Removal of cadmium and lead ions from aqueous solutions by novel dolomite-quartz@Fe3O4 nanocomposite fabricated as nanoadsorbent

The elimination of heavy metal ion contaminants from residual waters is critical to protect humans and the environment. The natural clay (dolomite and quartz) based composite Fe3O4 nanoparticles (DQ@Fe3O4) has been largely explored for this purpose. Experimental variables such as temperature, pH, heavy metal concentration, DQ@Fe3O4 dose, and contact time were optimized in details. The DQ@Fe3O4 nanocomposite was found to achieve maximum removals of 95.02% for Pb2+ and 86.89% for Cd2+, at optimal conditions: pH = 8.5, adsorbent dose = 2.8 g L−1, the temperature = 25 °C, and contact time = 140 min, for 150 mg L−1 heavy metal ion initial concentration. The Co-precipitation of dolomite-quartz by Fe3O4 nanoparticles was evidenced by SEM-EDS, TEM, AFM, FTIR, XRD, and TGA analyses. Further, the comparison to the theoretical predictions, of the adsorption kinetics, and at the equilibrium, of the composite, revealed that they fit, respectively to, the pseudo-second-order kinetic, and Langmuir isotherm. These both models were found to better describe the metal binding onto the DQ@Fe3O4 surface. This suggested a homogenous monolayer sorption dominated by surface complexation. Additionally, thermodynamic data have shown that the adsorption of heavy metal ions is considered a spontaneous and exothermic process. Moreover, Monte Carlo (MC) simulations were performed in order to elucidate the interactions occurring between the heavy metal ions and the DQ@Fe3O4 nanocomposite surface. A good correlation was found between the simulated and the experimental data. Moreover, based on the negative values of the adsorption energy (Eads), the adsorption process was confirmed to be spontaneous. In summary, the as-prepared DQ@Fe3O4 can be considered a low-cost-effective heavy metals adsorbent, and it has a great potential application for wastewater treatment.