carloc said:
Hi guys as much information as possible would help me. I want to melt down copper coins to make myself some bars. The coins I will be using contain 97% copper 2.5 percent zinc and .5 of a percent Tin. If I dissolve the copper in a nitric acid solution 50% nitric acid and 50% percent distilled water
1) what would i use to drop the copper the most effective way out of the solution
2) Would the copper that drops out be .999 fine
Note: the most effective way to drop the copper if handling an average of 2 killos at a time. Any help and advice would be great
Getting 999 from those coins, chemically, would be very difficult. At first glance, however, this would be about the most straightforward process. You'll probably end up wishing you had never started this project. I would strongly suggest first doing this in small quantities until you get the hang of how to gear it up.
(1) Dissolve in 50/50 HNO3. For 2kg it will take about 4.4 gallons of 50/50 nitric.
(2) Filter. The tin will be precipitated as a sludgy material called metastannic acid which is hard to filter. However, since there is only 11g of tin in 2kg, you might be able to filter it. I would probably let it settle first, if it will settle. Then I would filter the tops and, finally, try to filter the bottoms in the same filter. This might take forever.
(3) With the tin gone, you're left with a Cu/Zn solution. The copper can be cemented selectively with iron. It might speed things up to dilute the solution a little more and add a tiny bit of HCl. The zinc and dissolved iron will remain in solution. Filter and rinse, rinse, rinse, rinse, rinse to get rid of the acid, iron, and zinc.
If you just want copper bars, it would certainly make more sense to just melt down clean (no solder, etc.) scrap copper tubing which already is 999 pure. Even if you had to buy it new, it would be much easier and probably cheaper than to deal with those coins - no nitric, filtering, etc., needed. Maybe you could sell the coins and buy the tubing.
No matter what you do, the prevention of copper oxides forming while melting can be a big problem. Search the forum for ideas on that.
publius said:
If you truly want to separate the copper from Zinc (Zn) and Sn then melt it all together and use a sulfuric/copper sulfate cell.
I can't see how a Zn + Sn/Cu separation using a CuSO4/H2SO4 bath could happen, since Modern Electroplating says that brass (Cu/Zn) can be deposited from a sulfate bath (although the deposit is too crappy to be used in industry) and Sn is commonly plated from a sulfate/H2SO4 bath. Also, in my experience, the presence of zinc really screws up the integrity of the cathode deposit. At first, the copper plates beautifully as a solid deposit. When the zinc starts building up in the solution, the deposit starts degrading, gets spongy, and breaks loose from the cathode. Also, no matter how the deposit looks, if there is zinc and tin in the solution, there will be at least a little zinc and tin in the deposit. You'll never get 999 copper.
