X-ray Absorption Spectroscopy Investigation of Iodine Capture by Silver-Exchanged Mordenite

Capture of radioactive iodine is a significant consideration during reprocessing of spent nuclear fuel and disposal of legacy wastes. While silver-exchanged mordenite (AgZ) is widely regarded as a benchmark material for assessing iodine adsorption performance, previous research efforts have largely focused on bulk material properties rather than the underpinning molecular interactions that achieve effective iodine capture. As a result, the fundamental understanding necessary to identify and mitigate deactivation pathways for the recycle of AgZ is not available. We applied X-ray Absorption Fine Structure (XAFS) spectroscopy to investigate AgZ following activation, adsorption of iodine, regeneration, and recycle, observing no appreciable degradation in performance due to the highly controlled conditions under which the AgZ was maintained. Fits of the extended XAFS (EXAFS) data reveal complete formation of Ag-0 nanoparticles upon treatment with H-2, and confirm the formation of alpha-AgI within the mordenite channels in addition to surface y/beta-AgI nanoparticles following iodine exposure. Analysis of the nanoparticle size and fractional composition of a-AgI to y/beta-AgI supports ripening of surface nanoparticles, as a function of recycle. This work provides a foundation for future investigation of AgZ deactivation under conditions relevant to spent nuclear fuel reprocessing.