A rotating disk study of silver dissolution with thiourea in the presence of ferric sulfate |
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Authors: | Batric Pesic Thom Seal |
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Affiliation: | (1) College of Mines and Earth Resources, University of Idaho, 83843 Moscow, ID;(2) Differential Energy, Inc., 97869 Prairie City, OR |
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Abstract: | The rotating disk technique was used to study silver dissolution with thiourea as a function of sulfuric acid, ferric sulfate,
and thiourea concentrations. The effect of many foreign ions (Mn, Cu, Co, Ca, Na,etc.) and various additives was also examined. The dissolution of silver was zero order with sulfuric acid, first order with ferric
sulfate, and second order with thiourea. Among the foreign ions, copper had a dramatically negative effect. The strong oxidants
such as hydrogen peroxide and manganese dioxide were also detrimental for silver dissolution. According to the temperature
effect studied (5 °C to 35 °C), the activation energy was 22.6 kJ/ mole. Silver does not dissolve with thiourea in the absence
of ferric ions. Sulfuric acid does not participate in the dissolution reaction. The most important parameter for silver dissolution
is the ferric sulfate/thiourea ratio. In excess ferric sulfate, a solid silver-thiourea complex is formed, which precludes
transfer of silver into solution. In excess thiourea, the free thiourea reacts with formed solid silver-thiourea complex,
and silver goes into the solution, predominantly as the dimers of AgTU+
3 complexes. The solid silver-thiourea complex in question was characterized by various spectroscopic, microscopic, and chemical
analysis techniques. According to chemical composition, it corresponds to Ag2SO2·3TUH2O compound.
Formerly Graduate Student, University of Idaho |
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