Search Results (12)

The use of rhenium-based catalysts (Re₂C, Re₃B, ReB₂, and ReS₂) obtained by mechanosynthesis in the pyrolysis of cellulose and lignin from 500 to 800 °C using 10 and 20 wt.% of catalysts is reported. The mechanosynthesis of ReS₂ has been reported for the first time. The catalytic pyrolysis of cellulose resulted in maximum H₂ production at 800 °C and 10 wt.% catalyst, with 44% H₂ yield using a Re₃B catalyst. In contrast, lignin catalytic pyrolysis also showed maximum production under the same conditions, with an 86.1% H₂ yield using the NiO/SiO₂ catalyst; however, the catalyst did not drastically enhance H₂ production. H₂ formation by cellulose pyrolysis is a thermocatalytic process, whereas lignin pyrolysis is an entirely thermic process. A reaction mechanism was proposed to explain the H₂ formation by both catalytic cellulose and lignin pyrolysis. Full article

A calc–alkaline dioritic–andesitic–dacitic intrusive–volcanic complex of Early Oligocene (30 Ma) age and its Mesozoic sedimentary basement at Recsk host a well-preserved porphyry–skarn–polymetallic carbonate-replacement–epithermal mineral system. The unique occurrence offers an exceptional possibility to study these related mineralization types at a single locality. This study presents the textural–paragenetic, compositional characteristics, and systematics of sulfide mineral assemblages for the porphyry, skarn, and carbonate-replacement ore types, which are currently situated at a depth of 500–1200 m below the present surface. Detailed petrography combined with EPMA analyses of molybdenite, galena, sphalerite, tetrahedrite-group minerals and Bi-bearing sulfosalts allows for the establishment of characteristic mineral and chemical fingerprints for each mineralization type. Rhenium concentration in molybdenite, occurring as rare disseminations and quartz–carbonate veinlets in altered host rocks in all three mineralization types, shows a decreasing trend towards the more distal mineralization types. High Re contents ($\overline{\mathrm{x}}$ = 1.04 wt.%, max. up to 4.47 wt%) are typical for molybdenite from the porphyry mineralization, but Re is not homogeneously distributed, neither within individual molybdenite crystals nor on a mineralization scale. Copper and Se show opposite behavior in molybdenite, both becoming enriched in the more distal mineralization types. Silver, Bi, and Se concentrations increase in galena and tetrahedrite-group minerals, both towards the country rocks, making them the best candidates for vectoring within the whole hydrothermal system. For tetrahedrite-group minerals, Ag, Bi, Se, together with Sb and Zn, are the suitable elements for fingerprinting; all these are significantly enriched in the distal carbonate-replacement mineralization compared to the other, more proximal ore types. Additionally, further trends can be traced within the composition of sulfosalts. Lead-bearing Bi sulfosalts preferentially occur in the polymetallic carbonate-replacement veins, while being under-represented in the skarn and porphyry mineralization. Porphyry mineralization hosts Cu-bearing Bi sulfosalts dominantly, while skarn is characterized by Bi-dominated sulfosalts. Sphalerite, although present in all mineralization types, cannot be used for fingerprinting, vectoring, or thermobarometry based on EPMA measurements only. Trace element contents of sphalerite are low, often below the detection limits of the analyses. This is further complicated by the intense “chalcopyrite disease” occurring throughout the distal mineralization types. All the above-listed major, minor, and trace element ore mineral characteristics enable the characterization of the Recsk ores by mineral geochemical fingerprints, providing a possible vectoring tool in porphyry Cu–(Mo)–Au-mineralized systems. Full article

Rhenium (Re) is an extremely rare element, with a crustal abundance of approximately 0.4 parts per billion (ppb) and a sea water concentration of 8.3 parts per trillion (ppt). However, Re concentrations in anoxic marine sediments range from 2 to 184 ppb, which is attributed to reduction of the highly soluble perrhenate ion (Re(VII)O₄⁻) to insoluble Re(IV) species. Anoxic sediments typically contain Fe(II) and sulfide species, which could potentially reduce Re(VII) to Re(IV). In this study, we examined the interactions of KReO₄ with magnetite (Fe₃O₄), siderite (FeCO₃), vivianite (Fe₃(PO₄)₂•8H₂O), green rust (mixed Fe(II)/Fe(III) layered double hydroxide), mackinawite (FeS), and chemically reduced nontronite (NAu-1) using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to determine the valence state and speciation of Re. Uptake of Re by green rust was rapid, with ~50% associated with the solids within 2 days. In contrast, there was <10% uptake by the other Fe(II) phases over 48 days. Reduction of Re(VII) to Re(IV) was only observed in the presence of green rust, producing clusters of bidentate-coordinated Re(IV)O₆ octahedra.. These results suggest that except for green rust, the potential for other Fe(II)-bearing minerals to act as reductants for ReO₄⁻ in sedimentary environments requires further investigation. Full article

Rhenium is an extremely rare critical metal element in Earth’s continental crust. Owing to its extremely high melting point and heat-stable crystalline structure, rhenium is an essential component of alloy materials used in high-performance aircraft engines. Demand for rhenium resources is therefore growing. Currently, most rhenium is produced as a byproduct of molybdenum mining in porphyry copper–molybdenum deposits. Research has therefore focused on the enrichment characteristics of rhenium in this type of deposit, with little attention paid to rhenium in other types of deposits. This study reports the occurrence state and enrichment mechanism of rhenium in the Qianjiadian sandstone-type uranium deposit in the Songliao Basin, Northeast China. Sequential extraction revealed that the average proportions of different forms of rhenium are as follows: water-soluble (57.86%) > organic-sulfide-bound (13.11%) > residual (12.26%) > Fe/Mn oxide-bound (10.67%) > carbonate-bound (6.10%). Combining mineralogical analysis techniques such as SEM-EDS, EMPA, and XRD, it has been established that rhenium does not occur as a substitute in sulfides (e.g., molybdenite) or uranium minerals in various types of deposits. Instead, it is mainly adsorbed onto clay minerals and Fe-Ti oxides, and in a small number of other minerals (pyrite, organic matter, and pitchblende). Rhenium is similar to redox-sensitive elements such as uranium and vanadium, and it is transported in a water-soluble form by oxidizing groundwater to the redox transition zone for enrichment. However, unlike uranium, which generally forms as uranium minerals, rhenium is mainly adsorbed and enriched onto clay minerals (kaolinite and interlayered illite–smectite). Most of the rhenium in sandstone-type uranium deposits occurs in an ion-adsorption state, and is easily leached and extracted during in-situ leaching mining of uranium ores. This type of deposit demonstrates excellent production potential and will become a crucial recoverable resource for future rhenium supply. Full article

Modern trends in technological improvement for producing high-quality rhenium-containing molybdenum concentrates are aimed at developing environmentally friendly solutions com-pared to traditional ones, involving a reduction in consumption or complete replacement of toxic substances and the use of plant reagents and microorganisms and make it possible to eliminate energy-intensive processes of steaming and roasting. It is known that up to 25%–30% of Mo, Cu and Re goes to rough flotation tailings and is lost in wastes. Those losses are a consequence of the ore composition variability, chalcopyrite–molybdenite ratio, an increase in the proportion between primary copper sulfide and finely disseminated molybdenite and the recovery of floating pyrite. High rates of valuable metal recovery into bulk concentrate can be achieved by using new compositions of flotation reagents that selectively change the hydrophobic properties of the target minerals. The application of new reagent compositions, including novel chemicals—dithiopyrylmethane (DTM), composite reagent (CR) and conventional butyl xanthate (ButX)—was theoretically and experimentally substantiated for the effective rhenium extraction in the processing of hard-to-beneficiate complex molybdenum ores. It is identified that DTM forms a complex DTM–Re compound and chemically adsorbed on rhenium-containing molybdenite providing an increase in Re recovery into the bulk Cu–Mo–Re concentrate by 17%, reducing by two times the loss of rhenium with flotation tailings, and the subsequent 97.6% Re extraction of the molybdenum concentrate by autoclave leaching. Full article

One of the urgent tasks of modern materials science is the search for new materials with improved optoelectronic properties for various applications of optoelectronics and photovoltaics. In this paper, using ab initio methods, we investigate the possibility of forming new types of van der Waals heterostructures based on monolayers of triangulated borophene, and monolayers of rhenium sulfide (ReS), and rhenium selenide (ReSe₂)_, and predict their optoelectronic properties. Energy stable atomic configurations of borophene/ReS₂ and borophene/ReSe₂ van der Waals heterostructures were obtained using density functional theory (DFT) calculations in the Siesta software package. The results of calculating the density of electronic states of the obtained supercells showed that the proposed types of heterostructures are characterized by a metallic type of conductivity. Based on the calculated optical absorption and photocurrent spectra in the wavelength range of 200 to 2000 nm, it is found that borophene/ReS₂ and borophene/ReSe₂ heterostructures demonstrate a high absorption coefficient in the near- and far-UV(ultraviolet) ranges, as well as the presence of high-intensity photocurrent peaks in the visible range of electromagnetic radiation. Based on the obtained data of ab initio calculations, it is predicted that the proposed borophene/ReS₂ and borophene/ReSe₂ heterostructures can be promising materials for UV detectors and photosensitive materials for generating charge carriers upon absorption of light. Full article

The reaction of the K₄[{Re₆Sⁱ₈}(OH)^a₆]·8H₂O rhenium cluster salt with pyrazine (Pz) in aqueous solutions of alkaline or alkaline earth salts at 4 °C or at room temperature leads to apical ligand exchange and to the formation of five new compounds: [trans-{Re₆Sⁱ₈}(Pz)^a₂(OH)^a₂(H₂O)^a₂] (1), [cis-{Re₆Sⁱ₈}(Pz)^a₂(OH)^a₂(H₂O)^a₂] (2), (NO₃)[cis-{Re₆Sⁱ₈}(Pz)^a₂(OH)^a(H₂O)^a₃](Pz)·3H₂O (3), [Mg(H₂O)₆]_0.5[cis-{Re₆Sⁱ₈}(Pz)^a₂(OH)^a₃(H₂O)^a]·8.5H₂O (4), and K[cis-{Re₆Sⁱ₈}(Pz)^a₂(OH)^a₃(H₂O)^a]·8H₂O (5). Their crystal structures are built up from trans- or cis-[{Re₆Sⁱ₈}(Pz)^a₂(OH)^a_4−x(H₂O)^a_x]^x−2 cluster units. The cohesions of the 3D supramolecular frameworks are based on stacking and H bonding, as well as on H₃O₂₋bridges in the cases of (1), (2), (4), and (5) compounds, while (3) is built from stacking and H bonding only. This evidences that the nature of the synthons governing the cluster unit assembly is dependent on the hydration rate of the unit. Full article

Laser ablation MC-ICP-MS was used to measure the Os-isotope compositions of single sulfide grains, including laurite (RuS₂) and pentlandite [(Fe,Ni)₉S₈], from two chromitite bodies and host lherzolites from ophiolites of North Andaman (Indo-Burma-Sumatra subduction zone). The results show isotopic heterogeneity in both laurite (n = 24) and pentlandite (n = 37), similar to that observed in other chromitites and peridotites from the mantle sections of ophiolites. Rhenium-depletion model ages (T_RD) of laurite and pentlandite reveal episodes of mantle magmatism and/or metasomatism in the Andaman mantle predating the formation of the ophiolite (and the host chromitites), mainly at ≈0.5, 1.2, 1.8, 2.1 and 2.5 Ga. These ages match well with the main tectonothermal events that are documented in the continental crustal rocks of South India, suggesting that the Andaman mantle (or its protolith) had a volume of lithospheric mantle once underlaying this southern Indian continental crust. As observed in other oceanic lithospheres, blocks of ancient subcontinental lithospheric mantle (SCLM) could have contributed to the development of the subduction-related Andaman–Java volcanic arc. Major- and trace-element compositions of chromite indicate crystallization from melts akin to high-Mg IAT and boninites during the initial stages of development of this intra-oceanic subduction system. Full article

Re sulfides were discovered in Cu–Ni–platinum-group elements (PGE) ores of the Zhelos and Tokty-Oi intrusions. These intrusions can be considered as products of the mantle superplume responsible for Rodinia’s break-up. The mineral compositions were determined in situ in polished samples. Electron microprobe analyses were mostly consistent with a general formula of (Cu,Fe,Mo,Os,Re)₅S₈, (Cu,Fe,Mo,Os,Re)₄S₇, and (Cu,Fe,Mo,Re)S₂. One of the major features of Re sulfide from the Zhelos intrusion is its high osmium content. The ΣMe/S ratio for a part of our data is consistent with that of the tarkianite. Re sulfides from the Tokty-Oi have a ΣMe/S ratio similar to those in rheniite or dzeskazganite, but differ from them by the presence of Fe and Cu and the metal-to-metal ratio. The localization of the Re sulfide within the chalcopyrite suggests its crystallization from the residual Cu-rich liquid. Full article

We report an excellent growth behavior of a high-κ dielectric on ReS₂, a two-dimensional (2D) transition metal dichalcogenide (TMD). The atomic layer deposition (ALD) of an Al₂O₃ thin film on the UV-Ozone pretreated surface of ReS₂ yields a pinhole free and conformal growth. In-situ half-cycle X-ray photoelectron spectroscopy (XPS) was used to monitor the interfacial chemistry and ex-situ atomic force microscopy (AFM) was used to evaluate the surface morphology. A significant enhancement in the uniformity of the Al₂O₃ thin film was deposited via plasma-enhanced atomic layer deposition (PEALD), while pinhole free Al₂O₃ was achieved using a UV-Ozone pretreatment. The ReS₂ substrate stays intact during all different experiments and processes without any formation of the Re oxide. This work demonstrates that a combination of the ALD process and the formation of weak S–O bonds presents an effective route for a uniform and conformal high-κ dielectric for advanced devices based on 2D materials. Full article

Porphyry copper–molybdenum deposits (PCDs) are the world’s most important source of copper, molybdenum and rhenium. Previous studies have reported that some PCDs can have sub-economic to economic grades of critical metals, i.e., those elements that are both essential for modern societies and subject to the risk of supply restriction (e.g., platinum group elements (PGE), rare earth elements (REE), In, Co, Te, Ge, Ga, among others). Even though some studies have reported measured concentrations of Pd and Pt in PCDs, their occurrence and mineralogical forms remain poorly constrained. Furthermore, these reconnaissance studies have focused predominantly on porphyry Cu–Au deposits, but very limited information is available for porphyry Cu–Mo systems. In this contribution, we report the occurrence of critical metal (Pd, Pt, Au, Ag, and Te) inclusions in copper sulfides from one of the largest PCDs in the world, the supergiant Río Blanco-Los Bronces deposit in central Chile. Field emission scanning electron microscope (FESEM) observations of chalcopyrite and bornite from the potassic alteration zone reveal the presence of micro- to nano-sized particles (<1–10 μm) containing noble metals, most notably Pd, Au, and Ag. The mineralogical data show that these inclusions are mostly tellurides, such as merenskyite ((Pd, Pt) (Bi, Te)₂), Pd-rich hessite (Ag₂Te), sylvanite ((Ag,Au)Te₂) and petzite (Ag₃AuTe₂). The data point to Pd (and probably Pt) partitioning in copper sulfides during the high-temperature potassic alteration stage, opening new avenues of research aimed at investigating not only the mobility of PGE during mineralization and partitioning into sulfides, but also at exploring the occurrence of critical metals in porphyry Cu–Mo deposits. Full article

Single-layer, ultrasmall ReS₂ nanoplates embedded in amorphous carbon were synthesized from a hydrothermal treatment involving ammonium perrhenate, thiourea, tetraoctylammonium bromide, and further annealing. The rhenium disulfide, obtained as a low dimensional carbon composite (ReS₂/C), was tested in the hydrodesulfurization of light hydrocarbons, using 3-methylthiophene as the model molecule, and showed enhanced catalytic activity in comparison with a sulfide CoMo/γ-Al₂O₃ catalyst. The ReS₂/C composite was characterized by X-ray diffraction (XRD), Raman spectroscopy, N₂ adsorption–desorption isotherms, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The improved catalytic performance of this ReS₂/C composite may be ascribed to the presence of a non-stoichiometric sulfur species (ReS_2−x), the absence of stacking along the c-axis, and the ultra-small basal planes, which offer a higher proportion of structural sulfur defects at the edge of the layers, known as a critical parameter for hydrodesulfurization catalytic processes. Full article