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Title: A spectroscopic study of uranyl speciation in chloride-bearing solutions at temperatures up to 250 °C

The speciation of U in NaCl-bearing solutions at temperatures up to 250 °C and concentrations of NaCl up to 1.5 m has been investigated using an in situ spectroscopic technique. The recorded spectra permit us to identify the species present in the solutions as UO 2 2+, UO 2Cl +, and UO 2Cl 2°. UO 2Cl 3 - is also likely present at high temperatures and NaCl concentrations, but concentrations of this species are insufficient for derivation of the formation constants. No evidence was found for species of higher ligand (Cl-) number. Thermodynamic stability constants derived for these species show fair agreement with published data for 25 °C, but differ significantly from those predicted by an earlier high-temperature study (Dargent et al., 2013), which suggested that UO 2Cl 4 2- and UO 2Cl 5 3- contribute significantly to the mass balance of uranyl chloride complexes, especially at high temperature. In contrast, our data suggest that the main uranyl-chloride complex present in aqueous solutions at T >150 °C and concentrations of NaCl relevant to natural hydrothermal systems is UO 2Cl 2°. The values of the logarithms of thermodynamic formation constants (β) for the reaction UO 2 2+ + Cl - =more » UO 2Cl + are 0.02, 0.25, 0.55, 1.09, 1.59, and 2.28 derived at 25, 50, 100, 150, 200, and 250 °C, respectively. For the reaction UO 2 2+ + 2Cl - = UO 2Cl 2° the values of log β derived at these temperatures are 0.4, 0.58, 0.74, 1.44, 2.18, and 3.42. Values of the formation constant estimated for uranyl-chloride species predict the high concentrations of U observed by Richard et al. (2011) in fluid inclusions of the giant McArthur River unconformity-type uranium deposit.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ;  [2] ;  [1] ; ORCiD logo [1] ;  [2]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. McGill Univ., Montreal, QC (Canada). Dept. of Earth and Planetary Sciences
Publication Date:
Report Number(s):
LA-UR-17-23808
Journal ID: ISSN 0016-7037; TRN: US1702906
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 222; Journal ID: ISSN 0016-7037
Publisher:
The Geochemical Society; The Meteoritical Society
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Nuclear Energy (NE)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; uranyl; chloride; hydrothermal; speciation; aqueous solution
OSTI Identifier:
1406219