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  • 1
    ISSN: 1432-0495
    Keywords: Key words Pyrite oxidation ; Acid mine drainage ; Tailings ; landfill ; Sealing ; Modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Annually, an amount of approximately 13 million cubic meters of hard-coal tailings must be disposed of in the German Ruhr Valley. Besides the waste of land in a densily populated region, the disposal of the pyrite-bearing material under atmospheric conditions may lead to the formation of acid mine drainage (AMD). Therefore, alternative disposal opportunities are of increasing importance, one of which being the use of tailings under water-saturated conditions, such as in backfilling of abandoned gravel pits or in the construction of waterways. In this case, the oxidation of pyrite, and hence the formation of AMD, is controlled by the amount of oxygen dissolved in the pore water of tailings deposited under water. In case the advective percolation of water is suppressed by sufficient compaction of the tailings, oxygen transport can be reduced to diffusive processes, which are limited by the diffusive flux of dissolved oxygen in equilibrium with the atmospheric pO2. Calculations of the duration of pyrite oxidation based on laboratory experiments have shown that the reduction of oxygen is mainly controlled by the content of organic substance rather than the pyrite content, a fact that is supported by results from oxidation experiments with nitrate. A "worst case" study has lead to the result that the complete oxidation of a 1.5-m layer of hard-coal tailings deposited under water-saturated conditions would take as much as several hundred thousand years.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Heat and mass transfer 14 (1980), S. 231-244 
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Der Einströmvorgang metallischer Schmelzen in horizontale Zylinder wurde bis zu ihrer Erstarrung untersucht. Ein mathematisches Modell beschreibt das Temperaturfeld und die mittleren Geschwindigkeiten in dem Teil des Zylinders, der zu jedem Zeitpunkt gerade gefüllt ist. Damit kann das Fließvermögen als maximale Fließlänge allein aufgrund bekannter Größen berechnet werden. Ein empirischer Wärmeübergangskoeffizient wird nämlich dadurch umgangen, daß ein konzentrischer Luftspalt postuliert wird, der sich durch die Schrumpfung des erstarrten Metallringes bildet. — Gießversuche wurden mit reinen Metallen wie Sn, Pb, Zn und Al bei unterschiedlichen Gießtemperaturen und Druckhöhen durchgeführt. Die Fließfunktion wurde dabei mit kleinen Lichtschranken im zylindrischen Metallkanal (Ø 5 mm) gemessen. Die Abhängigkeit wird von einer allgemeinen Gleichung vorausgesagt, die aus den numerischen Ergebnissen abgeleitet wurde, und auch von ähnlichen Messungen anderer Autoren bestätigt.
    Notes: Abstract The entrance flow of molten metals into horizontal cylinders until their solidification has been studied. A mathematical model describes temperature field and mean velocities in that part of the cylinder just filled at each time. Thus fluidity as maximum flow length can be calculated as a function of known properties only. An empirical heat transfer coefficient is avoided by postulating a concentric air-gap which is formed by thermal contraction of the solidified annulus. — Casting experiments with pure metals such as Sn, Pb, Zn, and Al have been conducted for different temperatures and metal-heads. The flow function was measured with small photo-cells in a cylindrical metal form (ø 5 mm). The dependence of fluidity from material properties and casting parameters is predicted by a general formula, derived from the numerical results, and is verified also by similar experiments by other authors.
    Type of Medium: Electronic Resource
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