Cesium immobilization in metakaolin-based geopolymers elucidated by 133Cs solid state NMR spectroscopy

Geopolymers are promising candidates for nuclear-waste immobilization, and more specifically for the immobilization of radioactive cesium. Low-Si metakaolin-based geopolymers cured at temperatures of 40 degrees C in the presence of Cs ions generate a mixture of amorphous and crystalline phases including a Cs-bearing zeolite F phase. Using a combination of Cs-133 solid-state NMR and X-ray powder diffraction measurements we were able to show that Cs preferentially binds to zeolite F even when zeolite F is not the dominant phase in the matrix. Moreover, post-leaching NMR experiments indicate that zeolite F binds Cs more efficiently than the remaining crystalline or amorphous phases. Tailoring geopolymer formulations so that a large fraction of zeolite F is generated may therefore be a promising route for the production of immobilization matrices for cesium. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

Geopolymers are a promising option for immobilizing nuclear waste, particularly radioactive cesium. The study found that cesium ions preferentially bind to zeolite F, and zeolite F is more efficient in immobilizing cesium compared to other crystalline or amorphous phases.