Permeability change of packed bed with an amorphous silicate mineral by highly alkaline plume

To assess the influence of the highly alkaline plume on the permeability of natural barrier around the geological repository system, silica scale particles were packed in the column and its permeability change induced by the dissolution was traced with time. The silica scale particles mainly consist of SiO2 partially including Al2O3 and CaO. The dissolved silicic acid was measured by the silicomorybdenum-yellow method. The dissolution experiment was conducted using the 0.1 M NaOH solution for 41 days. After the dissolution test in the column, the surface of particles and the cross-section structure were observed, using SEM and EPMA. The experimental result showed that permeability did not change significantly in the process of the dissolution. On the other hand, the SEM images showed that after the dissolution test, pit structures appeared in the outside and the inside of the peaked particle. Moreover, EPMA clarified that the Si-rich parts selectively disappeared in the dissolution. That is, the dissolution rate of the Si-rich region is larger than that of the Al and Ca-rich region. Therefore, the dissolution of Si-rich region results in the production of pit structure. Nevertheless, such dissolution processes retained the essential structure of particle, which in turn did not remarkably change the pore structure between the particles. Such a behavior of permeability was also observed in other minerals. (author)