Adsorption of xenon and krypton on shales

Parameters for the adsorption of Xe and Kr on shales and related samples have been measured by a method that uses a mass spectrometer as a manometer. The gas partial pressures used were 10^?11 atm or less; the corresponding adsorption coverages are only small fractions of a monolayer, and Henry's Law behavior is expected and observed. Heats of adsorption in the range 2–7 kcal/mol were observed. Henry constants of the order of magnitude 1 cm³ STP g^?1 atm^?1 at 0 to 25°C are obtained by extrapolation.Adsorption properties are variable by sample, but the general range suggests that shales might be sufficiently good adsorbents that equilibrium adsorption with modern air may account for a nontrivial fraction of the atmospheric inventory of Xe (perhaps even Kr). It seems doubtful, however, that this effect can account for the deficiency (approximately a factor of 25) of atmospheric Xe in comparison with the planetary gas patterns observed in meteorites. If gas is adsorbed on interior surfaces in shale clays and can communicate with sample exteriors only through very narrow (10^?7 to 10^?6 cm) channels, and thus only very slowly, equilibrium adsorption may make substantial contributions to experimentally observed ‘trapped’ gases without the need for any further trapping mechanism.