Chalcogenide aerogels as sorbents for radioactive iodine

Iodine (¹²⁹I and ¹³¹I) 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 K_0.16CoS_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 Sb₄Sn₃S₁₂, Zn₂Sn₂S₆, and K_0.16CoS_x 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 °C, depending on the nature of iodine speciation. In the case of Sb₄Sn₃S₁₂ and Zn₂Sn₂S₆, iodine release was observed around 150 °C mainly in the form of SnI₄ and SbI₃, respectively. The NiMoS₄, CoMoS₄, and K_0.16CoS_x released elemental iodine at ∼75 °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 %.