title: Influence of chloride and Fe(II) content on the reduction of Hg(II) by magnetite.
abstract: Abiotic reduction of inorganic mercury by natural organic matter and native soils is well-known, and recently there is evidence that reduced iron (Fe) species, such as magnetite, green rust, and Fe sulfides, can also reduce Hg(II). Here, we evaluated the reduction of Hg(II) by magnetites with varying Fe(II) content in both the absence and presence of chloride. Specifically, we evaluated whether magnetite stoichiometry (x = Fe(II)/Fe(III)) influences the rate of Hg(II) reduction and formation of products. In the absence of chloride, reduction of Hg(II) to Hg(0) is observed over a range of magnetite stoichiometries (0.29 < x < 0.50) in purged headspace reactors and unpurged low headspace reactors, as evidenced by Hg recovery in a volatile product trap solution and Hg L(III)-edge X-ray absorption near edge spectroscopy (XANES). In the presence of chloride, however, XANES spectra indicate the formation of a metastable Hg(I) calomel species (Hg2Cl2) from the reduction of Hg(II). Interestingly, Hg(I) species are only observed for the more oxidized magnetite particles that contain lower Fe(II) content (x < 0.42). For the more reduced magnetite particles (x ≥ 0.42), Hg(II) is reduced to Hg(0) even in the presence of high chloride concentrations. As previously observed for nitroaromatic compounds and uranium, magnetite stoichiometry appears to influence the rate of Hg(II) reduction (both in the presence and absence of chloride) confirming that it is important to consider magnetite stoichiometry when assessing the fate of contaminants in Fe-rich subsurface environments.
authors.affiliation: Department of Civil and Environmental Engineering, The University of Iowa, Iowa City, Iowa 52242, United States.
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Pasakarnis
authors.forename: Maxim I
authors.initials: MI
authors.lastname: Boyanov
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Kemner
authors.forename: Bhoopesh
authors.initials: B
authors.lastname: Mishra
authors.forename: Edward J
authors.initials: EJ
authors.lastname: O'Loughlin
authors.forename: Gene
authors.initials: G
authors.lastname: Parkin
authors.forename: Michelle M
authors.initials: MM
authors.lastname: Scherer
mesh_terms: D002712:Chlorides / Q000737:chemistry*; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry*; D010084:Oxidation-Reduction; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D002712:Chlorides; D014874:Water Pollutants, Chemical; D007501:Iron; D008628:Mercury; D052203:Ferrosoferric Oxide