Radiotracer study of the electrophoretic behavior of Eu and its complexes with humic acid

Abstract

The interaction of Eu with purified/protonized Aldrich humic acid (HA) was studied by the free liquid/moving boundary electrophoresis used in combination with the radiotracer method. Introductory experiments were carried out to test electrophoretic behavior of Eu in HA-free solutions, and to determine mobility of Eu3+cation. To get the data for evaluation of parameters describing Eu binding to HA, titrations of HA (10 mg/L) with Eu were performed batchwise in the range 3.4×10-8-1.7-3M of Eu total concentration at pH 3, 4, 5 and 6, and 0.01 M ionic strength (NaClO4). In each batch, the degree of Eu complexation with HA was determined from152Eu electrophoretic mobilities in the cathodic direction. The experimental data were fitted with a discrete site model (Scatchard plot-like model) with two types of carboxylic sites. An additional information on the charge characteristics of the Eu-HA complexes has been obtained from the152Eu anodic mobilities.