 d and the concentrations of the spiked explosives compounds and TNT transformation products 2-amino-4,6-dinitrotoluene (2ADNT) and 4-amino-2,6-dinitrotoluene (4ADNT) were measured. Our results suggest soil mineralogical and geochemical compositions were not changed during piston-induced fracturing but morphological differences were evident with fractured soils exhibiting more angular surfaces, more fine grained particles, and some microfracturing that is not visible in the pristine samples. TNT, 2,4-DNT, RDX, and HMX exhibited greater analyte loss over time in batch solutions containing fractured soil particles compared to their pristine counterparts. 2ADNT and 4ADNT exhibited greater concentrations in slurries containing pristine soils than in slurries containing fractured soils. Explosives compound transformation is greater in the presence of fractured soil particles than in the presence of pristine soil particles. Our results imply fractured soil particles promote explosive compound transformation and/or explosives compounds have a greater affinity for adsorption to fractured soil particle surfaces.

Water Potentials Produced by Oven‐Drying of Soil Samples

Soil water content or potential can be adjusted in the laboratory by equilibrating the soil at different relative humidities. These relative humidities can be produced by the use of different saturated salt solutions or by heating the soil to different temperatures in a convection oven. Usually, the conditions for equilibrating the soil are expressed as relative humidities if salt solutions are used or as the temperature of drying if a convection oven is used. This dichotomy does not allow all the results to be compared or plotted on a common axis. In this paper, the Magnus–Tetens and the Arden Buck equations are used in combination with the Kelvin equation to show how the results from both types of equilibration can be presented on the same scale (e.g., water potential or pF). Two new equations show how the results from oven drying depend not only on the oven temperature, but also on the temperature and relative humidity of the air in the laboratory. For example, drying soil in an oven in one set of atmospheric conditions can produce a significantly different water potential than in different atmospheric conditions. The new equations enable the soil water potentials (or pF values) produced by oven drying to be calculated for all combinations of oven temperature and atmospheric conditions. Predictions from the equations are evaluated by comparing water retention data obtained by oven drying and by equilibration over saturated salt solutions. It is shown that the mean absolute error in gravimetric water content is 2.3 g kg−1 Equations are presented for the mean thickness of water films adsorbed on the surfaces of soil particles under different drying conditions. The amount of water adsorbed on particle surfaces is predicted to be zero at pF6.6.

Wien Effect Characterization of Interactions Between Ions and Charged Sites on Clay Surfaces of Variable-Charge Soils

To investigate the interactions of oppositely charged sites on the surfaces of variable-charge soil particles with cations and anions, and to evaluate the mean Gibbs free binding and adsorption energies of various cations on particles of red soil and latosol, clay fractions smaller than 2 μm were separated from samples of the two variable-charge soils. Ferric oxides were removed from part of the clay fractions, which were then saturated with various chlorides (NaCl, KCl, CaCl 2, CdCl 2 or LaCl 3). Electrical conductivities (EC) of dilute suspensions of the original and of the iron oxides-free clay fractions in deionized water were measured with the SHP-2 short high-voltage pulse apparatus, which enables measurement of the Wien effect at field strengths ( E) from 14 to 250 kV cm −1. The Wien effect (EC- E) curves revealed EC increases of red soil suspensions between 14 and 200 kV cm −1, of 8.3, 8.4, 12.1, 5.9, and 1.2 μScm −1 for NaCl, KCl, CaCl 2, CdCl 2, and LaCl 3, respectively, reflecting the differing interactions with the various cations and chloride. The EC increments with the iron-free red soil suspensions were higher, being 29.7, 17.2, and 15.3 μScm −1 for NaCl, CaCl 2, and CdCl 2, respectively. In the natural latosol suspensions the EC increments were practically zero, whereas in the iron-free fractions there were significant EC increments of 10.3, 5.7, 5.0, and 1.6 μScm −1 for NaCl, CaCl 2, CdCl 2, and LaCl 3, respectively.

Investigation of Surface Properties of Soil Particles and Model Materials with Contrasting Hydrophobicity Using Atomic Force Microscopy

Surface images and force measurements obtained using atomic force microscopy (AFM) were used to assess the hydrophobicity of particles from soils and model soil material (smooth glass and acid-washed sand (AWS) exposed to soil-derived humic acid (HA) or lecithin (LE)). Height and phase images, and phase distributions (from soil particles) show complex morphology and heterogeneously distributed organic matter. Forces at model surfaces indicate that, in air, reduction in adhesion corresponded with increased hydrophobicity, but in water, corresponded with a decrease (and serve to guide interpretation of data from natural particles). Adhesion forces on hydrophobic soil particles in water were larger than those for hydrophilic ones, but surface roughness and complexity may obscure any opposite trend for measurements in air. Combination of force measurements, applied forthe first time to soil particles, together with those on model surfaces, and independent assessments of hydrophobicity of corresponding single particle layers, indicate good, but not consistent qualitative agreement between hydophobicity at bulk and nanoscales. AFM is likely to facilitate detailed evaluation of soil particle surface hydrophobicity, which contributes to bulk wetting behavior of soils and other porous systems, including assessments of the potential for contributons to supehydrophobicity from surfaces at the micro- and nanoscales.

Effects of Chelating Agents on Zeta Potential of Cadmium-Contaminated Natural Clay

The effects of pH, ionic strength, cadmium concentration, and chelating agents on the zeta potential of a natural clay of high acid/base buffer capacity from Shanghai, China were investigated in this study, with a view to enhancing the efficiency of electrokinetic remediation of the cadmium-contaminated clay. An increase in the ionic strength of the background solution or cadmium concentration increases the zeta potential on soil particle surfaces, i.e., less negative. CAIW increases the zeta potential slightly but the effects are not pronounced. EDTA and phosphonates decrease the zeta potentials of soil particle surfaces, thus enhancing forward electroosmotic flow.