Distribution Coefficient in the Sorption of Radionuclides onto Ando Soil in the Presence of Humic Acid

Abstract

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