Arthur,
I demonstrate using the cell to strip these lids on my website videos. The cell is slow, but gives the highest yields (nearly 100% stripped) with the least amount of acid used. If you use a copper mesh basket set up, the stripping process is much faster, but is not as complete for each individual lid.
My second choice (and the one I use more often when I have large quantities of lids) is to treat the lids in a series of hot HCl and water baths. After each bath I pour off the spent acid and sort out the lids that the foils have lifted off of. This process does not get all the gold, but achieves nearly 90% yields. When the lids get down to the last few stubborn lids that won't strip using HCl, I switch to diluted AR to dissolve the foils and the remaining metallic lids. The gold from this process will need to be refined after it is precipitated. Be careful of foaming using this method or you will lose gold to overflows. Always use a catch dish under the reaction beaker.
The last method I use is hot 35% HNO3. Typically after a single pass through 35% HNO3 the remaining lids foils will loosen. Just as with the HCl treatment the foils will not completely lift and some loses in yield will be seen. The interesting thing about this method is that once the foils lift form the lids they are bright and shiny (passivated stainless ?). The foils are then processed with AR and refined a second time.
If the lids are the hick kind that are braze to the top of the cpu they likely contain a tungsten and copper (they are nearly as heavy as platinum) and are extremely difficult to dissolve with acids. For these types electrolytic stripping is best.
Steve
