BIOSORPTION OF TETRACYCLINE FROM AQUEOUS SOLUTION BY AZOLLA FILICULOIDES: EQUILIBRIUM KINETIC AND THERMODYNAMICS STUDIES

Azolla Filiculoides (AF) were used for the sorption of tetracycline (TC) from aqueous solution. A systematic study of the adsorption process was performed by varying adsorbent amount, initial TC concentration, sorption time and temperature. The equilibrium adsorption data were analyzed using four widely applied isotherms: Langmuir, Freundlich, Dubinin-Radushkevich and Temkin. The results revealed that Langmuir isotherm fit the experimental results well. Kinetic analyses were conducted using pseudo-first and second-order models and the intra particle diffusion model. The regression results showed that the adsorption kinetics were more accurately represented by pseudo-second-order model. The Standard free energy changes (Delta G(0)), standard enthalpy change (Delta H-0), and standard entropy change (Delta S-0) were calculated using adsorption equilibrium constants obtained from the Langmuir isotherm at different temperatures. All Delta G(0) values were negative; the Delta H-0 values and Delta S-0 values of Azolla Filiculoides biomass were 3.36 kJ/mol and 14.4 J/mol K, respectively. Results suggested that the TC adsorption on biomass was a spontaneous and endothermic process.