Mechanistic insights into As(III) removal from groundwater using iron net-based zero-valent iron: reaction pathways and inhibitory effects of phosphorus and silicon

Arsenic (As) contamination of groundwater poses a serious public health risk in many regions worldwide. Zero-valent iron (ZVI)-based systems are widely used for As removal. Nevertheless, their performance is strongly influenced by coexisting groundwater constituents such as phosphorus (P) and silicon (Si). This study systematically investigates the removal mechanisms of arsenite (As(III)) from groundwater using an iron net-based ZVI (IN-ZVI) system. Batch experiments were conducted to evaluate As(III) removal kinetics, iron dissolution behavior, and adsorption isotherms under varying P and Si concentrations. Spectroscopic analyses using X-ray Absorption Fine Structure (XAFS) and X-ray Photoelectron Spectroscopy (XPS) were employed to elucidate As(III) oxidation pathways and surface transformations of the iron net. Results show that As(III) removal followed first-order kinetics, whereas Fe(II) dissolution exhibited zero-order behavior. Increasing P and Si concentrations significantly suppressed both As(III) removal and iron dissolution, with P exerting a stronger inhibitory effect than Si. Langmuir and Freundlich isotherm analyses revealed a progressive decrease in adsorption capacity with increasing P and Si, attributed to competitive site occupation and surface passivation. XAFS results confirmed complete oxidation of As(III) to As(V) in the IN-ZVI system, while XPS analysis demonstrated extensive formation of Fe(III) oxides and deposition of P- and Si-bearing surface scales. These findings indicate that As(III) removal proceeds via corrosion-induced Fe redox cycling, reactive oxygen species-mediated oxidation, and subsequent adsorption of As(V) onto hydrous ferric oxides. The study highlights the critical role of groundwater chemistry in controlling ZVI reactivity and provides mechanistic insights for optimizing iron-based arsenic removal technologies in P and Si rich groundwater.