Remarkable effect of Co substitution in magnetite on the reduction removal of Cr(VI) coupled with aqueous Fe(II): Improvement mechanism and Cr fate

Ying Li, Gaoling Wei, Caihua Zhang, Xiaoliang Liang, Wei Chu, Hongping He, Joseph W. Stucki, Lingya Ma, Xiaoju Lin, Jianxi Zhu

Research output: Journal article publicationJournal articleAcademic researchpeer-review

8 Citations (Scopus)

Abstract

The interaction between magnetite and aqueous Fe(II) profoundly impacts the mineral recrystallization, trace-metal sequestration, and contaminant reduction. The iron ions in natural magnetite are extensively substituted by other cations. It is still unclear whether the substitution with thermodynamically favorable redox repairs (e.g., Co2+/Co3+) plays a vital role in the reducing capability of the coupled system. Herein, a series of Co-substituted magnetite samples (Fe3−xCoxO4, 0.00 ≤ x ≤ 1.00) were synthesized and tested for the reductive removal of Cr(VI) in the presence of Fe(II). Fe3−xCoxO4 had a spinel structure with the preferential occupancy of Co2+ on octahedral sites. No visible variation in the BET surface area was observed, whereas the surface site density increased gradually with Co substitution. Cr(VI) was found first adsorbed on the Fe3−xCoxO4 surface and then reduced to Cr(III) by the structural Fe2+ and the absorbed Fe(II), accompanied by the oxidation of bulk Fe2+ and surface Fe(II) in Fe3−xCoxO4 without phase transformation. The Cr(III) was precipitated on the Fe3−xCoxO4 surface with Fe(III), or substituted octahedral Fe in Fe3−xCoxO4. Both the reaction kinetics and the electron transfer efficiency revealed that Co substitution significantly improved the reactivity of Fe3−xCoxO4/Fe(II) towards Cr(VI) reduction. This was ascribed to the presence of the redox pairs Co2+/Co3+ and Fe2+/Fe3+ accelerating electron transfer from the Fe3−xCoxO4 interface to Cr(VI).

Original languageEnglish
Pages (from-to)400-408
Number of pages9
JournalScience of the Total Environment
Volume656
DOIs
Publication statusPublished - 15 Mar 2019

Keywords

  • Aqueous Fe(II)
  • Co-substituted magnetite
  • Cr microstructure
  • Heterogeneous reduction of Cr(VI)
  • Reaction mechanism

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

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