The Design Pathway for Developing Iodine Sorbents—Metal-Functionalized Silica Aerogels

The effective capture and immobilization of iodine, particularly the radioactive isotope iodine-129 (I-129) with a half-life of 15.7 million years, is a significant challenge in nuclear waste management due to its high volatility and mobility in the environment. Solid sorbents are preferred for this purpose due to their high efficiency, stability, and ease of handling. However, a systematic design pathway is essential to enhance their effectiveness. This pathway ensures that all critical factors are considered, from material selection to practical application and long-term stability. For example, the choice of support affects the overall sorption performance, and its functionalization increases the loading capacity and selectivity of the sorbent toward specific elements of interest and improves uptake kinetics. The support has to be chemically stable and compatible with targeted environments and process conditions, and it has to provide a high surface area with a high density of sorption sites. The pore structure plays a crucial role as well, because pores of different sizes and structures affect the sorption kinetics and capacity. Another factor is mechanical and chemical stability under radiation and in complex off-gas streams. The support can also contribute to the increased selectivity of the sorbent for iodine over other species present in the gas streams. Lastly, practical considerations such as the cost and availability of the support impact its suitability for large-scale applications. An intriguing option is to develop sorbents with a hierarchical structure or architecture at multiple length scales. They would consist of multiple levels of porosity and different metal chemistry than silver, e.g., Cu and Bi, and allow for increased surface area, improved mass transfer, and enhanced selectivity. This combination of pore sizes and chemical functionality would enable effective capture of iodine from complex off-gas streams. The presentation will discuss the design pathways, synthesis, and sorption performance of metal-functionalized silica aerogels and different strategies to sequester iodine. This will include results from durability tests.