The authoritative public forum
  for Metal Finishing since 1989
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Removal of tin and iron impurities from OF copper wire

I have chopped copper wire that contains 150-1500 ppm of tin and 50-200 ppm iron on its surface. I wish to remelt it to produce OF grade copper. How do I get rid of the excess tin and iron economically? Some say use Nitric acid, some advise use of Sodium Hydroxide, some advise use of properitory stripping chemicals. Which is the most economical of the two and how do I dispose the spent chemical?

Sanjay Mudbidri
Copper rod and wire - Klang, Selangor, Malaysia
2004

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You don't give much detail about the form the copper, tin and iron are in. If the tin and iron are free metal, then dissolve off the tin in strong sodium hydroxide at about 80 °C and the iron in 10-20% HCl at room temperature. This will leave you with clean copper. If the tin and iron are alloyed, you will need to strip them in either HCl or NaOH with a strong oxidising agent in it (say sodium nitrite). The beauty about the metals being removed under different conditions is that you can then recover the separate metals and resell them at a higher price than if they are contaminated. If the iron and tin are together, the resulting liquor can be used as a feed for refinement. The best route would be to use the HCl path, as both metals are very soluble in it. The alkaline route gives you a solution of tin, but the iron will form a sludge that will have to be removed.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004