Investigation of humic acid complexation behavior with uranyl ions using modified synthetic and natural humic acids

We investigated the influence of phenolic OH groups on the complexation beh avior of humic acid (HA) with UO22+ ions at pH 4. Starting from synthetic H A type M1, natural HA Aldrich, and natural HA Kranichsee, we synthesized mo dified HAs with blocked phenolic OH groups by derivatization with diazometh ane. The partial blocking of phenolic OH groups was confirmed by a radiomet ric method which quantitatively determined the functional groups and by FTI R spectroscopy. The complexation behavior of the chemically modified and un modified HAs with UO22+ ions was investigated by time-resolved laser-induce d fluorescence spectroscopy. The experimental data were evaluated with the metal ion charge neutralization model. We determined comparable complexatio n constants for all HAs. Two modified HAs (type M1 and Aldrich) had signifi cantly lower loading capacities for UO22+ ions (10.5 +/- 0.9% and 9.7 +/- 1 .6%, respectively) than the corresponding unmodified HAs (18.0 +/- 2.0% and 17.5 +/- 1.6%, respectively). This indicates that the blocking of the phen olic OH groups changes the complexation behavior of HAs.