Volume 92, Issue 7 -

The fluoride complexation of the group-4 elements Zr, Hf, and Rf, and of the pseudo-homolog Th, was previously investigated in mixed HNO 3 /HF solutions by studying K d values on both cation-exchange resins (CIX) and anion-exchange resins (AIX) using the automated rapid chemistry apparatus ARCA. On the CIX, the fluoride complexation of Rf was found to be weaker than that of Zr and Hf but stronger than that of Th. On the AIX, the competition for the binding sites by the counter ion NO 3 - was found to be stronger for the fluoride complexes of Rf than for those of Zr and Hf. The aim of the present work is to add independent evidence to the latter result by measuring K d values for Rf on the AIX in 0.1 M HNO 3 /0.5 M HF and in 0.01 M HF without any HNO 3 . The results are obtained via an activity ratio of the long-lived α -decay descendant of 261m Rf, 20-d 253 Es, using the multi-column technique (MCT). These experiments corroborate the seemingly much more pronounced competition of NO 3 - for the exchanging sites of the AIX with respect to [RfF x ] ( x -4)- than with [ZrF x ] ( x -4)- and [HfF x ] ( x -4)- .

The kinetics of the oxidation of U(IV) ions by nitrous acid in a 30% TBP solution have been determined. The rate equation was found to be: -d[U(IV)]/d t = k 2a ([U(IV)][HNO 2 ][HNO 3 ][H 2 O])/([HNO 3 ] 2 +β 3 [HNO 3 ][H 2 O]+ β 4 [H 2 O] 2 ), where, k 2a =0.405±0.055 M -1 min -1 at 55 °C ( β 3 ≈0.08; β 4 ≈0.007) and the activation energy was E =112±17 kJ mol -1 . The reaction mechanism appeared to involve interaction with the 1 st hydrolysis product of U(IV)–UOH 3+ . The data is compared with a previous study of the nitric acid oxidation of U(IV) in 30% TBP. This reaction is autocatalytic due to the formation of nitrous acid during the reaction. The kinetics of the decomposition of HNO 2 in 30% TBP (in the absence of U(IV)) have also been reported.

We have determined K d values for Mo and W in batch experiments on various anion-exchange resins in HCl and HNO 3 as well as in mixed HCl-HF and HNO 3 -HF solutions in order to create a data base and to select optimum conditions for the determination of K d values of Sg (element 106) in a future on-line experiment using continuous chromatography with the multi-column technique (MCT). Their influence by hydrolysis and fluoride complexation is discussed and the average charge of the complexes is determined from slope analyses. It is shown that the selectivity of anion exchangers for the Mo- and W complexes and, thus, the separation factors between them, depend strongly on the choice of the functional group of the anion-exchange resin.

Single crystals of [NpO 2 L(H 2 O)]·1/3H 2 O ( I ) and [PuO 2 L(H 2 O)]·H 2 O ( II ) (H 2 L — orthophthalic acid) have been synthesized, their structures have been determined by X-ray structural analysis. Actinide atoms in both compounds are seven-coordinated. The interaction between actinide dioxocations and phthalate anions results in formation of infinite tubes in I and layers in II . The structures are compared with those of other phthalate compounds of hexa- and pentavalent actinides, in particular, with the structure of [UO 2 L(H 2 O)]·H 2 O which differs from the structure II .

Improvement of the nuclear fuel reprocessing involves separating the minor actinides (Am(III) and Cm(III)) from the fission products. In the French strategy, the first step consists in the separation of the trivalent actinides and lanthanides from high-level liquid waste, for which malonamides RR´NCO(CHR´´)CONRR´ are promising ligands. These molecules have been optimized for reprocessing but still require basic chemical studies to describe the complexation mechanisms at a molecular scale. This paper discusses a thermodynamic and structural study of a Ln(III)-malonamide complex formed with the hydrosoluble tetraethylmalonamide ligand (TEMA=(C 2 H 5 ) 2 NCOCH 2 CON(C 2 H 5 ) 2 ) dissolved in a nitrate medium. Despite the simplified chemical system obtained with TEMA, its weak chemical affinity and its physical properties pushed the analytical techniques to their limits. The sensitivity of Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLIFS) combined with the major luminescent spectroscopic properties of Eu(III) (hypersensitive band and fluorescence lifetime) were successfully used to determine the equilibrium constant and hydration number in the Eu(III), TEMA, and NO 3 - system. Fluorescence lifetimes, connected with the first coordination sphere of the solvated metal, clearly show the inner-sphere location of nitrate in the Eu(NO 3 ) 2+ complex, the outer-sphere location of TEMA in the Eu(TEMA) 3+ complex, and the outer-sphere location of both ligands in the Eu(NO 3 )(TEMA) 2+ complex.

Permeation grouting with colloidal silica gel is a potentially effective means for creating hydraulic barriers to prevent the advective migration of radioactive contaminants in shallow permeable sediments. However, the effectiveness of silica gel grouted barriers in controlling transport of fission product radionuclides through sorption and diffusion is unknown. To resolve this question, static-batch sorption measurements with Cs + and Sr 2+ were conducted at ambient temperature (23 °C) and for times up to 96 days on silica gel and on two kaolinitic sediments from the Savannah River Site in South Carolina. Sorption experiments on the latter were conducted both in the presence and in the absence of silica gel. Cesium and strontium concentrations were varied between 10 -3 to 10 -8 M (mol/L) and 10 -4 to 10 -8 M, respectively. The pH values after one day varied for each experiment and ranged from 3.6 to 6.6. The pH of the solutions were, however, buffered by the sediments and/or silica gel, and changed little over the duration of the experiments. The fraction of both cesium and strontium retained on the solids increased with decreasing radioelement concentration. The sorption data were fitted to the Freundlich isotherm model.

After upgrading the Pakistan Research Reactor-1, the amount of liquid waste and its increased radioactivity content necessitated a pre-disposal treatment to bring the activity down to disposal limits. Amongst several radionuclides in the waste, 110m Ag and to some extent 124 Sb were of our concern due to their higher production rate. Different possible treatment processes were considered for the treatment of low-salt, low-level liquid waste of the institute. Making use of insolubilities and scavenging properties of certain precipitates of metal ions, some experiments on the actual waste samples were performed for the decontamination of the piled up waste effluent. Suitable reagent(s) and the optimum doses were to be investigated for the treatment and conditioning of the wastewater. Different scavenging agents like ferric chloride, ferrous sulfate, stannous chloride, in situ precipitated manganese hydroxide and lanthanum nitrate were studied for the removal of these two radionuclides. Selectivity of Fe 2+ and Fe 3+ as scavengers for silver and antimony was investigated. Excellent Decontamination Factors (>1000) were obtained very cost effectively with some of the reagents tried. Based on these experiments, a working procedure making use of Fe(II) hydrous oxide scavenging precipitation for the chemical treatment of the waste effluent was optimized. These experiments are presented.

The concentration of 18 minor and trace elements (essential, toxic and nonessential) in infant head hair was determined. The data provide the base-line values of these elements in head hair of infants of low- and medium-income group subjects. The statistical results show that there are significant correlations between some elements such as: Ca-Zn, Ca-Fe, Mg-Ca, Mg-Mn and Mg-Fe. The results obtained have been compared with the data reported in the literature. Our data show compatibility of elemental contents of infant head hair with those from some of the other geological regions but also deviate in some cases.

This work focuses on time-resolved laser fluorescence spectroscopy (TRLFS) of Pa(IV) in aqueous solution. Excitation at 308 nm causes a fluorescence emission with a peak maximum at about 460 nm. Thereby, the position of the band´s maximum depends on the concentration, the type of the acid, and the pH value. Increasing complexation of the Pa(IV) ion leads to an increasing hypsochromic shift of the emission band up to 46 nm. In contrast to the band position the half-width (61.6±1.4 nm) and the lifetime (16±2 ns) of the fluorescence emission do not change significantly with changes in the chemical environment of the Pa(IV). The results of this work show that speciation of Pa(IV) can be performed even in aqueous solution by using TRLFS.