In a bit of a pickle - wet recovery went wrong!

[SteveD]

Hi all,

I hope you can help me unpickle my mess!

Refining karat gold using nitric and aqua regia.

I came to this a noob, not having done any chemistry since A level many moons ago.

Wanting to refine some gold with the view of making 18k Palladium white gold I started with about 40g of 9k and about 10g of 18k, I calculated approx. 20g Au and decided to inquart with copper, so melted it with about 10g of copper wire thinking the remaining base metals in the alloy would make up the difference for inquartation, basic maths error! 60g of material of which 20g is Au gives a third which seems isn’t enough to get all the base metal out in a nitric boil, see below.

I boiled with Nitric and removed a quantity of blue liquid which I assume is copper nitrate.

I couldn’t get it to fully clear the blue colour and was starting to run out of nitric, so after most (not all) of the blue colour stopped coming from the boil I washed with distilled water, boiled with conc HCL then added nitric to start dissolving the gold.

I can only assume the amount of base metal was too low and the gold was ‘hiding’ more copper because on adding the nitric I got a lot of brown gas, and the solution turned more and more blue/green. Panicking a little I decanted all of the liquid into a fresh beaker (beaker 2) leaving some brown metal sponge behind in beaker 1. I then added waaay to much Sodium Meta bisulphate to the decanted liquid in beaker 2.

I added more HCL and nitric to the metal sponge in beaker 1 and heated it which started producing brown gas and turned blue then green.



So I stopped and put them to one side and did a bit more reading. I got a Stannous test kit – the liquid with the SMB excess in beaker 2 tests negative and the dissolved sponge liquid in beaker 1 positive.

The questions is what to do with each beaker?




Beaker 2 has a lot of SMB in it – which I’ve read can be dissolved out with water leaving any metal powder behind which can then be incinerated and meted into a button. The liquid above the layer of SMB tests negative with Stannous but the colour to me suggests something other than copper in it – can I be confident this isn’t Au?



There is also a slick of what I thing is gold particles on top of the liquid which I remember being something to do with grease? How do you sort this out – lift it off with filter paper and incinerate the paper? Use a solvent to drop it down?

With the dissolved sponge in beaker 1 I’m planning on adding SMB to drop any Au, filter then to incinerate and melt back to a button and start again (this time with silver to inquart.) Is this a sensible approach?

Thanks in advance – it’s harder than it looks isn’t it!

 

[FrugalRefiner]

Indeed, it can be harder than it looks in most youtube videos.

I'll touch on just a few points.

Wanting to refine some gold with the view of making 18k Palladium white gold I started with about 40g of 9k and about 10g of 18k, I calculated approx. 20g Au and decided to inquart with copper, so melted it with about 10g of copper wire thinking the remaining base metals in the alloy would make up the difference for inquartation, basic maths error! 60g of material of which 20g is Au gives a third which seems isn’t enough to get all the base metal out in a nitric boil, see below.

That's OK. Yes, you were a little under on your inquarting. 40 g of 9 kt should yield about 15 grams of gold (40 * 9 / 24), and 10 g of 18 kt should yield about 7.5 grams, so total expected gold would be somewhere around 22.5 grams, assuming everything was plumb. 22.5 * 4 would be a total weight of 90 grams. But that's still OK. While the general target of inquarting is 25% gold, it can work as low as 1/3 gold, but you will likely still have some base metal trapped in the gold after the nitric leach. It will simply get dissolved in the AR, but you will have a somewhat dirty solution. Not ideal, but it will still work.

I can only assume the amount of base metal was too low and the gold was ‘hiding’ more copper because on adding the nitric I got a lot of brown gas, and the solution turned more and more blue/green. Panicking a little I decanted all of the liquid into a fresh beaker (beaker 2) leaving some brown metal sponge behind in beaker 1. I then added waaay to much Sodium Meta bisulphate to the decanted liquid in beaker 2.

I added more HCL and nitric to the metal sponge in beaker 1 and heated it which started producing brown gas and turned blue then green.

AR will evolve brown gas when you dissolve gold, but the green color does indicate that some base metal remained. I hope you added sodium metabisulfite, not sodium metabisulfate.

So I stopped and put them to one side and did a bit more reading. I got a Stannous test kit – the liquid with the SMB excess in beaker 2 tests negative and the dissolved sponge liquid in beaker 1 positive.

The questions is what to do with each beaker?

Beaker 2 has a lot of SMB in it – which I’ve read can be dissolved out with water leaving any metal powder behind which can then be incinerated and meted into a button. The liquid above the layer of SMB tests negative with Stannous but the colour to me suggests something other than copper in it – can I be confident this isn’t Au?

Colors can be deceiving. Better to trust the stannous results. If you're still in doubt, add the solution to your stock pot.

There is also a slick of what I thing is gold particles on top of the liquid which I remember being something to do with grease? How do you sort this out – lift it off with filter paper and incinerate the paper? Use a solvent to drop it down?

Get a spray bottle, add a couple of drops of dishwashing liquid to it, then fill with water. Spray the floaters till they sink.

With the dissolved sponge in beaker 1 I’m planning on adding SMB to drop any Au, filter then to incinerate and melt back to a button and start again (this time with silver to inquart.) Is this a sensible approach?

You can incinerate it, but there's no need to melt it or inquart it. Just put all the metal powders back into AR and drop the gold again.

Dave

 

[snoman701]

Understand that the point of inquarting with silver is to use less nitric, as well as clean up any platinum or palladium in the mix. In the presence of silver, both platinum and palladium will be soluble in nitric, leaving only fine gold remaining.

As for the rest, I'd add copper and heat both with stirring. Once you test negative on both with stannous, filter out the powder and redissolve with HCl (4 mL per gram dry powder is plenty), adding only enough nitric to get everything into solution. Then proceed with sodium metabisulphite addition to precipitate your gold.

I don't add stuff to my stock pot anymore until I've evaporated away at least half of the liquid.

 

[SteveD]

Indeed, it can be harder than it looks in most youtube videos.

I'll touch on just a few points.

That's OK. Yes, you were a little under on your inquarting. 40 g of 9 kt should yield about 15 grams of gold (40 * 9 / 24), and 10 g of 18 kt should yield about 7.5 grams, so total expected gold would be somewhere around 22.5 grams, assuming everything was plumb. 22.5 * 4 would be a total weight of 90 grams. But that's still OK. While the general target of inquarting is 25% gold, it can work as low as 1/3 gold, but you will likely still have some base metal trapped in the gold after the nitric leach. It will simply get dissolved in the AR, but you will have a somewhat dirty solution. Not ideal, but it will still work.

AR will evolve brown gas when you dissolve gold, but the green color does indicate that some base metal remained. I hope you added sodium metabisulfite, not sodium metabisulfate.

Colors can be deceiving. Better to trust the stannous results. If you're still in doubt, add the solution to your stock pot.

Get a spray bottle, add a couple of drops of dishwashing liquid to it, then fill with water. Spray the floaters till they sink.

You can incinerate it, but there's no need to melt it or inquart it. Just put all the metal powders back into AR and drop the gold again.

Dave

That's great thanks for the comments. SMB - I did use metabisulphite happily.

 

[SteveD]

Understand that the point of inquarting with silver is to use less nitric, as well as clean up any platinum or palladium in the mix. In the presence of silver, both platinum and palladium will be soluble in nitric, leaving only fine gold remaining.

As for the rest, I'd add copper and heat both with stirring. Once you test negative on both with stannous, filter out the powder and redissolve with HCl (4 mL per gram dry powder is plenty), adding only enough nitric to get everything into solution. Then proceed with sodium metabisulphite addition to precipitate your gold.

I don't add stuff to my stock pot anymore until I've evaporated away at least half of the liquid.

OK I get the using less nitric, by copper I presume you mean copper bar to replace any gold ions in the solution?

 

[FrugalRefiner]

No, he's talking about the fact that you used copper to inquart your gold. There are two advantages to using silver to inquart:

1. Copper takes around three times as much nitric to dissolve the same weight as silver. So, when you use copper, you have to use a lot more nitric to leach it from your inquarted material.

2. If there are any PGMs (platinum group metals) in your original jewelry, especially platinum, if you use silver to inquart, the PGMs will tend to "follow the silver" into the nitric leach. It's an odd phenomenon. Platinum by itself will not dissolve in nitric alone, but when alloyed with silver it will if there's not too much. So, by using silver to inquart, you can dissolve the PGMs in the nitric leach, leaving you with cleaner gold when you move to AR.

Dave

 

[SteveD]

Ultimately I'm planning on - and this also drops into the noob camp - alloying the recovered gold into an 18k 'premium' white gold with casting pieces of palladium - as such I imagine I'm not worried about PGM's present, I think!

By 'add copper and heat both with stirring' add copper pieces, heat and stirr?

 

[Rreyes097]

Did you ever use any sulfamic acid to deal with any extra nitric in solution before using smb?

 

[cejohnsonsr1]

There’s a fundamental flaw in the process. Regardless of whether you use silver or copper to inquart, the separation and recovery process uses nitric and distilled water. AR (nitric and HCl) is used to dissolve the gold in the refining process AFTER the other metals have been removed.

 

[Shark]

I then added waaay to much Sodium Meta bisulphate to the decanted liquid in beaker

Bisulphate or bisulphite?

 

[SteveD]

Did you ever use any sulfamic acid to deal with any extra nitric in solution before using smb?

I didn't no - I'm sure I haven't got an excess in Beaker 2 since I decanted and there's still gold in Beaker 1. I've not put any SMB in Beaker 1 yet and am expecting an excess of Nitric in it so will get some sulfamic before continuing.

 

[SteveD]

Bisulphate or bisulphite?

Bisulphite!

 

[Yggdrasil]

I didn't no - I'm sure I haven't got an excess in Beaker 2 since I decanted and there's still gold in Beaker 1. I've not put any SMB in Beaker 1 yet and am expecting an excess of Nitric in it so will get some sulfamic before continuing.

If there is still undissolved Gold or base metal.
Begin by adding a bit more HCl.
If nothing happens, you may add a bit of Nitric, a few drops at a time.
Heating is advisable and stirring from time to time.

 

[Rreyes097]

If there is still undissolved Gold or base metal.
Begin by adding a bit more HCl.
If nothing happens, you may add a bit of Nitric, a few drops at a time.
Heating is advisable and stirring from time to time.

Yes I agree. Don't use that sulfamic acid unless you're ready for precipitation.

 

[SteveD]

All worked out in the end - thanks for the input!

 

[Yggdrasil]

All worked out in the end - thanks for the input!
View attachment 54841

Can you enlighten us on what worked in the end?
Nice button, but not very pure, there are still some Ag, Pd or Pt in there.
You can see on the fern pattern on the button.

 

[SteveD]

Can you enlighten us on what worked in the end?
Nice button, but not very pure, there are still some Ag, Pd or Pt in there.
You can see on the fern pattern on the button.

I wasn't too concerned about the presence of PGM's since I'm planning to alloy with Pd to make an 18k Au/Pd - do you think the over all quality of the alloy will be affected by the presence of Ag or Pt? I could re-inquart with silver rather than copper.

With Beaker 1 which was testing negative with Stanous I filtered and then boiled with water to remove any excess SMB the redisolved in AR and dropped it with SMB then filtered out the resulting precipitate.

Beaker 2 I added a bit more HCL, nothing happened so added the SMB then added the precipitate to the AR mixture above.

 

[Yggdrasil]

I wasn't too concerned about the presence of PGM's since I'm planning to alloy with Pd to make an 18k Au/Pd - do you think the over all quality of the alloy will be affected by the presence of Ag or Pt? I could re-inquart with silver rather than copper.

With Beaker 1 which was testing negative with Stanous I filtered and then boiled with water to remove any excess SMB the redisolved in AR and dropped it with SMB then filtered out the resulting precipitate.

Beaker 2 I added a bit more HCL, nothing happened so added the SMB then added the precipitate to the AR mixture above.

Alloying something not pure is a risk to take, you will not know how it will behave.
You may end up with something that can not be worked due to brittleness.

No need for inquarting now, just straight to AR and re-refine.

 

[SteveD]

So I cut up the button, boiled in AR, added sulfamide and dropped with SMB. Lost about 5% weight in the resulting button - it seems cleaner so thanks for the input.

 

[Yggdrasil]

So I cut up the button, boiled in AR, added sulfamide and dropped with SMB. Lost about 5% weight in the resulting button - it seems cleaner so thanks for the input.View attachment 55107

Keep your Chemicals correct. Sulfamide is one thing and Sulfamic acid is a completely different Chemical.

Sulfamide (IUPAC name: sulfuric diamide) is an organosulfur compound with the chemical formula SO₂(NH₂)₂ and structure H₂N−S(=O)₂−NH₂.
Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, sulphamic acid and sulfamidic acid. Formula: H₃NSO₃