So you've got a bunch of scrap that contains gold as well as a lot of other metals. Here is how to reclaim that gold and end up with .99+ pure gold. The process is to dissolve all of the base metals in acid and leave behind the gold, then purify the gold even further. What this does is make salts of the metals and those salts (most of them) are soluable in HCl. For some of the base metals it takes a little extra Oxygen to get this done, so adding Hydrogen Peroxide and/or using a fish tank bubbler, will provide extra oxygen and help things along. Next you actually dissolve the gold, that's right, make Gold Salt (Auric Chloride) and filter that. Replace the gold in that salt with sodium and Voila! Salt water and Gold Dust!
You will need:
You will be wise to also have:
Get the scrap as high yield as you can. Several ways to do this. Cut off the parts that have gold and discard the others. Use Lye to strip the coatings from on top of the PCB (printed circuit boards) and trim/pluck all the little pins.
Here is what you do:
Dissolve base metals in AP (Acid + Peroxide). Throw your scrap in a bucket then dump some Muriatic and Peroxide in there, fish tank bubbler helps too. Takes a week or so... Stir as much as you want, daily is good, but BE PATIENT! Time is the most important factor here. A week is minimum, really... Don't worry, the rest of the process has a little more instant gratification.
Strain and filter and you should have mostly gold flakes!
Wash the flakes with HCl. This is to be sure there are no base metals remaining.
Once it remains clear after adding HCl, you have likely gotten all of the base metals out.
Dissolve Gold! (this is one of the coolest parts)
HCl and Bleach will dissolve gold readily, making Auric Chloride!
After filtration, it should be very clear and gold in color.
Dilute the solution and heat to drive off excess Chlorine Gas
Add some SMB and the gold precipitates out!
Do a Stannous Test! This is to see if there is any gold left in solution.
Siphon/decant off solution.
Wash several times with small amounts HCl and boil off, then you should end up with this:
Evaporate remaining moisture.
Melt your gold!
Be prepared for it to be a VERY small amount!
Now, there are some mildly harsh chemicals used, but no nitric acid! You don't need AR (Aqua Regia) to dissolve gold or refine it. You certainly don't need Mercury and Cyanide! You will need some basic chemistry knowledge and some time to clean up the scrap.
This is the easiest way that I know of to refine gold from scrap. I'll be elaborating here in the near future as well.
Safety Note: Although this process doesn't use crazy acids or exotic reagents, it is VERY IMPORTANT to understand what processes and reactions are going on! At times you are creating Chlorine gas as well as Sulfurous compounds. These can be VERY Hazardous and even DEADLY. Be SURE to get a RESPIRATOR and GOOD GLOVES at least. Goggles and plastic apron a plus. Do this outside and be mindful of direction of the wind or create wind/ventilation. Even if you don't breathe them in or get them in your eyes, they can also damage skin and clothing not to mention hair.
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