Influence of temperature on sorption of europium onto smectite: The role of organic contaminants

In the near field environment of a spent fuel or vitrified high level waste repository the temperature in the bentonite buffer will remain elevated for a long time period (> 70–90 °C for 1000 years). To analyze the effect of temperature on the sorption, the sorption process of Eu(III) at 25°, 60° and 80 °C was investigated. To examine the sorption process and the influence of organic contaminants, wet chemistry, time-resolved laser fluorescence spectroscopy (TRLFS), XRD and soft X-ray spectromicroscopy (STXM) measurements were performed. the experimental time no changes in smectite mineralogy between 25° and 60 °C was observed. At 80 °C with increasing time an increase in the layer charge of the smectite was noticed. The formation of secondary phases was not observed in the experiments. In quartz cuvettes we observed no macroscopic or spectroscopic differences for the Eu(III) sorption from 25° to 80 °C. At low pH values (< 5.5) the formation of outer-sphere complexes was observed at the temperatures studied independent of the reaction vessel. In the sorption experiments at higher pH values (> 5.5) we noticed differences between the different reaction vessels at 60° and 80 °C. Whereas in quartz cuvettes we measured inner-sphere complexation at all temperatures, the experiments in the high density polyethylene (HDPE) reaction vessels indicated the incorporation of Eu(III) at 60° and 80 °C. It became evident that organic material released out of the HDPE reaction vessels was able to complex Eu(III).