# Electrical Contacts



## Long Shot (May 28, 2014)

Good day people,

I've searched this site for an answer to this question but can't seem to find exactly what I'm looking for. I have about 2 pounds of closely trimmed silver contacts from various devices (including some nice ones from old elevator switches) that have various base metals attached (some copper, some brass, some of an unknown - the elevator ones, they are "springy") and would like to process them with cementing in mind if that is the best option. I'm thinking that I could just put the HNO3 to them and let the copper base do it's thing? Any helpful suggestions and/or guidance would be appreciated. 8)


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## Westerngs (May 29, 2014)

If what you are thinking is that the copper already contained in the contacts will cement out the silver, that will not work. This would only work if you had such an excess of base metals that the silver would dissolve first, then the leftover base metals would cement out the silver. That is usually not the case, usually there is more silver than base metal in contacts.

You would need to separate the base metals out before dissolution. Once the silver has dissolved, add the base metals to cement out silver.

Make sure to use the least amount of nitric acid necessary to dissolve the silver.


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## Smack (May 29, 2014)

You can do it with the contacts still attached to copper but the cleaner they are the better. It will just take more Nitric to do the job, then still cement out with copper, or you could cement it with some silver plate scrap if you have some. Keep in mind that if at the end of the digestion if there is excess Nitric you will see Ag cement out on the copper then redissolve, that is ok, it will just take it a while for the copper to use up the excess Nitric and once it has it will completely cement out your silver and Pd if present.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=39&t=12656&p=140157&hilit=+silver+contacts#p140157

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=50&t=12283&p=122244&hilit=+silver+contacts#p122244


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## Ollie1016 (May 29, 2014)

Long Shot said:


> Good day people,
> 
> I've searched this site for an answer to this question but can't seem to find exactly what I'm looking for. I have about 2 pounds of closely trimmed silver contacts from various devices (including some nice ones from old elevator switches) that have various base metals attached (some copper, some brass, some of an unknown - the elevator ones, they are "springy") and would like to process them with cementing in mind if that is the best option. I'm thinking that I could just put the HNO3 to them and let the copper base do it's thing? Any helpful suggestions and/or guidance would be appreciated. 8)



Hello, 

I saw a tutorial on YT (Drew Metalsmith) and I think that he added Conc. HCL. And this dissolved a lot of the base metals, and left the silver untouched. He then proceeded to dissolve the remaining silver contacts in Nitric and cement out.

Hope this helped.

Ollie


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## Long Shot (May 29, 2014)

Thank you Smack for those links - they are very relative and useful, guess I just wasn't searching for the right phrase. I'll use the AP at 3:1 to rid myself of the base metals. Ollie - I found the Youtube video from Drew Metalsmith where he uses AR and a slight addition of AgCl as a "passivation" layer which dissolves the bases but not the silver, he then dissolves with straight HNO3. AP sounds like a lot cheaper route with less hassle. Westergs - I processed about 650 gms of high quality silver plated brass spade quad connectors awhile ago and they "self cemented", that is where the thinking came from but I get what you are saying. To be clear, here is a random sample of what I have:


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## Barrie Gold Buyer (May 30, 2014)

Just so readers know, ALOT of contacts have cadmium present and when melted it can be extremely hazardous to your health.


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## Long Shot (May 30, 2014)

Just so readers know - I intend to dissolve the clean contacts with HNO3 and cement out the silver.


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## Smack (May 30, 2014)

Long Shot, you'll need to incinerate after AP to get rid of the HCL before you go to Nitric or you could end up with some silver chloride.


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## Long Shot (May 30, 2014)

Thanks Smack, good advice. On that note, would I do that immediately after the wash, not letting them dry out or can I let them dry and accumulate a decent quantity and do the incineration in a large batch? I live in the city and my neighbour has a legal fire pit that he will light up now and then when there is enough wood around. I would use that and put the contacts in an enclosed steel box I have, place it in the center of the fire build and let er' roast. If I have to do them without letting them dry I can arrange something. I am still plugging through Hoke's book and although I am getting informed I am not at expert level - thinking the incineration volatilizes the chloride?


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## Smack (May 31, 2014)

They can dry out, if you start the incineration process with them wet they will soon dry anyway. You shouldn't have any chlorides to worry about doing them this way.


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## pimpneightez (May 31, 2014)

What's the best way to get the lead solder out of the equation? I have a bunch of relatively clean contacts. I can see some solder still attached to them. Is hot HCL the way to go? Then incinerate? If this is the best way how long do you have to keep them in the HCL? I was also thinking I could drop the silver by using Mylar keyboard sheets. Is this a good idea or should they be reclaimed separately?


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## Long Shot (May 31, 2014)

I suppose it seemed like a dumb question based on the answer Smack, just wasn't sure if the HCL would continue to build AgCl while sitting around. Thanks for your input, much appreciated.


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## Long Shot (May 31, 2014)

Pimp - Although I am no expert on this and other subjects related to PM recovery I do think I can say this, if you see lead solder around your contacts then they are not likely contacts. They are usually affixed to the base metals either by punch expansion or by silver solder. Contacts conduct current and can get hot, and that sort of heat would melt lead/tin solder in most cases. FYI - Hokes book, pgs 70-71 refers to using hot HCl to soften lead/tin solder that is exposed and then one has to scrape it off. Silver solder is broken loose with a higher temperature torch.

As far as using hot HCl goes, the method referred to is AP or acid/peroxide. Hydrochloric acid (HCl) is readily available as "Muriatic Acid", is 32% strength and is cheap - usually $10 to $15 a gallon or 3.785 litres here in little old Canada. Hydrogen peroxide (H2O2) is an oxidizer and adds, you guessed it, oxygen to the process. It is readily available at 3% strength and is cheap, $1 for 500 ml at our Dollarama in CA. You can buy stronger H2O2 at pool supply stores (up to 27%). AP methods typically use HCl to H2O2 at a 3:1 ratio and do remove base metals but it is slow (I have had my contacts in warm bordering on hot AP for about 30 hours and they are about half clean and have added AP twice to keep the strength up). AP only briefly attacks silver as the chlorine in the HCl reacts with the exposed silver and coats it with silver chloride (AgCl) which is impervious to further attack by the acid.

The gist of the conversation between Smack and myself is that when I go to process the cleaned contacts with nitric acid (HNO3), the remaining HCl (you can't get it all off with wash water) will react with the freed silver ions and create AgCl which is troublesome, or better yet a pain, to recover the silver from. By incinerating the cleaned contacts it takes the HCl out of the equation so when they are dissolved with HNO3 most of what will be in solution will be silver ions which are then easily "cemented out" with clean copper bar stock or tube. I have done this a few times with high quality, large amp contacts that I removed from their base metals with an oxy/acet torch by breaking loose the silver solder. You get a blue solution of HNO3, Ag, some Cu and whatever other slight additions may be in the alloy. You then dilute the solution with about 50% DI water (don't use tap water, it has that pesky chlorine in it) and when you add the Cu bar the silver exchanges with the copper and a grey mud forms around the bar stock and readily fall off to the bottom of the beaker. It does not get 100% of the Ag out but most. You decant the solution, filter and wash the mud with ample water (tap water can be used for this but I stick with DI), spread it out to dry in a flat dish and then when dry you can melt it with the torch and cast an ingot of about 89 - 90% purity, maybe better. From there, electrorefining will yield quite pure silver if done properly - another topic entirely.


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## Smack (May 31, 2014)

pimpneightez, I have never come across lead in breaker type contacts. I have never run them through HCL first, I just HNO3 them then drop with Cu. Mylars to drop silver? When you use another metal to drop one out of solution, the one your using to drop has to replace the one in solution so I don't think mylars would work at all, you could try though. Take a small sample say 50ml of solution and cut a small piece of mylar and stick it in. Then let us know what happens. I mentioned before about using silver plated scrap to drop Ag. that way you get even more silver during the cementing process.


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## pimpneightez (Jun 1, 2014)

My bad. I just assumed it was a lead/silver solder mix holding the contact points in place. So being that my contacts are fairly clean I could go right to nitric. I do have some with copper plating and gold plating in the mix. I don't think that would be an issue though. As far as the Mylar to drop I'm going have to agree that won't work. I guess it wouldn't hurt best case scenario would be you saturate the solution with silver. Only downside is you might have a more pure sample from the m ylars if you did them separately. I do have a bunch of small silver plated electrical parts. Makes sense to use them to drop the silver. I was just wondering if there are any other base metals used to plate silver that could mess with the purity.


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## justinhcase (Jun 1, 2014)

How pure is the silver on the contacts??
I was thinking if i add them complete with the copper bit's attached to cement silver from Silver Nitrate.
The copper would be eaten as it replaced the Silver in solution and the silver contacts would be left in the cemented silver.
If the silver contact alloy is strong enough to hold in one piece you could easily sieve them out from the cemented silver(I always sieve to find any little bit's of copper that have drooped off.)for conventional digestion.
And any contacts you miss will not do much harm as long as you are using a silver cell after that.
Any other base metals will have the same effect as copper, they will simply drop the next metal on the periodic table which will then in turn will drop the one above that like a daisy chain reaction until you mostly have silver.
Justin


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## Long Shot (Jun 1, 2014)

Smack - I have a bag full of silver plate flatware that I was wondering what to do with, excellent suggestion about using them to drop the Ag, never thought of that. Goes to prove why this forum is excellent!


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## justinhcase (Jun 1, 2014)

Humm.Not sure if silver plate would contain enough silver to warrant the extra time in washing.
i have found that if you have to much pollutant metal that is more reactive than copper it make the silver hard to wash out.
No matter how careful you are a good proportion of what is in solution stays with your desired metal.
Some one posted a very quick reverse electrolysis bath with a 12v battery which took the silver plate off very cleanly in seconds.
But the best use for silver plate is to donate it all to charity when you have enough.
I am not sure what the limit is in your country but over here You are aloud to claim up to 45% of the new cost of similar items as a tax deduction once you have donated it.a much more profitable use.


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## Smack (Jun 1, 2014)

I've used some of the tiny plated contacts, (you know, the ones that you can't get off without melting the whole thing into a blob) to cement silver.


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## Long Shot (Jun 1, 2014)

Smack - Yes I do know what you mean and that is also an interesting proposal to try.

Justinhcase - no such provision exists here in Canada. As a matter of fact, charity organizations here have to collect 13% tax on used items that are donated to them at point of sale. Sometimes there are some decent items donated but mostly it is junk that no one wants, i.e. leftovers from yard sales, etc.. Perhaps that would change if a provision such as you suggest existed. The Canadian government are world leaders when it comes to taxing but there is little room for tax deduction for the average, working person. Now if one is on welfare well that is a different story!


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