Sorption properties of152Eu and241 Am in geological materials: Eu as an analogue for monitoring the Am behaviour in heterogeneous geological environments

摘要

In order to confirm the similar behavior of Eu and Am in heterogeneous geological materials, we carried out the batch experiments for determining the sorption property of radionuclides,152Eu and241Am. We used four different types of core rocks including biotite banded gneiss, biotite gneiss, metabasite and andestic tuff, and selected two samples per each lithology, one of which is fracture-bearing and another is fracture-free. Except for metabasites, rock samples of each type are similar in their compositions. We calculated sorption ratios of two radionuclides from the experimental results. Biotite gneiss and tuff had similar sorption trends for152Eu and241Am regardless of the existence of fractures, whereas two metabasite samples showed very different sorption properties. Such difference in the sorption trends revealed a close relationship with chemical compositions of the host rocks. Nevertheless,152Eu and241Am showed similar adsorption trends for all the samples with variable contact times regardless of petrography and pH variations, and particularly, the sorption trends of152Eu and241Am in the metabasites were similar. This observation suggests that Eu and Am have similar sorption properties on geological materials. Therefore, Eu can be used as a useful analogue of Am in all kinds of geological environments regardless of variations in lithology and pH of groundwater. In addition, sorption ratios of152Eu and241 Am are correlated with the contents of P2O5 and TiO2, suggesting that the chemical components such as P2O5 and TiO2 might be important for deciphering the interaction between the radionuclide and groundwater.