Characterization of U(VI)-carbonato ternary complexes on hematite: EXAFS and electrophoretic mobility measurements

Bargar, J. R.; Reitmeyer, R.; Lenhart, J. J.; Davis, J. A.

Abstract:

We have measured U(VI) adsorption on hematite using EXAFS spectroscopy and electrophoresis under conditions relevant to surface waters and aquifers (0.01 to 10 ??M dissolved uranium concentrations, in equilibrium with air, pH 4.5 to 8.5). Both techniques suggest the existence of anionic U(VI)-carbonato ternary complexes. Fits to EXAFS spectra indicate that U(VI) is simultaneously coordinated to surface FeO6 octahedra and carbonate (or bicarbonate) ligands in bidentate fashions, leading to the conclusion that the ternary complexes have an inner-sphere metal bridging (hematite-U(VI)-carbonato) structure. Greater than or equal to 50% of adsorbed U(VI) was comprised of monomeric hematite-U(VI)-carbonato ternary complexes, even at pH 4.5. Multimeric U(VI) species were observed at pH ??? 6.5 and aqueous U(VI) concentrations approximately an order of magnitude more dilute than the solubility of crystalline ??-UO2(OH)2. Based on structural constraints, these complexes were interpreted as dimeric hematite-U(VI)-carbonato ternary complexes. These results suggest that Fe-oxide-U(VI)-carbonato complexes are likely to be important transport-limiting species in oxic aquifers throughout a wide range of pH values. Copyright (C) 2000 Elsevier Science Ltd.

Genre:

Article

ProdID:

70022384

Citation Author:

Bargar, J. R.; Reitmeyer, R.; Lenhart, J. J.; Davis, J. A.

Citation Contributing Office:

Citation Datum:

Citation Day:

Citation Edition:

Citation Editor:

Citation End Page:

2749

Citation Issue:

Citation Keywords:

Citation Language:

English

Citation Larger Work Title:

Geochimica et Cosmochimica Acta

Citation LatN:

Citation LatS:

Citation LonE:

Citation LonW:

Citation Month:

Citation No Pagination:

Citation Number Of Pages:

Citation Online Only Flag:

Citation Phsyical Description:

Citation Projection:

Citation Public Comments:

Citation Publisher:

Citation Series:

Citation Series Code:

Citation Series Number:

Citation Search Results Text:

Characterization of U(VI)-carbonato ternary complexes on hematite: EXAFS and electrophoretic mobility measurements; 2000; Article; Journal; Geochimica et Cosmochimica Acta; Bargar, J. R.; Reitmeyer, R.; Lenhart, J. J.; Davis, J. A.