Removal of chromium(VI) from wastewater by Mg-aminoclay coated nanoscale zero-valent iron

Nanoscale zero-valent iron (nZVI) coated by Mg-aminoclay (MgAC) was prepared by the liquid-phase reduction method for high-efficiency removal of Cr(VI). The particles (MgAC-nZVI) were characterized by X-ray diffraction (XRD), fourier transform infrared (FTIR), transmission electron microscope (TEM), zeta potential analysis and X-ray photoelectron spectroscopy (XPS). It was found that the positively charged MgAC was capable of inhibiting the aggregation of nZVI particles and improving their dispersion stability in aqueous solution. Batch experiments showed that an iron dose of 0.125 g center dot L-1 in the form of MgAC-nZVI, at an initial Cr(VI) concentration of 20 mg center dot L-1 could maintain a good performance on Cr(VI) removal at a wide pH range. It was proved that the presence of co-existing ions (Cu2+, Ni2+ and SO42-) except PO43- in the solution had positive influence on the removal of Cr(VI). Due to the large accessible surface area and the protonated amino groups (-NH3+) on the particle surface, MgAC-nZVI could remove Cr(VI) through fast adsorption and efficient reduction. The removal of Cr(VI) by using MgAC-nZVI was proved to be in accordance with the pseudo-second-order adsorption kinetics. Based on the identification of the reduction products, Cr(VI) was reduced by Fe-0 to form Cr(III). Eventually, the Cr(VI) was removed in a way of Cr(III)-Fe(III) co-precipitates adsorbed on the surface of MgAC-nZVI particles. Moreover, the MgAC-nZVI particles have a better performance of reusability than the uncoated nZVI.