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Title: Molecular-scale structure of uranium(VI) immobilized with goethite and phosphate

Abstract

The molecular-scale immobilization mechanisms of uranium uptake in the presence of phosphate and goethite were examined by extended X-ray absorption fine structure (EXAFS) spectroscopy. Wet chemistry data from U(VI)-equilibrated goethite suspensions at pH 4-7 in the presence of {approx}100 {micro}M total phosphate indicated changes in U(VI) uptake mechanisms from adsorption to precipitation with increasing total uranium concentrations and with increasing pH. EXAFS analysis revealed that the precipitated U(VI) had a structure consistent with the meta-autunite group of solids. The adsorbed U(VI), in the absence of phosphate at pH 4-7, formed bidentate edge-sharing, {triple_bond}Fe(OH){sub 2}UO{sub 2}, and bidentate corner-sharing, ({triple_bond}FeOH){sub 2}UO{sub 2}, surface complexes with respective U-Fe coordination distances of {approx}3.45 and {approx}4.3 {angstrom}. In the presence of phosphate and goethite, the relative amounts of precipitated and adsorbed U(VI) were quantified using linear combinations of the EXAFS spectra of precipitated U(VI) and phosphate-free adsorbed U(VI). A U(VI)-phosphate-Fe(III) oxide ternary surface complex is suggested as the dominant species at pH 4 and total U(VI) of 10 {micro}M or less on the basis of the linear combination fitting, a P shell indicated by EXAFS, and the simultaneous enhancement of U(VI) and phosphate uptake on goethite. A structural model for the ternary surface complexmore » was proposed that included a single phosphate shell at 3.6 {angstrom} (U-P) and a single iron shell at {approx}4.3 {angstrom} (U-Fe). While the data can be explained by a U-bridging ternary surface complex, ({triple_bond}FeO){sub 2}UO{sub 2}PO{sub 4}, it is not possible to statistically distinguish this scenario from one with P-bridging complexes also present.« less

Authors:
; ; ;  [1]
  1. WU
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
National Science Foundation (NSF)
OSTI Identifier:
1045687
Resource Type:
Journal Article
Journal Name:
Environ. Sci. Technol.
Additional Journal Information:
Journal Volume: 46; Journal Issue: (12) ; 06, 2012; Journal ID: ISSN 0013-936X
Country of Publication:
United States
Language:
ENGLISH
Subject:
54 ENVIRONMENTAL SCIENCES; ABSORPTION; ADSORPTION; CHEMISTRY; FINE STRUCTURE; GOETHITE; IRON; OXIDES; PHOSPHATES; PRECIPITATION; SPECTRA; SPECTROSCOPY; STRUCTURAL MODELS; URANIUM

Citation Formats

Singh, Abhas, Catalano, Jeffrey G, Ulrich, Kai-Uwe, and Giammar, Daniel E. Molecular-scale structure of uranium(VI) immobilized with goethite and phosphate. United States: N. p., 2012. Web. doi:10.1021/es300494x.
Singh, Abhas, Catalano, Jeffrey G, Ulrich, Kai-Uwe, & Giammar, Daniel E. Molecular-scale structure of uranium(VI) immobilized with goethite and phosphate. United States. doi:10.1021/es300494x.
Singh, Abhas, Catalano, Jeffrey G, Ulrich, Kai-Uwe, and Giammar, Daniel E. Thu . "Molecular-scale structure of uranium(VI) immobilized with goethite and phosphate". United States. doi:10.1021/es300494x.
@article{osti_1045687,
title = {Molecular-scale structure of uranium(VI) immobilized with goethite and phosphate},
author = {Singh, Abhas and Catalano, Jeffrey G and Ulrich, Kai-Uwe and Giammar, Daniel E},
abstractNote = {The molecular-scale immobilization mechanisms of uranium uptake in the presence of phosphate and goethite were examined by extended X-ray absorption fine structure (EXAFS) spectroscopy. Wet chemistry data from U(VI)-equilibrated goethite suspensions at pH 4-7 in the presence of {approx}100 {micro}M total phosphate indicated changes in U(VI) uptake mechanisms from adsorption to precipitation with increasing total uranium concentrations and with increasing pH. EXAFS analysis revealed that the precipitated U(VI) had a structure consistent with the meta-autunite group of solids. The adsorbed U(VI), in the absence of phosphate at pH 4-7, formed bidentate edge-sharing, {triple_bond}Fe(OH){sub 2}UO{sub 2}, and bidentate corner-sharing, ({triple_bond}FeOH){sub 2}UO{sub 2}, surface complexes with respective U-Fe coordination distances of {approx}3.45 and {approx}4.3 {angstrom}. In the presence of phosphate and goethite, the relative amounts of precipitated and adsorbed U(VI) were quantified using linear combinations of the EXAFS spectra of precipitated U(VI) and phosphate-free adsorbed U(VI). A U(VI)-phosphate-Fe(III) oxide ternary surface complex is suggested as the dominant species at pH 4 and total U(VI) of 10 {micro}M or less on the basis of the linear combination fitting, a P shell indicated by EXAFS, and the simultaneous enhancement of U(VI) and phosphate uptake on goethite. A structural model for the ternary surface complex was proposed that included a single phosphate shell at 3.6 {angstrom} (U-P) and a single iron shell at {approx}4.3 {angstrom} (U-Fe). While the data can be explained by a U-bridging ternary surface complex, ({triple_bond}FeO){sub 2}UO{sub 2}PO{sub 4}, it is not possible to statistically distinguish this scenario from one with P-bridging complexes also present.},
doi = {10.1021/es300494x},
journal = {Environ. Sci. Technol.},
issn = {0013-936X},
number = (12) ; 06, 2012,
volume = 46,
place = {United States},
year = {2012},
month = {10}
}