Assessing the immobilization performance of fly ash-based geopolymers for removal of cesium and treatment of radioactive wastewater

Geopolymers prepared from recycled fly ash have emerged as sustainable and effective solutions for the solidification of radioactive wastewater. In this study, fly ash-based geopolymers with varying 137 Cs concentrations are prepared, and their solidification effects as well as the compressive strength, porosity, microstructure, and leaching behavior after solidification are investigated. The results indicate the uniform incorporation of Cs into the prepared fly ash-based geopolymers. As the concentration of Cs in the geopolymers increases, the compressive strength decreases and porosity increases; however, the chemical structure remains almost unchanged. These observations are attributed to the electrostatic interaction between Cs + ions and the negatively charged [SiO 4 ] 4− and [AlO 4 ] 5− ions in the geopolymers. Moreover, the geopolymers exhibited lower leaching rates and cumulative leaching fractions in both deionized water and Beishan groundwater; the leaching rate and cumulative leaching fraction of 137 Cs in fly ash-based geopolymers were lower than the Chinese national standards. Further, the Cs solidification performances of the prepared geopolymers and traditional cement on real radioactive wastewater were compared. The fly ash-based geopolymers demonstrated a superior performance than traditional cement, making them a promising material for radioactive wastewater treatment. This study offers new insights into reducing radioactive waste and makes a substantial contribution to the knowledge of nuclear waste solidification processes employing fly ash-based geopolymers.