Bioleaching of Nickel and Cobalt from Lateritic Chromite Overburden Using the Culture Filtrate of Aspergillus niger

Extraction of metals (Ni, Co) from chromite overburden of Sukinda mines of Orissa, India, with the culture filtrate of Aspergillus niger was studied. Results showed that the amounts of metals leached varied directly with reaction temperature and period of fermentation. The culture filtrate was analyzed for citric and oxalic acids, and contained only oxalic acid—the concentration of which increased with time. Although this acid played the major role in leaching of metals, other unidentified metabolites present in the culture filtrate influenced the dissolution of the metals significantly. Maximum recovery of metals from raw and roasted ore samples was achieved at 80 °C with the 21-day culture filtrate containing the highest amount of oxalic acid. Under identical experimental conditions, much higher amounts of the metals were leached from roasted ore. Microstructures of the ore particles were studied by scanning electron microscopy and transmission electron microscopy; the bonding behaviors of metal compounds were identified by Fourier transform infrared spectroscopy which showed that the metals were leached after chelation with oxalic acid.     

Dihydroxamate based siderophore model, piperazine-1,4-bis-(N-methyl-acetohydroxamic acid (PIPDMAHA), as a chelating agent of molybdenum(VI)

Equilibrium studies based on pH-potentiometric and spectrophotometric measurements as well as some theoretical simulations are reported for the complexes of Mo(VI) with a dihydroxamate type siderophore analogue, the piperazine-1,4-bis-(N-methyl-acetohydroxamic acid) (PIPDMAHA). It has been found that the complexation process starts below pH 2 and that PIPDMAHA forms more stable O,O-hydroxamate bis-chelated complexes with Mo(VI) than any of the formerly studied dihydroxamic acids. The experimental data were fitted with two complexation models based either on dinuclear or on mononuclear species. However, ESI-MS showed that the dimmer is much more abundant than the monomer. This feature was further suggested by theoretical simulation studies, which indicated the dimeric species is more stable than the monomeric one.     

Microstructure characterization of titanium dioxide nanodispersions and thin films for dye-sensitized solar cell devices

This article reports on the microstructure characterization of titanium dioxide nanodispersions and thin films made thereof for dye-sensitized solar cell devices. Structure–property relationships have been investigated mainly using electron microscopy to assess how microstructure (crystalline structure, defects) and morphological (e.g. heterogeneities, inclusions, voids) features in the electron transport element of the solar cell device correlate with electrical performance, namely, short-circuit photocurrent density (J_sc). This work shows that for a nanodispersion synthesized in the laboratory different electrical performances are measurable depending on the thin film forming process, more specifically, heat-sintering at 450 °C or pressure-sintering at 500 bar. For the heat-sintered device J_sc is about 7.3 mA/cm² whereas for the pressure-sintered one this value is much lower, this difference being attributed to the existence of inclusions in the titanium dioxide matrix, which are spatially isolated from the rest of the electron transport element thereby limiting the charge transport process by promoting their premature recombination. PACS 68.37.Lp; 73.61.Le; 81.40.-z; 84.60.Jt     

Beiträge zur Chemie des Thalliums und Arsens

Zusammenfassung Verfasser untersuchten die Änderungen des Oxydationszustandes des Thalliums und Arsens in konz. Schwefelsäure und in Schwefelsäurehydraten. Es wurde festgestellt, daß Thallium(I) keine Veränderung erfährt, Thallram(III) jedoch quantitativ zu Thallium(I) reduziert wird. Während der Reduktion bildet sich Sauerstoffgas. Arsen(III) und Arsen(V) unterliegen bei ähnlichen Bedingungen weder einer Oxydation noch einer Reduktion.Diese Eigenschaften der beiden Elemente ermöglichen es, das Thallium nach Zerstörung bzw. Behandlung der Probe mit einem Gemisch aus konz. Schwefelsäure und Wasserstoffperoxyd auch in Gegenwart großer Arsenmengen direkt, ohne vorangehende Trennung zu bestimmen. Die Titrationen wurden mit KBrO₃-Lösung durchgeführt, als Indikator diente p-Äthoxychrysoidin.

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Summary A study has ben made of the changes in the oxidation state of thallium and arsenic in concentrated sulfuric acid and in hydrates of sulfuric acid. It was found that thallium(I) undergoes no change, whereas thallium (III) is reduced quantitatively to thallium(I). Oxygen gas is produced during the reduction. Under similar conditions, arsenic(III) and arsenic(V) exhibit neither an oxidation or a reduction.These properties of the two elements make possible a direct determination of thallium, even in the presence of considerable amounts of arsenic, and without a preliminary separation. The sample must be treated with a mixture of concentrated sulfuric acid and hydrogen peroxide. The titrations were made with KBrO₃ solution;p-ethoxychrysoidine serves as indicator.

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Résumé Les auteurs étudient les changements d'état d'oxydation du thallium et de l'arsenie dans l'acide sulfurique concentré et dans l'acide sulfurique hydraté. On a établi que le thallium-I ne subit pas d'altération, cependant que le thallium-III est réduit quantitativement en thallium-I. Pendant la réduction il se forme de l'oxygène. Dans les mêmes conditions, l'arsenic-III et l'arsenic-V ne subissent ni oxydation ni réduction.Ces propriétés des deux éléments rendent possible le dosage direct du thallium après décomposition ou traitement de l'essai par un mélange d'acide sulfurique concentré et d'eau oxygénée, même en présence de grandes quantités d'arsenic, sans séparation préalable. Les titrages ont été réalisés avec une solution de bromate de potassium en utilisant lap-éthoxychrysoïdine comme indicateur.

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Gewidmet zur 100. Wiederkehr des Geburtstages vonFriedrich Emich.     

A theoretical model investigation of the hydrogen-electrode processes of an alkaline H2---O2 fuel cell

Ab initio molecular orbital (MO) and self consistent field (SCF) computations have been carried out within the Restricted Hartree—Fock (RHF) formalism on the species involved in 22 possible reaction mechanisms associated with the anodic process: H₂ → 2H⁺ + 2e⁻ of the hydrogen—oxygen alkaline fuel cell. Such a model, which represents the gas phase reactions, may be regarded as a primary standard for any future study in which the catalyst of the electrode may be included.     

Synthesis and conformation of 2-fluoro-3-ketoestrane derivatives

Treatment of 3-methoxy-17β-acetoxyestra-2,5(10)-diene with perchloryl fluoride in aqueous dioxane or tetrahydrofuran yielded a 2-fluoro-3-ketosteroid with unusual properties. Unlike the known 2-fluoro-19-nortestosterone, this fluoroketone possessing a 5(10) double bond easily lost hydrogen fluoride to form estradiol 17-acetate; aromatization took place on melting, on exposure to pyridine or acid or even during chromatography on silica gel or Florisil. Because of the Δ-5(10) structure and the absence of the C₁₉ Me group, it is difficult to infer the exact orientation of the 2-fluorine substituent from its effect on the NMR spectrum, CD or the CO absorption in the IR. However, the properties of certain derivatives suggested that the fluorine substituent was 2β. Treatment of the unsaturated fluorketone with peracid gave a mixture of epoxides which on basic hydrolysis furnished two 2-fluoro-10-hydroxy-17-acetoxyestr-4-en-3-ones epimeric at C₁₀. The UV and NMR spectra of the 10-hydroxy epimer indicated an equatorial 2β-orientation of fluorine, whereas the 10β-hydroxy epimer showed an axial 2β-fluorine substituent which could be isomerized by acid to the more stable equatorial 2-configuration.