Hello Siampudan,
Take a look at this patent on Google Scholar:
Separation of contaminant material from copper wire and cable
United States Patent 4284428 Filed 10/29/1980
Assignee: Western Electric Co., Inc. (New York, NY) Keep in mind however that it is my personal experience that Western Electric, in the rush to patent, sometimes patents things that really do not work that well.
"Copper scrap from chopped and separated copper wire and cable is treated to remove contaminants still remaining on or mixed with the copper by sequential treatment, first in a sodium nitrate-potassium nitrate fused salt bath followed by a cuprous chloride fused salt bath."
Experimentation would be fairly simple.
Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
519 641- 3212