Applicability of equilibrium isotherm models for the biosorptive uptakes in comparison to activated carbon-based adsorption

The adsorption isotherm models available in the literature have generally developed for sorption onto metallic surfaces or activated carbon-based sorbents. However, biosorptive uptakes involve interactions of biopolymer-based surfaces with different types of pollutants, which are quite different from metal surfaces or activated carbon. So, in the present study, 16 different types of adsorption isotherm models have been studied. For a ready reference both types of sorbents, i.e., a biosorbent and activated carbon have been employed. Results show that in general the accuracy of models to fit experimental data improves with the degree of freedom. The Fritz-Schluender model gives the most accurate fit (R-2 0.85-0.99) to all experimental data in comparison to other models used both for activated carbon and the biosorbent. However, most widely used isotherm models, i.e., Langmuir and Freundlich, could be used to describe the sorption equilibrium of biosorptive processes with a fair degree of accuracy, owing to the mathematical ease in the use of these models. Trends of the applicability of various sorption equilibrium models to biosorptive uptakes are similar to those of activated carbon-based sorptions. Comprehensive equilibrium analysis has assisted in understanding the mechanistic aspects associated with different types of sorbents.