How to seperate mixed copper and silver?

[Ragnor]

I have been trying to work out acid dissolution of some mixed metal nuggets I recover while placer mining. These are course oxide coated nuggets. The primary metals would be lead, copper, silver, gold, PGE. Now obviously the gold and PGE is easily accomplished with nitric acid. However I am confused how the process will go with the mixed lead/copper/silver. Knowing that copper will precipitate the silver nitrate how then will I separate the copper and silver since the copper will prevent the silver from being dissolved in the acid and the lead, I assume would precipitate the copper.

I hoping the folks on here can clear up how that reaction would go when attempting to refine these mixed metal nuggets in nitric acid. thanks.

 

[4metals]

What you need to do with this material is first part with nitric and distilled water, assuming the silver and nitric soluble metals will make up 75% of the weight. If they do not, you need to inquart to get complete separation. I assume by PGE you mean Platinum group elements?

Once you have parted in nitric the silver copper lead and palladium will be in the nitric acid and the insolubles, gold and the rest of the platinum group, will be on the bottom.

Copper will displace the silver only after you have consumed the free nitric acid. So once you have filtered the solution you need to add copper to consume the free nitric acid and drop the silver. This will also drop palladium. If the palladium is not very high in concentration, a solution of DMG will selectively drop the Pd out of the nitric solution leaving the copper, lead, and silver. The copper will then cement out any silver as a metal leaving the other base metals in solution. The Pd will be in the form of a salt, palladium dimethylglyoxime.

The insolubles from the first nitric dissolve are processed in aqua regia using methods described in the forum.

 

[Ragnor]

What you need to do with this material is first part with nitric and distilled water, assuming the silver and nitric soluble metals will make up 75% of the weight. If they do not, you need to inquart to get complete separation. I assume by PGE you mean Platinum group elements?

Once you have parted in nitric the silver copper lead and palladium will be in the nitric acid and the insolubles, gold and the rest of the platinum group, will be on the bottom.

Copper will displace the silver only after you have consumed the free nitric acid. So once you have filtered the solution you need to add copper to consume the free nitric acid and drop the silver. This will also drop palladium. If the palladium is not very high in concentration, a solution of DMG will selectively drop the Pd out of the nitric solution leaving the copper, lead, and silver. The copper will then cement out any silver as a metal leaving the other base metals in solution. The Pd will be in the form of a salt, palladium dimethylglyoxime.

The insolubles from the first nitric dissolve are processed in aqua regia using methods described in the forum.

Thanks for the reply.
Yes, by PGE I am referring to the platinum group elements.

So, I understand your response to mean that as long as I use a slight excess of nitric acid then I will not have a problem with the silver precipitating out prematurely? Is this correct?

 

[4metals]

That is correct.

 

[kjavanb123]

In a small test I did recently, when added DMG to a nitrate solution that had silver and palladium, the yellow powder was more like pink in color, but when we dropped the silver with table salt, filtered it and added DMG to nitrate solution the powder color was exaclty canary yellow as it suppose to be.

My conclusion was DMG did not work on nitrate solution with silver and palladium.

The same scenario did not happen with copper palladium nitrate solution.

Regards
Kj

 

[anachronism]

Pink with DMG is Nickel unless I'm very much mistaken.

 

[4metals]

DMG will only indicate nickel in an alkaline solution so it is likely not the reason for the pink color.

I have always removed the silver as a chloride before recovering Palladium with DMG and as a result always had a yellow PdDMG salt.

 

[anachronism]

My DMG is made as an alkaline solution is that why I get the pink with Nickel 4metals?

 

[4metals]

The net pH of the solution you are testing should be acidic. If you test a small sample and the few drops of DMG are dissolved in caustic, the net pH may be alkaline and then it will indicate Nickel and not Palladium. If you are dropping a few drops of alkaline DMG into a 100 ml beaker of aqua regia, it should have a net pH that is acidic.

 

[Rocky888]

DMG does work on nitrate solutions with silver and palladium, you just have to dump it in dry and wait a few hours. At least that's my experience from refining MLCC's from nitric. If you dissolve DMG in sodium hydroxide and pour into weak nitrate solutions I've gotten anything from pink to dark red to white.

 

[anachronism]

4metals and Rocky

Thanks guys.