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Advice on purifying silver nitrate / plating out silver

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Q. I have some 10% Silver Nitrate solution contaminated with some unknown copper salts; probably nitrates.
I would like to drop the Silver out in as pure a state as possible in order to try to re-use for jewellery purposes.
Could I have some advice please on a simple method of plating out the Silver with minimal Copper contamination.
Would immersing a copper rod in it work well enough?
Regards,

Martin Rich
Engineering - Plymouth, UK


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A. Copper rod might work but I think that you can simply mix your solution with saturated salt solution-result must be white mass of silver chloride(rest of solution can be discarded). Chloride can be used for preparation of cyanide free silver plating solution (search www.uspto.gov website, where you can find some useful old patents ). Good luck!

Goran Budija
- Zagreb, Croatia


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A. If your silver nitrate is contaminated with copper, if you try to use it as an electrolyte, you will get a copper-silver codeposit. Silver plating is best done using cyanide and this is highly toxic and MUST NOT be used by the inexperienced - it could kill you and your neighbours! Furthermore the water companies do not like having cyanide thrown down their drains, so they could take you to court. There are non-cyanide systems, but they are not easy to use. If you still decide to do silver plating, you will need a silver anode, so that again increases your costs.
If you put some copper wire into the silver nitrate, you will get a black precipitate of colloidal silver as the copper is dissolved by the silver nitrate solution. this will be quite pure and can be remelted to give pure silver.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


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A. Throw some clean steel wool [linked by editor to product info at Rockler] in it, along with a little nitric acid. The silver ought to "cementate" out onto the iron. Then, take the resultant black glop, wash it with water, and throw it in some hydrochloric acid. This should dissolve the residual iron, leaving silver powder.

dave wichern Dave Wichern
- The Bronx, New York


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David, won't the hydrochloric acid also react with the silver to form insoluble silver chloride on the surface?

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

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Trevor, I think that the silver metal is going to be fairly inert to the HCl. I would use it in this application because it's very aggressive towards iron.

As for separating the Cu from the Ag, I think that nitric will dissolve both. It might work to use something like persulfate that they use in etches for Cu.

Dave Wichern
- The Bronx, New York

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Q. Thanks Trevor.
My chemistry knowledge is just good enough to have kept me away from the Cyanide route, but not good enough to best understand what is going on here.
I've tried the copper insertion technique using plumbing water pipe; this has dropped out the silver as a grey (not gray) mush. But washing well, and drying followed by melting has left me with a silver-like solid which analyses as still contaminated with Copper - not sure of the percentage. Any thoughts? I also don't know much about casting for jewellery; is the mould material critical, and what flux if any would be best?
Kind Regards
Martin Rich

Martin Rich
Engineering - Plymouth, UK


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A. If you have a silver-copper mix, you could use it as sterling silver!. However if you want pure silver from the contaminated solution, you will need to make sure the precipitated silver is thoroughly rinsed - there could be solution entrapped in the silver colloid. Also try heating the precipitated silver in dilute warm nitric acid; it may fume a bit with nitrogen dioxide gas, so do it in a fume cupboard. All being well, this should only dissolve the copper and leave the silver alone, but check it doesn't redissolve the silver by adding a couple of drops of sodium chloride solution to a small sample of the nitric acid washing solution; if it turns cloudy white, it has some silver in it. If this is the case, you will need to re-precipitate the silver with copper and wash it again with cold dilute nitric acid.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

December 11, 2013

A. Dear Sir,
Copper nitrate residue is difficult to remove and will result in a poor quality silver button. I use hot water and a little grain alcohol (4/1) as a rinse solution for silver cement. It takes many rinses to remove the copper nitrate. Test the rinse solution for traces of copper nitrate by taking 5 ml. in a test tube and adding a few grains of sodium hydroxide. If the copper ion is present, a greenish/blueish precipitate will form, eventually turning black. Continue the rinse process until no longer giving this reaction.
Hope this helps.
TMJ

Thomas M. Joseph
precious metals - Aurora, Colorado, USA

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