Influence of structural, textural and chemical parameters of silver zeolites on the retention of methyl iodide

Abstract

An experimental screening of silver-exchanged zeolites towards the trapping of methyl iodide was carried out with the general aim of limiting as much as possible the iodine release in case of severe nuclear accident. Hence, a systematic study was implemented in order to better understand the effects of some important parameters such as the zeolite structural type (FAU-X and Y, MOR, *BEA, MFI and FER) and chemical properties (namely the silver content and its speciation) on the adsorption behaviour. Characterization of 18 zeolitic sorbents, before or after iodine retention tests, was performed using elemental analyses, N 2 porosimetry at-196 °C, XRD, DR-UV-Vis spectroscopy and TEM. The distribution of silver species, namely as isolated Ag + cations or charged clusters in the internal porosity, and/or to a lesser extent as 2 metallic nanoparticles, was found to depend mainly on the zeolite structural type and the Si/Al ratio and to a lesser extent on silver content. CH 3 I retention properties were evaluated from dynamic adsorption tests carried out at 100°C. Quantitative exploitation of breakthrough curves showed that the silver faujasite zeolites of the Y type (Si/Al ratio = 2.5) with more than 15 wt% silver were the most efficient in order to achieve high adsorption capacities both at breakthrough and saturation. More generally, it is found that dispersed silver entities efficiently catalyze the dissociation of CH 3 I and the production of AgI precipitates.

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

“…[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).…”

“…The structure of the zeolite seems to have a non-negligible inuence on the adsorption capacity and retention of iodine species, as zeolites with small pores favour physisorption, whereas zeolites with larger pores favour retention by chemisorption and the formation of an AgI precipitate. 77 Inuence of the Si/Al ratio in the zeolite framework. The amounts of silver that can be exchanged in a zeolite greatly depend on the Si/Al ratio in the zeolite framework.…”

“…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%.…”

“…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]…”