Effect of dissolved soil organic matter on cesium adsorption by zeolite and illite.

In controlled landfill sites, soil layers are installed around radioactive waste to prevent the leaching of radioactive cesium (Cs). The Cs retention capacity of soil has been reported to be enhanced by mixing clay minerals. However, several studies have indicated that dissolved soil organic matter (DSOM) inhibits the Cs sorption by clay minerals. Therefore, this study assesses the effect of DSOM on the Cs sorption by zeolite and illite. Excitation emission matrix fluorescence spectroscopy was used for DSOM in the soil solution before and after contact with clay minerals. The results show that DSOM sorption onto clay minerals, particularly fulvic acid, inhibited Cs sorption. Batch sorption tests were conducted to obtain the sorption isotherms using two sample solutions, namely, soil and ionic solutions. Soil solution, which contained DSOM, was prepared by mixing soil and ultrapure water and filtration using a 0.3-μm glass fiver filter. Ionic solution was prepared by removing DSOM larger than 500 Da from the soil solution using dialysis. The amount of sorbed Cs in the soil solution was lower than that in the ionic solution. Comparing the Freundlich coefficients (K) between the soil and ionic solutions, we found that the K values of zeolite and illite for the ionic solution accounted for 6.4- and 4.4-fold higher than that for the soil solution, respectively.