Chemgineer
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Silver recovery
I've been trying to recover the silver from some ebay jewellery. I've added a stoichiometric amount of nitric acid but the outside of a ring has been
dissolved into a colourless solution and the substrate material which looks gold/copper colour isn't reacting... have I got some gold?
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clearly_not_atara
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Well that isn't what I expected from the title 
Some nickel alloys can resist nitric acid. But Au is a significant possibility — lots of people on eBay don't know how valuable their stuff is. A
density test will tell you.
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j_sum1
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Add a little HCl and see what happens.
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Herr Haber
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I never managed to use stoichiometric amounts of HNO3 to dissolve jewellry, plates, cups, forks, spoons etc.
Having a 3 liters reactor dedicated for that I usually put 1 kilogram of silverware in it.
In early times I probably used 50% more acid that was needed. The main reason was that I used azeotropic acid and simply used a dropping funnel to add
the acid. Just the exotherm will make you waste a lot of acid.
One interesting observation with more concentrated acid was the almost instant formation of crystals, not enough water to dissolve them and even more
NOx.
From my experience, using 40 to 55% HNO3 is ideal after submerging the silverware in distilled water in my reactor.
I just then let it sit for a couple of days and shake the reactor from time to time. After a couple of days I start mild heating. At this point there
is still plenty of acid that can react with the silverware.
I have done this and drained the reactor a couple of times. At the bottom, there is about half a centimeter of black sludge that wont dissolve. I know
there is gold since I dissolved some gold plated silverware but usually most of this sludge *will* dissolve in hot concentrated RFNA. There are some
tiny pieces of jewlry in there so I'm expecting the day when I treat this leftover sludge 
But in your case, plating gold with silver would be very weird. You should have a copper alloy that should also dissolve in your acid. I dont
recommend using acid to remove silver from plated silverware as it will be very expensive in acid since there is usually only about 10% of silver.
I tried electrolysis for that and you get to see a lot of that copper / gold color in the base metal. It's messy and stinks like hell. I wont do it
again.
I assume you didnt use concentrated nitric acid, that wouldnt react with copper ? If you have HCl and tin available you can probably make a testing
solution for gold.
Fingers crossed, it would be a cool find 
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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Herr Haber
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+1 on the nickel alloys, in my post above this is why I sometimes used crudely distilled hot RFNA on the sludge.
True also, the density between copper and gold should be pretty obvious even by hand if the item is big enough.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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Boffis
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If you "silver" was white gold say an alloy of silver and less than 40% or so gold the alloy losses silver to solution and leaves the gold behind.
This is the principle of "Parting" used in fire assaying of gold and silver.
The gold can be dissolved in aqua regia. A blue to green solution means Cu is present gold only gives a yellow solution.
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unionised
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The silver precipitates in what may be an unhelpful manner.
Of course, it's possible to recover the silver as the chloride - there aren't many insoluble chlorides so it is a useful purification step.
You can convert the chloride to metal by melting with sodium carbonate or borate.
It probably better to take the insoluble bits of metal and treat them separately with aqua regia.
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Boffis
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I recover silver via the chloride. Simply filter off the insoluble chloride and dissolve it in dilute ammonia and then ppt it onto a zinc or copper
plate. The silver metal separates easily from the copper plate as a fine, crystalline powder that is washed free of copper with dilute sulphuric acid,
washed with water and dried.
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Rainwater
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Cut it in half to expose the core material.
Remove the item first. Rinse, then add aqua regia.
Save your left overs
[Edited on 21-9-2022 by Rainwater]
"You can't do that" - challenge accepted
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Chemgineer
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It's silver plate dfor sure as i've precipitated that out now, it's not gold as the core is now a silver colour, it seemed to have a gold/copper layer
part way through but I haven't got any blue from copper in my solution. Perhaps it was a very thin layer plated over another core material and the
copper nitrate is not obvious as such a light concentration. I'll throw it out anyway as it's not silver or gold.
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j_sum1
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Quote: Originally posted by Rainwater  | Cut it in half to expose the core material.
Remove the item first. Rinse, then add aqua regia.
Save your left overs
[Edited on 21-9-2022 by Rainwater] |
Point well taken, unionised. Precipitation of AgCl is a useful purification step (or can be), but now might not be the best time to begin the
separation. There may yet be Ag in the core material that remains.
My thought was that AR would quickly reveal whether there is any gold in the undissolved material. It would be unusual, but stranger things have
happened.
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Herr Haber
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I'd cut it and put it in HCl first or try crushing it in a wise.
If it's now silvery I'm betting clearly_not_atara is right about nickel.
If it's a copper alloy or gold you'll crush it easily compared to nickel.
Plating nickel would be a good idea. Some people have severe allergies to it.
I love these misteries. I keep thinking I'd be happy if someone sent me a barrel of slag from a copper foundry.
Now... if someone wanted to give me slimes from a copper refinery... oh that would really make my day 
I'm pretty sure I'm not alone thinking like that on SM 
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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Rainwater
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sourceing from jewelry is the same as refining ore, with a lot of work already done
Next steps?
You have your crude silver nitrate solution.
How do you plan on purifying it?
Recrystallizations are for nerds.
Where dealing with heavy metal here.
[Insert Music Here]
You want to go all the way!!!
Are you going all the way?
AA is for quitters,
>3 9's fine if it's truly gonna shine
Standard methods include
Electrolysis
selective precipitation
thermal decomposition
Electrolysis (done it for gold, silver, and platinum. I'm not a fan. I've got no need for this level of purity)
PROS:
fewest amount of reagents needed
Fewest amount of steps
produces the purest product 4~5 9's
CONS:
reagents must be reasonably pure (>95%) C I C O
takes a long time
loss of product based on the volume of the solution
unprocessed slim containing other products($$$) which require more steps
selective precipitation (always my step 2, regardless of the source)
PROS:
seperate all metals in solution
product can be >99% pure
gives you some cool looking colors
diministrate your impressive techniques and style as a chemist
CONS:
lots of reagents (3~12)
multiple pathways needed based on contaminates
product loss in filtering steps
easy to screw up and hot to fix
Thermal decomposition (my favorite starting point)
PROS:
simple
impossible to screw up .... mostly
FIRE... good
setup can be as simple as a rocket stove
easy to scale up and handle large batches with an ever declining capital cost.
CONS:
FIRE.... bad
complex systems can get expensive, but require less work
simple systems can be cheap, but require a lot of work
apparatus are disposable.
molten metal can burn you, short out electrical components, and explode just because you said your day couldn't get any worse.
product will be less pure.
"You can't do that" - challenge accepted
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j_sum1
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sreetips has a steady stream of videos on yt. (kadriver on this board.) He demonstrates a large number of techniques. Most of his work is in gold
where his preferred technique is inquarting with silver followed by repeated dissolving in AR, filtering, and precipitation with metabisulfite.
For silver he goes for electrolysis to achieve high purity product (9999). The crystals he gets look gorgeous.
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Herr Haber
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I'd have said most of his work is on Silver rather than gold but that's not the point.
The man is the best source for information on this topic by far on Youtube and more broadly, on the Internet.
He is also a lot more humble than many Youtubers. I remember him saying in a video on palladium "I'm not a professional, I've only done this reaction
15 times".
Which is sometimes more than a professional can say...
I like his tone of voice and can only think of how good a teacher he must have been in his career in the Navy.
I believe I saw YT suggesting me one of his latest videos on Rhodium. Not a lot of people are as knowledgeable in PGM as he is.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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