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Title: Uranium immobilization and nanofilm formation on magnesium-rich minerals

Polarization-dependent grazing incidence X-ray absorption spectroscopy (XAS) measurements were completed on oriented single crystals of magnesite [MgCO 3] and brucite [Mg(OH) 2] reacted with aqueous uranyl chloride above and below the solubility boundaries of schoepite (500, 50, and 5 ppm) at pH 8.3 and at ambient (P CO2 = 10 –3.5) or reduced partial pressures of carbon dioxide (P CO2 = 10 –4.5). X-ray absorption near edge structure (XANES) spectra show a striking polarization dependence (χ = 0° and 90° relative to the polarization plane of the incident beam) and consistently demonstrated that the uranyl molecule was preferentially oriented with its O axial = U(VI) = O axial linkage at high angles (60–80°) to both magnesite (101¯4) and brucite (0001). Extended X-ray absorption fine structure (EXAFS) analysis shows that the “effective” number of U(VI) axial oxygens is the most strongly affected fitting parameter as a function of polarization. Furthermore, axial tilt in the surface thin films (thickness ~ 21 Å) is correlated with surface roughness [σ]. Our results show that hydrated uranyl(-carbonate) complexes polymerize on all of our experimental surfaces and that this process is controlled by surface hydroxylation. Lastly, these results provide new insights into the bonding configuration expectedmore » for uranyl complexes on the environmentally significant carbonate and hydroxide mineral surfaces.« less
Authors:
 [1] ;  [2] ;  [1] ;  [3] ;  [1]
  1. Univ. of Manchester, Manchester (United Kingdom)
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  3. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., Stanford, CA (United States)
Publication Date:
Grant/Contract Number:
EP/I036389/1; P41RR001209; AC02-76SF00515
Type:
Published Article
Journal Name:
Environmental Science and Technology
Additional Journal Information:
Journal Volume: 50; Journal Issue: 7; Journal ID: ISSN 0013-936X
Publisher:
American Chemical Society (ACS)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 58 GEOSCIENCES
OSTI Identifier:
1254518
Alternate Identifier(s):
OSTI ID: 1256059