Th. Univ.--Chimie analytique--Paris 6, 1989. / Résumé en anglais. Bibliogr. p. 261-267.

Thesis (Ph. D. in Chemistry)--University of California, Berkeley, Jan. 1961. / TID-4500 (15th ed.). "UCRL-9296." Includes bibliographical references (leaves 44-45).

No description available.

Thesis--University of California, Berkeley, November 1956. / "Contract no. W-7405-eng-48." Bibliography: leaves 114-121.

No description available.

Thesis--University of California, Berkeley, 1960. / "UC-4 Chemistry General" -t.p. "TID-4500 (15th Ed.)" -t.p. Includes bibliographical references (p. 141-149).

The aim of the work described in this thesis was to develop a more extensive knowledge of the chemistry of neptunium compounds by making rare, air- and moisture sensitive, low formal oxidation state neptunium compounds with full structural and synthetic characterization. The thesis contains three results chapters. Chapter one introduces neptunium chemistry as a background to the results presented. The first review on the molecular non-aqueous neptunium chemistry is provided and the literature reports to date discussed in the context of this. Chapter two describes exploratory synthetic and structural investigations of the organoneptunium complexes supported by the cyclopentadienyl anion, Cp = (C5H5)-, and the (trimethylsilyl)cyclopentadienyl anion, Cp' = (C5H4[Si(CH3)3])-. The syntheses of [Np(Cp)3]n and Np(Cp')3 complexes are detailed and the effect of the trimethylsilyl group of the ligand on the structure and reactivity have been investigated. Complexes were characterized by single crystal X-ray diffractometry, NMR and ATR(IR) spectroscopy. Both organoneptunium complexes were studied in reactions designed to expand the neptunium redox envelope. Notably, the complex Np(Cp')3 is reduced by KC8 in the presence of 2.2.2-cryptand to afford a product assigned as neptunium(II) complex, K(2.2.2-cryptand)[Np(Cp')3] that is thermally very unstable above approx. -10 ºC, in direct analogy to previously reported uranium, thorium and lanthanide complexes of the general formula, K(2.2.2-cryptand)[M(Cp')3]. The reaction between Np(Cp)3Cl and KCp in THF afforded the unanticipated K[NpIII(Cp)4] product as a result of a single-electron reduction presumably arising from Np–C σ-bond homolysis reactivity. This behaviour appears to be unique amongst the actinides for the An(IV)/An(III) redox couple. Chapter three focuses on oxo-bridged homo and heterometallic complexes. The reaction of NpCp3 with dioxygen afforded not only the simple oxide, (μ-O)[An(Cp)3]2, but also a small quantity of the unexpected new trinuclear oxo- neptunium(IV) compound [{(Cp3Np)(μ-O)}2{Np(Cp)2}], which interestingly contains the rare C2v-symetric [An(Cp)2]2+ structural moiety. This oxo-bridged environment is not paralleled in uranium chemistry. The two isostructural oxides, (μ-O)[An(Cp)3]2 (An = U, Np), allow a comparative study of the magnetic exchange phenomena between the two actinide centres demonstrating an exceedingly strong antiferromagnetic coupling, which is largely independent of the communicated Kramers NpIV (5f3, 4I9/2) or non-Kramers UIV (5f2, 3H4) ions. To design heterobimetallic systems, the uranyl(VI) complexes, [(UVIO2)(THF)(H2L)], supported by the calix[4]pyrrole Schiff base macrocycles, H4LOct and H4LEt, were singly-reduced to uranyl(V) with either of the actinide complexes Np(Cp)3 or U(Cp)3, affording isostructural [(Cp3)AnIVOUVO(THF)(H2L)]. Preliminary investigations of the magnetism of the AnIV-O-UV are reported, although their analysis gave counterintuitive results. Chapter four explores the redox chemistry and molecular and electronic structure of neptunium(III) complexes of the doubly deprotonated trans-calix[2]benzene[2]pyrrole, H2(LAr), macrocycle which has a unique π-bonding potential and conformational flexibility. Interestingly, the reactions with neptunium(IV) chloride yielded mono- and dinuclear neptunium(III) complexes, [(LAr)NpCl] and [(LAr)Np2Cl4(THF)3], with a subsequent elimination of the ligand radical; both complexes adopted η6:κ1:η6:κ1 bis(arene) sandwiched structural motif. In a direct analogy to the redox behaviour occurring in the salt metathesis between Np(Cp)3Cl and KCp, the spontaneous reduction derives from the favourable Np(IV)/Np(III) redox system. The reduction of complex [(LAr)NpCl] with NaK3 in DME produces near-black solutions consistent with [NpII(LAr)(DME)] that in the absence of excess NaK3 gradually convert to the metallated (LAr-H)3- neptunium(III) complex, [K(DME)(LAr-H)NpIII(OMe)]2, featuring the actinide centre bound with a ‘metallocene-type’ geometry provided by the two η5-bound pyrrolides of the ligand. The neptunium(III) compounds were characterized in the solid state by single crystal X-ray diffractometry, ATR(IR) spectroscopy and in a solution by NMR and UV-Vis-NIR spectroscopy.

Thesis (Ph. D. in Chemistry)--University of California, Berkeley, Jan. 1959. / Also issued as UCRL 8439. Includes bibliographical references (leaves 72-76).

Subsurface contamination is common at nuclear sites and it is likely that radioactive wastes will be managed in the long-term via burial in a deep Geological Disposal Facility (GDF). The migration of radionuclides in the geosphere from such sites is a major societal concern. In particular, long-lived, redox-active radionuclides (in the case of this thesis: 99Tc and Np) can migrate over large distances due to their high solubility under oxic conditions. Bioremediation has been proposed as a mechanism to limit the migration of 99Tc and Np in the environment. Here, an electron donor is supplied to the subsurface and soluble Tc(VII) and Np(V) are reduced to poorly soluble Tc(IV) and Np(IV), respectively. Reduction occurs via direct microbial action (termed bioreduction) or through radionuclide reaction with the by-products of microbial metabolism (primarily Fe(II)). Given the ubiquity of microorganisms and Fe in the geosphere, similar reactions can be expected in the deep subsurface surrounding a GDF. Once reduced, the long-term stability of the Tc(IV) and Np(IV) phases will significantly impact migration rates. Oxidative dissolution of Tc(IV)- and Np(IV)-bearing solids has been demonstrated in the literature and can be pervasive, thus questioning the efficacy of bioreduction. However, these studies have been conducted over short time-scales and during a single period of oxidation. Given the long half-life of 99Tc and Np and the ephemeral nature of redox conditions in the subsurface, there is a need to better understand 99Tc and Np biogeochemistry during longer time-scales and across multiple redox cycles. In this thesis, microcosm experiments have been used to address this knowledge gap. Sediment and groundwater used in the microcosms were representative of the Sellafield Ltd. nuclear site. For Tc, three successive redox cycles (reduction followed by oxidation with O2) over 2 years, gradually reduced the extent of Tc remobilisation during oxidation, and molecular scale characterisation of solids revealed that sediment associated Tc was always present as Tc(IV). Further, over time sequential extractions and EXAFS revealed an increased significance of Tc-Fe bonding in the sediment at the expense of TcO2. Despite this, a small but significant fraction of Tc(IV) was also found to be stable in solution during the experiments and XAS and TEM analysis suggested this was Tc(IV) associated with magnetite colloids. In other experiments completed with higher concentrations of bioavailable Fe (added as ferrihydrite to sediments, and in pure culture experiments with Geobacter sulfurreducens), the significance of Tc-Fe bonding was again highlighted, and potential Tc(IV) incorporation into biogenic magnetite was also documented. In experiments with Np, virtually all of the Np(V) added to oxic groundwater was removed to the sediment commensurate with microbially mediated Fe(III) reduction. Further, in systems with elevated bioavailable Fe, Np removal from solution was more extensive. Taken together, the data for Tc and Np reveals critical links between redox-active radionuclides and Fe cycling in sediments over periods of years and across multiple redox cycles. Furthermore, these processes help to predict the long-term fate of radioactive contamination at the Sellafield Ltd. nuclear site and have implications for contaminated land worldwide.

In many countries the current plan for the management of intermediate and high level radioactive wastes is to dispose of the radioactive materials underground in a Geological Disposal Facility (GDF) to prevent release of radioactivity to the environment. In the UK, the repository for intermediate level waste may be backfilled with cementitious material and it is clear that grout and cement will be used during many disposal concepts. Upon saturation, the cement will react creating a region of hyperalkaline geochemical conditions extending away from the GDF, within which, significant changes in radionuclide behaviour are expected. Therefore, this thesis utilises a range of experimental and analytical techniques to try to gain a mechanistic understanding of the behaviour of some key radionuclides (U(VI), Np(V) and Eu(III) as an analogue for Cm(III)/Am(III)) in a range of high pH systems of direct relevance to any cementitious GDF. U(VI) interaction with calcite (calcium carbonate, a common component in high pH cements and the natural environment) surfaces was studied in the 'old' (Ca(OH)2 solution; pH 10.5) and 'young' (Na+, K+, Ca2+; pH 13.3) leachates. In the 'old' leachate, luminescence spectroscopy, batch experiments and kinetic modelling suggested that at low concentrations (smaller or equal to 0.42 µM) a Ca2UO2(CO3)3-like surface complex formed. At higher concentrations, batch experiments, extended X-ray absorption fine structure spectroscopy and luminescence suggested that a surface mediated precipitation mechanism was controlling U(VI) concentrations. Further TEM analysis confirmed that a calcium uranate (CaUO4) solid phase was forming on the calcite surfaces. In the 'young' leachate, batch experiments showed that U(VI) had little affinity for the calcite surface, with no statistically relevant removal from solution observed over a 18 month period. Small angle X-ray diffraction data demonstrated that the U(VI) was probably present in the form of U(VI) intrinsic colloids. Np(V) solubility and sorption to calcite under hyperalkaline conditions were studied using batch, X-ray absorption spectroscopy, and geochemical modelling techniques. It was determined that Np(V) solubility in 'old' cement leachates was consistent with the literature. However, in 'young' cement leachates, an unidentified calcium containing phase was controlling solubility. It was demonstrated that sorption to calcite in 'old' leachates was controlled by the formation of a >CO3NpO2 surface complex, whereas, in the 'young' leachates interaction with the calcite surface was controlled by a precipitation mechanism. Eu(III) sorption to a potential GDF backfill material, Nirex Reference Vault Backfill (NRVB) cement, was studied. The kinetics of removal were rapid with 98.5% Eu(III) removal within 24 hours. Ultrafiltration experiments indicated that all Eu(III) remaining in solution was associated with NRVB derived colloids. Additional experiments using ethylenediaminetetraacetic acid (EDTA) as a competing ligand show that removal from solution was significantly reduced at high concentrations (>0.01 M). These EDTA experiments also indicated some irreversibility in the systems, possibly caused by incorporation into the C-S-H or calcite structures.