Speciation of uranyl sorbed at multiple binding sites on montmorillonite

Journal Article · Thu Sep 01 04:00:00 EDT 1994 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(94)90154-6· OSTI ID:6447483

Chisholm-Brause, C; Buscher, C T; Eller, P G; Morris, D E; Conradson, S D ^[1]

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1. Los Alamos National Lab., NM (United States)

The authors have investigated the structures of U(VI) complexes as uranyl moieties sorbed onto a reference montmorillonite, SAz-1, using X-ray absorption fine structure spectroscopy (XAFS). The uranyl-loaded clays were prepared from aqueous solutions of uranyl nitrate in the pH range from 3.0 to 3.5. The U concentrations on the clay ranged from 1.7 to 34.6% of the reported cation exchange capacity (CEC = 1.2 meq/g) of the clay. For all samples, XAFS results indicate that there are two axial oxygen atoms at 1.78-1.80 [angstrom], as expected for the uranyl moiety. The average numbers and distances of equatorial oxygen atoms about uranyl sorbed on the clay vary significantly as a function of surface coverage. At high coverage (34.6% CEC), the average number and distance of equatorial oxygen atoms are near those found for the fully hydrated uranyl species in aqueous solution. However, there are fewer equatorial oxygen atoms at a shorter average distance about uranyl sorbed at low coverage (1.7% CEC). At moderate coverage (7.3% CEC), the average number and distance of equatorial oxygen atoms are intermediate between those at higher and lower coverage. These changes suggest that sorbing U is reacting with at least three different sites on the clay as U concentration increases. The existence of multiple surface sites and sorption complexes which are structurally distinct from solution species need to be considered for rigorous modeling of sorption processes.

• OSTI ID: 6447483
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 58:17; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400702 -- Radiochemistry & Nuclear Chemistry-- Properties of Radioactive Materials
54 ENVIRONMENTAL SCIENCES
540230* -- Environment
Terrestrial-- Radioactive Materials Monitoring & Transport-- (1990-)
ACTINIDE COMPLEXES
ACTINIDE COMPOUNDS
CLAYS
COMPLEXES
CONTAMINATION
ENVIRONMENTAL TRANSPORT
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MASS TRANSFER
MATERIALS
MONTMORILLONITE
PH VALUE
SOILS
SORPTION
SORPTIVE PROPERTIES
SPECTRA
SURFACE PROPERTIES
URANIUM COMPLEXES
URANIUM COMPOUNDS
URANYL COMPLEXES
URANYL COMPOUNDS
X-RAY SPECTRA