Chromium (VI) adsorption from wastewater using porous magnetite nanoparticles prepared from titanium residue by a novel solid-phase reduction method.

Porous magnetite nanoparticles were successfully synthesized by reduction of titanium residue with pyrite under nitrogen protection, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, vibrating sample magnetometer, X-ray photoelectron spectroscope, zeta potential and Brunauer-Emmett-Teller method. The XRD analysis confirmed the formation of porous magnetite nanoparticles with single spinel structure. The SEM image demonstrated that porous magnetite nanoparticles displayed spherical shape with the average diameter of ~51nm. The surface area of porous magnetite nanoparticles with high magnetic moment (78emu·g-1) was 11.1m2g-1. The experimental results revealed that equilibrium adsorption behavior of Cr(VI) was well described by Langmuir isotherm model with the maximum adsorption capacity of 14.49mgg-1 at 298.15K, and kinetic data was found to fit well with pseudo-second-order model. The adsorption rate for Cr(VI) was controlled by both boundary layer diffusion and intraparticle diffusion. Thermodynamics analysis showed that the adsorption processes of Cr(VI) were endothermic and spontaneous. In addition, the adsorption of Cr(VI) on porous magnetite nanoparticles was classified as chemisorption adsorption, which depended on electrostatic attraction accompanied with reduction of Cr(VI) to Cr(III). Porous magnetite nanoparticles were readily regenerated and used repeatedly for Cr(VI) adsorption at least five cycles. Furthermore, the experimental results indicate that porous magnetite nanoparticles have a promising application for Cr(VI) adsorption from wastewater.