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Trace Element and Contaminant Fate during Fe(II )-Catalyzed Iron Oxide Surface Transformations

Trace Element and Contaminant Fate during Fe(II )-Catalyzed Iron Oxide Surface Transformations. Jeffrey G. Catalano Goldschmidt 2013. Acknowledgements. Contributors. Financial Support. Andrew Frierdich (U. Wisconsin) Katherine Becker (Wash U) Margaret Anne Gray Hinkle (Wash U)

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Trace Element and Contaminant Fate during Fe(II )-Catalyzed Iron Oxide Surface Transformations

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  1. Trace Element and Contaminant Fate during Fe(II)-Catalyzed Iron Oxide Surface Transformations Jeffrey G. Catalano Goldschmidt 2013

  2. Acknowledgements Contributors Financial Support Andrew Frierdich(U. Wisconsin) Katherine Becker (Wash U) Margaret Anne Gray Hinkle (Wash U) Yun Luo (GIA) BamideleOtemuyiwa (Wash U) FrédéricMoynier(Wash U) US NSF Geobiology and Low-Temperature Geochemistry US NSF CAREER ACS Petroleum Research Fund Washington University in St. Louis Argonne National Laboratory US DOE/BES Geosciences Research Program Earth and Planetary Sciences • Washington University

  3. Biogeochemical Iron Cycling: Alteration of Iron Oxidation States Microorganisms drive the cycling of iron between Fe(III) and Fe(II) This redox cycling is never instantaneous and is often incomplete Fe(II) and Fe(III) often coexist in many natural systems and may react These secondary abiotic reactions constitute a “hidden component” of iron cycling Earth and Planetary Sciences • Washington University Figure from: Weber et al. (2007) Nature Rev. Micro.4, 753-764

  4. Mineral Recrystallization during Fe Cycling Oxidative Fe(II) Adsorption Williams and Scherer (2004) Electron Conduction Yanina and Rosso (2008) Atom Exchange Handler et al. (2009) Earth and Planetary Sciences • Washington University

  5. Effect of Fe(II)-Promoted Iron Oxide Recrystallization on Trace Element Fate Excess Co Release during Fe Reduction Fe(II)-Enhances TE Adsorption to Goethite From: Coughlin and Stone (1995) ES&T29, 2445-2455; Zachara et al. (2001) GCA65, 75-93 • Trace element adsorption onto goethite is enhanced in the presence of Fe(II) • Fe(II) also causes a fraction of adsorbed Ni and Co to be bound irreversibly, suggesting entrapment in the mineral structure • Microbial reductive dissolution of Co-substituted goethite shows excess, nonstoichiometric Co release Earth and Planetary Sciences • Washington University

  6. Effect of Fe(II)-Fe(III) Reactions on Trace Element Fate is Uncertain • Trace elements often incorporate into or adsorb on iron oxides • These elements are contaminants, micronutrients, or geochemical proxies How does recrystallization affect adsorbates? What happens to trace elements substituting in iron oxides during recrystallization? Earth and Planetary Sciences • Washington University

  7. Effect of Fe(II) on As(V) Surface Speciation pH 7 EXAFS spectroscopy shows that As(V) surface complex structure is unchanged in the presence of Fe(II) Earth and Planetary Sciences • Washington University Catalano et al. (2011) ES&T45, 8826–8833

  8. Fe(II)-Induced Metal Incorporation into Iron Oxides 4 g/L solid, 0.2 mM Ni(II), ±1 mM Fe(II), pH 7.5, 80 days • Fe(II) induces substantial changes in XANES and EXAFS spectra of Ni adsorbed onto hematite and goethite • Comparison with the spectra of Ni incorporated into and adsorbed onto hematite and goethite show clear isosbestic points • Indicates two-component mixing, i.e., adsorbed and incorporated Ni • Up to 50% of the adsorbed Ni becomes incorporated Earth and Planetary Sciences • Washington University Frierdich et al. (2011) Geology39, 1083-1086

  9. Zn Incorporation into Goethite Controls on and Possible Signatures of Metal Incorporation Green Rust Forms Zn Isotope Fractionation Substantial Zn incorporation occurs after 5 days of reaction Longer reaction times and higher pH promote incorporation Distinct Zn stable isotope fractionations produced by adsorption on goethite and hematite Possible fractionation from incorporation into goethite Earth and Planetary Sciences • Washington University

  10. Goethite Fe(II)-Catalyzed Metal Release from Substituted Iron Oxides Hematite 1 g/L solid, pH 7, 1 mM MOPS, 0.01 M NaCl Frierdich et al. (2011) Geology39, 1083-1086 Frierdich and Catalano (2012) ES&T46, 1519-1526 • Metal-substituted iron oxides are stable under circumneutral conditions • Little release occurs in electrolyte solutions • Fe(II) induces the release of nearly 10% of incorporated Ni or Zn from hematite or goethite after 2 weeks of reaction • Release rates orders of magnitude slower than Fe(II) adsorption but comparable to Fe(II)-iron oxide isotope exchange • Release varies among metals and minerals • Goethite: Ni release greater than Zn • Hematite: Zn release greater than Ni Earth and Planetary Sciences • Washington University

  11. Fe(II) Activates Trace Element Cycling Through Iron Oxides • Promotes equilibration among the mineral, mineral surface, and fluid • Metal incorporation in regions of Fe(II) oxidative adsorption and growth • Metal release in regions of Fe(III) reductive dissolution Earth and Planetary Sciences • Washington University Frierdich et al. (2011) Geology39, 1083-1086

  12. Copper, Cobalt, and Manganese Release Behaviors Suggest Reduction by Fe(II) Limited, transient release of copper suggests reduction of Cu(II) to Cu(I) Substantial Co and Mn release observed from iron oxides containing insoluble Co(III) and Mn(III/IV) Earth and Planetary Sciences • Washington University Frierdich and Catalano (2012) ES&T46, 11070-11077

  13. Evidence for Trace Element Reduction: Excess Fe(II) Consumption More Fe(II) is removed from solution when iron oxides contain reducible trace elements Earth and Planetary Sciences • Washington University Frierdich and Catalano (2012) ES&T46, 11070-11077

  14. Spectroscopic Confirmation of Trace Element Reduction Cu(II) is reduced to Cu(I); form is unknown Co(III) is reduced to Co(II), some released to solution but substantial remains in mineral Mn in solid is reduced only to Mn(III); all Mn(II) produced is released to solution Earth and Planetary Sciences • Washington University Frierdich and Catalano (2012) ES&T46, 11070-11077

  15. Effect of Fe(II)-induced Recrystallization on Trace Element Fate Varies with Structural Compatibility Incompatible Element (e.g., As, Se) Compatible Element (e.g., Mn, Co, Ni, Cu, Zn) • Elements that cannot substitute into iron oxides are little affected by Fe(II)-induced recrystallization • Compatible elements cycle through iron oxides • Cycling of elements through iron oxides competes with (e.g., Cu) or is aided by (e.g., Co, Mn) redox transformations • Fe cycling substantially alters the fate and bioavailability of trace element contaminants and micronutrients Earth and Planetary Sciences • Washington University

  16. Iron Oxide Recrystallization without Fe(II)? No Fe(II) 80 d Rxn No Fe(II) • Ni incorporation into goethite observed in absence of Fe(II) • Ni release from iron oxides observed at acidic pH without Fe(II), suggesting proton-promoted recrystallization • Recrystallization may be rate-limited by [Fe]TOT in solution • Processes that enhance [Fe]TOT may stimulate metal repartitioning Earth and Planetary Sciences • Washington University Data from: Frierdich and Catalano (2012) ES&T46, 1519-1526

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