Equilibrium, kinetic and thermodynamic studies on the sorption of 4-hydroxyphenol on Cr-bentonite

With synthetic wastewater, the sorption characteristics of 4-hydroxyphenol on Cr-bentonite were investigated using a lab-scale batch experiment technique. The effects of relevant parameters, such as pH value of solution, contact time and temperature of solution were examined. Equilibrium modeling data were fitted to linear Langmuir and Freundlich models. Dubinin-Redushkevich (D-R) isotherm was applied to describe the nature of 4-hydroxyphenol uptake and it was found that it occurred physically. The pseudo first-order, second-order kinetic models and intraparticle diffusion model were used to describe the kinetic data. The pseudo second-order kinetic model provided excellent kinetic data fitting (R2 > 0.999) and intraparticle diffusion affects 4-hydroxyphenol uptake. Thermodynamic functions, the change of free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) of sorption were also calculated. These parameters show that the sorption process of 4-hydroxyphenol on Cr-bentonite is spontaneous and exothermic at 15–45 °C. The results indicate that there is significant potential for Cr-bentonite as an adsorbent material for phenolic compounds removal from aqueous solutions.