Kinetics of Homogeneous and Surface-Catalyzed Mercury(II) Reduction by Iron(II)

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 x 10(+3) L (mol min)(-1). Compared to the homogeneous case, goethite (alpha-FeOOH) and hematite (alpha-Fe2O3) increased and gamma-alumina (gamma-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 x 10(+3), 4.69 x 10(+3), and 1.08 x 10(+2) L (mol min)(-1) for hematite, goethite, and gamma-alumina, respectively. Hg(0) production coupled to reduction by Fe(II) May be an important process to consider in ecosystem, Hg studies