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Leaching behavior of iodine anion from metakaolinite-sodium-silicate-based geopolymer

メタカオリナイト-ケイ酸ナトリウムジオポリマーからの陰イオン形ヨウ素の浸出挙動

香西 直文; 宇都宮 聡*; 大貫 敏彦*

Kozai, Naofumi; Utsunomiya, Satoshi*; Onuki, Toshihiko*

$$^{129}$$Iは放射性廃棄物処分の安全評価において極めて重要な核種である。本研究では、セメント代替物質候補であるジオポリマーのヨウ素イオン閉じ込めに関する基礎的性能を調べた。ケイ酸ナトリウムジオポリマー固化体は陰イオン形ヨウ素を化学的に閉じ込める能力がないことがわかり、I$$^{-}$$は固化体から容易に溶出する。IO$$_{3}$$$$^{-}$$の80%程度は閉じ込められ、それはポリマー構造中に物理的に閉じ込められたためである可能性が高い。ジオポリマーの作製に必要な水分量に溶かすことができるそれらのヨウ素陰イオンはわずかである。ヨウ素の陰イオンをLDHに吸着させて固化することによって、固化可能なヨウ素イオン量を大きく増やすことができた。

$$^{129}$$I is one of the most important fission products for safety assessment of radioactive waste repositories. This study investigated basic characteristics of a cement-alternative material candidate, "geopolymer (GP)", on iodine (I$$^{-}$$ and IO$$_{3}$$$$^{-}$$) confinement. It was found that representative GP, metakaolinite- sodium silicate - based GP, has no ability to chemically retain those iodine anions. I$$^{-}$$ was easily leached from GP solidified bodies. Approximately 80% of IO$$_{3}$$$$^{-}$$ was retained by GP solidified bodies, which was probably due to physical confinement in the polymer structure. Amount of iodine anions that can be solidified in GP solidified bodies was small since iodine anions do not much dissolve in the liquid used for GP synthesis. However, we also found that a larger amount of iodine anions can be solidified by iodine anions adsorbing layered double hydroxide is solidified in geopolymer.

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