Actinide Chemistry Research Articles

Room-temperature ionic liquids: new solvents for f-element separations and associated solution chemistry

Ionic liquids (ILs) are composed of organic cations and either organic or inorganic anions that remain liquid over a wide temperature range, including room temperature. IL characteristics can be dramatically adjusted (e.g., hydrophobic vs. hydrophilic) by changing the anion type, or subtly altered by changing the length or number of alkyl groups appended to the cation. Changing alkyl chain lengths in the 1-alkyl-3-methylimidazolium cation, in combination with PF6− or N(SO2CF3)2− anions, produces hydrophobic ILs with rheological properties suitable for their use in liquid/liquid separations. Actinides exhibit significant partitioning to these ILs from aqueous solutions with the addition of an extractant (e.g., octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide) to the IL. Ionic liquids can, thus, be considered for actinide chemistry as a new class of materials with adjustable solvent characteristics, unique properties, and the potential for enhancing the principles of “green” chemistry in various chemical processes. Here we highlight the unique physical properties of some ILs and their use in liquid/liquid separations.

Actinide Materials Research Supported by the Office of Basic Energy Sciences, U.S. Department of Energy

ABSTRACTThe fundamental research topic in actinide chemistry and materials sciences is the role that the 5f electrons play in bond formation, which provides the central focus for DOE BES-supported actinide science. Structural systematics of the actinide metals, oxides, and other compounds as a function of atomic number are well established. Magnetic measurements have shown that the light actinide metals have delocalized 5f orbitals (i.e., the 5f electrons form bands), whereas the f electrons become localized at americium. Thus, the magnetic behavior of the first part of the actinide series resembles that of the d transition metals whereas the heavier actinides exhibit behavior similar to the rare earth metals. Spectroscopic results have established electronic energy levels, crystal field splitting, and near-neighbor coordination. The 5f orbitals participate in the band structure of materials that contain the light actinide metals and some of their intermetallic compounds, and perhaps in molecular compounds. Molecular-level information on the geometry and bonding in solids, at surfaces, and in clusters can now be obtained at BES-supported facilities.

Electrochemical techniques in analytical, preparatory and industrial chemistry of actinides

A new electrochemical technique for studying and performing redox reactions of uranium and transuranium elements as well as for their determination in flow-through conditions is described. The technique is based on the application of flow through electrolyzer with space porous working electrode made from carbon fiber material. The following aspects of the application of the electrochemical techniques were investigated and discussed: derivative coulography for analytical purposes and for determination of parameters of electrochemical processes, coulometric determination of U and Pu in nitric acid solutions in flow through conditions, electrochemical stabilization of oxidation states of U, Np and Pu in flow through conditions both in water solutions and in extraction chromatography separating systems, chemically modified column electrode and electrodeposition of insoluble compounds. The techniques are applicable in industrial scales as well

Progress towards Understanding the Interactions between Hydroxamic Acids and Actinide Ions

BNFL has undertaken a wide-ranging research programme to investigate the fundamental properties of hydroxamic acids and, in particular, their reactions with actinide ions. Most work has focussed on simple hydroxamic acids (R = H and CH3) although some comparative data with more complex molecules including di-hydroxamates have been obtained. Properties of hydroxamic acids studied to date include, hydrolysis in nitric acid, decomposition to gases, pKa's and redox potentials. The redox and co-ordination chemistry of actinides by hydroxamic acids has been investigated using a range of techniques and stability constants for both 4f and 5f hydroxamate complexes have been determined. In conjunction with these fundamental studies, more applied work has been carried out to assess the applications of simple hydroxamic acids under process conditions. A large database of solvent extraction distribution data has been accumulated and, from this, extraction algorithms describing how hydroxamic acids modify actinide extraction in to TBP have been derived. Also the effects of hydroxamic acids on U and Np mass transfer have been studied in single stage centrifugal contactors and this has been modeled theoretically. The third stage of our development work so far has looked at the actual design and testing of novel hydroxamic acid based flowsheets which selectively strip Np(IV) and Pu(IV) from a uranium loaded TBP stream.

Recent developments in computational actinide chemistry.

This review describes recent computational investigations into the electronic and geometric structures of molecular actinide compounds. Following brief introductions to (i) the effects of relativity in chemistry and (ii) ab initio and density functional quantum chemical methods, four areas of contemporary research are discussed. These are pi backbonding in uranium complexes, the geometric structures of bis benzene actinide compounds, the valence electronic structure of the uranyl ion, and the inverse trans influence in pseudo-octahedral [AnOX5]n-. Comparisons are made with experimental studies, and similarities and differences between d- and f-block chemistry are highlighted.

Gas-phase chemistry of bare and oxo-ligated protactinium ions: a contribution to a systematic understanding of actinide chemistry.

Gas-phase chemistry of bare and oxo-ligated protactinium ions has been studied for the first time. Comparisons were made with thorium, uranium, and neptunium ion chemistry to further the systematic understanding of 5f elements. The rates of oxidation of Pa(+) and PaO(+) by ethylene oxide compared with those of the homologous uranium ions indicate that the first and second bond dissociation energies, BDE[Pa(+)-O] and BDE[OPa(+)-O], are approximately 800 kJ mol(-1). The relatively facile fluorination of Pa(+) to PaF(4)(+) by SF(6) is consistent with the high stability of the pentavalent oxidation state of Pa. Reactions with ethene, propene, 1-butene, and iso-butene revealed that Pa(+) is a very reactive metal ion. In analogy with U(+) chemistry, ethene was trimerized by Pa(+) to give PaC(6)H(6)(+). Reactions of Pa(+) with larger alkenes resulted in secondary and tertiary products not observed for U(+) or Np(+). The bare protactinium ion is significantly more reactive with organic substrates than are heavier actinide ions. The greatest difference between Pa and heavier actinide congeners was the exceptional dehydrogenation activity of PaO(+) with alkenes; UO(+) and NpO(+) were comparatively inert. The striking reactivity of PaO(+) is attributed to the distinctive electronic structure at the metal center in this oxide, which is considered to reflect the greater availability of the 5f electrons for participation in bonding, either directly or by promotion/hybridization with higher-energy valence orbitals.

Third-order Douglas–Kroll ab initio model potential for actinide elements

A relativistic ab initio model potential (AIMP) method with the third-order Douglas–Kroll (DK3) approximation has been developed for the whole series of the actinide elements from Th to Lr. Two different cores, i.e., [Xe, 4f,5d] and [Xe, 4f], have been employed and the corresponding valence basis sets, (14s10p11d9f)/[6s5p5d4f] and (14s10p12d9f)/[6s5p6d4f], are presented for all actinides. The mean absolute errors of the AIMP relative to the all-electron results for the atomic SCF valence orbital energies (ε) and the radial expectation values (〈r〉) are 0.003 (0.001) hartree and 0.004 (0.006) bohr with the small (large) core set. The spectroscopic properties of the Σ+1 ground state of thorium monoxide, ThO, are calculated at the SCF and complete active space SCF levels. The DK3-AIMP results again satisfactorily reproduce the all-electron DK3 results. The large core set gives almost the same results as the small set for atomic and molecular calculations, suggesting that the 5d electrons can safely be omitted from the valence electrons in actinide chemistry.

8th Int. Conf. on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere (MIGRATION '01)

8th Int. Conf. on the Chemistry and Migration Behavior of Actinides and Fission Products in the Geosphere (MIGRATION '01)

Aquatic chemistry and solubility phenomena of actinide oxides/hydroxides

Abstract The present paper gives an overview of the solubility behavior of actinide oxides/hydroxides, taking into account hydrolysis reactions up to colloid formation. The analogies, systematic trends, and differences in the hydrolysis and solubility constants of actinides in the oxidation states An(III) to An(VI) correlate with the charge and size of the actinide ions. The formation of amorphous and crystalline solids and the discrepancies between the corresponding experimental solubility data may be explained as an effect of particle size. However, using thermodynamic data for the stable crystalline solids, the predicted solubilities are often significantly lower than experimental data (even in long-time experiments), indicating that the solubility is controlled by the surface properties. Typical examples are the known U(VI) solids schoepite and sodium diuranate. The most striking example is provided by the tetravalent actinides. Above the threshold of hydrolysis, the dissolution of microcrystalline or crystalline An(IV) oxides is found to be irreversible. The measured concentrations approach those of the amorphous hydroxides or hydrous oxides.

Hexaphyrin(1.0.1.0.0.0): An Expanded Porphyrin Ligand for the Actinide Cations Uranyl (UO22+) and Neptunyl (NpO2+)

Applications of actinide chemistry, whether for energy or defense purposes, have left a legacy of potential waste hazards. The new expanded porphyrin ligand 1 forms stable complexes with both uranyl (UO22+) and neptunyl (NpO2+) ions and presents a potential new avenue for waste remediation.

Hexaphyrin(1.0.1.0.0.0): An Expanded Porphyrin Ligand for the Actinide Cations Uranyl (UO22+ ) and Neptunyl (NpO2+ ).

Applications of actinide chemistry, whether for energy or defense purposes, have left a legacy of potential waste hazards. The new expanded porphyrin ligand 1 forms stable complexes with both uranyl (UO22+ ) and neptunyl (NpO2+ ) ions and presents a potential new avenue for waste remediation.

Lead substitution and elimination study

Because of the inherent risks of hazardous materials, every opportunityto eliminate or substitute them should be considered. Within the Nuclear MaterialTechnology Division, lead is used as shielding for a variety of operations,which include actinide chemistry, radiochemistry, and analytical chemistry.Lessons learned from recent exposures to lead demonstrate the urgency of replacinglead as a shielding media. In this study, available substitutes and coatingsare identified, and cost comparisons for each technology are discussed.

Radiochemistry in India

A major expansion in the experimental programme of Atomic Energy occurred with the establishment of Atomic Energy Establishment at Trombay (AEET). Along with the setting up of the India's first reactor APSARA, a prototype radiochemistry laboratory was set up at the Trombay site. This laboratory was to serve as a training ground for a team of chemists, chemical engineers and metallurgists in the handling of high radioactive substances. This prototype laboratory having an active area of 375 m 2 . and associated service area was fully commissioned and was operational by 1958. In view of high technology involved in the design and operation of a Class A radioactive laboratory, Dr. H. Bhabha sought the support of United Kingdom Atomic Energy Authority (UKAEA). This laboratory at south site of Trombay complex had two radioactive wings equipped with six fume hoods in each wing. In addition, there were a large number of β, γ boxes and glove boxes. There was a well equipped counting room with facilities for α and β counting and γ spectrometry with a 100 channel analyser. The experience gained during this period became useful in planning the future facilities such as plutonium laboratory at Fuel Reprocessing Plant, the Radiological Laboratories at Trombay, BARC, and similar laboratories at IGCAR. Initially, radiochemistry research programme was based on the availability of APSARA reactor for nuclear and radiation chemistry studies and plutonium, protactinium, and actinium obtained from UKAEA for research in actinide chemistry. Dr. M.V. Ramaniah who had taken over as Head, Radiochemistry Division in 1965 was the driving force for the completion and commissioning of radiological laboratories at Trombay around 1969. The chemistry wing of the new complex has 14 laboratories of size 7 × 10m, three low active laboratories of size 6 × 10m, a modern counting room equipped with state-of-the-art instruments, and an alpha tight hot cell with master slave manipulators. Each laboratory room was provided with a large number of fume hoods and glove boxes, conditioned fresh air supply with 10−12 air changes/hr, well managed liquid effluent system connecting all the laboratories and state-of-the-art health and safety devices for continuous monitoring of radioactivity. The alpha tight hot cell was commissioned for synthesis of transplutonium elements as well as burn up studies. The laboratory is equipped with a variety of modern instrumentation such as mass spectrometer, ESR spectrometer, modern spectrophotometer, thermal analyser, XRD system, and α and γ spectrometer. The area of research and development were also broadened with the availability of variable energy cyclotron at Calcutta and medium energy heavy ion accelerator Pelletron at TIFR, Mumbai. The area of research activities which are actively being carried out are (1) Nuclear chemistry, (2) Actinide and process chemistry, (3) Studies on solid state chemistry and spectroscopy of actinide and analytical spectroscopy, and (4) Training and services. This paper highlights some of the important achievements in the first two areas in brief.

The bioinorganic chemistry of actinides in blood

The behaviour of actinides (An) in mammalian blood is controlled largely by their strong tendency to hydrolyze and form complexes at physiological pH (∼7.0). Except for U(VI) and Th(IV), with 70–90% associated with blood cells, the plasma is the predominant transport medium for An in blood. Numerous studies have demonstrated that, in human and animal blood plasma, Pu(IV), Th(IV), Pa(V), U(VI), and Np(V) appear to bind strongly to the iron-transport protein transferrin (Tf), although the binding characteristics may vary from element to element. The trivalent An, Ac(III), Am(III), Cm(III) and Cf(III), apparently bind to Tf, but also to other proteins, and the association with transferrin appears to be much weaker than that of the other actinides.

Capture of Pu(V), Np(V) and Pu(VI) from alkaline solutions by hydroxides of Pu(IV), Th(IV) and La(III)

In systematic studies of actinide chemistry in alkaline solution, it was found that Pu(IV) hydrous oxide can remove significant amounts of plutonium present in higher oxidation states from solution. By spectrophotometry it was found that the capture of Pu(VI) by Pu(IV) hydrous oxide is negligible whereas Pu(V) and Np(V) are highly adsorbed. Quantitative characterization of the process was investigated by a radiometric method based on 239Np-labeled neptunium. The influence of temperature, alkali concentration, and the Pu/Np molar ratio on the extent of capture of Np(V) by PuO 2 xH 2O was investigated.

Chemistry of actinide and lanthanide metal ions (M+) in laser ablation of dispersions of inorganic compounds in polyimide and polytetrafluoroethylene

The positive ions produced during excimer laser ablation of a polyimide (PI) or polytetrafluoroethylene (PTFE) matrix containing a small concentration of a solid compound comprising an actinide (Th, U) and/or lanthanide (La, Ce, Pr, Eu, Tb, Ho, Tm, Yb, Lu) were determined by time-of-flight mass spectrometry. The polyatomic mass spectra were dominated by species of the general form, M+–L, where M+ is the actinide/lanthanide and L is some fragment ligand from the polymer. For PI, primary products were M+–CcHh with c=2 or 4 and h=0 or 1. For PTFE, the main products were generally Mf+ with f=1 or 2. Although the studied metals are largely similar in their condensed phase chemistries, rational differences were evident in the compositions of the ablation products, which often corresponded to molecules identified in high-temperature vaporization of inorganic solids. For the M+–CcHh species, the degree of hydrogenation, i.e., h=0 or 1, consistently reflected the relative thermodynamic stabilities of the binary carbide molecules, MC2, which in turn closely correlate with those of the gaseous MO. Thus, U and Ce form especially robust monoxide and dicarbide molecules and, accordingly, produced primarily the bare dicarbide, MC2+. In contrast, the monoxides and dicarbides of Eu and Tm are relatively weakly bound and their PI ablation products incorporated hydrogen to produce more substantial yields of MC2H+. The compositions of the highly ionic metal fluorides produced from PTFE ablation reflected the relative stabilities of successive metal-ion oxidation states. For example, the yield of the difluoride ion, MF2+(≈M3+F2−), relative to that of the monofluoride, MF+(≈M2+F−), was found to decrease in the order, CeF2+>HoF2+>TmF2+, which is the inverse of the ordering of the +2 to +3 ionization energies: Ce<Ho<Tm. The observation of coherent thermochemical effects in metal-ion chemistry in ablation plumes suggests quasiequilibrium high-temperature conditions. Chemical speciation in laser ablation of metal–polymer aggregates is central to the formation of novel metal-doped polymer materials by pulsed laser deposition, and may be utilized to enhance elemental specificity in direct laser ablation sampling for mass spectrometric analysis. The described techniques are, furthermore, applicable to microscale investigation of the fundamental chemistry of scarce and radioactive transuranic actinides.

High-Level Nuclear Waste Management: How Physics Can Help

ABSTRACTThe potential value of Partitioning/Transmutation (P/T) strategies for high-level nuclear waste management has been investigated (one would be tempted so say “periodically”) since 1970. The basic physics phenomena are well understood, and scenarios for the fuel cycle can be imagined. However, the criteria to judge the impact of P/T are matter for discussion (and controversy). Moreover the relation to disciplines other than reactor physics can be significant (e.g. innovative fuels and Actinide chemistry).A number of key issues are revisited here and will be discussed in some detail.

ERNESTO GIESBRECHT, GREAT CHEMICAL EDUCATOR AND FATHER OF BRAZILIAN INORGANIC CHEMISTRY

Ernesto Giesbrecht, Brazil s foremost inorganic chemist, and chemical educator was born in Ponta Grossa, Parana, Brazil in 1921 and passed away in Sao Paulo in 1996. He obtained the Bachelor Degree in Chemistry from the University of Sao Paulo in 1943 and was awarded a Doctor of Science Degree by the same institution in 1947. He worked at the University of Sao Paulo most of his life and published over one hundred and fifty scientific papers dealing with alkaloids, compounds of sulfur, selenium, and tellurium, chemical education, and the chemistry of Lanthanides and actinides. He trained approximately thirty research scientists in inorganic chemistry, which eventually spread chemical education and inorganic chemistry throughout Brazi I. Prof. Ernesto Giesbrecht was a great chemical educator and may be considered the father of Brazilian Inorganic Chemistry.

A Convenient Entry into Trivalent Actinide Chemistry: Synthesis and Characterization of AnI3(THF)4 and An[N(SiMe3)2]3 (An = U, Np, Pu)

The reaction of excess, oxide-free amalgamated uranium metal turnings with elemental iodine or bromine in coordinating solvents at 0{degree}C provides dark purple UI{sub 3}(THF){sub 4}(1), royal blue UBr{sub 3}(THF){sub 4} (2), purple UI{sub 3}(dme){sub 2} (3), or jet black UI{sub 3}(py){sub 4} (4) in 65-80% isolated yield (THF = tetrahydofuran, dme = 1,2-dimethoxyethane, py = pyridine). Neptunium and plutonium metal also react cleanly with elemental iodine in aprotic coordinating solvents to give yellow-orange NpI{sub 3}(THF){sub 4} (5), off-white PuI{sub 3}(THF){sub 4} (6), and gray PuI{sub 3}(py){sub 4} (7) in 80-90% isolated yields. These organic-solvent-soluble Lewis base adducts of early actinide trihalides are precursors to a variety of inorganic and organometallic actinide complexes. Reaction of AnI{sub 3}(THF){sub 4} complexes (U, Np, Pu) 1, 5, and 6 in THF solution with 3 equiv of sodium bis(trimethylsilyl)amide provides the volatile, solvent-free tris(silylamide) complexes An[N(SiMe{sub 3}){sub 2}]{sub 3} [An = U (8), Np (9), Pu (10)] in 80-90% yields. The neptunium and plutonium silylamides are the first examples of homoleptic amido complexes of the transuranic elements. Compounds 1-10 have been fully characterized by variable-temperature proton NMR, IR, UV/vis/near-IR, thermal gravimetric, and elemental analyses. Single-crystal X-ray diffraction data for 1 revealed a pentagonal bipyramidal coordinationmore » geometry about the central uranium atom with two axial iodide ligands (U-I = 3.111(2) {Angstrom} (average)) and one equatorial iodide ligand (U-I = 3.167(2) {Angstrom}). All four THF ligands lie in the equatorial plane with an average U-O distance of 2.52(1) {Angstrom}. Crystal data for 1 (at 23{degree}C): monoclinic space group P2{sub 1}/c, with a = 8.750(3) {Angstrom}, b = 16.706(16) {Angstrom}, c = 17.697(7) {Angstrom}, {beta} = 93.64(3){sup o}, V = 2582 {Angstrom}{sup 3}, d{sub calc} = 2.33 g cm{sup {minus}3}, Z = 4.« less

Lanthanide and actinide chemistry at high CO/ ratios in the solar nebula

Chemical equilibrium calculations were performed to study the condensation chemistry of the REE and actinides under the highly reducing conditions which are necessary for the formation of the enstatite chondrites [1,2]. Our calculations confirm that the REE and actinides condensed into oldhamite (CaS), the major REE and actinide host phase in enstatite chondrites, at a carbon-oxygen ( CO/) ratio ⩾ 1 in an otherwise solar gas. Five basic types of REE abundance patterns, several of which are analogous to REE abundance patterns observed in the Ca, Al-rich inclusions (CAIs) in carbonaceous chondrites, are predicted to occur in meteoritic oldhamites. All of the reported REE patterns in oldhamites in enstatite chondrites can be interpreted in terms of our condensation calculations. The observed patterns fall into 3 of the 5 predicted categories. The reported Th and U enrichments and ratios in meteoritic oldhamites are also consistent with predictions of the condensation calculations. Finally, pure REE sulfides are predicted to condense in the 10 -6 to 10 -9 bar range and may be found in enstatite chondrites if they formed in this pressure range.