Effect of reduced humic acid on the transport of ferrihydrite nanoparticles under anoxic conditions

Peng Liao, Wenlu Li, Dengjun Wang, Yi Jiang, Chao Pan, John D. Fortner, Songhu Yuan

Research output: Journal article publicationJournal articleAcademic researchpeer-review

32 Citations (Scopus)

Abstract

Humic acid (HA) occurs ubiquitously in the subsurface environments and is well-known to play a critical role in the fate and transport of ferrihydrite nanoparticles (NPs) and NPs-associated contaminants. Under anoxic conditions, HA can readily be reduced by microorganisms or geochemical reducing species, and the mechanisms and kinetics of ferrihydrite reduction by reduced HA (HAred) are well-documented; however, the role of these redox reactions on the transport of ferrihydrite NPs is largely underestimated. This study provides new knowledge regarding the role of HA (both reduced HA (HAred) and oxidized HA (HAox)) of environmentally relevant concentrations (0–50 mg C/L) on the transport of ferrihydrite NPs in anoxic sand columns. Our findings show that, regardless of the redox state, the presence of a low concentration of HA (3 mg C/L) inhibited ferrihydrite NP's transport due to enhanced aggregation (and deposition) between positively charged ferrihydrite NPs and negatively charged HA molecules. In contrast, higher HA (both HAred and HAox) concentration (≥10 mg C/L) significantly enhanced the mobility of ferrihydrite NPs, primarily due to the enhanced electrostatic and steric stabilization originating from excessively adsorbed HA molecules. Interestingly, the transport of ferrihydrite NPs is substantially lower in the presence of HAred than in the presence of HAox. This distinct effect (HAred vs. HAox) on the particle transport is attributed to the fact that reductive dissolution of ferrihydrite NPs occurs in the presence of HAred (ferrihydrite dissolves and thus total breakthrough decreases), but not in the presence of HAox. Furthermore, the abatement extent of ferrihydrite NPs transport triggered by the presence of HAred is dependent on dissolved HAred concentration. Taken together, our findings provide direct, and much needed insights into the distinct roles of redox state of HA on the transport of redox-sensitive metal-bearing NPs in porous media.

Original languageEnglish
Pages (from-to)347-357
Number of pages11
JournalWater Research
Volume109
DOIs
Publication statusPublished - 1 Feb 2017
Externally publishedYes

Keywords

  • Ferrihydrite nanoparticles
  • Humic acid
  • Mechanism
  • Porous media
  • Redox state
  • Transport

ASJC Scopus subject areas

  • Ecological Modelling
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution

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