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CESIUM SORPTION TO ILLITE AS AFFECTED BY OXALATE

¹ Department of Crop and Soil Sciences and Center for Multiphase Environmental Research, P.O. Box 646420, Washington State University, Pullman, WA 99164-6420, USA
² Idaho National Engineering and Environmental Laboratory, P.O. Box 1625, Idaho Falls, ID 83415, USA

^* E-mail address of corresponding author: lawendling{at}wsu.edu

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. ‘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.

Key Words: Frayed-edge Sites • Phytoremediation • Rhizosphere • Weathering