Determination of rhenium in molybdenite by neutron-activation analysis

A neutron-activation method is described for the determination of rhenium in molybdenite. Radiochemical separation by a carrier technique was carried out very rapidly by means of successive liquid-liquid extraction processes. The recovery of rhenium, which was determined by a spectrophotometric method, was about 93%. About 10 samples could be analysed within 6 hr in parallel runs.     

Substoichiometric determination of manganese by neutron-activation analysis

A simple and rapid method for the substoichiometric determination of traces of manganese in various materials by neutron-activation analysis has been developed. After dissolution of the irradiated test sample, manganese(II) carrier is added and subsequently oxidised by peroxodisulphate to the heptavalent state. The permanganate thus formed is finally extracted into chloroform as tetraphenylarsonium permanganate using a substoichiometric amount of tetraphenylarsonium chloride. This single separation step isolates radiochemically pure manganese-56 in the analysis of a relatively simple material in which interfering elements (gold, rhenium, etc.) are absent. When this is not true, a preliminary separation of manganese from the irradiated sample, based on the extraction of manganese diethyldithio-carbamate into chloroform and followed by stripping of the manganese with dilute sulphuric acid, must be used. A simultaneously irradiated standard containing manganese must be treated in exactly the same way as a test sample. In the materials analysed by the new method 10(-5) to 10(-3)% of manganese has been determined.     

Determination of arsenic and antimony in biological materials by solvent extraction and neutron activation

Arsenic and antimony in digested biological samples can be extracted with pyrrolidinecarbodithioate at pH 1 into chloroform and stripped with nitric acid for neutron-activation analysis (NAA). The extraction method eliminates interferences from matrix species, including Br and Na, making the accurate determination of low levels of As and Sb in biological materials feasible. The detection limits under the experimental conditions used are 0.005 and 0.006 mug/g for arsenic and antimony, respectively. A comparison of the results obtained for As and Sb in NBS biological standards by this method and by non-destructive instrumental neutron-activation analysis (INAA) is also given.     

Neutron activation determination of rheumium in rocks and ores after preliminary extraction with pyridine

A simple neutron-activation method for the determination of rhenium based on a preliminary extractive separation of the latter from molybdenum and tungsten is described. The sample is decomposed with sodium peroxide, a small amount of water is added and the resulting pulp is extracted with pyridine. The extract is evaporated to dryness, the residue is dissolved in water and the solution is passed through a column packed with Dowex 50WX8 in H⁺ form to eliminate the metal impurities. The HReO₄ passed, after neutralization with ammonia, is evaporated to dryness in penals, which then are irradiated with thermal neutrons.     

Substoichiometric separation in activation analysis: extraction of co-ordinatively-unsolvated salts

The necessary conditions have been examined for the use of extraction of coordinatively-unsolvated salts for substoichiometric separations in activation analysis, especially the influence of interfering ions and of the concentration of the carrier. A study has been made of the substoichiometric extraction of halide ions, oxyanions and anionic metal complexes by means of the tetraphenylarsonium ion into chloroform and dichloroethane, and of the extraction of alkali metal ions into nitrobenzene with tetraphenylborate. Substoichiometric extraction can be combined with neutron-activation analysis for the determination of traces of iodine, caesium, rubidium, manganese, rhenium, chromium, thallium, gold, gallium and tantalum.     

Instrumental neutron-activation determination of phosphorus in biological materials by bremsstrahlung measurement

The determination of phosphorus in biological materials by instrumental neutron-activation analysis by the reaction (31)P (n, lambda)(32)p is described. The bremsstrahlung produced by (32)P is measured in a well-type NaI(T1) detector. The samples are measured in the polyethylene irradiation container with no additional handling between irradiation and measurement. The sources of error have been studied and the proposed method has been applied to the determination of phosphorus in ten internationally cerfified materials.     

Recovery of rhenium from sulfuric acid solutions with activated coals

Equilibrium and kinetic characteristics of rhenium sorption from sulfuric acid solutions (pH 2) by activated coals produced from coal raw materials (China) were studied. Constants of the Henry equation describing isotherms of rhenium sorption by activated coals were calculated. The effective diffusion coefficients of rhenium in the coals were determined. The dynamic characteristics of rhenium sorption and desorption were determined for the activated coal with the best capacity and kinetic characteristics.     

Standard Reference Materials® (SRMs) for measurement of inorganic environmental contaminants

NIST has developed an extensive collection of environmental SRMs, starting with fuel and biologically related materials in the late 1960s and now encompassing all sectors of environmental research. Advances in analytical methodology, including multi-element isotope-dilution mass spectrometry (IDMS) and expanded instrumental neutron-activation analysis (INAA) capabilities, enable value assignment based on fewer but better-characterized independent analytical techniques. The special advantages of IDMS for determination of S and Hg and for multi-element characterization of small-sample air particulate matter (SRM 2783) by IDMS and INAA are emphasized. Developments in materials production include the issuance of fresh-frozen biological materials and of jet-milled natural-matrix materials with improved homogeneity, including highly homogeneous air particulate matter and sediment SRMs for small-sample analytical techniques.     

Recent advances of rhenium separation and enrichment in China: Industrial processes and laboratory trials

The recent progresses in the separation and enrichment of rhenium were reviewed in this paper, especially, the advances in China.     

Rhenium oxohalides: synthesis and crystal structures of ReO3Cl(THF)2, ReOCl4(THF), Re2O3Cl6(THF)2, and Re2O3Cl6(H2O)2

Convenient methods to prepare solvated rhenium oxochlorides are described; these compounds should serve as useful starting materials for rhenium chemistry. Treatment of perrhenic acid, HReO(4), with chlorotrimethylsilane or with thionyl chloride, followed by addition of tetrahydrofuran, forms the new oxochloride complexes ReO(3)Cl(THF)(2) and ReOCl(4)(THF), respectively. Small amounts of two dinuclear oxochlorides, which evidently resulted from adventitious hydrolysis, were also isolated: Re(2)O(3)Cl(6)L(2), where L = THF or H(2)O. All four compounds were characterized by X-ray crystallography. The rhenium(vii) complex ReO(3)Cl(THF)(2) adopts a distorted octahedral geometry in which the three oxo ligands are in a facial arrangement; the rhenium(vi) complex ReOCl(4)(THF) adopts a trans octahedral structure. The two dinuclear rhenium(vi) compounds both have a single, nearly linear, bridging oxo group; on each Re center, the three terminal chlorides adopt a mer arrangement, and the terminal oxo and the coordinated Lewis base are mutually trans. The water ligand in the aqua complex is hydrogen bonded to nearby THF molecules. IR data are given.     

Determination of rhenium in plant materials

Methods for rhenium extraction from plant materials were studied using model systems and the ¹⁸⁶Re isotope. Conditions are described for the quantitative extraction of rhenium with acid and alkali solutions from plant ash and with ethanol and salt solutions from fresh green matter. Procedures for the analysis of real plant materials based on a combination of rhenium extraction with high-sensitive methods of its determination (catalytic, neutron activation, and solid-phase spectroscopy) were developed. Laboratory and field versions of the method are proposed. Analytical results for plant samples taken in different regions are presented.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 97–103.Original Russian Text Copyright © 2005 by Borisova, Demin, Gatinskaya, Ermakov, Ryabukhin, Bozhkov.     

Field determination of rhenium in plants using catalytic test methods with dimethyldithiooxamide and Sulfonitrazo P

Methods for the field determination of rhenium in plants have been developed. The speciation of rhenium in solutions throughout the process of sample preparation has been investigated. It has been shown that, in the initial ethanol and water-salt extracts, rhenium occurs as perrhenate ions. Perrhenate ions have been established to be partially reduced in time to give Re(VI). Since test methods have been developed for determining rhenium as perrhenate-ions, their partial reduction in the process of sample preparation can lead to an low level of the results. The optimal conditions for preserving rhenium as perrhenate ions have been determined. Two procedures (in four versions) providing the determination of as low as 5 ng of rhenium in a 1-g sample with an error below 23% have been proposed. The developed procedures have been applied in the places of the collection of plant materials for the regional investigation of the occurrence of rhenium in the territories of different ore contents.     

Electrochemical deposition and characterization of mixed-valent rhenium oxide films prepared from a perrhenate solution

Cathodic electrodeposition of mixed-valent rhenium oxides at indium tin oxide, gold, rhenium, and glassy carbon electrodes from acidic perrhenate solutions (pH = 1.5 +/- 0.1) prepared from hydrogen peroxide and zerovalent rhenium metal is described. Cyclic voltammetry, variable angle spectroscopic ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), UV-vis spectroelectrochemistry, and electrochemical quartz crystal microbalance (EQCM) data indicate that the chemical nature of the electrodeposited rhenium species depends mainly upon the potential and supporting electrolyte. The presence of SO4(2-) as a supporting electrolyte inhibits the adsorption of perrhenate, ReO4-, at non-hydrogen adsorbing electrode materials. However, in acidic perrhenate solutions containing only protons and ReO4- anions, strong adsorption of ReO4- at potentials preceding hydrogen evolution occurs. This leads to the formation of an unstable ReIII2O3 intermediate which catalytically disproportionates to form mixed-valent rhenium films consisting of 72% ReIVO2 and 28% Re0. During the hydrogen evolution reaction (HER), hydrogen polarization causes the principle deposit to be more reduced, consisting of roughly 64% ReIVO2 and 36% Re0. Conclusively, metallic rhenium can be deposited at potentials preceding the HER at non-hydrogen adsorbing electrode materials, especially in the absence of SO4(2-) anions.     

Determination of technetium-99 in environmental material with rhenium as a yield monitor

The ability of the close analogue element rhenium to act as a satisfactory non-isotopic yield monitor for the analysis of⁹⁹Tc in environmental materials is explored and its performance critically evaluated in a new radioanalytical method designed specifically for use with rhenium as both carrier and yield monitor. The advantages and limitations of rhenium for this purpose are compared with isotopic tracers such as^99mTc,^97mTc and^95mTc. When employed in a well designed analytical scheme, rhenium, which has received only limited consideration in the past, is shown to be a cheap, reliable alternative to isotopic tracers.     

Determination of aluminium in aerosols by flameless atomic-absorption spectrometry

A method is reported for the determination of aluminium in aerosols collected on Whatman 41 cellulose filters. In the destruction procedure, provision was made to eliminate silica by hydrofluoric acid treatment. Analysis of the solutions was performed by the flameless atomic-absorption technique. The accuracy was checked by using data from instrumental neutron-activation analysis (INAA) and standard reference materials. An analogue integrator gave a better linearity and detection limit than conventional peak-reading.     

Rhenium alkoxides

The data on synthesis of individual and heterometallic alkoxide and oxoalkoxide derivatives of rhenium are summarized. Their structures are considered, characteristic features and peculiarities of the structures are analyzed. Data on the thermal decomposition of rhenium alkoxides and its application for the preparation of rhenium-based metallic and oxide materials are given. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2177–2188, October, 2005.     

Semipermeable ion-exchange membranes as a preconcentration matrix for trace analysis by electrochemical and neutron-activation techniques

Ion-exchange membranes were used in conjunction with neutron-activation analysis and anodic stripping voltammetry for the determination of certain trace metal ions. The various parameters which govern the applicability, limitations and sensitivity of the methods were investigated. A new membrane "barrier" electrode assembly was introduced and found to be useful for the anodic stripping determination of trace metal ions in the presence of surface active materials.     

Separation studies of molybdenum(VI) and rhenium(VII) using TPPO as an extractant

A simple, rapid and reproducible method for the extractive separation of molybdenum(VI) and rhenium(VII) is proposed using triphenylphosphine oxide (TPPO) dissolved in toluene as an extractant. The extractions are carried out from the hydrochloric and hydrobromic acid medium. The extraction of molybdenum is quantitative from 2.54-3.10 M hydrochloric acid and from 3.76-3.98 M hydrobromic acid, and that of rhenium is from 6.78-7.91 M hydrochloric acid. The probable nature of the extractable species is established using log distribution ratio-log concentration plots. The method permits mutual separation of molybdenum(VI) and rhenium(VII) and is applicable for the analysis of alloys and pharmaceutical sample. The detection limits for molybdenum(VI) and rhenium(VII) are 0.8 ppm and 4 ppm respectively.     

Preparation and characterization of a set of IAEA reference air filters for quality control in air-pollution studies

Several sets of reference air filters were prepared as part of an IAEA evaluation of the performance of laboratories involved in air-pollution studies. Each set comprised three polycarbonate membrane filters, two of which were loaded with urban air particulate matter (APM) obtained in Vienna or Prague, and one unloaded filter. The filters were loaded by filtration of a suspension of the APM materials in water. The homogeneity both of bulk APM materials and of the loaded filters was evaluated and found suitable by determining several elements by instrumental neutron-activation analysis (INAA), proton-induced X-ray emission (PIXE), and micro-X-ray energy-dispersive fluorescence analysis (micro-EDXRF). After evaluation of the homogeneity, INAA, PIXE, EDXRF, atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES), and ICP mass spectrometry (ICP-MS) were used to characterize the filter materials and establish "target values" and their associated standard deviations for 15 elements. Problems encountered during the preparation of these unique, simulated air filters and the criteria for setting both the target values and standard deviations are presented.     

Application of Silica Chemically Modified by Sulfur-Containing Groups to the Separation and Determination of Platinum and Rhenium in Catalysts Based on Aluminum Oxide

Adsorbents based on silica chemically modified by sulfur-containing groups (dithiocarbamate, thiodiazolethiol, mercaptophenyl, and aminobenzothiazole) quantitatively extract (recovery ≥99%) platinum( IV) from solutions ranging from 4 M HCl to pH 6. Under the conditions of the adsorption separation of platinum(IV), rhenium(VII) is not extracted and remains in the solution. The subsequent quantitative (98–99%) adsorption of rhenium(VII) is achieved in the presence of a 1000-fold excess of tin(II) chloride. Adsorption on the surface of adsorbents leads to the formation of platinum(II) complexes with sulfur-containing groups, luminescent at 77 K on irradiation with UV light. The luminescence spectra of surface platinum( II) complexes are located in the region of 550–700 nm. In the adsorption of rhenium(III) in the presence of tin(II) chloride, intensely colored brown complexes of rhenium formed on the surface of adsorbents. Electron paramagnetic resonance showed that, in the surface complexes, rhenium is in the oxidation state 2+. Silicas chemically modified by sulfur-containing groups were used in the development of procedures for the sequential isolation and determination of platinum and rhenium in solutions after the decomposition of aluminum–platinum–rhenium catalysts.