Influence of Calcium Carbonate on U(VI) Sorption to Soils

The high stability of calcium uranyl carbonate complexes in the circumneutral pH range has a strong impact on U(VI) sorption in calcareous soils. To quantify this influence, sorption of U(VI) to soils in the presence of naturally occurring calcium carbonate was investigated by conducting batch exper...

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Bibliographic Details
Published in:Environmental science & technology 2003-12, Vol.37 (24), p.5603-5608
Main Authors: Zheng, Zuoping, Tokunaga, Tetsu K, Wan, Jiamin
Format: Article
Language:English
Subjects:
Adsorption
Aluminum Silicates - chemistry
Applied sciences
Biological and physicochemical properties of pollutants. Interaction in the soil
Calcium
Calcium Carbonate - chemistry
Carbon
Clay
contaminants
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Environmental impact
Exact sciences and technology
Hydrogen-Ion Concentration
polluted soils
Pollution
Pollution, environment geology
Soil and sediments pollution
soil pH
Soil Pollutants, Radioactive - analysis
Soils
Solubility
uranium
Uranium - analysis
Uranium - chemistry
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Summary:The high stability of calcium uranyl carbonate complexes in the circumneutral pH range has a strong impact on U(VI) sorption in calcareous soils. To quantify this influence, sorption of U(VI) to soils in the presence of naturally occurring calcium carbonate was investigated by conducting batch experiments in which either U(VI) concentration or solution pH was varied. Two soils containing different calcium carbonate concentrations were selected, one from Oak Ridge, TN, and another from Altamont Pass, CA. The results show that the presence of calcium carbonate in soils strongly affects U(VI) sorption. Higher concentrations of soil calcium carbonate lead to a pronounced suppression of the pH-dependent sorption curve in the neutral pH range because of the formation of a very stable neutral complex of calcium uranyl carbonate in solution. A surface complexation model considering both strong and weak sites for ferrihydrite and ionizable hydroxyl sites for clay minerals was compared with experimental results, and U(VI) binding parameters were reasonably estimated. Fair agreement was found between the model predictions and sorption data, which span a wide range of U(VI) concentrations and pH. The results also show that appropriate solution-to-solid ratios need to be used when measuring distribution coefficients in calcareous soils to avoid complete CaCO3 dissolution and consequent dilution of calcium uranyl carbonate complexes.
ISSN:0013-936X
1520-5851
DOI:10.1021/es0304897