Understanding Partition Coefficient, Kd, Values, Appendix G

APPENDIX G Partition Coefficients For PlutoniumAppendix G Partition Coefficients For Plutonium G.1.0 Background A number of studies have focussed on the adsorption behavior of plutonium on minerals, soils, and other geological materials. A review data from diverse literature sources indicated that Kd values for plutonium typically range over 4 orders of magnitude (Thibault et al., 1990). Also, from these data a number of factors which influence the adsorption behavior of plutonium have been identified. These factors and their effects on plutonium adsorption on soils and sediments were used as the basis for generating a look-up table. These factors are: C Typically, in many experiments, the oxidation state of plutonium in solution was not determined or controlled therefore it would be inappropriate to compare the K data dobtained from different investigations. C In natural systems with organic carbon concentrations exceeding ~10 mg/kg, plutonium exists mainly in trivalent and tetravalent redox states. If initial plutonium concentrations -7exceed ~10 M, the measured K values would reflect mainly precipitation reactions and dnot adsorption reactions. C Adsorption data show that the presence of ligands influence plutonium adsorption onto soils. Increasing concentrations of ligands decrease plutonium adsorption. C If no complexing ligands are present plutonium adsorption increases with increasing pH (between 5.5 and 9.0). C Plutonium is known to ...