Dilute Aqua Regia and SMB

[Yggdrasil]

I'm not intending to point fingers here.
Bear in mind I have not used it myself yet,
but all and any of the videos and descripions I have seen, points to the reaction to be exothermic.
I think it was Snoman who referred to it as endothermic, which I consider to be just an typing error,
but it would be nice to get the nomenclature corrected for future reference.

 

[g_axelsson]

Maybe in this case using a base to neutralize the acid is the right way to go.

When the solution becomes basic the metal ions will precipitate out as hydroxides. Then the solution can be filtered and washed to get rid of nitrates and chlorides.

Then the gold hydroxide can probably be calcined and turned back into metallic gold or dissolved back into gold chloride with HCl and precipitated with SMB.

This is just speculation from my side, this is nothing I have tested myself and I'm not sure it will work or even precipitate most of the gold. Calcining the gold hydroxide might lead to large losses as dust.
Try it on your own risk, but you seem to be good at theoretical calculations and you might have access to better tables of solubility constants so you can check it before testing.
I also suggest a couple of test tube sized trials before committing a larger lot.

Göran

 

[snoman701]

It would also add copper where there doesn't need to be copper. Why contaminate something if it's not necessary. 8)

It already has copper in it. The cost to dispose of copper laden aqua regia doesn't change by concentration. Add a chelator and it goes up considerably.

The copper is 100ppm if I read right Sno. That's 100g per tonne. Did you read that bit wrong? 8) 8)

No, I didn't read it wrong.

100 PPM in solution might as well be 1000 when it comes to waste disposal.

Now, as for endothermic or exothermic. The addition of sulfamic acid crystals to hot aqua regia with free nitric causes the temperature of the solution to go down. While the reaction is exothermic, the dissolution is endothermic.

Do you premix a sulfamic acid solution and add it?

 

[g_axelsson]

Maybe in this case using a base to neutralize the acid is the right way to go.

When the solution becomes basic the metal ions will precipitate out as hydroxides. Then the solution can be filtered and washed to get rid of nitrates and chlorides.

Then the gold hydroxide can probably be calcined and turned back into metallic gold or dissolved back into gold chloride with HCl and precipitated with SMB.

This is just speculation from my side, this is nothing I have tested myself and I'm not sure it will work or even precipitate most of the gold. Calcining the gold hydroxide might lead to large losses as dust.
Try it on your own risk, but you seem to be good at theoretical calculations and you might have access to better tables of solubility constants so you can check it before testing.
I also suggest a couple of test tube sized trials before committing a larger lot.

Göran

Just found this thread... proving that everything has already been discussed on the forum. :lol:
https://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=3959

Göran

 

[snoman701]

well, it was also sort of the OP's plan in their first post

 

[Platdigger]

Another thing about using a hydroxide, at least in this situation, is that the nitrates are still recoverable.
That is of course if there is any interest in recovering them.

 

[anachronism]

Well at 140 degrees C the Gold Hydroxide turns to gold oxide, so reducing that to gold metal is another step too. This is fun 8) 8)

 

[Platdigger]

I found this post made by "SilverNitrate" The context was the original poster was asking if "Anybody on this forum ever use sodium hydroxide for a precipitant on A/R ?"

SilverNitrate posted: "I do, if only seeking gold from your AR, you must slowly add it (NaOH in water) to the AR until just before a color change (turn cloudy)."