Industrial & Engineering Chemistry Research, Vol.59, No.32, 14467-14475, 2020
Modeling of Mixed Mechanism Adsorption Processes Driven by Surface Adsorption and Internal Ion Exchange
In this work, a number of kinetic models describing adsorption processes that occur via a mixed mechanism of both simultaneous surface adsorption and internal ion exchange were developed. The proposed models exhibit higher R-2 values in fitting experimental results, for such systems compared to extensively used single-factor kinetic models. Among the simulated parameters within these models, the ion exchange rate coefficient (I-R) in adsorbent-based models and the reaction order (n) in adsorbate-based models were identified as key factors to analyze the combined adsorption processes, which may enable the rational design or selection of adsorbate materials. Furthermore, the constructed models were also successfully applied to other processes with mixed mechanisms, including photochemical surface adsorption-immobilization and photocatalytic degradation- ion exchange, where the positive I R values and reaction order (n) values larger than unity were considered as important evidence for the coexistences and contributions of submechanisms. Finally, the obtained concentration profiles in the adsorbent were compared to energy-dispersive X-ray spectroscopy mapping images, which further confirm the accuracy and applicability of the proposed models, providing measurements for quantities such as the diffusion coefficient, equilibrium ion concentration, and depth of the "ion exchange plane".