Immobilization of Radioactive Spent Zeolites in Glass Composite Matrix: A Combined Design of Experiment Approach
摘要
In this work, spent zeolites from the liquid radioactive waste treatment process that contains cesium-137 were immobilized in a glass composite matrix. The combined design of the experiment method was employed to assess how the properties of glass composite wasteforms were affected by the spent zeolite loading (40–80 wt%), and heat treatment process temperature (650–850 °C). The experimental data and suggested correlations for the final wasteform’s volume reduction ratio and Cs leaching rate were assessed using Design Expert 12.0 software based on polynomial models. The lack-of-fit test, model analysis, and coefficient of determination (R2) were employed to verify the models’ sufficiency. The results show that the volume reduction ratio increases with increasing temperature and decreases with increasing waste loading. Investigations indicate that the optimal conditions for waste immobilization are provided by the glass composite matrix with 70% spent zeolite synthesized at 750 °C. This leads to the lowest Cs leaching rate (1.94 × 10−6 g/cm2.day) and the most significant volume reduction ratio (62.69%). When these optimal conditions were applied to actual radioactive waste, gamma analysis revealed no cesium leakage. The effective encapsulation of spent zeolites in the glass composite matrix is confirmed by the microstructural analysis of these wasteforms. According to the results, the final wasteform was in favorable conditions, confirming the successful immobilization of radioactive spent zeolites in the glass composite matrix.