The chemistry of plutonium partitioning to an acidic, sandy sediment

Knowledge of the chemistry controlling the partitioning of actinides to soils and sediments in natural systems is essential for modeling their environmental fate and developing safe and cost-effective strategies for remediation. Plutonium (Pu) is known to cycle between sediments and the water column in warm, monomictic reservoirs. The geochemical processes that influence Pu mobility in such systems remain elusive; however, the mechanisms of sorption and release are controlled by the chemistry of the interaction between Pu and specific components of the sediment.;Sequential extraction methods were used to elucidate Pu partitioning in a sediment matrix. Two sequential extraction methods were employed, and the methods provided similar results. The majority of the Pu was extracted from the bulk sediment by the treatment intended to target oxidizable components such as natural organic matter. Filter pore size was varied to study the effects of colloidal and suspended material. A fraction of the Pu in this sediment is colloidal, and that material is refractory rather than oxidizable. Finally, studies of Pu distributions in various particle size fractions of the sediment indicate isotopic fractionation with larger fractions of 238Pu being associated with smaller particles than 239+240Pu. When the amount of organic matter associated with each size fraction is considered, these studies suggest that the partitioning of 239+240Pu is more influenced by organic matter than the 238Pu.;Based on these results the feasibility of ex-situ remediation technologies such as supercritical fluid extraction (SFE) is considered. Ligand assisted SFE was applied to this sediment, and changes in the partitioning of actinides and other metals was determined. This work suggests that under suitable chemical conditions, SFE can be used to extract many metal cations, including actinides, from the sediment while minimizing the generation of secondary waste streams.