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Title: Uranium speciation in acid waste-weathered sediments: The role of aging and phosphate amendments

Uranium speciation and lability are strongly coupled to mineral transformations in silicate sediments, particularly for sediments subjected to weathering in acidic, high-level radioactive waste, as occurred at the Department of Energy's Hanford (WA) site. Here, uncontaminated Hanford sediments were reacted for 365 days with acidic (pH 3), uranium-bearing waste solutions, with and without phosphate in batch experiments, prior to detailed characterizations using electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. In PO 4-reactant free systems, uranium speciation was controlled initially by precipitation of compreignacite [K 2(UO 2) 6O 4(OH) 6·8H 2O]- and becquerelite [Ca(UO 2) 6O 4(OH) 6·8H 2O]-like species. Subsequent further removal of uranium coincided with that of Si and accumulation of boltwoodite, [(K, Na)(UO 2) 2O 4(HSiO 4) 2•0.5(H 2O)]-like species of uranium at 180 and 365 days. When present, PO 4 exerted a direct and strong control over U speciation. Furthermore, the detection of meta-ankoleite, [K 2(UO 2) 2O 4(PO 4) 2·6H 2O] at all reaction times when U was present emphasizes the importance of dissolved phosphate as a control on U speciation. Here, meta-ankoleite appears well crystallized and when it occurs as the principal product of sediment weathering, its low solubility is expected to limit dissolvedmore » U(VI) concentrations in groundwater. Although boltwoodite solubility is also low, it is formed more slowly (and only when PO 4 is absent), after initial precipitation of more soluble, less crystalline uranyl hydroxides. In the context of Hanford crib waste our results suggest that with PO 4 present, nearly all uranium would have precipitated in the upper soil.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [3] ;  [5] ;  [6] ;  [7] ;  [8]
  1. Univ. of Vermont, Burlington, VT (United States). Dept. of Geology
  2. Univ. of Arizona, Tucson, AZ (United States). Dept. of Soil Water and Environmental Science; Univ. of Notre Dame, IN (United States). Dept. of Civil and Environmental Engineering and Earth Sciences
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  4. Anchor QEA, LLC, Portland, OR (United States)
  5. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Pohang Univ. of Science and Technology (POSTECH) (Korea, Republic of)
  6. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  7. Univ. of California, Merced, CA (United States). School of Natural Sciences
  8. Univ. of Arizona, Tucson, AZ (United States). Dept. of Soil Water and Environmental Science
Publication Date:
Grant/Contract Number:
SBR-DE-SC0006781; AC0576RL01830
Accepted Manuscript
Journal Name:
Applied Geochemistry
Additional Journal Information:
Journal Volume: 89; Journal Issue: C; Journal ID: ISSN 0883-2927
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; uranium; Hanford; acid waste; phosphate; uranyl silicates
OSTI Identifier: