AR is black

[wisco_gold]

I have been searching and think I might know what's up with my solution. I am dissolving thick gold foils (that should be free of base metals, if there was any left it would be trace amounts of copper)

It started off quite quickly when I started dissolving the foils. They were covered in concentrated hydrochloric acid and then dilute nitric acid was added as needed to dissolve the foils. After 5 hours or so the solution turned a dark black color and I continued to add nitric acid as it didn't seem like it was dissolving anymore. It then had turned a very dark honey colored yellow a few hours later but didn't seem to be dissolving anymore. Well after a couple more additions of dilute nitric acid I've gotten the foils down to almost nothing but the solution is staying black and the foils don't seem to be dissolving in at all anymore. I'm guessing that my solution is oversaturated and that I'm going to have to pour it into a bigger container and add more HCL and nitric acid to complete but want to make sure with you guys first.

 

[FrugalRefiner]

Better to decant the solution off the remaining solids, then add fresh acid. That way you're adding full strength acids to the solids instead of adding them to the existing solution which dilutes the fresh acid.

Dave

 

[wisco_gold]

Better to decant the solution off the remaining solids, then add fresh acid. That way you're adding full strength acids to the solids instead of adding them to the existing solution which dilutes the fresh acid.

Dave

That makes sense, thank you. Should I then proceed to denox and precipitate the still blackish colored AR (that was decanted)?


Edited for clarification of my question

 

[FrugalRefiner]

Yes. Then send the remaining solutions to the stock pot to collect any remaining values. Any gold you drop from the dirty solution will also be dirty, so refine it a second time to increase purity.

Dave

 

[wisco_gold]

Yes. Then send the remaining solutions to the stock pot to collect any remaining values. Any gold you drop from the dirty solution will also be dirty, so refine it a second time to increase purity.

Dave

Thank you,

This is pretty frustrating, I had these foils in a nitric bath for almost an entire day adding fresh nitric until no more reaction and then rinsed well and made aqua regia. I couldn't even observe anymore copper. Getting pretty discouraged at this point. Anyways to thanks again for your time.