Preparation of thiol-modified Fe3O4@SiO2 nanoparticles and their application for gold recovery from dilute solution

A novel magnetic nanomaterial was developed for gold recovery from dilute solutions. Fe3O4 nanoparticles were prepared by co-precipitation method, and SiO2 was coated on Fe3O4 nanoparticles by hydrolyzation of Na2SiO3 for protecting the core from being oxidized or dissolved under acid solution, and then thiol groups were modified on the Fe3O4@SiO2 through silanization reaction. Characterization with transmission electron microscope (TEM), energy-dispersive spectroscope (EDS), and X-ray photoelectron spectroscopy (XPS) proved that SiO2 and thiol groups were successfully covered on the surface of Fe3O4 nanoparticles to form Fe3O4@SiO2-SH adsorbent, which was readily separated from solution with a magnet because of superparamagnetism of Fe3O4 core. The formation of the stable Au-S bond between thiol group and gold element could be applied for gold recovery from solution. The adsorption behavior of Fe3O4@SiO2-SH for gold followed Langmuir isotherm model, and the maximum adsorption capacity was 84.75 mg/g at pH 5. When the initial concentration of gold was 5 mg/L, the gold in solution was completely adsorbed by Fe3O4@SiO2-SH, and when the gold concentration was 10 mg/L, 98.8% gold was adsorbed. With the solution pH increasing from 3 to 7, the adsorption capacity for gold showed a slight decrease, and the adsorbents still remained good adsorbability under high salinity condition. Gold loaded on the adsorbent could be easily desorbed by 1 mol/L or 2 mol/L HCl containing 2% of thiourea, and the adsorbents showed good reusability after 5 times recycle. (c) 2013 Elsevier B.V. All rights reserved.