Chalcogenide Aerogels as Sorbents for Radioactive Iodine

Abstract

Iodine ( 129 I and 131 I) 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 NiMoS 4, CoMoS 4, Sb 4 Sn 3 S 12, Zn 2 Sn 2 S 6, and K 0.16 CoS x ( 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 iodine–sulfide interactions. Analysis of the iodine-loaded specimens revealed that the iodine chemically reacted with Sb 4 Sn 3 S 12, Zn 2 Sn 2 S 6, and K 0.16 CoS x to form the metal complexes SbI 3, SnI 4, and, KI, respectively. The NiMoS 4 and CoMoS 4 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 °C, depending on the nature of iodine speciation. In the case of Sb 4 Sn 3 S 12 and Zn 2 Sn 2 S 6, iodine release was observed around 150 °C mainly in the form of SnI 4 and SbI 3, respectively. The NiMoS 4, CoMoS 4, and K 0.16 CoS x released elemental iodine at ∼75 °C, which is consistent with physisorption. Preliminary investigations on consolidation of iodine-loaded Zn 2 Sn 2 S 6 chalcogel with Sb 2 S 3 as a glass forming additive produced glassy material whose iodine content was around 25 mass %.