Back to the original question.
I have these silicon wafers (lots of them), that have a lot of gold on them. Like the whole backside of them and in between. How would I process something like that? And get rid of all the silicon?
I don't understand what you mean by "in between" - please explain.
A refinery I worked for got these gold backed silicon wafers by the drumloads from companies in the Silicon Valley. I think the gold is evaporated or sputtered onto the silicon. I don't remember the gold thickness but I don't think it is very thick. It would certainly add up in quantity. I also don't remember how we processed them. We probably used cyanide, since it was common back then. It was also cheap, fast, safe, and efficient.
Since the government has taken away the marvelous cyanide, you are stuck using some form of acid chloride. This would include the standard aqua regia, HCl/bleach, and HCl/peroxide processes. None of these should attack the silicon. They should only attack the gold. You would then drop the gold from the solution, as normal.
The problem with working with these wafers, when whole, is that they tend to stick to each other when wet. The acid then has to penetrate through the edges of the stuck together wafers and, this can be a slow process. This can be sped up by first breaking up, or grinding up, the wafers.
If you grind up the wafers, there may be a potential health hazard with the dust, if you don't wear a proper mask. I would read the stuff on this link.
http://www.msha.gov/S&HINFO/SILICO/SILICO.HTM
When you breathe silica (silicon oxide) dust, there is the possibility of getting silicosis, a lung disease. Although we're talking about pure silicon and not the silicon oxide covered in the link, I think I would take the same precautions, were it me. Better safe than sorry.
