Study on Radon Adsorption–Migration Behavior and Parameter Inversion in a Granular Activated Carbon Column

To reveal the radon adsorption and migration behavior in granular activated carbon (GAC) columns during breakthrough curve measurements and to determine the radon adsorption coefficient more accurately, this study developed a three-dimensional geometric model of a granular packed carbon column based on the radon adsorption-diffusion convection kinetic model. The CFD method was employed to study the effects of particle size and effective diffusion coefficient on radon migration in particles and columns. The limitations of the traditional method for determining the radon adsorption coefficient (DAC) based on semipenetration time were revealed: this method leads to systematic underestimation (at high flow rates with small carbon mass) or overestimation (due to neglect of radon decay with large carbon mass). To overcome these issues, a numerical inversion method was established to simultaneously determine the radon adsorption coefficient and the intraparticle effective diffusion coefficient, validated by using multiple experimental breakthrough curves. The results demonstrate that the inversion method yields adsorption coefficients consistent with static method results and remains nearly invariant under varying flow rates and GAC masses, showing superior robustness and reliability. This study highlights the inaccuracies of conventional approaches and provides a more accurate, robust inversion technique for the determination of the radon adsorption coefficient.