報告書番号

U99057

タイトル（和文）

放射性廃棄物処分の性能評価に与えるコロイドの影響 --セメント水和物からのコロイドの発生とその特性評価--

タイトル（英文）

Investigation on colloid generation from cement hydrates and their characterization

概要 （図表や脚注は「報告書全文」に掲載しております）

放射性廃棄物の処分システムの性能に与えるコロイドの影響評価に資するため、潜在的なコロイド源と考えられるセメント系材料から浸出するコロイドを観察し、その量、粒径、組成を測定した。またそのコロイド的特性を評価した。ポゾラン材料高含有OPCセメント（以下、HFSC）と高炉スラグ混合セメント（以下、OPC/BFS）の浸漬試験から浸出したコロイドのTEM観察から、HFSCからはSi-Al-Caを主成分とする平均粒径50nm-200nm程度のコロイドが、1E+10から1E+12個/l確認された。これらのコロイド数濃度や粒径は浸漬試験の固液比によって変化した。このコロイドの特性を表面電位や粒径変化から評価した結果、浸漬液中のカルシウム濃度に強く依存することを確認した。DLVO理論による評価により、浸漬試験の結果が定量的に評価された。

概要 （英文）

The association of contaminants with mobile colloidal particles present in groundwater has been recognized as a potentially important mass transfer mechanism for contaminant migration, such as radionuclides, in the subsurface environment. In the case of a cementitious repository system, the cementitious materials may provide a significant source of colloids, especially for the low-ionic-strength groundwaters and for the long-term degradation of cements by dissolution. Leaching experiments were performed using pulverized fuel ash-silica fume blended cement (HFSC) and blast furnace slag blended portland cement (OPC/BFS) mixed with low ionic strength simulated groundwater at liquid to solid ratio of 10:1, 50:1 and 100:1 either at room temperature or 60℃ for 2-8 months. Colloids in the leachates were observed by TEM with the ultracentrifugal deposition method. The number concentration of colloid for the leachate of the HFSC was in the range of 1E+10‐1E+12 N/l. It depended on the solid to liquid ratio in the leaching experiments. The colloid particles were composed dominantly of Si-Al-Ca. The mean particle size of colloids was 50nm-200nm.The colloid generated from HFSC was characterized by the zeta potential measurement of the particles and by the change in particle diameter distribution as a function of Ca concentration in the leachates. The results showed that the colloidal stability of the particles was affected by Ca concentration in the leachates. The application of DLVO theory to the obtained data could succeed in the estimation of the dependence of colloid population on solid to liquid ratio in the leaching experiments.

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