Investigations on the capacity and mechanism of iron uptake by nano zero-valent iron particles

Nano zero-valent iron (nZVI) particles have been identified as one of the potential candidate for the removal of various metal ions. This study addresses the effectiveness of nZVI on iron removal from an aqueous solution containing Fe2+/Fe3+ in the ratio of 2.5:0.5, which is not studied so far. Liquid-phase reduction technique was utilized to synthesize the nZVI. The characterization of nZVI and its interaction with iron in aqueous solution was found using transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible spectroscopy (UV-Vis spectroscopy) and Fourier transform infrared spectroscopy (FTIR). It was found that the nZVI particles were largely spherical with size varying from 80-99 nm. Abundant oxygen functional groups detected in the FTIR spectrum serve as the accessible sites for iron adsorption. SEM and XRD studies provided a clear image of core-shell structure of nZVI. The study also investigated the role of pH, iron concentration, nZVI dosage and contact time on the uptake behaviour of contaminant iron. A removal efficiency of 63% was achieved in 3 h, with optimum nZVI loading of 5 g l(-1), from a solution having initial iron concentration of 0.5 mg l(-1) at natural solution pH 6.85. This efficiency was increased to 70% at optimum pH 10. The batch study revealed that adsorption kinetics followed pseudo-second-order kinetics with R-2 value of 0.99 and data followed Dubinin-Radushkevich isotherm. Outcomes of the study recommend that nZVI could turn into a promising adsorbent for iron removal from aqueous solutions.