Phase transformation of nanoscale zero-valent iron and concurrent arsenite sequestration under oxic water environment

Abstract

Nanoscale zero-valent iron (nZVI) may partially or completely transform to iron (hydr)oxides when it is used to remove arsenite [As(Ⅲ)]. It is necessary to explore the dynamic phase transformation of nZVI and concurrent arsenic valent changes since reactivity is relevant to the exiting species. In this study, X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), Raman spectrum, and scanning electron microscope (SEM) were used to probe the phase transformation of nZVI under the varied simulated polluted water, including different As(Ⅲ) concentration, pH, and co-existing anions. The mainly final product of nZVI corrosion was lepidocrocite (γ-FeOOH) evaluated by XRD. Because of proton release, As(Ⅲ) made more Fe0 corroded in the initial reaction and the corrosion process was faster in the later stage. The formation of iron (hydr)oxides was the main factor affecting the removal of As(Ⅲ) between pH 2–8. And the co-existing anions promoted the corrosion of Fe0, which weakened the negative effect of competitive adsorption on As(Ⅲ) removal to some extent. This research will provide vital information on the evolution and fate of nZVI under environmental conditions, as well as As(Ⅲ) stabilization and mobilization for nZVI treatment system.