Unprecedented xenon collection and separation from air on silver-exchanged zeolites

Abstract

Low level measurements of atmospheric radioxenon, such as for the verification of the Comprehensive Nuclear-Test-Ban Treaty, require complex collection, separation and detection systems. The collection and separation of Xe in this context is particularly challenging owing to its very low natural abundance in air (i.e. 87 ppb) and its inertness. For the detection part, the collected Xe gas needs also to be depleted of Rn to minimize interferences on the radioxenon detection. Historically, the collection and separation of atmospheric radioxenon has been performed with a complex succession of adsorptive columns using molecular sieves and activated carbons. In this work, we demonstrate the potential of two silver-exchanged zeolites to collect and separate Xe directly from dry air in a single adsorptive column. These two silver-exchanged zeolites show unprecedented Xe adsorption capacities in air (> 3 cm³SATP/kg) and Xe selectivities in air (> 1000). They also allow to efficiently separate Xe from Rn and thermally recover Xe with a high purity. However, the moisture content of the gas stream can have a negative effect on the xenon adsorption properties in these adsorbents. The results are compared to a typical activated carbon, used in this context, but also to two metal-organic frameworks with promising properties for Xe/Kr separation.