Comparative removal of naphthalene by adsorption on different sand/bentonite mixtures

Abstract

The purpose of this study was to advance the understanding of naphthalene (polycyclic aromatic hydrocarbon) adsorption on sand/bentonite mixtures in the context of their use in the lining of waste disposal facilities. Batch adsorption studies were carried out to estimate the adsorption capacities of sand/bentonite mixtures. Different percentages of the bentonite (0% to 12%) in sand/bentonite mixtures were tested. These mixtures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). It was found that the mixture with 2% of bentonite adsorbs the highest amount of naphthalene over the whole range of initial naphthalene concentrations studied (Co: 2.5-22 mg L-1); this optimal fraction was therefore selected. The effect of the initial naphthalene concentration, percentage of the bentonite in the sand/bentonite mixture and temperature on the adsorption was investigated. The adsorption isotherms, established for every percentage of bentonite, revealed that the naphthalene adsorption follows a linear Freundlich isotherm for the optimal fraction of bentonite (2%). The kinetic study showed that the process obeys a pseudo-second-order equation model. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°) indicated an endothermic and spontaneous nature of the naphthalene adsorption. The adsorption of naphthalene is more favorable at high temperatures and activation energy (8.263 kJ mol-1) suggests a physical adsorption. Keywords: Adsorption; Naphthalene; Bentonite; Sand/bentonite mixture.