Large amounts of aqueous film-forming foams (AFFFs) have been applied during military training and fire-fighting activities. As a result, high concentrations of fluorinated chemicals, the key extinguishing components in AFFFs, and chlorinated solvents contained in ignition fluids used during fire training, are often encountered together in the groundwater of the AFFF-impacted sites. Many fluorinated chemicals can be transformed to the highly persistent perfluoroalkyl acids (PFAAs). Since the 1990s, nanoscale zerovalent iron (NZVI) has been proposed as an in situ remediation agent for metal and chlorinated solvent contaminated groundwater. It is necessary to investigate the interaction between PFAAs and NZVI at sites where NZVI-based remediation is attempted. In this study, we did not find any degradation of PFAAs after incubation with either bare NZVI or surface-modified NZVI. However, we found the sorption of PFAAs to NZVI was 2–4 orders of magnitude higher than those reported for sediments and soils. FTIR spectra indicated specific interactions between sulfonate and carboxylate groups and the NZVI surface, but nonspecific interactions dominated the sorption of PFAAs to NZVI. Sorption of perfluorooctanesulfonic acid (PFOS) was further characterized to explore the influence of polyelectrolytes used for colloidal stabilization of NZVI, solution pH, and dissolved natural organic matter. In addition, we investigated the impact of aging of NZVI under anaerobic (oxidation by water) and aerobic (oxidation by water and dissolved oxygen) conditions and NZVI sulfidation on the sorption of PFOS to NZVI. Sorption isotherms of PFOS to synthesized iron phases (Fe(OH)2, γ-Fe2O3, Fe3O4, γ-FeOOH, and FeS) formed on the surface of NZVI after aging and sulfidation were used to explain the variation in sorption for aged and sulfidized NZVI. The results suggest that application of NZVI could reduce PFAA aqueous concentrations in groundwater despite changes to its surface chemistry with aging.

Sorption of perfluoroalkyl acids to fresh and aged nanoscale zerovalent iron particles

256th National Meeting (2018)

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