A method of classifying the influence of intraparticle diffusion in adsorption systems: characteristic curves of the diffusion-chemisorption kinetic model

Abstract This review evaluates 70 published studies with R2 > 0.95 that apply the diffusion-chemisorption (D-C) model to adsorption systems. It also incorporates an experimental component to demonstrate the practical applicability of the derived characteristic curves and equations. The study introduces a new framework for classifying adsorption systems based on intraparticle diffusion, leveraging a solid-phase mass transfer index (RDC) and characteristic curves derived from the D-C kinetic model. Additionally, new equations were developed to rapidly estimate the half-time of adsorption reactions and map operating time as a function of sorbent saturation. The characteristic curves based on the published studies revealed four distinct zones for RDC ranging from 0 to infinity. Type I curves correspond to large particle sizes and highly porous adsorbents, whereas Type IV curves represent powdered and low-porosity adsorbents. The concurrence to Types I, II, III, and IV curves from the 70 published studies were 8.5%, 36%, 32.5%, and 23%, respectively. To demonstrate the usefulness of the developed equations, the adsorption of Cu(II) ions by Fomes fasciatus was successfully evaluated to elucidate the influence of intraparticle diffusion and predict adsorption performance. This type of analysis offers a valuable tool for researchers and designers to identify adsorbents for specific adsorbates and explicate transport mechanisms. Further, it minimizes the need for extensive sampling and enables the comparison of adsorbent performances.