SIM E-waste Recovery

[haveagojoe]

Why can't I just dissolve the copper and nickle base metals in nitric acid leaving only the gold, silver and whatever trace metals weren't listed in the missing 0.2% of the 99.8% accounted metals from the XRF test?

You can. It's just expensive, hazardous and will produce waste acid. If you have done an expected yield calculation as I suggested, you will see that using Nitric to dissolve the base metals will not be economical.

HCl and peroxide won't immediately dissolve copper by themselves. The common approach we use, nicknamed AP after "Acid Peroxide" is actually a Copper Chloride etch. It needs some copper to be already in solution for it to work, since the etching is achieved through a redox reaction (oxidation-reduction) of Copper (ii) Chloride oxidizing metallic copper into Copper (i) Chloride. The Copper (i) Chloride then takes on Oxygen to form Copper (ii) Chloride and can subsequently oxidize further metallic copper. Hydrogen Peroxide can be used as the source of the additional oxygen for this reaction, but since HCl+Hydrogen peroxide can also dissolve gold, we generally prefer to use an air bubbler to replenish the oxygen supply to keep the reaction going and to prevent the buildup of Copper (i) Chloride which is recognizable as an insoluble whitish sediment.
To create Copper Chloride solution, use a piece of oxidized copper- which has green verdigris on its surface. Either dip it or scrape it into a small volume of HCl. The solution should turn slightly green; this means it contains Copper (ii) Chloride. Only a small amount is needed since it will create more through the reaction cycle.
Copper Chloride etching solution can be reused many, many times, so acid waste is kept to a minimum.