# CuO in Ag after dropping it with Cu



## WillGreen (Nov 14, 2012)

Dear All, 

I had some silver - both sterling and fine - with solder on it, so I decided to refine it. 
I never did this before and I am sure I made some mistakes. 
I put all the silver in a bowl, put some nitric acid and a bit of hot water on it and let the acid do its work. 
When the reaction was finished, I put some copper sheet (I didn’t weigh anything) in it and the silver dropped. At this point, I left the bowl outside for the night - it’s cold in Ireland at night here, so the following days, I found some blue crystals in the solution. Okay, this is not so bad. The problem occurred when trying to remove some of the copper which did not resolve. Some silver cement is sticking to the copper, so I try to brush it off with a water spray gun: the silver gets loose, but I am also getting some deep red liquid, copper oxide of some sort, I’m sure. Of course, I want all the copper out before I dry and melt the silver cement, but I do not know how. Is there a way? Or should I melt everything I have so far and use electrolysis to get the silver pure? I have never done this before and my only source is a video I found on You Tube (actually made by a member of this forum). 

Excuse me for asking such obvious questions. 

With best regards, 

Will


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## henos (Nov 14, 2012)

Rinse the precipitate, add nitric acid 1/1 with distilled water, dissolve the heat.
Add water and filtrate. Add NaCl or HCl. The rest you can find on the forum.


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## WillGreen (Nov 14, 2012)

Thank you. 
I am out of HCl at the moment. 
I just checked our kitchen salt - it has ferrocyanide in it (to keep it dry, I suppose). Do you think it would do? 

Best regards, 

Will


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## MysticColby (Nov 14, 2012)

ummmm, not sure how that helps him. he's already past that part.

you didn't mention it, but it's best to filter the dissolved silver into another container (it removes anything that didn't dissolve - dirt, oxides, etc). I use a coffee filter for this, but Whatman #1-6 are better choices if you don't mind spending a bit more.

CuO is one of the reasons you can't get above 99.4% pure silver from cementing on copper.
To remove as much CuO as possible, add HCl. preferably after rinsing away the copper nitrate (blue/green liquid). have the cemented silver in a beaker, add water to about a 1:1 slurry, then add a little HCl. It shouldn't take much, maybe 10 ml concentrated HCl for every 1L silver-water total volume? More CuO would require more HCl, but I wouldn't expect much CuO to be present. Stir for a few minutes. The water should get blue/green as the copper dissolves (HCl dissolves CuO to CuCl). After this, rinse with water again until after all the blue/green is gone. Then continue as usual. The End 

I like to dip my copper pieces I use for cementing in dilute HCl before adding to silver nitrate (then thoroughly rinse). It would take a long time for any copper to oxidize while submerged in the acidic silver nitrate solution (it can happen, so don't leave copper nitrate in with cemented silver for long periods of time)


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## MysticColby (Nov 14, 2012)

the NaCl or HCl that hanos recommended is instead of cementing on copper. the purpose of it is to precipitate silver as silver chloride (which wouldn't precipitate the copper, as copper chloride is highly soluble in water). It's really annoying dealing with silver chloride - avoid it if possible.


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## MysticColby (Nov 14, 2012)

hmmm... for lack of HCl. I know it's easily purchasable for cheap from places like Home Depot. I'm not sure if there's any decent substitute for this use. I know lemon juice + vinegar will remove copper oxide off of copper pieces, but it would probably be pretty hard to remove from silver cement, so I don't recommend it.


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## WillGreen (Nov 15, 2012)

Thank you Mystic Colby, 

I ordered some HCl and then we will see. 
I will follow your advice, but I am a bit confused: doesn't HCl attack both silver and copper, although slowly? 
If so, how will the HCl take care of the CuO problem without dealing with the silver? 
I am only asking. 

Kind regards, 

Will


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## butcher (Nov 15, 2012)

I must not understand this thread very well?
Do not wash silver powder in HCl.

I assume after dissolving silver you removed solution from powders that did not dissolve in nitric acid and filtered, (leaving gold or other metals which nitric would not attack), then added copper to the filtered solution to cement silver and palladium if any.

if you cemented silver (as silver metal powders) from a solution of silver nitrate and copper nitrate, the blue crystals are probably water soluble copper nitrate, brushing the copper to remove silver you may have brushed off some copper, adding a little dilute nitric solution would dissolve the copper (decanted solution could be checked for silver either cementing on copper or precipitating as a chloride).

I would not add salt or HCl to the silver powders cemented with copper it would coat the silver chloride and create trouble melting and losses of silver.

(Do not add HCl or salt to your elemental metal silver powders).

I believe henos, was saying wash cemented powers in dilute nitric acid with heat to dissolve the copper, and wash with water (Hot), filter the silver (although I normally just decant solutions), and I believe henos was also saying to recover silver from the wash water as a chloride using HCl or salt. Which I agree with (as a way to get silver from wash solution), but I would not form chlorides of my silver powders. 

When washes come clear take a small sample and add some household ammonia if you still have copper in solution the rinse water will turn bright blue indicating you can wash more copper out of your silver.

if you do not have HCl use copper to cement any silver from wash water or collect the tiny bit in your stock pot.


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## WillGreen (Nov 16, 2012)

Dear Butcher and Mystic Colby, 

Thank you for your input. 
I was thinking about what Mystic Colby said about removing CuO with lemon juice and vinegar. 
I know that this works, many things work, citric acid for example is used by some who do not trust Sparex. 
Sparex is a traditional pickling compound for jewellers. It is globular sodium bisulphate. It cleans stuff well enough after soldering etc. 
I was wondering if I could use Sparex to clean the copper out of the silver cement. It's probably a bit naive, maybe not. 
What do you think? 
The silver cement looks exactly as it should look, but there is some red powder in it - the CuO and it has to disappear. 

With best regards, 

Will


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## MysticColby (Nov 16, 2012)

but HCl doesn't dissolve silver, why would you lose silver if you add HCl to silver cement? and wouldn't sulfuric behave the same way? (dissolve CuO but not silver)

At first, I thought henos was outlining the entire dissolve silver and precipitate as a chloride procedure. I recall that nitric does dissolve copper oxide, but it would also dissolve the silver. so you then have silver nitrate in solution. At one point I wondered if copper oxide would double-displacement with silver nitrate to produce copper nitrate and silver oxide. I believe I never found a suitable answer for that one, though I do know that heating silver oxide will decompose to metallic silver.

It's likely not even a major contaminant. If melted, just add a bit more borax, and most of the CuO will get stuck in it. The resulting silver will be a little less pure - how pure did you need it? under ideal conditions, the best cemented silver possible is around 99.4%. this batch would produce something a bit lower; maybe 98-99%?

I am unfamiliar with Sparex, but I would question if it would do anything to the silver or get stuck in the cement or convert the copper to something that also sticks in the cement.


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## butcher (Nov 16, 2012)

Cemented silver when dry can have very fine powders of silver, using a chemical to clean them like HCL, sulfuric or a sulfate could probably convert some of the silver to silver salts of these acids or add salts to these powders.

These fine powders would react much easier than a solid bar of silver metal will.

I would use the dilute nitric would dissolve any copper oxide that can be removed, and hot water washes, the check washes for silver.

This there is less chance of creating problems with your silver by creating other silver salts, with additions of other acids or salts of acids.


MysticColby,
Silver may not dissolve in hydrochloric acid, but HCl will defiantly react with silver, and will form a silver chloride passivated layer, and these cemented finely divided silver powders would either convert to silver chloride or would be coated in silver chloride.


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