Houston I think we have a problem

[johnalden082]

I had 750 grams mechanically cleaned, ran through ultrasonic and incinerated gold-filled junk. Which consisted of necklaces, rings, bracelets and watch bands caps. Use distilled water and nitric acid boils to remove base metals. After there was no more reaction or fumes, let it cool down. I then filtered and rinsed the foils, then incinerated the foils and filter. Then used hydrochloric and incremental doses of nitric acid. Used sulfamic acid to make sure there wasn't any nitric left, there was no reaction. Used sodium metabisulfate to precipitate the gold, let it set over night. There was about an 1inch layer of thick green slime at the bottom. What can I do to try and salvage the gold ?

 

[Yggdrasil]

I had 750 grams mechanically cleaned, ran through ultrasonic and incinerated gold-filled junk. Which consisted of necklaces, rings, bracelets and watch bands caps. Use distilled water and nitric acid boils to remove base metals. After there was no more reaction or fumes, let it cool down. I then filtered and rinsed the foils, then incinerated the foils and filter. Then used hydrochloric and incremental doses of nitric acid. Used sulfamic acid to make sure there wasn't any nitric left, there was no reaction. Used sodium metabisulfate to precipitate the gold, let it set over night. There was about an 1inch layer of thick green slime at the bottom. What can I do to try and salvage the gold ?

How did you use the Sulfamic acid?
How much Sulfamic was used and how much SMB at which pH?

 

[Yggdrasil]

I had 750 grams mechanically cleaned, ran through ultrasonic and incinerated gold-filled junk. Which consisted of necklaces, rings, bracelets and watch bands caps. Use distilled water and nitric acid boils to remove base metals. After there was no more reaction or fumes, let it cool down. I then filtered and rinsed the foils, then incinerated the foils and filter. Then used hydrochloric and incremental doses of nitric acid. Used sulfamic acid to make sure there wasn't any nitric left, there was no reaction. Used sodium metabisulfate to precipitate the gold, let it set over night. There was about an 1inch layer of thick green slime at the bottom. What can I do to try and salvage the gold ?

Did you test with Stannous before and after?

 

[FrugalRefiner]

Used sodium metabisulfate to precipitate the gold

Was it sodium metabisulfate or metabisulfite?

Dave

 

[Lino1406]

Assuming sodium metabisulfite was used, then just water addition to dissolve excess salts will remediate the situation, but not much gold is expected

 

[Lino1406]

I had 750 grams mechanically cleaned, ran through ultrasonic and incinerated gold-filled junk. Which consisted of necklaces, rings, bracelets and watch bands caps. Use distilled water and nitric acid boils to remove base metals. After there was no more reaction or fumes, let it cool down. I then filtered and rinsed the foils, then incinerated the foils and filter. Then used hydrochloric and incremental doses of nitric acid. Used sulfamic acid to make sure there wasn't any nitric left, there was no reaction. Used sodium metabisulfate to precipitate the gold, let it set over night. There was about an 1inch layer of thick green slime at the bottom. What can I do to try and salvage the gold ?

 

[Yggdrasil]

Was it sodium metabisulfate or metabisulfite?

Dave

Good catch Dave, it slipped straight by me.

 

[johnalden082]

Was it sodium metabisulfate or metabisulfite?

Dave

My bad miss spelled it is metabisulfite. Fumble fingers at work

 

[johnalden082]

How did you use the Sulfamic acid?
How much Sulfamic was used and how much SMB at which pH?

I put maybe a 1/8 of a teaspoon of sulfamic directly into the solution with no kind of reaction. Then I did a stannous test which showed positive, used 9 tablespoons of smb got white foam and did another stannous test and one was negative. I did not check the ph of the solution.

 

[Yggdrasil]

I put maybe a 1/8 of a teaspoon of sulfamic directly into the solution with no kind of reaction. Then I did a stannous test which showed positive, used 9 tablespoons of smb got white foam and did another stannous test and one was negative. I did not check the ph of the solution.

Sulfamic need to be used hot, but if you did incremental Nitric additions you probably could have skipped it.
If your Stannous was negative then your Gold had precipitated already, the foaming is what liberates the SO₂ which drops the Gold.
If it creates brown fumes there is still excess Nitric.

The sludge on the bottom is probably your Gold.
Wash it well in hot water until the wash water is colorless, then you can re-refine it.
Add your wash waters to the Stock pot.

 

[johnalden082]

Sulfamic need to be used hot, but if you did incremental Nitric additions you probably could have skipped it.
If your Stannous was negative then your Gold had precipitated already, the foaming is what liberates the SO₂ which drops the Gold.
If it creates brown fumes there is still excess Nitric.

The sludge on the bottom is probably your Gold.
Wash it well in hot water until the wash water is colorless, then you can re-refine it.
Add your wash waters to the Stock pot.

Thank very much for that information. I will try that and see what happens. Have a great day.

 

[Ultrax]

Most likely you have a redissolution of gold in metabisulfite, and therefore a gold sulfite complex masking test of stannous chloride.
It will not be possible to extract gold from the SO-complex by anything other than complete evaporation and calcination at a temperature of at least 800 C.

 

[Yggdrasil]

Most likely you have a redissolution of gold in metabisulfite, and therefore a gold sulfite complex masking test of stannous chloride.
It will not be possible to extract gold from the SO-complex by anything other than complete evaporation and calcination at a temperature of at least 800 C.

Interesting, I have never heard about that.
Can you give some more details?

 

[Ultrax]

I already wrote about it somewhere on the forum.
If SMB is over-poured (without pre-hydrolysis), a group of parallel reactions starts with the reduction of gold with sulfur dioxide, the other part of SO2 goes to the formation of hydrosulfite, and the reaction with hydrochloric acid proceeds in parallel (Na2S2O5 + 2 HCl = 2 NaCl + H2O + 2 SO2) and sharply exponentially shifts the acidity to the neutral/alkaline zone. And in neutral and alkaline environments, a very intensive and fast redissolution of even metallic gold into the Au(SO3)2-complex begins to occur. Therefore, the freshly deposited gold nanoparticles instantly move into the sulfite complex. The stability constant is very high, so you cannot break it chemically. Neutral or alkaline aqueous Au(SO3)2 solutions are extremely stable. Stannous chloride will show nothing. Therefore, such solutions are poured into the sewer in most cases

P. S. Formally, gold in Au(SO3)2 in a very acidic solution (concentrated HCl) can be precipitated with zinc, BUT even non-quantitative precipitation takes several days. We didn't have the patience to wait that long

 

[Yggdrasil]

I already wrote about it somewhere on the forum.
If SMB is over-poured (without pre-hydrolysis), a group of parallel reactions starts with the reduction of gold with sulfur dioxide, the other part of SO2 goes to the formation of hydrosulfite, and the reaction with hydrochloric acid proceeds in parallel (Na2S2O5 + 2 HCl = 2 NaCl + H2O + 2 SO2) and sharply exponentially shifts the acidity to the neutral/alkaline zone. And in neutral and alkaline environments, a very intensive and fast redissolution of even metallic gold into the Au(SO3)2-complex begins to occur. Therefore, the freshly deposited gold nanoparticles instantly move into the sulfite complex. The stability constant is very high, so you cannot break it chemically. Neutral or alkaline aqueous Au(SO3)2 solutions are extremely stable. Stannous chloride will show nothing. Therefore, such solutions are poured into the sewer in most cases

P. S. Formally, gold in Au(SO3)2 in a very acidic solution (concentrated HCl) can be precipitated with zinc, BUT even non-quantitative precipitation takes several days. We didn't have the patience to wait that long

Thanks Ultrax.
I guess that is the reason we keep the solutions highly acidic and add the SMB in small doses.
Deano told about how to make compressed SMB balls which dissolved slowly.
I found that idea quite nice.

 

[tiggertree]

Smb can be purchased as small aspirin sized tablets.
These are sold as Camden tablets used for sterilzing.
Maybe they will have the same slow effect?

 

[tiggertree]

May not be a good idea to use camden tablets as they only contain about 0.5gm of smb each plus filler.

 

[Ultrax]

I'd rather just bubble the SO2 gas made from SMB through the pregnant solution. This will ensure you don't have any problems. It's a little more difficult, but the result is worth it.

 

[Yggdrasil]

I'd rather just bubble the SO2 gas made from SMB through the pregnant solution. This will ensure you don't have any problems. It's a little more difficult, but the result is worth it.

I totally agree, and as a benefit it will remove the need for deNOxing the solution, just bubble SO2 until the Gold drops completely.
No additional salts in the mix

 

[Lino1406]

I already wrote about it somewhere on the forum.
If SMB is over-poured (without pre-hydrolysis), a group of parallel reactions starts with the reduction of gold with sulfur dioxide, the other part of SO2 goes to the formation of hydrosulfite, and the reaction with hydrochloric acid proceeds in parallel (Na2S2O5 + 2 HCl = 2 NaCl + H2O + 2 SO2) and sharply exponentially shifts the acidity to the neutral/alkaline zone. And in neutral and alkaline environments, a very intensive and fast redissolution of even metallic gold into the Au(SO3)2-complex begins to occur. Therefore, the freshly deposited gold nanoparticles instantly move into the sulfite complex. The stability constant is very high, so you cannot break it chemically. Neutral or alkaline aqueous Au(SO3)2 solutions are extremely stable. Stannous chloride will show nothing. Therefore, such solutions are poured into the sewer in most cases

P. S. Formally, gold in Au(SO3)2 in a very acidic solution (concentrated HCl) can be precipitated with zinc, BUT even non-quantitative precipitation takes several days. We didn't have the patience to wait that long

Na2S2O5 is smb. Hydrosulfite, Na2S2O4 if formed, reduces gold in alkaline environment if at all formed. (To produce it zinc is needed)