“How do ions behave in soil?” is an important question in many fields, including radioactive waste treatment. Among various soil minerals, clay minerals are particularly important.
 Until now, ion adsorption on clay minerals has been studied separately for ions, leading to a lack of systematic understanding. Therefore, we analyzed the adsorption behavior of various ions using molecular-level experiments and supercomputer simulations. We found that adsorption behavior can be understood systematically by focusing on two factors: “hydration energy” and “ionic radius.” Building on this finding, we predicted that radium, with its large ionic radius, would be strongly adsorbed on clay minerals. This prediction was confirmed by analyzing environmental soil samples. These results showed the applicability of the finding.
 Our finding can be widely applied for adsorption reaction on clay minerals. Therefore, the discovery advances our understanding of radionuclide behavior in soil and also contributes to other fields, such as resource exploration, planetary science (e.g., Mars and asteroids such as Ryugyu), and agricultural efficiency improvement.

This study was conducted as a joint project with the University of Tokyo and Osaka University, and supported by JSPS KAKENHI Grant Numbers JP19K23432, JP21H02090, JP21K18917, JP23K17034.