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Exchange Capacity (exchange + capacity)

Distribution by Scientific Domains
Polymers and Materials Science35%
Earth and Environmental Science30%
Life Sciences13%
Chemistry13%
Engineering7%

Kinds of Exchange Capacity

  • cation exchange capacity
    		•
  • ion exchange capacity
    		•

    Selected Abstracts

    Characterization of an Area Polluted by Copper and Zinc: the Relation between Soil Texture, Mineralogy and Pollutant Concentration

    ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 6 2009
    Caterina RINAUDO
    Abstract: Twenty-four soil samples were collected at three depths from an approximately 2.5 acre contaminated site in southern Piedmont (Italy) and then analyzed. The main soil parameters determined were: pH, Cation Exchange Capacity (CEC), particle size distribution, total organic carbon (TOC) content and retained metal concentration. The mineral phases were identified by X-Ray Powder Diffraction (XRPD). All of the samples contained Zn and Cu resulting from industrial contamination during the last century, and those obtained at depths of 20,40 cm consistently showed the highest levels. To determine which size fraction was most active in the retention process, the samples were separated into four fractions (,2 mm, ,63 ,m, ,30 ,m and ,2 ,m) and the amount of pollutant measured in each. It was found that metal retention was the highest in the clayey fraction, whose clay minerals were identified by XRPD after K+ and Mg2+ saturation, glycerol treatment and heating to 550° C. The clayey fraction was also the richest in TOC, and a direct correlation between TOC amount and metal retention was observed. [source]

    Biodegradable Polylactide and Its Nanocomposites: Opening a New Dimension for Plastics and Composites

    MACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2003
    Suprakas Sinha Ray
    Abstract The academic and industrial aspects of the preparation, characterization, mechanical and materials properties, crystallization behavior, melt rheology, and foam processing of pure polylactide (PLA) and PLA/layered silicate nanocomposites are described in this feature article. Recently, these materials have attracted considerable interest in polymer science research. PLA is linear aliphatic thermoplastic polyester and is made from agricultural products. Hectorite and montmorillonite are among the most commonly used smectite-type layered silicates for the preparation of nanocomposites. Smectites are a valuable mineral class for industrial applications because of their high cation exchange capacities, surface area, surface reactivity, adsorptive properties, and, in the case of hectorite, high viscosity, and transparency in solution. In their pristine form, they are hydrophilic in nature, and this property makes them very difficult to disperse into a polymer matrix. The most common way to overcome this difficulty is to replace interlayer cations with quaternized ammonium or phosphonium cations, preferably with long alkyl chains. In general, polymer/layered silicate nanocomposites are of three different types: (1) intercalated nanocomposites, in which insertion of polymer chains into the layered silicate structure occurs in a crystallographically regular fashion, regardless of polymer to layered silicate ratio, with a repeat distance of few nanometer; (2) flocculated nanocomposites, in which intercalated and stacked silicate layers are sometimes flocculated due to the hydroxylated edge,edge interactions between the silicate layers; (3) exfoliated nanocomposites, in which individual silicate layers are uniformly distributed in the polymer matrix by average distances that totally depend on the layered silicate loading. This new family of composite materials frequently exhibits remarkable improvements in its material properties when compared with those of virgin PLA. Improved properties can include a high storage modulus both in the solid and melt states, increased flexural properties, a decrease in gas permeability, increased heat distortion temperature, an increase in the rate of biodegradability of pure PLA, and so forth. Illustration of the biodegradability of PLA and various nanocomposites. [source]

    Sulfonated poly(phenylene oxide) membranes as promising materials for new proton exchange membranes

    POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2006
    Shifang Yang
    Abstract Poly(phenylene oxide) (PPO) was sulfonated to different ion exchange capacities (IECs) using chlorosulfonic acid as the sulfonating agent. Tough, ductile films were successfully cast from sulfonated PPO (SPPO) solutions in N -methyl-2-pyrrolidone or N,N -dimethylformamide. The obtained membranes had good thermal stability revealed by thermogravimetric analysis (TGA). Compared with an unsulfonated PPO membrane, the hydrophilicity and water uptake of the SPPO membranes were enhanced, as shown by reduced contact angles with water. The tensile test indicated that the SPPO membranes with IEC ranging from 0.77 to 2.63,meq/g were tough and strong at ambient conditions and still maintained adequate mechanical strength after immersion in water at room temperature for 24,hr. The results of wide-angle X-ray diffraction (WAXD) showed amorphous structures for PPO and SPPO while the peak intensity decreased after sulfonation. The proton conductivity of these SPPO membranes was measured as 1.16,×,10,2,S/cm at ambient temperature, which is comparable to that of Nafion 112 at similar conditions and in the range needed for high-performance fuel cell proton exchange membranes. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Rock weathering creates oases of life in a High Arctic desert

    ENVIRONMENTAL MICROBIOLOGY, Issue 2 2010
    Sara Borin
    Summary During primary colonization of rock substrates by plants, mineral weathering is strongly accelerated under plant roots, but little is known on how it affects soil ecosystem development before plant establishment. Here we show that rock mineral weathering mediated by chemolithoautotrophic bacteria is associated to plant community formation in sites recently released by permanent glacier ice cover in the Midtre Lovénbreen glacier moraine (78°53,N), Svalbard. Increased soil fertility fosters growth of prokaryotes and plants at the boundary between sites of intense bacterial mediated chemolithotrophic iron-sulfur oxidation and pH decrease, and the common moraine substrate where carbon and nitrogen are fixed by cyanobacteria. Microbial iron oxidizing activity determines acidity and corresponding fertility gradients, where water retention, cation exchange capacity and nutrient availability are increased. This fertilization is enabled by abundant mineral nutrients and reduced forms of iron and sulfur in pyrite minerals within a conglomerate type of moraine rock. Such an interaction between microorganisms and moraine minerals determines a peculiar, not yet described model for soil genesis and plant ecosystem formation with potential past and present analogues in other harsh environments with similar geochemical settings. [source]

    Ni2+ removal from aqueous solutions using conditioned clinoptilolites: Kinetic and isotherm studies

    ENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 1 2009
    Semra Çoruh
    Abstract The aim of this study is to investigate the effects of conditioning with NaCl and HCl solutions on removal of Ni2+ ions from aqueous solutions using natural clinoptilolite. Batch studies were performed to evaluate the effects of various parameters such as chemically conditioning, adsorbent amount, contact time, initial pH of the solution, mixing temperature, and initial metal ions. The results clearly showed that the conditioning improved both the exchange capacity and the removal efficiency. Langmuir, Freundlich, Temkin, and Dubinin-Kaganer-Radushkevich (DKR) isotherm models were adopted to describe the adsorption isotherms. Adsorption isotherms of Ni2+ ions could be best modeled by Langmuir equation. Three simplified models including pseudo-second-order, intraparticle diffusion and Elovich were used to test the adsorption kinetics. These results indicate a significant potential for the natural and conditioned clinoptilolites as an adsorbent/ion-exchange material for heavy metal removal. © 2008 American Institute of Chemical Engineers Environ Prog, 2009 [source]

    Zeolite synthesis employing alkaline waste effluents from the aluminum industry

    ENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 2 2002
    A. La Iglesia
    Zeolites 4A, 13X, Y, and HZSM5 have been synthesized from alkaline residues from aluminum finishing plants. These residues could contain concentrations of sodium aluminate and sodium hydroxide between 200 and 300 Kg/m3, and small concentrations of heavy metal cations (Cd, Co, Cr, Cu, Mn, and Zn). These contaminants make handling and disposal of these residues difficult. However, the physicochemical properties of the synthesized zeolites (cation exchange capacity of 3 mmol g,1, specific surface area between 600,900 m2g,1, particle size distribution between 0.5,2 ,m and whiteness of 97%) make them useful as detergents and catalysts. Analysis of the chemical composition of the raw materials and the reaction products demonstrates that the heavy metal cation content in the synthesized zeolites is low enough to allow their industrial use (lower than that of the original residues). Therefore, the production of various types of zeolites for industrial use could be used for the elimination of these residues from the aluminum industry. [source]

    Soil factors controlling the toxicity of copper and zinc to microbial processes in Australian soils

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2007
    Kris Broos
    Abstract Two soil microbial processes, substrate-induced nitrification (SIN) and substrate-induced respiration (SIR), were measured in the topsoils of 12 Australian field trials that were amended separately with increasing concentrations of ZnSO4 or CuSO4. The median effect concentration (EC50) values for Zn and Cu based on total metal concentrations varied between 107 and 8,298 mg kg,1 for Zn and 108 and 2,155 mg kg,1 Cu among soils. The differences in both Zn and Cu toxicity across the 12 soils were not explained by either the soil solution metal concentrations or CaCl2 -extractable metal concentrations, because the variation in the EC50 values was larger than those using total concentrations. Toxicity of Zn and Cu decreased with increasing soil pH for SIN. For Cu, also increasing cation exchange capacity (CEC) and percent clay decreased the toxicity towards SIN. In contrast to SIN, soil pH had no significant effect on toxicity values of SIR. Significant relationships were found between the EC50 values for SIR and background Zn and CEC for Zn, and percent clay and log CEC for Cu. Relationships such as those developed in this study will permit Australian environmental regulation to move from single-value national soil quality guidelines to soil-specific quality guidelines and permit soil-specific risk assessments to be undertaken. [source]

    Factors influencing the sorption of oxytetracycline to soils

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2005
    Aaryn D. Jones
    Abstract Veterinary antibiotics such as oxytetracycline (OTC) increasingly are found in the environment and often come into direct contact with soils via the release of animal wastes. Oxytetracycline is known to sorb strongly to soils by interaction with soil organic matter, clay minerals, and metal oxides. However, current knowledge of the influence of soil properties on OTC sorption is limited, as is our ability to predict OTC sorption to soils. This work was aimed at identifying properties that most influence the extent of OTC sorption in a suite of soils from the eastern United States representing a wide range in soil properties. Thirty soils were well characterized, an OTC soil-water distribution coefficient (Kd) was determined for each soil, and statistical analyses were employed to determine appropriate soil descriptors of OTC sorption. Soil texture, cation exchange capacity, and iron oxide content seemed to most influence the extent of OTC sorption in soils with organic carbon (OC) content between 0 and 4%. Thus, the knowledge of these three soil properties would be key to anticipating the extent of OTC sorption and gaining insight into OTC fate within a given soil system. Notably, OC content appeared to influence OTC sorption only in a soil with 9% OC. [source]

    Impact of common European tree species on the chemical and physicochemical properties of fine earth: an unusual pattern

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2010
    L. Mareschal
    Case studies are necessary to assess the effects of changes to tree species on the physicochemical and chemical properties of soils. To achieve this, the fine earth under five tree species was investigated. This study was performed in the Breuil-Chenue experimental forest site located in the Morvan Mountains (France). This site contains two adjacent blocks with replicated stands. The native forest (old beech and oak coppice with standards) was partially clear-felled and replaced in 1976 with mono-specific plantations of European beech, Norway spruce, Laricio pine and Douglas fir. The same changes in soil properties were revealed in both blocks, thus confirming the tree species effect. The percentage of exchangeable acidity on the cation exchange capacity (CEC) was greater under spruce, Douglas fir and pine than under the other species. Spruce stands, and to a lesser extent those of Douglas fir and pine, had a less acidic soil pH than hardwood stands (which was unusual in view of the data in the literature) and smaller CEC values. The small quantities of carbon added to the soil under these tree species provide an explanation for these effects through a partial control of both CEC and pH. This case study thus demonstrated that the tree species effect was not unequivocal and different criteria are necessary for its interpretation. Tree species significantly influenced certain aspects of the chemical properties of topsoil and have the potential to have an impact on current soil fertility. [source]

    Cation exchange in forest soils: the need for a new perspective

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2008
    D. S. Ross
    Summary The long-term sustainability of forest soils may be affected by the retention of exchangeable nutrient cations such as Ca2+ and the availability of potentially toxic cations such as Al3+. Many of our current concepts of cation exchange and base cation saturation are largely unchanged since the beginnings of soil chemistry over a century ago. Many of the same methods are still in use even though they were developed in a period when exchangeable aluminium (Al) and variable charge were not generally recognized. These concepts and methods are not easily applicable to acid, highly organic forest soils. The source of charge in these soils is primarily derived from organic matter (OM) but the retention of cations, especially Al species, cannot be described by simple exchange phenomena. In this review, we trace the development of modern cation exchange definitions and procedures, and focus on how these are challenged by recent research on the behaviour of acid forest soils. Although the effective cation exchange capacity (CECe) in an individual forest soil sample can be easily shown to vary with the addition of strong base or acid, it is difficult to find a pH effect in a population of different acid forest soil samples. In the very acidic pH range below ca 4.5, soils will generally have smaller concentrations of adsorbed Al3+. This can be ascribed to a reduced availability of weatherable Al-containing minerals and a large amount of weak, organic acidity. Base cation saturation calculations in this pH range do not provide a useful metric and, in fact, pH is modelled better if Al3+ is considered to be a base cation. Measurement of exchangeable Al3+ with a neutral salt represents an ill-defined but repeatable portion of organically complexed Al, affected by the pH of the extractant. Cation exchange in these soils can be modelled if assumptions are made as to the proportion of individual cations that are non-specifically bound by soil OM. Future research should recognize these challenges and focus on redefining our concepts of cation retention in these important soils. [source]

    Using soil knowledge for the evaluation of mid-infrared diffuse reflectance spectroscopy for predicting soil physical and mechanical properties

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008
    B. Minasny
    Summary Mid-infrared diffuse reflectance spectroscopy can provide rapid, cheap and relatively accurate predictions for a number of soil properties. Most studies have found that it is possible to estimate chemical properties that are related to surface and solid material composition. This paper focuses on prediction of physical and mechanical properties, with emphasis on the elucidation of possible mechanisms of prediction. Soil physical properties that are based on pore-space relationships such as bulk density, water retention and hydraulic conductivity cannot be predicted well using MIR spectroscopy. Hydraulic conductivity was measured using a tension-disc permeameter, excluding the macropore effect, but MIR spectroscopy did not give a good prediction. Properties based on the soil solid composition and surfaces such as clay content and shrink-swell potential can be predicted reasonably well. Macro-aggregate stability in water can be predicted reasonably as it has a strong correlation with carbon content in the soil. We found that most of the physical and mechanical properties can be related back to the fundamental soil properties such as clay content, carbon content, cation exchange capacity and bulk density. These connections have been explored previously in pedotransfer functions studies. The concept of a spectral soil inference system is reiterated: linking the spectra to basic soil properties and connecting basic soil properties to other functional soil properties via pedotransfer functions. [source]

    A model incorporating the diffuse double layer to predict the electrical conductivity of bulk soil

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2007
    M. A. Mojid
    Summary A model has been developed to predict the electrical conductivity of bulk soil. The total soil-water content is divided into free water and water in the diffuse double layer (DDL) around clay particles. These two fractions of soil water conduct electrical current through the soil and are assumed to act in parallel with the soil solid. The volume of water in the DDL is evaluated from the surface area of the clay and the thickness of the DDL. The surface area of the clay is estimated from its cation exchange capacity (CEC) and surface charge density. A transmission coefficient correcting for the effect of the tortuous flow path of current through the soil, and a proportionality constant relating the electrical conductivity of water in the DDL to that of free water, are included in the model. The transmission coefficient is a function of the contents of water and clay and has been modelled in terms of these factors. The values of the proportionality constant and those relating to the transmission coefficient were optimized for five different soils. The electrical conductivities of the five soils estimated by the model compare well with the measured values, which, however, deviate systematically from predictions by the three-component model of Rhoades et al. [source]

    Effect of earthworm activity (Aporrectodea giardi) on atrazine adsorption and biodegradation

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2006
    T. Alekseeva
    Summary We investigated the influence of earthworm (Aporrectodea giardi) activity on soil properties and on atrazine (AT) adsorption and biodegradation by comparing a coarse-textured smectite-free wetland soil (Brittany, France) with the earthworm casts derived from the top horizon of this soil. Casts are characterized by lower pH, are enriched in organic carbon (OC) and clay content, have a larger cation exchange capacity, and a greater exchangeable Ca content. The clay mineralogy of the soil studied and casts is characterized by a muscovite,kaolinite,chlorite association. In addition, the clay fraction of the soil contains lepidocrocite (,-FeOOH), which was not found in the casts. Atrazine adsorption isotherms were reasonably well described by the Freundlich equation and were all non-linear. The mean amounts of adsorbed AT for starting concentrations of 3,30 mg litre,1 ranged from 8 to 34%, being largest in earthworm casts. Soil AT adsorption capacity was well correlated with OC content. Non-decomposed organic matter present in the coarse size fractions and specific compounds present in earthworm casts (proteins, mono- and polysaccharides, polyphenols, sugars, lignin) and microbial and fungal biomass contribute to AT adsorption. Weak electrostatic (physical) sorption of AT on organic compounds and on mineral surfaces prevails. For casts, the formation of additional hydrophobic interactions between AT and SOM is proposed. We also studied AT biodegradation by the model bacterium Pseudomonas sp. strain ADP in the presence of soils or earthworm casts. An enhancement of the AT disappearance rate was observed in the presence of all the solid matrices tested compared with that obtained in an aqueous medium. The biodegradation rate was shown to be dependent not only on the OC content of the solid matrix, but mainly on its composition and structure. [source]

    Concentrations of Ag, In, Sn, Sb and Bi, and their chemical fractionation in typical soils in Japan

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2006
    H. Hou
    Summary We determined concentrations of Ag, In, Sn, Sb and Bi, and fractionated them by sequential extraction procedures, in five Japanese soils: Andosol-1 (grassland), Andosol-2 (forest), Cambisol (forest), Fluvisol (vegetable garden) and Regosol (forest). Average concentrations of Ag, In, Sn, Sb and Bi were 0.17 ± 0.08, 0.081 ± 0.019, 2.2 ± 0.5, 0.83 ± 0.32 and 0.32 ± 0.12 mg kg,1, respectively. Average distributions of the chemical fractions (omitting those with an abundance < 5%) were: Ag, residual (60%) > H2O2 -extractable, organically bound (H2O2 -Org) (18%) > metal,organic complex-bound (Me-Org) (10%) > amorphous metal oxide-bound (am-MeOx) (8.3%); In, residual (61%) > H2O2 -Org (12%) > Me-Org (8.7%) , crystalline Fe oxide-bound (cr-FeOx) (8.2%) > am-MeOx (7.4%); Sn, residual (40%) > Me-Org (19%) > carbonate-bound (12%) > cr-FeOx (9.0%) > H2O2 -Org (7.8%) > am-MeOx (6.9%); Sb, residual (34%) > Me-Org (18%) > am-MeOx (16%) > cr-FeOx (8.9%) , H2O2 -Org (8.7%) > easily reducible metal oxide-bound (re-MeOx) (6.8%) > carbonate-bound (6.1%); Bi, am-MeOx (26%) , H2O2 -Org (26%) > Me-Org (19%) > residual (17%) > cr-FeOx (12%). Proportions of the mobilizable (exchangeable + carbonate-bound + Me-Org + re-MeOx) metal fractions were in the order Sn , Sb > Bi > Ag ? In, and Cambisol > Andosol-2 > Regosol > Andosol-1 > Fluvisol. The proportions were predicted by multiple regression equations including pH, surface area, C contents, cation exchange capacity and clay content of the soils as independent variables (R2 > 0.96, P < 0.02). [source]

    Neural network models to predict cation exchange capacity in arid regions of Iran

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2005
    M. Amini
    Summary Design and analysis of land-use management scenarios requires detailed soil data. When such data are needed on a large scale, pedotransfer functions (PTFs) could be used to estimate different soil properties. Because existing regression-based PTFs for estimating cation exchange capacity (CEC) do not, in general, apply well to arid areas, this study was conducted (i) to evaluate the existing models and (ii) to develop neural network-based PTFs for predicting CEC in Aridisols of Isfahan in central Iran. As most researches have found a significant correlation between CEC and soil organic matter content (OM) and clay content, we also used these two variables for modelling of CEC. We tested several published PTFs and developed two neural network algorithms using multilayer perceptron and general regression neural networks based on a set of 170 soil samples. The data set was divided into two subsets for calibration and testing of the models. In general, the neural network-based models provided more reliable predictions than the regression-based PTFs. [source]

    Characterizing organic matter of soil aggregate coatings and biopores by Fourier transform infrared spectroscopy

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2004
    R. H. Ellerbrock
    Summary In some soils, aggregate coatings and walls of biopores differ in the content of clay and organic carbon from that of the aggregate interiors or the soil matrix. The composition of the organic matter on aggregates and on the surfaces of biopores is largely unknown. We have compared the composition of organic matter between inner and outer parts of aggregates and between biopore walls and the soil matrix in a loamy arable soil and a sandy forest one. Hot-water- and sodium-pyrophosphate-extractable organic matter was analysed by Fourier transform infrared (FT-IR) spectroscopy. For the sandy forest soil, the FT-IR spectra showed that organic matter from the walls of root channels contains fewer functional groups with absorption bands at 1740,1710 cm,1 and 1640,1600 cm,1 than that from burrow fillings. For the arable soil, the content of these functional groups in hot-water-soluble organic matter from the coatings is less than in that from the interiors in the topsoil, and the reverse is so in the subsoil, probably because water-soluble organic matter containing these functional groups has moved from topsoil to subsoil. The results indicate that root channels in the forest soil have more reactive zones in an otherwise relatively inert sandy matrix, whereas aggregate coatings in the arable subsoil have a greater cation exchange capacity and a greater sorption potential for hydrophobic substances than the aggregate interiors. [source]

    Soil solution concentration of Cd and Zn canbe predicted with a CaCl2 soil extract

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2003
    F. Degryse
    Summary Risk assessment of heavy metals in soil requires an estimate of the concentrations in the soil solution. In spite of the numerous studies on the distribution of Cd and Zn in soil, few measurements of the distribution coefficient in situ, Kd, have been reported. We determined the Kd of soils contaminated with Cd and Zn by measuring metal concentrations in the soil and in the soil solution and attempted to predict them from other soil variables by regression. Soil pH explained most of the variation in logKd (R2 = 0.55 for Cd and 0.70 for Zn). Introducing organic carbon content or cation exchange capacity (CEC) as second explanatory variable improved the prediction (R2 = 0.67 for Cd and 0.72 for Zn), but these regression models, however, left more than a factor of 10 of uncertainty in the predicted Kd. This large degree of uncertainty may partly be due to the variable degree of metal fixation in contaminated soils. The labile metal content was measured by isotopic dilution (E value). The E value ranged from 18 to 92% of the total metal content for Cd and from 5 to 68% for Zn. The prediction of Kd improved when metals in solution were assumed to be in equilibrium with the labile metal pool instead of the total metal pool. It seems necessary therefore to discriminate between ,labile' and ,fixed' pools to predict Kd for Cd and Zn in field contaminated soils accurately. Dilute salt extracts (e.g. 0.01 m CaCl2) can mimic soil solution and are unlikely to extract metals from the fixed pool. Concentrations of Cd and Zn in the soil solution were predicted from the concentrations of Cd and Zn in a 0.01 m CaCl2 extract. These predictions were better correlated with the observations for field contaminated soils than the predictions based on the regression equations relating logKd to soil properties (pH, CEC and organic C). [source]

    Predicting carbon content in illitic clay fractions from surface area, cation exchange capacity and dithionite-extractable iron

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2002
    M. Kahle
    Summary We used the specific surface area (SSA), the cation exchange capacity (CEC) and the content of dithionite-extractable iron (Fed) to predict the content of organic carbon in illitic clay fractions of topsoils from loess. We determined SSA (BET-N2 method) and CEC of clay fractions after removing organic C or reducing oxides or both. The CEC and the SSA of the carbon- and oxide-free clay fraction explained 56% and 54% of the variation in C content, respectively. The Fed content of the clay fractions was strongly and negatively related to the C content, and with the SSA of the carbon-free clay fraction it predicted C content almost completely (R2 = 0.96). The results indicate that the amount of cations adhering to the silicate clay minerals and the size of the silicate mineral surface area are important properties of the mineral phase for the storage potential of C. The reason for the negative relation between iron oxides and C content remains unclear. [source]

    Iron reduction and changes in cation exchange capacity in intermittently waterlogged soil

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2002
    F. Favre
    Summary The long-term effects of intermittent flooding on soil properties were studied in field experiments on a Vertisol cropped with rice in Senegal. The dominant clay minerals were smectite and kaolinite. When the soil was reduced after flooding, its cation exchange capacity (CEC) increased to twice that of its oxidized, unflooded state. Mössbauer spectroscopy showed an increase in smectite structural FeII upon reduction, which explained a part of the increase in CEC. The rest of the increase was attributed to the removal of iron oxyhydroxide coatings by reductive dissolution. The reduction and dissolution of oxides under the field conditions were substantiated by analysis of the surfaces of vermiculites buried in the Ap horizons of the cropped and the non-cropped soils. The redox-induced CEC changes were found to be reversible after 22 cycles of rice cropping. Nevertheless, the structural Fe and free Fe contents of the rice field Ap horizon were less than those of soil in uncropped neighbouring land, suggesting that inundation induced weathering and eluviation of the minerals. The observed changes in CEC and related redox reactions may substantially modify proton, anion and cation balances in intermittently flooded soils. [source]

    Synthetic Strategies for Controlling the Morphology of Proton Conducting Polymer Membranes,,

    FUEL CELLS, Issue 2 2005
    Y. Yang
    Abstract The nanostructure and morphology of proton conducting polymers is of considerable interest in the search for next generation materials and optimization of existing ones. Synthetic methodologies for tailoring molecular structures that promote nanoscopic phase separation of ionic and non-ionic domains, and the effect of phase separation on parameters such as proton conductivity, are considered. Rather than distinguish proton conducting polymers according to chemical class, they are categorized under sub-headings of random, block, and graft copolymers. The synthetic methodology available to access archetypal polymer structures is dependent on the nature of the monomers and restrictive compared to conventional non-ionic polymer systems. Irrespective of the methodology, ionic aggregation and phase separation are consistently found to play an important role in the proton conductivity of low ion exchange capacity,(IEC) membranes, but less of a role in high IEC membranes. Significant research is required to further develop relationships between polymer architecture, morphology, and electrolytic properties. [source]

    H2xMnxSn3-xS6 (x,=,0.11,0.25): A Novel Reusable Sorbent for Highly Specific Mercury Capture Under Extreme pH Conditions

    ADVANCED FUNCTIONAL MATERIALS, Issue 7 2009
    Manolis J. Manos
    Abstract The H2xMnxSn3-xS6 (x,=,0.11,0.25) is a new solid acid with a layered hydrogen metal sulfide (LHMS). It derives from K2xMnxSn3,xS6 (x,=,0.5,0.95) (KMS-1) upon treating it with highly acidic solutions. We demonstrate that LHMS-1 has enormous affinity for the very soft metal ions such as Hg2+ and Ag+ which occurs via a rapid ion exchange process. The tremendous affinity of LHMS-1 for Hg2+ is reflected in very high distribution coefficient KdHg values (>106,mL g,1). The large affinity and selectivity of LHMS-1 for Hg2+ persists in a very wide pH range (from less than zero to nine) and even in the presence of highly concentrated HCl and HNO3 acids. LHMS-1 is significantly more selective for Hg2+ and Ag+ than for the less soft cations Pb2+ and Cd2+. The Hg2+ ions are immobilized in octahedral sites between the sulfide layers of the materials via Hg,S bonds as suggested by pair distribution function (PDF) analysis. LHMS-1 could decrease trace concentrations of Hg2+ (e.g. <100,ppb) to well below the acceptable limits for the drinking water in less than two min. Hg-laden LHMS-1 shows a remarkable hydrothermal stability and resistance in 6,M HCl solutions. LHMS-1 could be regenerated by treating Hg-loaded samples with 12,M HCl and re-used without loss of its initial exchange capacity. [source]

    Linking flux network measurements to continental scale simulations: ecosystem carbon dioxide exchange capacity under non-water-stressed conditions

    GLOBAL CHANGE BIOLOGY, Issue 4 2007
    KATHERINE E. OWEN
    Abstract This paper examines long-term eddy covariance data from 18 European and 17 North American and Asian forest, wetland, tundra, grassland, and cropland sites under non-water-stressed conditions with an empirical rectangular hyperbolic light response model and a single layer two light-class carboxylase-based model. Relationships according to ecosystem functional type are demonstrated between empirical and physiological parameters, suggesting linkages between easily estimated parameters and those with greater potential for process interpretation. Relatively sparse documentation of leaf area index dynamics at flux tower sites is found to be a major difficulty in model inversion and flux interpretation. Therefore, a simplification of the physiological model is carried out for a subset of European network sites with extensive ancillary data. The results from these selected sites are used to derive a new parameter and means for comparing empirical and physiologically based methods across all sites, regardless of ancillary data. The results from the European analysis are then compared with results from the other Northern Hemisphere sites and similar relationships for the simplified process-based parameter were found to hold for European, North American, and Asian temperate and boreal climate zones. This parameter is useful for bridging between flux network observations and continental scale spatial simulations of vegetation/atmosphere carbon dioxide exchange. [source]

    Conversion of hardwood forests to spruce and pine plantations strongly reduced soil methane sink in Germany

    GLOBAL CHANGE BIOLOGY, Issue 6 2003
    WERNER BORKEN
    Abstract Well-drained forest soils are thought to be a significant sink for atmospheric methane. Recent research suggests that land use change reduces the soil methane sink by diminishing populations of methane oxidizing bacteria. Here we report soil CH4 uptake from ,natural' mature beech forests and from mature pine and spruce plantations in two study areas of Germany with distinct climate and soils. The CH4 uptake rates of both beech forests at Solling and Unterlüß were about two,three times the CH4 uptake rates of the adjacent pine and spruce plantations, indicating a strong impact of forest type on the soil CH4 sink. The CH4 uptake rates of sieved mineral soils from our study sites confirmed the tree species effect and indicate that methanotrophs were mainly reduced in the 0,5 cm mineral soil depth. The reasons for the reduction are still unknown. We found no site effect between Solling and Unterlüß, however, CH4 uptake rates from Solling were significantly higher at the same effective CH4 diffusivity. This potential site effect was masked by higher soil water contents at Solling. Soil pH (H2O) explained 71% of the variation in CH4 uptake rates of sieved mineral soils from the 0,5 cm depth, while cation exchange capacity, soil organic carbon, soil nitrogen and total phosphorous content were not correlated with CH4 uptake rates. Comparing 1998,99, annual CH4 uptake rates increased by 69,111% in the beech and spruce stands and by 5,25% in the pine stands, due primarily to differences in growing season soil moisture. Cumulative CH4 uptake rates from November throughout April were rather constant in both years. The CH4 uptake rates of each stand were separately predicted using daily average soil matric potential and a previously developed empirical model. The model results revealed that soil matric potential explains 53,87% of the temporal variation in CH4 uptake. The differences between measured and predicted annual CH4 uptake rates were less than 10%, except for the spruce stand at Solling in 1998 (17%). Based on data from this study and from the literature, we calculated a total reduction in the soil CH4 sink of 31% for German forests due in part to conversion of deciduous to coniferous forests. [source]

    Geomorphologic control on pollutant retardation at the groundwater,surface water interface

    HYDROLOGICAL PROCESSES, Issue 24 2008
    J.W.N. Smith
    Abstract The results of research on the pollutant retardation potential of permeable riverbed sediments in catchments with significant groundwater,surface water (GW-SW) interaction are presented. The fraction of organic carbon and cation exchange capacity of fluvial sediments in various geomorphologic environments have been quantified. Sediments in selected reaches of the rivers Tern and Leith (UK), from the underlying Permian sandstone aquifers, and from along the length of the rivers Severn and Eden into which the Tern and Leith discharge have been investigated. Statistical analyses show significant variation in the geochemistry and pollutant retardation potential of sediments from different geomorphologic features, and between upland and lowland rivers. The sorption potential of fine-grained sediments deposited in pools was greater than sand in runs and coarser deposits in riffles. Similarly, sediments in lowland rivers were found to have a greater retardation potential than those in upland rivers. There was generally greater retardation potential in fluvial sediments of all types than in the underlying aquifers, and in lowland rivers the fluvial sediment retardation potential greatly dominated that of the aquifer. The findings demonstrate the potential for pollutant retardation processes in riverbed sediments of sandstone catchments, and suggest that consideration of retardation processes at the groundwater,surface water interface should be included into environmental risk-assessment studies, in order to better assess and manage the effects of contaminated groundwater discharges to rivers, particularly in lowland catchments. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Maternal and fetal microvasculature in sheep placenta at several stages of gestation

    JOURNAL OF ANATOMY, Issue 3 2010
    Shireen A. Hafez
    Abstract Maternal and fetal microvasculature was studied in ewes at days 50, 90 and 130 of gestation using microvascular corrosion casting and scanning electron microscopy. Microvascular corrosion casts of caruncles at day 50 were cup-shaped with a centrally located cavity. Branches of radial arteries entered the caruncle from its base and ramified on the maternal surface of the caruncle. Stem arteries broke into an extensive mesh of capillaries forming crypts on the fetal surface. The architecture of the caruncle at day 90 was similar to what was found at day 50 but the vascularity and the depth of the crypts increased in correspondence to increased branching of fetal villi. The substance of the caruncle was thicker at day 130 compared with day 50, with no remarkable difference compared with day 90. Capillary sinusoids of irregular form and diameter were observed on the fetal surface of the caruncle at all stages. These sinusoids may reduce blood flow resistance and subsequently increase transplacental exchange capacity. A microvascular corrosion cast of the cotyledon was cup-shaped with wide and narrow sides. Cotyledonary vessels entered and left the cotyledon from the narrow side. A cotyledonary artery gave proximal collateral branches immediately after entering the cotyledon and then further branched to supply the remaining portion of the cotyledon. Vessel branches broke into a mesh of capillaries forming the fetal vascular villi. Fetal villi that were nearest to the center of the cotyledon were the longest. Capillaries forming villi were in the form of a web-like mesh, were irregular in size and had sinusoidal dilations. The architecture of the cotyledon at day 90 was similar to day 50, but the vascularity increased. Branching of the fetal villi became more abundant. This extensive branching presumably allows a higher degree of invasion and surface contact to maternal tissues. At day 130, the distal portions of the fetal villi showed low ridges and troughs to increase the surface area for diffusion. Branching of fetal villi appears to influence the elaboration of maternal crypts in all stages of gestation. However, correspondence between crypts and villi is restricted to distal portions of fetal villi. [source]

    Polymer electrolyte membranes having sulfoalkyl grafts into ETFE film prepared by radiation-induced copolymerization of methyl acrylate and methyl methacrylate

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009
    Truong Thi Hanh
    Abstract Polymer electrolyte membranes (PEMs) containing alkylsulfonic acid grafts can be prepared by radiation-induced graft copolymerization of methyl acrylate (MA) and methyl methacrylate (MMA) into a poly(ethylene- co -tetrafluoroethylene) film followed by sulfonation of the MA units in the copolymer grafts using an equimolar complex of chlorosulfonic acid and 1,4-dioxane (ClSO3H-Complex). PEMs with MA/MMA copolymer grafts that are 33%,79% MA units were prepared by preirradiation with a dose of 20 kGy and grafting in bulk comonomers at 60°C. The grafted films are treated with ClSO3H-Complex to obtain PEMs with ion exchange capacity of 0.36-0.81 mmol/g (sulfonation degrees of 20%,40%) and proton conductivity of 0.04-0.065 S/cm. These values can be controlled by changing the MA content the sulfonation occurring at an ,-carbonyl carbon. The PEMs with higher MMA content showed higher durability in water (80°C) and under oxidative conditions (3% H2O2) at 60°C. This is because the PMMA grafts in the PEMs have no proton at an ,-carbonyl carbon, which is considered to be a trigger of the degradation of grafting polymers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]

    Cation exchange finishing of nonwoven polyester with polycarboxylic acids and cyclodextrins

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007
    L. Ducoroy
    Abstract We describe a chemical method for the finishing of polyester nonwoven fabrics that aimed to obtain ion exchange textiles. This approach was based on the use of polycarboxylic acids (PCA) and cyclodextrins as carbohydrate compounds and finishing agents, respectively. It was observed that the reaction between these reactants yielded a crosslinked polymer that was physically anchored onto the fibers. This polymer can be considered as a resin issued from the esterification between the COOH groups of the PCA with the OH groups of the carbohydrate. As the esterification reaction was not complete, many free carboxylic groups remained on the surface of the coating polymer. This feature offered the ion exchange properties to the textile support. In this article, we described the pad-dry-cure process and showed the influence of the curing parameters (time and temperature), the nature, and the concentration of the components and the pH of the impregnating bath. The grafting rate (in wt %) and the ion exchange capacity (IEC) were observed in parallel. First, it was observed that the best IEC capacity (that could reach 1 mmol/g) was obtained when an ideal compromise was applied between time and temperature of curing. We also evidenced that IEC depended on the nature and on the concentration of the PCA (chosen among citric acid, 1,2,3,4-butanetetracarboxylic acid, and polyacrylic acid) and on the pH of the impregnating bath. Finally, it was observed that cyclodextrins were more appropriate than starch as finishing coreactants. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3730,3738, 2007 [source]

    Floristic inventory and diversity assessment of a lowland African Montane Rainforest at Korup, Cameroon and implications for conservation

    AFRICAN JOURNAL OF ECOLOGY, Issue 3 2010
    Innocent Ndoh Mbue
    Abstract Twenty modified-Whittaker plots were stratified at different sampling locations from February to May of 2008 in the central zone of Korup National Park, Cameroon. Our interest was to assess floristic diversity and investigate their relationship with environmental variables. Diversity profiles and rank abundance,curves were used for diversity analysis while canonical correspondence analysis and species,response curves were used to investigate the relationships between the response and explanatory variables. Of the 66 families identified, the Rubiaceae (999 species) were the most abundant. The Sterculiaceae (basal area = 10.482 m2 ha,1) were the dominant family, while the co-dominant families included the Ebenaceae (basal area = 9.092 m2 ha,1) and the Euphorbiaceae (basal area = 8.168 m2 ha,1). Soil variables explained 54.3% of total variation in family distribution. Canonical axes were related to different environmental gradients: axis1 was related to increasing canopy cover (r = 0.6951); axis 2, increasing Magnesium (r = 0.8465) and effective cation exchange capacity (r = 0.5899); axis 3, increasing effective cation exchange capacity (r = 0.5536); while axis 4, increasing Phosphorus concentration (r = 0.5232). Our results demonstrate the advantage which diversity profiles have over single or combination of indices, and the importance of using a combination of methodologies in diversity analysis. Résumé De février à mai 2008, vingt parcelles de Whittaker modifié ont été stratifiées à différents sites d'échantillonnage dans la zone centrale du Parc National de Korup, au Cameroun. Nous voulions évaluer la diversité floristique et étudier son lien avec diverses variables environnementales. Nous avons employé des profils de diversité et des courbes de rangs d'abondance pour l'analyse de la diversité, tandis que nous utilisions une analyse canonique des correspondances et des courbes de réponse des espèces pour étudier les relations entre les réponses et les variables explicatives. Sur les 66 familles identifiées, les Rubiacées (999 espèces) étaient les plus abondantes. Les Sterculiacées (surface basale = 10,482 m2 ha,1) étaient la famille dominante et, parmi les familles co-dominantes, il y avait les Ebénacées (surface basale = 9,092 m2 ha,1) et les Euphorbiacées (surface basale = 8,168 m2 ha,1). Des variables du sol expliquaient 54,3% de la variation totale de la distribution des familles. Les axes canoniques ont été liés aux différents gradients environnementaux; l'axe 1 était liéà une couverture croissante de la canopée (r = 0,6951); l'axe 2 à une augmentation du magnésium (r = 0,8465) et à la capacité réelle d'échange de cations (r = 0,5899); l'axe 3 à une capacité réelle croissante d'échanges de cations (r = 0,5536); et l'axe 4 à une concentration croissante en phosphore (r = 0,5532). Nos résultats montrent l'avantage que les profils de diversité ont sur des indices uniques ou combinés et l'importance d'utiliser une combinaison de méthodologies dans une analyse de diversité. [source]

    Treatment of low turbidity water by sweep coagulation using bentonite

    JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 5 2005
    Yun-Hwei Shen
    Abstract A novel strategy of sweep coagulation to treat low turbidity water is presented herein. Study findings demonstrated that an Na+ -saturated bentonite with medium cation exchange capacity (CEC) resulted in significant turbidity removal at a bentonite dosage of 30 mg dm,3. Bentonite dispersion with fully delaminated platelets tended to undergo a more porous type of coagulation with intense face-to-face interactions of platelets and effectively entrapped TiO2 particles in band-type structures. This type of coagulation usually results in a large volume of settled flocs with a fluffy structure and excellent turbidity removal efficiency for sweep coagulation. The sign and magnitude of electrical charge on TiO2 particles has a minor effect on the efficiency of sweep coagulation. Copyright © 2005 Society of Chemical Industry [source]

    Ammonia exchange on clinoptilolite from mineral deposits located in Mexico

    JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2004
    Roberto Leyva-Ramos
    Abstract This work investigated the ion exchange of ammonia on clinoptilolite obtained from mineral deposits located in San Luis Potosi and Sonora, Mexico. Experimental ion exchange isotherm data were obtained in a batch adsorber. The effects of temperature and solution pH on the ion exchange capacity were studied and it was found that the exchange capacity was slightly increased by augmenting the temperature and by decreasing the pH from 6 to 3. The ion exchange capacity was independent of the diameter of the zeolite particles. The reversibility of ion exchange was analyzed by desorbing the ammonia exchanged on the zeolite. The ion exchange was reversible when 1% NaCl solution was used as the desorbing solution, but more ammonia was desorbed using 1% KCl solution in the desorption step. It was concluded that a considerable amount of ammonia was exchanged on the clinoptilolite and that the exchange capacity was slightly dependent on the temperature and pH. Copyright © 2004 Society of Chemical Industry [source]