Gold will not precipitate from dirty solution after addition of SMB

[Kale.niemiec]

I've refined gold using this method many times. Most often from scrap jewelry but recently I got my hands on a few hundred ceramic cpus. I dissolved all the gold and base metals in aqua regia. After I added about 5-10ml of sulphuric acid to precipitate any silver and lead. I filtered the solution and and after cooling, added SMB but no precipitate formed. There should be about 2 grams of gold. Anybody have any ideas. I assume the problem is from copper chloride or some of the other base metals. How do I solve my problem? Thanks

 

[Topher_osAUrus]

More likely than not, it is due to excess oxidizer. How did you remove the extra nitric?

Sulfamic acid is best, it converts to sulfuric, so it does double duty by removing nitric and precipitating the lead as its sulfate.

You could always just cement the gold on copper, then redissolve it with minimal acid, and precipitate as usual.

 

[Kale.niemiec]

I evaporated the solution down and added HCL and repeated. I was thinking of trying ferrous sulfate. Can you tell me a bit about cementing the gold on copper. Thanks

 

[Topher_osAUrus]

Its step one of the waste treating process, which usually collects traces of precious metals that werent reduced by chemical means. It works under the basis of the reactivity series of metals. How have you been treating all your previous waste solutions?

 

[anachronism]

One question. If you have processed a few hundred ceramic CPUs are you sure you're only expecting 2g of gold and if so why 2g please?

 

[Kale.niemiec]

I only processed about 36 cpus. AMD's that should yield about 0.06g per cpus. These are not the higher yielding k-6 or 5.

 

[anachronism]

You're not far out on your numbers then. Are you sure that you've got all your Nitric now? Can I assume you have a positive stannous test right now?

I'm not a fan of coppering a solution when there are alternatives, so can you get some ferrous sulphate?