Study on the Adsorption of Elemental Iodine onto Painted Surfaces in Aqueous Systems

摘要: Radioactive iodine, particularly 131I, poses significant environmental and health risks in nuclear accident scenarios due to its high volatility and radiotoxicity. This study systematically investigates the adsorption behavior of aqueous I2 on epoxy-painted surfaces under simulated severe accident conditions at 25°C, 55°C, and 85°C. The adsorption kinetics were found to follow the pseudo-second-order model, with the apparent adsorption rate constant varying from (1.0 ± 0.1) × 10-5 to (3.8 ± 0.2) × 10-4 m2∙mg-1·min-1. The distribution coefficients of iodine between the painted surface and aqueous phase increased with temperature and aqueous I2 concentration at 85°C, ranging from 24.0 ± 2.4 L·m-2 to 566.2 ± 56.6 L·m-2. This is attributed to the simultaneous occurrence of I2 reduction to I- on the painted surfaces, which has been confirmed by X-ray photoelectron spectroscopy analysis. The adsorption isotherm follows the Freundlich model. There appears to be a critical temperature between 25°C and 55°C, as evidenced by changes in adsorption behavior. Below this critical temperature, the Freundlich isotherm constant n > 1 and the adsorption is predominant, while at higher temperatures, adsorption occurs simultaneously with significant I2–paint redox reactions, leading to a Freundlich isotherm constant n < 1.