The effects of silica sand content and temperature on diffusion of selenium in compacted bentonite under reducing conditions

摘要

Apparent diffusivities (Da) in compacted bentonite for Se were obtained at a dry density of 1.6 Mg/m~3 as a function of silica sand content (0-50wt%) and temperature (22.5, 60 °C) under reducing conditions. A Na-bentonite, Kunigel-Vl and ~(75)Se were used as a clay material and as a tracer in diffusion experiments, respectively. The obtained Da values showed a tendency to increase with increasing silica sand content and temperature. The Da values were moreover well correlative with smectite partial density, defined by the density of smectite aggregates in bentonite. This indicates that Se diffusion is predominantly controlled by the properties in part of smectite. The activation energies for Da values calculated from the temperature dependencies were in a range of 17 to 32 kJ/mol, but neither systematic tendency with respect to dry density nor smectite partial density was found.