Ternary Fe-Zn-Al layered double-hydroxides for interactive removal of cd and pb from aqueous solutions: Isotherms, kinetics and application to real samples

Abstract

The ongoing influx of trace elements in our water systems from industrial wastewater poses a need for water decontamination. In this study, Fe-Zn-Al LDH was synthesised via the co-precipitation method as an adsorbent in the decontamination of Cd and Pb from surface and groundwater. The synthetic technique was used because it is simple and effective. The synthesised Fe-Zn-Al LDH was characterised by instruments including X-ray powder diffraction (P-XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS). The FTIR showed that the dominant characteristic groups of Fe-Zn-Al LDH were OH, CO₃^2-, NO₃^-, M-O and M-O-M, which are the expected functional groups. The SEM-EDS confirmed the elemental composition of the material, and XRD also confirmed the lamellar structure of Fe-Zn-Al LDH by having characteristic peaks of LDH. Under optimum conditions, adsorption kinetics and equilibrium studies were conducted to investigate possible adsorption mechanisms involved during the removal process. The kinetics data fitted the Elovich and pseudo-second-order models, with the relatively highest correlation coefficient for both analytes compared to the pseudo-first-order model. It was also observed that the Langmuir and the Freundlich models show the best agreement with adsorption equilibrium data. The maximum adsorption capacities for Cd and Pb were calculated using the Langmuir model equation and were 11.9 and 280 mg/g. Moreover, because of its high adsorption affinity and fast adsorption kinetics, the Fe-Zn-Al LDH proved to be a suitable adsorbent material for Cd and Pb removal from water samples, with removal efficiencies ranging from 80–98 %.