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 (lMt-1) was investigated in the presence of oxatate 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. 'planar' 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.