Molecular characterization of uranium(VI) sorption complexes on iron(III)-rich acid mine water colloids

Ulrich, Kai-Uwe; Roßberg, André; Foerstendorf, Harald; Zänker, Harald; Scheinost, Andreas C.

doi:10.1016/j.gca.2006.08.031

Cited by 91 publications

(83 citation statements)

References 72 publications

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“…In all spectra, the Fourier transform shows a peak near 3.48 Å that has been attributed by previous workers to a bidentate edge-sharing (E2) inner-sphere complex (e.g., Waite et al, 1994;Bargar et al, 1999;Moyes et al, 2000;Ulrich et al, 2006). However, for all of our samples (surface loading 0.21-2.6 wt% U), we can fit the $3.48 Å peak entirely to multiple scattering within the cluster shown in Fig.…”

Section: Exafs Of U(vi) Sorbed To Goethitesupporting

confidence: 64%

“…Bargar et al (1999Bargar et al ( , 2000 have interpreted an analogous feature in the spectrum of UO 2 2þ on hematite as resulting from a U-C scattering in a ternary UO 2 CO 3 complex. Ulrich et al (2006) find that the 2.9 feature is also present in the EXAFS of UO 2 2þ sorbed to ferrihydrite at pH 8 when pCO 2 =10 À3.5 bar. Furthermore, they find evidence for the expected carbonate oxygen at 4.3 Å .…”

Section: Exafs Of U(vi) Sorbed To Goethitementioning

confidence: 70%

“…Furthermore, they find evidence for the expected carbonate oxygen at 4.3 Å . On the other hand, Ulrich et al (2006) also find the 2.8-2.9 Å peak (but without the 4.3 Å oxygen) at pH 5.5 when pCO 2 <2· 10 À6 bar. Ulrich et al (2006) proposed that the 2.9 Å ligand is an oxygen on the surface FeO 6 polyhedron; however, the structure they proposed requires a physically unrealistic distance between the UO 2 2þ axial oxygen and the FeO 6 surface oxygens.…”

Section: Exafs Of U(vi) Sorbed To Goethitementioning

confidence: 82%

“…On the other hand, Ulrich et al (2006) also find the 2.8-2.9 Å peak (but without the 4.3 Å oxygen) at pH 5.5 when pCO 2 <2· 10 À6 bar. Ulrich et al (2006) proposed that the 2.9 Å ligand is an oxygen on the surface FeO 6 polyhedron; however, the structure they proposed requires a physically unrealistic distance between the UO 2 2þ axial oxygen and the FeO 6 surface oxygens. Even if the E2 complex occurs on ferrihydrite, it cannot explain the 2.9 Å peak in goethite where the E2 complex cannot be significant at high surface loading.…”

Section: Exafs Of U(vi) Sorbed To Goethitementioning

confidence: 82%

“…1). EXAFS spectra of uranium on ferrihydrite (Ulrich et al, 2006) and hematite (Bargar et al, 1999) show evidence for a U-C scattering indicating the presence of UO 2 CO 3 ternary complexes. The nature and significance of these complexes on goethite is unclear.…”

Section: Introductionmentioning

confidence: 98%

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Surface complexation of U(VI) on goethite (α-FeOOH)

Sherman

Peacock

Hubbard

2008

Geochimica et Cosmochimica Acta

196

163

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Sorption of U(VI) to goethite is a fundamental control on the mobility of uranium in soil and groundwater. Here, we investigated the sorption of U on goethite using EXAFS spectroscopy, batch sorption experiments and DFT calculations of the energetics and structures of possible surface complexes. Based on EXAFS spectra, it has previously been proposed that U(VI), as the uranyl cation UO 2 2þ , sorbs to Fe oxide hydroxide phases by forming a bidentate edge-sharing (E2) surface complex, >Fe(OH) 2 UO 2 (H 2 O) n . Here, we argue that this complex alone cannot account for the sorption capacity of goethite (a-FeOOH). Moreover, we show that all of the EXAFS signal attributed to the E2 complex can be accounted for by multiple scattering. We propose that the dominant surface complex in CO 2 -free systems is a bidentate corner-sharing (C2) complex, (>FeOH) 2 UO 2 (H 2 O) 3 which can form on the dominant {101} surface. However, in the presence of CO 2 , we find an enhancement of UO 2 sorption at low pH and attribute this to a (>FeO)CO 2 UO 2 ternary complex. With increasing pH, U(VI) desorbs by the formation of aqueous carbonate and hydroxyl complexes. However, this desorption is preceded by the formation of a second ternary surface complex (>FeOH) 2 UO 2 CO 3 . The three proposed surface complexes, (>FeOH) 2 UO 2 (H 2 O) 3 , >FeOCO 2 UO 2 , and (>FeOH) 2 UO 2 CO 3 are consistent with EXAFS spectra. Using these complexes, we developed a surface complexation model for U on goethite with a 1-pK model for surface protonation, an extended Stern model for surface electrostatics and inclusion of all known UO 2 -OH-CO 3 aqueous complexes in the current thermodynamic database. The model gives an excellent fit to our sorption experiments done in both ambient and reduced CO 2 environments at surface loadings of 0.02-2.0 wt% U.

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Section: Exafs Of U(vi) Sorbed To Goethitesupporting

confidence: 64%

Section: Exafs Of U(vi) Sorbed To Goethitementioning

confidence: 70%

Section: Exafs Of U(vi) Sorbed To Goethitementioning

confidence: 82%

Section: Exafs Of U(vi) Sorbed To Goethitementioning

confidence: 82%

Section: Introductionmentioning

confidence: 98%

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Surface complexation of U(VI) on goethite (α-FeOOH)

Sherman

Peacock

Hubbard

2008

Geochimica et Cosmochimica Acta

196

163

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X‐Ray Absorption Fine Structure Spectroscopy in Fe Oxides and Oxyhydroxides

et al. 2016

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X-ray absorption ﬁne structure (XAFS) spectroscopies [1–3] have advanced\ud rapidly since the development of synchrotron radiation facilities that provide\ud intense X-ray radiation with a continuous spectrum that can reach 120 keV.\ud XAFS consists of measuring a signal proportional to the absorption coeﬃcient,\ud (E), as a function of the energy E of the incident X-ray radiation near and above\ud the binding energy of a core level electron in an atom

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A novel ATR‐FTIR technique for identifying colloid composition in natural waters

McGuire

Herman

2014

Hydrological Processes

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Although understanding colloid composition has been frequently cited as essential to predicting contaminant transport in natural waters, most current methods to collect and identify colloid composition chemically alter the colloids prior to analysis and fail to identify colloid mineralogy and organic components. This paper presents a new, low‐cost method employing attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR) to identify colloids including organic material in concentrated suspensions. The concentration method employing tangential ultrafiltration at a steady temperature prevents redistribution of dissolved phase and suspended sediments into the colloidal fraction through post‐sampling reactions. ATR‐FTIR allows for direct analysis of concentrated suspensions rather than requiring drying that may alter composition in the colloidal phase, for example, by precipitating carbonates in samples from karst waters. The ability of this technique to monitor variation in colloidal composition is demonstrated through the examination of colloids under two different flow conditions in a karst aquifer and the West Branch of the Susquehanna River in Central Pennsylvania. Copyright © 2014 John Wiley & Sons, Ltd.

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Molecular characterization of uranium(VI) sorption complexes on iron(III)-rich acid mine water colloids

Cited by 91 publications

References 72 publications

Surface complexation of U(VI) on goethite (α-FeOOH)

Surface complexation of U(VI) on goethite (α-FeOOH)

X‐Ray Absorption Fine Structure Spectroscopy in Fe Oxides and Oxyhydroxides

A novel ATR‐FTIR technique for identifying colloid composition in natural waters

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