Volume 93, Issue 4 -

We studied the coordination environment of neptunium(IV) in complexes with various natural and synthetic humic and fulvic acids at pH 1 by X-ray absorption fine structure (XAFS) spectroscopy. The results were compared to those obtained for the interaction of neptunium(IV) with Bio-Rex70, a cation exchange resin having solely carboxylic groups as metal binding functional groups. In both neptunium humate complexes and neptunium Bio-Rex70 sorbates, Np 4+ is surrounded by about 10 oxygen atoms at an average distance of 2.36±0.02 Å. This verifies that the carboxylic groups are the main complexing sites of the humic substances responsible for binding neptunium(IV) in the acidic pH range. The data suggest a predominant monodentate coordination of the carboxylate groups to neptunium(IV) ions.

Miniature hollow fibre modules were fabricated and used as phase contactors for chemical liquid–liquid extraction. They were tested for americium(III) selective extraction, using three different extractants of relevance to the European Partitioning and Transmutation strategy. Americium could be removed from the feed phase to >99.9% in all cases. Only few ten millilitres of feed phases were consumed running a test. This is the major advantage of the miniature hollow fibre modules over commercially available modules which have been used previously.

Detection and quantification of the aquo ions of Pu in 1 M HClO 4 was carried out using a 1-meter liquid core waveguide (LCW) coupled to a fiber optic UV-Vis spectrometer. Detection limits of 7 × 10 −7 M for Pu(VI), 1.6 × 10 −5 M for Pu(V), 5 × 10 −6 M for Pu(IV) and 8 × 10 −6 M for Pu(III) were achieved. The limits of detection represent increases of 18 to 33 times those achievable using a conventional 1-cm path length. Because of the much lower detection limits of the LCW, routine identification of the oxidation states in dilute Pu solutions can be made.

Uranium in solution can be precipitated over a wide pH range, from acidity and alkalinity, depending upon the solution and the precipitant used. The precipitate is generally filtered and the solution resultant contains uranium that should be recovered. This work is aimed at the selection of an appropriate resin for uranium recovery from alkaline solutions in the presence of ammonia, carbonate and fluoride. The ability of uranium extraction of 3 types of polymeric strong base resin was assessed. Laboratory solutions were prepared to determine the influence of the ions like ammonia, carbonate and fluoride on the uranium recovery by resins. The uranium concentration was 100 mg/L and the solution pH ranged from 9.2 to 10.4. The results, obtained by batch experiments, showed that excess of carbonate and fluoride completely inhibit uranium uptake in the pH range studied. Even low concentrations of fluoride and carbonate decrease uranium adsorption by resins. The optimum concentration was below 2.5 g/L (0.04 mol/L) and 5.0 g/L (0.26 mol/L) for carbonate and fluoride, respectively. The presence of high concentration of ammonia up to 20 g/L (1.20 mol/L) did not inhibit the uranium exchange process. Among the three types of resins studied IRA 910U was the most promising adsorbent for uranium at the conditions employed in this work.

The retention, mobility, and bio-availability of U(VI) in contaminated soils depend strongly on release of U(VI). Laboratory batch experiments were performed to evaluate the factors (ionic strength of the extraction solution and solution volume to solid mass ratio) controlling the release of U(VI) from contaminated soil at Oak Ridge, Tennessee. Increase in ionic strength shows an evident effect on U(VI) release as indicated by the increase in release rates and associated release mass of U(VI). The ratio of solution volume to solid mass ( V / M ) has a significant impact on the release of U(VI). Increase in the V / M ratio shows a negligible effect on the U(VI) release over a 4-day period. However, at Day 30 and Day 120, larger V / M ratios cause greater U(VI) release. The maximum U(VI) concentrations observed in the release experiments are in the range of schoepite solubility estimated under conditions relevant to the experiments, suggesting that schoepite solubility primarily controls the U(VI) release, but that solubilization and desorption effects cannot be distinguished using macroscopic methods.

A novel solid phase extractant is prepared by chemically immobilizing catechol with diazotized aminopropyl silica gel. The resulting catechol functionalized silica gel (CASG) was characterized by FTIR, and microanalysis and was used for selective enrichment of uranium(VI) from other inorganic ions. The optimum pH range for maximum sorption of uranium(VI) and thorium(IV) was found to be in the range 3.5–6.0. The above actinides were eluted with 10 cm 3 of 1.0 mol dm −3 HCl and determined by using an Arsenazo III spectrophotometric procedure. The calibration graph was rectilinear over the uranium(VI) concentration in the range 2–100 μg dm −3 with a relative standard deviation of 2.15% (for 25 μg of uranium(VI) present in 1.0 dm 3 of sample). The validation of the developed preconcentration procedure was carried out by analyzing marine sediment (MESS-3, NRC, Canada) and soil (IAEA soil-7, Austria) reference materials. The developed preconcentration method enables a simple instruments like a spectrophotometer gave comparable values of uranium(VI) to that of standard inductively coupled plasma-mass spectrometric values during the analysis of real soil and sediment samples.

The sorption behavior of Sr 2+ ions on natural minerals rich in kaolinite and magnesite was studied using SEM/EDS, XPS, XRPD, AAS/AES and DRIFT techniques. Quantitative analysis of the XPS data shows that magnesite is more effective in Sr 2+ uptake than kaolinite. DRIFT spectra and XRPD patterns indicate that the structures of both minerals were not affected upon Sr 2+ sorption. Intercalation of DMSO in kaolinite lamellae aiming at increasing the interlayer space did not significantly enhance the sorption capacity of the clay towards Sr 2+ probably due to the lack of a negative charge on the accessible sites. EDS mapping indicated that while the sorbed Sr is equally distributed on surface of natural kaolinite, it was associated – to a larger extent – with the regions richer in Mg in the case of natural magnesite. Comparing the uptake mechanisms of natural magnesite with that of pure MgCO 3 , it was seen that while natural magnesite sorbed Sr 2+ mainly through an ion exchange type mechanism, the formation of SrCO 3 coprecipitate was detected on the surface of the MgCO 3 at higher loadings.

Field studies have shown that the uptake of radionuclides by fungi depends on its nutritional mechanism (mycorrhizal or saprophytic), but this fact is only fully demonstrated for radiocaesium. To extend this conclusion to other radionuclides likely to be released in semi-natural ecosystems, we carried out a series of experiments under controlled laboratory conditions of the growth of mycelium of mycorrhizal and saprophytic fungi ( Pleurotus eryngii and Hebeloma cylindrosporum respectively) on liquid culture media containing known added activities of 60 Co, 85 Sr, and 134 Cs. The radionuclide incorporated most efficiently into Pleurotus eryngii was 134 Cs, and into Hebeloma cylindrosporum was 60 Co. For 134 Cs and 85 Sr, we also analysed the influence that the content of the chemically analogue elements K and Ca respectively in the culture medium had on its uptake. For both species, the uptake of 134 Cs is not correlated with the content of K in the media, but it is the uptake of 85 Sr increasing with it. These results seem to be independent of the nutritional mechanism. The influence of linearity in the uptake of 134 Cs and 85 Sr with increasing concentrations of Cs and Sr in the culture medium was also studied. For Pleurotus eryngii it was observed a decrease in the uptake of 134 Cs with increasing Cs content in the medium, and an increase in the uptake of 85 Sr with increasing Sr content in the medium.

The PET radionuclide Cu-64 ( t 1/2 = 12.7 h) can be easily produced utilizing the nuclear reaction 64 Ni( p , n ) 64 Cu. A high Cu-64 production rate was obtained using high-purity enriched nickel metal on the internal tangential target of the CS-30 cyclotron. Radio-copper was isolated after column chromatography using a semi-remote apparatus. Use of reagents with little or no carrier copper yields high specific activity Cu-64 pharmaceuticals prepared from the isolated [ 64 Cu]CuCl 2 . [ 64 Cu]Cu-ATSM was prepared in greater than 1.21±0.40 Ci/mmol (45±15 GBq/mmol) at EOB.

A correlation is established between thermodynamic data for hypothetical macroscopic amounts of elements and experimentally accessible data on gold surfaces. The correlation between the experimentally determined standard adsorption enthalpies of elements on gold surfaces and their standard sublimation enthalpies is shown to be valid over a broad data range for various elements from light noble gases (Kr) up to heavy metals (Pb, Bi). This type of correlation is indispensable to derive thermodynamic data for macroscopic amounts of elements from results of adsorption chromatographic experiments with single atom amounts. It is also necessary to predict the behavior of single atoms from given or estimated thermochemical data. The conditions under which this correlation is valid are elaborated. Finally, predicted data for the elements 112 and 114 are used to link them to the corresponding sublimation or adsorption data. The obtained prediction intervals are of exceptional importance for the design of sophisticated experimental setups for the chemical investigation of transactinide elements on a single atom scale.