Multiple Scenarios of Bentonite Alteration

Oda, Chie  ; Sasaki, Ryoichi; Honda, Akira; Savage, D.*; Arthur, R. C,*

The multiple scenarios of bentonite alteration were ideveloped based on the possible mineralogical changes derived from knowledge of both experiments and observation of natural systems. It was focused that the mineral reaction involving hyperalkaline fluid thermodynamically depends on the variable chemical condition in bentonite buffer and that kinetics is important as well as thermodynamic stability in controlling their occurrence, i.e., the kinetic controls operate to remain metastable minerals over the long term. The mineralogical consequences of the interaction between clays and alkaline fluid are summarized as follows. / -Clay and gel illite / -Clay and gel metastable zeolite stable zeolite and feldspar / -Clay and gel stable zeolite and feldspar The typical minerals for each category (illite group, metastable zeolite group and stable zeolite and feldspar group) were selected. The scenarios give the range of potential secondary minerals occurring in chemical schemes of the bentonite alteration by cement pore fluids, and thus reasonable assumptions on the simulation of the chemical and mineralogical evolutions of geological disposal system for TRU waste.