Difference in expansion and dehydration behaviors between NH
- and K-montmorillonite
NH
-およびK-モンモリロナイトの膨張・脱水挙動の違い
川喜田 竜平
; 齋藤 彬人*; 佐久間 博*; 安楽 総太郎
; 菊池 亮佑*; 大竹 翼*; 佐藤 努*
Kawakita, Ryohei; Saito, Akito*; Sakuma, Hiroshi*; Anraku, Sohtaro; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*
Montmorillonite (Mt) expansion and swelling are key factors for barrier performance of bentonite in trans-uranic (TRU) and high-level radioactive waste disposals. In the case of co-located geological disposal of TRU waste with high level waste, ammonium ion (NH![$$_4$$](/search/images/ERPTIJA.gif)
) which is changed from nitrate ion leached from TRU waste has possibility to contact with bentonite, exchange interlayer cation of Mt to form NH
-Mt, and deteriorate its performance. Because of similar hydration energy of NH![$$_4$$](/search/images/ERPTIJA.gif)
to K
, NH
-Mt could have lower expandability or change to non-expandable mineral as reported on K-Mt. Therefore, expansion and alteration behaviors of NH
-Mt, especially comparison to the behaviors of K-Mt, are necessary to understand for safety assessment of the waste disposal. In this study, the hydration behavior of NH
-Mt was investigated by XRD and molecular dynamics (MD) simulation in comparison with K-Mt. XRD profiles under Relative Humidity (RH) control showed that expansion of NH
-Mt was similar to that of K-Mt at more than RH40% with slightly different d-values. However, expansion of NH
-Mt kept at lower than RH20%, while K-Mt easily dehydrate at the same RH. MD simulation revealed that hydrogen bonding (HB) in NH![$$_4$$](/search/images/ERPTIJA.gif)
molecules causes the difference in hydration behavior between NH
- and K-Mt, as HB cause larger basal spacing at dehydrated state and easier hydration. This gap on hydration may attribute the difference in alteration to non-expandable minerals after dehydration, indicating that NH![$$_4$$](/search/images/ERPTIJA.gif)
have lower possibility for alternation and smaller effect on barrier performance of bentonite than K
.