Insights on mitigation of chemical clogging of zero-valent iron for nitrobenzene reduction: the role of oxygenated anion modification

Abstract

Clogging of zero-valent iron (ZVI) is among the most prominent technical bottlenecks limiting its application in long-term groundwater remediation. In this study, three ZVI species with different oxygenated anion modifications on the surface—micron ZVI (mZVI), oxalated mZVI (OX-mZVI), and phosphorylated mZVI (P-mZVI)—were selected to conduct a comparative study on the clogging problem during remediation of nitrobenzene-contaminated groundwater. The clogging degree (Φ_C) was innovatively employed to quantify ZVI clogging, and the clogging mechanisms of influencing factors were uncovered by analyzing changes in Φ_C, reactivity, volume expansion, iron valence state, and iron corrosion product (FeCP) species. Results revealed that the clogging resistance of ZVI decreased in the following order: P-mZVI > OX-mZVI > mZVI. The reduction process of nitrobenzene controlled the increase of Φ_C, and the reduction of NO₃⁻—a groundwater background ion—served as an indicator for clogging stage changes. Surface chemistry analysis revealed that the increase of Φ_C originated from the volume expansion effect of FeCPs. Iron corrosion increased the Fe(III) content, producing Fe₃O₄ and FeOOH, which roughened the ZVI surfaces and formed dense agglomerates via crystal expansion, causing chemical clogging by occupying pore space. Overall, enhancing the electron selectivity and surface hydrophobicity of ZVI using surface modification methods can enhance its anti-clogging performance.

Graphical abstract

Keywords

Zero-valent iron / Clogging / Iron corrosion products / Volume expansion / Groundwater

Highlight

	● Anti-clogging performance decreases in the order P-mZVI > OX-mZVI > mZVI.
	● Strong electron-withdrawing substances determine increased clogging.
	● The increase in clogging degree is due to the volume expansion effect of FeCPs.
	● Enhanced electron selectivity and hydrophobicity improve anti-clogging performance.

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