Iron oxide formation from FeCl2 solutions in the presence of uranyl (UO22+) cations and carbonate rich media

Doornbusch, Brodie; Bunney, K.; Gan, Bin; Jones, Franca; Gräfe, Markus

doi:10.1016/j.gca.2015.02.038

Cited by 17 publications

(46 citation statements)

References 59 publications

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“…In the second procedure, Se desorption from Se(IV)-bearing hematite and ferrihydrite samples was studied as a function of OHconcentration. The used technique is based on a method of Doornbusch et al (2015) for iron oxide dissolution, but was adjusted for use under alkaline conditions. For this purpose, a specific amount of Se-bearing iron oxide powder was treated several times with NaOH of various concentrations (m/V = 3.4 g/L).…”

Section: Desorption Studiesmentioning

confidence: 99%

Uptake mechanisms of selenium oxyanions during the ferrihydrite-hematite recrystallization

Börsig

Scheinost

Shaw

et al. 2017

Geochimica et Cosmochimica Acta

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Se is an essential nutrient at trace levels, but also a toxic environmental contaminant at higher concentrations. The mobility of the trace element Se in natural environments is mainly controlled by the occurrence of the highly soluble Se oxyanions-selenite [Se(IV)] and selenate [Se(VI)]-and their interaction with geological materials. Since iron oxides are ubiquitous in nature, many previous studies investigated Se retention by adsorption onto iron oxides. However, little is known about the retention of Se oxyanions during the formation process of iron oxides. In this paper, we therefore studied the immobilization of Se oxyanions during the crystallization of hematite from ferrihydrite. In coprecipitation studies, hematite was synthesized by the precipitation and aging of ferrihydrite in an oxidized Se(IV)-or Se(VI)-containing system (pH 7.5). Hydrochemical data of these batch experiments revealed the complete uptake of all available Se(IV) up to initial concentrations of c(Se) 0 = 10-3 mol/L (m/V ratio = 9.0 g/L), while the retention of Se(VI) was low (max. 15 % of c(Se) 0). In case of high initial Se(IV) concentrations, the results also demonstrated that the interaction of Se with ferrihydrite can affect the type of the final transformation product. Comparative adsorption studies, performed at identical conditions, allowed a distinction between pure adsorption and coprecipitation and showed a significantly higher Se retention by coprecipitation than by 2 adsorption. Desorption studies indicated that Se coprecipitation leads to the occurrence of a resistant, non-desorbable Se fraction. According to time-resolved studies of Se(IV) or Se(VI) retention during the hematite formation and detailed spectroscopic analyses (XPS, XAS), this fraction is the result of an incorporation process, which is not attributable to Fe-for-Se substitution or the Se occupation of vacancies. Se initially adsorbs to the ferrihydrite surface, but after the transformation of ferrihydrite into hematite, it is mostly incorporated by hematite. In systems without mineral transformation, however, Se remains as a sorption complex. In case of Se(VI), an outer-sphere complex forms, while Se(IV) forms a mixture of bidentate mononuclear edge-sharing and bidentate binuclear corner-sharing inner-sphere complexes. The results of this study demonstrate that incorporation of Se oxyanions by hematite is an important retention mechanism in addition to pure adsorption, which may affect the migration and immobilization of Se oxyanions in natural systems or polluted environments.

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Section: Desorption Studiesmentioning

confidence: 99%

Uptake mechanisms of selenium oxyanions during the ferrihydrite-hematite recrystallization

Börsig

Scheinost

Shaw

et al. 2017

Geochimica et Cosmochimica Acta

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“…Uranium can also be incorporated into the Fe(III) phases as the Fe(III) precipitates within the sediments (Doornbusch et al, 2015;Massey et al, 2014;Nico et al, 2009;Stewart et al, 2009) and form U-oxide complex crystals during long-term aging. In both the source material (before reduction) and, especially for O2 reoxidized sediments, uranium coatings were associated with Fe oxide/carbonate particulate formation.…”

Section: Uranium Sequestration Mechanismsmentioning

confidence: 99%

Uranium sequestration in sediment at an iron-rich contaminated site at Oak Ridge, Tennessee via. bioreduction followed by reoxidation

Phillips

et al. 2019

Journal of Environmental Sciences

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This study evaluated uranium sequestration performance in iron-rich (30 g/kg) sediment via bioreduction followed by reoxidation. Field tests (1383 days) at Oak Ridge, Tennessee demonstrated that uranium contents in sediments increased after bioreduced sediments were re-exposed to nitrate and oxygen in contaminated groundwater. Bioreduction of contaminated sediments (1200 mg/kg U) with ethanol in microcosm reduced aqueous U from 0.37 to 0.023 mg/L. Aliquots of the bioreduced sediment were reoxidized with O2, H2O2, and NaNO3, respectively, over 285 days, resulting in aqueous U of 0.024, 1.58 and 14.4 mg/L at pH 6.30, 6.63 and 7.62, respectively. The source-and the three reoxidized sediments showed different desorption and adsorption behaviors of U, but all fit a Freundlich model. The adsorption capacities increased sharply at pH 4.5 to 5.5, plateaued at pH 5.5 to 7.0, then decreased sharply as pH increased from 7.0 to 8.0. The O2-reoxidized sediment retained a lower desorption efficiency at pH over 6.0. The NO3-reoxidized sediment exhibited higher adsorption capacity at pH 5.5 to 6.0. The pH-dependent adsorption onto Fe(III) oxides and formation of U coated particles and precipitates resulted in U sequestration, and bioreduction followed by reoxidation can enhance the U sequestration in sediment.

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“…32 Retention of radionuclides by embedding them into Fe host minerals is advantageous over the reduction process in redox-stratified environments because the resultants are recalcitrant to remobilization and extraction. 33 Scavenging U(VI) by interacting with Fe(II) has been studied previously, most of which were performed in anaerobic environments. 34−36 Although thermodynamically favorable, homogeneous reduction of U(VI) by Fe(II) has not been observed at neutral pH in an anaerobic system.…”

Section: Introductionmentioning

confidence: 99%

“…As the intermediate precipitates transform into more stable phases (iron oxyhydroxides), the binding of U(VI) may be stabilized and incorporated into the structure of the precipitates. 33 It has been found that the formative species of Fe precipitates is closely related to the aqueous Fe(II) concentration (Table S1 of the Supporting Information), which has influence on the retention efficiency of U(VI). 37,38 Many researchers focused on the interactions of U(VI) and goethite, the formation of which is favored in a relatively high Fe(II) concentration.…”

Section: Introductionmentioning

confidence: 99%

“…37,38 Many researchers focused on the interactions of U(VI) and goethite, the formation of which is favored in a relatively high Fe(II) concentration. 7,33 However, the knowledge about the reactivity and retention ability of Fe precipitates forming in dilute aqueous Fe(II) solutions, which are typically relevant to reduce soil pore and ground waters, is still lacking. During the formation of Fe precipitates, the retention of U(VI) involves incorporation as well as adsorption.…”

Section: Introductionmentioning

confidence: 99%

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Retention of U(VI) by the Formation of Fe Precipitates from Oxidation of Fe(II)

Mei

Tan

et al. 2018

ACS Earth Space Chem.

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The fate of radionuclide contaminants can be strongly affected by the Fe(II) oxidation process at natural redox boundaries because the formative Fe precipitates may serve as scavengers for radionuclides. In this regard, we investigated the retention efficiency of U(VI) by the formative Fe precipitates in dilute FeCl2 solutions under mild oxidative conditions. The formed precipitates were characterized using spectroscopic methods. The results identified that the presence of U(VI) facilitated the formation of Fe precipitates as lepidocrocite. The high retention efficiency of U(VI) through co-precipitated reaction is ascribed to the synergetic effect of incorporation and adsorption processes. The successive acid-washing experiments, energy-dispersive X-ray spectra, and excitation–emission matrix spectra revealed that adsorbed U was washed off, while incorporated U was still in the precipitates. As a redox-active trace element, U incorporated into the solids could be in the state of U(V) or U(VI) as analyzed from X-ray photoelectron spectroscopy. These results may be of value in evaluating the potential of permanent retention of a trace element through redox and precipitation of iron oxides.

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Iron oxide formation from FeCl2 solutions in the presence of uranyl (UO22+) cations and carbonate rich media

Cited by 17 publications

References 59 publications

Uptake mechanisms of selenium oxyanions during the ferrihydrite-hematite recrystallization

Uptake mechanisms of selenium oxyanions during the ferrihydrite-hematite recrystallization

Uranium sequestration in sediment at an iron-rich contaminated site at Oak Ridge, Tennessee via. bioreduction followed by reoxidation

Retention of U(VI) by the Formation of Fe Precipitates from Oxidation of Fe(II)

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