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Authors: | Xia, Chen |
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Keywords: | thiosulfate gold ammonia copper ethylenediamine phosphate pyrite pyrrhotite arsenopyrite chalcopyrite chalcocite bornite galena lead Eh-pH Oxygen Extraction Leaching Pre-aeration Passivation |
Issue Date: | 2010 |
Series/Report no.: | Canadian theses |
Abstract: | The
effects of some associated minerals on thiosulfate gold leaching were
studied through thermodynamic analysis and leaching experiments on
composite ore samples containing various minerals and a reference
silicate gold ore.
In the leaching test on the reference gold ore, about 93% of gold was
extracted within 3.0 hours. The presence of various amount of pyrite,
pyrrhotite, chalcopyrite, arsenopyrite, chalcocite, bornite, and some
lead species, has significant detrimental effects.
Under reduced oxygen conditions, the thiosulfate consumptions could be
significantly reduced. High gold extractions (i.e. >= 90%) were
observed in the leaching tests with reduced dissolved oxygen (i.e., 0.7%
oxygen in the supplied gas) in the absence or in the presence of
sulfide minerals such as pyrite, pyrrhotite, arsenopyrite and
chalcopyrite. High copper concentration and a pre-aeration step was also
found to largely increase the gold extractions under such conditions.
Thiosulfate-copper-ethylenediamine system was found effective in the
leaching of gold. The leaching kinetics was significantly slower than
that of the conventional thiosulfate-copper-ammonia leaching. The
consumption of thiosulfate, however, was largely reduced. This leaching
system worked effectively on the reference gold ore within a wider pH
range (e.g., 6-11), with or without ammonia. The presence of ammonia in a
low concentration improved the leaching rate but also increase the
consumption of thiosulfate. Comparable gold extractions were observed in
the leaching of the composite ores containing various sulfide minerals,
such as pyrite, pyrrhotite, chalcocite, galena and chalcopyrite.
The leaching of gold in the presence of iron sulfides was also improved
by applying chemical additives, such as, carbonate, calcium, galena,
phosphate, and additional hydroxide anion. It is proposed that these
additives either passivated the harmful surface of sulfide minerals or
masked some detrimental aqueous species.
Finally, some improved leaching methods concluded in this study were
applied on a few industrial ore samples in order to demonstrate the
effectiveness of these methods. It was found that by comprehensively
applying these improved thiosulfate leaching strategies, satisfactory
gold extractions and thiosulfate consumption results were archived on
these ores. |
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