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

Abstract

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 °C and in 0.01 mol/L NaClO4 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 A 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.