Volume 106, Issue 4

The solubility and redox behavior of hydrous Pu(IV) oxide was comprehensively investigated by an experimental multi-method approach as a function of different redox conditions in 0.1 M NaCl solutions, allowing a detailed characterization of Pu(IV) and Pu(III) solubility and solid phase stability in these systems. Samples were prepared at ~3≤pH m ≤~6 (pH m =–logmH+)${{\text{m}}_{{{\text{H}}^{\text{ + }}}}})$ and ~8≤pH m ≤~13 at T =(22±2)°C under Ar atmosphere. No redox buffer was used in one set of samples, whereas mildly and strongly reducing redox conditions were buffered in two series with hydroquinone or SnCl 2 , respectively, resulting in (pe+pH m )=(9.5±1) and (2±1). XRD, XANES and EXAFS confirmed the predominance of Pu(IV) and the nanocrystalline character of the original, aged PuO 2 (ncr,hyd) solid phase used as a starting material. Rietveld analysis of the XRD data indicated an average crystal (domain) size of (4±1) nm with a mean cell parameter of (5.405±0.005) Å. The solubility constant of this solid phase was determined as log ∗​K°s,0$^ * K{^\circ _{{\text{s}},0}}$=–(58.1±0.3) combining solubility data in acidic conditions and redox speciation by solvent extraction and CE–SF–ICP–MS. This value is in excellent agreement with the current thermodynamic selection in the NEA-TDB. Synchrotron-based in-situ XRD, XANES and EXAFS indicate that PuO 2 (ncr,hyd) is the solid phase controlling the solubility of Pu in hydroquinone buffered samples. Under these redox conditions and ~8≤pH m ≤~13, the solubility of Pu is very low (~10 −10.5 m) and pH-independent. This is consistent with the solubility equilibrium PuO 2 (am,hyd)+2H 2 O(l)⇔ Pu(OH) 4 (aq). Although in-situ XRD unequivocally shows the predominance of PuO 2 in Sn(II)-buffered systems, XANES analyses indicate a significant contribution of Pu(III) (30±5%) in the solid phases controlling the solubility of Pu at (pe+pH m )=(2±1). For this system, EXAFS shows a systematic shortening of Pu–O and Pu–Pu distances compared to the starting Pu material and hydroquinone-buffered systems. The solubility of Pu remains very low (~10 −10.5 m) at pH m >9, but shows a very large scattering (~10 −9 –10 −10.5 m) at pH m =8. Experimental observations collected in Sn(II) buffered systems can be explained by the co-existence of both PuO 2 (ncr,hyd) and Pu(OH) 3 (am) solid phases, but also by assuming the formation of a sub-stoichiometric PuO 2− x (s) phase. This extensive study provides robust upper limits for Pu solubility in alkaline, mildly to strongly reducing conditions relevant in the context of nuclear waste disposal. The potential role of Pu(III) in the solid phases controlling the solubility of Pu under these conditions is analysed and discussed in view of the current NEA-TDB thermodynamic selection, which supports the predominance of PuO 2 (am,hyd) and constrains the formation of Pu(OH) 3 (am) at pH m >8 outside the stability field of water.

Extraction behavior of tris(2-methylbutyl) phosphate (T2MBP), a higher homologue of tri- n -butyl phosphate (TBP), in the extraction of U(VI) and Pu(IV) from nitric acid media has been evaluated in the present study. Distribution ratios for the extraction of these metal ions by T2MBP were measured as a function of equilibrium aqueous phase nitric acid concentration, extractant concentration and temperature to understand the temperature effects on extraction. Enthalpies of extraction of T2MBP/ n -dodecane-U(VI)-HNO 3 and T2MBP/ n -dodecane-Pu(IV)-HNO 3 systems were calculated from the distribution ratio data using “second law” method. The data reveal that the extraction of U(VI) by T2MBP is exothermic in nature, whereas that of Pu(IV) is endothermic.

The interaction of salicylic acid with zirconium diphosphate surface and its reactivity toward uranium (VI) was investigated. The interaction of salicylic acid with zirconium diphosphate was firstly studied using several analytical techniques including atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The sorption of uranium (VI) onto surface-modified zirconium diphosphate was evaluated by the classical batch method at room temperature. This study showed that the uranium (VI) sorption onto zirconium diphosphate is influenced by the presence of salicylic acid. A fluorescence spectroscopy study revealed the presence of a uranyl specie onto the modified solid surface. The spectroscopy results were then used to restrain the modeling of experimental sorption data, which are interpreted in terms of a constant capacitance model using the FITEQL code. The results indicated that interaction between the uranium (VI) and the surface of zirconium diphosphate modified with salicylic acid leads to the formation of a ternary surface complex.

Complexation of a new macrocyclic compound, 2,6-dimethylformamide-calix[4]pyridine ( L 1 ), with Eu(III) was studied by spectrophotometry. Stability constants of the Eu(III)/ L 1 complex in different solvents were determined. The results reveal that L 1 forms moderately strong complexes with Eu(III) and other lanthanides in aprotic solvents and shows little binding ability with transition metals. Moreover, the binding strength of L 1 weakens significantly in protic solvents. Using 2-bromodecanoic acid as the synergistic reagent, L 1 extracts Am(III) and Eu(III) successfully with a separation factor of SF Am/Eu =1.3, and the distribution ratios of Am(III) and Eu(III) increases as the aqueous acidity is decreased. DFT computational studies were conducted to corroborate the solvent extraction data, and compare the coordination properties of Am(III)/Eu(III) complexes with L 1 and a related, 2,6-diformamide-calix[4]pyridine ( L 2 ). The computational results suggest that L 2 could form stable complexes [ML] 3+ and ML(NO 3 ) 3 [where M represent Am(III) or Eu(III)] in aqueous phase, in sharp contrast to the case of L 1 where such complexes in aqueous phase are not stable.

N , N- dihexyloctanamide (DHOA) is being considered as a promising extractant in the aqueous reprocessing of spent nuclear fuels. In view of rise in temperature of the solvent during reprocessing of fast reactor fuel, the present study aimed at evaluating the physical properties such as density, viscosity, and interfacial tension and Pu(IV) extraction behavior in 1.1 M DHOA/ n -dodecane as a function of temperature and duration of heating. The influence of nitric acid in altering the physical properties with respect to temperature was evaluated. Physical properties and extraction behavior of the solvent changed to a remarkable extent with temperature. Quantitative amount of Pu(IV) could be back-extracted from loaded, solvent in three contacts at 313 K. FT-IR studies were carried out to evaluate the thermal stability of the solvent. Thus, the performance of the solvent, 1.1 M DHOA/ n -dodecane is satisfactory at higher temperatures also.

Removal of actinides (trivalent, tetravalent and hexavalent) from nitric acid medium was studied using solid-liquid extraction technique employing polymeric encapsulated beads (PEBs) using an indigenously synthesized, unexplored novel monoamide, N,N′-bis(2-ethyl hexyl) α-hydroxy acetamide (BEHGA). The PEBs were synthesized by phase inversion technique. The structure and morphology of the synthesized PEBs were evaluated by employing various characterization techniques like FT-IR, TGA and SEM. The well characterized PEBs were studied for its Am(III), Pu(IV) and U(VI) sorption behavior from nitric acid medium. Kinetics studies showed that the sorption is fast with equilibrium being reached within 60 min of equilibration. The sorption mechanism follows pseudo-second-order mechanism with intraparticle diffusion playing an important role. Langmuir isotherm model was found to best describe the sorption isotherm. The maximum Am(III) sorption capacity of the PEBs was found to be 8.45 mg/g (experimental) and 8.43 mg/g (Langmuir). Back extraction was possible using 0.5 M HNO 3 . Stability of the PEBs was found to be quite good with no significant structural deformation or leaching out of the extractant in 4.0 M HNO 3 solution for at least up to 8 days.

The present study is oriented to synthesis of radioiodinated olmesartan medoxomil (OM) for potential cardiac imaging. Olmesartan medoxomil has been labeled with [ 125/131 I] using chloramine-T (Ch-T) as an oxidizing agent. The key effective factors such as amount of oxidizing agent, amount of substrate, pH, reaction temperature and reaction time, have been systematically studied to get high radiochemical yield of the [ 125 I]olmesartan medoxomil reaching values of 98.5%. The labeled compound was separated and purified using thin layer chromatography (TLC), paper electrophoresis and high performance liquid chromatography (HPLC). The biological distribution indicates the suitability of [ 125 I]olmesartan medoxomil as a novel tracer to image heart with high heart/blood ratio within 30 min which was detected by gamma camera.

In the present work, materials, namely mud, sand mud, ferruginous sandstone and sandstone with different densities are used to evaluate the effect of chemical composition and moisture content on the self-attenuation coefficient factor at γ-energy range from 59.5 to 1332.5 keV. The results revealed that the attenuation coefficient increases with increasing the moisture content until the material saturate with moisture. The average value of increasing linear attenuation coefficients based on increasing moisture content are 14.3%, 16.0%, 18.2%, 28.1% and 24.8% at γ-energies 59.5, 356.0, 661.7, 1173.4 and 1332.5 keV, respectively. Chemical composition of material affected on the values of attenuation, i.e. the elements with high density have high attenuation coefficient. Significant effect of self-attenuation correction factor was observed at low γ-energies up to 500 KeV. Application of the calculated correction of environmental sample with low radioactivity content has been carried out.