The Influence of Crystal Edges on Clay-Humus Complexation

Varadachari, Chandrika; Mondal, Ajijul Haque; Ghosh, Kunal

doi:10.1097/00010694-199503000-00005

Cited by 21 publications

(4 citation statements)

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“…In CaCl2 solutions, 2,4-D sorption may occur through anion exchange, Ca-bridging, and hydrophobic interactions. In the presence of phosphate at the concentrations used in this study (2-3 orders of magnitude higher than 2,4-D), 2,4-D sorption from both anion exchange and Ca-bridging will be negligible (12,23,(32)(33)(34)(35)(36)(37); therefore, differences in 2,4-D sorption between CaCl2 and Ca(H2PO4)2 systems are due to anion exchange and Ca-bridging (eq 1). In CaSO4 solutions, 2,4-D sorption occurs primarily through Ca-bridging and hydrophobic interactions; therefore, differences in sorption between CaCl2 and CaSO4 electrolytes are attributed to anion exchange (eq 2).…”

Section: Methodsmentioning

confidence: 97%

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Quantifying the Contribution of Different Sorption Mechanisms for 2,4-Dichlorophenoxyacetic Acid Sorption by Several Variable-Charge Soils

Hyun

Lee

2005

Environ. Sci. Technol.

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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 approximately equal to 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. Differences in 2,4-D sorption from CaCl2 and KCl were attributed specifically to Ca-bridging between 2,4-D's carboxyl group and the silanol edge on kaolinite and quartz and ranged from negligible to 40% depending on the soil mineral type. Differences in sorption from CaCl2 and CaSO4 was attributed to anion exchange, which ranged from 16 to 91%, followed the trends with pKa developed previously for other organic acids, and correlated well to the soil anion to cation exchange capacity ratio (AEC/CEC). The sum of anion exchange and Ca-bridging contributions agreed well with the sorption estimated to be from hydrophilic domains. All other sorption was attributed to hydrophobic processes, which correlated well to a linear free-energy relationship between pH-dependent organic carbon-normalized sorption coefficients and pH-dependent octanol-water partition coefficients developed for several other organic acids.

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Section: Methodsmentioning

confidence: 97%

“…The greater 2,4-D sorption was eliminated in the absence of Ca 2+ . Ca-bridging on mineral surfaces has also been reported as a potential retention mechanism for several other organic acids ( − ).…”

Section: Introductionmentioning

confidence: 99%

Quantifying the Contribution of Different Sorption Mechanisms for 2,4-Dichlorophenoxyacetic Acid Sorption by Several Variable-Charge Soils

Hyun

Lee

2005

Environ. Sci. Technol.

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“…Since surface hydroxyls are characteristic for variable charge surfaces, sorption of negatively charged organics by ligand exchange should be most important in oxide-rich and allophanic soils, such as Andisols (Sollins et al, 1996). Other bounding types involved in sorption between SOC and metals include cation bridging (Varadachari et al, 1995), water bridging, hydrogen bounding, and van der Waals forces (Burchill et al, 1981). However, distinction between potential types is impossible bearing in mind the methodology of this study.…”

Section: Aggregate Structure In South Chilean Andisolsmentioning

confidence: 99%

Aggregate and soil organic carbon dynamics in South Chilean Andisols

et al. 2005

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Abstract. Extreme sensitivity of soil organic carbon (SOC) to climate and land use change warrants further research in different terrestrial ecosystems. The aim of this study was to investigate the link between aggregate and SOC dynamics in a chronosequence of three different land uses of a south Chilean Andisol: a second growth Nothofagus obliqua forest (SGFOR), a grassland (GRASS) and a Pinus radiata plantation (PINUS). Total carbon content of the 0-10 cm soil layer was higher for GRASS (6.7 kg C m −2 ) than for PINUS (4.3 kg C m −2 ), while TC content of SG-FOR (5.8 kg C m −2 ) was not significantly different from either one. High extractable oxalate and pyrophosphate Al concentrations (varying from 20.3-24.4 g kg −1 , and 3.9-11.1 g kg −1 , respectively) were found in all sites. In this study, SOC and aggregate dynamics were studied using size and density fractionation experiments of the SOC, δ 13 C and total carbon analysis of the different SOC fractions, and C mineralization experiments. The results showed that electrostatic sorption between and among amorphous Al components and clay minerals is mainly responsible for the formation of metal-humus-clay complexes and the stabilization of soil aggregates. The process of ligand exchange between SOC and Al would be of minor importance resulting in the absence of aggregate hierarchy in this soil type. Whole soil C mineralization rate constants were highest for SGFOR and PINUS, followed by GRASS (respectively 0.495, 0.266 and 0.196 g CO 2 -C m −2 d −1 for the top soil layer). In contrast, incubation experiments of isolated macro organic matter fractions gave opposite results, showing that the recalcitrance of the SOC decreased in another order: PINUS>SGFOR>GRASS. We deduced that electrostatic sorption processes and physical protection of SOC in soil aggregates were the main processes determining SOC stabilization. As a result, high aggregate carbon concentraCorrespondence to: D. Huygens (dries.huygens@ugent.be) tions, varying from 148 till 48 g kg −1 , were encountered for all land use sites. Al availability and electrostatic charges are dependent on pH, resulting in an important influence of soil pH on aggregate stability. Recalcitrance of the SOC did not appear to largely affect SOC stabilization. Statistical correlations between extractable amorphous Al contents, aggregate stability and C mineralization rate constants were encountered, supporting this hypothesis. Land use changes affected SOC dynamics and aggregate stability by modifying soil pH (and thus electrostatic charges and available Al content), root SOC input and management practices (such as ploughing and accompanying drying of the soil).

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“…Anteriormente, Parfitt et al (1977) haviam observado que as SH podem interagir com gibbsita e óxidos de ferro tanto via troca de ligantes como via pontes de hidrogênio. O mecanismo de pontes de cátions pode tornar-se extremamente importante para a fixação de SH em superfícies laterais de caulinita e nas basais de ilita (Varadachari et al, 1995), enquanto em esmectitas a interação de SH e polímeros de hidroxi-Al nas entrecamadas foi relatada como sendo de natureza forte, uma vez que a remoção da matéria orgânica não foi completa após tratamento com perclorato de sódio (Singer & Huang, 1993). A interação por meio de pontes de hidrogênio de SH e caulinita, esmectitas e ilita foi constatada por meio de técnicas espectroscópicas por Ristori et al (1992).…”

Section: Introductionunclassified