Development of the equilibrium adsorption layer model for describing the dynamic adsorption of radioactive gases

Abstract

The technique of adsorption is commonly employed to capture volatile radionuclides, finding extensive use in various fields, including gas treatment in nuclear power plants, protection of personnel, and capture systems for medical radioactive isotopes. An adequate mathematical description is essential for the design, calculation, and prediction of the output concentration and distribution of radionuclides in the sorbent bed over time. The theory of chromatography for non-radioactive adsorptives can now be considered detailed. However, its applications for radioactive gases are not as numerous and are generally limited to the simplest cases (stationary adsorption mode, linear isotherm). The present investigation improves upon the current model of the equilibrium adsorption layer by incorporating the radioactive decay of the adsorptive. At any given time, the complete description of the radionuclide distribution in the mobile and solid phase can be obtained through the resulting equation system, regardless of the type of adsorption isotherm. Simple analytical solutions were also obtained for the most practical case of linear adsorption isotherm. The frontal adsorption of the short-lived isotope ²²⁰Rn on activated AG-3 at 30 °C was studied in the air flow rate from 1 to 8 l/min (superficial linear air velocity from 50 to 430 cm/min). The experimental results were fully corresponded to the theoretical representations described in the paper.