Mysterious Yellow Solution after Gold Pecipitate

[Harold_V]

This is where the remainder of the gold is! Not in the mysterious yellow solution that I thought it was in. Now here's my question to the experts: I know I need to run these bits and pieces of leftover gold through AR again, I dont like the idea of putting it back in AR again for there was no/very little reaction with these bits and pieces to AR. (using Lazersteve's Modified Poormans Aqua Regia), I was thinking of melting these pieces, without inquarting, and pouring it into cornflakes again before putting it on AR. Is this the right thing to do???

Depends.
If you are certain that the silver was not fully removed because you jumped the gun and removed the gold prematurely, yeah, you can re-melt, using soda ash and borax (to recombine any silver that may be present as silver chloride, with the material). Pour to a cone mold, then separate the button from the flux, re-melt and pour shot again.

If you did NOT use heat in the initial process (dissolving the silver and base metals with nitric), you now see why that's not a good idea. If you have the ratio correct, all of the silver will be removed, making it dead easy to dissolve the remaining gold, which is now honeycombed because of the removal of silver and base metals. When it won't dissolve in AR, it's generally because you have not removed the silver, so when it hits a layer where silver remains, it quickly forms an impervious layer that can not be penetrated by AR, so action quickly comes to a halt. You can boil the material for days without further dissolution.

The other issue can be that you erred when you inquarted. If you got the ratio wrong, and the gold content is above 35%, removing the base metals and silver can be challenging, even impossible. If you boiled (or at least heated) the nitric solutions and added more than might have been required to dissolve all the silver, yet some remained, that may be an indicator that your calculations for inquartation were not correct. Only you can answer that one.

In any case, re-melting and adding a little more silver should solve the problem.

Harold

 

[lazersteve]

Too bad I saw this thread so late in the conversation.

I recall the intial email, but did not realize the OP had posted additional details on the forum.

Homemade nitric acid should not be used for dissolving silver or inquarted gold for reasons already discussed above.

When evaporating excess nitric from solutions HCl is used to drive off the NOx, and water dilution (or ice) is used to precipitate silver chloride dissolved by the muriatic acid. For the record, I do not evaporate my gold solutions as I keep careful control on the nitric additons. If by chance too much is used, I simply burn it off with sulfamic or SMB. On the karat gold DVD I used just enough nitric acid and no evaporation was needed.

You may be chasing a trace of gold from the looks of the solution. If you believe you are missing more than a few grams of gold, I doubt it is in the solution you posted photos of. Proper testing of karat jewelry is very important to a successful inquartation and achieving calculated yields. Mismarked, unmarked, and incorrect calculations arising from failure to exclude stone weight and under karating (1/2 karat in the US) can lead one to believe they have more gold than they actual do.

If I had seen the photos I see above, I simply would have advised you to cement the remaining gold with copper an start over.

The salts that form during evaporation are from your homemade nitric acid and SMB yuo added both of which crystallize out of the solution as the water and acids evaporate.

Sorry for the delay response.

Steve