Coagulation of humic substances and dissolved organic matter with a ferric salt: an electron energy loss spectroscopy investigation.
Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS) was used to investigate the coagulation of natural organic matter with a ferric salt. Jar-test experiments were first conducted with a reconstituted water containing either synthetic or natural extracts of humic substances, and then with a raw water from Moselle River (France). The characterization of the freeze-dried coagulated sediment by EELS in the 250-450 eV range, showed that Fe-coagulant species predominantly associate with the carboxylic groups of organic matter, and that this interaction is accompanied by a release of previously complexed calcium ions. The variation of Fe/C elemental ratio with iron concentration provides insightful information into the coagulation mechanism of humic substances. At acid pH, Fe/C remains close to 3 over the whole range of iron concentrations investigated, while a much lower atomic ratio is expected from the value of optimal coagulant dosage. This suggests that a charge neutralization/complexation mechanism is responsible for the removal of humic colloids, the aggregates being formed with both iron-coagulated and proton-neutralized organic compounds. At pH 8, the decrease in Fe/C around optimal coagulant concentration is interpreted as a bridging of stretched humic macromolecules by Fe-hydrolyzed species. Aggregation would then result from a competition between reconformation of humic chains around coagulant species and collision of destabilized humic material. EELS also enabled a fingerpriting of natural organic substances contained in the iron-coagulated surface water, N/C elemental analyses revealing that humic colloids are removed prior to proteinic compounds.
Jung
A-V
AV
Laboratoire Environnement et Minéralurgie, UMR 7569 CNRS-INPL-ENSG, 15 avenue du Charmois, BP 40, 54501 Vandaeuvre, France. av1jung@hotmail.com
Chanudet
V
V
Ghanbaja
J
J
Lartiges
B S
BS
Bersillon
J-L
JL
D003102:Colloids; D005290:Ferric Compounds / Q000032:analysis* / Q000737:chemistry; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D046529:Microscopy, Electron, Transmission; D009930:Organic Chemicals / Q000032:analysis; D046590:Spectroscopy, Electron Energy-Loss; D014867:Water / Q000737:chemistry
D003102:Colloids; D005290:Ferric Compounds; D006812:Humic Substances; D009930:Organic Chemicals; D014867:Water