Proposition of cesium-free mineralization for volume reduction and reuse of radioactive contaminated soil in Fukushima

Shimoyama, Iwao   ; Honda, Mitsunori   ; Kogure, Toshihiro*; Baba, Yuji  ; Hirao, Norie; Okamoto, Yoshihiro  ; Yaita, Tsuyoshi; Suzuki, Shinichi

We have proposed a low-pressure sublimation method for Cs removal from radioactive-contaminated soil in Fukushima. In this work, we investigated compositional and structural changes of Cs-sorbed weathered biotite (WB) before and after low-pressure sublimation with addition of NaCl-CaCl salts, to study Cs desorption mechanism from clay minerals. X-ray fluorescence spectroscopy clarified that 100% of Cs was removed with the salts at 700 C. Moreover, we found that 99% of K in WB was removed as well with the salts. On the other hand, Ca increased with heating temperature. X-ray diffraction analysis clarified that the reflections from WB disappeared and a number of new reflections appeared after the treatment with the salts. These results indicate WB changed to some silicates, and we clarified that the dominant silicate was augite using transmission electron microscopy. Based on these results, we propose a new idea, Cs-free mineralization, for Cs removal from clay minerals utilizing the mechanism in which monovalent large cations are discharged with accompanying phase transition from clay minerals to other minerals.