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汚染土壌の減容化と再利用を目指したCsフリー鉱化法の提案

Proposition of Cs free mineralization for reduction and reuse of contaminated soil

下山 巖; 本田 充紀; 小暮 敏博*

Shimoyama, Iwao; Honda, Mitsunori; Kogure, Toshihiro*

放射性Csにより汚染された土壌に対する除染法は確立していない。我々は非放射性$$^{133}$$Csを飽和収着した風化黒雲母をモデル土壌とし、NaCl-CaCl$$_{2}$$混合塩と共に低圧環境下で700$$^{circ}$$Cの加熱処理を行うとCsと共にKがほぼ100%除去され、Caの組成比が温度と共に増加する蛍光X線分析の結果を得た。加熱処理後のX線回折スペクトルは大きく変化し、粘土鉱物からの相変化を示唆する結果が得られた。透過型電子顕微鏡を用いた構造解析を行い、700$$^{circ}$$Cでの主な生成物がCaを主要元素とする普通輝石であることを明らかにした。我々は、塩由来のCaが輝石形成を誘起すると共にイオン半径の大きいK$$^{+}$$とCs$$^{+}$$は輝石を構築できないため排出されるというモデルに基づき、土壌除染と再利用を可能にするCsフリー鉱化法を提唱する。

The decontamination method has not been established for soil contaminated with radioactive Cs. We adopted weathered biotite (WB) which sorbed non-radioactive $$^{133}$$Cs as a model contaminated soil and applied heating treatment to the WB at 700$$^{circ}$$C under a low pressure condition of 14 Pa with NaCl-CaCl$$_{2}$$ mixed salt. X-ray fluorescence analysis showed that almost all Cs and K were removed from the sample at 700$$^{circ}$$C and Ca became dominant with temperature. X-ray diffraction spectra largely changed after the heating treatment indicating some phase transition from WB. Transmission electron microscopy analysis clarified that augite was the dominant product after the heating treatment at 700$$^{circ}$$C. These results suggest a model that Ca derived from the mixed-salt induced the formation of augite, and that K$$^{+}$$ and 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.

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