The double influence mechanism of pH on arsenic removal by nano zero valent iron: electrostatic interactions and the corrosion of Fe0

Abstract

The pH has a significant impact on arsenic (As) removal by nano zero valent iron (nZVI). However, most studies consider the influence mechanism just from the aspect of electrostatic interactions. In this study, based on the different As(V) adsorption capacity of nZVI and zero valent iron (ZVI) after normalization by specific surface area, we deeply analyze the comprehensive mechanism of arsenic adsorption by nZVI at varying pH values. Batch experiment shows that pH variation has a weaker influence on the As(V) adsorption by nZVI compared to ZVI. X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) analysis indicated that with the coexistence of low concentration As(V) species, the increasing pH value condition does not significantly change the phase of ZVI; however, it decreases the lepidocrocite (γ-FeOOH) and increases the magnetite/maghemite (Fe₃O₄/γ-Fe₂O₃) content in the corrosion products of nZVI, while the latter has stronger adsorption affinity to As(V). An increase in the solution pH causes a change in the nature of the corrosion products, enhancing the adsorption affinity of nZVI towards As(V), which complements the negative impact from electrostatic repulsive-force. This study clearly demonstrated that the corrosion of nZVI plays a more important role in As(V) adsorption compared to electrostatic interactions. This indicates that nZVI is a promising nanomaterial with unique properties that aid in the removal of As(V) in a broad pH range and complicated environment.