J. Phys. IV France 104 (2003) 421
Soft X-ray spectro-microscopy investigation of the formation and ageing of Eu(III)-induced humic acid aggregatesJ. Rothe, M. Plaschke and M.A. Denecke
Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung, P.O. Box 3640, 76021 Karlsruhe, Germany
Aggregation of Aldrich humic acid at pH 4.3 and after loading with Eu(III)-cations at pH 5.3 is investigated by scanning transmission X-ray microscopy (STXM). C 1s-NEXAFS spectra extracted from STXM image stacks for the low pH aggregates show no significant variation, whereas Eu(III)-humate formation is observed to be accompanied by segregation into zones with different optical densities. These zones exhibit distinctly different NEXAFS features, indicative of the presence of a separation of organic species or components. Increasing humate aggregate densification over a period of several months is observed. The spectrum of the unloaded HA cannot be reproduced by a superposition of spectra extracted from the segregated humate zones; there is a distinct metal bonding effect on the molecular states of the functional groups involved in complexation.
© EDP Sciences 2003