Rodney D. Hunt

Room Temperature Ionic Liquids for Separating Organics from Produced Water

Abstract The distribution of polar organic compounds typical of water contaminants (organic acids, alcohols, and aromatic compounds) associated with oil and gas production was measured between water and nine hydrophobic, room‐temperature ionic liquids. The ionic liquids used in this study were 1‐butyl‐3‐methylimidazolium bistrifluoromethanesulfonylimide, 1‐hexyl‐3‐methylimidazolium bistrifluoromethanesulfonylimide, 1‐octyl‐3‐methylimidazolium bistrifluoromethanesulfonylimide, 1‐butyl‐3‐methylimidazolium hexafluorophosphate, trihexyltetradecylphosphonium bistrifluoromethanesulfonylimide, 1‐butyl‐1‐methyl‐pyrrolidinium bistrifluoromethanesulfonylimide, trihexyltetradecylphosphonium dodecylbenzenesulfonate, tributyltetradecylphosphonium dodecylbenzenesulfonate, and trihexyltetradecylphosphonium methanesulfonate. Sensitivity of the distribution coefficients to salinity, temperature, concentration, and pH was investigated. Partitioning into the ionic liquid varied considerably. Acetic acid did not significantly partition into the ionic liquid phase, except for the sulfonate‐anion ionic liquids. The solubility of hexanoic acid in the ionic liquids was significant, where uptake of the protonated form from aqueous solution was observed for all of the ionic liquids studied. Other organics also showed high distribution coefficients, up to several hundred in the case of toluene and 1‐nonanol. The distribution coefficients for toluene, 1‐nonanol, cyclohexanone, and hexanoic acid were independent of ionic liquid‐to‐water ratio over the range from 0.02 to 1.0. The ionic liquids showed a large capacity for some organics, with solubilities measured above 100 g·L−1. Regeneration of the ionic liquids by rinsing and heating was studied, with mixed success. These experiments show that certain hydrophobic ionic liquids do have an affinity for organic contaminants in aqueous solution. However, practical application of the ionic liquids tested for detection or removal of selected water‐soluble organics from the aqueous waste streams appears to be limited by the small, but significant, solubility of the ionic liquids in the aqueous phase and by difficulty in solvent regeneration. Further work aimed at determination of ionic liquids that dissolve target compounds and are nonhazardous and less soluble in aqueous solutions is recommended.

Wet-chemical synthesis of monodispersed barium titanate particles : hydrothermal conversion of TiO2 microspheres to nanocrystalline BaTiO3

Abstract A low-temperature hydrothermal reaction scheme has been developed to produce pure, ultrafine, uniform-sized, nanocrystalline barium titanate (BaTiO 3 ) microspheres from two inorganic precursors: synthesized titania microspheres and barium hydroxide solutions. The size and morphology of titania (TiO 2 ) microspheres were controlled using isopropanol to fine-tune the dielectric constant of the isopropanol–water mixed solvent system. Monodispersed titania microspheres approximately 0.1–1 μm in diameter were successfully synthesized for the further conversion to barium titanate. Barium titanate and titania microspheres were characterized by scanning electron microscopy (SEM) and room-temperature X-ray diffraction (RTXRD). High-temperature XRD (HTXRD) was also utilized for in situ study of the phase transformations and changes of crystallite size with calcination temperatures. The titania microspheres were predominant in the anatase (plus some brookite) phase at room temperature and were converted to the rutile phase when the calcination temperature was increased from 650°C to 900°C. Monodispersed barium titanate microspheres were successfully synthesized from optimized titania via a hydrothermal reaction (≤100°C) in barium hydroxide solutions. The size and morphology of the barium titanate particles remained the same as the precursor titania particles, indicating a “shrinking-core” diffusion–reaction mechanism. Barium carbonate in the form of witherite was also found along with the formation of barium titanate, especially under conditions with higher Ba/Ti ratios, but a formic acid washing procedure effectively removed this impurity phase from the barium titanate samples. The as-prepared barium titanate was in the cubic nanocrystalline form and did not change when the temperature was increased from room temperature to as high as 750°C. The cubic phase was also stable at high temperatures for over 5 h.

Reactions of pulsed‐laser evaporated uranium atoms with molecular oxygen: Infrared spectra of UO, UO2, UO3, UO2+, UO22+, and UO3–O2 in solid argon

Uranium atoms from the Nd:YAG laser ablation of a uranium target were codeposited with molecular oxygen and excess argon at 12 K. Infrared spectra following the U+O2 reaction revealed a wide range of reaction products. The 776.0 cm−1 band due to UO2 was the strongest product absorption, strong UO3 bands were observed at 852.5 and 745.5 cm−1, and a weak UO absorption appeared at 819.8 cm−1. These product absorptions are in agreement with earlier work, which evaporated UO2 from a tungsten Knudsen cell at 2000 °C. The 16O2/18O2 reaction gave only U 16O2 and U 18O2, which verified an insertion mechanism. New product absorptions were observed at 952.3, 892.3, and 842.4 cm−1. The 842.4 cm−1 absorption due to the UO3–O2 complex and the 892.3 cm−1 band assigned to the charge‐transfer complex (UO2+)(O2−) grew markedly at the expense of the other uranium oxides during annealing the matrix to allow diffusion and reaction of O2. With 25% 16O2, 50% 16O18O, and 25% 18O2 samples, the 952.3 cm−1 band became a sharp tripl...

Matrix infrared spectra of NUN formed by the insertion of uranium atoms into molecular nitrogen

Pulsed‐laser ablated uranium atoms were codeposited with 14N2(15N2) and excess Ar at 12 K. The Fourier transform infrared (FTIR) spectrum revealed a single product, UN2, which exhibited a ν3 absorption at 1051.0 cm−1. Ultraviolet (UV) photolysis increased the yield of UN2 by threefold and showed that electronic excitation facilitated the insertion reaction. N2 perturbed UN2 bands at 1041.3 and 1031.5 cm−1 grew sharply during matrix annealings. In 14N15N experiments the ν1 and ν3 modes of 14NU15N were observed at 987.2 and 1040.7 cm−1, respectively; FG matrix calculations were performed to determine Fr=8.27 mdyn/A and Frr=0.12 mdyn/A and to estimate the IR‐inactive ν1 modes of U14N2 and U15N2 at 1008.3 and 985.7 cm−1, respectively. Energetic considerations suggest that the U+N2 insertion reaction has little exothermicity and that the activation energy for this reaction may be provided by hypothermal uranium atoms.

Separation of Ionic Liquid Dispersions in Centrifugal Solvent Extraction Contactors

Abstract Separations of dispersions formed by mixing immiscible organic room‐temperature ionic liquids (IL)/hydrocarbon/and aqueous systems using a centrifugal solvent‐extraction contactor have been successfully demonstrated in proof‐of‐concept testing. This accomplishment is significant in that physical property factors that are typical of ionic liquid systems (e.g., similar densities of the bulk phases, low interfacial tensions, and high viscosities) are typically unfavorable for dispersion separation, particularly in continuous processes. Efficient separation of dispersions containing ionic liquid solvents is essential for utilization of these compounds in liquid‐liquid extraction applications to maximize both solute transfer efficiency and solvent recovery. Efficient solvent recovery is of particular concern in IL applications because of the high cost of most IL solvents. This paper presents the results of initial experiments with three hydrophobic ionic liquids to determine how their physical properties affect phase mixing and phase disengagement in contact with an aqueous solution using a centrifugal contactor. While the results of the reported work are promising, additional work is needed to optimize existing mathematical models of contactor hydraulics to address special considerations involved in IL‐based processes and to optimize the equipment itself for IL applications.

Uranium kernel formation via internal gelation

Summary In the 1970s and 1980s, U.S. Department of Energy (DOE) conducted numerous studies on the fabrication of nuclear fuel particles using the internal gelation process. These amorphous kernels were prone to flaking or breaking when gases tried to escape from the kernels during calcination and sintering. These earlier kernels would not meet today´s proposed specifications for reactor fuel. In the interim, the internal gelation process has been used to create hydrous metal oxide microspheres for the treatment of nuclear waste. With the renewed interest in advanced nuclear fuel by the DOE, the lessons learned from the nuclear waste studies were recently applied to the fabrication of uranium kernels, which will become tri-isotropic (TRISO) fuel particles. These process improvements included equipment modifications, small changes to the feed formulations, and a new temperature profile for the calcination and sintering. The modifications to the laboratory-scale equipment and its operation as well as small changes to the feed composition increased the product yield from 60% to 80%–99%. The new kernels were substantially less glassy, and no evidence of flaking was found. Finally, key process parameters were identified, and their effects on the uranium microspheres and kernels are discussed.

Preparation of spherical, dense uranium fuel kernels with carbon

The internal gelation process and a suitable broth formulation with an uranium concentration of 1.3 M was used to produce air-dried uranium trioxide dihydrate (UO3·2H2O) and carbon microspheres with crush strengths greater than 600 g per microsphere. The addition of carbon lowered the slow-pour densities of the air-dried microspheres by a minimum of 9% if all other conditions were held constant. The crush strengths of the air-dried microspheres with and without carbon remained very good. These microspheres were not prone to leach when they were washed with ammonium hydroxide, and they did not have the tendency to crack during subsequent heat treatments. For the UO3·2H2O microspheres with and without carbon, dehydration occurred at the same rate. The dehydration was accompanied by spontaneous reduction of the urania to UO2.67. In the same temperature range, hydrogen and carbon can be used to further reduce the urania to uranium dioxide. Therefore, the loss of carbon during calcination appears to be unavoidable. The current recommendation on calcinations is to use a temperature of 600 °C or higher to minimize the loss of carbon. Dense and strong uranium fuel kernels with carbon were produced in argon at 1680 °C.

CAUSTIC LEACHING OF HIGH-LEVEL RADIOACTIVE TANK SLUDGE: A CRITICAL LITERATURE REVIEW

ABSTRACT The Department of Energy (DOE) must treat and safely dispose of its radioactive tank contents, which can be separated into high-level waste (HLW) and low-level waste (LLW) fractions. Since the unit costs of treatment and disposal are much higher for HLW than for LLW, technologies to reduce the amount of HLW are being developed. A key process currently being studied to reduce the volume of HLW sludges is called enhanced sludge washing (ESW). This process removes, by water washes, soluble constituents such as sodium salts, and the washed sludge is then leached with 2–3 M NaOH at 60–100°C to remove nonradioactive metals such as aluminum. The remaining solids are considered to be HLW while the solutions are LLW after radionuclides such as 137Cs have been removed. Results of bench-scale tests have shown that the ESW will probably remove the required amounts of inert constituents. While both experimental and theoretical results have shown that leaching efficiency increases as the time and temperature o...

Monosodium Titanate in Hydrous Titanium Oxide Spheres for the Removal of Strontium and Key Actinides from Salt Solutions at the Savannah River Site

Abstract Fine powders of monosodium titanate effectively remove strontium and plutonium from alkaline salt supernatant. At the Savannah River Site, larger, porous particles with monosodium titanate were desired for continuous column operations. The internal gelation process was used to make hydrous titanium oxide microspheres with 32 and 50 wt% monosodium titanate. With actual supernatant, the microspheres with 50 wt% monosodium titanate produced average batch distribution coefficients of 35,000 mL/g for plutonium and 99,000 mL/g for strontium. These microspheres were tested using a simulant and a flow rate of 5.3 bed volumes per hour. The plutonium removal dropped from 99% to 94% while the strontium removal remained nearly 100%. The microspheres exhibited good flow performance and no particle degradation.

Synthesis of phase-pure U2N3 microspheres and its decomposition into UN

Uranium mononitride (UN) is important as a nuclear fuel. Fabrication of UN in its microspherical form also has its own merits since the advent of the concept of accident-tolerant fuel, where UN is being considered as a potential fuel in the form of TRISO particles. However, not many processes have been well established to synthesize kernels of UN. Therefore, a process for synthesis of microspherical UN with a minimum amount of carbon is discussed herein. First, a series of single-phased microspheres of uranium sesquinitride (U2N3) were synthesized by nitridation of UO2+C microspheres at a few different temperatures. Resulting microspheres were of low-density U2N3 and decomposed into low-density UN. The variation of density of the synthesized sesquinitrides as a function of its chemical composition indicated the presence of extra (interstitial) nitrogen atoms corresponding to its hyperstoichiometry, which is normally indicated as α-U2N3. Average grain sizes of both U2N3 and UN varied in a range of 1-2.5 μm. These also had a considerably large amount of pore spacing, indicating the potential sinterability of UN toward its use as a nuclear fuel.