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

This study was performed for estimating the potential of adsorption technique using surfactant (cetyltrimethylammonium bromide)-modified zeolite (CTAB-Z) for eliminating Tetracycline (TC) from an aqueous solution. The effects associated with variation of included parameters (i.e., the initial TC concentration, temperature, contact time, adsorbent dose, and stirring 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 values 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 regeneration 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 increment G degrees < 0 was confirmed; however, it was endothermic in nature since a positive value for enthalpy ( increment H degrees = 43.84 kJ/mol) was detected. Moreover, based on the values of increment S degrees = 0.652 kJ/mol, the randomness at the solid-liquid interface was improved.