Kinetics of aging process on reduced Ag exchanged mordenite in dry air and humid air

Abstract

Aging effects of off‐gas streams including dry air and humid air on reduced silver exchanged mordenite (Ag0Z) were studied. Aged Ag0Z was prepared by exposing Ag0Z to dry air and humid air at different aging temperatures, time, and water vapor concentrations. Iodine loading capacity on the aged Ag0Z was obtained through a continuous‐flow adsorption system. Significant iodine loading capacity losses were observed after the Ag0Z was exposed to dry air and humid air. Physical and chemical analyses were conducted to observe the physical and chemical changes of Ag0Z after being aged. From iodine adsorption data and sample analyses, it was found that iodine loading capacity on the aged Ag0Z in dry air and humid air decreases with increasing aging temperatures, time, and water vapor concentrations. The pseudo reaction model describes experimental data well and the oxidation of Ag0 is the rate determining step in the aging process.

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

“…All five samples followed the same I 2loading procedures as described in section 2.1. 19,20,26 Ag 2 S displays the highest uptake capacity in this experiment with a mass gain of ∼86.8 wt %, followed by Ag 0 -aerogel at ∼36.5 wt %, and Ag 0 Z at ∼12.5 wt %. These differences are simply attributable to the different Ag content of each sample (87.1 wt % for Ag 2 S, ∼35.5 wt % for Ag 0 -aerogel, 23 and ∼12 wt % for Ag 0 Z).…”

“…Our previous studies have focused on the processes governing aging in two prototypical porous Ag adsorbents, Ag 0 Z and reduced Ag functionalized silica aerogel (Ag 0 -aerogel), in gas streams containing the aforementioned off-gas components. 19−22 Ag 0aerogel is a relatively new material developed at Pacific Northwest National Laboratory (PNNL), and its high Ag content and adequate specific surface area aid in iodine capture, making it an appealing alternative to zeolites that have traditionally been the primary focus in this area. 23,24 By exposing Ag 0 Z and Ag 0 -aerogel to gas streams containing the aforementioned off-gas components at 150 °C, we found that NO 2 significantly reduced the I 2 capacity for both materials (∼90% reduction after 1 month), 21,22 while O 2 , H 2 O, and NO were less impactful (30%−80% reduction for Ag 0 Z and ∼20% reduction for Ag 0 -aerogel after 1 month).…”

“…23,24 By exposing Ag 0 Z and Ag 0 -aerogel to gas streams containing the aforementioned off-gas components at 150 °C, we found that NO 2 significantly reduced the I 2 capacity for both materials (∼90% reduction after 1 month), 21,22 while O 2 , H 2 O, and NO were less impactful (30%−80% reduction for Ag 0 Z and ∼20% reduction for Ag 0 -aerogel after 1 month). 19,20 Though the existence of the aging phenomenon is well established, there are still, nevertheless, some discrepancies that arise when attempting to understand its underlying processes. The formation of new Ag species after aging is, for example, a key feature in our previous studies though these aging byproducts may or may not directly reduce the I 2 capacity of the adsorbent.…”

“…One major obstacle to the use of Ag adsorbents is, however, their tendency to steadily lose capacity (i.e., age) when they are exposed to other SNF reprocessing off-gas components (e.g., O 2 , H 2 O, NO x ) at elevated temperatures for prolonged periods of time. Our previous studies have focused on the processes governing aging in two prototypical porous Ag adsorbents, Ag 0 Z and reduced Ag functionalized silica aerogel (Ag 0 -aerogel), in gas streams containing the aforementioned off-gas components. − Ag 0 -aerogel is a relatively new material developed at Pacific Northwest National Laboratory (PNNL), and its high Ag content and adequate specific surface area aid in iodine capture, making it an appealing alternative to zeolites that have traditionally been the primary focus in this area. , By exposing Ag 0 Z and Ag 0 -aerogel to gas streams containing the aforementioned off-gas components at 150 °C, we found that NO 2 significantly reduced the I 2 capacity for both materials (∼90% reduction after 1 month), , while O 2 , H 2 O, and NO were less impactful (30%–80% reduction for Ag 0 Z and ∼20% reduction for Ag 0 -aerogel after 1 month). , Though the existence of the aging phenomenon is well established, there are still, nevertheless, some discrepancies that arise when attempting to understand its underlying processes.…”

“…As such, this manuscript is intended to facilitate our understanding of the aging process in Ag 0 -aerogel by examining the adsorption of I 2 on Ag 2 S and Ag 2 SO 4 . Commercial Ag 2 S and Ag 2 SO 4 powders underwent adsorption in a dry air steam with 50 ppmv I 2 at 150 °C (a prototypical I 2 -loading conditions applied to other Ag adsorbents). − , The mass change was recorded to help us calculate the I 2 capacity. To examine the evolution of the adsorbents’ physical and chemical properties, we characterized pristine and I 2 -loaded samples through scanning electron microscopy with energy dispersive X-ray spectroscopy analysis (SEM-EDX), powder X-ray diffraction (PXRD), diffuse reflectance UV–visible spectroscopy (UV–vis DRS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS).…”