Iodine Vapor Reactions with Pure Metal Wires at Temperatures of 100–139 °C in Air

Abstract

± 5 °C) with exposure times of 24 h at each temperature. Over these temperatures, some of the metals showed increased mass gain with higher temperatures (i.e., In, Ag, Cu), Sn showed decreased iodine capture at increased temperatures, and most metals (i.e., Mo, Nb, Ni, Pd, Pt, and Ta) showed little to no mass gain at all temperatures. Silver mordenite (AgZ) was used as a standard during these studies and showed a consistent mass gain (m % I ) of 10.6 → 12.8% over this temperature range. The values of the mass of iodine captured per mass of starting metal (g g −1 ) ranged widely across the study, with the highest values achieved for (in descending order) Sn-T 100 °C (4.37), In-T 139 °C (3.34), Sn-T 123 °C (1.98), In-T 123 °C (1.57), Ag-T 139 °C(1.19), In-T 100 °C (0.97), and Cu-T 139 °C (0.71). In some cases, the metal-iodide complex was not stable at the experimental temperature, and it was clear some volatility had occurred during the experiment based on discoloration in the vials. These results show that some metals can have extensive reactions with I 2(g) without showing metal-iodide preferences over metal-oxide formation based on thermodynamic predictions. It is possible that materials such as these could be implemented near nuclear facilities to getter I 2(g) in the event of a nuclear accident.

Radioiodine sorbent selection criteria

“…The environmental stability of the metal iodide formed after capture considers the chemical surface reactivity and morphological changes that could occur during operation and upon long-term storage after capture ( Figure 1E ). Some examples of where this is important were documented in a recent paper by Riley et al (2021) where some of the highest performing pure metals for I 2(g) capture were indium (forming InI 3 ) and tin (forming SnI 4 ). While In and Sn metals have a tremendous affinity for I 2(g) forming a triiodide and tetraiodide (i.e., 76.8 and 81.0 mass% iodine, shown in Figure 2B ), respectively, neither MI x complex is environmentally stable.…”

“… Summary of various parameters for consideration when selecting sorbents for radioiodine: (A) optimal capture performance including different types of Ag-zeolites that have different Ag loadings ( Riley et al, 2022b ) (criterion-1), (B) sorbent kinetics including examples based off actual data for I 2 ( Riley et al, 2014 ) for sulfide-based chalcogels and CH 3 I for Ag 0 -aerogels ( Tang et al, 2021 ) [in parts per billion by volume (ppbv) CH 3 I concentration streams] (criterion-2), (C) performance under relevant conditions based off data for I/Cl coadsorption ( Matyáš et al, 2021b ) and other studies in this area ( Riley et al, 2021 ; Riley et al, 2022a ) (criterion-3), (D) inherent properties of sorbent substrate ( Riley et al, 2021 ) (criterion-4), and (E) iodide stability and disposition pathways ( Riley et al, 2021 ; Reiser et al, 2022 ) (criterion-5). …”

“…Figure 2 shows some of the elements that have been explored in various forms for the capture of volatile iodine along with the expected MO y I x compounds based on expected metal oxidation states in the iodine-loaded complexes ( Maeck et al, 1968 ; Maeck and Pence 1970 ; Pence et al, 1970 ; Pence et al, 1972 ; Matyáš et al, 2011 ; Riley et al, 2017 ; Riley et al, 2020 ; Matyáš et al, 2021a ; Riley et al, 2021 ; Tesfay Reda et al, 2021 ). In practice, several of these base metals do not show iodine capture under saturated conditions so specialized conditions might be needed to realize their potential ( Riley et al, 2021 ). Figure 2B provides an overview of the large range in maximum iodine loadings possible by simply selecting different getter metals.…”

“…Studies examining alternative metals have typically incorporated them into oxide-based [e.g., zeolites ( Maeck and Pence 1970 ; Pence et al, 1972 ), silica ( Matyáš et al, 2011 ; Riley et al, 2017 ; Riley et al, 2020 )] or carbon-based ( Muhire et al, 2022 ) substrates. As the choices of substrate and getter loading method can affect iodine capture, a recent study was conducted using pure metallic substrates to eliminate these artifacts ( Riley et al, 2021 ). This study demonstrated that silver, and other pure metals such as Al 0 , Cu 0 , In 0 , and Sn 0 can be used to capture large quantities of iodine in saturated conditions at various temperatures.…”

“…In the reprocessing of used nuclear fuel, extremes in pH are observed depending on the process, such as acidic pH conditions [e.g., HNO 3(g) , HF (g) ] in off-gas streams or highly basic pH conditions in a caustic scrubber solution or a molten hydroxide scrubber (i.e., pH ≥ 12) ( Riley et al, 2016 ). It is also an issue if the stability of the sorbent varies with temperature as some metals behave differently at low temperatures versus high temperatures ( Riley et al, 2021 ). An additional point is that the performance of different getters can vary in terms of their abilities to scavenge low concentrations of the target species from a larger volume of competing species (e.g., Cl 2 ) ( Matyáš et al, 2021b ).…”