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Seunghun Hyun – One of the best experts on this subject based on the ideXlab platform.

  • quantifying the contribution of different sorption mechanisms for 2 4 dichlorophenoxyacetic acid sorption by several variable charge soils
    Environmental Science & Technology, 2005
    Co-Authors: Seunghun Hyun
    Abstract:

    Previous research with phenolic, carboxylic, and urea type organic acids demonstrated that hydrophilic sorption was primarily due to Anion Exchange, which was linearly correlated to chemical acidity (pKa) and the soil Anion Exchange Capacity. However, for dichlorophenoxyacetic acid (2,4-D), sorption by a kaolinitic soil was much higher than expected relative to all other organic acid−soil data. The enhanced sorption was hypothesized to involve calcium bridging of 2,4-D to hydrophilic domains. In this study, the mechanisms contributing to 2,4-D sorption by variable-charged soils were probed and quantified by measuring sorption from CaCl2, KCl, CaSO4, KH2PO4, and Ca(H2PO4)2 solutions. Linear sorption coefficients estimated for 2,4-D sorption from the different electrolytes decreased as follows:  CaCl2 > KCl > CaSO4 > Ca(H2PO4)2 ≅ KH2PO4. Differences in 2,4-D sorption from CaCl2 and phosphate solutions were attributed to sorption by hydrophilic domains, which ranged between 46 and 94% across soils. Differenc…

  • Significance of Anion Exchange in pentachlorophenol sorption by variable-charge soils.
    Journal of Environmental Quality, 2003
    Co-Authors: Seunghun Hyun
    Abstract:

    Sorption data and subsequent predictive models for evaluating acidic pesticide behavior on variable-charge soils are needed to improve pesticide management and environmental stewardship. Previous work demonstrated that sorption of pentachlorophenol (PCP), a model organic acid, was adequately modeled by accounting for pH-and pK a -dependent chemical speciation and using two organic carbon-normalized sorption coefficients; one each for the neutral and Anionic species. Such models do not account for organic Anion interaction to positively charged surface sites, which can be significant for variable-charge minerals present in weathered soils typical of tropical and subtropical regions. The role of Anion Exchange in sorption of ionizable chemicals by variable-charge soils was assessed by measuring sorption of PCP by several variable-charge soils from aqueous solutions of CaCl 2 , CaSO 4 , Ca(H 2 PO 4 ) 2 as a function of pH. Differences in sorption from phosphate and chloride electrolyte solutions were attributed to pentachlorophenolate interactions with Anion Exchange sites. Suppression of PCP sorption by phosphate ranged from negligible in a soil with essentially no positively charge sites, as measured by negligible Anion Exchange Capacity, to as much as 69% for variable-charge soils. Pentachlorophenolate Exchange correlated well with the ratio of pH-dependent Anion Exchange Capacity to net surface charge. Sorption reversibility of PCP by both CaCl 2 and Ca(H 2 PO 4 ) 2 solutions was also demonstrated. Results for PCP clearly demonstrate that sorption to Anion Exchange sites in variable-charge soils should be considered in assessing pesticide mobility and that phosphate fertilizer application may increase the mobility of acidic pesticides.

  • Significance of Anion Exchange in Pentachlorophenol Sorption by Variable‐Charge Soils
    Journal of environmental quality, 2003
    Co-Authors: Seunghun Hyun, Linda S. Lee, P. Suresh C. Rao
    Abstract:

    Sorption data and subsequent predictive models for evaluating acidic pesticide behavior on variable-charge soils are needed to improve pesticide management and environmental stewardship. Previous work demonstrated that sorption of pentachlorophenol (PCP), a model organic acid, was adequately modeled by accounting for pH-and pK a -dependent chemical speciation and using two organic carbon-normalized sorption coefficients; one each for the neutral and Anionic species. Such models do not account for organic Anion interaction to positively charged surface sites, which can be significant for variable-charge minerals present in weathered soils typical of tropical and subtropical regions. The role of Anion Exchange in sorption of ionizable chemicals by variable-charge soils was assessed by measuring sorption of PCP by several variable-charge soils from aqueous solutions of CaCl 2 , CaSO 4 , Ca(H 2 PO 4 ) 2 as a function of pH. Differences in sorption from phosphate and chloride electrolyte solutions were attributed to pentachlorophenolate interactions with Anion Exchange sites. Suppression of PCP sorption by phosphate ranged from negligible in a soil with essentially no positively charge sites, as measured by negligible Anion Exchange Capacity, to as much as 69% for variable-charge soils. Pentachlorophenolate Exchange correlated well with the ratio of pH-dependent Anion Exchange Capacity to net surface charge. Sorption reversibility of PCP by both CaCl 2 and Ca(H 2 PO 4 ) 2 solutions was also demonstrated. Results for PCP clearly demonstrate that sorption to Anion Exchange sites in variable-charge soils should be considered in assessing pesticide mobility and that phosphate fertilizer application may increase the mobility of acidic pesticides.

David A. Laird – One of the best experts on this subject based on the ideXlab platform.

  • Aluminum and iron biomass pretreatment impacts on biochar Anion Exchange Capacity
    Carbon, 2017
    Co-Authors: Michael Lawrinenko, Dapeng Jing, Chumki Banik, David A. Laird
    Abstract:

    Abstract Some biochars have significant Anion Exchange Capacity (AEC) under acidic pH conditions but typically have little or no AEC at neutral to alkaline pHs. We hypothesized that metal oxyhydroxide surface coatings on biochar will increase biochar Anion Exchange Capacity (AEC) at higher pHs by virtue of the high point of zero net charge of metal oxyhydroxides. Here we report that pyrolysis temperature and the distribution of metal oxyhydroxides in biochars prepared by slow pyrolysis of biomass pre-treated with Al or Fe trichlorides strongly influenced biochar AEC. Biochars produced at 700 °C exhibit greater AEC than biochars similarly prepared at 500 °C. Spectroscopic (FTIR, XPS, and SEM-EDS) studies provided evidence for the formation of Al O C organometallic moieties on biochar surfaces that formed during pyrolysis. To a lesser extent, Fe also formed Fe O C surface structures on biochar, but most Fe was present in discrete crystalline phases ranging from zerovalent iron to ferric oxides. These organometallic bonding structures are a means of supporting metal oxides on biochar carbon and are responsible for broader metal atom distributions, which can increase AEC through the development of metal oxyhydroxide surface coatings that exhibit high points of zero net charge.

  • Accelerated aging of biochars: Impact on Anion Exchange Capacity
    Carbon, 2016
    Co-Authors: Michael Lawrinenko, David A. Laird, Robert L. Johnson, Dapeng Jing
    Abstract:

    Little is known about the stability of biochar Anion Exchange Capacity (AEC) and by what mechanisms AEC changes as biochar ages and weathers in soil environments. The goal of this study was to investigate chemical changes that may occur during ageing of biochar in neutral or alkaline soils and to assess the impact of ageing on AEC. To simulate and accelerate ageing, biochars were oxidized in alkaline hydrogen peroxide for 4 months. Spectroscopic evidence (FTIR, XPS and 13C-NMR) revealed that ageing increased carbonyl and alcoholic character in biochars produced at 500 °C and effected endoperoxide formation in biochars produced at 700 °C; the latter exhibited greater arene carbon character. Ageing caused biochar AEC to decline on average by 54% with greater decreases in biochars produced at 500 °C in contrast to biochars produced at 700 °C. The AEC of biochar derived from alfalfa meal and cellulose produced at 700 °C did not change significantly (p = 0.20 and p = 0.50, respectively) with ageing. Stability of AEC in the high temperature biochars is attributed to the presence of oxonium groups in bridging positions of arene carbon, which are sterically resistant to nucleophilic attack.

  • Anion Exchange Capacity of biochar
    Green Chemistry, 2015
    Co-Authors: Michael Lawrinenko, David A. Laird
    Abstract:

    Biochar has gained recent interest as a soil amendment and agent for carbon sequestration. Some biochars have significant levels of Anion Exchange Capacity (AEC), which may reduce leaching of Anionic nutrients in soil. Little is known about the nature of Anion Exchange sites on biochar surfaces and what production conditions promote AEC in biochar. We report that the AEC of biochars produced from four feedstocks (maize stover, cellulose, alfalfa meal, and albumin) ranged from 0.602 to 27.76 cmol kg-1 and increased with decreasing pH (p < 0.0001) and peak pyrolysis temperature. A cellulose biochar, composed almost entirely of C, H, and O, exhibited significant AEC at pH 8 suggesting that pH independent O containing functional groups contribute AEC. Fourier transform infrared spectroscopy revealed a prominent 1590 cm-1 band, which we attribute in part to C-O+ stretching in oxonium heterocycles. Both the C1s and O1s X-ray photoelectron (XPS) spectra of the biochars provide additional evidence for oxonium heterocycles. The N1s XPS spectra of albumin biochars indicated the presence of pyridinic groups. We conclude that oxonium functional groups contribute pH independent AEC and that both pyridinic functional groups and non-specific proton adsorption by condensed aromatic rings contribute pH dependent AEC to biochars.

P. Suresh C. Rao – One of the best experts on this subject based on the ideXlab platform.

  • Significance of Anion Exchange in Pentachlorophenol Sorption by Variable‐Charge Soils
    Journal of environmental quality, 2003
    Co-Authors: Seunghun Hyun, Linda S. Lee, P. Suresh C. Rao
    Abstract:

    Sorption data and subsequent predictive models for evaluating acidic pesticide behavior on variable-charge soils are needed to improve pesticide management and environmental stewardship. Previous work demonstrated that sorption of pentachlorophenol (PCP), a model organic acid, was adequately modeled by accounting for pH-and pK a -dependent chemical speciation and using two organic carbon-normalized sorption coefficients; one each for the neutral and Anionic species. Such models do not account for organic Anion interaction to positively charged surface sites, which can be significant for variable-charge minerals present in weathered soils typical of tropical and subtropical regions. The role of Anion Exchange in sorption of ionizable chemicals by variable-charge soils was assessed by measuring sorption of PCP by several variable-charge soils from aqueous solutions of CaCl 2 , CaSO 4 , Ca(H 2 PO 4 ) 2 as a function of pH. Differences in sorption from phosphate and chloride electrolyte solutions were attributed to pentachlorophenolate interactions with Anion Exchange sites. Suppression of PCP sorption by phosphate ranged from negligible in a soil with essentially no positively charge sites, as measured by negligible Anion Exchange Capacity, to as much as 69% for variable-charge soils. Pentachlorophenolate Exchange correlated well with the ratio of pH-dependent Anion Exchange Capacity to net surface charge. Sorption reversibility of PCP by both CaCl 2 and Ca(H 2 PO 4 ) 2 solutions was also demonstrated. Results for PCP clearly demonstrate that sorption to Anion Exchange sites in variable-charge soils should be considered in assessing pesticide mobility and that phosphate fertilizer application may increase the mobility of acidic pesticides.