Removal of Cr(VI) by hollow micron zero-valent iron in groundwater containing different ions: Mechanisms and mineralized products

Abstract

The development of zero-valent iron in-situ reactive zone technology is restricted by the poor mobility and reactivity of zero-valent iron. Hence，hollow micron zero-valent iron (H-mZVI) was prepared through rapid liquid reduction and used to remove Cr(VI) from aqueous solution. Scanning electron microscopy confirmed that H-mZVI had a hollow structure, particle size of approximately 1 µm, and rough surface. X-ray diffraction indicated that H-mZVI was mainly composed of ZVI. Brunauer–Emmett–Teller results showed that H-mZVI had a large specific surface area (25.54 m2/g) and pore volume (0.12 cm3/g). The Cr(VI) removal efficiency of H-mZVI was 6.18 times that of solid micron zero-valent iron (S-mZVI), and the removal reaction conformed to first-order reaction kinetics. Electrochemical test results revealed that the electron transport efficiency was stronger, Fe2+ concentration in aqueous solution was larger, and the decrease in oxidation–reduction potential was more obvious in H-mZVI than in S-mZVI. Desorption experiment and X-ray photoelectron spectroscopy showed that H-mZVI removed Cr(VI) primarily through reduction and secondarily through adsorption. The effects of conventional ions and humic acid (HA) on Cr(VI) removal by H-mZVI were in the order of PO43->HA>NO3->CO32->HCO3->Cl-=Mg2+=Ca2+. The corrosion products and their proportions varied in the presence of different ions.