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    Gold cementation on copper in thiosulfate solution: Kinetic, electrochemical, and morphological studies

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    Author
    Lee, Jaeheon
    Issue Date
    2003
    Keywords
    Engineering, Chemical.
    Engineering, Metallurgy.
    Engineering, Materials Science.
    Advisor
    Hiskey, J. Brent
    
    Metadata
    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    Cyanidation has been used for more than a century for precious metal recovery and it is still in use today. Cyanide is a very toxic chemical and if not used appropriately will cause environmental problems. There is considerable attention devoted to the development of non-cyanide lixiviants for the process of gold and silver ores. Thiosulfate solution is one of the proposed alternatives to cyanide and gold cementation by copper has been suggested as a promising method for gold recovery from leaching solution. Copper powder and rotating disc electrode were used for the kinetic study. The rate of gold cementation on copper disc is proportional to the initial gold concentration and disc rotating speed. The cementation reaction exhibited two distinct kinetic regions, an initial slow rate followed by an enhanced rate. The activation energy of the reaction was 5.9 kJ/mol at low copper concentration and the reaction is mass transport controlled. With 30 ppm initial copper concentration, there was noticeable decrease in the reaction rate in high temperature range. EDS, XRD, and XPS analysis revealed that the deposits are a Au-Cu alloy instead of pure gold. The alloy composition ranged from Au₃Cu to AuCu₃ depending on the initial Cu/Au mole ratio in solution and applied potential. Electrochemical studies were performed using rotating disc electrode and electrochemical quartz crystal nanobalance. Evans' diagrams were constructed under various experimental conditions. Corrosion current increased with increasing gold concentration, disc rotating speed, as well as thiosulfate concentration. These results confirmed those obtained in the kinetic study. Corrosion potential measurements indicated that passivation onset time was changed by gold concentration, copper concentration and disc rotating speed. Gold(I)-thiosulfate reduction was found to occur at approximately -250 mV vs. SHE using EQCN. Copper adions on the gold surface contributed to the underpotential deposition of copper and the underpotential deposition is the mechanism of alloy formation in cementation system. (Abstract shortened by UMI.)
    Type
    text
    Dissertation-Reproduction (electronic)
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Science and Engineering
    Degree Grantor
    University of Arizona
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