Title: Capture of Iodine from Nuclear-Fuel-Reprocessing Off-Gas: Influence of Aging on a Reduced Silver Mordenite Adsorbent after Exposure to NO/NO₂

Abstract

Iodine radioisotopes released during nuclear fuel reprocessing must be removed from the off-gas stream before discharge. One promising material for iodine capture is reduced silver mordenite (Ag⁰Z). Nevertheless, the adsorbent’s capacity will degrade, or age, over time when the material is exposed to other off-gas constituents. Though the overall impact of aging is known, the underlying physical and chemical processes are not. To examine these processes, Ag⁰Z samples were prepared and aged in 2% NO₂ in dry air and in 1% NO in N₂ gas streams at 150 °C for up to six months. Aged samples were then characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray absorption spectroscopy. These techniques show that aging involves two overarching processes: (i) oxidation of the silver nanoparticles present in Ag⁰Z and (ii) migration of oxidized silver into the mordenite’s inner network. Silver on the nanoparticle’s surface is oxidized through adsorption of O₂, NO, and NO₂. Additionally, Raman spectroscopy and X-ray absorption spectroscopy indicate that nitrates are the primary products of this adsorption. Most of these nitrates migrate into the interior of the mordenite and exchange at framework binding sites, returning silver to its unreduced state (AgZ). The remaining nitrates exist atmore » a persistent concentration without aggregating into bulk-phase AgNO₃. X-ray absorption spectroscopy results further indicate that iodine adsorption occurs on not just Ag⁰Z but also on AgZ and a portion of the nitrates in the system. AgZ adsorbs a sizable quantity of iodine early in the aging process, but its capacity drops rapidly over time. For well-aged samples, nitrates are responsible for up to 95% of mordenite’s iodine capacity. Overall, these results have enhanced our understanding of the aging process in silver mordenite and are expected to guide the development of superior adsorbents for the capture of radioactive iodine from reprocessing off-gas.« less

Authors:

Wiechert, Alexander I.  ^[1];

• Search DOE PAGES for author "Wiechert, Alexander I."
• Search DOE PAGES for ORCID "0000-0002-9951-7258"

Ladshaw, Austin P.  ^[2];

• Search DOE PAGES for author "Ladshaw, Austin P."
• Search DOE PAGES for ORCID "0000-0002-0157-6410"

Moon, Jisue ^[3]; Abney, Carter W. ^[3]; Nan, Yue  ^[4];

• Search DOE PAGES for author "Nan, Yue"
• Search DOE PAGES for ORCID "0000-0001-8731-3568"

Choi, Seungrag ^[4]; Liu, Jiuxu ^[4]; Tavlarides, Lawrence L.  ^[4];

• Search DOE PAGES for author "Tavlarides, Lawrence L."
• Search DOE PAGES for ORCID "0000-0002-7671-0469"

Tsouris, Costas  ^[2];

• Search DOE PAGES for author "Tsouris, Costas"
• Search DOE PAGES for ORCID "0000-0002-0522-1027"

Yiacoumi, Sotira ^[1]

---

+ Show Author Affiliations

1. Georgia Inst. of Technology, Atlanta, GA (United States)
2. Georgia Inst. of Technology, Atlanta, GA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
4. Syracuse Univ., NY (United States)

Publication Date:

Thu Oct 22 00:00:00 EDT 2020

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1684654

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

ACS Applied Materials and Interfaces

Additional Journal Information:

Journal Volume: 12; Journal Issue: 44; Journal ID: ISSN 1944-8244

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; adsorption; nuclear fuel reprocessing; separations; off-gas iodine; silver mordenite