Nanoscale process in the alteration of bentonite-iron system under the hyper alkaline conditions

Abstract

In the nuclear waste disposal, a barrier material, bentonite, is predicted to lose its barrier function by reaction under hyper alkaline conditions. In this study, compacted bentonite with Fe plate has been reacted with Ca(OH)₂ saturated solutions of groundwater and 5.0 mol/L sodium nitrate solution at 60°C for 7-21 days. A variety of analytical techniques including SEM, TEM and XAFS have been utilized. Iron-bearing minerals and Fe nanoparticles occur in bentonite reacted after 7 days. In addition, bentonite was intensively altered and porous needle-like materials formed. The occurrence of Fe nanoparticles and alteration of bentonite can be key factors to facilitate the mobility of radionuclides under certain condition similar to the present study.