Alkaline diffusion in compacted bentonite: Experiments and modeling

摘要

Cement-bentonite interaction will occur in deep geological repositories for radioactive waste.The diffusion processes and mineralogical transformations produced by alkaline fluids in a compacted bentonite column are studied. A hyper-alkaline solution (K-Na-OH, pH = 13.5, 60 °C) represents the degrading concrete in a repository over a short timescale (100's of years) and a Ca(OH)2 saturated solution (pH= 12.5) represents the control maintained by an evolved concrete over a long timescale (1000's of years). Results with bentonite from after 6 months. Alkaline cations have diffused beyond this mineralogical alteration zone, and are exchanged by Mg2 + in the interlayer region of smectites, but no K-silicates have formed. The absence of zeolites in the alteration assemblage was not expected. Reactive transport simulations are able to reconcile main characteristics of the evolution of the alkaline front.