Retention of Eu(III) in muscovite environment: Batch and spectroscopic studies

Abstract

Retention of trace Eu(III) in the medium enriched with muscovite was investigated under aerobic conditions combining batch experiments and spectroscopic techniques including time resolved laser-induced fluorescence spectroscopy (TRLFS), extended X-ray absorption fine structure (EXAFS), and X-ray photoelectron spectroscopy (XPS). The underlying retention mechanisms were explored by identifying the coordination structures of adsorbed Eu(III) on muscovite. Batch experiments showed that the sorption of Eu(III) on muscovite was strongly dependent on pH and ionic strength. TRLFS showed that the H2O/OH− molecules in the first coordination shell of adsorbed Eu(III) reduced over pH ∼7.0, indicating that inner-sphere complexation was the dominant mechanism for Eu(III) sorption on muscovite. In the presence of inorganic ligands, Eu(III) retention was enhanced by phosphate while suppressed by sulfate, and TRLFS showed that the enhanced Eu(III) retention in the presence of phosphate was mainly attributed to the formation of ternary surface complex. EXAFS and XPS results further confirmed that the P-bridge type ternary surface complex was the main sorption species in the observed system. The proposed Eu(III) retention mechanism in present work can provide an important experimental reference for predicting the migration behaviors of Ln/An(III) in mica-rich terrains at a molecular scale.