[en] At the Pacific Northwest Laboratory (PNL), we performed two sets of experiments to determine the effects of pertinent operational parameters and gas compositions on organic radioiodine [in particular methyl iodide (CH³I)] capture by silver mordenite (AgZ). In the first set of experiments, we studied the effects of (1) hydrogen pretreatment of AgZ, (2) change in particle size of AgZ, and (3) the presence of water in the gas phase. In the second set of experiments we evaluated on a semi-quantitative basis the effects of nitric oxide (NO), nitrogen dioxide (NO²), superficial face velocity, and temperature on CH³I capture by reduced (hydrogen pretreated) silver mordenite (Ag₀Z). These studies have shown that AgZ, especially Ag₀Z, is an effective trap for CH³I. However, its effectiveness varies with changes in operational parameters and is affected by other gases found in the process off gas of a nuclear reprocessing plant. Optimum trappig efficiency was achieved with Ag₀Z rather than AgZ, 20-40 mesh Ag₀Z rather than 0.16 cm extrudate, moisture in the gas stream, higher temperatures up to 200₀C, absence of NO, and lower superficial face velocities down to 3.75 m/min. Additionally, CH³I can be converted to elemental iodine (I²) in the presence of NO or NO² by controlling the operational parameters. Since I² is easier to trap than organic iodides, this should improve trapping efficiency,