Volume 102, Issue 10

The solubility of different forms of precipitated 242 PuO 2 (am) were examined in solutions containing aqueous Fe(II) over a range of pH values. The first series of 242 PuO 2 (am) suspensions were prepared from a 242 Pu(IV) stock that had been treated with thenoyltrifluoroacetone (TTA) to remove the 241 Am originating from the decay of 241 Pu. These 242 PuO 2 (am) suspensions showed much higher solubilities at the same pH value and Fe(II) concentration than previous studies using 239 PuO 2 (am). X-ray absorption fine structure (XAFS) spectroscopy of the precipitates showed a substantially reduced Pu–Pu backscatter over that previously observed in 239 PuO 2 (am) precipitates, indicating that the 242 PuO 2 (am) precipitates purified using TTA lacked the long range order previously found in 239 PuO 2 (am) precipitates. The Pu(IV) stock solution was subsequently repurified using an ion exchange resin and an additional series of 242 PuO 2 (am) precipitates prepared. These suspensions showed higher redox potentials and total aqueous Pu concentrations than the TTA purified stock solution. The higher redox potential and aqueous Pu concentrations were in general agreement with previous studies on 242 PuO 2 (am) precipitates, presumably due to the removal of possible organic compounds originally present in the TTA purified stock. 242 PuO 2 (am) suspensions prepared with both stock solutions showed almost identical solubilities in Fe(II) containing solutions even though the initial aqueous Pu concentrations before the addition of Fe(II) were orders of magnitude different. By examining the solubility of 242 PuO 2 (am) prepared from both stocks in this way we have essentially approached equilibrium from both the undersaturated and oversaturated conditions. The final aqueous Pu concentrations are predictable using a chemical equilibrium model which includes the formation of a nanometer sized Fe(III) reaction product, identified in the 242 PuO 2 (am) suspension both by use of 57 Fe Mössbauer spectroscopy and transmission electron microscopy (TEM) analysis.

The complexation properties of Am(III) and Eu(III) with a serial of novel N -heterocyclic tetradentate ligands, 2,9-bis(dialkyl-1,2,4-triazin-3-yl)-1,10-phenanth-rolines (BTPhens), have been calculated by density functional theory (DFT) coupled with relativistic small-core pseudopotential. It is found that the nitrogen atoms in triazine rings favor metal cations more than those in phenanthroline skeleton. The Am-N bond lengths are comparable to or even shorter than those of Eu-N bonds based on the larger radii of Am(III) than Eu(III). The effect of alkyl substituents on the complex structures is limited but they can adjust the complexation reaction and extraction kinetics. Additionally, the solvent effect can decrease the probability of the complexation reactions greatly and the solvation energies of Am(III) and Eu(III) might be the primary driving force in the complexation selectivity. The complexation reactions for forming ML(NO 3 ) 3 and [ML 2 (NO 3 )] 2+ complexes are believed to dominate the selective extraction separation of Am(III) from Eu(III) in nitric acid media, which agrees well with the experimental results. The comparisons of BTPhens with BTBPs in dipoles and electronic structures confirm that the BTPhens exhibit more favourable extraction kinetics and selectivity for minor actinides.

In this study, a simple and rapid dispersive liquid–liquid microextraction (DLLME) was developed for the determination of uranium in water samples prior to high performance liquid chromatography with diode array detection. 1-(2-pyridylazo)-2-naphthol (PAN) was used as complexing agent. The effect of various parameters on the extraction step including type and volume of extraction and dispersive solvents, pH of solution, concentration of PAN, extraction time, sample volume and ionic strength were studied and optimized. Under the optimum conditions, the limit of detection (LOD) and preconcentration factor were 0.3  μ g L −1 and 194, respectively. Furthermore, the relative standard deviation of the ten replicate was <2.6%. The developed procedure was then applied to the extraction and determination of uranium in the water samples.

Pyrohydrolysis method was studied for the separation of Cl and F from U-Zr and U-Pu-Zr alloy nuclear fuels and determination by ion chromatography. A detailed study was performed on pyrohydrolysed products of U-Zr alloy, obtained on heating in moist argon and oxygen atmospheres using X-ray powder diffraction (XRD) and thermogravimtric methods. Using oxygen as the carrier gas pyrohydrolysis performed at 900 ℃ was complete within 30 min. It was found that, moist oxygen as carrier gas only could open the matrix completely within stipulated time. This was attributed to the formation of α -U 3 O 8 , which was not possible in moist argon heating for 30 min. The pyrohydrolysis in moist Ar required 60–90 min for complete removal of halides. The method was then successfully extrapolated to U-Pu-Zr alloys. The results showed recovery up to 90% or above for the optimized conditions.

Two novel diglycolamide-grafted silica-based resins (DGSRs) were used for the sorption of trivalent actinides and lanthanides from 3 M nitric acid solutions. The sorption of Am(III) onto the resin containing one diglycolamide (DGA) moiety (DGSR-I) was less efficient than the resin containing two DGA moieties (DGSR-II) with Lagergren first order rate constants of (1.20 ± 0.03) × 10 – 3  s – 1 and (2.01 ± 0.05) × 10 – 3  s – 1 , respectively. The maximum sorption of Eu(III) (used as a representative of the trivalent lanthanide/actinide ions in radioactive wastes) was 10.4 ± 1.1 mg g – 1 and 13.9 ± 1.3 mg g – 1 by the DGSR-I and DGSR-II, respectively. The sorption of Eu(III) on the grafted silica resins followed the Langmuir monolayer sorption phenomenon with sorption energies of 16.5 ± 2.05 and 17.8 ± 1.6 kJ mol – 1 for DGSR-I and DGSR-II, respectively. Column experiments revealed that the breakthrough capacity of Eu(III) on the DGSR-II column was higher than that on the DGSR-I column. Efficient elution could be achieved with a 0.01 M EDTA solution. The radiolytic stability of the resins was ascertained by exposing the resins to a gamma ray dose up to 1030 kGy resulting in a decrease of the K d values with about 50%; at doses <500 kGy the K d values remained unaffected.

The use of composite materials based on metal ferrocyanides combined with natural mineral sorbents for treatment of high salinity Cs-containing liquid radioactive waste (LRW) was investigated. The study indicated that among the investigated composites, the best sorption characteristics for Cs were shown by materials based on copper ferrocyanide. Several factors affecting the removal of cesium from LRW, namely total salt content, pH and organic matter content, were also investigated. High concentrations of complexing organic matter significantly reduced the sorption capacity of ferrocyanide sorbents.

For the modeling of cesium sorption on biotite, samples of natural biotite separated from gneissic rocks were converted into monoionic potassium, sodium, and calcium forms, and sorption isotherms for Cs/K, Cs/Na and Cs/Ca exchange were determined at pH 6 and 8 in E-4–E-8 M Cs solutions. Selectivity coefficients for Cs/K, Cs/Na, and Cs/Ca ion exchange reactions were calculated from the isotherm data, using the Gaines-Thomas convention. At Cs loadings below 1% of the total ion exchange capacity, the overall selectivity coefficient for Cs/Ca exchange was approximately five and seven orders of magnitude higher than those for Cs/Na and Cs/K exchange, respectively. Based on the selectivity coefficients, the ion exchange isotherms were modeled with the U.S. Geological Survey PhreeqC program, assuming three different types of ion exchange site: sites on the basal planes on biotite crystal surfaces with 95% site abundance, probable interlayer sites on crystal edges [frayed edge sites (FESs)] (0.02%) and third-type sites (5%), the physical background of which is unclear. Of these three types, the FES sites were superior in Cs selectivity, while the planar sites exhibited the lowest selectivity, and the third-type sites had selectivity between these two. The functionality of the model was successfully verified by modeling the Cs sorption isotherms on crushed mica gneiss rock in saline groundwater. Determination of the exchangeable ions K, Na, Ca, and Cs on the basal plane and edge surfaces by scanning electron microscopy-energy-dispersive x-ray spectroscopy (SEM-EDX) supports the results of modeling: edge sites highly prefer Cs ions and also Ca and Na ions but not K ions.

Adsorption of Sr on multi-walled carbon nanotubes (MWCNTs) was investigated to explore their possible use as an efficient adsorbent for nuclear waste streams. MWCNTs were purified and oxidized with HNO 3 prior to testing adsorption. Oxidized MWCNTs were then employed in batch experiments as sorbent of Sr from aqueous solutions. The Box–Behnken experimental design was used to suitably vary the parameters of interest, i.e. , temperature, initial Sr 2+ concentration, and shaking time. Langmuir, Freundlich and Dubinin–Radushkevich models were applied to fit the adsorption isotherms. The Dubinin–Radushkevich model exhibited the best agreement. Adsorption kinetics was also studied; it was well described by a pseudo-second-order rate model. Adsorption thermodynamics was investigated in the temperature range 293–333 K; the variations of the standard free energy ( ΔG ○ ), standard enthalpy ( ΔH ○ ) and standard entropy ( ΔS ○ ) were obtained. Oxidized MWCNTs show the potential to be a promising candidate for the pre-concentration and solidification of Sr from large volumes of aqueous solution.

Tritium labeling was introduced into detonation nanodiamonds (ND) through the tritium thermal activation method. Two target preparation techniques were developed to increase the radioactivity and the specific radioactivity of the labeled product: the desiccation of the waterless solvent suspension and the lyophilization of the hydrosol. The specific radioactivity of the labeled product was shown to correlate with the hydrogen content in the starting material and to achieve 2.6 TBq/g.

While the 90 Sr/ 90 Y generator is the exclusive source of obtaining `no carrier added' 90 Y for targeted therapy, the presence of trace metals in the radiolabeling solutions poses a serious challenge owing to their ability to diminish the 90 Y complexation yields with bifunctional chelators (BFCs). p-SCN-Bn-PCTA is a novel ligand having faster complexation kinetics with a number of radiometals. In this work, a systematic investigation was performed to evaluate the chelating ability of p-SCN-Bn-PCTA for 90 Y and the influence of trace metal ions on it's complexation with 90 Y in comparison to p-SCN-Bn-DTPA and p-SCN-Bn-DOTA using 90 YCl 3 obtained from an electrochemical generator. Results from our study indicate that while p-SCN-Bn-PCTA gave very good radiolabeling yields with 90 Y when the reaction was carried out by heating for few minutes, it was most sensitive to the presence of trace metals, especially Fe(III). An independent and useful observation is that p-SCN-Bn-PCTA could be considered as the ligand of choice for assessing the chemical purity of generator derived 90 Y.