Zn(II), Pb(II), and Cd(II) adsorption from aqueous solution by magnetic silica gel: preparation, characterization, and adsorption.

A novel magnetic silica gel adsorbent (Fe3O4-Si-COOH) was successfully prepared by introducing carboxyl group in situ to improve the performance for Pb(II), Zn(II), and Cd(II) adsorption. Infrared spectroscopy (IR), scanning electron microscope (SEM), transmission electron microscope (TEM), thermo-gravimetric analyzer (TGA), the Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) characterizations suggested that Fe3O4-Si-COOH has been successfully prepared. The adsorption performance was evaluated by batch experiments with different initial concentrations, ionic strength, contact time, and pH. The adsorption kinetics data followed pseudo-second-order model and exhibited a three-stage intraparticle diffusion mode. Isothermal adsorption equilibrium data were best fitted by the Freundlich model and the adsorption capacity were 155, 110, and 93 mg/g (initial concentration 210 mg/L) for Pb(II), Zn(II), and Cd(II), respectively. The result of X-ray photoelectron spectroscopy (XPS) survey spectrum suggested that the main adsorption mechanism is that the H+ of carboxyl groups exchanged with heavy metal ions in the adsorption processes. In addition, the adsorbed Fe3O4-Si-COOH could be regenerated and the adsorption capacity of reused Fe3O4-Si-COOH could maintain 80.3% after five cycles. Hence, the Fe3O4-Si-COOH could be a kind of potential material for removing Pb(II), Zn(II), and Cd(II) from wastewater. Graphical abstract.