Gold precipitation in aqua regia does not work

damocles

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Hello to all,

I am new on the forum but I already spent many hours reading a lot of posts ;-)

I have a concern about the precipitation of gold with aqua regia and no way to understand what I am doing wrong.

Let me explain

I started by removing the gold from the components in a mixture of 50% nitric acid at 60%+ 50% distilled water.
I made a mixture for the aqua regia of 25Ml nitric acid at 60% + 75Ml hydrochloric acid at 30% .
I dissolved my gold in it then filtered the solution which was quite yellow.

I added +- 4 or 5x the volume of distilled water and 3 spoons of urea which I dissolved well to neutralize the solution.

Then I started to add the sodium matabisulfite SMB, after the first spoon the liquid became transparent I kept on adding SMB 3 spoonfuls even 4 without success impossible to make the precipitation of gold.

Then I said to myself that maybe the neutralization was not done, so I added water and SMB again without success.
Since I'm a beginner, I do several tests and when I don't use urea and no SMB and I just add a mixture of water and iron sulphate II to the aqua regia the precipitation works.
But really wanting to understand why with urea and SMB it doesn't work I tried again but nothing to do no gold precipitate.

Finally I tried as a last resort to add iron sulfate II but this time the liquid did not turn black but orange with a sulfur smell and after 2 hours it became very clear again

Could someone tell me where I made the mistake and if it is still possible to recover the gold in the solution I have?

Thank you for reading, any help is welcome ;-) .

I added a picture to show how it look the black marks were there before, it's not the new gold.

Damocles
 

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Yggdrasil

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We need more information than this.
What kind of components and how much.

Then to some of the mistakes:
Waay to much AR.
One liter of AR (100cl) would dissolve many Ozt of
pure gold.

Never ever use AR this way, it will have too much Nitric.
Cover what you want to dissolve in HCl then
add Nitric by pipette drop by drop in hot (not boiling) solution until all is dissolved or there are no more reaction.
If all is not dissolved, add a bit more HCl and continue
dripping Nitric to check if more can react.
If there is no more metal you can of course stop.

Urea is not recommendet to use, it will only remove the NO2
Better to do the evaporation route or Sulfamic acid.

And do not dilute it this much.
Your gold may come out but so fine you won't even see it.

So the advice is read Hokes, then read it again.
Get some proper beakers and continue to study.
 

damocles

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Hello Poa,

Thank you for your answer, I did write it wrong it was not Cl but Ml I did correct my initial post.
Yes 1L of AR to disolve 1Gr gold was a lot :)

Actually I have +- 2L of mixture I would like to precipitate the gold.

Will answer in details tomorrow.

Thx
 

Yggdrasil

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Just out of the top of my head.
You have diluted the solution 20 times more or less.
So it does not matter what you did next,
even if everything was perfect, you would need
a magnifyer and a lot of time to see the gold.
Depending on the amount of course.

Have you tested with Stannous chloride?
It will say if you have gold or not in solution.

What I think would be best is to evaporate down to
original 100ml and continue from there.
Most likely the gold if precipitated will be redissolved
by this and such help the denoxxing.
The option then is to continue evaporating to syrup according to Hokes, cement out with copper or denoxx with Sulfamic acid.
We will se if it changes when we get more information.
 

damocles

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Hello Poa,

I only diluted the solution at the very end because I couldn't make the gold precipitate.

And useless to make a test there is well gold in it I did put 0.5gr in the AR + the gold of 200gr of computer waste wich was +- 1gr of gold +- 12K

According to my information and possible I am wrong, to neutralize AR you can dilute up to 10x before adding urea to be sure that AR is well neutralized.
So I think it should still be possible to precipitate gold even with a 20x dilution.

Evaporating is not a solution I am in a temperate country it will take weeks to evaporate

The worst thing is that with the Iron Sulfate II it worked, I should have continued with it.

Poa could you tell me how high the PH of AR should be before doing the gold precipitation with SMB?

Now after 12 hours of rest the liquid is water colored again and I see a very small sign of precipitation In the bottom of the bucket, but a little bit there should be more

Thank you very much for your answer.
 

Slochteren

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I still would test with stannous to see where your gold did go, still in solution or percipatated in fine particles. Guessing where your gold is, is a route to failure. To see 0,5 gram in 1 liter solution can be hard to see. And 1 gram from gold from 200 gram computerscrap seems a lot to me, I would expect 0,1 gr.

Verstuurd vanaf mijn STK-LX1 met Tapatalk

 

damocles

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Hello Slochteren,

Well I did add 0.5gr 12 k gold inside + the gold I got back from fingers I did scrap from memory and battery connector on laptop motherboard.

Most of the time I get +- 0.40gr per 100gr so in this case I think I should at least have 1gr and when I did it before with the Iron sulfate there was much more precipitation that what I see now.

For the Stannous chloride I will need to order it somewhere then it will take some day's, but I am still sure the gold is still in the water .

Thx for your help ;-)
 

damocles

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I did read a bit on Stannous chloride and I did order 50gr that should arrive this week ;-)

Could anyone tell me how much weight I need to use and if I can mix a part with water to make a solution to test for the presence of gold in a next solution ?

Thx ;-)
 

damocles

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It seem like the precipitation started very slowly after some more addition of SMB.
But this is very slow I will wait 24h more and see what I have at the bottom of the bucket ;-)
 

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FrugalRefiner

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damocles said:
Could anyone tell me how much weight I need to use and if I can mix a part with water to make a solution to test for the presence of gold in a next solution ?

Here is a link to Lou's formula A freaking nightmare on 4th Street. Use the dry stannous chloride, HCl, and water as he recommends. The tin powder isn't essential, it just keeps the solution from deteriorating as quickly. Same with the heptane or mineral spirits.

Dave
 

damocles

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Hello FrugalRefiner,

Thank you very much for your answer, quick question I just want to make sure I understand correctly.

Pure tin powder is the SnCl2 dihydrate ?

Thx
 

FrugalRefiner

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No, stannous chloride dihydrate (SnCl2) is a salt of tin. In an aqueous solution, the stannous chloride undergoes hydrolysis. Adding the HCl helps prevent it. But the stannous chloride also oxidizes from the oxygen in the air. Keeping some metallic tin in the container helps prevent this.

You can simply dissolve some of the stannous chloride dihydrate in water and use it, but it will have a very short shelf life. The HCl and metallic tin help it to last much longer.

Dave
 

g_axelsson

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Or in a bind, you could make stannous from computer scrap and a bit of HCl.

Anything soldered with tin solder can be used, for example those ram modules you cut the fingers off. I did it once from crystal oscillators, I used HCl to remove tin before it went to aqua regia and it worked just as well as the one I make from pewter. I got an old banged up cast tin bowl that I have been cutting pieces off for the last ten years.

Göran
 

g_axelsson

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damocles said:
Poa could you tell me how high the PH of AR should be before doing the gold precipitation with SMB?

Now after 12 hours of rest the liquid is water colored again and I see a very small sign of precipitation In the bottom of the bucket, but a little bit there should be more

I'm not PoA but I'll give you an answer anyhow...

I've precipitated gold with SMB from really acidic solutions like pure HCl and it works. On the other hand I've had real problem to precipitate gold from almost neutral gold solutions and I had to add more HCl to get it to drop.

With too acidic solution the SMB turns into SO2 gas immediately and never dissolves into the liquid so it is mostly wasted. But too weak and the SMB only dissolves and doesn't release any SO2 that actually precipitates the gold. Your problem was probably too high pH and a too diluted solution.

To precipitate gold from a diluted solution takes a longer time than from a more concentrated one. The gold particles have to aggregate into heavier particles until they are large enough to sink and in a dilute solution it's fewer gold particles in same volume so it just takes longer time.

Personally I think about 5-10% HCl (only guessing, never measured though) is a good concentration to drop gold with SMB. I rarely have a problem with gold precipitating nowadays and I rarely wait more than 5 minutes until I pour off the clear liquid in my stock pot.

Göran
 

damocles

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Ok ok I understand very better so I will leave bit of metallic tin in the container ;-) Thank you Dave.

Thank you for your answer Göran yes but it seem a bit more complicate and I did order stannous chloride so I will use it with HCL and distilled water and a bit of tin metal in the container will be more easy.

It is more an experience for me than something else just want to do it properly I am in the computer business and since now 20 years I put a lot of computer parts for trash paying the recycling center to take everything.

Now before to bring everything to the recycling center I scrap the gold and when I have some hundreds of grams I make the whole thing to get in my hands one or two grams 22 or 24k gold ;-) and this is funny too I learn something new :)

No big returns but with time yes it could become a bigger and bigger nuget :)

My last picture it seem like to come good now :) reduced back to 250Ml

Oliver
 

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damocles

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Hello Göran,

Thank you for your very interesting answer,

I've precipitated gold with SMB from really acidic solutions like pure HCl and it works. On the other hand I've had real problem to precipitate gold from almost neutral gold solutions and I had to add more HCl to get it to drop.

Could you tell me what should be the PH after adding water and urea, so before to use the SMB ?

I did read on some other forum that to neutralize the AR you need to add up to 4 or 5x the volume in water then only add the urea is this right ?

Also when I add the water and urea do I need to wait some hours or can I directly add the SMB ? due that I did add directly or 10 min later .

With too acidic solution the SMB turns into SO2 gas immediately and never dissolves into the liquid so it is mostly wasted. But too weak and the SMB only dissolves and doesn't release any SO2 that actually precipitates the gold. Your problem was probably too high pH and a too diluted solution.

I completely agree this is also what I was thinking and when I did add the SMB there was a bad smell of sulphur not sure it was normal.But I dont know the PH I need to have before adding the SMB.

And following my idea add more regular city water with high PH should neutralize more the acid reason why I added finally so much water and 24h later when I added again SMB I got the precipitation.

Now one more question I also once used Iron sulphate mixed with water +- 2x the AR volume and I added it to the AR then I added 2x the initial AR volume again water and I got very faster precipitation from the gold.

Following what I understand with the Iron Sulphate it will precipitate any metals and with SMB only the gold.
But in my case I remove all metals already with the Nitric and water bad I make to get the gold off the PCB so is it really needed to use Urea and SMB to make this job ?

Should it not just be more easy to only use Iron Sulphate II ?

Sorry if I've been a bit long but it's exciting actually and I have a lot of questions in waiting ;-)

Oliver
 

damocles

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Ok so here the result 0.34gr of gold I am almost sure that some gold left in the remaining liquid but I give up on this one.

Next time I'll do it directly with the iron sulfate much easier.

Will keep the liquid to test the tannous chloride ;-)
 

g_axelsson

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damocles said:
Hello Göran,

Thank you for your very interesting answer,

I've precipitated gold with SMB from really acidic solutions like pure HCl and it works. On the other hand I've had real problem to precipitate gold from almost neutral gold solutions and I had to add more HCl to get it to drop.

Could you tell me what should be the PH after adding water and urea, so before to use the SMB ?

I did read on some other forum that to neutralize the AR you need to add up to 4 or 5x the volume in water then only add the urea is this right ?

Also when I add the water and urea do I need to wait some hours or can I directly add the SMB ? due that I did add directly or 10 min later .

I've never used urea myself. Don't have it, doesn't need it. I'm just careful to not use too much nitric. So far I've recovered and refined over 100 grams of gold from electronic scrap.

damocles said:
With too acidic solution the SMB turns into SO2 gas immediately and never dissolves into the liquid so it is mostly wasted. But too weak and the SMB only dissolves and doesn't release any SO2 that actually precipitates the gold. Your problem was probably too high pH and a too diluted solution.

I completely agree this is also what I was thinking and when I did add the SMB there was a bad smell of sulphur not sure it was normal.But I dont know the PH I need to have before adding the SMB.

And following my idea add more regular city water with high PH should neutralize more the acid reason why I added finally so much water and 24h later when I added again SMB I got the precipitation.

Now one more question I also once used Iron sulphate mixed with water +- 2x the AR volume and I added it to the AR then I added 2x the initial AR volume again water and I got very faster precipitation from the gold.

Following what I understand with the Iron Sulphate it will precipitate any metals and with SMB only the gold.
But in my case I remove all metals already with the Nitric and water bad I make to get the gold off the PCB so is it really needed to use Urea and SMB to make this job ?

Should it not just be more easy to only use Iron Sulphate II ?

Sorry if I've been a bit long but it's exciting actually and I have a lot of questions in waiting ;-)

Oliver

You never neutralize by dilution, you only dilute your acid. To truly neutralize acid you need a base. We don't call it neutralize to remove nitrates from a solution, we call it denoxing a solution. People who don't know what they are doing and only mimic something they have read or watched on youtube often talks about neutralize nitric acid and so the misconception is perpetuated.

Both SMB and iron sulfate is quite selective for gold, although there are some quirks with both chemicals. I prefer SMB as I really likes to get a colorless solution instead of the dark iron stained solution after dropping gold with copperas. There are other chemicals that can be used, I've seen a list with about ten different chemicals that could be used. Just from memory I've seen SMB (or sulfur dioxide), copperas, oxalic acid, ascorbic acid, copper powder, hydrogen peroxide, stannous chloride and nitrite mentioned as a precipitant. I'm sure I'm forgetting some too. Some chemicals are better than other depending on the circumstance.

The more you learn the more you will realize that it's not black and white. Especially when working with electronic scrap.

You should read Hoke, it will answer some of your questions as well as give you more. :wink:

Göran
 

Yggdrasil

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I totally agree with Gøran.
I'm just really careful with the nitric.
The SMB can forgive some, as the gold is redissolved and such depleating the extra nitric/nox.
Do not really know how much though.
For the time beeing I'm living a nomadic life in South East Asia, so my access to the net is sporadic.
As a result my replying and reading is sporadic too.
:D 8)

Edit: Spelling
 

nickvc

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If you still believe you have gold in solution simply put a copper bar or a piece of copper sheet into your solution, that will cement any values left in solution.
 
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