Surface Of Soil Particles Research Articles

Clay charge reversal effects on aqueous polymer sorption on lateritic soils

The effects of charge reversal about the measured point of zero charge (pH 0 ≈ 5.2) of untreated and treated Sete Lagoas lateritic soil of Brazil on aqueous polymer sorption was investigated. The polymers are anionic sodium carboxymethyl cellulose (CMCA), nonionic polyethylene oxide (PEO), and cationic polyacrylamide (PAM). They were prepared at aqueous concentrations and pH ranges of 0.1–2.0 g l −1 and 2–9, respectively. Soil treatment involved the removal of iron oxides by treatment with dithionate–bicarbonate–citrate. Batch sorption test results show that the presence of iron oxides in lateritic soil tends to suppress sorption of CMCA (especially at pH = pH 0) and PEO (for the whole pH range) but has uncertain effects on cationic PAM sorption. CMCA sorption on the untreated soil improves on either side of pH 0, in direct proportionality to solution concentration, except at pH < 4.0, where disassociation of the polymer molecules may decrease sorption energy. Increase in the sorption of non-cationic polymers (CMCA and PEO) at pH > pH 0 is attributable to dispersion of clay, cation bridging and polymer molecular reconfiguration. For cationic PAM, electrostatic bonding to negatively charged soil particle surfaces accounts for the sorption increase. For treated soil samples, polymer sorption pattern is similar to those expected for the montmorillonitic clayey soils of temperate zones. These results indicate that the pH 0 of lateritic soils, within the regime that exists in the field, should be considered in assessing the potential effectiveness of polymer dust suppressants for tropical lateritic soils.

The form, distribution and mobility of arsenic in soils contaminated by arsenic trioxide, at sites in southeast USA

Soils from many industrial sites in southeastern USA are contaminated with As because of the application of herbicide containing As 2O 3. Among those contaminated sites, two industrial sites, FW and BH, which are currently active and of most serious environmental concerns, were selected to characterize the occurrence of As in the contaminated soils and to evaluate its environmental leachability. The soils are both sandy loams with varying mineralogical and organic matter contents. Microwave-assisted acid digestion (EPA method 3051) of the contaminated soils indicated As levels of up to 325 mg/kg and 900 mg/kg (dry weight basis) for FW and BH soils, respectively. However, bulk X-ray powder diffraction (XRD) analysis failed to find any detectable As-bearing phases in either of the studied soil samples. Most of the soil As was observed by scanning electron microscopy, coupled with energy dispersive X-ray spectroscopy (SEM/EDX), to be disseminated on the surfaces of fine-grained soil particles in close association with Al and Fe. A few As-bearing particles were detected in BH soil using electron microprobe analysis (EMPA). Synchrotron micro-XRD and X-ray absorption near-edge structure (XANES) analyses indicated that these As-rich particles were possibly phaunouxite, a mineral similar to calcium arsenate, which could have been formed by natural weathering after the application of As 2O 3. However, the scarcity of those particles eliminated them from playing any important role in As sequestration. Synthetic acid rain sequential batch leaching experiments showed distinct As leaching behaviors of the two studied soil samples: BH soil, which has the higher As content, showed a slow, steady release of As, while FW soil, with a lower As content, showed a much quicker release and lower overall retention of As upon leaching. Sequential chemical extraction experiments were carried out using a simplified 4-step sequential chemical extraction procedure (SCEP) previously developed to characterize the fractionation of As and better understand the different leaching behaviors of the two studied soils. It was shown that only about 50% of the total extractable As was removed by the first two extraction steps, which represented the most weakly bonded and readily available As for environmental leaching. Compared with the sequential leaching experiments, it was further indicated that only half of the As associated with phases extracted by the second SCEP step was mobilized by SPLP leaching. Although microwave-assisted acid digestion results showed similar Al and Fe contents in both soils, the sequential chemical extraction experiments indicated that BH soil has a much higher content of amorphous Al and Fe phases and that a comparably higher portion of soil As was associated with those materials. The experimental results suggest that remediation efforts for the contaminated sites can be directed towards enhancing the formation of more stable As-bearing compounds in the soils to reduce the environmental leachability of As.

Adsorption of heavy metals in glacial till soil

The charged sites on soil particles are important for the retention/adsorption of metals. Metallic counterions can neutralize the intrinsic charges on the surfaces of soil particles by forming complexes. In this study, efforts have been made to determine the effect of surface potential, pH, and ionic strength on the adsorption of four metal ions, hexavalent chromium Cr(VI), trivalent chromium Cr(III), nickel Ni(II) and cadmium Cd(II), in glacial till soil. Batch tests were performed to determine the effect of pH (2–12) and ionic strength (0.001–0.1 M KCl) on zeta potential of the glacial till soil. The point of zero charge (pH PZC ) of glacial till was found to be 7.0±2.5. Surface charge experiments revealed the high buffering capacity of the glacial till. Batch adsorption experiments were conducted at natural pH (8.2) using various concentrations of selected metals. The adsorption data was described by the Freundlich adsorption model. Overall glacial till shows lower adsorption affinity to Cr(VI) as compared to cationic metals, Cr(III), Ni(II) and Cd(II).

Determination of 3,6-dinitrobenzo[ e]pyrene in surface soil and airborne particles by high-performance liquid chromatography with fluorescence detection

We developed a sensitive analytical method and an efficient clean-up method to quantify 3,6-dinitrobenzo[ e]pyrene (3,6-DNBeP) in surface soil and airborne particles. After purification using a silica gel column and two reversed-phase columns, 3,6-DNBeP was reduced to 3,6-diaminobenzo[ e]pyrene by a catalyst column and analyzed by high-performance liquid chromatography (HPLC) with a fluorescence detector. 3,6-DNBeP was detected in all of the soil samples and airborne particles examined. The concentration of 3,6-DNBeP in surface soil and airborne particles was determined in the ranges of 347–5007 pg/g of soil and 137–1238 fg/m 3, respectively.

Non-linear radiation in the Boussinesq equation of the agricultural drainage

Water flow to subterranean drains is described by using the Boussinesq equation subjected to radiation type boundary conditions; these conditions establish a relationship between drainage flux and water head at the drain. Analyzed radiation conditions are a quadratic polynomial equivalent to the Hooghoudt equation and a power function; both conditions contain linear and quadratic radiations. Evidence is given that these last radiations correspond to the extreme probabilistic models of water flow proposed, respectively, by Purcell [Purcell, W.R., 1949. Capillary pressures their measurement using mercury and the calculation of permeability thereform. Petr. Trans., Amer. Inst. Mining Metall. Eng. 186, 39–48] and Childs and Collis-George [Childs, E.C., Collis-George, N., 1950. The permeability of porous materials. Proc. R. Soc., Ser. A 201, 392–405]. Hooghoudt type radiation results from a convex combination of extreme radiations using a reference flux and an interpolation factor as parameters. Power radiation is established from both fractal geometry concepts and partially correlated water flow by soil structure. This fractal radiation contains a reference flux and an exponent equal to double of the surface soil-particles fractal dimension with regards to Euclidean soil dimension. Considering that convex radiation is an approximation to fractal radiation, the least square method allows us to establish a relationship between the interpolation factor and the exponent of the fractal radiation. We use a numerical solution to the Boussinesq equation subjected to radiation conditions to describe a drainage experiment performed in the laboratory. The results shows that the cumulative drained depth is better represented by fractal and convex radiations rather than by extreme ones.

Chemical factors in soil freezing and frost heave

Chemical factors that are essential in frost heaving of soils are examined through consideration of the process of ice formation in soils and the role of temperature gradients in generating water potential gradients in freezing soils. Unfrozen films are maintained around soil particles in frozen soils. The osmotic potentials at the ice–water interface of the unfrozen films and in the frozen fringe, the thin zone between the frozen and unfrozen soil, generated by dissolved salts and exchangeable cations that satisfy soil particle surface charge, are controlled by the local temperature. The coldest location and the most negative osmotic potentials at the ice–water interface are located immediately below the base of the ice lens, in the unfrozen films that separate the underlying soil particles from the ice lens. An osmotic potential gradient is generated because the osmotic potential at the water–ice interface in the frozen fringe becomes less negative with increasing temperature and distance from the ice lens. As water freezes onto the ice lens, re-supply of water to the unfrozen film along the osmotic potential gradient is the temperature-gradient-induced mechanism that generates the force that lifts the overlying frozen soil. Models that recognize this driving mechanism should improve predictions of soil freezing and frost heave, analysis of contaminant transport in freezing and frozen soils, and other aspects of the soil-freezing and frost-heave processes.

Problem Soils of the Paddy Fields in the Eastern Coastal Plain of the Red River Delta, Vietnam

Although the Red River Delta is one of the grain cradles in the rice-producing areas of Vietnam, this area contains salt-affected area. In this study, we aim to clarify the distribution and characteristics of problem soils which have led to the land use condition as follows. The salt-affected land in the eastern region of the Red River Delta can be divided into two groups : one is the land affected by saline soils and the other is by acid sulfate soils. The acid sulfate soils in Hai Phong exhibit high ion concentrations adsorbed on the soil particle surface; their organic matter content assists in the high ion adsorption capability. The contribution of Na+ concentration to the Electric Conductivity (EC) value is considered to be influenced by seawater and there is a linear relationship between the Na + concentration and Electric Conductivity in Nam Dinh. The increase in the total salt particles represented by the Eelctric Conductivity value indicates the contribution of Na+ as opposed to Ca2+ and Mg2+. The contribution of Ca2+ and Mg2+ + is more than that of Na+. The influence of seawater on the paddy fields in Nam Dinh and in Hai Phong has resulted in a difference in the balance between Na+ and [Ca2+ and Mg2+] concentrations on the surface soil. The acid sulfate soil in Hai Phong exhibits high ion concentrations adsorbed on the soil particle surface. The Sodium Adsorption Ratio and Electric Conductivity values of the coastal agricultural soils can be evaluated with regard to the balance of the adsorbed cations on the soil surface.

The Factors and Assumed Mechanisms of the Hardening of Red Soils and Yellow Soils in Subtropical Okinawa Island, Japan

Red soils and Yellow soils in Okinawa Island have the problem of severe hardening in dry conditions. It is important for the improvement and management of these soils to make the factors and mechanisms that affect the soil hardening clear. For this purpose, the properties and the degree of hardening of 43 topsoil samples in upland fields in the central area of Okinawa Island were determined. The results showed that the clay content and pH values were positively related to the degree of hardening. It is well known that clayey soils become very hard by air-drying because of the remarkable shrinkage, however, the pH-dependency of soil hardening has not been reported. Some investigations on the cause of the pH-dependency suggested that some physico-chemical conditions such as charge on the surface of soil particles in high-pH conditions, and the remarkable shrinkage of alkaline soils due to a large amount of calcium ions, enhance the hardening of these soils. The pH-dependency of hardening was also observed in the Red soils and Yellow soils in Kyushu Island, and this phenomenon probably occurs in soils with properties similar to the Red soils and Yellow soils in Okinawa, such as some Ultisols, Alfisols or Inceptisols in tropical, subtropical or temperate regions in the world.

Characterization of Soil Particle Surfaces Using Adsorption Excess Isotherms

Measurement of adsorption excess isotherms of methanol-benzene mixtures was applied to the characterization of soil particle surfaces. The sorption capacity and Gibbs energy of sorption of the solid-liquid interface were determined for montmorillonite, three types of soil, and their humin fractions. The soils were found to be less polar or less hydrophilic than the clay, and the humin fraction of soils was found to be less hydrophilic than the whole soils. The soil and humin samples have heterogeneous surfaces which can be divided in two regions on the basis of their relative polarity. The x-axis intersection of the straight section of isotherm assigns the relative proportions of the hydrophilic and hydrophobic regions of the surface.

Processing contaminated soils and sediments by high power ultrasound

Following the successful application of high power ultrasound to some areas of mineral processing, attention was directed towards the remediation of contaminated soils and sediments. Laboratory experiments have produced high contaminant destruction rates with surprisingly low energy costs and work at pilot plant scale is under way. The process relies on the phenomenon of cavitation to destroy contaminants such as PCBs, polycyclic aromatic hydrocarbons and organochlorides which adsorb to the surface of soil particles because of their inherent hydrophobicity. Such chemicals persist in the environment because of their chemical stability and they bioaccumulate, posing a serious health threat to animals and humans. High power ultrasound allows low-cost, on-site remediation and circumvents many of the shortcomings posed by conventional remediation technologies. Results are presented for a range of contaminants and the underlying physics of the technology is explained.

Uptake and Translocation of Arsenic and Phosphorus in pho2 Mutant and Wild Type of Arabidopsis thaliana

ABSTRACT A pot experiment was conducted in a growth chamber to investigate the difference in arsenic (As) uptake and translocation by the pho2 mutant and wild type (WT) of Arabidopsis thaliana (L.) Heynh. The pho2 mutant had higher shoot phosphorus (P) and As concentrations than did WT, but had lower shoot P uptake and similar total shoot As uptake relative to WT because of its smaller shoot biomass. Similarly, root P uptake and As uptake were lower in pho2, but pho2 had similar root P and slightly higher As concentrations than those of WT. Furthermore, specific P and As uptake and P and As translocation from roots to shoots in pho2 were higher than in WT. The results indicate that a small portion of As may have been co-translocated with P from roots to shoots. Addition of 10 mg As kg− 1 enhanced the growth of WT without P addition. Addition of 10 mg P kg− 1 promoted plant yield and As uptake, and further addition up to 40 mg P kg− 1 reduced shoot and root As concentrations. The results indicate that the overall effect of phosphate on As accumulation in the plants may be related to competition between P and As on the surfaces of soil particles and plant roots.

Nitrogen and Carbon Dioxide Adsorption by Soils

High-resolution nitrogen (77 K) and carbon dioxide (273 K) adsorption at subatmospheric pressures has been studied for a range of model soils of various origins with different organic matter (OM) contents. It is demonstrated that N2 and CO2 molecules probe different regions of soil particles. Nitrogen is adsorbed primarily on the outer surface of soil particles, while CO2 has a higher affinity to OM domains. Low-pressure nitrogen adsorption reveals that soil particle surfaces consist of clay/mineral domains with discrete patches of OM. A linear correlation has been found between the CO2 uptake and the amount of organic carbon reduced per unit of the external surface area. A new method for discriminating the microporosity of soil particles and accessibility of OM has been proposed.

The Extract of Lead from Lead Contaminated Soil and its Enrichment

It is important to establish washing methods for contaminated soils by toxic metals such as lead in rifle shooting areas. In the lead-contaminated soils weathered after a long period, metal lead is extracted as ion, and is penetrated into the ground, depositing on the surface of soil particles or immersing into the pores of the particles mainly as a lead carbonate. Therefore it is difficult to remove lead from the weathered contaminated soils by conventional soil washing techniques such as sizing or gravity separation. In this study, a new method is proposed for removing lead from the contaminated soil. Lead components in the soil are extracted into the solution by sodium citrate as a chelating agent, and the extracted lead is precipitated on the surface of iron powder by redox reaction. Then the iron powder is recovered by physical separation techniques such as magnetic separation. Thermodynamic calculation showed that removal efficiency of lead was higher when leaching iron powder, sodium citrate, and lead carbonate simultaneously than when leaching first lead carbonate by sodium citrate and then adding iron powder to the lead citrate solution. This calculation result was supported by ICP and XRD results. The XRD pattern for the iron powder recovered by magnetic separation indicated that lead is present as solid form on the powder. The recovered powder would be used as a lead source in smelting process.

The pH-dependency of the Hardening of Red and Yellow Soils by Air-drying

The degree of the hardening of air-dried blocks was determined for forty-two samples of the Red soils and Yellow soils in the central area of Okinawa Island by an unconfined compression test. The result showed that the degree of hardening is positively correlated to clay content and soil pH. It is widely known that fine soils generally become hard by air-drying, however the mechanism of pH-dependency of soil hardening was not clear. Therefore some experiments were conducted in order to investigate four hypotheses concerning the pH-dependency of hardening, i.e. clay mineralogical characteristics, subtle differences in particle-size distribution, effects of high-pH condition itself and effects of the calcium ion that is usually abundant in high-pH soils. The result of these investigation suggested that the severe hardening of high-pH soils is caused by both some physico-chemical states of the surface of soil particles under high-pH conditions, and a large amount of the calcium ion that enhances the shrinkage of soil in the air-drying process. The enhancement of soil hardening will occur if the soil pH is raised by some inadequate soil managements such as overliming. Therefore, it is important for avoidance of the problem of soil-hardening in cultivated fields to conduct a suitable soil management based on enough soil pH information.

Modeling Sorption of Cd, Hg and Pb in Soils by the NICA-Donnan Model

Metal adsorption is an important process at the soil-solution interface that controls metal bioavailability and toxicity. In this study, batch adsorption experiments were conducted to investigate the binding of Cd, Hg and Pb in soils collected from around metal smelters in Quebec and Ontario, Canada. It was found that soil organic matter enhanced the retention of Cd, Hg and Pb. Assuming that the surfaces of soil particles behaved similarly to organic matter, we used the Non-Ideal Competitive Adsorption (NICA)-Donnan model to derive the parameters for surface complexation of the three metals. The shape of the Cd, Hg and Pb adsorption isotherms are briefly discussed with respect to the results of the experimental measurements and the model predictions. The average values of the NICA-Donnan model parameters could be used to give reasonable predictions of metal sorption in the soils of this study.

Effect of surfactant alkyl chain length on soil cadmium desorption using surfactant/ligand systems

The effect of surfactant alkyl chain length on soil Cd desorption was studied using nonionic surfactants of polyethylene oxide (PEO) of PEO chain lengths of 7.5 (Triton X-114), 9.5 (Triton X-100), 30 (Triton X-305), or 40 units (Triton X-405) in combination with the I − ligand. Triplicate 1 g soil samples were equilibrated with 15 ml of surfactant–ligand mixture, at concentrations of 0.025, 0.50 or 0.10, and 0.0, 0.168 or 0.336 mol/l, respectively. After shaking the samples for 24 h, the supernatant fraction was analyzed for Cd content to determine the percent of Cd desorbed from the soil. After five successive washings, 53%, 40% and 25% of Cd had been desorbed by 0.025, 0.050 or 0.10 mol/l of Triton X-114, respectively, in the presence of 0.336 mol/l of I −, whereas with the same conditions, Triton X-100 desorbed 61%, 57% and 56% Cd and either Triton X-305 or Triton X-405 desorbed 51, 40 and 14 to 16% Cd. The most efficient Cd desorption was obtained using 0.025 mol/l Triton X-100 in admixture with 0.336 mol/l I −. Increased surfactant concentration was detrimental to Cd desorption consistent with a process that blocked ligand access to the soil particle surface. After 5 washings,the cumulative cadmium desorption decreased with increasing surfactant alkyl chain length, indicating that the metal–ligand complexes are preferably stabilized by the micelles' hydrophobic octyl phenyl (OP) group rather than by the hydrophilic PEO group. In the absence of ligand, the surfactants alone desorbed less than 1% Cd from the contaminated soil, suggesting that the ligand, rather than the surfactant, extracts the metal, to be subsequently stabilized within the surfactant micelles.

Effect of Combined Application of Methyl Isothiocyanate and Chloropicrin on Their Transformation

Combining several soil fumigants to increase the broad spectrum of pest control is a common fumigation practice in current production agriculture. In this study, we investigated the effect of combined application of chloropicrin and methyl isothiocyanate (MITC) on their transformations and persistence in the environment. In aqueous solution, no direct reaction between MITC and chloropicrin occurred and relatively slow rates of hydrolysis of these compounds were observed in aquatic environments free of suspended solids. The transformation of chloropicrin, however, was accelerated in aqueous solution with MITC because of a reduction reaction with bisulfide (HS(-)), which is a by-product of MITC hydrolysis. In soil, when fumigants were applied simultaneously, the degradation of MITC was suppressed under the bi-fumigant application due to the inhibition of soil microbial activity and a possible abiotic competition with chloropicrin for a limited number of reaction sites on the surface of soil particles. However, the degradation rate of chloropicrin was significantly enhanced in the bi-fumigant soil system, which was primarily attributed to the reaction of chloropicrin and HS(-). Two sequential application approaches were developed to investigate the feasibility of the combined application of metam sodium (parent compound of MITC) and chloropicrin in soil and assess their potential effects on environmental fate. For both application sequences, the degradation of chloropicrin was accelerated and that of MITC, as a major breakdown product of metam sodium, was inhibited in soil.

Wet and dry deposition patterns of plutonium in Daejeon, Korea

Plutonium in wet and dry deposition samples collected monthly at the Korea Institute of Nuclear Safety (KINS), Daejeon, Korea was determined during the period from January 2000 to August 2000. Monthly 239,240Pu deposition in Korea showed a maximum in the spring season (March to May), which was several times greater than that in Japan and corresponds to a seasonal cycle of soil dust fallout originating from the East Asian arid areas. The trajectory analysis of dust storms suggests that 239,240Pu deposition in Korea in spring is originating from plutonium-bearing surface soil particles from the East Asian arid areas. A significant part of the 239,240Pu deposition in spring in Korea is attributable to dry deposition.

Study on size distribution of total aerosol and water-soluble ions during an Asian dust storm event at Jeju Island, Korea.

Soil dust particles transported from loess regions of the Asian continent, called Asian dust, highly influences the air quality of north-eastern Asia and the northern Pacific Ocean. In order to investigate the effects of these dust storms on the chemical composition of atmospheric aerosol particles with different size, measurements of size distributions of total aerosol and major ion species were carried out on Jeju Island, Korea during April 2001. Juju Island was chosen for the study because the levels of emissions of anthropogenic air pollutants are very low. A 5-stage cascade impactor was used to sample size-fractionated aerosol particles. Samples were analyzed for major water-soluble ions using Dionex DX-120 ion chromatograph. The average mass concentration of total aerosol was found to be 24.4 and 108.3 microg m(-3) for non-Asian dust and Asian dust periods, respectively. The total aerosol size distribution, measured during the non-Asian dust period, was bimodal, whereas the coarse particles dominated the size distribution of total aerosol during the Asian dust period. It was found that SO4(2-), NH4+ and K+ were mainly distributed in fine particles, while Cl-, NO3-, Na+, Mg2+ and Ca2+ were in coarse particles. Although SO4(2-) was mainly distributed in fine particles, during the Asian dust period, the concentrations in coarse particles were significantly increased. This indicates heterogeneous oxidation of SO2 on wet surfaces of basic soil dust particles. The NH4+ was found to exist as (NH4)2SO4 in fine particles, with a molar ratio of NH4+ to SO4(2-) of 2.37 and 1.52 for non-Asian dust and Asian dust periods, respectively. Taking into account the proximity of the sampling site to the sea, and the observed chloride depletion, coarse mode nitrate, during the non-Asian dust period, is assumed to originate from the reaction of nitric acid with sodium chloride on the surfaces of sea-salt particles although the chloride depletion was not shown to be large enough to prove this assumption. During the Asian dust period, however, chloride depletion was much smaller, indicating coarse nitrate particles were mainly produced by the reaction of nitric acid with surfaces of basic soil particles. Most chloride and sodium components were shown to originate from sea-salt particles. Asian dust aerosols, arriving at Jeju Island, contained considerable amounts of sea-salt particles as they passed over the Yellow Sea. Ca2+ was shown to be the most abundant species in Asian dust particles.

Ultrasonically aided mineral processing technique for remediation of soil contaminated by heavy metals

In this study, power ultrasound was used as aiding method for the mineral processing technique, which have recently been developed for the remediation of soil contaminated by heavy metal containing bullets, their broken parts and alteration products. Power ultrasound was used to disperse the soil to remove metals and metal compounds from soil particle surfaces instead of attrition conditioning. The soil diluted with water was treated using 22 kHz ultrasound power of 100 W up to 500 W. The effect of different ultrasonic treatment time and pulsation of ultrasound were studied on the purity of sink and float fractions in heavy medium separation process, screen fractions, and mineral concentrates and tailings from flotation process. Ultrasound enhanced the remediation of soil fractions in all the studied cases. Optimisation of the ultrasonic power will be done in the continuation study.