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Shimoyama, Iwao; Honda, Mitsunori; Kogure, Toshihiro*; Baba, Yuji; Hirao, Norie; Okamoto, Yoshihiro; Yaita, Tsuyoshi; Suzuki, Shinichi
no journal, ,
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.
Shimoyama, Iwao; Honda, Mitsunori; Kogure, Toshihiro*; Hirao, Norie*; Baba, Yuji; Okamoto, Yoshihiro; Yaita, Tsuyoshi; Suzuki, Shinichi
no journal, ,
We adopted low pressure heating treatments for Cs saturated and sorbed weathered biotite (WB) with some alkaline salts, e.g., CaCl, KCl, NaCl to develop decontamination method for radioactive Cs contaminated soil in Fukushima, and analyzed the samples before and after the treatments using X-ray fluorescence analysis, X-ray diffraction, transmission electron microscopy, and thermal desorption spectroscopy. When we heated WB at 700 C with CaCl, the structure of WB completely decomposed, and almost 100% of Cs and K sorbed in WB were removed from the sample. We observed that the Ca content in the product increased with temperature, which induced phase change from WB to augite and wadalite. These results indicate that Cs
and K that are large monovalent cations were discharged by formation of these products. Meanwhile, the addition of KCl removed only 55% of Cs at 700 C through ion exchange reaction keeping the layered structure of WB. Based on these phenomena, we propose the idea of Cs free mineralization that enables us to decontaminate soil using phase change from clay minerals to other minerals by reactions with alkaline salts.
Shimoyama, Iwao; Honda, Mitsunori; Kogure, Toshihiro*; Baba, Yuji; Hirao, Norie*; Okamoto, Yoshihiro; Yaita, Tsuyoshi; Suzuki, Shinichi
no journal, ,
The decontamination method has not been established for soil contaminated with radioactive Cs. We adopted weathered biotite (WB) which sorbed non-radioactive 
Cs as a model contaminated soil and applied heating treatment to the WB at 700C under a low pressure condition with CaCl or KCl salt. X-ray fluorescence analysis showed that almost all Cs was removed after the heating at 700C with CaCl and Ca became dominant with temperature. X-ray diffraction and transmission electron microscopy analysis indicated some phase transition from WB after the heating treatment. These results suggest a model that Ca derived from the salt induced the formation of augite, and that Cs were eliminated from the product as these large-size cations cannot constitute augite. Based on this model, we propose Cs free mineralization which can achieve decontamination and reuse of soil in Fukushima.
Shimoyama, Iwao; Honda, Mitsunori; Kogure, Toshihiro*; Baba, Yuji; Okamoto, Yoshihiro; Chiba, Noriaki; Yaita, Tsuyoshi; Suzuki, Shinichi
no journal, ,
We have found that Cs can be largely removed from weathered biotite (WB) in Fukushima by low-pressure heating treatment with some alkaline salts, but the detail of the mechanism is still unclear. We analyze compositional and structural change of WB using XRF, XRD, TEM, and NEXAFS. NaCl-CaCl mixed salt and WB were mixed in a weight ratio of 1/1 and heated in a low-pressure condition. Excess salt in the sample was removed by rinsing with distilled water. Cs/Si ratio decreased to 11% and 0 % by the treatment at 600C and 700C, respectively. We found decrease of K with Cs. Meanwhile, Ca and Cl increased with temperature. XRD analysis clarified that new peaks appeared above 500C and peaks of WB disappeared at 700C. TEM analysis clarified that augite and wadalite were dominant products after the heating treatment. NEXAFS analysis clarified that Ca and Cl have different chemical bonding depending on atmospheric and low pressures. Based on these results, we propose Cs free mineralization for decontamination of soil in Fukushima.