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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*; Okamoto, Yoshihiro; Baba, Yuji; Hirao, Norie*; Shiwaku, Hideaki; Yaita, Tsuyoshi; Suzuki, Shinichi
no journal, ,
It is necessary to establish Cs decontamination method for reduction and reuse of radioactive contaminated soil in Fukushima. We adopted 
Cs-sorbed weathered biotite (WB) as a model soil and studied composition and structure changes of WB by heating treatments with NaCl-CaCl alkaline salt under low-pressure. Cs was removed from WB by 100% by the heating treatment at 700C and we found that augite was formed as the dominant product. This result suggests that Cs ions 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 contaminated soil. Furthermore, we present our recent progress based on X-ray absorption fine structure (XAFS) spectroscopy in SPring-8 and Photon Factory to study the detail of the chemical reaction through Cs free mineralization.
Shimoyama, Iwao; Honda, Mitsunori; Kogure, Toshihiro*; Baba, Yuji; Yaita, Tsuyoshi; Okamoto, Yoshihiro
no journal, ,
We study radioactivity concentration of contaminated soil in Fukushima to examine the effectiveness of cesium free mineralization (CFM) and analyze structural change of the soil using X-ray diffraction (XRD). CaCl or KCl was added to the soil and heated in air or under low-pressure conditions. In the case of CaCl, decontamination ratio Rd showed similar tendency for both air and low-pressure heating, and we found that Rd reached to 97% after heating at 790C. XRD analysis showed that basal reflection peaks of clay minerals in the soil disappeared and quite different XRD patterns were observed between air and low-pressure heating treatments. These results indicate that CFM is effective for decontamination of actual Fukushima soil, and product by CFM largely depends on pressure condition during heating. On the other hand, Rd was higher for low-pressure heating than for air heating with KCl, and XRD showed that clay minerals remained after the heating treatment. This means different mechanisms of Cs removal from contaminated soil exist for heating treatments with KCl and CaCl.
Shimoyama, Iwao; Kogure, Toshihiro*; Okumura, Taiga*; Baba, Yuji; Okamoto, Yoshihiro
no journal, ,
In this work, we examined Cs-free mineralization (CFM) for decontamination of Fukushima soil with four alkaline chloride additives below 800C in air and under low-pressure conditions. In the case of CaCl, radioactivity concentration largely decreased in both air and low-pressure conditions, and decontamination ratio reached to 97% at 790C. In the case of MgCl, we found a tendency that decontamination ratio was higher under low-pressure condition than in air and it was more than 99% after three cycles of heat treatments at 695C. KCl and NaCl reagents also showed similar tendency, and decontamination ratio reached to 93% and 97% for KCl and NaCl, respectively, after five cycles of heat treatments at 790C. Structural analysis of products clarified that heat treatments with CaCl and MgCl decomposed biotite which is the major Cs sorbent in the soil in Fukushima. On the other hand, similar decomposition was not observed when KCl and NaCl were used as additives. Based on these results, CFM was confirmed to be effective for soil decontamination, and we found that Cs removal process depends on the valence of metal ions as chlorides.
Shimoyama, Iwao; Kogure, Toshihiro*; Okumura, Taiga*; Baba, Yuji
no journal, ,
Cs removal processes from soil largely depend on reagents and pressure in cesium free mineralization. We have proposed a hypothesis that monovalent cations remove Cs from clay minerals through ion exchange and divalent cations remove Cs through phase transformation of clay minerals based on results using CaCl and KCl reagents. In this work, we used MgCl and NaCl reagents to verify this hypothesis and studied decontamination ratio and structural change of mineral phase in soil. We found that the examination with these reagents supports our hypothesis, but both phase transformation and ion exchange were enhanced under low-pressure conditions. Because sea water includes NaCl and MgCl as major components, we attempted to use sea water salt as a reagent and demonstrated that soil can be decontaminated by about 99% after heat treatment at 790 C under low pressure conditions. This result indicates the processing cost of heat treatment can be decreased using cheap sea water.
Shimoyama, Iwao; Kogure, Toshihiro*; Okumura, Taiga*; Baba, Yuji
no journal, ,
We study decontamination ratio and structural change of soil after heat treatments with four kinds of alkaline chloride reagents in air and under low-pressure conditions to optimize soil decontamination method. Each reagent was added to contaminated soil with the weight ratio of 1/1, and we measured radioactivity and analyzed crystal phases of the samples after the heat treatments for 2 hours. In the case of CaCl, only small differences in decontamination ratio were observed in air and low-pressure conditions, and decontamination ratio reached to about 95% at 790C. After the processing, biotite in soil decomposed and products depended on in air and under low-pressure conditions. Whereas, in the case of MgCl, decontamination ratios were 40 and 90% after the heat treatments at 695C in air and under low-pressure conditions, respectively. We found that decomposition and phase transformation of biotite were more facilitated under low-pressure conditions than in air. Also, in the cases of NaCl and KCl, soil decontamination was more facilitated under low-pressure conditions; decontamination ratios were 15 and 94% after the heat treatments with NaCl at 790C in air and under low-pressure conditions, respectively. However, biotite remained after the heat treatments both in air and under low-pressure conditions. Based on this result, we conclude that ion exchange was the dominant Cs removal process for NaCl and KCl.
Shimoyama, Iwao; Kogure, Toshihiro*; Okumura, Taiga*; Baba, Yuji
no journal, ,
More than 99% of radioactive Cs can be removed from soil by heat treatment at more than 1000C, however, its high cost inhibits application of this method. In this work, we attempted heat treatment with four kinds of chloride reagents under low-pressure condition to decrease processing temperature. Each reagent was added to contaminated soil and heat treatment was applied in air and under low-pressure conditions for two hours. In the case of CaCl, the difference in decontamination ratio was small for different pressure conditions and decontamination ratio reached to 95% at 790C. On the other hand, MgCl, NaCl, and KCl had higher decontamination ratios under low-pressure conditions than in air. When MgCl was added, decomposition and phase transformation of biotite in soil was facilitated under low-pressure conditions, and decontamination ratios at 695C were 40 and 90% in air and under low-pressure conditions, respectively. In the cases of NaCl and KCl, biotite remained after the heat treatments and Cs was removed through ion exchange. When NaCl was added, decontamination ratios at 790C were 15 and 94% in air and under low-pressure conditions, respectively. Based on these results, we propose heat treatment with sea water salt as a reactant.
Shimoyama, Iwao; Baba, Yuji
no journal, ,
Soil decontamination is generally difficult because radioactive Cs can be strongly fixed in clay minerals, whereas efficient decontamination is possible when clay minerals are converted to different minerals which cannot include Cs in their crystal structures by reacting with some alkaline salts at high temperatures. So far, it is not clear why reaction temperature is largely decreased if some chloride is chosen as a reactant. In this work, we analyzed chemical bonding states of Cl using X-ray absorption spectroscopy (XAFS) for the samples after heat treatments of weathered biotite and NaCl-CaCl mixed salt and interpreted XAFS spectra using molecular orbital (MO) calculations to study the role of chlorine on phase transformation of clay minerals. We found that there existed not only monovalent-negative Cl sites but also high-valent positive Cl sites. We also estimated structural stabilities of some silica model clusters with chlorine using semiempirical MO calculations and clarified that formation of Cl-O bonds destabilizes silica network to decrease reaction temperature. These results suggest that Cl has some catalytic effect on phase transformation of clay minerals.
Shimoyama, Iwao
no journal, ,
Cs-free mineralization is a decontamination method to remove radiocesium from soil by converting clay minerals to different minerals through chemical reaction with additives, and its efficiency considerably depends on reagents. In this work, nitrate reagents were used to decrease processing temperatures. Weathered biotite (WB) which sorbed non-radioactive Cs was used as model soil. WB was heated with an additive for two hours and analyzed using X-ray fluorescence and X-ray diffraction after rinsing with water and drying. When calcium nitrate was added, Cs removal ratio reached to 100%at 450C in Ar atmosphere, and this achieves significant decrease of processing temperature as compared with the cases of chloride reagents. In the case of NaCl or KCl addition, ion exchange was the major Cs removal process at 700C, whereas in the case of NaNO
or KNO addition, phase transformations were induced at 634C under vacuum, which suggests that Cs removal process depends on the anion in the reagent. In the case of calcium nitrate, the phase transformation temperature decreased to approximately 500C, however, ion it is presumed that ion exchange was the major Cs removal process at 450C because WB was preserved at this temperature.
Shimoyama, Iwao; Baba, Yuji*
no journal, ,
Management of radioactive contaminated soil is an unsolved problem after the nuclear incident in Fukushima, but soil decontamination is generally difficult due to the existence of micaseous clay minerals in which radiocesium is strongly fixed. Cesium-free mineralization (CFM) can remove Cs from the soil through the conversion process from clay minerals to other minerals and the choice of reactant is critically important for this method. Because CaCl has higher decontamination efficiency than CaCO and Ca(OH) and facilitates phase transformation of clay minerals around 700C, it is deduced that Cl has a catalytic effect on phase transformation, however, the detail is not clear. In this work, Cs-sorbed weathered biotite (WB) was used as a model soil and chemical bonding states of Cl was studied using X-ray absorption spectroscopy and molecular orbital calculations. We clarified that Cl interacted with WB at 400C and Cl and higher valent Cl sites were formed by bonding with O in WB besides Cl
sites in the early stage of the reaction. Because formation of Cl-O bonds can destabilize the silica network, Cl can facililate decomposition and phase transformation of WB at moderate temperatures.
Shimoyama, Iwao; Baba, Yuji*
no journal, ,
Cs-free mineralization enable soil decontamination at lower temperature than conventional heat treatments because Cs is removed through conversion of clay minerals to different minerals, but the efficiency depends on additives. CaCl derives high decontamination ratio accompanying phase transformation of clay minerals at 700C, however, the effect of Cl is unclear. In this work, Cs-sorbed weathered biotite (Cs-WB) was used as a model soil, and the interaction between Cl and Cs-WB before phase transformation was investigated using NEXAFS spectroscopy. Cs-WB was reacted with NaCl-CaCl and excessive salt was removed by water rinsing. NEXAFS spectrum of the sample prepared at 400C showed three kind of Cl sites which are attributed to -1, +1, and high valencies based on the DV-X
molecular orbital calculations. Because +1 and high valence Cl sites with Cl-O bonding destabilize silica framework, this interaction can facilitate decomposition of clay minerals at moderate temperatures. The comparison of other chloride reagents suggests that the effect of Cl depends on the valence of counter cation in the reagent.
; Effect of chlorine on phase transformation of a clay mineralShimoyama, Iwao
no journal, ,
Radiocesium-contaminated soil is a severe unsolved problem in environmental remediation of Fukushima. Cesium-free mineralization (CFM) is a soil decontamination method by heating, and the characteristics of CFM is that Cs is removed by converting clay minerals which fix Cs in soil to other minerals through chemical reactions. CFM has succeeded Cs removal from weathered biotite (WB) at much lower temperature (700C) with CaCl reactant than conventional heat treatments. By contrast, phase transformation of WB did not occur at the temperature with Ca(OH) and CaCO reactants, which suggests some effect of Cl for phase transformation, however, the detail is unclear. The interaction between Cl and WB was studied using X-ray absorption spectroscopy. The Cl spectrum of the sample prepared at 400C with CaCl showed multiple components which are interpreted as negative monovalent, positive monovalent, and positive high-valent Cl sites based on molecular orbital (MO) calculations. Comparison of structural stability of some silica model clusters by MO calculations indicates that formation of O-Cl bonds destabilizes the system more efficiently than formation of Si-Cl bonds. These results suggest that O-Cl bonds destabilize clay minerals and facilitates phase transformation of clay minerals at lower temperatures.
