After the copper is gone, there is stainless and gold left. I would agree with 4metals that the high nitric low HCl will work well on this combination. I would, however, reduce the HCl to about 3%, to start. The formula would be 50% HNO3/3% HCL/47% tap water, all percentages by volume. Run at room temperature. I would put the SS/Au in a bucket and cover with a little excess of this solution. I would expect that foils would dissolve within an hour or two. It will help to occasionally rotate the bucket gently back and forth to force solution exchange inside the SS sleeves. The same solution can often be used to process several batches of material. If it slows down too much, add another 2 or 3% HCl.
I have run many 1000s of pounds of similar material using this solution. After filtering the garbage out of the solution, I always precipitated the gold directly from the solution with hydrazine sulfate (HS). It probably took a HS/gold ratio of from 1:1 to 3:1. No dilution or elimination of nitric is necessary. I just sprinkled the HS on the solution, in increments, and stirred it in (there could be foam so make sure the precipitating vessel has enough space). Brown gold powder will appear fairly quickly. Moderately dilute Hydrazine Hydrate could surely be used instead of the HS. Test effluent with stannous chloride.
I always re-refined the gold powder in AR.
As with anything new, run very small test lots first to make sure it works and to allow yourself to get the "hang" of the process. Although I don't think you'll have any problem with stainless steel, some weird alloys will, as Steve said, dissolve in the solution and produce a runaway reaction. Also, some obscure alloys introduce something that inhibits the hydrazine from dropping the gold. Try a little sample first.
