Adsorption kinetics and isotherm parameters of naphthalene onto natural- and chemically modified bentonite from aqueous solutions

Polycyclic aromatic hydrocarbons (PAHs) have widely been studied and a special concern because of their mutagenic and carcinogenic activities. In this study, natural- and chemically modified-bentonite were characterized by means of N₂ adsorption method, XRD, SEM, FT-IR, elemental and thermal analysis and zeta potential techniques and their adsorption behavior were then investigated toward naphthalene, which is the first member of the PAHs. The effects of various experimental parameters such as pH, contact time and temperature on adsorption were tested in the experiments. The optimum pH values for naphthalene adsorption onto natural bentonite (NB) and hexadecyltrimethylammonium bromide modified bentonite (HB) were found to be as 4.00 and 5.97, respectively. The equilibrium contact time was 60 min for both of the adsorbent. A comparison of the linear and nonlinear method of three widely used kinetic models, which are Lagergren-first order, the pseudo-second-order and Elovich kinetics, and the most popular isotherms, which are Langmuir and Freundlich, were examined to the experimental data of the adsorption of naphthalene onto NB and HB. The kinetic results indicated that the pseudo-second-order kinetic model with high correlation coefficients was more suitable than the other kinetic models e.g. Lagergren first-order and Elovich. All results showed that the modified bentonite can be used as an adsorbent to remove PAHs from aqueous solutions by using adsorption method due to its effectiveness, simplicity and low-cost than the other conventional methods.