Conclusion
The aging processes on Ag0Z in dry air and humid air
as off-gas streams from the spent nuclear fuel reprocessing system were
studied. Iodine loading capacity of Ag0Z after being
aged in gas streams including dry air and humid air (d.p. -40oC, -15 oC, and +15oC) at 100 oC, 150oC, and 200 oC for up to 6 months
were obtained. Iodine loading capacity of Ag0Z aged in
dry air and humid air (d.p. -15 oC) at 150oC for 1 month decreased by roughly 35% and 50%,
respectively, which indicate that humid air has more adverse impact on
the performance of the Ag0Z. Besides, aging
temperatures and water vapor concentrations are key factors which have
negative influences on the Ag0Z; iodine loading
capacity was decreased with increasing aging temperatures and water
vapor concentrations.
The aging mechanisms of Ag0Z in dry air and humid air
were suggested with SEM, XRD, and XPS analyses. It was found that the
mechanism includes the following steps; (1) oxidation of
Ag0 to Ag+, (2) migration of
Ag+ from the surface to the pores/channels of
mordenite crystals, (3) binding of Ag+ within the
zeolite framework by replacing the H, and (4) binding of the generated
H+ with O2- or HO-producing H2O. In addition, given that similar reactions
in both dry air and humid air and faster aging process occur in humid
air than dry air, the kinetics of the overall aging process were most
likely controlled by the oxidation reaction of Ag0.
Furthermore, the Pseudo reaction model with the oxidation reaction of
Ag0 from dry air and humid air aging processes is
capable to describe the kinetics of deactivation on
Ag0Z. The results of iodine loading capacity and model
fitting reveal that the Ag0Z lost a significant iodine
capacity when being exposed to dry air and humid air. While the kinetics
of the aged Ag0Z in dry air and humid air were
suggested in this study, future work should be involved not only in
further understanding of the aging processes in gas mixture of dry air
and humid air, but in ascertaining alternative adsorbents which are
tolerant to dry air and humid air off-gas streams.