Unravelling the potential of iodine isotopic exchange in CH3131I capture by K127I-impregnated activated carbons

The efficient capture of radioactive methyl iodide (CH₃¹³¹I) is a critical issue for nuclear safety and radioprotection. Co-impregnated activated carbons (AC), with triethylenediamine (TEDA) and potassium iodide (K¹²⁷I), are widely employed for this purpose. However, the specific role of KI in CH₃¹³¹I retention through isotopic exchange reaction remains poorly understood. This study provides groundbreaking insights by systematically investigating the retention behavior of KI/AC versus non-impregnated activated carbons (NI AC) under different operating conditions. Advanced characterization techniques, including N₂ porosimetry, high-resolution transmission electron microscopy (HRTEM), and H₂O adsorption isotherms, were first employed to elucidate the structural and chemical properties of the adsorbents. Subsequently, CH₃¹³¹I retention tests were conducted by measuring the Decontamination Factors (DF) at various configurations covering a broad range of relative humidities (RH) (20–90 %), temperatures (20–96 °C), residence times (0.125–0.5 s) and elution times (1–18 h). Results reveal that while NI AC exhibits a drastic performance decline at high RH attributable to water physisorption, KI/AC demonstrates enhanced retention, counterbalancing moisture effects via isotopic exchange. Furthermore, elevated temperatures significantly amplify DF for KI/AC, unveiling for the first time the thermally activated nature of the isotopic exchange mechanism. Prolonged residence time further enhance performance for KI/AC compared to NI AC, suggesting multiple mechanistic steps in isotopic exchange reaction. Consequently, a detailed mechanism for this reaction has been proposed.

This work advances the understanding of CH₃¹³¹I capture mechanisms ensuring improved performance under diverse nuclear safety scenarios.