Cesium Sorption to Illite as Affected by Oxalate

Cesium uptake by plants depends on adsorption\desorption reactions in the soil, as well as root uptake processes controlled by the plant. In this study, sorption and desorption of Cs+ on reference illite (IMt-1) was investigated in the presence of oxalate to gain understanding of mechanisms by which plant root exudates may influence Cs+ bioavailability in micaceous soils. Cesium sorption on illite decreased significantly as oxalate concentration increased from 0.4 to 2 mM. Cesium desorption from illite increased significantly with increasing oxalate concentration. Desorption of Cs+ by exchange with Na+, Ca2+ and Mg2+ was significantly enhanced in the presence of oxalate as selectivity for Cs+ decreased with respect to these ions in the presence of oxalate. On the other hand, oxalate had little effect on the Cs+\K+ selectivity coefficient. This suggests that oxalate treatments increase the relative proportion of exchange sites that are not highly selective for Cs+ and K+; e.g. ʹplanarʹ sites. The results indicate that oxalate plays an important role in Cs+ binding on illite and, therefore, plant rhizosphere chemistry is likely to alter Cs+ bioavailability in micaceous soils.