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Title: Fate and transport of uranium (VI) in weathered saprolite

We conducted batch and column experiments to investigate sorption and transport of uranium (U) in the presence of saprolite derived from interbedded shale, limestone, and sandstone sequences. Sorption kinetics were measured at two initial concentrations (C0; 1, 10 mM) and three soil:solution ratios (Rs/w; 0.005, 0.25, 2 kg/L) at pH 4.5 (pH of the saprolite). The rate of U loss from solution (mmole/L/h) increased with increasing Rs/w. Uranium sorption exhibited a fast phase with 80% sorption in the first eight hours for all C0 and Rs/w values and a slow phase during which the reaction slowly approached (pseudo) equilibrium over the next seven days. The pH-dependency of U sorption was apparent in pH sorption edges. U(VI) sorption increased over the pH range 4e6, then decreased sharply at pH > 7.5. U(VI) sorption edges were well described by a surface complexation model using calibrated parameters and the reaction network proposed by Waite et al. (1994). Sorption isotherms measured using the same Rs/w and pH values showed a solids concentration effect where U(VI) sorption capacity and affinity decreased with increasing solids concentration. Moreover, this effect may have been due to either particle aggregation or competition between U(VI) and exchangeable cations for sorptionmore » sites. The surface complexation model with calibrated parameters was able to predict the general sorption behavior relatively well, but failed to reproduce solid concentration effects, implying the importance of appropriate design if batch experiments are to be utilized for dynamic systems. Transport of U(VI) through the packed column was significantly retarded. We also conducted transport simulations using the reactive transport model HydroGeoChem (HGC) v5.0 that incorporated the surface complexation reaction network used to model the batch data. Model parameters reported by Waite et al. (1994) provided a better prediction of U transport than optimized parameters derived from our sorption edges. The results presented in this study highlight the challenges in defining appropriate conditions for batch-type experiments used to extrapolate parameters for transport models, and also underline a gap in our ability to transfer batch results to transport simulations.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [2] ;  [5]
  1. Samsung C&T Corp., Seoul (Republic of Korea)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Chinese Academy of Sciences (CAS), Beijing (China)
  4. Univ. of Tennessee, Knoxville, TN (United States)
  5. Chonnam National Univ., Gwangju (Republic of Korea)
Publication Date:
OSTI Identifier:
1185310
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Journal of Environmental Radioactivity
Additional Journal Information:
Journal Volume: 139; Journal Issue: C; Journal ID: ISSN 0265-931X
Publisher:
Elsevier
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 54 ENVIRONMENTAL SCIENCES Uranium(VI); Transport; Modeling; Saprolite