[H-CG20] Nuclear Energy and Geoscience

[HCG20-P09] Comparative study on specifications of several metakaolin products and their geopolymer performances: Potential application of domestic metakaolin products

*Takeuchi Nozomi¹, Kikuchi Ryosuke², Tsubasa Otake², Yogarajah Elakneswaran², Xiaobo Niu² (1.Graduate School of Engineering, Hokkaido University, 2.Division of Sustainable Resources Engineering, Graduate School of Engineering, Hokkaido University)

Keywords:AAM, Radioactive waste, Leaching, kaolin

The solidification processing for radioactive wastes is important technology for ensuring environmental protection and safety during the operation and decommissioning of nuclear power plants. Geopolymer (GP), which is made from aluminosilicate and alkali-activator is one of the most useful materials due to high ability to immobilize hazardous pollutants, flowability and high compressive strength. However, such performance may depend on the specification of raw material, and thus, we need to select the appropriate raw materials, such as metakaolin, to stabilize the performance. In this study, 14 metakaolin products are examined in their specifications and properties of fresh and cured GP. The metakaolin studied includes 6 products (non-commercial) made from the kaolin ore collected in Japan, accounting for the supply risk in future and the ease of optimizing the metakaolin manufacturing process. Compared to foreign metakaolin products, domestic ones have a higher amount of impurity minerals, such as quartz, feldspar and mica, and higher specific surface area due to its foliated morphology. Then, potassium GPs with SiO₂, K₂O, Al₂O₃, and H₂O molar ratios of 1:1:1:13 were prepared using each metakaolin product, and fresh and cured properties were compared. After 28 days of curing at 20°C, the uniaxial compressive strength of GP was above 8.08 MPa for all samples, yielding the sufficient strength required for solidification of radioactive wastes. Domestic metakaolins showed 9.52 - 11.6 MPa, while foreign ones showed 8.08 - 21.0 MPa, depending on the products. The retention capacity of Cs, one of the major radionuclides, was examined by leaching test, and the leaching rate at 5 days was 13.66% for domestic metakaolin and 6.78 - 31% for foreign metakaolin. These results showed that even commercial metakaolin products have significant variances in GP performance, and that despite the high impurity content of domestic metakaolins, the strength and Cs retention ability are comparable to those of foreign metakaolin products.