Molybdenite as a rhenium carrier : first results of a spectroscopic approach using synchrotron radiation

The chemical and physical properties of rhenium render it a highly demanded metal for advanced applications in important industrial fields. This very scarce element occurs mainly in ores of porphyry copper-molybdenum deposits associated with the mineral molybdenite, MoS2, but it has also been found in granite pegmatites and quartz veins as well as in volcanic gases. Molybdenite is a typical polytype mineral which crystal structure is based on the stacking of [S-Mo-S] with molybdenum in prismatic coordination by sulphide anions; however, it is not yet clearly established if rhenium ions replace Mo4+ cations in a disordered way or else, if such replacement gives rise to dispersed nanodomains of a rhenium-rich phase. As a contribution to clarify this question, an X-ray absorption spectroscopy (XANES) study using synchrotron radiation was performed at the Re L3-edge of rhenium-containing molybdenite samples. Obtained results are described and discussed supporting the generally accepted structural perspective that rhenium is mainly carried by molybdenite through the isomorphous replacement of Mo, rather than by the formation of dispersed Re-specific nanophase(s)

Selenium speciation in waste materials from an exhausted Iberian Pyrite Belt mine

Selenium is an essential nutrient for humans, animals and microorganisms, but it becomes toxic at concentrations slightly above the nutritional levels. This naturally occurring trace element can be released to the environment from various anthropogenic sources such as mining, agricultural, petrochemical and industrial processes and its toxicity is developed along a complex cycle involving adsorption by soil components and subsequent accumulation by plants. In the environment, selenium can occur in several oxidation states ranging from selenide (Se=) to elemental selenium (Se0), selenite (Se4+) and selenate (Se6+). Selenium contents above 900 ppm were recently assigned in mine wastes from the sulphur factory at the São Domingos exhausted pyrite mine exploited in the Iberian Pyrite Belt (south Portugal) since Roman times until 1966. Aiming at a sustainable remediation of this mining site, an X-ray absorption spectroscopy study using synchrotron radiation, combined with X-ray diffraction, was undertaken to clarify the speciation state of selenium and the nature of Se-carrier phase(s). The results show that selenium does not significantly replace sulphur under the form of selenate in the dominant sulphate phases and occasionally remains as a substituting selenide anion in debris of the original sulphides present in the mine waste materials

New insights about the introduction of the Portuguese oyster, Crassostrea angulata, into the North East Atlantic from Asia based on a highly polymorphic mitochondrial region

It is commonly presumed that the Portuguese oyster Crassostrea angulata was introduced into the North East (NE) Atlantic from Asia. The analysis of the nucleotide sequence of a highly polymorphic non-coding mitochondrial region (major noncoding region - MNR) of C. angulata samples collected in Europe (Portugal), Africa (Morocco) and Asia (Shantou and Taiwan) provided new insight into the introduction of this species into the NE Atlantic. Sixty haplotypes and a nucleotide diversity of 0.0077 were observed in 130 analyzed sequences. Higher nucleotide diversity levels were observed in NE Atlantic sites than in Asian sites and significant genetic differentiation was found between the two. Our results suggest that C. angulata might have been introduced to the NE Atlantic by multiple introductory events, though the exact origins remain unknown since none of the analyzed Asian sites seemed to have been a source of introduction. The nucleotide diversity of C. angulata was higher than that previously reported for Pacific oyster C. gigas in Europe and Asia for the same mitochondrial region. The results obtained in the present study suggest that NE Atlantic C. angulata stocks are a unique genetic resource, which highlights the importance of their conservation

Chromium (VI) ion adsorption features of chitosan film and its chitosan/zeolite conjugate 13X film

This research evaluated the importance of the adsorption properties of chitosan a chitosan/zeolite conjugate film for the removal of Cr(VI) ions from solutions in the 5–260 mg/L concentration range, when the pH was adjusted to 4.0 and 6.0. The uptake capacities of the films formed by chitosan and by the chitosan/zeolite conjugate were calculated by mass balance. The equilibrium isotherms were fitted to the Langmuir, Freundlich and Redlich-Peterson models. The chitosan film seems to be a good sorbent for Cr(VI) at pH 4, but its physical instability suggests the need for a more resilient support. Due to this fact zeolite was added to the chitosan matrix in solution and a chitosan/zeolite (CS/Zeo) film was thus formed. The solubility of the film and the characterization of the different matrices by FTIR, TGA and X-Ray showed that a cross-linked structure was formed between the chitosan and zeolite and the solubility of the film increased. In this study, the low manufacturing cost of the CS/Zeo matrix, the good uptake of Cr(VI) at acidic pH (17.28 mg/g) and the non desorption of Cr(VI) from the film in water suggests this combination should be tested in industrial environment.The authors are grateful for the Coordination of Improvement of Higher Education Personnel (CAPES - Brazil) for PhD fellowship and the financial support received from Financier of Studies and Projects (FINEP - Brazil), National Council for Scientific and Technological Development (CNPq - Brazil), Catholic University of Pernambuco (UNICAP - Brazil), University of Minho (UMINHO - Portugal). They also acknowledge Antonio Soares Vicente (UMINHO - Portugal) who kindly supplied the chitosan

Optical Studies in Red/NIR Persistent Luminescent Cr‐Doped Zinc Gallogermanate (ZGGO:Cr)

Zn1+xGa2‐2xGexO4 (ZGGO:Cr)‐persistent phosphor, with a molar fraction, x, of x = 0.1, doped with a 0.5% molar of chromium, was synthesised via solid‐state reaction at 1350 °C for 36 h. X‐ray diffraction measurements and Raman spectroscopy evidence a single crystalline phase corresponding to the cubic spinel structure. Room temperature (RT) photoluminescence (PL) and afterglow decay profiles were investigated using above and below bandgap excitation. In both cases, persistent PL was observed for almost 8 h, mainly originating from a Cr3+ defect, the so‐called N2 optical centre. RT PL excitation and diffuse reflectance allow identification of the best pathways of Cr3+ red/NIR emission, as well as estimation of the ZGGO bandgap energy at 4.82 eV. An in‐depth investigation of the observed luminescence at 15 K and temperature‐dependent PL under site‐selective excitation reveals the spectral complexity of the presence of several optically active Cr3+ centres in the ZGGO host that emit in almost the same spectral region. Furthermore, the temperature dependence of the R‐lines’ intensity indicates the existence of thermal populating processes between the different optical centres. Such observations well account for a wide distribution of defect trap levels available for carrier capture/release, as measured by the persistent luminescence decay, from which the carriers are released preferentially to the N2 Cr3+‐related optical centre.publishersversionpublishe