Pamela L. Gordon

Synthesis and energetic content of red oil

Abstract ‘Red oil’ materials, resembling those produced during destructive incidents at Hanford and Savannah River, have been prepared following prolonged heating of uranyl nitrate, nitric acid, tributylphosphate (TBP) and a hydrocarbon diluent either under reflux conditions or within a high-pressure bomb reactor. Phase inversions, a characteristic feature of ‘red oil’ formation, were observed only when a cyclic hydrocarbon diluent was employed and were not observed when a straight chain hydrocarbon was used. The energetic content of the ‘red oil’ materials was found to be in the range from 30 to 444 J g −1 (7.2–106.1 cal g −1 ) as determined by DSC in open pans in the temperature range 20–350°C, with a typical value being 200 J g −1 (47.8 cal g −1 ). A ‘baseline’ Purex solution of UO 2 (NO 3 ) 2 (TBP) 2 released 120 J g −1 (28.7 cal g −1 ) upon heating through the same temperature range.

Chemical Speciation of Neptunium(VI) under Strongly Alkaline Conditions. Structure, Composition, and Oxo Ligand Exchange

Hexavalent neptunium can be solubilized in 0.5-3.5 M aqueous MOH (M = Li(+), Na(+), NMe4(+) = TMA(+)) solutions. Single crystals were obtained from cooling of a dilute solution of Co(NH3)6Cl3 and NpO2(2+) in 3.5 M [N(Me)4]OH to 5 °C. A single-crystal X-ray diffraction study revealed the molecular formula of [Co(NH3)6]2[NpO2(OH)4]3·H2O, isostructural with the uranium analogue. The asymmetric unit contains three distinct NpO2(OH)4(2-) ions, each with pseudooctahedral coordination geometry with trans-oxo ligands. The average Np═O and Np-OH distances were determined to be 1.80(1) and 2.24(1) Å, respectively. EXAFS data and fits at the Np L(III)-edge on solid [Co(NH3)6]2[NpO2(OH)4]3·H2O and aqueous solutions of NpO2(2+) in 2.5 and 3.5 M (TMA)OH revealed bond lengths nearly identical with those determined by X-ray diffraction but with an increase in the number of equatorial ligands with increasing (TMA)OH concentration. Raman spectra of single crystals of [Co(NH3)6]2[NpO2(OH)4]3·H2O reveal a ν1(O═Np═O) symmetric stretch at 741 cm(-1). Raman spectra of NpO2(2+) recorded in a 0.6-2.2 M LiOH solution reveal a single ν1 frequency of 769 cm(-1). Facile exchange of the neptunyl oxo ligands with the water solvent was also observed with Raman spectroscopy performed with (16)O- and (18)O-enriched water solvent. The combination of EXAFS and Raman data suggests that NpO2(OH)4(2-) is the dominant solution species under the conditions of study and that a small amount of a second species, NpO2(OH)5(3-), may also be present at higher alkalinity. Crystal data for [Co(NH3)6]2[NpO2(OH)4]3·H2O: monoclinic, space group C2/c, a = 17.344(4) Å, b = 12.177(3) Å, c = 15.273 Å, β = 120.17(2)°, Z = 4, R1 = 0.0359, wR2 = 0.0729.

A Model for Trivalent Actinides in Media Containing High Carbonate Concentrations − Structural Characterization of the Lanthanide Tetracarbonate [Co(NH3)6][Na(μ-H2O)(H2O)4]2[Ho(CO3)4]·4H2O

The identity of the limiting HoIII species in aqueous solutions with high carbonate concentrations has been determined to be Ho(CO3)45−. Single crystals of [Co(NH3)6][Na(μ−H2O)(H2O)4]2[Ho(CO3)4]·4H2O were obtained by the addition of [Co(NH3)6]3+ to an aqueous 0.04 M solution of HoIII in 2.1 M Na2CO3. The asymmetric unit contains the anion, [Ho(CO3)4]5−, a [Co(NH3)6]3+ cation and two Na+ cations, which are bound to H2O molecules in an edge-sharing bioctahedral geometry. The [Ho(CO3)4]5− anion is eight coordinate with four bidentate carbonate ligands bound to the Ho atom. The molecule has essentially C2v symmetry with two coplanar carbonates making a vane, which is perpendicular to a similar vane produced by the other two carbonate ligands. An alternative way to this view molecule is through the geometry of the C atoms, which are found in a distorted tetrahedron. The average Ho−O distance was determined to be 2.361(5) A, while the average Ho−C distance was 2.784(6) A. The IR and Raman spectra were determined in both the solid state and solution in order to confirm the solution speciation. The Raman data show a single CO32− stretch for the solid at 1062 cm−1. The solution data show multiple peaks with the most prominent being at 1048 cm−1, which is consistent with the literature reports of an equilibrium mixture. The IR data for the solids confirm the X-ray results showing bidentate carbonate ligands by the splitting of the ν3 band of the CO32−. The crystal data for [Co(NH3)6][Na(μ-H2O)(H2O)4]2[Ho(CO3)4]·4H2O are as follows: monoclinic space group P2/n, a = 8.7091(5) A, b = 10.8744(6) A, c = 15.7971(9) A, β = 93.117(1)°, Z = 2, R1 = 0.0307, wR2 = 0.0756.

Investigation of red oil decomposition by simulated Hanford tank wastes

Abstract Samples of ‘red oil’ have been placed in contact with simulated Hanford tank wastes, and Differential Scanning Calorimetry used to compare energetic content both before and after exposure to these waste simulants. Of the 85 samples studied, 44 samples had their energy content reduced by 90% or more following contact with waste simulant, while 77 of the 85 samples showed at least a 50% fall in energy content. All 85 samples showed at least some reduction in energetic content. The duration of contact between red oil and waste simulant was generally a few hours or days, and the overwhelming majority of the data suggest that contact times of several years, as would be typical in Hanford waste tanks, would further reduce the energy content of red oil to negligible quantities.

First single-crystal X-ray diffraction study of a lanthanide tricarbonate complex: [Co(NH3)6][Sm(CO3)3(H2O)]·4H2O

The first single-crystal X-ray diffraction study of a lanthanide tricarbonate complex, namely [Co(NH3)6][Sm(CO3)3(H2O)]·4H2O, is reported and reveals a zigzag chain structure of 9-coordinate samarium metal centers bridged by μ-η2∶η1 carbonate ligands.

Identification of oligomeric uranyl complexes under highly alkaline conditions

By utilizing X-ray absorption methods, e.g., extended x-ray absorption fine structure (EXAFS) and single crystal x-ray diffraction (XRD), as well as Raman, UV-Vis and fluorescence spectroscopy, we have shown that an equilibrium exists between the monomeric uranyl hydroxide species UO2(OH)42− and UO2(OH)53−, which is dependent upon hydroxide concentration. Upon further study of this system, we have now determined that a new hydrolysis product is present in equilibrium with the monomeric uranyl hydroxide species, which is favored at higher UO22+ concentrations.