Abstract

Identification and characterization of the surface interactions of environmental contaminants is important for predicting their speciation and mobility. Presence of naturally occurring macro-molecular organic complexant, such as humic acid, which interacts strongly with the metallic contaminants as well as various mineral surfaces, complicates the delineation of these interactions and the responsible surface species. X-Ray Absorption Fine Structure Spectroscopy (XAFS), being an element specific probe, has been extensively used for the local structure characterization of the surface species. However, strong dependence of backscattering amplitude on the atomic number of the backscatters causes problem in identifying overlapping interactions. Herein, XAFS analysis was assisted by wavelet transform of XAFS data to identify the ternary interactions in the alumina-humic acid-Eu(III) sorption system. Under the varying addition order of HA and Eu(III) to the alumina suspension at pH ~6, both the two ternary sorption systems indicated the existence of two ternary species, one having HA and the other Eu as the bridging component. The ternary sorption system in which HA was first equilibrated with alumina before Eu, showed higher formation of HA bridged species and vice versa. Application of wavelet transform to identify interactions and using this information for XAFS analysis is thus a potent technique for environmental studies.

Keywords:Europium; Sorption; Alumina; Humic acid; XAFS Wavelet-transform