Fe(II) Sorption on Hematite: New Insights Based on Spectroscopic Measurements
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- 作者：Philip Larese-Casanova ; Michelle M. Scherer
- 刊名：Environmental Science & Technology
- 出版年：2007
- 出版时间：January 15, 2007
- 年：2007
- 卷：41
- 期：2
- 页码：471 - 477
- 全文大小：143K
- 年卷期：v.41,no.2(January 15, 2007)
- ISSN：1520-5851
文摘
We collected Mössbauer spectra of 57Fe(II) interactingwith 56hematite (
-Fe2O3) over a range of Fe(II) concentrationsand pH values to explore whether a sorbed Fe(II) specieswould form. Several models of Fe(II) sorption (e.g.,surface complexation models) assume that stable, sorbed Fe(II) species form on ligand binding sites of Fe(III) oxidesand other minerals. Model predictions of changes in bothspeciation and concentration of sorbed Fe(II) speciesare often invoked to explain Fe(II) sorption patterns, aswell as rates of contaminant reduction and microbialrespiration of Fe(III) oxides. Here we demonstrate that, atlow Fe(II) concentrations, sorbed Fe(II) species aretransient and quickly undergo interfacial electron transferwith structural Fe(III) in hematite. At higher Fe(II)concentrations, however, we observe the formation of astable, sorbed Fe(II) phase on hematite that we believe tobe the first spectroscopic confirmation for a sorbed Fe(II) phase forming on an iron oxide. Low-temperatureMössbauer spectra suggest that the sorbed Fe(II) phasecontains varying degrees of Fe(II)-Fe(II) interaction and likelycontains a mixture of adsorbed Fe(II) species and surfaceprecipitated Fe(OH)2(s). The transition from Fe(II)-Fe(III) interfacial electron transfer to formation of a stable,sorbed Fe(II) phase coincides with the macroscopicallyobserved change in isotherm slope, as well as the estimatedsurface site saturation suggesting that the finite capacityfor interfacial electron transfer is influenced by surfaceproperties. The spectroscopic demonstration of two distinctlydifferent sorption endpoints, that is an Fe(III) coatingformed from electron transfer or a stable, sorbed Fe(II)phase, challenges us to reconsider our traditionalinterpretations and modeling of Fe(II) sorption behavior(as well as, we would argue, of any other redox active sorbate-sorbent couple).
-Fe2O3) over a range of Fe(II) concentrationsand pH values to explore whether a sorbed Fe(II) specieswould form. Several models of Fe(II) sorption (e.g.,surface complexation models) assume that stable, sorbed Fe(II) species form on ligand binding sites of Fe(III) oxidesand other minerals. Model predictions of changes in bothspeciation and concentration of sorbed Fe(II) speciesare often invoked to explain Fe(II) sorption patterns, aswell as rates of contaminant reduction and microbialrespiration of Fe(III) oxides. Here we demonstrate that, atlow Fe(II) concentrations, sorbed Fe(II) species aretransient and quickly undergo interfacial electron transferwith structural Fe(III) in hematite. At higher Fe(II)concentrations, however, we observe the formation of astable, sorbed Fe(II) phase on hematite that we believe tobe the first spectroscopic confirmation for a sorbed Fe(II) phase forming on an iron oxide. Low-temperatureMössbauer spectra suggest that the sorbed Fe(II) phasecontains varying degrees of Fe(II)-Fe(II) interaction and likelycontains a mixture of adsorbed Fe(II) species and surfaceprecipitated Fe(OH)2(s). The transition from Fe(II)-Fe(III) interfacial electron transfer to formation of a stable,sorbed Fe(II) phase coincides with the macroscopicallyobserved change in isotherm slope, as well as the estimatedsurface site saturation suggesting that the finite capacityfor interfacial electron transfer is influenced by surfaceproperties. The spectroscopic demonstration of two distinctlydifferent sorption endpoints, that is an Fe(III) coatingformed from electron transfer or a stable, sorbed Fe(II)phase, challenges us to reconsider our traditionalinterpretations and modeling of Fe(II) sorption behavior(as well as, we would argue, of any other redox active sorbate-sorbent couple).