Enhancing the Removal of Organic Pollutant-Methylene Blue- by a Morroccan Natural Clay

Abstract

In this study, the removal of a cationic dye namely, methylene blue (MB) by natural clay (NC) from aqueous solution was investigated. The morphology, structure and surface state of NC were characterized using X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM)) and Optical Microscope, respectively. Affecting factors solution pH, dye concentration, contact time and temperature were investigated.  The maximum removal was obtained at basic pH. The experimental equilibrium data were examined using Langmuir, Freundlich, Temkin and Dubinin–Radushkevich. The equilibrium data for cationic dye adsorption was fitted to the Langmuir, and the maximum adsorption capacity of natural clay for MB was up to 25 mg.g⁻¹. The adsorption kinetic dye was analyzed using pseudo-first order, pseudo-second order, Elovish and the intraparticle diffusion model.  The kinetic data of cationic dye could be better described by the pseudo second-order model. The thermodynamic parameters such as the change in free energy (ΔG^o), enthalpy (ΔH^o) and entropy (ΔS^o) of adsorption were determined. These values show that the adsorption was exothermic and spontaneous.