Permeability Change of Crystalline Silicate Mineral-Packed Bed Column by Highly Alkaline Plume
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0985-NN11-16
Permeability Change of Crystalline Silicate Mineral-Packed Bed Column by Highly Alkaline Plume Hideo Usui1, Yuichi Niibori1, Osamu Tochiyama2, and Hitoshi Mimura1 1
Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, Aramaki Aza Aoba 6-6-01-2, Aoba-ku, Sendai, 980-8579, Japan 2
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, 980-8577, Japan ABSTRACT For the construction of the geological disposal system, the use of the cementitious material may change the permeability of the natural barrier around the repository. Cementitious materials may alter the pH of ground water to highly alkaline. Also, the potential permeability change of the natural barrier is one of the notable factors for performance assessments of geological disposal systems. In the high pH region, the solubility of silica is very high compared to that in the natural pH (around 8). Therefore, highly alkaline groundwater would dissolve and alter a part of rock surface. Usui et al. (2005) reported that the change of mineral pore structure due to chemical reaction is the key factor to consider the change of the permeability [5-6]. Moreover, such a change of the pore structure was considered to be the result of the spatial heterogeneity of chemical composition. Since such spatial heterogeneity exists also in the sedimentary rocks consisting of crystalline minerals such as quartz and feldspar, we need to examine natural rock, in order to obtain more reliable understanding about the change of permeability induced by highly alkaline groundwater (plume). In this study, silica sand as crystalline mineral was packed in the column, and the effect of dissolution induced by the highly alkaline plume on the permeability-change was examined. The silica sand particles mainly consist of SiO2 and include Al2O3, FeO, and K2O. The volumetric flow rate and the pressure difference between the inlet and outlet of the column were measured, and the permeability was calculated. At the same time, the concentrations of elements in the fluid were measured by ICP-AES. The experimental result showed that permeability decreased gradually, although the silica sand was continuously dissolved in the column. The behavior of the permeability is considered to be the result from the rearrangement of the particles, or precipitation of secondary mineral. In the column test using the silica sand as packed mineral, the flow-path seems to be clogged by the rearrangement of the particles rather than the increase of the pore space between the particles.
INTRODUCTION The use of the cementitious material for the construction of the geological disposal system may change the permeability of the natural barrier around the repository [1-2]. The minerals that constitute the natural barrier have high solubility under alkaline conditions [3-4]. Therefore, the dissolution reaction induced by highly alkaline plume may increase the permeability of the natural barrier. On the
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