Abstract
Annals of Environmental Science
Volume 2, April 2008, Pages 1-6
www.aes.northeastern.edu, ISSN 1939-2621
The Stability of Uranium(VI) Complexes of Humates and Fulvates in Biphasic Systems
J. Riggle and R. von Wandruszka, Department of Chemistry, University of Idaho, Moscow, Idaho, USA
Received September 25, 2007; in final form March 7, 2008; Accepted April 10, 2008
Slight momentary heating of aqueous solutions containing humic substances (HSs) and uranyl ions (UO22+) yielded humic flocs that carried the bulk of the ion down with them. These biphasic systems were at near-neutral pH, and after returning to ambient temperatures they remained intact and were analyzed by determining the free uranyl concentration in the aqueous phase. Phosphate enhanced UO22+ fluorescence was used for this, allowing the determination of the stability constants of HS-uranyl complexes in the floc. The neutral pH of the systems and the relatively unencumbered nature of the analysis provided a realistic picture of the complex formation in natural environments. The log K values of the complexes were found to lie in the 5-7 range and were independent of the total acid content of the humates and fulvates considered. Stability constants obtained for different size fractions of a humic acid were generally smaller than those of the whole material and decreased with molecular size. A comparison of humates and fulvates showed similar trends. The observations suggested that larger HSs polyanions, generally having a greater aliphatic content, provide a cage effect and are able to sequester UO22+ more effectively than smaller size fractions.
Developed by the