Effects of Calcium Ions on the Sorption of Am(III) and Eu(III) onto Kaolinite in the Presence of Humic Acid

Abstract

The sorption of actinides onto minerals depending on groundwater chemistry plays an important role in the safety aspects of geological disposal of high-level waste. The effects of Ca(II) on the sorption of Am(III) and Eu(III) onto kaolinite in the presence of humic acid (HA) were examined in this study. Distribution coefficients (Kd) of Am(III) and Eu(III), and the fractional adsorption (fHA) of HA on kaolinite were determined by a batch method under initial Ca(II) concentrations of 0 to 1.0 × 10-3 M at a constant ionic strength of 0.1 M (NaClO4) and pH region from 3.5 to 10 in an N2 atmosphere at 298 K. The Kd increased with increasing Ca(II) concentrations in regions higher than 1.0 X10-4 M and in the range of pH 7 to 10. In this pH region, fHA was also enhanced by introducing Ca(II). Concentrations higher than 1.0 × 10-4 M Ca(II) can be regarded as a bridge between kaolinite and HA. It is very likely that the increase in the adsorbed HA on kaolinite, where the HA includes very stable Am(III) and Eu(M) humates, results in an increase in the Am(III) and Eu(IH) distribution coefficients.