Reaction facilitation effect of alkaline chloride on Cs removal through phase transformation of a clay mineral

Shimoyama, Iwao   ; Baba, Yuji*  

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.