# Recover silver from molybdenum



## D1DR (Nov 13, 2016)

Hi Guys, new to the forum here, so please forgive my ignorance. I am new to refining and have successfully refined silver from electrical contacts and Sterling scrap a few times using nitric acid. Recently I acquired 4lbs of contacts that contain about 50% silver (Ag) 50% molybdenum (Mo) this had been confirmed by 2 separate XFR scanners. 

I have tried to desolve the contacts using 1 part 70% nitric acid and 1 part distilled water (warmed to about 160F) the result does not produce the usually light blue silver silver nitrate (AgNO3) nor does it completely dissolve the contact even if I add more 70% Nitric acid to the process. Instead the liquids is dark green and there is a light yellow powder residue left over as well as porous looking shape of the original contact. 

Questions:

1. Is nitric acid the correct acid to refine silver from Mo?

2. Has anyone successfully done something similar and can you share your process?

3. Can you provide any general advice?

Thanks in advance every one.


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## Lou (Nov 13, 2016)

They suck. That's just how it is. Breaking them into small pieces helps.

When they're all done that yellow powder should be left. Low concentration nitric works best


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## D1DR (Nov 13, 2016)

Thanks for you response. So I just need to keep at it and it should work out in the end?


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## kurtak (Nov 14, 2016)

D1DR said:


> So I just need to keep at it and it should work out in the end?



Correct - the Ag/Mo point are just more difficult to dissolve so take "more" time - run the heat below but near a boil & run the solution a bit more "dilute" then 50/50 to compensate for evaporation

I have only encountered the Ag/Mo points once & that was several years ago & if memory serves me right it took a couple days (maybe even 3 days) with heat to get them dissolved

Kurt


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## upcyclist (Nov 14, 2016)

D1DR said:


> I have tried to desolve the contacts using 1 part 70% nitric acid and 1 part distilled water (warmed to about 160F) the result *does not produce the usually light blue silver silver nitrate (AgNO3) *nor does it completely dissolve the contact even if I add more 70% Nitric acid to the process. Instead the liquids is dark green and there is a light yellow powder residue left over as well as porous looking shape of the original contact.


(emphasis mine) I think you might be mistaking the blue for silver--when you dissolve Sterling silver (or other copper/silver alloys) in nitric, the resulting liquor is light blue because of of the _copper _nitrate. Silver nitrate is colorless.


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## D1DR (Nov 14, 2016)

Thank you Upcyclist! I most definitely was confusing copper nitrate for silver nitrate based on your explanation. That makes sense now why I'm getting the odd green color, it must be the Mo in the nitric.


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## D1DR (Nov 14, 2016)

Thank you Kurtak! Wow 3 days that's crazy!

In the other batches I've done I have to frequently add distilled water to compensate for evaporation (about every hour). Did you do that every few hours for 3 days?


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## Lou (Nov 14, 2016)

I don't know about him but I just put them in a large glasses kettle with a condenser and a way to add peroxide, which seems to help.

You can also do them electrolytically, or so another refiner has told me--I never tried.


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## kurtak (Nov 15, 2016)

D1DR said:


> Thank you Kurtak! Wow 3 days that's crazy!
> 
> In the other batches I've done I have to frequently add distilled water to compensate for evaporation (about every hour). Did you do that every few hours for 3 days?



If you are having to add water every hour to compensate for evaporation you are evidently not using a watch glass on top of your reaction vessel

You should ALWAYS use a watch glass when dissolving PMs - not doing so will result in some loss of values as well as the evaporation problem & as well loss of the "full" potential of the acid to dissolve the metal (meaning using more acid to complete the dissolving of the metal)

With a watch glass on your reaction vessel - & depending on how much time it is on the hot plate it will reduce your need to add water (as a result of evaporation) to not needing to do it at all to "maybe" only once a day in a day long time spent on the hot plate

if your using a glass vessel like a beaker or old coffee pot a small plate (like a salad plate or coffee cup saucer plate) works for a watch glass (curved side down) that way the evaporation is limited to what is able to steam out at the spout 

If you are using a SS pot - put the SS lid on it (good ONLY for reactions of nitric only - does NOT work for HCl &/or AR reactions)

The watch glass stops the loss of values going out the top of the vessel in the form of the acid "mist" (which has acid dissolved metal ions in it) created by the reaction

It also prevent the water leaving the vessel as water "vapor" (steam) because the vapor condenses on the watch glass & drips back down into the solution - so you only lose the little bit of vapor that goes out at the spout 

And the watch glass keeps the Nox condensed in the vessel which allows for some of it to be re-absorbed by the water thereby getting more complete use of the acid which means less acid needed to dissolve the metal

Kurt


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## D1DR (Nov 16, 2016)

Thanks everyone for all the great advice!


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## D1DR (Nov 17, 2016)

Lou said:


> I don't know about him but I just put them in a large glasses kettle with a condenser and a way to add peroxide, which seems to help.
> 
> You can also do them electrolytically, or so another refiner has told me--I never tried.



Lou, what percentage of hydrogen preroxide do you use? Just low concentration like 2-3% in drug store bottles or concentrated, and what ratios to nitric acid?

I found and link about the hazards of mixing hydrogen peroxide and nitric acid below. 

http://hydrogen-peroxide.us/chemical-catalyst-decomposition/Solvay-Hydrogen-Peroxide-Nitric-Acid-Hazards-2005.pdf

Definitely Seems like something you need to be really careful with but I do want to try it if it will help with the Ag/Mo contacts.


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## Lou (Nov 18, 2016)

It mostly helps with keeping the fumes down but peroxide is a solvent for Mo, W, Re by itself. 

Issue is, silver metal catalytically decomposes peroxide to water and steam. This means don't add more than a few mL H2O2/L nitric solution at a time--half the time the peroxide is working on the moly, half the time it's getting decomposed. 

I always used the 30% w/v.


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## D1DR (Nov 19, 2016)

Thanks again for all your help Lou! I'll give this a try in the next week or 2.


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