# PbSO4 precipitate in my AgNO3?



## Jaffajake (Jul 12, 2012)

Hello guys! I have a query for you. Today I was precipitating some silver out of a sterling silver refing that I'm currently doing and I saw a white cloud form when I accidentally introduced some sulphuric acid into my nitrate solution and saw an instant white precipitate. I've read that this can be due to the acid reacting to lead that may be in solution and turning it into lead sulphate. I initially thought it was silver sulphate forming, but I thought that was somewhat soluble. Any help would be very much appreciated because I'm starting to go bald from scratching my head too much! Thanks,
Jake.


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## Lou (Jul 13, 2012)

If it came from soldered pieces, probably is lead.

We see that lead solder lowers sterling assay by 2-3%.


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## Jaffajake (Jul 13, 2012)

I think it is a lead contaminate because the precipitate isn't dissolving back into solution whereas silver sulphate would dissolve back. I don't want to risk adding anymore to precipitate lead if all I'm doing is precipitating the silver. That would be counter productive. Thanks for letting me know about the assay though, I didn't realise silver solder contains lead, but then again, I did realise it needed something in there to bring down the melting point.


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## NoIdea (Jul 13, 2012)

Boil in concentrated caustic soda, it will disolve the lead sulphate(and most lead compounds), and turn your silver chloride to insoluble silver oxide, and filter. It's alot easyier filtering silver oxide than silver chloride.

Hope this helps.

Deano


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## Lou (Jul 13, 2012)

Silver oxide is soluble in excess base, enough to matter.


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## Jaffajake (Jul 13, 2012)

Right, so i can boil AgO in lye without having to turn it into AgCl. That process will be enough to remove the lead. Thanks,
Jake.


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## NoIdea (Jul 13, 2012)

Lou said:


> Silver oxide is soluble in excess base, enough to matter.



True true, i should have added, the filtrate from the alkali digest, including the wash water, went into the same container, after cooling, a black precipitate had formed, this i re-filtered through the same filter. 

In essence, after the filtrate had been diluted, from the wash water, and cooled to room temperature, which down under is about 8 - 12deg.C at the moment,(Brrrrr) :lol: , any silver oxide should have dropped, hope hope. :lol: 

Silver oxide is more soluble in water than alkali solutions, from what i can gather, please correct me if i am wrong :shock: :lol: 

Deano


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## Jaffajake (Jul 15, 2012)

That all sounds fine. I don't think that silver oxide would be able to dissolve in water, because it's only Ag with an oxygen atom attached to it. You'd need the strong base or an acid to dissolve it.


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## NoIdea (Jul 15, 2012)

Jaffajake said:


> That all sounds fine. I don't think that silver oxide would be able to dissolve in water, because it's only Ag with an oxygen atom attached to it. You'd need the strong base or an acid to dissolve it.



Wiki says silver oxide solubility in water is 0.025g/lt, where my ISI hand book say it's 0.0022g/lt, so it's not really that soluble.

For my purpose, after dilution of the hydroxide leach, silver oxide drops out of solution.

Just found this, should shed some light on things.

Deano


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## Jaffajake (Jul 16, 2012)

Right, that makes sense


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