Kinetic Studies of the Uranium(VI) and Humic Acid Sorption onto Phyllite, Ferrihydrite and Muscovite


Kinetic Studies of the Uranium(VI) and Humic Acid Sorption onto Phyllite, Ferrihydrite and Muscovite

Schmeide, K.; Brendler, V.; Pompe, S.; Bubner, M.; Heise, K. H.; Bernhard, G.

We studied the kinetics of uranium(VI) and humic acid adsorption by the rock material phyllite and by the minerals ferrihydrite and muscovite at pH 6.5 under aerobic conditions. The sequence in which uranium and humic acid were added to the solid containing solutions was varied in order to obtain more detailed information on the sorption mechanisms. The results showed that sorption of uranium and humic acid onto phyllite and ferrihydrite is rapid, that onto muscovite is slower. The initial uranium sorption rates were found to depend on the sequence of addition of uranium and humic acid. For ferrihydrite the initial uranium sorption rate decreased with increasing amounts of uranyl humate complexes in solution. In contrast, addition of humic acid to muscovite resulted in a faster uranium sorption, since the amount of easily accessible surface sites for uranyl ions is enhanced largely by sorbed humic acid. Phyllite showed an overlapping of different processes which is attributed to the complex nature of the phyllite rock. The total uranium uptake decreased in the following order: ferrihydrite > phyllite > muscovite. The results have shown that the amount of uranium sorbed on minerals in equilibrium is determined by the total number of surface sites as well as their affinity and accessibility to solutes. For ferrihydrite indications to mineral dissolution in the presence of humic acid were found. The results of the kinetic experiments confirm that the sorption behavior of phyllite to uranium and humic acid is dominated by minor amounts of ferrihydrite, that is formed as secondary mineral phase due to weathering of phyllite. The contribution of minerals, naturally present in the rock material phyllite, to the total sorption behavior of phyllite could also be shown.
Furthermore, we compared the sorption behavior of two different humic acids, a natural humic acid Kranichsee HA and a 14C-labeled synthetic humic acid type M1, onto phyllite in the pH range 3.5 to 9.5 by batch experiments. Their influence on uranium(VI) sorption onto phyllite was also studied and compared to uranium sorption in the absence of humic acid. Results revealed that sorption of humic acids and their effect on uranium sorption is influenced by the total content of humic acid functional groups and its fractions that are actually involved in sorption reactions or are available for binding of uranyl ions, together with the molecular size and the amount of aromatic structural elements of humic acids. The results also confirmed that the synthetic humic acid 14C-M1 is suitable for experiments studying the kinetics and reversibility of uranium and humic acid sorption onto minerals in the pH range 3.5 to 7.5 since its sorption behavior and its influence on uranium sorption is comparable to that of natural humic acids.

  • Contribution to external collection
    FZKA 6524, Wissenschaftliche Berichte Forschungszentrum Karlsruhe, (G. Buckau, ed.). Karlsruhe 2000, pp. 149-169.

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Publ.-Id: 3237