Volume 91, Issue 3 -

The thermochromatographic behavior of berkelium chlorides in various chlorinating gases was studied. Using Cl 2 or a mixture of Cl 2 /SOCl 2 , two peaks were observed in a thermochromatographic column. The "high temperature" peak corresponds to BkCl 3 and the "low temperature" one corresponds most probably to BkCl 4 . Using both the model of mobile adsorption and the of Monte Carlo method, the adsorption enthalpies were determined. The possible chemical reactions in a chromatographic column are discussed.

Extraction of Am(III) and Eu(III) from NO 3 - , ClO 4 - , SCN - and NO 3 - + ClO 4 - media with tri- n -octyl phosphine oxide (TOPO) in xylene has been carried out at 15, 25, 30 and 35°C. Under the extraction conditions the species M(NO 3 ) 3 ·3TOPO, M(SCN) 3 ·4TOPO, M(ClO 4 ) 3 ·4TOPO and MNO 3 (ClO 4 ) 2 ·4TOPO are predominantly extracted at all the temperatures (M=Am or Eu). The two phase equilibrium constant (log K ex ) follows an order SCN - > NO 3 - + ClO 4 - > ClO 4 - > NO 3 - . Extraction enthalpies have been calculated in each system from the temperature dependence of the K ex . The thermodynamic parameters Δ G , Δ H and Δ S have been discussed and compared with other mono- and bidentate organophosphorus extractants for Am(III) and Eu(III) from same aqueous medium. The -Δ H values for the two-phase reaction follow an order NO 3 - + ClO 4 - > ClO 4 - > SCN - > NO 3 - for both metal ions. This has been explained on the basis of heat energies involved with the formation of ML 3 complex (L being the anion used), the transfer of ML 3 to the organic phase and the attachment of TOPO molecules, and also on the limiting partial molal volume of the anions.

The complexation of Am(III) and Eu(III) with humic acid of different molecular sizes was measured and the data for the ≥300kD and ≥10kD sized HA at p c H 4.0 and 6.0 was analyzed by the Charge Neutralization Model (CNM) and the Polyelectrolyte Model (PM). For the PM, solvent extraction was used to obtain the stability constants of 241 Am at tracer concentration. For the CNM, ultrafiltration was used to determine the loading capacity and the stability constants for Eu(III) at macro concentrations. There was a difference of 1-2 orders of magnitude in the stability constants from the two models. The 5 D 0 – 7 F 0 excitation spectra of Eu(III) as a function of loading of HA was found to have a shift in wavenumbers of the peak maximum, indicating that the coordination environment of Eu(III) varied with pH, presumably due to variation in the number of functional groups of the humate bound to the metal ion.

Distribution studies of Pu and Th have been carried out under varying acidity/ligand concentrations to optimise the conditions for their separation employing di(2-ethylhexyl)isobutyramide (D2EHIBA) in n -dodecane as extractant. In view of the selective complexation of D2EHIBA towards hexavalent metal ions over tetravalent metal ions, the focus of the present work is to identify a suitable oxidant of Pu. Amongst various oxidising agents investigated for the oxidation of Pu to Pu(VI), AgO appears to be a promising candidate as (i) it is thermodynamically as well as kinetically a favourable oxidant and (ii) unlike Cr(VI) and Ce(IV), it is not co-extracted with Pu towards the organic phase.

Preparation, crystal structure and properties revealed through IR and visible absorption spectroscopy study of Np(V,VI), Pu(VI) compounds formed with pertechnetate anions are reported. Spectrophotometric study of Np(V) and Pu(VI) in NH 4 TcO 4 aqueous solutions (TcO 4 - concentration ranging between 0.2-0.5 M) shows only a slight interaction of NpO 2 + and PuO 2 2+ -ions with pertechnetate oxoanions in solution. On the contrary, for Np(V), Np(VI) and Pu(VI) pertechnetates in solid state, changes in the spectra clearly evidence the coordination of the actinides(V,VI) with TcO 4 - -anions. That is in agreement with Np(VI) pertechnetate X-ray structural analysis performed on a single crystal.

The alpha-emitter 210 Po is an activation product of liquid lead-bismuth, a low melting eutectic under investigation as a coolant of the next generation fast nuclear reactors. Experiments were performed to measure the gaseous polonium chemical species for assessing the radioactivity release from a Pb-Bi bath upon contact with a gas stream. The vapor pressure of lead polonide was measured over the 400-550°C temperature range and found to be in agreement with an existing correlation derived from data at higher temperatures. Also, it was experimentally confirmed that the presence of steam in the gas stream above the Pb-Bi melt substantially increases the amount of polonium released due to the formation of the volatile compound H 2 Po. The free-energy variation of the H 2 Po formation reaction was determined, permitting the calculation of the Po gas phase speciation under the experimental conditions.

Alpha particle activation of natural Bi 2 O 3 results in the formation of astatine radionuclides. A simple and rapid separation method of astatine is presented from the bulk target matrix bismuth by employing liquid-liquid extraction (LLX) method using methylisobutylketone (MIBK) and hydrochloric acid. Back extraction of astatine was performed by ethylenediaminetetraacetic acid (EDTA) solution at pH 10.

The synergistic extraction of trivalent lanthanoids Nd, Eu and Tm with mixtures of 3-phenyl-4-(4-fluorobenzoyl)-5-isoxazolone (HFBPI) and dicyclohexano-18-crown-6 (DC18C6) in 1,2-dichloroethane from nitrate solutions has been investigated. The results demonstrated that these trivalent lanthanoids were extracted into 1,2-dichloroethane as Ln(FBPI) 3 with HFBPI alone and as Ln(FBPI) 3 · DC18C6 in the presence of crown ether. The equilibrium constants of the above extracted complexes have been deduced by non-linear regression analysis. The equilibrium constants of the synergistic species were found to increase monotonically with decrease in ionic radii of these metal ions. The addition of a crown ether to the metal chelate system not only enhanced the extraction efficiency significantly but also improved the selectivites among these trivalent lanthanoids. Solid complexes of these metal ions with HFBPI and with mixtures of HFBPI and crown ether have also been isolated and characterised by IR and 1 H NMR spectroscopic techniques.

Stability constants for the 1:1 and 1:2 complexes of Ni(II)+Oxalate have been determined using solvent extraction. Data collected in 0.3m to 5.0m NaCl aqueous solutions at 20.0±0.1°C yielded values of log β 101 ranging from 3.71 to 3.98(±0.06) and of log β 102 from 6.44 to 6.95(±0.06), which agree well with values from the literature. The data were analyzed by the Pitzer model with a value of μ 0 / RT =-17.47 for the 1:1 complex calculated from the data and literature values. A single neutral-ion interaction parameter λ NiOx-Cl =-0.179 was used to describe the ionic strength dependence of the 1:1 complex. For the 1:2 complex, a value for μ 0 / RT =-11.31 and the Pitzer parameters values, β 0 NiOx₂²⁻-Na⁺ =-0.0644 and β 1 NiOx₂²⁻-Na⁺ =0.8545, were determined. These standard chemical potential values are based on a model for oxalate deprotonation reported earlier.

Iodine-129 and technecium-99 are commonly the largest contributors to the calculated health risk associated with long-term nuclear-waste burial. The high proportion of risk from these radionuclides is due to their large inventories in many types of waste, long half-lives, and the perception that they are highly mobile in sediments. In most aquifer systems, these radionuclides exist as anions, iodide (I - ) and pertechnetate (TcO 4 - ), and sorb poorly to soils that possess a net negative charge. A series of iodide and pertechnetate sorption experiments were conducted over a pH range of 3 to 9. The two soils used in this study possessed a pH-dependent charge; one soil was collected from a wetland and derived most of its charge from organic matter, whereas the second soil was collected from an upland site and derived most of its charge from Fe/Al-oxide coatings. Although both soils had nearly identical particle size distributions, pH values, and mineral compositions, they had dissimilar surface charge and I - and TcO 4 - sorption behavior. The pH where the wetland soil did not have any net charge (more specifically, the Point-of-Zero-Salt Effect) was 4.4. The pH where the upland soil did not have any net charge was 4.1. Under ambient conditions, the wetland soil had a pH of 4.2 and a slight positive net charge of +0.1meq/100g. The upland soil had a natural pH of 5.0 and a net charge of -0.25meq/100g. Both iodide and pertechnetate sorbed appreciably more to the wetland soil than to the upland soil, likely the result of more anion sorption sites derived from the organic matter in the wetland soil. In both soils, iodide sorption was greater and exhibited a greater pH-dependency than pertechnetate sorption. Pertechnetate exhibited anion exclusion (negative K d values) or no sorption at pH values above the Point-of-Zero-Salt Effect. Iodide sorption decreased markedly as the pH increased to the zero-point-of-charge, and remained largely unchanged at pH values above the zero-point-of-charge.

Concentration distributions of 238 U, 232 Th, 226 Ra, 210 Po, 137 Cs and 238,239,240 Pu in sediment samples, collected along the Romanian sector of the Danube River and the Black Sea coast, indicated the same pattern of accumulation of the radionuclides in the investigated samples. The mineralogical structure of sediment samples investigated by X-ray diffraction on random and oriented slides and the cation exchange capacity determined by the silver-thiourea procedure were used to explain this pattern of accumulation. The clay mineral content of the samples, the type of clay mineral and the geochemical behaviour of the radionuclides are discussed as important factors for a preferential accumulation of contaminants in sediments.