Manuscript Eu-HA-Fe.pdf (109.8 kB)
Competitive effect of iron(III) on metal complexation by humic substances : characterisation of ageing processes
journal contribution
posted on 2008-01-15, 16:46 authored by Holger Lippold, Nick Evans, Peter Warwick, H. KupschAiming at an assessment of counteractive effects on colloid-borne migration of actinides in
the event of release from an underground repository, competition by Fe(III) in respect of
metal complexation by dissolved organic matter was investigated for the example of Eu(III)
as an analogue of trivalent actinides. Complexation with different humic materials was
examined in cation exchange experiments, using 59Fe and 152Eu as radioactive tracers for
measurements in dilute systems as encountered in nature. Competitive effects proved to be
significant when Fe is present at micromolar concentrations. Flocculation as a limiting
process was attributed to charge compensation of humic colloids. Fe fractions bound to humic
acids (HA) were higher than 90%, exceeding the capacity of binding sites at high Fe
concentrations. It is thus concluded that the polynuclear structure of hydrolysed Fe(III) is
maintained when bound to HA, which is also inferred from UV-Vis spectrometry. The
competitive effect was found to be enhanced if Fe and HA were contacted before Eu was
added. Depending on the time of Fe/HA pre-equilibration, Eu complexation decreased
asymptotically over a time period of several weeks, the amount of bound Fe being unchanged.
Time-dependent observations of UV-Vis spectra and pH values revealed that the ageing effect
was due to a decline in Fe hydrolysis rather than structural changes within HA molecules. Fe
polycations are slowly degraded in contact with humic colloids, and more binding sites are
occupied as a consequence of dispersion. The extent of degradation as derived from pH shifts
depended on the Fe/HA ratio.
History
School
- Science
Department
- Chemistry
Citation
LIPPOLD, H. ... et al, 2007. Competitive effect of iron(III) on metal complexation by humic substances : characterisation of ageing processes. Chemosphere, 67 (5), pp. 1050-1056Publisher
© ElsevierPublication date
2007Notes
This article was published in the journal, Chemosphere [© Elsevier]. It is also available at: http://www.sciencedirect.com/science/journal/00456535ISSN
0045-6535Language
- en