Investigation of the adsorption process of methylene blue on diatomite from a kinetic and thermodynamic perspective

The adsorption of methylene blue on diatomite has been studied. Kinetics, thermodynamics and adsorption isotherms were used to identify retention mechanisms. The experiments, carried out in batch mode, for the determination of the kinetics, were carried out after adjustment of the parameters influencing the system, such as the pH, the temperature, the mass of adsorbent. The adsorption process of methylene blue onto diatomite is effectively represented by the Langmuir model, which indicates an adsorption capacity of roughly 166.66 mg/g. This is confirmed by the fact that the correlation coefficient exceeds that obtained with the Freundlich model; furthermore, the separation factor indicates that this adsorption is favorable. The results obtained were modeled according to the kinetic equations of the pseudo-first order, pseudo-second order, as well as that related to intraparticle diffusion. The experimental results of the global reaction are perfectly tunable to the pseudo-second order, with very large regression coefficients. Thermodynamics and adsorption isotherms predict the passage of a spontaneous endothermic surface reaction.