2021 Volume 32 Pages 136-146
In the thermal treatment of waste contaminated with radioactive cesium (Cs), Cs compounds are concentrated in fly ash. Hence, the Cs in the fly ash must be immobilized. In this study, thermal changes of kaolin reagents and the properties of dissolution to alkaline solution were investigated. Then, a model fly ash containing Cs was produced in a high-temperature thermal treatment plant to evaluate the immobilization of Cs. Using the calcined aluminosilicates and the model fly ash, geopolymer solidification of Cs was conducted. As a result, metakaolin was easy to dissolve in alkaline solution compared to calcined pyrophyllite, and the Cs leaching ratio from the solidified material with metakaolin was low. It was challenging to evaluate the influences of the aluminosilicates and alkali concentration in the solution on the Cs immobilization only by the composition ratios of solidified materials such as Si/Al. However, using Sidissolved/Aldissolved, the balance of Al and Si that directly contributed to Cs immobilization became clear. The dissolution properties of aluminosilicates to alkaline solution were an important factor for the control of Cs immobilization.
