Abstract
The application of layered double hydroxides (LDHs) of MgFe and its composites with biochar of Eucalyptus camdulensis (Eb) and ethylenediaminetetraacetic acid (EDTA) was explored in a batch study to mitigate toxic lead ions (Pb2+) from synthetic wastewater solutions. SEM images revealed that MgFe/LDH composites with Eb were successfully formed, while FTIR spectra confirmed the successful adsorption of Pb2+ onto the MgFe/LDH and composite adsorbents. Batch equilibrium was attained after 60 min, then the adsorption capacity gradually increased. An increase in adsorption capacity (and a 60% decrease in the percentage removal) was observed by increasing the initial Pb2+ concentration, and the highest value was 136 mg g-1 for MgFe/LDH-Eb_EDTA. A 50-60% increase in both the adsorption capacities and percent removal was seen in the pH range of 2-6. The second-order kinetic model had a nearly perfect fitting, suggesting that chemisorption was the mechanism controlling adsorption. The Langmuir isotherm model best presented the adsorption data, suggesting that the Pb2+ adsorption was monolayer, and predicted a better affinity between the adsorbent surface and absorbed Pb2+ for MgFe/LDH-Eb_EDTA in comparison to the other two adsorbents. The D-R isotherm suggested that the adsorption system was physical based on E values for all three adsorbents, while the Temkin isotherm model suggested that Pb2+ adsorption was heterogeneous. Finally, the Sips and R-P isotherms predicted that the adsorption of Pb2+ on the surface of the adsorbents was homogeneous and heterogeneous.