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How are gold and silver recovered from copper-refining slimes?
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gold processing
The Tanami gold mine, Northern Territory, Australia.
During the electrolytic refining of copper, precious metals like gold and silver collect as insoluble impurities known as anode slimes at the bottom of the refining tank.12
To recover these metals, the slimes are first smelted in a furnace to oxidize base metals, resulting in a metallic mixture called doré. This doré is cast into anodes for further separation, a process known as parting.
The recovery process typically involves:
- Electrolytic Refining: The doré anodes are placed in an electrolytic cell containing a silver-copper nitrate solution. Using systems such as the Moebius or Thum Balbach, silver dissolves and deposits onto cathodes, while gold remains in the resulting slimes.13
- Chemical Parting: Gold recovered from the electrolytic slimes is further purified by boiling it in sulfuric acid and potassium nitrate to dissolve any remaining silver. Alternatively, traditional chemical methods may involve dissolving the silver in nitric acid, leaving behind a gold residue.3