Risks of Nanoscale Byproducts Generated during the Interzeolite Transformation for Cesium Sequestration

Abstract

The development of radionuclide-sequestering materials should be directed toward eliminating all possibilities of radionuclide release based on a comprehensive understanding of all chemical reactions. Here, we report that undesired chemical reactions occurring during the interzeolite transformation for Cs sequestration and the resulting minor amounts of nanoscale byproducts can increase the release of Cs. Most studies developing radionuclide-sequestering materials have not examined the presence of byproducts and whether they affect the release of radionuclides; however, we demonstrated for the first time that these neoformed byproducts not only increase the release of radionuclides but also delay the rate of interzeolite transformation into Cs-sequestering pollucite. Moreover, we report that pore characteristics and the high specific surface area of the byproducts can greatly distort the results of the Cs release from Cs-sequestering pollucite. We found that the mechanism of undesired chemical reactions was due to the charge-compensating Ca ions present in the parent zeolite, and we suggest a strategy to minimize the release of Cs through a design that suppresses the generation of byproducts by pre-eliminating Ca ions before interzeolite transformation. We expect our study to raise awareness that minor amounts of byproducts generated during the synthesis and development of radionuclide-sequestering host material can negatively affect the sequestration of radionuclides. Also, we accentuate the requirement for a strategic design to prevent the risks that could increase the release of radionuclides in advance.