| Abstract: |
Understanding plutonium geochemical behavior is imperative to the development of schemes for remediation of plutonium environmental contamination and accurate assessment of risks posed by the disposal of plutonium bearing wastes. The primary mechanism of plutonium mobility in the environment is subsurface transport. The mobility of plutonium is significantly influenced by redox and complexation reactions. Although the effects of surface mediated redox reactions on plutonium’s subsurface mobility have been previously documented, little has been done to determine the impact of organic materials on sorption behavior and oxidation states. To adequately predict the behavior of plutonium in the environment, the influence of natural organic matter on plutonium geochemical behavior must be understood.
This work primarily investigates the sorption of plutonium to gibbsite in the presence of organic material with the goal of accurately modeling the sorption behavior over the pH range 3-9. Sorption of plutonium to gibbsite in the presence of Suwannee River Fulvic Acid Standard I, desferrioxamine B (DFOB), citric acid, and Leonardite humic acid was examined to determine the influence of organic ligand character on plutonium sorption. These organic materials are ubiquitous in the environment, and their presence generally drives plutonium to the tetravalent oxidation state in surface and ground waters. Batch sorption experiments involving ternary systems containing plutonium, gibbsite, and one of the studied organic materials at a concentration of 5 or 50 mg C/L have revealed a definite impact of the organic materials when compared with the binary system containing only plutonium and gibbsite. In the binary system, greater than 90% of the plutonium sorbed to the gibbsite. However, the addition of organic ligands altered the sorption behavior, dependent on the pH of the system. Using a surface complexation model, aqueous stability constants, and assuming the formation of ternary surface complexes, the results of the batch sorption experiments were modeled. The data and models achieved in this study will allow for more adequate predictions of the movement of plutonium in the environment when incorporated into geochemical models. |
