Band 94, Heft 3 -

The extraction of zirconium and hafnium from hydrochloric acid media was studied using the crown ethers dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6 (DC18C6) and dicyclohexano-24-crown-8 (DC24C8) as extractants. The goal was to find an extraction system that exhibits a high selectivity between the members of group 4 of the periodic table and is suitable for the study of rutherfordium. It was found that Zr and Hf are both extracted using DB18C6, DC18C6 and DC24C8. The extraction yield increases with increasing acid concentration and increasing concentration of crown ether. The extracted species most likely consists of an ion-association complex formed between a Zr or Hf chloro complex and a hydronium crown ether complex. Conditions can be found for each extractant that provide for the separation of Zr from Hf. This selective separation between Zr and Hf makes the extraction with crown ethers from HCl well suited to study the extraction behaviour of Rf and compare it to the behaviour of Zr and Hf. These extraction systems can be used to determine whether the extraction behaviour of Rf is similar to Zr, similar to Hf or follows the trend established by the lighter homologs. The extraction kinetics are fast enough for the study of the 78-s isotope 261m Rf.

Room temperature molten salts for possible application of recovery of fission palladium from irradiated nuclear fuel/wastes have been investigated. The redox behavior of a solution of palladium(II) chloride and 1-butyl-3-methylimidazolium chloride (bmimCl) at glassy carbon working electrode has been studied at various temperatures using cyclic voltammetry. The voltammogram of bmimCl-PdCl 2 consists of a single reduction and two oxidation waves indicating that Pd 2+ undergoes a single step two-electron quasi-reversible reduction process at the working electrode. Controlled potential deposition of palladium on platinum electrode gave a black deposit, which was characterized to be metallic palladium. Extraction of palladium by Aliquat-336 has been studied as a function of nitric acid concentration and the redox behavior of palladium in Aliquat-336 phase has been investigated by cyclic voltammetry. The results suggest that some aqueous insoluble room temperature ionic liquids can act both as extractant and electrolytic medium and also have the potential of recovering of palladium from nuclear wastes.

Solvent extraction method was used to determine the stability constants of Tc(IV) with oxalate anions in NaCl solutions ranging in concentration from 0.5 M to 2.0 M. All experiments were conducted in an atmosphere-controlled chamber under Ar atmosphere (<1.0 ppm O 2 ). A reducing agent (hydrazine) was used during extractions to maintain technetium in the tetravalent oxidation state. Independent tests confirmed that the oxidation state of technetium did not change during extractions. The distribution ratio of Tc(IV) between the organic and aqueous phases was found to decrease as the concentration of oxalic acid increased. At the oxalic acid concentrations used in these experiments, the complexes TcO(Ox) and TcO(Ox) 2 2- were found to be the dominant aqueous species. Based on these data, the thermodynamic stability constants of Tc(IV) with oxalate complexes were calculated by the Specific Ion Interaction Theory (SIT).

As a clinically well established PET tracer, 6-[ 18 F]fluoro-L-dopa is prepared by a multi-step synthesis if [ 18 F]fluoride is to be used for labelling. The [ 18 F] label is introduced in the first step, i.e. 6-[ 18 F]fluoroveratraldehyde is prepared first with yields reported in the literature ranging between 20 and 50%. To obtain higher over-all yields in the synthesis of 6-[ 18 F]fluoro-L-dopa, the 18 F incorporation in the first step was optimised by determining the yield dependencies on solvent, concentration of the precursor, temperature and time of the reaction. Thus, the product is formed with a yield of 89 ± 2% ( n = 15) when using 20 mg of 6-nitroveratraldehyde in 1 mL DMF at 140 °C within a reaction time of 10 min.

Isonicotinic acid hydrazide (isoniazid) is one of the most effective agents in tuberculosis therapy. Hence it was chosen as ligand for 99m Tc labeling and imaging in the developed animal model with a gamma camera. Direct labeling of isoniazid with technetium-99m was studied. Factors affecting the radiolabeling efficiency such as amount of reducing agent, pH and time of the reaction were studied. Biodistribution of the labeled compound was performed in Sprague–Dawley rats. The localization kinetics of the radiolabeled complex was also studied in the developed animal model by injecting 100–125 MBq 99m Tc-isoniazid intravenously in the ear of rabbit and the images were taken with a gamma camera. Optimum conditions gave > 98% labeling efficiency of 99m Tc-isoniazid. Biodistribution studies in rats revealed that the maximum uptake was in kidneys (15%, 8% and 2.5% at 0.5, 4 and 24 hours, respectively), indicating renal excretion of the 99m Tc-isoniazid. High accumulation was obtained in liver (10%, 11% and 4% at 0.5, 4 and 24 hours, respectively) and significant radioactivity was also seen in the intestines (8%, 6% and 1% at 0.5, 4 and 24 hours, respectively), indicating hepatobiliary excretion of the complex. Less than 2% uptake in stomach until 24 hours confirmed good in vivo stability of the complex. 99m Tc-isoniazid initially accumulated in infective lesions of S. aureus in rabbits due to hyper-vascularity, but because of its non specificity for S. aureus the residency of 99m Tc-isoniazid was low and it showed rapid wash out from the lesion, whereas residency of tubercular lesion was high and it remained in the tubercular lesion in the delayed images also. The results suggest that 99m Tc-isoniazid is a specific agent for localization of tubercular lesions.

The sorption of > 93% of Hg(II) ions is achieved onto sunflower stem (50 mg/4.5 cm 3 ) from deionized water (D.W.) in 10 minutes equilibration time between two phases. The kinetics of sorption follows Reichenberg, Lagergren and Morris-Weber equations. The first order rate constant of sorption computed from Lagergren equation is 0.28 ± 0.01 min -1 . The sorption data obey Dubinin–Radushkevich (D–R) and Freundlich isotherms. The Freundlich sorption capacity K F = 13 ± 6 mmol g -1 , 1/ n = 0.68 ± 0.03 and D–R saturation capacity C m = (2.9 ± 0.4)×10 2 μmol g -1 , β = -0.0047 ± 0.0002 mol 2 kJ -2 and mean free energy = 10.3 ± 0.2 kJ mol -1 . The variation of sorption with temperature (293–318 K) gives Δ H = - 32 ± 2 kJ mol -1 , Δ S = 123 ± 6 J mol -1 K -1 , Δ G 298 K = - 4.30 ± 0.05 kJ mol -1 . Ascorbate, Sr(II) and Y(III) enhance the sorption whereas disufite, iodide, Cd(II), bisulfite and thiocyanate suppress the sorption. Selectivity studies indicate that Hg(II) ions can be separated from I(I) and Cs(I) using sunflower stem column. The sorbent may be used as a scavenger for the preconcentration of Hg(II) ions from its very dilute solutions or treatment of industrial and municipal effluents containing Hg(II) ions. A possible mechanism of biosorption of Hg(II) ions onto the sunflower stem is suggested.

For the assessment of air quality of two cities in Pakistan, Instrumental Neutron Activation Analysis (INAA) and Atomic Absorption Spectrometry (AAS) have been used. In all 26 elements were determined in suspended particulate matter (SPM) and soil samples. The SPM levels from different locations of Rawalpindi and Lahore indicate unhealthy to hazardous air quality much above the World Health Organization (WHO) guidelines. Metrological conditions and nature of soil that contains clay components mainly contribute to the inventory of the SPM elements of these cities. The calculated enrichment factors (EF) also indicate the dominance of the soil components. Contributions of inorganic elements due to heavy traffic with automotive exhaust and other commercial activities in this area have been identified. Areas of Qurtaba Chowk and Bank Square in Lahore in particular showed high EF for lead depicting burning of the automotive fuel and road dust. The accuracy and precision of the work has been maintained through the concurrent use of IAEA Reference Materials.

An engineering and analytical chemical program was used to evaluate a proposed process to remove plutonium from contaminated soils at the Department of Energy's Idaho National Engineering and Environmental Laboratory Site. The design was based on the premise that the chemical process would be extremely efficient, reducing up to 250 nCi/g total transuranic contamination including both plutonium, in several chemical forms, and americium to less than 10 nCi/g. To ensure the effectiveness of the process on even heat-treated forms of plutonium, a very aggressive cerium IV catalyzed hot nitric acid leach step was used. Laboratory experiments showed that the chemistry could indeed remove plutonium, but due to the secondary wastes generated by coincident dissolution of the soil matrix, the process did not meet other design requirements.

The paper presents results on determination of 90 Sr in bilberry and cowberry leaves ( Vaccinium myrtillus and Vaccinium vitis-idaea ) and the use of these plants as bio-monitors of radiostrontium contamination in Poland. Radiostrontium was determined by mean of liquid scintillation spectrometry preceded by radiochemical separation using Sr-resin and 85 Sr tracer. The approximate map of 90 Sr contamination of Poland is presented. The activity ratio between 90 Sr and obtained earlier data for 137 Cs in the same samples is discussed. The enhancement of radiostrontium content observed in northeastern Poland seems to be the trace of hot-particles fallout from initial Chernobyl cloud, which passed over Polish territory toward Scandinavia.