Uranium Contamination at the 300 Area of the Hanford Site
Release rates of uranium from contaminated sediments are dependent on several key environmental factors which significantly influence the fate and transport of uranium in sediments and groundwater. Two of these factors include the form(s) in which the uranium contamination exists in the sediments and the compositions of pore fluids and groundwater that will react with these sediments. Solid-phase characterization of one contaminated sample was used in conjunction with semi-selective extraction analyses of six samples collected from the 300 Area of the U.S. Department of Energy’s Hanford Site to identify the form of uranium in the sediments. Static and flow-through column leaching experiments were used to evaluate the effect of solution composition (i.e., ionic strength and carbonate concentration) on the leach rates of uranium from these sediments. Results of scanning electron microscopy analyses indicated that the majority of the uranium in the most contaminated sediment was present as discrete uranium phases (possibly as a calcium uranyl silicate) and co-precipitates. Column leach tests showed that uranium effluent concentrations did not achieve steady-state conditions over the duration of the experiments (several months); they continued to decrease slowly over time, indicating that the release of uranium from the contaminated sediments was a multi-rate kinetically controlled process. Subsequent static leach experiments on the residual column leached material indicated that uranium release from the contaminated sediments was highly dependent on U(VI) aqueous complexation with carbonate, with the percentage of remobilized uranium ranging from 0.05 to 27% over a range of carbonate solution concentrations from 0.87 to 12.2 mM, respectively.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 910528
- Report Number(s):
- PNNL-SA-46616; 830403000; TRN: US0704145
- Resource Relation:
- Related Information: Proceedings of the Third International Conference on Remediation of Contaminated Sediments (New Orleans, Louisiana; Jan 24–27, 2005), B4-08
- Country of Publication:
- United States
- Language:
- English
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