Arsenate and Chromate Retention Mechanisms on Goethite. 1. Surface Structure

Fendorf, S. E.; Eick, Matthew J.; Grossl, Paul R.; Sparks, Donald L.

doi:10.1021/es950653t

Cited by 909 publications

(743 citation statements)

References 24 publications

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“…As noted above, this reflects the much higher concentration of Fe and Al in these two soils and probably also their much lower pH values. The formation of a variety of inner-sphere surface complexes of arsenate with Fe oxides has been observed in spectroscopic studies (Waychunas et al, 1993;Fendorf et al, 1997).…”

Section: Comparison Of As Fractionation In Unpolluted and As-amended mentioning

confidence: 99%

The ageing effect on the bioaccessibility and fractionation of arsenic in soils from China

et al. 2007

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Ingestion of contaminated soil has been recognized as an important exposure pathway of arsenic for humans, especially for children through outdoor hand-to-mouth activities. An improved sequential extraction procedure was employed in an attempt to reveal the relationship between bioaccessibility and fractionation of As in five soils from China. Arsenic bioaccessibility in acidic (%pH 4.5) soils reached approximately stable levels after a sharp decline within one week of ageing. In contrast, As bioaccessibility in higher pH (>6.0) soils was found to be significantly higher and took two weeks of ageing to reach stable levels. The artificially added As was more labile than indigenous As. The main proportions of added As were found in the specifically sorbed and amorphous and poorly-crystalline hydrous Fe/Al oxide-bound fractions. Correlation analysis shows that the non-specifically and specifically sorbed As are likely to constitute the main proportion of bioaccessible soil As. The soil content of amorphous and crystalline Fe/Al oxides and soil pH appear to be the key factors controlling, not only the time needed to reach a steady state, but also the magnitude of the bioaccessibility of As added to the soils.

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Section: Comparison Of As Fractionation In Unpolluted and As-amended mentioning

confidence: 99%

The ageing effect on the bioaccessibility and fractionation of arsenic in soils from China

et al. 2007

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“…Extended X-ray absorption fine structure (EXAFS) is sensitive to crystal structure and the local environment of the absorbing atoms, and thus, can be employed to identify and quantify the local structure of arsenate binding with iron (Waychunas et al, 1986. Several recent EXAFS investigations have shown that at least two complexes exist in As(V)eiron oxide adsorption system: binuclear bidentate complex and monodentate mononuclear complex Waychunas et al, 1993;Fendorf et al, 1997;Wang et al, 2010). However, detailed knowledge has been lacking on the nature of arsenic complexation at the surfaces of starch-stabilized magnetite nanoparticles.…”

Section: Introductionmentioning

confidence: 99%

XAFS study of starch-stabilized magnetite nanoparticles and surface speciation of arsenate

Zhang

Pan

Zhao

et al. 2011

Environmental Pollution

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a b s t r a c tIt has been shown that starch can effectively stabilize nanoscale magnetite particles, and starch-stabilized magnetite nanoparticles (SMNP) are promising for in situ remediation of arsenic-contaminated soils. However, a molecular level understanding has been lacking. Here, we carried out XAFS studies to bridge this knowledge gap. Fe K-edge XAFS spectra indicated that the FeeO and FeeFe coordination numbers of SMNP were lower than those for bare magnetite particles, and these coordination numbers decreased with increasing starch concentration. The decrease in the average coordination number at elevated stabilizer concentration was attributed to the increase in the surface-to-volume ratio. Arsenic K-edge XAFS spectra indicated that adsorbed arsenate on SMNP consisted primarily of binuclear bidentate (BB) complexes and monodentate mononuclear (MM) complexes. More BB complexes (energetically more favorable) were observed at higher starch concentrations, indicating that SMNP not only offered greater adsorption surface area, but also stronger adsorption affinity toward arsenate.

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“…Experimentally measured equilibrium adsorption constants, therefore, bear the property of inconstancy in nature. Although it is now possible to measure the microscopic adsorption structures from samples using spectroscopic methods such as X-ray absorption fine structure (XAFS) [15,[18][19][20], it is extremely difficult to experimentally catch up the reaction pathways and activation barriers for the ion adsorption at mineralwater interfaces. Moreover, little is known about the interrelation of different MEA states.…”

Section: Introductionmentioning

confidence: 99%

Studies on the reaction pathway of arsenate adsorption at water–TiO2 interfaces using density functional theory

Pan

Zhang

2011

Journal of Colloid and Interface Science

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a b s t r a c tReaction pathway information of transition states and intermediate species is crucial for understanding the adsorption mechanism of pollutants at mineral-water interfaces. However, it has been difficult to obtain such information using existing experiments. Here, the activation barriers, transition states, intermediate species and surface complexes of arsenate adsorption on TiO 2 surfaces were studied using DFTbased reaction pathway calculations. The results indicated that the bidentate binuclear (BB) adsorption structure was formed through a monodentate mononuclear (MM) metastable-equilibrium adsorption (MEA) state. A two-step adsorption mechanism was proposed on the basis of the detailed picture of bond breaking and bond formation during each reaction step. When the adjacent surface sites were occupied, the transform from MM mode to BB mode was greatly inhibited so that both MM and BB coexisted in the equilibrium adsorption sample. The BB complex was energetically more stable than the MM complex, and so, the adsorption irreversibility was fundamentally related to the ratio BB:MM in the final equilibrium state. This mechanism may also explain the initial concentration effect, where, for the given adsorption experiment of arsenate on TiO 2 under the same thermodynamic conditions, both equilibrium constants and the BB:MM ratio in equilibrium adsorption samples changed with the reaction kinetics.

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Arsenate and Chromate Retention Mechanisms on Goethite. 1. Surface Structure

Cited by 909 publications

References 24 publications

The ageing effect on the bioaccessibility and fractionation of arsenic in soils from China

The ageing effect on the bioaccessibility and fractionation of arsenic in soils from China

XAFS study of starch-stabilized magnetite nanoparticles and surface speciation of arsenate

Studies on the reaction pathway of arsenate adsorption at water–TiO2 interfaces using density functional theory

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