Adsorption of tetracycline antibiotic from aqueous solutions using natural Iraqi bentonite

Abstract

Natural Iraqi bentonite was employed in this study as inexpensive adsorbent for the removal of Tetracycline hydrochloride antibiotic from aqueous solutions. The removal of about 90% of the Tetracycline was achieved under the optimum adsorption conditions of 2 h equilibrium time, 0.2 g bentonite dose, 20 mg/L initial Tetracycline concentration, and at a pH between 6 and 7. The thermodynamic investigation was carried out at various temperatures ranging between 20-40 °C. The resulted thermodynamic parameters emphasize a decrease of the randomness, an exothermic, and a spontaneous nature of the adsorption process arising from the negative values of the entropy change, the enthalpy change, and the Gibbs free energy change, respectively. The kinetic studies showed that the pseudo-second order model could fulfill a better fit of the experimental data, and more than one process would influenced the diffusion of tetracycline from the solution into the bentonite. The Isotherm studies reveals that Langmuir model provided a best fit to the isotherm curve, with a maximum adsorption capacity of 23.69 mg g-1. The results suggest that Natural Iraqi bentonite can be used as a cost-effective adsorbent for the removal of Tetracycline hydrochloride from aqueous mediums.