Enhanced adsorption of ciprofloxacin from an aqueous solution using a novel CaMgAl-layered double hydroxide/red mud composite

Abstract

This work reports on CaMgAl-layered double hydroxide (LDH) based red mud (RM) composite prepared via a co-precipitation method, characterized by transmission electron microscopy (TEM), powder X-ray diffraction patterns (XRD), field-emission scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Brunauer-Emmett-Teller analysis (BET), and Fourier transform infrared spectra (FTIR) and subsequently used for elimination of ciprofloxacin (CIP) from an aqueous solution in batch mode experiments. Langmuir isotherm model provided a better fit of CIP adsorption onto CaMgAl/RM composites than a Freundlich isotherm model; indicating a monolayer adsorption phenomena. Pseudo-second-order kinetic models describe the kinetics of adsorption while the adsorption mechanisms were controlled by external mass transfer and intra-particle diffusion. Thermodynamic analysis indicated that the CIP adsorption onto CaMgAl-LDH/RM was exothermic and spontaneous in nature. The prepared adsorbent exhibited superior affinity towards CIP adsorption which yielded a maximum CIP adsorption capacity of up to 138 mg/g. The higher removal efficiency (89.45 %) was reached under the best conditions (pH 7, agitation speed 150 rpm, adsorbent dosage 0.5 g/100 ml, concentration of contaminant 70 ppm, and 90 min contact time). Moreover, the synthesized adsorbent can be recovered after six consecutive regeneration cycles with a minimal reduction in the adsorption ability of 31 %. In conclusion, this study demonstrated that the CaMgAl-LDH/RM composite could be a promising adsorbent for removing antibiotics from wastewater.

Keywords

• Adsorption
• Ciprofloxacin
• Layered double hydroxides
• Isotherm
• Kinetics
• Thermodynamic