# Silver Electrical Contact Refining Question - Help Needed.



## golddigger (Oct 20, 2007)

I have a few Lbs of silver / silver-cadmium alloy electrical contacts from relays, motor starters, etc. Most are mounted on copper or brass tabs, and clipped as close to the contact as possible.

Any ideas how to separate, purify, etc? I think I can figure out how to deal with the copper, but the cadmium has me stumped. The spec sheet on the relays reads; “Choice of silver-cadmium oxide or silver-tin oxide contacts.” So I’m not exactly sure what alloy they contain.

Any suggestions would be appreciated, either on this board or to [email protected]


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## Harold_V (Oct 21, 2007)

Here's a "Reader's Digest" version of a method to extract the silver:

Heat the contacts to redness, to incinerate contaminants (including oils), then dissolve them in nitric acid and water. You can use tap water, but expect a small amount of silver chloride to be the result. No big deal------and cheaper than using distilled water, which is the other option. Start with a 50/50 mix of water and acid, and allow the acid to work until it is exhausted before using more. As long as there's any copper, brass, or silver present, nitric will remain active until consumed. Dilute that solution with a little more water, decant, placing the solution on copper (below), then start with more acid/water. Do this until everything is dissolved. Watch that silver isn't poured off when the acid is spent. Silver will cement out on the base metals unless there is a little unused acid present. * Keep iron (steel) out of this process.* 

Recover the dissolved silver by cementing it on copper. Use pieces that are large, so you don't leave minute bits of copper behind when the silver has been precipitated. Fish out the copper and wash the silver "cement" with water until the wash is clear, dry, then melt. It's a good idea to use some borax when melting, which will absorb oxides of base metals that are sure to be present. The silver should be of decent quality. Copper won't precipitate any other elements that might be in solution with the silver, aside from those that are worth money-----platinum and palladium, should any of that get involved in the process. While platinum won't dissolve in nitric, that changes in the presence of silver, so on occasion you'll find traces of platinum in silver, although very rarely. When you do, the solution will be green, not blue. Palladium will readily dissolve in nitric, so if you happen to mix some with your silver, it will be recovered later, in the silver parting cell, assuming you go that far with your project. If you're interested in that idea, we can talk about that, too.

Cadmium will remain in solution and won't be an issue for you where silver is concerned.

Luck!

Harold


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## Fever (Mar 1, 2011)

Harold-

Could you enlighten me as to what problems Iron would create if dissolved along with Silver contacts in nitric acid? I have some contacts that seem to be an Iron button with a Silver contact soldered on top of it. I guess it could also be a Stainless button with a Silver contact on top. Maybe even Nickel? I'm not sure how to proceed chemically given the presence of the Iron. What is the best way to take it out of the equation?

Thanks very much!

Fever


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## Harold_V (Mar 2, 2011)

I don't recall having that problem, but unless it's extreme, I don't think you have anything about which to worry. If it's stainless, it likely won't present any problems, and if it's steel, it may dissolve, but it won't cement with copper. Some will drag down, but it will be removed when you melt the silver. If memory serves, silver and iron do not alloy----in fact, it's one of the ways to separate gold from iron, which will alloy. 

On the outside chance that you find iron is troublesome, after you've cemented the silver, there's nothing wrong with giving it a cold wash in HCl. That should remove the iron. 

Might be a good idea to give a report on your experience. That's how we all learn. 

Harold


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## lunker (Mar 2, 2011)

You will want to remove any Cd in the contacts prior to selling. I jumped the gun and sent in six pounds of clean contacts to specialty metals. They knocked the payables down to 70% from 90+% .A big difference, And well worth the effort. Lesson learned.


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## Fever (Mar 2, 2011)

Thanks for the sage advice Harold. I will follow that plan to a T, and report back when I have results.

lunker- I don't believe any of my contacts contain Cadmium, but due to the fact that I will be chemically digesting them and cementing the Silver out of solution, any Cadmium present would remain in solution, posing zero threat to the purity of the cemented Silver. I feel for ya! A 70% return on what you assumed would be a 90% return for your efforts is definitely a kick in the butt. If refiners can find a way to chisel away at your profits, they will do their best to find one! Rightfully so, I'd have to agree, as they do not want to pay for alleged values that aren't truly represented in an assay. I would encourage you to look into refining any future lots of Silver contacts yourself, at least through the cementation phase, so that you know definitively that you are producing an acceptable purity of Silver for later refinement or sale.

Fever


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## Drewbie (Mar 3, 2011)

The cadmium in solution after your processing would pose an environmental hazard and you'd want to deal with it as such.


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## lunker (Mar 3, 2011)

It was just a matter of lazyness on my part.I've learned not to be lazy when it comes to following a refining method.I guess I needed another lesson for everything else.


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