Removing an antibiotic from aqueous solution using sepiolite-rich dolomite – kinetic, isotherm, and thermodynamic studies

Abstract

The adsorptive removal of the antibiotic drug amoxicillin (AMX) from aqueous solutions was investigated using sepiolite-rich dolomite, a cheap and natural adsorbent. AMX, one of the most frequently prescribed antibiotics, can pose environmental and health risks if not adequately treated in wastewater. Sepiolite-rich dolomite is a mineral with low sepiolite content, meso/macroporous structure, large pore diameter and volume, and divalent cations, which affect its adsorption performance for AMX removal from aqueous environments. These characteristics were examined by single-component batch adsorption methods. From the results obtained, it was observed that dolomite, which is very rich in sepiolite under optimum conditions, attained a maximum AMX adsorption capacity of 123.46 mg/g. Adsorption is mainly governed by electrostatic interactions, ion exchange, and pore-filling mechanisms. It is clear that mesoporosity is the major controlling factor in sepiolite-rich dolomite in terms of sorption intensity and capacity compared to surface area. The Freundlich isotherm model and pseudo second-order kinetic model were found to be the best fit for the AMX adsorption results. Additionally, scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), and Fourier transform ınfrared spectroscopy (FTIR) analysis revealed that sepiolite-rich dolomite has a strong affinity for AMX and the adsorption of AMX is strongly influenced by exchangeable cations and molecules such as Ca²⁺ and Mg²⁺, and H₂O in zeolite-like channels, Si-OH groups located on basal surfaces, and the open channel defects (OCD) in its structure.