Volume 99, Issue 11 -

A formation of Am(VI) carbonate complexes has been observed under ozonation of Am(III) in guanidinium carbonate solutions. New [C(NH 2 ) 3 ] 4 [AmO 2 (CO 3 ) 3 ]·2H 2 O tricarbonate complex has been isolated and studied by the X-ray analysis. The Am atom has oxygen environment as distorted hexagonal bipyramid with three CO 3 2− ions in equatorial plane and oxygen atoms of the AmO 2 group in the apical positions. Averaged Am–O CO 3 bond length is 2.431(13) Å, the length of Am=O bond is 1.750(12) Å. In crystal hydrogen bonds between [C(NH 2 ) 3 ] + cations, water molecules and [AmO 2 (CO 3 ) 3 ] 4− complex anions link the fragments of structure into the three-dimensional network. To compare the peculiarities of the structure of tricarbonate complexes it was prepared [C(NH 2 ) 3 ] 4 [AnO 2 (CO 3 ) 3 ], where An = U(VI), Np(VI) and Pu(VI). In structure of [C(NH 2 ) 3 ] 4 [AnO 2 (CO 3 ) 3 ] an actinide contraction appears as a slight shortening of the bond lengths in the actinyl groups AnO 2 : 1.80 Å for U, 1.78 Å for Np 1.76 Å Pu. The An–O CO 3 bond length in the equatorial plane of hexagonal bipyramids remains almost unchanged in the series from U to Am. An analysis of the structures showed that hydrogen bonding played an important role in crystal formation.

The complex formation of U(VI) with humic acid (HA) in the presence of carbonate was studied by time-resolved laser-induced fluorescence spectroscopy at low temperature (cryo-TRLFS) at pH 8.5. In the presence of HA, a decrease of the luminescence intensity of U(VI) and no shift of the emission band maxima in comparison to the luminescence spectrum of the UO 2 (CO 3 ) 3 4− complex, the dominating U(VI) species under the applied experimental conditions in the absence of HA, was observed. The formation of a ternary U(VI) carbonato humate complex of the type UO 2 (CO 3 ) 2 HA(II) 4− starting from UO 2 (CO 3 ) 3 4− was concluded from the luminescence data. For this complex a complex stability constant of log K =2.83 ± 0.17 was determined. Slope analysis resulted in a slope of 1.12 ± 0.11, which verifies the postulated complexation reaction. The results agree very well with literature data. Speciation calculations show that the formation of the ternary U(VI) carbonato humate complex can significantly influence the U(VI) speciation under environmental conditions.

The development of effective remediation strategies requires a comprehensive understanding of contaminant behavior in the environment. At the Hanford Site, located in southeastern Washington State (United States of America), seasonal fluctuations of the nearby Columbia River cause flushing of the 300 Area uranium (U) plume in the lower vadose zone. The variation of water chemistry alternately promotes adsorption and desorption of U from sediment. Therefore, the following question arises: what is the mobility of U in groundwater that has only recently became associated with sediment relative to U that has been associated with the sediment for decades? Geochemical transformations, including surface complexation, precipitation, and/or physical processes will impact U speciation as the contact time with sediment increases. To investigate this question, dissolved 233 uranyl nitrate [UO 2 (NO 3 ) 2 ] was added to U-contaminated Hanford Site sediment and incubated for up to 1 year. Following 1-week, 1-month, and 1-year incubation periods, the extraction of U from the sediment was accomplished using either batch or continuous leach techniques, and multiple extractants. The elution of 233 U during continuous leaching was influenced by the incubation period. The change in the 235 U/ 233 U ratio eluted was indicative of the extraction of different U phases, and was a function of the incubation period. Removal of 233 U by batch extraction clearly showed the effects of the incubation period and extractant. The extractability of the 233 U spike by some extractants is independent of incubation period (up to 1 year) suggesting it is present as either sorbed or surface precipitate phases. Model simulation of the data provides insight into the processes involved with the extraction of U from the sediment.

Solvent extraction studies on separation of trivalent actinides from lanthanides using 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl) pyridines have shown promising results with respect to separation factor and efficiency in acidic medium. In order to understand their complexation behavior, the stability constant (log β ) of trivalent lanthanides (La, Nd, Eu, Tb, Ho, Tm, Lu) with 2,6-bis(5,6-diethyl-1,2,4-triazin-3-yl)pyridine (ethyl-BTP) have been determined in methanol medium (ionic strength 0.01 M) using spectrophotometric titrations. The stoichiometry of the complexes is found to vary with the ionic size of lanthanide ion. The variation in log β across the lanthanide series is attributed to variation in solvation characteristics of the metal ion. Comparison of log β for Ln(III)–ethyl-BTP complexes with other alkyl derivatives showed increase in the stability with increasing length of the alkyl group due to hydrophobic interaction. In the case of Eu(III), the speciation was also corroborated by time resolved fluorescence spectroscopy. The thermodynamic parameters (Δ G , Δ H , Δ S ) for complexation of Eu(III) with ethyl-BTP, were determined by microcalorimetry, which revealed strong metal ion–ligand interaction with the reactions driven mainly by enthalpy.

Studies on the extraction of Cs(I) from nitric acid medium were carried out using three commercial calix-crown ligands, viz . calix[4]arene-bis-crown-6, calix[4]arene-bis-1,2-benzocrown-6 and calix[4]arene-bis-2,3-naphthocrown-6 dissolved in different room temperature ionic liquids (RTILs), viz. 1-butyl-3-methyl-imidazolium hexafluorophosphate (C 4 mim·PF 6 ), 1-hexyl-3-methyl-imidazolium hexafluorophosphate (C 6 mim·PF 6 ) and 1-octyl-3-methyl-imidazolium hexafluorophosphate (C 8 mim·PF 6 ). The distribution ratio of Cs(I) decreased with increased alkyl chain length of RTILs. The effect of nitric acid concentration on distribution behaviour of Cs(I) by calix[4]arene-bis-1,2-benzocrown-6 was investigated. The extraction of Cs(I) from HNO 3 was found to be exothermic and extraction was found to be enthalpy driven. Selective extraction of Cs(I) could be achieved from a mixt ure of various fission product elements like Tc, Mo, Zr, Ce, Ru, La, Ba, and Sr.

In the study the activities of polonium 210 Po and uranium 234 U, 238 U in plants, collected near phosphogypsum waste heap in Wiślinka (northern Poland), were determined by using the alpha spectrometry. The obtained results revealed that the concentrations of 210 Po, 234 U, and 238 U in the analyzed plants were differentiated. In the analyzed flora organisms the highest amounts of polonium and uranium were found in ruderal plant samples as well as willow samples ( Salix viminalis ) from protection zone of phosphogypsum waste heap. The concentrations of 210 Po, 234 U and 238 U in the analyzed plants were higher in roots than in green parts of plants. The higher concentrations of 210 Po and 238 U radionuclides were estimated for hydrophyte (common sedge Carex nigra Reichard), the favourite habitat of which is particularly wet meadow and for plants co llected in the vicinity of phosphogypsum waste heap. The major source of polonium and uranium in analyzed plants is root system. The values of 234 U/ 238 U activity ratio in all analyzed plants are closed to one, what indicated that source of uranium in analyzed plants is phoosphogypsum. The highest uranium and polonium concentrations were characterized for plants, which are covered with tomentose. The comparability polonium and uranium contents were confirmed in edible plants, but higher accumulation was determined in ripe species than immature species of vegetables. The higher polonium and uranium concentrations were noticed in green parts of plant, the lower in roots. Polonium concentration in cultivated plants samples was not species diverse. Therefore, the significant source of polonium and uranium in analyzed plants is wet and dry atmospheric falls gathering the soil and air dust from phosphogypsum waste dump. The maximum 210 Po and 238 U radionuclides concentrations were found in green parts of red beet ( Beta vulgaris esculenta ), the minimum in garden radish ( Raphanus radicula ). That's interesting too, that both species have hypocotyls tubers, but tuber of red beet is large than garden radish. In our opinion these differences may be connected with turgidity because leaves and root of radish garden were withered.

In this work, we describe a novel electrochemical approach to deposit 63 Ni coatings on the inner surface of a copper annular ring for its application as an ionization source in electron capture detector of gas chromatograph. A description of the electrolytic cell, the process of deposition and the experimental set up used, analysis of the nickel deposit and results are presented in this article. Sources containing ∼370 MBq (∼10 mCi) 63 Ni could be prepared. The quality of the prepared source in terms of nonleachability, uniform distribution of activity and stability that are necessary before application were evaluated and found to be highly satisfactory.

Indium-DTPA-tagged liposomes were studied in the present work as carriers of in vivo 212 Pb/ 212 Bi generator to be used in targeted alpha therapy. The liposomal uptake of 212 Pb, into preformed liposomes, was investigated using different lipophilic chelate (DCP, 2,3-dimercapto-1-propanol (BAL), sodium acetate, and A23187), as a function of various parameters (temperature, concentrations of lipids, Pb, DTPA, ...) with 212 Pb as a tracer. Different formulations of liposomes were tested to evaluate the radiolabeling efficiency. No complexing agent was necessary for the passage of Pb 2+ through the membrane. It occurs naturally via a partial permeability of the lipid bilayer, which increases with the temperature. A complexing agent (DTPA) appears necessary to concentrate Pb in the internal compartment of the liposomes. Conditions were found ( T =65 ºC, internal DTPA concentration of 0.025 M, pH 7.4, ...) yielding a high and rapid uptake of 212 Pb in liposomes. The protocol established provides a novel method for the efficient entrapment of about 2–3 Pb atoms per liposome with a yield of 75% in conditions relevant for nuclear medicine.

Trace impurities of chlorine in the zircaloy-2 and Zr-2.5% Nb alloy matrix have been determined using neutron activation analysis (NAA) and off-line γ -ray spectrometric technique. The results have been compared with the values obtained from pyrohydrolysis-IC and spark source mass spectrometric method. The limit of internal precision error from the neutron activation technique is 6.7% for zircolloy-2 and 9% for Zr-2.5% Nb alloy, which are lower than that of pyrohydrolysis-IC and spark source mass spectrometric measurements respectively. For both alloys the results from present work based on NAA technique are slightly higher than the results based on the other two methods but are comparable within the uncertainty.