# Questions on refining silver contacts w/ Nitric acid



## weedoublewide (Feb 16, 2020)

Good afternoon,

I'm doing some research and reading to find the best possible way to perform my experiment.

I have quite the abundance of small silver contact pads that are still soldered to the copper arms. When I've used a torch in the past to desolder them, it doesn't turn out well and I hate just throwing them away lol.

So I wanted to try dissolve the silver that's still soldered to the copper in Nitric Acid then refine it from the solution in several batches. 
Now from what I've read, you use copper to cement out your silver from the solution after you've finished dissolving your silver batch. 

So my question is, will putting the silver pad that's still attached to the copper arm dissolve first and then cement out after all the silver is dissolved? Or will a different line of events happen? 

Furthermore, I'm pretty sure some of my pads have cadmium in them and its a very dangerous metal when it is vaporized (Yes I always use a respirator and a fan when separating the larger silver pad from the copper). 

My second question is; What if I wanted to recover my silver from the cadmium using the same process? Would the cadmium be left over in the solution?

I assume some pretty dangerous fumes would be generated as well. 

I'm still reading and figuring stuff out, figured I'd ask before I swam. 

Thank you in advance for your help,


double


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## butcher (Feb 16, 2020)

If I cannot remove the contact (desolder the pad) with a torch, I will cut the contact away from as much of the base metal as possible, in order to limit the amount of nitric used on base metals.



The base metals and silver will dissolve into solution, contact points may have metals involved in the alloy that may not dissolve easily or at all such as tungsten, gold, platinum group...

As the nitric acid is consumed, it takes heat to completely consume the nitric acid, or it would take a terribly long time to complete at room temperature and without the strong agitation of the heated molecules...

When there is plenty of free nitric acid both silver copper and other metals are dissolved into solution, the solution becomes saturated with the different metal ions or becomes a soup of ionic salts.

Now we may have lots of silver ions some copper and other base metal ions surrounding the material to be dissolved, which may have a harder time coming into contact with the free nitric acid left in solution or in the soup of metal ions.

Once free nitric is consumed ( or almost consumed) and there are plenty of metal ions in solution these metal ions come into contact with atoms of other metals they may trade places with undissolved metal which are more reactive, for instance, silver ions in contact with a copper buss bar (or copper remaining on the material) will take an electron from the copper thus the silver ion becomes a silver atom which will join with other silver atoms to form a silver powder (cemented silver), and the copper atom missing its electron goes into solution as a copper salt, on the other hand, if free nitric is still in solution it may redissolve the cemented silver on heating, the silver molecules get more excited and bump into each other more and when the cemented silver comes into contact with the remaining free nitric acid could dissolve it back into solution...


From where cadmium is placed in the reactivity series of metals we see it will dissolve in the nitric acid.
and if you used copper to cement the silver the cadnium ions will stay in solution.

but if we cemented the copper from solution using iron, the iron will also displace the cadnium metal from solution along with your copper...


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## weedoublewide (Feb 28, 2020)

All all that makes sense, thank you

I do have one final question, 

So what color is the cemented silver powder look like? I've read its a fine powder, but what color should one expect?


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## butcher (Feb 28, 2020)

Gray just like cement, that is why they called it cementing silver...


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## weedoublewide (Feb 28, 2020)

sometimes is struggle putting one and one together...college can only teach you so much :shock:


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## weedoublewide (Feb 28, 2020)

So the pads are trimmed as close to the silver as possible, can you assume it is 50% Ag and 50% Cu for a close approximation of how much 50/50 solution you'll need?

I figure this since half of the pad is Cu or brass and the other half is Ag (actually a mix but for now assume 95%).


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## anachronism (Feb 28, 2020)

And cementing copper is called cementing because it's gray like cement. Oh... wait...


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## weedoublewide (Feb 28, 2020)

DUN DUN DUN..


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## etack (Mar 2, 2020)

You have a pic of your contact? There’s an abundance of experience in removing contacts on here we might give you some pointers. 

Eric


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## nickvc (Mar 2, 2020)

If you have an abundance of these contacts and can separate the non cadmium ones then melting some into a bar and using that to cement your dissolved silver will also recover some more of your silver for free and give you a free source of copper.


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## Beercan 51 (Mar 2, 2020)

So, I am wondering why AP solution is not considered. I am far from an expert, and still learning. I also have no good source for nitric acid, so what little i do have is only to be used when I know what I'm doing. thanks, Jim


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## weedoublewide (Mar 2, 2020)

nickvc said:


> If you have an abundance of these contacts and can separate the non cadmium ones then melting some into a bar and using that to cement your dissolved silver will also recover some more of your silver for free and give you a free source of copper.


Let me see if I understood that right. 
Take the non cadmium contacts and melt it into a bar, with the silver and copper still attached as one. Then use that to cement your solution once its time to recover the silver? 



Beercan 51 said:


> So, I am wondering why AP solution is not considered. I am far from an expert, and still learning. I also have no good source for nitric acid, so what little i do have is only to be used when I know what I'm doing. thanks, Jim



I didn't roll with the AP solution because it added an extra recovery step to the process. Plus I have access to nitric and HCL at work so I just went with the more dangerous one, like a toddler lol. 

Do you use it for the smaller contact pads like in the photo? and if so whats your percent yield normally?




etack said:


> You have a pic of your contact? There’s an abundance of experience in removing contacts on here we might give you some pointers.
> 
> Eric



Here's an assortment of some of the smaller pads I've trimmed. With the larger pads, a torch works really well with removing them from the copper bar. But in this case, its to much heat and melts everything, even with the smaller tip.


Thank you everyone with your questions and help.

double


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## FrugalRefiner (Mar 2, 2020)

They're pretty closely trimmed. You can use them in your stock pot. They will use up any excess acid, cement any residual PMs, and leave the contacts to be processed free of the base metals. It's a frugal approach. 8) 

Dave


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## etack (Mar 3, 2020)

Those small ones a coil hot plate works really well. It gets them hot and doesn't burn them up.

https://www.walmart.com/ip/Mainstays-Single-Burner/812501747?wmlspartner=wlpa&selectedSellerId=0&adid=22222222227278080936&wl0=&wl1=g&wl2=c&wl3=336252467694&wl4=pla-653175837017&wl5=9015767&wl6=&wl7=&wl8=&wl9=pla&wl10=8175035&wl11=online&wl12=812501747&veh=sem&gclid=EAIaIQobChMI6uLj48j95wIVyEXVCh0cVgLfEAQYASABEgKED_D_BwE

Eric


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## weedoublewide (Mar 3, 2020)

etack said:


> Those small ones a coil hot plate works really well. It gets them hot and doesn't burn them up.
> 
> https://www.walmart.com/ip/Mainstays-Single-Burner/812501747?wmlspartner=wlpa&selectedSellerId=0&adid=22222222227278080936&wl0=&wl1=g&wl2=c&wl3=336252467694&wl4=pla-653175837017&wl5=9015767&wl6=&wl7=&wl8=&wl9=pla&wl10=8175035&wl11=online&wl12=812501747&veh=sem&gclid=EAIaIQobChMI6uLj48j95wIVyEXVCh0cVgLfEAQYASABEgKED_D_BwE
> 
> Eric



You just changed my whole world. I got one of those already set up. 
I'll be right back!


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## weedoublewide (Mar 3, 2020)

Well my burner didn't work, either I didn't leave them on long enough or it doesn't get hot enough. 

What type of solder do they normally use between the silver and copper/brass?


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## weedoublewide (Mar 3, 2020)

So I put 100g of silver pads in my little mixing dish and put 100mL of nitric acid and 100 mL of distilled water (opened for about a day). 

I mixed it all together and set it outside for a couple hours and came back to stir and noticed some white clear crystals in the bottom. It almost looks like AgCl but I'm not sure how that could've happened. Unless the distilled water got contaminated by being open. 


The water went straight to blue which was odd because the previous smaller batches I experimented with went from a emerald green then blue when I added the copper pieces to it. 


Any thoughts?


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## weedoublewide (Mar 4, 2020)

The only thing I can think of is either my distilled water water became contaminated from being open for a day. Or I need to add more nitric acid to the solution. 

I’ll be trying it later today when I get home from school, 
I’m all ears on past experiences or ideas. 

Thabk you in advance,
Double


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## FrugalRefiner (Mar 4, 2020)

It doesn't look like silver chloride. Leaving distilled water open wouldn't cause it to become contaminated with chlorine. It might be silver nitrate. I would try adding some distilled water and a little heat (just not in that measuring cup) to see if it dissolves.

Dave


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## weedoublewide (Mar 4, 2020)

FrugalRefiner said:


> It doesn't look like silver chloride. Leaving distilled water open wouldn't cause it to become contaminated with chlorine. It might be silver nitrate. I would try adding some distilled water and a little heat (just not in that measuring cup) to see if it dissolves.
> 
> Dave



Lol my teacher literally just said something about silver nitrate crystals and my brain went oh. Shit. Duh. 

I appreciate the help Dave I do.


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## g_axelsson (Mar 24, 2020)

weedoublewide said:


> Well my burner didn't work, either I didn't leave them on long enough or it doesn't get hot enough.
> 
> What type of solder do they normally use between the silver and copper/brass?



Smaller contact points like this are often spot welded to the base metal. So no solder at all in that case.

Göran


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## g_axelsson (Mar 24, 2020)

weedoublewide said:


> The water went straight to blue which was odd because the previous smaller batches I experimented with went from a emerald green then blue when I added the copper pieces to it.



Emerald green can be caused by several reasons. Since copper nitrate is blue and silver nitrate is colorless the green color comes from something else. 

- NOx gases dissolved adds red to a solution and that would make it looking more green, it would go away when the reaction calms down and the NOx gases leaves the solution.

- If there are some palladium in the contact points the red palladium nitrate gives the solution a green color that stays even after the reaction is over.
For a good example of this, look at the solution when I removed the palladium contamination from a gold button via inquartion.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=61&t=19840#p236827

Göran


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