Evaluation of Silver Zeolites Sorbents Toward Their Ability to Promote Stable CH₃I Storage as AgI Precipitates

Abstract

In this study, up to 13 different silver zeolites sorbents were prepared by repeated ion exchange from their parent structures (FAU X and Y, MOR, *BEA, MFI, FER), characterized, and evaluated for their ability to capture methyl iodide in the context of a nuclear severe accident. A novel methodology was implemented to establish structure-activity relationships between sorbent properties and iodine trapping stability. After saturation of the zeolite bed with CHI during a dynamic breakthrough experiment at 100 °C, a two-step quantitative desorption method was elaborated with the aim to quantify separately the CHI fractions trapped by physisorption, chemisorption, or reacted as AgI precipitates. Besides, an analysis of the mechanisms involved in CHI sorption and decomposition processes was also carried out. Overall, Ag/Y zeolites displayed the highest fractions trapped as stable AgI precipitates, thanks to the presence of high amounts of dispersed silver species at accessible locations in the large supercages, and their low sodium content.

Porous sorbents for the capture of radioactive iodine compounds: a review

“…The amounts of silver that can be exchanged in a zeolite greatly depend on the Si/Al ratio in the zeolite framework. In fact, Chebbi et al 77 and Azambre et al 74 obtained silver loadings of greater than 20 wt% aer several cation exchange steps in NaXand NaY-type zeolites. However, in the case of MFI-, MOR-, FERand *BEA-type zeolites the silver loading never exceeded 10 wt%.…”

“…[163][164][165][166][167][168] In the particular case of the capture of iodine species, the adsorption properties and cation exchange capacities of zeolites make them interesting and remarkable candidates for this application. In the literature, several zeolites of different structural types have been studied for the capture of iodine species, such as mordenite (MOR structural type), 29,34,74,76,77,79,80,[169][170][171][172][173][174][175][176][177][178] NaX and NaY zeolites (FAU type), 5,60,75,77,78,88,132,179 ZSM-5 (MFI type), 74,77 ferrierite (FER type) and zeolite beta (*BEA type) 74,77 (ESI, Table 3 †).…”

“…Later, numerous studies were carried out on this topic, especially during the 1970s and 1980s 21,29,34,38,40,47,52,180 and then between 2000 and 2017. 5,8,71,[74][75][76][77][78][79][80][169][170][171][173][174][175][176][177][184][185][186][187][188] These studies focused on the determination of the inuence of various parameters such as the temperature ( C), silver content (wt%), Si/Al ratio, supercial velocity, and pretreatment of the material on the adsorption capacities of silver-exchanged zeolites (ESI, Table 3 †). Other works focused on issues such as aging of the material under different atmospheres (NO x , humidity).…”

“…for a better understanding of iodine capture and its performance. [74][75][76][77][78][79][80][81] In addition, new porous sorbents have been added to the list of potential sorbents for iodine trapping, including titanosilicates, 82,83 mesoporous silicas, 6,81,[84][85][86] silverimpregnated silica and alumina (Ag/SiO 2 and Ag/Al 2 O 3 , respectively), 19,35,52,61,65,70,[87][88][89][90][91][92][93][94][95][96][97] silver-functionalized aerogels, chalcogels, 7,98-108 macroreticular ion exchange resins, 16,39,41,42,[44][45][46]50,53,55 metal-and covalent-organic frameworks (MOFs and COFs, respectively) 6,14, and porous organic polymers (POPs). [133][134][135]…”

Effects of the cation and Si/Al ratio on CH3I adsorption by faujasite zeolites

“…Since the Fukushima disaster in 2011, many efforts were devoted to revisit the behavior of zeolitic sorbents because they were identified to present potentially satisfying performances even under severe accidental conditions [12][13][14][15]. Nevertheless, and before their potential application in FCVS-equipped nuclear power plants, several important issues remained to be solved about the effect of zeolitic parameters on their adsorption behavior, especially under extrapolated accident conditions (ionizing and oxidative conditions, presence of inhibitors (H 2 O, CO x , NO x , H 2 , chlorine compounds…), working temperature 25-250°C [16]…).…”