Separations chemistry for f elements: Recent developments and historical perspective

With the end of the cold war, the principal mission in actinide separations has changed from production of plutonium to cleanup of the immense volume of moderately radioactive mixed wastes which resulted from fifty years of processing activities. In order to approach the cleanup task from a proper perspective, it is necessary to understand the nature of the problem and how the wastes were generated. In this report, the history of actinide separations, both the basic science and production aspects, is examined. Many of the separations techniques in use today were developed in the 40`s and 50`s for the identification and production of actinide elements. To respond to the modern world of actinide separations new techniques are being developed for separations ranging from analytical methods to detect ultra-trace concentrations (for bioassay and environmental monitoring) to large scale waste treatment procedures. Some of these new methods are ``improvements`` or adaptations of the historical techniques. Total actinide recovery, lanthanide/actinide separations, and selective partitioning of actinides from inert constituents are of primary concern. This report, offers a historical perspective, review the current status of f element separation processes, and suggest areas for continued research in both actinide separations and waste cleanup/environment remediation

Variation of Stability Constants of Thorium Citrate Complexes with Ionic Strength

Citrate is among the organic anions which are expected to be present in the wastes planned for deposition in the WIPP repository. In this study, a solvent extraction method has been used to measure the stability constants of Th(IV) with citrate anions in aqueous solutions with (a) NaClO4 and (b) NaCI as the back-ground electrolytes. The ionic strengths were varied up to 5 m (NaCl) and 14 m (NaClO4). The data from the NaClO4 solutions at varying pH values were used to calculate thermodynamic stability constants through the use of Specific Ion Interaction Theory (SIT)

Research in Actinide Chemistry. Final Report, March 1, 1993--February 28, 1996

The present three-year grant period has been a fruitful one for the laboratory as research entered some new areas while continuing in others in which the group has been successful. As in past grant periods, the principal focus has been on complexation of actinide elements with inorganic and organic ligands. The ligands to study have been chosen for their value (known or potential) in actinide separations or for their potential role in environmental behavior of the actinides. Since the radioactivity of some actinides limits the variety of techniques which can be used in their study, we have used {open_quotes}oxidation state analogs{close_quotes}. These analogs have the same oxidation state and very similar chemical behavior but are stable or very long-lived. Also, the analogs are chosen for their redox stability to avoid uncertainties in interpretation of systems in which several oxidations may coexist (e.g., in the case of Pu). Examples of such analogs which we have used are: Nd(III), Eu(III) for Pu(III), Am(III), Cm(III); Th(IV) for U(IV), Pu(IV); NpO{sub 2}{sup +} for PuO{sub 2}{sup +}; UO{sub 2}{sup 2+} for NpO{sub 2}{sup 2+}, PuO{sub 2}{sup 2+}. These analogs have allowed use of techniques which can increase significantly our understanding of actinide complexation

Research in Actinide Chemistry

This research studies the behavior of the actinide elements in aqueous solution. The high radioactivity of the transuranium actinides limits the concentrations which can be studied and, consequently, limits the experimental techniques. However, oxidation state analogs (trivalent lanthanides, tetravalent thorium, and hexavalent uranium) do not suffer from these limitations. Behavior of actinides in the environment are a major USDOE concern, whether in connection with long-term releases from a repository, releases from stored defense wastes or accidental releases in reprocessing, etc. Principal goal of our research was expand the thermodynamic data base on complexation of actinides by natural ligands (e.g., OH[sup [minus]], CO[sub 3][sup 2[minus]], PO[sub 4][sup 3[minus]], humates). The research undertakes fundamental studies of actinide complexes which can increase understanding of the environmental behavior of these elements

Research in Actinide Chemistry. Progress Report, March 1, 1980-February 28, 1981

Visible spectroscopy, NMR (/sup 1/H/sub 1/, /sup 6/C/sub 13/, /sup 57/La/sub 139/) spectroscopy, potentiometry, and calorimetry were used in lanthanide studies which have allowed much more thorough interpretation of actinide tracer studies. In the last several years, the studies were expanded to include actinides in the IV, V and VI oxidation states. Part of the research during this time was directed to investigation of actinide interaction with naturally occurring polyelectrolytes such as humic and fulvic acids. Since redox reactions seemingly occur in some of these interactions, a study of plutonium and neptunium redox behavior in the presence of organic complexing agents was started. Preliminary data are given for reduction of Np(VI) by various organic acids