Fixed-Bed Adsorption of Ciprofloxacin onto Bentonite Clay: Characterization, Mathematical Modeling, and DFT-Based Calculations

Abstract

The objective of this paper was to examine the adsorption of the antibiotic ciprofloxacin (CIP) in a calcined Verde-lodo (CVL) clay-packed fixed-bed system. The characterization study of the fresh and contaminated clay indicated filling of the clay pores by the CIP (pore volume decreased from 65.4 to 31.1 cm³ g–¹) and did not evidence significant changes in the clay texture. The fixed-bed system reached a breakthrough adsorption capacity of 0.038 mmol g–¹ (12.6 mg g–¹) and a mass transfer zone of 4.29 cm. Five mathematical models were fitted to the breakthrough curves, and the dual-site diffusion displayed the best fit to the experimental data (R² > 0.98). The adsorption performance of CIP was compared to that of the antibiotic ofloxacin, reported in the literature, in which density functional theory (DFT) computations were performed to clarify the particularities of the adsorption of both compounds onto CVL clay.