Keywords: Adsorption, isotherm; iron oxide nanoparticles; landfill leachate

Abstract

This study was conducted to investigate the efficiency of the adsorption of iron oxide nanoparticles (IONPs) for the removal of dissolved chemical oxygen demand (dCOD) in landfill leachate. The IONPs were directly prepared via the sodium borohydride (KBH4) reduction method. Adsorption kinetics, isotherm, and thermodynamic studies are developed to design the model for dCOD removal. Pseudo-first-order (PFO) and pseudo-second-order (PSO) models have been studied to fit the experimental data. The regression results showed that a PSO model represented the adsorption kinetics more accurately. The Weber–Morris intraparticle diffusion model was used to analyse the adsorption kinetics data. The plot of qt versus t1/2 represents multilinearity, which showed that the adsorption processes occurred in more than one step. Adsorption isotherms were analysed using the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D-R), and isotherms model. Equilibrium data were well fitted to the D-R isotherm model. The Langmuir model was used to calculate the maximum monolayer adsorption, which demonstrated a value of 69.44 mg/g. Thermodynamic parameters, such as free energy changes (ΔG°), enthalpy (ΔH°), and entropy (ΔS°), were evaluated between the temperatures of 25°C and 40°C. The ΔG° was noticed to have progressively decreased from −10.68, −10.87, −11.07, and −11.27 kJ/mol with increasing temperature. The ΔH° and ΔS° values were found to be 1.23 kJ/mol and 39.96 J/mol.K, respectively. The results showed that the overall adsorption process was endothermic and spontaneous. This suggested that the IONPs could be a viable adsorbent in managing higher dCOD problems associated with landfill leachate.