High Rhenium Research Articles

SORPTION EXTRACTION OF RHENIUM BY DIFFERENT IONITES FROM URANIUM SORPTION COLUMNS

This text discusses the importance of rhenium in modern science and technology, particularly its significance in various production spheres due to its properties. The purpose of this work is extracting rhenium is the mother liquors of uranium production.However, due to its low concentration in raw materials, research into more advanced extraction methods is necessary. One such method is sorption extraction of rhenium.Currently, extensive research is being conducted to obtain highly effective sorbents for rhenium. Among the most promising are ion-exchange resins such as Purolite A660/4759, Puromet MTS9300, SQD 201U, and Biolite 200U. Conditions for rhenium sorption using these resins from standard, model, and mother solutions under various acidity levels have been studied, along with conditions for desorption of this metal from the sorbents.The latter two, SQD 201U and Biolite 200U, demonstrated high efficiency. Conclusion.They exhibited high rhenium sorption results from acidic solutions, showing high selectivity in both sorption and desorption concerning rhenium. Their sorption capacity for rhenium in strongly acidic solutions exceeded 21 mg/g. When sorbing from model and mother solutions, these sorbents showed a rhenium sorption degree exceeding 60%. During desorption, the rhenium desorption degree from these sorbents using a mixture of acids reached values higher than 85%.Therefore, ion-exchange resins SQD 201U and Biolite 200U perform well in industrial solution conditions, allowing their use in extracting rhenium from uranium mother liquors.

Rhenium recovery from highly concentrated sulfuric media using AMR anionite in column mode

The paper deals with the study of rhenium recovery by AMR anionite from model high-acidic sulfuric solution as well as its desorption by ammonia solution in column experiments. Total dynamic exchange capacity was calculated. Experimental data were processed using the Thomas, Yoon-Nelson and Bed Depth Service Time models, basic parameters were calculated. It was found that total dynamic exchange capacity calculated by Thomas fit was the closest to the experimental value. Rhenium desorption was examined using ammonia solution. Rhenium recovery degree and concentration factor were calculated. The elution curve featured a clear peak that allows producing eluate with high rhenium concentration. The presented results may be used when designing technologies for rhenium sorption from different process solutions and during recycling rhenium-containing alloy wastes.

Development of 186/188Re-Chitosan as an Effective Therapeutic Agent for Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is an inflammatory chronic disease characterized by inflammation, pain, swelling and disability, and radiosynovectomy is one of the disease treatment lines. In this study, the possibility of providing rhenium-186/rhenium-188 chitosan radiopharmaceuticals, optimization of conditions for their production and bio-distribution are reported. In order to build perrhenic acid for labeling, natural rhenium was exposed to radiation. Radionuclidic and radiochemical purities of (186/188Re)-NaReO4 were examined by gamma spectroscopy and paper chromatography methods, respectively. Labeling of chitosan with rhenium was done in different acidic situations. The radiochemical purity 186/188Re-chitosan was applied by radio thin layer chromatography (RTLC). Lastly, the bio-distribution of the radiolabeled chitosan was studied in various organs after intra articular injection of the complex to lab rats. Gamma spectrometry confirmed the high rhenium radionuclidic purity. Chromatography results showed that perrhenic acid was produced with purity greater than 97% and rhenium chitosan labeling was done over 98% in pH = 3. Dissection results showed a high bio-distribution of 186/188Re-chitosan after injection into the joint with no leakage to surrounding organs. According to the results, there is a possibility of labeling rhenium with chitosan in very high radiochemical purity. Regarding the high retention of these radiopharmaceuticals in joints with no leakage to surrounding organs, 186/188Re-chitosan can be applied as new radiosynovectomy drugs for rheumatoid arthritis treatment.

Синергетическая экстракция рения (VII) смесями на основе высокомолекулярных алифатических спиртов и кетонов из сернокислых растворов.

Rhenium(VII) solvent extraction with synergistic mixtures of neutral extractants (octyl alcohols and ketones) from sulphuric acid media has been investigated. It was observed that the synergistic effect appeared under solvent extraction from high acid solutions, consisting ≥ 5 mol/L H2SO4.The synergistic coefficients were up to 2–2,3 providing 97,5–98,7% rhenium(VII) extraction efficiency at one SX step. High rhenium(VII) SX efficiency maintained in the wide range of extraction mixtures compositions (10–50 % v/v of ketone).

A 10 nm Asymmetric Graphene–Rhenium Disulfide Field‐Effect Transistor for High‐Speed Application

Field‐effect transistor devices with exfoliated 2D materials are potent in various optical and electronics applications including photodetectors, valleytronics, spintronic, circuits, memory, and optical modulators. However, these devices endure limited gate control, low carrier mobility, and high operating voltage. This study introduces a new asymmetric graphene–rhenium disulfide heterojunction Schottky barrier metal–oxide–semiconductor field‐effect transistor engineered with high graphene carrier mobility and high rhenium disulfide Ion–off ratio in a 10 nm channel‐length device. The proposed device has better gate control ability, Ion–off ratio of 106, high carrier mobility (87.44 cm2 V−1 s−1), and low subthreshold swing of 43.12 mV dec−1 in the subthreshold region at 0.05 V applied drain voltage. The significant reduction in subthreshold swing at low voltage opens a suite of high‐switching‐speed low‐powered nanologic applications for the upcoming Internet‐of‐Things era. The material properties of graphene–rhenium disulfide heterojunctions are derived using an ab initio quantum transport simulation tool.

Experimental research on the pressure oxygen leaching rhenium of waste platinum-rhenium catalyst with low acid

Experimental material was the waste platinum-rhenium catalyst; X diffraction was used to characterize the material, and the results showed that the main phase of the waste platinum-rhenium catalyst was Al2O3. The process of rhenium pressure oxygen leaching in platinum-rhenium catalyst with low acid was put forward. The effects of leaching pressure, leaching temperature, leaching time, initial acidity of sulfuric acid and liquid-solid ratio on the leaching rate of rhenium during leaching were investigated in this paper. The results showed that the initial acidity of sulfuric acid had a significant effect on the leaching rate of platinum and rhenium. As the acidity increased, the leaching rate of platinum and rhenium also increased, and the leaching rate of carrier Al2O3 also increased. The experimental results show that the leaching of the optimal process conditions were as follows: leaching pressure 5 MPa, leaching time 3h, leaching temperature 140 °C, the initial sulfuric acid concentration 10%, liquid-solid ratio 4:1, mixing speed 350 rpm. Under these conditions, the leaching rate of rhenium and platinum was 98.11% and 83.59% respectively, and the slag rate was 75.56%. In order to prevent platinum from dispersing, ferrous sulphate was added at the end of the leaching process to reduce the platinum into the leaching residue. This process has the advantages of simple operation, high rhenium leaching rate, less impurity elements in the leaching liquid and low acidity, etc., which can provide reference for rhenium extraction from the waste platinum-rhenium catalyst.

A Unique Find of Rhenium-bearing Wolframite in Ongonites of the Russian Far East

Accessory wolframite with an extraordinarily high rhenium content (2.93–3.52%) in ongonite from the Badzhal area in the Far East is described. The capacity of tungsten isomorphic substitution with rhenium in wolframite is studied. The appearance of rhenium-bearing wolframite is caused by specific conditions of the crystallization of rare-metal granite magmas.

Zircon and molybdenite geochronology and geochemistry of the Kalmakyr porphyry Cu–Au deposit, Almalyk district, Uzbekistan: Implications for mineralization processes

Copper, gold and molybdenum mineralization of the Kalmakyr porphyry deposit in Uzbek Tien Shan occurs as stockworks, veinlets and disseminations in the phyllic and K-silicate alteration zones developed predominantly in a middle to late Carboniferous intrusive complex composed of monzonite and granodiorite porphyry. Zircon U–Pb dating yielded an age of 327.2±5.6Ma for the ore-hosting monzonite and an age of 313.6±2.8Ma for the ore-bearing granodiorite porphyry. Re–Os dating of seven molybdenite samples from stockwork and veinlet ores yielded model ages from 313.2 to 306.3Ma, with two well-constrained isochron ages of 307.6±2.5Ma (five stockwork ores) and 309.1±2.2Ma (five stockwork ores and two veinlet ores), respectively. These results indicate that Cu–Au mineralization post-dated the emplacement of the monzonite, started right after the emplacement of the granodiorite porphyry, and lasted for ca. 7Ma afterward. The geochronological and geochemical data suggest that the Kalmakyr deposit was formed in a late Carboniferous mature magmatic arc setting, probably related to the latest subduction process of the Turkestan Ocean beneath the Middle Tien Shan. The εHf(t) values of zircon grains from the monzonite vary from +11 to +1.7, with an average of +5.1, and those of zircon grains from the granodiorite porphyry range from +5.7 to −1.8, with an average of +2.4. These data indicate that the magma of both monzonite and granodiorite porphyry was derived from partial melting of a thickened lower crust with input of mantle components and variable crustal contamination, and that there was more mantle contribution to the formation of the monzonite than the granodiorite porphyry. The high rhenium concentrations of molybdenite (98–899ppm) also indicate major mantle contribution of rhenium and by inference ore metals. The relatively high EuN/EuN∗ values (average 0.68), Ce4+/Ce3 values (average 890) and Ce/Nd values (average 36.8) for zircon grains from the granodiorite porphyry than those from the monzonite (average EuN/EuN∗=0.33, average Ce4+/Ce3=624, average Ce/Nd=3.9) suggest that the magma for the syn-mineralization granodiorite porphyry has higher oxygen fugacity than that for the pre-mineralization monzonite. Based on these data, it is proposed that while the monzonite was emplaced, the oxygen fugacity and volatile contents in the magma were relatively low, and ore metals might disperse in the intrusive rock, whereas when the granodiorite porphyry was emplaced, the oxygen fugacity and volatile contents in the magma were increased, favoring copper and gold enrichment in the magmatic fluids. The Kalmakyr deposit formed from a long-lived magmatic-hydrothermal system connected with fertile magmatic sources in relation to the subduction of the Turkestan Ocean beneath the Middle Tien Shan.

Genesis of the giant Zijinshan epithermal Cu-Au and Luoboling porphyry Cu–Mo deposits in the Zijinshan ore district, Fujian Province, SE China: A multi-isotope and trace element investigation

The Zijinshan ore district occurs as one of the largest porphyry-epithermal Cu–Au–Mo ore systems in South China, including the giant Zijinshan epithermal Cu–Au deposit and the large Luoboling porphyry Cu–Mo deposit. The mineralization is intimately related to Late Mesozoic large-scale tectono-magmatic and hydrothermal events. The Cu–Au–Mo mineralization occurs around intermediate-felsic volcanic rocks and hypabyssal porphyry intrusions. In this study, we summarize previously available Re–Os isotopes, zircon U–Pb age and trace elements, and Sr–Nd–Pb isotope data, and present new Pb–S and Re–Os isotope data and zircon trace elements data for ore-related granitoids from the Zijinshan high-sulfidation epithermal Cu–Au deposit and the Luoboling porphyry Cu–Mo deposit, in an attempt to explore the relationship between the two ore systems for a better understanding of their geneses. The ore-bearing porphyritic dacite from the Zijinshan deposit shows a zircon U-Pb age of 108–106Ma and has higher zircon Ce4+/Ce3+ ratios (92–1568, average 609) but lower Ti-in-zircon temperatures (588–753°C, average 666°C) when compared with the barren intrusions in the Zijinshan ore district. Relative to the Zijinshan porphyritic dacite, the ore-bearing granodiorite porphyry from the Luoboling deposit show a slightly younger zircon U–Pb age of 103Ma, but has similar or even higher zircon Ce4+/Ce3+ ratios (213–2621, average 786) and similar Ti-in-zircon temperatures (595–752°C, average 675°C). These data suggest that the ore-bearing magmatic rocks crystallized from relatively oxidized and hydrous magmas. Combined with the high rhenium contents (78.6–451ppm) of molybdenites, the Pb and S isotopic compositions of magmatic feldspars and sulfides suggest that the porphyry and ore-forming materials in the Luoboling Cu–Mo deposit mainly originated from an enriched mantle source. In contrast, the ore-bearing porphyritic dacite in the Zijinshan Cu–Au deposit might be derived from crustal materials mixing with the Cathaysia enriched mantle. The fact that the Zijinshan Cu–Au deposit and the Luoboling Cu–Mo deposit show different origin of ore-forming materials and slightly different metallogenic timing indicates that these two deposits may have been formed from two separate magmatic-hydrothermal systems. Crustal materials might provide the dominant Cu and Au in the Zijinshan epithermal deposit. Cu and Au show vertical zoning and different fertility because the gold transports at low oxygen fugacity and precipitates during the decreasing of temperature, pressure and changing of pH conditions. It is suggested that there is a large Cu–Mo potential for the deeper part of the Zijinshan epithermal Cu–Au deposit, where further deep drilling and exploration are encouraged.

Meta-study: Analysis of thermoelectric figure of merit parameters for silicides with various doping agents

Thermoelectric (TE) materials are increasingly promising for power generation in medium to high-temperature environments. Recent research on thermoelectric generators (TEGs) has determined the thermodynamic properties which impact the total efficiency and figure of merit (ZT) of these materials. A large Seebeck coefficient, high electrical conductivity and low thermal conductivity optimise ZT. This meta-study investigates silicides for potential TEG applications due to their high chemical stability and higher natural abundance than other TE materials. Data on the thermoelectric properties of CrSi2, FeSi2, Mg2Si and MnSi2, with a range of dopants, was sourced from a wide scope of literature and is analysed. The above thermodynamic properties contributing to ZT for each of these materials are graphed between 300 and 1000 K. It was found that chromium silicides are most effective at a temperature range of 600-800 K, and undoped magnesium silicides are most effective around 900 K. Oxide addition to β-FeSi2 produced relatively high ZT scores (ZT ≈ 0.5) among iron silicides. Rhenium substitution in manganese silicides produced a maximum figure of merit (1.05) at 900 K. Supersaturation via liquid quenching was determined to maintain high rhenium substitution and this technique may be the key to further improving the thermoelectric properties of other silicides.

Electrodeposition, properties, and composition of rhenium–nickel alloys

The process of deposition of the Re–Ni alloy, its current efficiency, and the alloy composition are studied as a function of the current density and the solution temperature. The hydrogen content in the deposits, their surface morphology, internal structure, and properties as the cathodic material for HER are examined. It is assumed that besides the high rhenium content, the high catalytic activity of nickel–rhenium alloys is associated with the high degree of their structural disordering.

Submersion criticality safety of tungsten-rhenium urania cermet fuel for space propulsion and power applications

Nuclear thermal rockets are the preferred propulsion technology for a manned mission to Mars, and tungsten–uranium oxide cermet fuels could provide significant performance and cost advantages for nuclear thermal rockets. A nuclear reactor intended for use in space must remain subcritical before and during launch, and must remain subcritical in launch abort scenarios where the reactor falls back to Earth and becomes submerged in terrestrial materials (including seawater, wet sand, or dry sand). Submersion increases reflection of neutrons and also thermalizes the neutron spectrum, which typically increases the reactivity of the core. This effect is typically very significant for compact, fast-spectrum reactors. This paper provides a submersion criticality safety analysis for a representative tungsten/uranium oxide fueled reactor with a range of fuel compositions. Each submersion case considers both the rhenium content in the matrix alloy and the uranium oxide volume fraction in the cermet. The inclusion of rhenium significantly improves the submersion criticality safety of the reactor. While increased uranium oxide content increases the reactivity of the core, it does not significantly affect the submersion behavior of the reactor. There is no significant difference in submersion behavior between reactors with rhenium distributed within the cermet matrix and reactors with a rhenium clad in the coolant channels. The combination of the flooding of the coolant channels in submersion scenarios and the presence of a significant amount of spectral shift absorbers (i.e. high rhenium concentration) further decreases reactivity for short reactor cores compared to longer cores.

The Three‐Dimensional Morphology of Topologically Close Packed Phases in a High Rhenium Containing Nickel Based Superalloy

The Three‐<scp>D</scp>imensional Morphology of Topologically Close Packed Phases in a High Rhenium Containing Nickel Based Superalloy

Re–Os and U–Pb geochronology of the Duobaoshan porphyry Cu–Mo–(Au) deposit, northeast China, and its geological significance

The large-scale Duobaoshan porphyry Cu–Mo–(Au) deposit is located at the north segment of the Da Hinggan Mountains, northeast China. Six molybdenite samples from the Duobaoshan deposit were selected for Re–Os isotope measurement to define the mineralization age of the deposit, yieldings a Re–Os isochron age of 475.9±7.9Ma (2σ), which is accordant with the Re–Os model ages of 476.6±6.9–480.2±6.9Ma. This age is consistent with the age of the related granodiorite porphyry, which was dated as 477.2±4Ma by zircon U–Pb analysis using LA-ICP-MS. These ages disagree with the previous K–Ar age determinations that suggest a correlation of intrusive rocks of the Duobaoshan area with the Hercynian intrusive rocks of Carboniferous–Permian age. These ages demonstrate that the Duobaoshan granodiorite porphyry and related Cu–Mo deposit occurred in the Early Ordovician. The rhenium content of molybdenite varies from 290.9 to 728.2μg/g, with an average content of 634.8μg/g. The high rhenium content in molybdenite of the Duobaoshan deposit suggests that the ore-forming materials may be mainly of mantle source.

Gaseous products of dimethylamine borane oxidation in chemically catalyzed deposition of nickel-rhenium-boron coatings

The gaseous products of the oxidation of hydride hydrogen of the dimethylamine borane (DMAB) (CH3)2NH · BH3 reducer used for depositing Ni-Re-B coatings and hydrolysis of DMAB on them were studied by mass spectrometry of the isotope composition of the gas. The oxidation level of hydride hydrogen of the DMAB reducer was found to depend on the catalytic activity of the Ni-Re-B alloy, on which heterogeneous hydrolysis takes place. For Ni-Re-B alloys with low rhenium concentrations (0–13 at %), the heterogeneous hydrolysis of DMAB proceeds with hydride hydrogen oxidation to the atomic state, as it does in the deposition of the Ni-B alloy. In contrast, at high rhenium concentrations (40–46 at %), the oxidation proceeds to the proton H+, leading to an antibatic dependence of the hydrolysis and alloy reduction rates. An analysis of the partial rates of the process and isotope composition of the evolved gas revealed two different mechanisms of the chemical-catalytic reduction of Ni-Re-B alloys at concentrations of potassium perrhenate of 0–4 and 4–16 mM in solution.

Timing of skarn deposit formation of the Tonglushan ore district, southeastern Hubei Province, Middle–Lower Yangtze River Valley metallogenic belt and its implications

The Tonglushan ore district in the Middle–Lower Yangtze River Valley metallogenic belt includes the Tonglushan Cu–Fe, the Jiguanzui Au–Cu, and the Taohuazui Au–Cu skarn deposits. They are characterized by NE-striking ore bodies and hosted at the contact of Triassic carbonate rocks and Late Mesozoic granitoid deposits. New Sensitive High-Resolution Ion Microprobe (SHRIMP) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA–ICP-MS) zircon U–Pb, molybdenite Re–Os, and phlogopite 40Ar– 39Ar ages indicate that these skarn deposits formed between 140.3 ± 1.1 and 137.3 ± 2.4 Ma. These dates are identical to the zircon U–Pb ages for host quartz diorites ranging from 140 ± 2 to 139 ± 1 Ma. These results confirm that both skarn mineralization and related intrusions were initiated during the Early Cretaceous. The high rhenium contents (261.4–1152 μg/g) of molybdenites indicate that a metasomatic mantle fluid was involved in the ore-forming process of these skarn ore systems. This conclusion is consistent with previously published constraints from sulfur, deuterium, and oxygen isotope compositions, and the geochemical signatures, and Sr–Nd isotopic data of the mineralization-hosting intrusions. Geological and geochronological evidence demonstrates that there were two igneous events in the Tonglushan ore district. The first resulted in the emplacement of quartz diorite during the Early Cretaceous (140 ± 2 to 139 ± 1 Ma), and the second is characterized by the eruption of volcanic rocks during the mid-Early Cretaceous (130 ± 2 to 124 ± 2 Ma). The former is spatially, temporally and genetically associated with skarn gold-bearing mineralization (140.3 ± 1.1 to 137.3 ± 2.4 Ma). The recognition of these two igneous events invalidates previous models that proposed continuous magmatism and associated mineral deposits in the Middle–Lower Yangtze River Valley metallogenic belt.

Rhenium distribution in molybdenite: Results of microprobe scanning (Copper Porphyry Deposits, the Urals)

The geochemistry of rhenium in ores of copper porphyry deposits from various regions has been con� sidered in numerous papers presented in the reviews (1-3 and others). We have recently systematized anal� yses for the Urals (4). Estimations of this element in different parts of separate molybdenite grains are very scarce (3, 5, 6, and others). Data on rhenium scanning in molybdenite grains are not available. However, the pattern of rhenium distribution in molybdenite grains is very important for understanding of the conditions of its precipitation and further redistribution within deposits especially those that have undergone low� temperature modifications and deformations. Patterns of rhenium distribution in separate molybdenite grains were obtained by scanning on the SX�100 microprobe at the Institute of Geology and Geochemistry, Ural Division, Russian Academy of Sciences. The diameter of the beam was 1 μm, U = 25 kV, I = 30 nA, and the detection limit of rhenium is 0.02 wt %. The standards were presented by metallic rhenium, molybdenum, and pyrite. The ReMα line was analytical. The neighboring CaK α line becomes gently sloping near the ReM α line and practically does not influence the measured rhenium concentration, but clearly fixes calcite grains (Fig. 1) because of the duration of significant exposure. Backscattered elec� tron study of the polygon and scanning using the CaK α spectral line provides evidence for the absence of cal� cite in the areas of high rhenium concentrations. In the preliminary stage of this study, rhenium concen� trations were measured in single microareas of molybdenite grains. Grains with high rhenium con� centrations were subjected to scanning. The scanning polygon was approximately limited by the contours of the molybdenite grains. The exposure time for the two samples described here was 16 and 6 h. Most copper porphyry deposits of the Urals are paragenetically controlled (7) by lowpotassium small intrusions of (gabbro)-diorite-plagiogranodiorite composition with an absolute prevalence of quartz diorite or quartz diorite porphyry related to mesoand hypabyssal depth facies ("diorite" model). The age varies from S to C2. Plagiogranitoids are hydrother� mally altered everywhere. Less serecitized and propyl� itized quartz diorites are characterized by low values of the ( 87 Sr/ 86 Sr)t ratio (from 0.7038-0.7048 to 0.7052), high eNd(T) values (4.1-7.5, in single samples decreas� ing to 0.9-2), and low TR concentrations (29- 67 ppm), without the Eu anomaly (8). These data evi� dence that orebearing granitoids contain a prevailing portion of the mantle component; they should be related to the island arc geochemical type being formed at the expense of the metabasic source in the lower crust-upper mantle or in the upper mantle. Judging from the low 87 Sr/ 86 Sr ratio (0.704-0.705) in vein carbonates, δ 18 О (7.4…8.5‰, SMOW), δD (-49…-61‰, SMOW), and δ 34 S (0 ± 2‰, CDT), CDT) in other hydrothermal minerals, the initial fluid had a magmatic nature and inherited the geochemical characteristics of orebearing granitoids. Thus, rhe� nium may also have a mantle primary source. The magmatic parameters of the fluid are also typical for many other hydrothermal deposits (9 and others). Common values of the Cu/Mo ratio in deposits of the Urals with a dioritoid substrate are 70-400, with cop� per contents of 0.3-0.8 wt %, molybdenum contents of 5-27 (up to 80 and higher) ppm, rhenium contents of up to 0.3-2 ppm (4). The concentration of rhenium in molybdenite varies significantly reaching 0.63 wt %, as is evident from our recent measurements (see below). Deposits of the "diorite" model are consid� ered to be very favorable for rhenium accumulation in ores (1 and others). However, sometimes significant rhenium concentrations (0.1-0.3 wt % and higher) are also observed in molybdenites from deposits of "monzonite" and "granodiorite" models, for which

Studies on the formation of atomic and molecular ions of uranium and thorium in thermal ionization mass spectrometry

Abstract Studies are reported on the formation of atomic (M + ) and molecular (MO + ) ions of thorium and uranium in thermal ionization mass spectrometry. The studies were performed by using different synthetic mixtures with Th/U amount ratios as 10, 1 and 0.1. The results obtained on the formation of atomic and molecular ions from these synthetic mixtures employing high purity rhenium double filament assemblies are presented. It was observed that the presence of Th on the filament during TIMS analysis of U enhances the stability of UO + ion. Further, ThO + ion is ideal for the isotopic analysis of Th by TIMS whereas U + or UO + ion may be used for the isotopic analysis of U. These studies will be extremely useful to optimize the filament heating parameters for the simultaneous/sequential isotopic analysis of Th and U by TIMS. The optimized conditions of analysis were employed for the determination of 232 U in a synthetic U sample containing traces of 232 Th.

Methyltrioxorhenium heterogenized on commercially available supporting materials as cyclooctene metathesis catalyst

Methyltrioxorhenium (MTO) is immobilized on various commercially available supporting materials by sublimation under vacuum. Up to 15 wt% MTO (10 wt% Re) can be immobilized on the different supporting materials. Metathesis experiments with cis-cyclooctene as substrate are performed aiming at a high yield of low molecular weight metathesis products (dimers, trimers, tetramers), which are interesting for aroma and flavour industries. Up to ca. 60% of these desired products can be obtained. A high rhenium loading leads usually to good catalytic activities of the materials in the cyclooctene metathesis. Prolonged reaction times lead to higher yields of the high molecular weight metathesis products. When the same catalyst material is used repeatedly in several catalytic runs, leaching of the grafted Re compounds plays an increasing role, resulting in a reduction of the catalyst performance. None of the examined commercially available carrier materials, however, presents an ideal means for the heterogenization of MTO to obtain particularly high amounts of the desired low molecular weight metathesis products of cyclooctene.

Enhanced mantle-to-crust rhenium transfer in undegassed arc magmas

Variations in the 187Os/188Os isotopic signature of mantle and mantle-derived rocks have been thought to provide a powerful chemical tracer of deep Earth structure. Many studies have inferred from such data that a long-lived, high-rhenium component exists in the deep mantle (187Re is the parent isotope decaying to 187Os, with a half-life of approximately 42 billion years), and that this reservoir probably consists of subducted oceanic crust. The interpretation of these isotopic signatures is, however, dependent on accurate estimates of rhenium and osmium concentrations in all of the main geochemical reservoirs, and the crust has generally been considered to be a minor contributor to such global budgets. In contrast, we here present observations of high rhenium concentrations and low Yb/Re ratios in arc-type melt inclusions. These results indicate strong enrichment of rhenium in undegassed arc rocks, and consequently the continental crust, which results in a crustal estimate of 2 p.p.b. rhenium, as compared to previous estimates of 0.4-0.2 p.p.b. (refs 4, 5). Previous determinations of rhenium in arc materials, which were largely measured on subaerially erupted samples, are likely to be in error owing to rhenium loss during degassing. High mantle-to-crust rhenium fluxes, as observed here, require a revaluation of geochemical models based on the 187Re-187Os decay system.