Sustainable wastewater decontamination from chlortetracycline using kaolin-alginate beads: adsorption mechanisms and practical applications.

Abstract

Addressing the need for cost-effective alternatives to activated carbon (AC) for chlortetracycline (CTC) removal, this study developed sustainable kaolin-alginate composite beads (KN@Alg). The adsorption performance of KN@Alg was systematically evaluated compared with pristine KN and AC through kinetics, isotherms and thermodynamics. Regeneration cycles and X-ray photoelectron spectroscopy analysis were employed to assess reusability and elucidate mechanisms. Results demonstrated that incorporating of KN into the alginate matrix significantly enhanced the adsorption capacity to 68.74 mg g^-1, surpassing that of KN (42.76 mg g^-1) and approaching that of AC (102.96 mg g^-1). KN@Alg achieved 93.7% removal efficiency in dynamic experiments, demonstrating practical applicability. Thermodynamics confirmed a spontaneous and exothermic process. Mechanistic studies revealed that CTC uptake onto KN@Alg involves multifunctional mechanisms, including n-π interactions, hydrogen bonding, electrostatic attraction, cation exchange and calcium ion-bridging. Notably, KN@Alg exhibited superior renderability, retaining approximately 76% efficiency after four cycles, outperforming both AC and KN. Compared with the high cost of AC, KN@Alg integrates the rigid framework of KN with the functional advantages of alginate, addressing the limitations of low adsorption capacity and instability of pure components while achieving comparable removal efficacy. These findings highlight KN@Alg as a sustainable, cost-effective alternative for CTC-contaminated water treatment.