Insights into solid−liquid adsorption kinetics: Theory, mechanisms, and practical guidelines

Adsorption is a widely used unit operation for concentrating solutes from large solution volumes onto small quantities of solid adsorbents. Understanding adsorption kinetics is essential for assessing the process efficiency and the impact of operating variables. Kinetic data are typically analyzed using theoretical models that reveal adsorption mechanisms, variations in pore size, and diffusion behavior, which are critical parameters for designing fixed bed adsorption systems and developing in silico simulations. Adsorption kinetic models are generally classified as empirical, semiempirical, or theoretical, each offering distinct insights into adsorption mechanisms. The choice of model depends on whether the aim is to fit experimental data or to interpret the underlying mechanism. This review summarizes the most widely used kinetic models, their mathematical foundations, and physical interpretations. Practical guidance is provided on model selection, identification of rate-limiting steps, and the use of error functions to determine the best-fitting kinetic expression, with examples from wastewater treatment applications.