Green Chemistry Education Network
Flinn scientific catalog mentioned that one could switch from concentrated to 6M nitric acid to oxidize copper in the first reaction of the copper to copper lab (aka sequence of chemical reactions, copper recycling) if one used their copper foil (0.005" thick).
In our original set up (conc. nitric + copper wire) the copper completely dissolved in 3 minutes. When I tested the wire with 6M nitric, it took > 30 minutes and the foil they suggested took about 12 minutes. Both of these would have taken too long for the lab period. I found another source of copper that is 0.001" thick which dissolves the copper in 2-3 minutes. The source I found for the thin foil was http://basiccopper.com/.
There is a good copper cycle lab from the NY State Pollution Prevention Institute that uses 1M sulfuric acid and 1M hydrochloric acid for this as an alternative. There are a couple things that have higher hazards associated with them (i.e., magnesium powder), but this lab is a good alternative to the copper cycles that are typically done with concentrated nitric acid. Here is a link to the full lab: http://hhw.uvlsrpc.org/files/2613/7218/4212/NYSP2I_Green_Chem_Modul.... I've uploaded the lab too (hopefully they don't mind me posting it here!).