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| Titel |
Mechanisms of trace metal sorption in Pseudomonas putida-birnessite assemblages |
| VerfasserIn |
J. Peña, K. D. Kwon, J. R. Bargar, G. Sposito |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066865
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| Zusammenfassung |
| Biogenic manganese oxides (MnO2) are ubiquitous nanoparticulate minerals that
contribute strongly to the adsorption of nutrient and toxicant metals in aquatic and
terrestrial environments. The formation of these minerals is catalyzed by a diverse and
widely-distributed group of bacteria and fungi, often through the enzymatic oxidation of
aqueous Mn(II) to Mn(IV). The biogenic Mn(IV) oxide found in field settings, as well as that
produced by model bacteria in laboratory culture, is typically layer-type hexagonal birnessite
containing abundant cation vacancy sites and enmeshed in an organic matrix of bacterial cells
and extracellular polymeric substances.
In this talk I summarize the results from laboratory-scale research designed to investigate
the mechanisms of metal sorption by the bacterial biomass-birnessite assemblages formed by
Pseudomonas putida GB-1 when grown in the presence of 1 mM Mn(II) at circumneutral pH
values. The goals of this research were first, to identify the structure of the surface complexes
formed by trace metals (e.g., Ni, Cu and Zn) on biogenic birnessite and second, to
determine the conditions under which the bacterial cell surfaces and extracellular
polymeric substances contribute to metal sorption. Macroscopic and spectroscopic
experiments were performed at varying pH values (6 – 8) and over a wide-range of metal
concentrations.
Extended X-ray absorption fine structure (EXAFS) spectroscopy and first-principles
calculations based on density functional theory showed that cation vacancy sites in birnessite
drive mineral reactivity, but that surface speciation varies from metal to metal. For, Ni we
identified two species, Ni bonded to three surface oxygen atoms vacancy sites as a
triple-corner-sharing (TCS) complex and Ni incorporated at vacancy sites, with surface
speciation varying with pH and surface loading. Zinc formed TCS complexes at vacancy
sites, with the proportion of Zn in tetrahedral or octahedral coordination geometry influenced
by solution pH, background electrolyte, surface loading, and time of Zn addition relative to
MnO2 precipitation. Copper bonding at vacancy sites was found to be important as
well, but the geometry of additional surface complexes, suggested by the EXAFS
spectra, could not be identified. Based on the results from EXAFS spectroscopy, we
concluded that the bacterial biomass does not limit Ni or Zn sorption at vacancy
sites, contributing to metal sorption at very high surface loadings (> 0.1 mol Me
mol-1 Mn). However, Cu, a transition metal with a high affinity for both organic and
mineral functional groups and facile redox reactivity, was found to interact strongly
with the biomass over all surface loadings investigated. This research advances our
understanding of the surface reactivity of biogenic birnessite and sheds light on metal
retention mechanisms in composite microbe-mineral assemblages, which regulate the
concentrations and distribution of nutrient and toxicant metals in diverse ecosystems. |
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