Influence of calcium carbonate on U(VI) sorption to soils
Uranium contamination of the subsurface resulting from pastradioactive waste disposal and storage practices represents a seriousenvironmental contamination problem at a number of sites. Under oxidizinggeochemical conditions, the mobility of U(VI) in subsurface is primarilycontrolled by sorption. In many soil systems, calcite represents animportant mineral phase which likely affects U(VI) sorption behavior. Toquantify this influence, sorption of U(VI) to soils in the presence ofnaturally occurring calcium carbonate was investigated by conductingbatch experiments in which either U(VI) concentration or solution pH wasvaried. Two soils containing different calcite concentrations wereselected, one from Oak Ridge, Tennessee, and another from Altamont Pass,California. The results show that the presence of calcium carbonate insoils strongly affects U(VI) sorption. Higher concentrations of soilcalcium carbonate lead to a pronounced suppression of the pH-dependentsorption curve in neutral pH range, because of the formation of a verystable neutral complex of calcium uranyl carbonate (Ca2UO2(CO3)3) insolution. A surface complexation model considering both strong and weaksites for ferrihydrite and ionizable hydroxyl sites for clay minerals wascompared with experimental results, and U(VI) binding parameters werereasonably estimated. Fair agreement was found between the modelpredictions and sorption data, which span a wide range of U(VI)concentrations and pH. The results also show that selection ofappropriate solution-to-solid ratios is important when measuringdistribution coefficients in calcareous soils because the impact ofcalcium carbonate on U(VI) sorption in natural systems can beartificially diminished by dilution.
- Research Organization:
- Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
- Sponsoring Organization:
- USDOE Director. Office of Science. Biological andEnvironmental Research
- DOE Contract Number:
- AC02-05CH11231
- OSTI ID:
- 926551
- Report Number(s):
- LBNL--54565; BnR: KP1301010
- Journal Information:
- Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 12 Vol. 37
- Country of Publication:
- United States
- Language:
- English
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