Organic Iodine Removal from Simulated Dissolver off-Gas Systems Utilizing Silver-Exchanged Mordenite

摘要

The removal of methyl iodide by adsorption onto silver mordenite was studied using a simulated off-gas from the fuel dissolution step of a nuclear fuel reprocessing plant. The adsorption of methyl iodide on silver mordenite was examined for the effect of NO/sub x/, humidity, iodine concentration, filter temperature, silver loadings and filter pretreatment. The highest iodine loading achieved in these tests was 142 mg CH sub 3 I per g of substrate on fully exchanged zeolite, approximately the same as elemental iodine loadings. A filter using fully exchanged silver mordenite operating at 200 exp 0 C obtained higher iodine loadings than a similar filter operating at 150 exp 0 C. Pretreatment of the sorbent bed with hydrogen rather than dry air, at a temperature of 200 exp 0 C, also improved the loading. Variations in the methyl iodide concentration had minimal effects on the overall loading. Filters exposed to moist air streams attained higher loadings than those in contact with dry air. Partially exchanged silver mordenite achieved higher silver utilizations than the fully exchanged material. The partially exchanged mordenite also achieved higher loadings at 200 exp 0 C than at 250 exp 0 C. The iodine loaded onto these beds was not stripped at 500 exp 0 C by either 4.5% hydrogen or 100% hydrogen; however, the iodine could be removed by air at 500 exp 0 C, and the bed could be reloaded. A study of the regeneration characteristics of fully exchanged silver mordenite indicates limited adsorbent capacity after complete removal of the iodine with 4.5% hydrogen in the regeneration gas stream at 500 exp 0 C. The loss of adsorbent capacity is much higher for silver mordenite regenerated in a stainless steel filter housing than in a glass filter housing.