Smectite alteration and its influence on the barrier properties of smectite clay for a repository

摘要

Hydrothermal tests were conducted to investigate smectite alteration and its influence on the barrier properties of a smectite clay for a repository. Examinations of the X-ray diffraction patterns of the starting material and reacted samples and the silica release rate in the solution revealed that the smectite was transformed into randomly interstratified illite-smectite by a smectite-to-illite conversion when it was hydrothermally treated under a potassium concentration of 0.5 M, maintaining a 1 g/20 ml of solid sample-to-solution ratio. Temperature was observed to be a key factor controlling the conversion reaction. The smectite alteration affected the barrier properties of smectite clay for a repository: when the temperature increased, the percentage of the expandable smectite layers in the randomly interstratified illite-smectite decreased, the layer charge was more negative, and the cation exchange capacity and the sorption capacity for the cesium and nickel ions were reduced.