Coal fly ash as raw materials for stable solidification of radioactive cesium via microwave sintering: mechanism and chemical durability

Radioactive cesium represents a substantial risk to both human health and environmental safety due to its persistent and hazardous nature. Simultaneously, large quantities of coal fly ash (CFA) are produced annually without sufficient resource utilization. In this study, a combination of microwave sintering technology and CFA was utilized to fabricate pollucite [CsAlSi 2 O 6 ] ceramic designed to immobilize radioactive cesium. The CsAlSi 2 O 6 ceramic derive from CFA with > 98% cesium retention was achieved via microwave sintering at 850 °C for 30 min, which was ~ 300 °C lower and ~ 11% cesium retention rate higher that those of reported Cs-bearing hollandite. The influence of Cs 2 CO 3 content and sintering temperature on the phase evolution of the sintered samples were systematically examined. The chemical durability of the sintered forms was further assessed. The results indicated that the Cs(I) elements were uniformly distributed within the sintered matrix. Furthermore, the maximum solid solubility of Cs 2 CO 3 in the sintered forms was found to be 39 wt% at 850 °C. Notably, the solidified samples exhibited exceptional chemical durability, with normalized leaching rate of Cs + ions (LR Cs ) maintaining consistently low (~ 1.0 × 10 –6  g m −2  d −1 ) after 42 days. This study provides a valuable reference for the potential resource utilization of CFA in the stable solidification of radioactive cesium via microwave sintering, offering a promising strategy for future application.