Chalcogenide Aerogels as Sorbents for Radioactive Iodine

Iodine (I-129 and I-131) is one of the radionuclides released in nuclear fuel reprocessing and poses a risk to public safety due to its involvement in human metabolic processes. In order to prevent the release of hazardous radioactive iodine into the environment, its effective capture and sequestration is pivotal. In the context of finding a suitable matrix for capturing radioactive iodine, several sulfidic chalcogels were explored as iodine sorbents including NiMoS4, CoMoS4, Sb4Sn3S12, Zn2Sn2S6, and K0.16CoSx (x = 4-5). All of the chalcogels showed high uptake, reaching up to 225 mass % (2.25 g/g) of the final mass owing to strong chemical and physical iodinesulfide interactions. Analysis of the iodine-loaded specimens revealed that the iodine chemically reacted with Sb4Sn3S12, Zn2Sn2S6, and K0.16CoSx to form the metal complexes SbI3, SnI4, and, KI, respectively. The NiMoS4 and CoMoS4 chalcogels did not appear to undergo a chemical reaction with iodine since iodide complexes were not observed with these samples. Once heated, the iodine-loaded chalcogels released iodine in the temperature range of 75 to 220 degrees C, depending on the nature of iodine speciation. In the case of Sb4Sn3S12 and Zn2Sn2S6, iodine release was observed around 150 degrees C mainly in the form of SnI4 and SbI3, respectively. The NiMoS4, CoMoS4, and K0.16CoSx released elemental iodine at similar to 75 degrees C, which is consistent with physisorption. Preliminary investigations on consolidation of iodine-loaded Zn2Sn2S6 chalcogel with Sb2S3 as a glass forming additive produced glassy material whose iodine content was around 25 mass %.