Whittish-grey powder in refined gold

[Renaldas]

Refined small batch of contacts several days ago and got interesting results I cant understand. There were about 20 gramms of thick gold plated contacts with solder on them. Processed with AR, filtered, added clear filtered solution left from previuos treatments (mostly, copper solution) plus dissolved precipitant and carmabide to neutralize excess nitric and drop precious metals, washed this precipitant and processed one more time thru AR process. Got nice orange solution, filtered it again, neutralized excess of nitric acid with carbamide and added chemical grade SMB powder. After gold precipitated, I noticed, that there was large amount of fine whittish-grey powder inbetween gold powder. This powder was not able to dissolve in boiling hydrochloric acid. I processed this gold-grey powder precipitate via AR one more time and got nice orange solution, but there was a huge amount of white precipitate on the bottom of the vessel (about half volume of all original precipitate). Filtered it one more time, neutralized nitric with carbamide and added SMB powder again. And again got the same result with "dirty gold" precipitate. Then I simply heated my beaker and noticed fizzing occuring mostly in the places where this "mud" was concentrated. After about 10 minutes of fizzing, grey substance dissapeared, and nice brown gold powder left.
What could possibly this grey precipitate powder be?

 

[Renaldas]

It is a pity, but some mud left after my solution cooled down. Tried to wash for several times with boiling water, with ammonia and with HCl, but I cant get rid of these particles.

 

[Renaldas]

And one more interesting observation. After I dissolved all this powder in nearly boiling AR, I got clear orange solution without any precipitate. But as soon as the solution began to cool, white precipitate began to form, and here you see it.

 

[samuel-a]

Lose the UHP.

That's the only variable the i can think of, assuming you eliminate AgCl properly.

Use just enough nitric to dissolve the gold, so that you won't have to nutrlize it later.

Don't pre mix the AR, add the nitric with small incriments at a time, let each addition to react completely with the gold before the next addition.
Add until no more reaction of solids occur upon addition.
Heat will serve you well, about 80-90C.

Good luck.

 

[qst42know]

When all was in solution did you use any sulfuric acid to precipitate lead?

Lead chloride would be my guess.

 

[Renaldas]

Lose the UHP.

That's the only variable the i can think of, assuming you eliminate AgCl properly.

Use just enough nitric to dissolve the gold, so that you won't have to nutrlize it later.

Don't pre mix the AR, add the nitric with small incriments at a time, let each addition to react completely with the gold before the next addition.
Add until no more reaction of solids occur upon addition.
Heat will serve you well, about 80-90C.

Good luck.

Thank you for a response!
But ... what does "Lose the UHP" mean?

 

[Renaldas]

When all was in solution did you use any sulfuric acid to precipitate lead?

Lead chloride would be my guess.

Sulfuric acid was added first two times to AR in several drops to milliliter ratio. Last time there was no sulfuric acid, only AR, where all the substance dissolved when solution was very hot and began to precipitate again when it cooled down.
This time I simply waited for a solution to fully cool down and filtered this precipitate, after this I precipitated gold again with SMB, boiled it, washed several times with boiling water and HCl, and it seems, that no more whittish precipitate left.

 

[qst42know]

Dilute and cold to filter for silver which would be the other suspect.

 

[samuel-a]

UHP = Urea Hydrogen Peroxide (AKA Carbamide peroxide)
For some strange reason i thought you used it. Now i see you used plain urea (Carbamide). Anyway no need for it, just follow the last suggestion about the nitric.
Treat AgCl/PbCl properly and you are good to go.