Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-04-21T02:33:06+00:00
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Boiling Carbon in Aqua Regia (5 replies)

1 year ago

What happens if I boil pregnant carbon in aqua regia? Does it remove the adsorbed gold into solution? If so, can I bring the carbon loading to below 2gpt insuch a process?

Tarun Karakoti
1 year ago
Tarun Karakoti 1 year ago

The following reasoning may be speculative so take it w/a grain of salt: aqua regia is a very strong oxidizer forming the NOCl complex (3:1 HCl:HNO3) it will dissolve your current materials of construction the gold CN complex will likely dissociate forming soluble Au chloro-complexes a portion of which may be reduced to elemental Au on the activated carbon; you will liberate significant quantities of NOx unless others have a more positive perspective of this operation or at least bench scale experimentation to refer to, I would not recommend it.

Bill Rico
1 year ago
Bill Rico 1 year ago

I think some gold will diffuse out of the carbon but it will reach equilibrium. It is known that AuCl3 is reduces to gold metal in contact with activated carbon. If you are thinking to recover gold from carbon you should look at elution processes. If it is old carbon where you want to recover the gold burn it in a controlled way!

Something like this happen on the carbon but bear in mind that if you have an excess of nitric acid the gold reduction may not occur: 4AuCl3+6H2O+3C→4Au°+12HCl+3CO2

Alan Carter
1 year ago
Alan Carter 1 year ago

Gold cyanide is incredibly stable, will not be attacked by aqua regia and can even be distilled. Gold chloride is easily decomposed even with heat as in the Miller Process and readily becomes gold cyanide when exposed to free cyanide.

1 year ago
Hauptsturm 1 year ago

Dissolving noble metals the aqua regia plays two roles: it oxidizes the metal and forms its stable complex. When your metal is surrounded by excess of organic matter you will spend a lot of aqua regia to burn all this organics and only after that the metal can be dissolved.

Tarun Karakoti
1 year ago
Tarun Karakoti 1 year ago

Continuing with the discussion as it appears to have generated some interest: In acidic solutions such as loaded C in AR, the CN complex will precipitate out as AuCN solids with liberation of HCN gas Au(CN)2- + H+ = AuCN + HCN and/or form mixed ligand complexes such as[Au(CN)2Cl2]- ; I believe he is correct in terms of the stability of the Au(CN)2- complex (Beta 2=2*10^38) as compared to AuCl2- (Beta 2=10^9) so thermodynamically, it does not appear that reduction to metallic Au will occur in the presence of AR & carbon unless Au is already in the chloride state as the Au+1 or Au+3 complex.

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