Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Uranium represents the most abundant radionuclide in nuclear waste and its behavior is a major concern for geological waste disposal. The speciation of Uranium in solution affects its mobility in porous media and must in consequence be well understood. The dissolved organic matter (DOM) present in pore waters of geological formations can change the speciation and the geochemical behavior of uranium [1]. DOM present in the potential host rock formation Boom Clay in Belgium differs in size (from hundreds to thousands of Da), solubility at different pH (humic and fulvic acids) and functionality. Due to DOM polydispersity and polyfunctionality, its interaction with U(VI) could involve various mechanism which need to be studied in details. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is a well-known technique used to characterize U(VI) speciation and complex formation with inorganic and organic ligands. This method was already successfully applied to derive complex stability constants of U(VI) and humic acids [2]. The objective of the present work is to perform a systematic and multi-parametric study on the U(VI) complexation with BC DOM fractions using TRLFS.
Two DOM fractions different in molecular size were separated, concentrated and purified from natural Boom Clay organic matter: one “colloidal” (100 kDa – 0.45 µm) and one “small” (< 1 kDa). The separation and concentration were performed using ultrafiltration and solid phase extraction methods. The size distribution and reactivity of final fractions were characterized using size-exclusion chromatography, X-ray photoelectron spectroscopy and potentiometric titrations. Complex formation of U(VI) with different DOM fractions was studied using TRLFS in presence and absence of carbonates in 0.1 M NaClO4 for a pH range 4-12.5.