Abstract
Electrolytic copper contains, on average, 10 ppm silver as impurity, which leads to a loss of silver as a cashcow product for copper smelters.Most of silver included in blister copper anodes passes into anode slime when electrolyzed, keeping the elemental state. However, once a part of elemental silver dissolves from the anode or from anode slime for some reason, then silver can co-deposit with electrolytic copper cathode, since silver is nobler than copper. In the present work, the dissolution behavior of silver from anode slime was examined by using granular silver as a model of the slime.We have shown that the silver dissolution is caused by dissolved oxygen in the electrolyte, and that thiourea and/or chloride ions as usual additives play a role to suppress the silver dissolution approximately to two thirds.Moreover, it was found that the dissolution of silver was suppressed to less than 1ppm by galvanic contacting of the granular silver with less noble metals (Pb or Cu) immersed in the same electrolyte. This indicates that the use of Pb or Cu lining at the bottom of electrolytic cells can suppress silver dissolution from the anode slime settled to the bottom, reducing the silver loss to electrolytic copper.
