Simultaneous adsorption of cadmium, zinc, and lead ions from aqueous solution by Montmorillonite clay coated with MgCuAl-LDH nanoparticles

Abstract

In this work, Montmorillonite (MMt) coated with MgCuAl-layered double hydroxide (LDH) nanoparticles as a new adsorbent (MCA-LDH@MMt) was synthesized via a low supersaturation characterized using BET, TEM, XRD, SEM/EDS, and FT-IR analysis. The adsorption studies were conducted in a ternary-batch system of three heavy metal ions (cadmium, zinc, and lead). The results showed that the MMt was successfully loaded with MgCuAl nanoparticles with a porosity of 44.63 % and a specific surface area of 76.63 m²/g. In addition, the surface morphology analysis showed that there were several changes in elemental dispersion, molar ratio, and molecular weights during the preparation of the used adsorbent. The influence of environmental parameters on the adsorption behavior was studied in detail, whereby the maximum adsorption capacity for the three metals ions was achieved at pH 5, 120 min contact time, 0.2 g/100 mL dose, and 50 mg/l initial metal ion concentration at 25 ± 1 °C. A pseudo-second-order model well correlates the kinetic data of the three metal ions (R² > 0.991). The Cd²⁺ and Zn²⁺ isotherm data exhibited high compatibility with the Langmuir model, while the Freundlich model better fitted the Pb²⁺ isotherm data. The maximum adsorption capacity from the Langmuir model was 91.6, 164.9, and 129.2 mg/g for Cd²⁺, Zn²⁺, and Pb²⁺, respectively. Also, the adsorption process of the three metal ions onto $\text{MCA}-\text{LDH}@\text{MMt}$ was primarily characterized by their spontaneous and exothermic nature. In conclusion, this study demonstrated that MCA-LDH@MMt is an effective adsorbent for the simultaneous adsorption of cadmium, zinc, and lead in aqueous solution, with the ability to recover the synthesized adsorbent after four consecutive cycles with a minimal reduction in adsorption ability.