David E. Hobart

13C NMR characterization of actinyl(VI) carbonate complexes in aqueous solution

Abstract The ligand exchange reaction between free and coordinated carbonate on 242 Pu VI O 2 ( 13 CO 3 ) 3 4− and 243 Am VI O 2 ( 13 CO 3 ) 3 4− systems was examined by variable temperature 13C pulsed nuclear magnetic resonance (NMR) techniques. A modified Carr-Purcell-Meiboom-Gill NMR pulse sequence was used for the experimental determination of ligand exchange parameters for paramagnetic actinide complexes. Eyring analysis provided activation parameters of ΔG 295 ‡ = 53 kJ M −1 , ΔH ‡ = 35 kJ M −1 and ΔS 295 ‡ = −61 J M −1 K −1 for the plutonyl triscarbonate system, suggesting an associative transition state for the plutonyl(VI) carbonate self-exchange reaction.

Chemical and physical processes of radionuclide migration at Yucca Mountain, Nevada

The understanding and prediction of radionuclide migration within the geosphere of a high-level radioactive waste repository requires knowledge of chemical and physical processes. In this paper, we present an overview of the investigations being performed at Los Alamos National Laboratory for the site characterization activites of the Yucca Mountain Project. The areas of investigation include: the determination of solubility concentration limits and chemical speciation for fission products and actinides; the collection of sorption data and understanding of sorption mechanisms; and the transport mechanism of advection, diffusion, and dispersion.

The Role of Siderophores in the Transport of Radionuclides

Iron exists in aerobic soil and water environments most commonly as insoluble Fe(III). Siderophores are powerful, microbially produced chelating agents that are used to mobilize the insoluble Fe(III) cation. Over 80 siderophores have been isolated and characterized, with some reportedly having iron-binding constants as high as 10{sup 52}. Fe(III) and Pu(IV) are similar in their charge/ionic radius ratio (4.6 and 4.2, respectively); therefore, Pu(IV) may serve as analog to Fe(III). It is possible that some radioactive wastes could be chelated by naturally occurring siderophores, thereby altering the transport rates of those elements through the subsurface environment. This investigation was initiated to investigate that possibility. The binding of {sup 239}(IV) by four chelating agents is reported in this paper: a siderophore isolated and purified from a Pseudomonas sp.; desferal, a ferrioxamine siderophore commonly used for deferration therapy; EDTA, ethylenediaminetetraacetic acid; and, citrate, trisodium salt.