Distribution coefficient in the sorption of radionuclides onto Ando soil in the presence of humic acid. Influence of the molecular size of humic acid

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 (Kd) in the sorption of 60Co on this type of soil was only slightly affected by the presence of HA. The Kd of 85Sr as the HA concentration increased. The Kd of 241Am decreased as the HA concentration increased and the Kd 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 100,000 MW. These results suggest that the Kd in the case of 60Co and 85Sr is mainly controlled by sorption of both cationic species and humic compounds, while the Kd of 241Am is controlled by the sorption of HA. (author)