Simultaneous toxic Cd(II) and Pb(II) encapsulation from contaminated water using Mg/Al-LDH composite materials

Abstract

The Layered double hydroxides (LDHs) were used for the toxic diverse metal ions accumulation owing to their functional sites and complexation capabilities. Their intercalation with ligands like sodium hexametaphosphate (SHMP) can enhance the active sites for heavy metal adsorption. Here, the Mg/Al-LDHs were inscribed with SHMP using the co-precipitation method to detoxify wastewater by removing lead (Pb2+) and cadmium (Cd2+). Mg/Al LDH-SHMP composite adsorbent was investigated using several instrumentations such as XRD, FT-IR, and FE-SEM-EDX for identifying the functional and morphological properties which are accountable for lead and cadmium cations adsorption. The adsorption was studied in a batch method to investigate the adsorption performance by optimizing pH, adsorbent dose, time of contact, concentration, and adsorption temperature. The adsorption isotherm, thermodynamics, kinetics of the adsorption progress, and mechanism were thoroughly investigated. The pseudo-second-order model gave the highest outcomes in terms of fitting the kinetic data, with the greatest correlation coefficient for both cations. The trend of isotherm was adjacent to the Langmuir model with the highest removal amount of 45.66 and 24.34 mgg−1 for Pb2+ and Cd2+, respectively. The thermodynamic investigation exhibited that the adsorption reaction was spontaneous endothermic, and random in character. The capacity for absorption improved as a result of the higher temperature. Moreover, Pb2+ and Cd2+ accumulation onto the Mg/Al LDH-SHMP surface was plausible with surface complexations, isomorphic substitution, precipitation, and heavy metal chelation. The Mg/Al LDH-SHMP composite could be an ideal material for Pb2+ and Cd2+ accumulation from the wastewater for its high adsorption capacity and fast adsorption kinetics.