Silver Sulfide and Silver Sulfate as Aging Byproducts and Adsorbents for Gaseous Iodine Capture in Spent Nuclear Fuel Reprocessing

Abstract

While it is considered a promising adsorbent for radioiodine capture in spent nuclear fuel reprocessing off-gas, silver functionalized silica aerogel (Ag0-aerogel) experiences a capacity loss when exposed to other off-gas components (O2, H2O, NO, and NO2) through a process known as aging. Ag2S and Ag2SO4 were identified as major byproducts of aging, but their impact on iodine adsorption remains unclear. Thus, to further investigate aging, we loaded Ag2S and Ag2SO4 powders with molecular iodine (I2) at 150 °C and characterized their properties. The I2 adsorption capacity of Ag2SO4 was 0.12 wt % after 72 h, suggesting its formation directly reduces the capacity of the Ag0-aerogel. Conversely, Ag2S had an iodine capacity of 86.8 wt % and near total Ag utilization after 240 h. Given its high capacity and availability, we evaluated the feasibility of Ag2S as an I2 adsorbent in future applications. Several drawbacks need to be overcome, including the relatively slow uptake rate, potential emission of another hazardous byproduct (SO2), and potential aging effects (e.g., Ag2S conversion to Ag2SO4) before Ag2S can be applied for the radioiodine capture process.