Sciencemadness Discussion Board

Making silver nitrate - impure silver

yankeex - 9-4-2012 at 13:26

Ok I have got some old scrap silver which is anywhere between .500 to .925 so it contains more or less amounts of copper. If I just dump them into HNO3, would this ruin the silver nitrate obtaining process or is there any way to remove the impurities in any feasible way?

weiming1998 - 9-4-2012 at 16:41

You can remove the copper+other metal impurities by first dissolving the silver in nitric acid, then boiling/evaporating the solution of AgNO3/Cu(NO3)2 dry, then heat very strongly in a ventilated place.

According to Wikipedia(http://en.wikipedia.org/wiki/Copper(II)_nitrate), copper nitrate decomposes to CuO at 180 degrees Celsius.
Silver nitrate decomposes into elemental silver though, when heated(http://en.wikipedia.org/wiki/Silver_nitrate) because silver oxide's decomposition temperature is lower than silver nitrate's. The silver/copper oxide/oxides mix can then be separated with the addition of some non-oxidizing acid, like cold H2SO4, which removes the oxides and leaves you with almost pure silver.

Another way to extract silver is to first dissolve the impure silver, then putting waste copper into the solution. Silver as pure crystals will crystallize out.

Also, this probably belongs in the Beginnings, not Organic Chemistry.
[Edited on 10-4-2012 by weiming1998]

[Edited on 10-4-2012 by weiming1998]

cyanureeves - 9-4-2012 at 18:34

i like to add salt to the dissolved sterling and make the curd like silver chloride because the copper remains in solution as a blue liquid that is visible so you can decant it. the silver chloride can then be washed again and again with plain water until no more hint of blue remains as silver chloride is insoluble in water.then i like to add hcl acid and water to the silver chloride and drop zinc pennies rid of their copper shell. you can see the displacement take place before you as the silver chloride turns black like a thunder cloud passing over the earth. the black stuff is silver metal mud that can be washed also again and again with water to rid it of zinc chloride or you can just melt the pure silver and digest it again with nitric. dropping a clean piece of copper in your blue solution of dissolved silver alloy will also displace the silver which will grow around the copper like a crystal fungus.just make sure your blue solution is diluted with water when you do the copper displacement method.

MrHomeScientist - 10-4-2012 at 08:01

Here's the process I'd try:
First, dissolve the sterling silver in HNO<sub>3</sub> to form silver and copper nitrates in solution. Then, add a source of chloride ions to the solution (NaCl solution seems most convenient) to precipitate out AgCl as a white solid. Filter this off, rinse a few times with water, and then dissolve the precipitate in ammonia solution. Filter off any remaining impurities that appear as insoluble residue. Finally, add nitric acid again to convert to silver nitrate.
You'll have some ammonium nitrate impurities though, and now that I look at it this might be difficult to separate. Ammonium and silver nitrates have similar solubilities in water. Hmm.

P.S. I haven't tried the ammonia dissolution step myself - I found it referenced in "Handbook of Inorganic Chemicals", Patnaik, p.839

annaandherdad - 10-4-2012 at 12:48

I've done some of this in the last year or so and have tried various methods. Sterling silver is about 93% silver and 7% copper---I found quantitatively that this was close to the mark in a sample I had.

The best way I found was to dissolve the impure silver in nitric acid. Weigh the (impure) silver first so you have an upper bound on the amount of silver. Then add NaCl---the amount I added was based on the weight of the impure silver, so that I had an excess of NaCl but not too much. I don't know if a large excess of NaCl would be harmful (eg., causing some of the AgCl to go back into solution) but I wasn't taking any chances. AgCl is highly insoluble in H20 but you will also have HNO3, NaCl, Na2NO3, and various copper compounds present (plus maybe some other metal nitrates). Anyway, filter and wash the AgCl.

This can be reduced to metallic Ag by boiling in a solution of NaOH plus dextrose. I followed a recipe in an article I found in the chemistry literature---I don't have the reference handy but I'll look it up for you and post again. The silver can then be filtered and washed (both water and acetone, the latter to get rid of any organic materials left from the sugar and its decomposition).

If you want AgNO3, you can redissolve the silver in HNO3, and crystallize. I did this in a desiccation chamber with NaOH to absorb the H2O and HNO3 vapors. Got some nice, clear AgNO3 crystals that way, but it took a long time.

Another method I tried that didn't work well was to insert copper after getting the solution of silver and copper nitrates after the first dissolution in HNO3. One does get beautiful silver crystals forming, but I found that when I would shake them off the copper and filter them out, that little bits of copper were sticking to the silver. So, when I redissolved in HNO3, I still had some copper contaminating the solution. The route through AgCl and reduction worked better.

cyanureeves - 10-4-2012 at 14:53

i think its better to melt the silver because all other impurities will remain in solution or in their salts and will not withstand the heat enough to go back to metallic state.

nezza - 11-4-2012 at 01:08

weiming is right. Copper nitrate decomposes at a much lower temperature than silver nitrate. I have made pure silver nitrate from sterling silver by this route :-

1. Dissolve silver/copper alloy in HNO3
2. Evaporate to dryness
3. Heat gently - the Copper nitrate decomposes before the silver nitrate
4. Extract with water - a colourless solution of silver nitrate is obtained. This can be evaporated and crystallised or just filtered an used as is.

Note that if there are other metals in the alloy apart from copper this will not work.

froot - 11-4-2012 at 02:34

A retired metallurgist once told me that they used to purify gold from old jewellry and concentrate using the aqua regia method but with a twist. He would dissolve the metals in aqua regia and afterwards neutralise by adding urea. The silver would drop out and be filtered off. Not sure what sort of complex this would create or weather the copper complex would have different solubility to the silver. If I was doing this I would try dissolving a sample in HNO3 after which I would add urea to see if the same would happen.

bolbol - 8-2-2015 at 12:27

I made some Silver Nitrate yesterday with a troy ounce of silver advertised as 99.99%. I used 25 mls of distilled water and 30 mls of conc nitric acid for this. After it all dissolved and cooled down, I got silver nitrate crystalizing at the bottom and i got a liquid solution that has a blue tint to it... Is this normal for a 99.99% stuff

cyanureeves - 8-2-2015 at 12:43

bolbol i dont think .01 impurity would make a blue tint of any kind. i have dissolved 99% silver and have gotten no blue tint, but how blue is it?dark blue as in a lot of copper or just a light blue tint?i think you got dirty bullion because i ordered a troy once from china that i suspected to be adulterated because it weighed less than 31 grams.the bullion did not turn blue as copper does but maybe does have zinc or something that doesnt tinge.i never weighed the pure silver either but it was alot so it was good enough for me i guess. the loss was minimal to me but i know it will add up if the seller does this by kilograms.

bolbol - 8-2-2015 at 13:03

It was like 31.18 grams if i remember correctly.. and its just a very light blue tint but still noticeable when you look at it. I was hoping I'd get pure silver nitrate now I think I should throw in some copper and get all the silver out and redissolve the silver powders in nitric acid again. Unless there is an easier way?

unionised - 8-2-2015 at 13:19

Adding copper to get rid of copper isn't a brilliant idea.

You can precipitate silver as the acetate, (essentially all other acetates are soluble) then heat it to get silver. (Be careful, the reaction can get violent
Or- probably easier, you can precipitate the silver as the chloride by adding salt or hydrochloric acid, then wash the AgCl with lots of water to remove the Cu.

Then heat the chloride with an excess of sodium carbonate to get sliver metal.

On the other hand, if the silver was anything like 99.99% pure then you should be able to get practically pure AgNO3 by recrystallisation from hot water.


http://en.wikipedia.org/wiki/Recrystallization_%28chemistry%...


[Edited on 8-2-15 by unionised]

bolbol - 8-2-2015 at 13:25

Well if it was 99.99% pure I don't think I'd get that blue tint. Even through videos ive seen on youtube every solution after the reaction is over turns into clear colorless solutions.

I like the silver acetate idea but my goal is to get silver nitrate not silver metal. Would vinegar work if I added it to a silver nitrate solution


unionised - 8-2-2015 at 13:40

Really, I'd recommend recrystallising it before I tried anything else- it is by far the easiest route.

Vinegar wouldn't work unless you also added some alkaline material to strip out all the excess acid.
You can see the blue colour of solutions of copper salts down to a few tens of parts per million.
Once you get the silver pure, you can redissolve it in nitric acid.

bolbol - 8-2-2015 at 14:24

I will recrystalize it and the rest that remains in solution ill redo with copper I guess.. I just dont want the recrystalized stuff to have a blue tint to it...

bolbol - 31-3-2015 at 22:57

I'd like to know if anyone ever made AgNO3 with 99.9% purity silver bullion american or not and didn't get a blue tinted solution after the reaction was over and the NO2 color was out of solution.

I switched to Canadian silver which is 99.99% and no more copper presence is detected but I have seen some good priced silver online that is 99.9% and before buying I'd like to know others experience

morganbw - 1-4-2015 at 00:02

Quote: Originally posted by bolbol  
I'd like to know if anyone ever made AgNO3 with 99.9% purity silver bullion american or not and didn't get a blue tinted solution after the reaction was over and the NO2 color was out of solution.

I switched to Canadian silver which is 99.99% and no more copper presence is detected but I have seen some good priced silver online that is 99.9% and before buying I'd like to know others experience

It has been maybe 30 years ago, but yes -> no blue.

Sulaiman - 1-4-2015 at 04:52

I made silver nitrate with a US 99.9% 1oz. eagle a couple of months ago, just the tiniest hint of blue/green
BUT
the silver nitrate produced was light sensitive
which it should not be if perfectly pure.

I intend to do a recrystallization some time soon ......

bolbol - 1-4-2015 at 10:34

I've never successfully been able to recrystallize Silver nitrate. The crystals barely drain and the remaining solution when dried still leaves a colored tint that is apparent when compared to something like more pure AgNO3

AndrewCampbell - 2-11-2015 at 19:07

I have never thought that I could possibly perform my own science experiment in the comfort of my own home to successfully separate silver from copper. However, with advices from experienced enthusiasts like you people, nothing is ever impossible if we are determined to achieve them.