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2026 Vol.31, Issue 2 Preview Page

Research Article

Thermodynamic Eh-pH Analysis of Passivation Product Pathways of NZVI under Various Oxidation Conditions

산화 조건 변화에 따른 NZVI 부동태화 생성물 형성 경로의 열역학적 Eh-pH 해석연구

Sunho Yoon1
,
Sungjun Bae1*
윤 선호1
,
배 성준1*
1Department of Civil and Environmental Engineering, College of Engineering, Konkuk University, Seoul 05029, Republic of Korea
1건국대학교 공과대학 사회환경공학부
*Corresponding Author
30 April 2026. pp. 27-40
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Abstract

Numerous studies have reported the formation of passivation products of nanoscale zerovalent iron (NZVI) under oxic conditions. However, inconsistent observations, particularly regarding the formation of magnetite (Fe3O4) and lepidocrocite (γ-FeOOH), remain unresolved. In this study, the passivation behavior of NZVI under various oxidation conditions was interpreted from a thermodynamic perspective. Fe3O4 was predominantly formed under O2, H2O2, and NO3− conditions, whereas γ-FeOOH was preferentially formed under HCl, persulfate, and HCO3− conditions. By integrating pH-Eh trajectories with Pourbaix diagram analysis, passivation product formation was found to be governed not only by overall oxidizing conditions but also by pH-Eh pathways influenced by coexisting anions. In particular, γ-FeOOH formation is thermodynamically favored along pathways passing through the green rust stability region compared to pathway involving Fe3O4. Under pure O2 purging conditions, Fe3O4 undergoes sequential transformation to γ-FeOOH, indicating that intermediate phases influence the transformation pathway and kinetics. Cr(VI) removal experiments revealed phase-dependent reactivity. Fe3O4 exhibitted reduction-dominated removal, whereas γ-FeOOH showed adsorption-dominated behavior. This indicates that additional electron transfer properties of passivation products control residual reactivity. These findings provide a thermodynamic framework linking phase formation to reactivity and enable improved prediction of NZVI performance under varying geochemical conditions, although the role of green rust requires further experimental validation.

Keywords
Nanoscale zerovalent iron
Passivation products
pH-Eh diagram
Mineral transformation
Oxidation con-ditions
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Information
  • Publisher :The Korean Society of Soil and Groundwater Environment
  • Publisher(Ko) :한국지하수토양환경학회
  • Journal Title :Journal of Soil and Groundwater Environment
  • Journal Title(Ko) :지하수토양환경
  • Volume : 31
  • No :2
  • Pages :27-40
  • Received Date : 2026-03-31
  • Revised Date : 2026-04-06
  • Accepted Date : 2026-04-21
  • DOI :https://doi.org/10.7857/JSGE.2026.31.2.027
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