John V. Muntean

The nature and fate of natural resins in the geosphere. IX Structure and maturation similarities of soluble and insoluble polylabdanoids isolated from Tertiary Class I resinites.

Abstract Soluble polylabdanoids were isolated from five Tertiary Class I resinites by sequential extraction and were characterized by 13 C and 1 H NMR spectroscopy and Py–GC–MS. The structure and maturation characteristics of soluble extracts were strikingly similar to those observed for polylabdanoids in the native resinite. Soluble and insoluble materials undergo parallel geotransformation processes similar to those observed previously, including (i) exomethylene and total olefinic carbon depletion, (ii) double bond redistribution as indicated by ∑C14/∑C15 pyrolysis product ratios and (iii) A-ring defunctionalization. Resonances at 138 and 127 ppm in 13 C NMR spectra were shown to be those of aromatic and olefinic structures in mature samples, indicating that double bond content had been overestimated in the past. Proton NMR analyses have revealed several structural features previously unobserved. Resonances at 5.3 ppm of mature polymers were assigned to trisubstituted olefins in cyclized/cross-linked polylabdanoids. Further evidence in support of this pathway is derived from 13 C NMR spectra, from which an increase in aliphatic carbon content paralleling the loss of olefinic structures was observed.

The nature and fate of natural resins in the geosphere - VIII - NMR and Py-GC-MS characterization of soluble labdanoid polymers isolated from holocene class I resins.

Soluble polylabdanoids isolated by sequential solvent extraction have been characterized by liquid-state {sup 13}C- and {sup 1}H NMR and {sup 13}C-{sup 1}H HMQC (heteronuclear correlation) NMR spectroscopy in addition to solid-state NMR and Py-GC-MS techniques. Two Holocene resins originating from Santander, Colombia and Mombasa, Kenya were analyzed. Soluble polymers were isolated by extraction with a 1:1 (v/v) methylene chloride-methanol mixture following sequential extractions with methylene chloride and methanol. The molecular weight of polymer extracts was shown by GPC analyses to exceed that of non-polymeric occluded terpenoids. Py-GC-MS, solid-state {sup 13}C CP/MAS and {sup 13}C cross-polarization/depolarization NMR spectroscopy results indicated that chemical compositions of soluble polymers isolated from immature resins are highly representative of the structure of corresponding insoluble polymers, i.e. polylabdatrienes. These data provide evidence for cross-linking or cyclization of side-chain olefinic carbons during or shortly after polymerization. Generally, the characterization of soluble resin polymers by liquid-state NMR spectroscopy has proven to be an excellent means for investigating the maturation mechanism of polylabdanoid resinites, and has potential for furthering the application of Class I resinites as geothermal indicators.

Extraction and Reductive Stripping of Pertechnetate from Spent Nuclear Fuel Waste Streams

An approach directed at rapid sequestration and disposal of technetium-99 from UREX (uranium extraction) liquid waste streams is presented. This stream is generated during reprocessing of light-water-reactor spent fuel to recycle the actinides and separate fission products for waste disposal. U and Tc are co-extracted from a nitric acid solution using tri-n-butylphosphate in dodecane, so that Tc(VII) is present in the strip solution after the actinide separations. The goal is to separate uranyl from the pertechnetate in this U-Tc stream and then sequester Tc in the metallic form. Our approach is based on reductive stripping of pertechnetate either from aqueous solution (for column extractions) or organic solvents (for liquid-liquid extractions). In both of these methods, metallic zinc in the presence of formic acid serves as a reducing agent, and 99Tc is recovered as a co-precipitate of Zn(II) hydroxide and hydrous Tc(IV) oxide, with a Zn:Tc ratio between 1:1 and 2:1 mol/mol. This solid residue can be reduced to a Zn-Tc alloy by high temperature (500–700°C) hydrogenation, and the resulting heterophase alloy can be added to a metallic Fe-Zr-Mo waste form that is processed at 1600°C, with subsequent loss of Zn by evaporation. Alternatively, Zn and Tc can be separated and 99Tc sequestered as NH4TcO4 for further reduction to Tc(0) metal. The aqueous Zn reduction process removes ∼90% of 99Tc per cycle. The nonaqueous Zn reduction in 1:1 methanol – formic acid removes 60–70% of 99Tc per cycle, depending on the extracting agent (such as a tetraalkylammonium nitrate). The extracting agent is recycled in the process. The pertechnetate is extracted from the aqueous phase into 1,2-dichloroethane, which is removed by evaporation and reused. The residue is either calcined and steam reformed to Tc(0) or processed by the nonaqueous Zn reduction method. These methods can be used not only to remove the pertechnetate from the U-Tc product stream, but also to sequester the pertechnetate from aqueous waste streams generated through the processes described in this paper, thereby closing the cycle. The same approaches can be used to close the 99Tc cycle for other methods that are currently being developed at Los Alamos and Argonne National Laboratories.

Ion Transport Mechanisms in Liquid–Liquid Interface

Interfacial liquid-liquid ion transport is of crucial importance to biotechnology and industrial separation processes including nuclear elements and rare earths. A water-in-oil microemulsion is formulated here with density and dimensions amenable to atomistic molecular dynamics simulation, facilitating convergent theoretical and experimental approaches to elucidate interfacial ion transport mechanisms. Lutetium(III) cations are transported from the 5 nm diameter water pools into the surrounding oil using an extractant (a lipophilic ligand). Changes in ion coordination sphere and interactions between the interfacial components are studied using a combination of synchrotron X-ray scattering, spectroscopy, and atomistic molecular dynamics simulations. Contrary to existing hypotheses, our model system shows no evidence of interfacial extractant monolayers, but rather ions are exchanged through water channels that penetrate the surfactant monolayer and connect to the oil-based extractant. Our results highlight the dynamic nature of the oil-water interface and show that lipophilic ion shuttles need not form flat monolayer structures to facilitate ion transport across the liquid-liquid interface.

The vanadium(V)-catalyzed oxidation of (1-hydroxyethylidene)bisphosphonic acid, CH3C(OH)(PO3H2)2, by hydrogen peroxide in aqueous solution

Abstract The vanadium(V)-catalyzed oxidation of (1-hydroxyethylidene)bisphosphonic acid, CH 3 C(OH)(PO 3 H 2 ) 2 , by hydrogen peroxide in aqueous solution has been studied at temperatures between 50 and 80°C. In contrast to vanadium(V), six-valent Mo and W are without significant catalytic action, as is SeO 2 , while OsO 4 is only weakly catalytic. With excess substrate a limiting stoichiometry is reached in which ca. 4 mol H 2 O 2 are consumed per mol of substrate oxidized. With excess H 2 O 2 , the reaction competes with catalytic decomposition of the peroxide, and a substantial excess of peroxide is required to consume the substrate completely. The reaction is optimal near pH 1. At higher pH it becomes slower, while at lower pH the catalytic decomposition of H 2 O 2 comes to predominate. The principal reaction products are phosphoric and acetic acids and carbon dioxide, along with lesser quantities of CO and formic acid. The consumption of substrate in the presence of a large excess of H 2 O 2 follows first-order kinetics, but the apparent first-order rate constant shows a weak positive dependence on initial substrate concentration, which may be pH-related, and at high substrate concentration it shows a weak negative dependence on initial [H 2 O 2 ]. The principal reactant appears to be the diperoxovanadium(V) anion, OV(O 2 ) − 2 , but the apparent rate shows a greater-than-first-order dependence on catalyst concentration, suggesting a secondary reaction path involving a dimeric peroxovanadium species. A free-radical mechanism has been proposed in which one-electron reduction of the vanadium accompanies oxidation of the substrate to an intermediate alkoxyl radical species that can yield either acetic acid or CO 2 . This mechanism is supported by the observation that vanadium(V) itself oxidizes the substrate at a measurable rate.

Actinide Complexes in Hydrometallurgical Separations: Observations on Complexation and Solvation

Though other approaches have positive features and could eventually supplant hydrometallurgical separations, solvent extraction and ion exchange (and related techniques) are technologically the most important methods for actinide processing and analysis, and likely will remain so for the next few decades. From uranium mining to actinide transmutation, increased understanding of the fundamental interactions between actinide cations, chelating agents, oxidizing and reducing agents, and the solvents (aqueous and non-aqueous) that serve as the medium for chemical manipulations is essential if these techniques are to advance in the 21st century. Research continues around the world in this field, principally in those countries actively involved in (or considering) actinide partitioning and recycle. In this presentation, the results of a variety of investigations designed to provide new insights into the nature of actinide interactions with solutes and solvents will be presented. Among the key issues discussed will be aspects of the thermodynamics and kinetics of actinide-ligand interactions, of structural features of actinide complexes in solutions, and of the nature of interactions of free actinide cations and their complexes with solvent molecules. Each of the systems discussed will have some significance in actinide separations science with primary emphasis on solvent extraction and ion exchange. Work performed under the auspices of the US Department of Energy Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences under contract number W-31-109-ENG-38.