title: Kinetics of homogeneous and surface-catalyzed mercury(II) reduction by iron(II).
abstract: Production of elemental mercury, Hg(0), via Hg(II) reduction is an important pathway that should be considered when studying Hg fate in environment. We conducted a kinetic study of abiotic homogeneous and surface-catalyzed Hg(0) production by Fe(II) under dark anoxic conditions. Hg(0) production rate, from initial 50 pM Hg(II) concentration, increased with increasing pH (5.5-8.1) and aqueous Fe(II) concentration (0.1-1 mM). The homogeneous rate was best described by the expression, r(hom) = k(hom) [FeOH(+)] [Hg(OH)2]; k(hom) = 7.19 × 10(+3) L (mol min)(-1). Compared to the homogeneous case, goethite (α-FeOOH) and hematite (α-Fe2O3) increased and γ-alumina (γ-Al2O3) decreased the Hg(0) production rate. Heterogeneous Hg(0) production rates were well described by a model incorporating equilibrium Fe(II) adsorption, rate-limited Hg(II) reduction by dissolved and adsorbed Fe(II), and rate-limited Hg(II) adsorption. Equilibrium Fe(II) adsorption was described using a surface complexation model calibrated with previously published experimental data. The Hg(0) production rate was well described by the expression r(het) = k(het) [>SOFe((II))] [Hg(OH)2], where >SOFe((II)) is the total adsorbed Fe(II) concentration; k(het) values were 5.36 × 10(+3), 4.69 × 10(+3), and 1.08 × 10(+2) L (mol min)(-1) for hematite, goethite, and γ-alumina, respectively. Hg(0) production coupled to reduction by Fe(II) may be an important process to consider in ecosystem Hg studies.
authors.affiliation: Department of Civil and Environmental Engineering, University of Maine, 5711 Boardman Hall, Orono, Maine 04469, United States. aria@umit.maine.edu
authors.forename: Aria
authors.initials: A
authors.lastname: Amirbahman
authors.forename: Douglas B
authors.initials: DB
authors.lastname: Kent
authors.forename: Gary P
authors.initials: GP
authors.lastname: Curtis
authors.forename: Mark C
authors.initials: MC
authors.lastname: Marvin-Dipasquale
mesh_terms: D000327:Adsorption; D000537:Aluminum Oxide / Q000737:chemistry; D002384:Catalysis; D005290:Ferric Compounds / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry; D007700:Kinetics; D008628:Mercury / Q000737:chemistry*; D008903:Minerals / Q000737:chemistry; D008956:Models, Chemical; D010084:Oxidation-Reduction; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D058085:Iron Compounds; D008903:Minerals; D014874:Water Pollutants, Chemical; C094886:goethite; C000499:ferric oxide; D007501:Iron; D008628:Mercury; D000537:Aluminum Oxide