Co-Adsorption of Iodine and Water By Reduced Silver-Exchanged Mordenite

Reduced silver-exchanged mordenite (Ag⁰Z) is one of the most promising adsorbents for retention of volatile iodine-129 in the off-gases of spent nuclear fuel reprocessing facilities. It is considered being used as an alternative to liquid scrubbing systems in the future nuclear fuel reprocessing plants. In our previous work, single-component adsorption processes of iodine and water on Ag⁰Z at the potential operation conditions have been studied. However, it is of importance to extend the efforts to the co-adsorption process of iodine and water on Ag⁰Z, as the off-gas streams mainly contain both gaseous iodine and water. The presence of water in the off-gas stream may impact both the kinetics and equilibrium adsorption capacity of Ag⁰Z for iodine. Therefore, co-adsorption of iodine and water is experimentally and theoretically investigated in this work. The efforts are also to support the development of advanced modeling tools for the separation and recovery of radioisotopic gases in off-gas streams of nuclear fuel reprocessing.

Single-layer Ag⁰Z adsorption experiments were performed to obtain both kinetics and equilibrium data of co-adsorption using continuous-flow adsorption systems. The temperature studied is 150^oC which is the optimal adsorption temperature for iodine adsorption on Ag⁰Z. The ranges of water concentration in terms of dew point and iodine concentration in the gas streams studied are -40 – 0 ^oC and 10 – 50 ppmv, respectively. It is found that the adverse impact of water on the iodine capacity of Ag⁰Z increases with the increasing water concentration. The reasons could be a) blocking of pores by water molecules and b) possible deactivation of Ag⁰ at the presence of water. Detailed mechanisms are being studied. The co-adsorption equilibrium data are used to validate the predictions made by the multi-component adsorption model -GPAST (Generalized Predictive Adsorption Solution Theory) - with parameters obtained from single-component adsorption. Work is also in progress to study the kinetics of the co-adsorption process with multi-component kinetic models and to determine the mechanisms of the co-adsorption process. The results will be compared with the single-component adsorption kinetics to determine the impact of water on the kinetics of iodine adsorption.