Distribution Coefficient in the Sorption of Radionuclides onto Ando Soil in the Presence of Humic Acid. Influence of the Molecular Size of Humic Acid.

Abstract

Influence of humic acid (HA) on the sorption of 60 Co, 85 Sr and 241 Am onto Ando soil was examined with respect to HA of various molecular sizes. Distribution coefficient (K d ) in the sorption of 60 Co on this type of soil was only slightly affected by the presence of HA. The K d of 85 Sr as the HA concentration increased. The K d of 241 Am decreased as the HA concentration increased and the K d of HA showed a similar trend. In the solution, 241 Am selectively formed stable compounds with an HA ranging from 30,000 to 100,000 in molecular weight (MW), whereas 60 Co and 85 Sr preferentially but weakly interacted with HA fractions smaller than 100,000 MW. These results suggest that the K d in the case of 60 Co and 85 Sr is mainly controlled by sorption of both cationic species and humic compounds, while the K d of 241 Am is controlled by the sorption of HA.