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This content will become publicly available on May 26, 2016

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 [MgCO3] 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 (PCO2 = 10–3.5) or reduced partial pressures of carbon dioxide (PCO2 = 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 Oaxial = U(VI) = Oaxial 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 expected for uranyl complexes on the environmentally significant carbonatemore » 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:
OSTI Identifier:
1254518
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