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| Titel |
Effect of adsorbed extracellular polymeric substances (EPS) on colloidal mobility of nanoparticulate iron oxides |
| VerfasserIn |
Sneha Pradip Narvekar, Kai Uwe Totsche |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082334
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| Zusammenfassung |
| Solubility and transport of nutrients and pollutants is affected by the presence of colloidal
nanoparticles (CNP) which may act as mobile geosorbents. In soils and aquifers, pure and
organically modified Fe- and Mn-oxy-hydroxides are of particular importance due to their
ubiquitous presence and also due to their progressive use for environmental cleanup.
Stability and aggregation behavior control the mobility of CNP and depend on
pH, ionic strength, and the presence of monovalent or divalent anions. In natural
environments, however, iron oxides are usually covered by organic matter. Such
coverage will completely change the colloidal surface properties and impose additional
control on the colloidal mobility. Important sources for natural organic coatings are
extracellular polymeric substances (EPS), i.e., complex mixtures of biopolymers
consisting of polysaccharides and proteins and variable amounts of lipids and nucleic
acids.
The objective of our study was to quantify the effect of EPS coatings on the colloidal
stability, mobility and reactivity of hematite by column experiments. Columns (10 cm à 5
cm) were filled with glass beads (0.25 mm ø) as porous medium and operated in sterile closed
flow conditions. Nanoparticulate hematite was coated to different degrees by extracellular
polymeric substances (EPS) extracted from, liquid cultures of Bacillus subtillis. The pH was
kept constant at 7. The hematite particles exhibited increasing colloidal stability with
increasing amounts of EPS. Critical colloidal concentration (CCC) of the particles increased
from 95 mM NaCl for uncoated particles to 250 mM NaCl for coated particles. EPS coated
hematite did not react with the porous medium and stayed mobile while the uncoated
hematite was immobile due to adsorption to the glass beads. Also colloidally unstable
hematite particles did not show any mobility. Thus the organic coatings enhanced the
colloidal stability, which consecutively increased the mobility of the particles. Also, the
reactivity of these particles to the porous medium is reduced due to the masking of the
reactive hematite surface sites with EPS. EPS coated CNP may define the major
part of mobile material in natural environments like soils, sediments and aquifers. |
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