Sorption of Eu(III) on GMZ bentonite in the absence/presence of humic acid studied by batch and XAFS techniques

Bentonite has been extensively studied because of its strong sorption ability and low permeability. In this work, the Na-bentonite from Gaomiaozi County (China) has been characterized by XRD, FTIR and acid-base titration. The sorption of Eu(III) on Na-bentonite in the absence/presence of humic acid (HA) was studied at T = 25 +/- 2 degrees C and in 0.01 mol/L NaClO(4) solution. The effects of pH, HA, contact time and initial Eu(III) concentrations were also investigated. The results indicate that the sorption of Eu(III) on Na-bentonite was dependent on pH values. The presence of HA had little effect on Eu(III) sorption at low pH values, but decreased Eu(III) sorption at high pH values. X-ray absorption fine structure spectroscopy (XAFS) was applied to characterize the local structural environment of the adsorbed Eu(III) on bare Na-bentonite and HA-bentonite hybrids. The results indicate that Eu(III) was bound to O atoms at a distance of about 2.39 angstrom at pH 4.15. The results are crucial for the evaluation of the sorption and migration of other trivalent lanthanides and actinides in bentonite as backfill materials.