Behavior of interlayer cation and expandability in ammonium-montmorillonite

Saito, Akito*; Sakuma, Hiroshi*; Oda, Chie  ; Honda, Akira; Sato, Tsutomu*

Chemical transformations of montmorillonite, a key component of bentonite, by ammonium ion as a reducing product of nitrate, may influence the suitable physical properties like expandability of the bentonite as the buffer material in deep geological disposal system for nitrates containing radioactive waste. Basal spacing of ammonium-montmorillonite before or after the interaction with 1M-ammonia water (pH12) was studied by XRD. Molecular dynamics method was also used to simulate the behavior of cation and water in the interlayer of ammonium-montmorillonite. The experimental results suggested that the interlayer cation in montmorillonite did not change from ammonium ion even after the interaction with ammonia water (pH12) which ammonia(aq) was dominant species in, and crystalline swelling behavior of ammonium-montmorillonite differed from that of montmorillonite containing other type of interlayer cation. MD calculation indicated these features may be due to the hydrogen bond between ammonium ion and basal oxygen of montmorillonite.