Speciation and transformations of sorbed Pu on geologic materials: wet chemical and spectroscopic observations

摘要

The movement of dissolved plutonium (Pu) in the environment can be retarded by sorption and precipitation processes. The affinity of Pu for natural solid materials can vary greatly according to the properties of the sorbing material and the speciation of the Pu. Examples of natural materials in geologic media that sorb Pu are microbes, organic matter, colloids, clay minerals and Fe and Mn oxides. Wet chemical techniques such as sequential or selective extractions have customarily been used to define the geochemical associations of Pu in environmental systems and to identify the oxidation state of sorbed Pu species. Unfortunately, the investigation of sorption processes has been bound by limitations in analytical techniques and by the complex oxidation-state speciation of Pu. Micro-analytical techniques, such as microprobe synchrotron-based X-ray fluorescence (micro-XRF) mapping and other techniques can be used to detect the spatial distribution of sorbed Pu and other co-associated elements on geologic surfaces. Once identified by micro-XRF mapping, small regions of Pu enrichment may be probed with microprobe X-ray absorption structure spectroscopic techniques to obtain information on the oxidation state speciation, coordination environment and bonding environment of Pu on individual mineral micro-phases on geologic materials. In this presentation, the results and interpretations of wet chemical analyses and spectroscopic studies on the speciation and spatial distribution of sorbed Pu on natural materials will be discussed. Observations from the open literature on Pu sorption behavior on natural surfaces and Pu coprecipitation with minerals will also be presented.