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Abstract  

The study concerns the extraction of tungstate from solutions containing sulphuric acid within a broad range of pH using Primene JMT sulphate in benzene modified with octanol as an extractant. On the basis of the equilibrium composition of both phases, by the determination of metal and sulphate groups concentrations, pH and IR spectrum of the organic phase, it was confirmed that Primene JMT enables the extraction of monomeric and polymeric forms of tungsten anionic species in a broad range of pH (2–7.5). The process is similar to that of the extraction of V(V) and Mo(VI), an anion exchange mechanism and a mechanism probably involving an addition can be distinguished.

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Abstract  

Two distinct analytical methods have been described for analysis of W in tungsten ores. For the proposed study, thick and thin samples were analyzed by using X-ray fluorescence technique with great accuracy. Standard comparison method is based on the measurement of K line for tungsten. Also, W has been determined in similar ore samples by neutron activation analysis followed by X-ray spectrometry employing a238Pu-Be neutron source. The measured Re K-X rays are emitted in internal conversion of137W produced during thermal neutron activation.

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Nano Ni–W catalysts with different tungsten contents prepared by mixing alkaline nickel carbonate with ammonium tungstate show high activity and good sulfur tolerance for hydrogenation of thiophene-containing ethylbenzene. The catalysts were characterized by XRD, TPR, SEM, Raman and BET. The results show that the activity of the catalysts for ethylbenzene hydrogenation is affected profoundly by W loading and the best result was obtained on catalyst with W/Ni ratio equal to 0.16. The increase of activity of the catalyst can be attributed to the interaction between Ni and W doped and the increase of the surface area of the catalyst.

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Abstract  

5-(4-Pyridyl)nonane has been evaluated as a solvent for trace amounts (<5·10–5 M) of tungsten(VI) from aqueous chloride-thiocyanate solutions. Remarkable enhancements in metal extractability are observed on the addition of SCN to aqueous hydrochloric acid solutions. Extremal partition coefficients are obtained from 0.1 M HCl in 0.2 M KSCN. Diminutions of the metal extractability are produced by relatively high (>0.5 M) SCN concentrations and increased concentration of the supporting acid. Slope analysis data, under optimal parameters, indicates the most probable composition of the extractable species as WO2(SCN)2·2PYN. Neutral anions do not have any significant effect on the D values. Behaviour of a number of metal ions has been checked using optimal aqueous conditions of extraction. The investigation shows that the reagent has a great potential for the preconcentration of a number of metal ions including the common toxins.

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Abstract  

A non-destructive activation analytical method developed for the determination of the axial concentration distributions of Al, Si and K residual additives in sintered tungsten rods is briefly described. A 14 MeV neutron generator is used to produce the reactions27Al(n, p)27Mg,28Si(n, p)28Al and39K(n, 2n)38K and the activities are compared with standards. A weighted least-squares fitting program is used for peak area determination of the scintillation spectra. A scheme of the irradiating and measuring arrangement with a pneumatic sample-transfer system is presented. The system is applicable to large-scale routine analysis and lends itself well to automation. The results of preliminary measurements with this arrangement are given.

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Abstract  

The effect of pH on the percent extraction of vanadium(V), iron(II), cobalt(II), nickel(II), copper(II), molybdenum(VI), tungsten(VI) and uranium(VI) by -benzoinoxime in different solvents has been studied. The maximum recovery is not appreciably affected by the nature of the solvent, but occurs at different pH values for different metals. The pH corresponding to maximum extraction increases with increasing hydrolysis pK of the species in aqueous solution, and decreases with increasing stability constant of the complexes formed. Alpha-benzoinoxime allows the separation of these metal ions into three groups: V(V), Mo(VI) and W(VI) are extracted at pH=2, U(VI) at pH=5, Fe(II), Cu(II), Co(II) and Ni(II) at around pH=10.

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This paper discusses the changes in the structure and thermal reduction of nanosize hexagonal ammonium tungsten bronze (HATB), (NH4)0.33−xWO3−y, which were caused by K+ ion exchange (doping) and studied by XRD, XPS, 1H-MAS NMR, FTIR, SEM and TG/DTA-MS. Comparison of the cell parameters of undoped and doped HATB revealed that both a and c cell parameters decreased after the ion exchange reaction, which showed that smaller K+ ions partly replaced the larger NH4 + ions in the hexagonal channels of HATB. After the reaction, from the hexagonal channels less NH3 evolved, which also supported the incorporation of K+ ions into the hexagonal channels.

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Abstract  

A radiochemical separation procedure has been developed to determine traces of uranium in tungsten and molybdenum. In this procedure the fission product140Ba, as indicator nuclide for uranium, is selectively separated from the matrix activities and from all other long-lived activation and fission products and obtained at high purity. The radionuclide in the final fraction is sufficiently pure so that it can be measured with high counting efficiency by -counting. The separation procedure consists of two steps: a cation-exchange separation to separate barium from the anionic matrix tungste or molybdate, and many other elements. In the second step the Ba-fraction is further purified by precipitation of barium as barium chloride in 8M hydrochloric acid. The precipitate is then dissolved in water for -counting via the Cerenkov effect. The chemical yield for barium is 94.6±2.6%. When samples of 0.1 g, a thermal neutron flux of 2·1013 n·cm–2·s–1, an irradiation time of 10 hours and a measuring time of 2 hours were applied, then the detection limit of uranium was 4 ng/g.

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Abstract  

A new method for the simultaneous determination of molybdenum and tungsten in biological materials by neutron activation analysis has been developed. It involves a single step radiochemical separation of both elements by extraction chromatography using -benzoinoxime supported on Bio-Beads SM 2. Good accuracy and precision of the method was demonstrated analyzing Bowen's Kale and IAEA's H-8 /Horse Kidney/ reference materials. The method was applied to check the reliability of the results obtained by one standard and one newly developed spectrophotometric methods for the molybdenum content in some plant materials.

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Abstract  

Adsorption of carrier-free radiotracers 181W and 93mMo produced in the 181Ta(p, n) and natNb(p, n) reactions, respectively, on anion-exchange resin was studied in mixed solution of HF and HNO3 in a concentration range of 10−4–10−1 M HF/0.1 M HNO3. Distribution coefficients (K d) of 181W and 93mMo at 70 °C showed the V-shaped variation with the minimum at around 10−1 M HF/0.1 M HNO3, although variation of the K d values for 93mMo was quite small compared with that for 181W. Formation of oxofluoro complexes for W and Mo is briefly discussed.

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