Understanding the Mechanism of Uranium Removal from Groundwater by Zero-Valent Iron Using X-ray Photoelectron Spectroscopy

Fiedor, Joseph N.; Bostick, W.D.; Jarabek, Robert J.; Farrell, James

doi:10.1021/es970385u

Cited by 242 publications

(144 citation statements)

References 21 publications

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“…This result was supported by Bostick et al [29] and Fiedor et al [30] Fiedor et al [30] explained the absence of reduction with the fact that the purging mixture to maintain anoxic conditions contained CO 2 . This CO 2 (dissolved HCO 3 -or CO 3 2-) forms stable complexes with U(VI) and favors its remaining in the bulk solutions.…”

Section: Introductionsupporting

confidence: 52%

Mechanism of uranium removal from the aqueous solution by elemental iron

Noubactep¹,

Schöner

Meinrath

2006

Journal of Hazardous Materials

124

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The effectiveness of elemental iron (Fe 0 ) to remove uranium (U) from the aqueous phase has been demonstrated. While the mitigation effect is sure, discrepancies in the removal mechanism have been reported. The objective of this study was to investigate the mechanism of U(VI) removal from aqueous phases by Fe 0 . For this purpose a systematic sequence of bulk experiments was conducted to characterize the effects of the availability and the abundance of corrosion products on U(VI) removal. Results indicated that U(VI) removal reactions did not primary occur at the surface of the metallic iron. It is determined that U(VI) co-precipitation with aging corrosion products is a plausible explanation for the irreversible fixation under experimental conditions. Results of XRD analyses did no show any U phases, whereas SEM-EDX analyses showed that U tended to associate with rusted areas on the surface of Fe 0 .Recovering U with different leaching solutions varied upon the dissolution capacity of the individual solutions for corrosion products, showing that the irreversibility of the removal 2 depends on the stability of the corrosion products. U(VI) co-precipitation as removal mechanism enables a better discussion of reported discrepancies.

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Section: Introductionsupporting

confidence: 52%

Mechanism of uranium removal from the aqueous solution by elemental iron

Noubactep¹,

Schöner

Meinrath

2006

Journal of Hazardous Materials

124

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“…In aqueous solution a hydroxylated film immediately forms on the surface of elemental iron. 49,50 Some of these surface hydroxyls are exchangeable, and oxyanions, such as chromate, can form both monodentate surface complexes and biatomic-bidentate surface complexes where an oxygen is shared between the oxyanion and a surface iron atom. [51][52][53] The net surface charge of a hydoxylated iron surface is pH dependant (protons readily exchange with the surface groups to produce OH 2 + , OH, or O -depending on pH.…”

Section: Sem Analysis Of Cr-reacted Zvi Couponsmentioning

confidence: 99%

“…50,53 Indeed most sorption studies investigating ZVI assume that sorption equilibrium is achieved in significantly less than 24hrs. 52,58 Thus the data Figure 1, which shows Cr(VI) removal over a period from about 2 to 20 days, strongly suggests that Cr(VI) sorption has time to reach equilibrium and that Cr(VI) reduction is the rate limiting step controlling the overall rate of Cr(VI) removal from solution.…”

Section: Sem Analysis Of Cr-reacted Zvi Couponsmentioning

confidence: 99%

Chromate Reduction in Highly Alkaline Groundwater by Zerovalent Iron: Implications for Its Use in a Permeable Reactive Barrier

Fuller

Stewart

Burke

2013

Ind. Eng. Chem. Res.

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It is not currently known if the widely used reaction of zero valent iron (ZVI) and Cr(VI) can be used in a permeable reactive barrier (PRB) to immobilise Cr leaching from hyper alkaline chromite ore processing residue (COPR). This study compares Cr(VI) removal from COPR leachate and chromate solution by ZVI at high pH. Cr(VI) removal occurs more rapidly from the chromate solution than from COPR leachate. The reaction is first order with respect to both [Cr(VI)] and the iron surface area, but iron surface reactivity is lost to the reaction.Buffering pH downwards produces little change in the removal rate or the specific capacity of iron until acidic conditions are reached. SEM and XPS analysis confirm that reaction products accumulate on the iron surface in both liquors, but that other surface precipitates also form in COPR leachate. Leachate from highly alkaline COPR contains Ca, Si and Al that precipitate on the iron surface and significantly reduce the specific capacity of iron to reduce Cr(VI). This study suggests that although Cr (VI) reduction by ZVI will occur at hyper alkaline pH, other solutes present in COPR leachate will limit the design life of a PRB. 4

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“…The temporally resolved mode is particularly useful for matrices containing multiple uranyl species (e.g., complexes with inorganic and organic [HS] species). X-ray absorption fine structure spectroscopy (XAFSS) and X-ray photoelectron spectroscopy (XPS) have been used to provide information on the U oxidation state and the coordination environment of UO 2 2+ in solids (e.g., sediments) and at the solid-water interface (Table 1) [53,54,55]. Both in water and at the solid-water interface, the formation of multinuclear uranyl complexes may be detected as precursors to solid phase formation [56,57].…”

Section: Sedimentmentioning

confidence: 99%

Uranium Speciation and Bioavailability in Aquatic Systems: An Overview

Markich

2002

The Scientific World JOURNAL

200

142

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The speciation of uranium (U) in relation to its bioavailability is reviewed for surface waters (fresh-and seawater) and their sediments. A summary of available analytical and modeling techniques for determining U speciation is also presented. U(VI) is the major form of U in oxic surface waters, while U(IV) is the major form in anoxic waters. The bioavailability of U (i.e., its ability to bind to or traverse the cell surface of an organism) is dependent on its speciation, or physicochemical form. U occurs in surface waters in a variety of physicochemical forms, including the free metal ion (U 4+ or UO 2 2+ ) and complexes with inorganic ligands (e.g., uranyl carbonate or uranyl phosphate), and humic substances (HS) (e.g., uranyl fulvate) in dissolved, colloidal, and/or particulate forms. Although the relationship between U speciation and bioavailability is complex, there is reasonable evidence to indicate that UO 2 2+ and UO 2 OH + are the major forms of U(VI) available to organisms, rather than U in strong complexes (e.g., uranyl fulvate) or adsorbed to colloidal and/or particulate matter. U(VI) complexes with inorganic ligands (e.g., carbonate or phosphate) and HS apparently reduce the bioavailability of U by reducing the activity of UO 2 2+ and UO 2 OH + . The majority of studies have used the results from thermodynamic speciation modeling to support these conclusions. Time-resolved laser-induced fluorescence spectroscopy is the only analytical technique able to directly determine specific U species, but is limited in use to freshwaters of low pH and ionic strength. Nearly all of the available information relating the speciation of U to its bioavailability has been derived using simple, chemically defined experimental freshwaters, rather than natural waters. No data are available for estuarine or seawater. Furthermore, there are no available data on the relationship between U speciation and bioavailability in sediments. An understanding of this relationship has been hindered due to the lack of direct quantitative U speciation techniques for particulate phases. More robust analytical techniques for determining the speciation of U in natural surface waters are needed before the relationship between U speciation and bioavailability can be clarified.

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Understanding the Mechanism of Uranium Removal from Groundwater by Zero-Valent Iron Using X-ray Photoelectron Spectroscopy

Cited by 242 publications

References 21 publications

Mechanism of uranium removal from the aqueous solution by elemental iron

Mechanism of uranium removal from the aqueous solution by elemental iron

Chromate Reduction in Highly Alkaline Groundwater by Zerovalent Iron: Implications for Its Use in a Permeable Reactive Barrier

Uranium Speciation and Bioavailability in Aquatic Systems: An Overview

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