Understanding Partition Coefficient, Kd, Values, Appendix D

APPENDIX D Partition Coefficients For CesiumAppendix D Partition Coefficients For Cesium D.1.0 Background Three generalized, simplifying assumptions were established for the selection of cesium Kd values for the look-up table. These assumptions were based on the findings of the literature reviewed we conducted on the geochemical processes affecting cesium sorption. The assumptions are as follows: C Cesium adsorption occurs entirely by cation exchange, except when mica-like minerals are present. Cation exchange capacity (CEC), a parameter that is frequently not measured, can be estimated by an empirical relationship with clay content and pH. C Cesium adsorption onto mica-like minerals occurs much more readily than desorption. Thus, K values, which are essentially always derived from adsorption studies, will dgreatly overestimate the degree to which cesium will desorb from these surfaces. C Cesium concentrations in groundwater plumes are low enough, less than approximately -710 M, such that cesium adsorption follows a linear isotherm. These assumptions appear to be reasonable for a wide range of environmental conditions. However, these simplifying assumptions are clearly compromised in systems with cesium -7concentrations greater than approximately 10 M , ionic strengths greater than about 0.1 M, and pH values greater than about 10.5. These assumptions will be discussed in more detail in the following sections. Based on the assumptions and ...