Natural clinoptilolite zeolite for the removal of ciprofloxacin and caffeine

Abstract In this study, the adsorption performance of natural zeolite (NZ) for ciprofloxacin (CIP) and caffeine (CAF) removal from aqueous solutions was evaluated through batch, stability, binary‐mixture, and fixed‐bed experiments. The physicochemical characteristics of NZ were investigated by X‐ray diffraction, Fourier‐transform infrared spectroscopy, and scanning electron microscopy coupled with energy‐dispersive X‐ray spectroscopy. The characterization confirmed clinoptilolite as the main zeolitic phase, together with quartz, dolomite, and calcite as accessory mineral phases. Batch experiments yielded equilibrium adsorption capacities of 0.2536 mg/g for CIP and 0.1776 mg/g for CAF under the evaluated conditions. The adsorption kinetics of both contaminants were accurately described by the pseudo‐second‐order model, with excellent agreement between experimental and calculated equilibrium capacities ( R 2 = 0.9994 for CIP and 0.9996 for CAF). Among the equilibrium models evaluated, Temkin provided the best overall fit for both contaminants, suggesting heterogeneous adsorption sites and coverage‐dependent adsorption energies. Intraparticle diffusion analysis indicated that pore diffusion was not the sole rate‐controlling step. Stability experiments showed that NZ maintained its adsorption performance under the evaluated conditions. A preliminary binary‐mixture experiment resulted in adsorption behavior comparable to that observed for the individual contaminants, suggesting no pronounced difference in their adsorption under the tested conditions. Fixed‐bed experiments conducted at low and high influent concentrations demonstrated the applicability of NZ under continuous‐flow conditions. These findings indicate that unmodified natural zeolite exhibits measurable adsorption toward CIP and CAF and can serve as a low‐cost material for preliminary water‐treatment applications. However, the relatively low removal efficiencies highlight the need for further optimization of operating conditions, adsorbent dose, contact time, and fixed‐bed configuration before practical application.