dwt9999 said:
I process just about everything through the Nitric acid prior to putting it into the AR. I was under the impression that it is best to get ANY silver out of the way prior to processing for gold.
If silver is alloyed with gold, it has the potential to prevent AR from dissolving gold if it's high enough in concentration. The silver chloride film that slowly develops is very hard, and isolates the alloy from exposure to the AR. It slowly builds as a green/gray coating on the metal in question, and soon the dissolving action grinds to a halt. You can literally boil your metal for days on end in AR once that happens and it won't dissolve. That's why it's so important to inquart alloys to get the gold down to 6 K, then remove it with nitric.
If the silver content is low enough, the silver simply converts to chloride and falls free from the alloy as such. Gold alloy that is less than 10% silver will slowly dissolve, but it's far better to not have any silver present if possible. The biggest problem is that the chloride acts like a huge sponge and absorbs the gold solution. Endless washing reduces the content, but it's almost impossible to recover completely. If you properly recycle the wastes from filtration, you recover the vast majority of values in that operation, so they're not lost.
So far all I have melted down are a few things that look copper instead of gold, and the silver I have tried to get out is very brittle! I am going to keep trying until I get something right, it is far to muck fun to stop now!!
If you're tossing all kinds of junk in the pot, you may be introducing lead to the operation. I'm not quite sure how it affects silver, but it's death on the ductility of gold. You can minimize lead by not dissolving unknown items, but if you happen to get involved with lead, it has a peculiar property of precipitation on its own as lead nitrate if you allow the solution to cool. Once the lead precipitates, you can decant the solution and recover the silver with copper. Do you know about the testing solution that shows a blood red color when applied to silver? It can help you avoid dissolving things that are of no value.
While being brittle isn't exactly a good thing, you shouldn't expect silver to come down cleanly. Recovered silver is a perfect candidate for a silver cell, but is highly unlikely to be of great quality.
If your purpose in silver is to accumulate it, not just to sell it, store the silver until you have a good quantity, then you can build a simple silver cell and part it properly. It's really about the only way you'll come up with good quality, and if you work with any of the platinum group metals, you might be pleasantly surprised to find you recover them when you part the silver. You'll usually find gold traces as well. It's hard to make perfect separations.
One comment. Because silver and gold can not be in any common acid solution together, they are extremely easy to separate. According to Sir T.K. Rose, a few silver atoms are known to behave as if they are gold atoms, so you might expect a trace showing in once refined gold. Otherwise, if you use good practice, your gold should be pretty much silver free.
If you're using the AR process for gold, be certain to include a few drops of sulfuric acid in each batch. That precipitates lead as lead sulfate, which is then filtered off when you filter your gold chloride solution. It insures that you don't carry lead through the process.
Welcome. I hope some of this is, indeed, helpful.
Harold
