Adsorptive removal of tetracycline from aqueous solution by surfactant-modified zeolite: equilibrium, kinetics and thermodynamics

Abstract

This study was performed for estimating the potential of adsorption technique using surfac - tant (cetyltrimethylammonium bromide)-modified zeolite (CTAB-Z) for eliminating Tetracycline (TC) from an aqueous solution. The effects associated with variation of included parame - ters (i.e., the initial TC concentration, temperature, contact time, adsorbent dose, and stir ring rate) on TC adsorption efficiency were evaluated. Based on our studies, CTAB-Z could remove 99.8% of TC; this is indicative of the acceptable efficiency of CTAB-Z for adsorption of TC from synthetic wastewater. The equilibrium time for TC adsorption was 90 min. The employment of adsorption isotherms models (e.g., Langmuir, Freundlich, Redlich–Peterson (R-P), Cobble Corrigan (K-C), Dubinin-Radushkevich (D-R) and Temkin) highlighted better fitness of the adsorption data with the Langmuir isotherm, and based on this model, the val ues of 74.1, 85.1, 97.9, and 108.4 mg/g was obtained for monolayer adsorption capacity of TC at 288, 298, 308, and 318 K, respectively. The results achieved from five desorption regenera tion cycles indicated a reduction in the removal efficiencies of CTAB-Z from 99.8% to 89.2%. According to the results of thermodynamic parameters, the spontaneous and feasible nature of the studied process based on ∆ G ° < 0 was confirmed; however, it was endothermic in nature since a positive value for enthalpy (∆ H ° = 43.84 kJ/mol) was detected. Moreover, based on the values of ∆ S ° = 0.652 kJ/mol, the randomness at the solid-liquid interface was improved.