Filtration problems and small gold particles in solution

[Ghazx]

Hi everyone i need some advice to improve this work for large-scale and speed up the process

Here is my work

1. Someone asked me to recover gold from slag sample .

2. The slag came from gold-laden carbon that was smelted with copper and charcoal.

3. I used aqua regia to dissolve the sample after I crushed it.

4. The result was a gelatinous liquid with floating tiny white particles.

5. It was very hard to filter it, but I did it patiently.

6. I used sodium metabisulfite to precipitate gold from the resulting liquid.

7. The gold was suspended in the solution like nanoparticles.

8. I let it settle, but some gold was still present in the solution.

9. I tried a pretreatment with nitric acid, and again the gelatinous precipitate appeared.

10. This time, I saw little shiny gold at the bottom of the beaker.

11. I discarded the gelatinous solution by decantation and dissolved the gold in aqua regia.

The total sample was 600g.

The first run was 400g and yielded 1g of gold.

The second run was a 200g sample, yielding 0.5g of gold.

My problem was the gelatinous solution, which may have trapped some gold inside it. How can I get rid of it?

And how can I make the small gold particles coagulate together?

When I started to read CM Hoke, she mentioned that this book does not cover this issue.

Sorry for my English and for being overly verbose.

 

[Yggdrasil]

Hi everyone i need some advice to improve this work for large-scale and speed up the process

Here is my work

1. Someone asked me to recover gold from slag sample .

2. The slag came from gold-laden carbon that was smelted with copper and charcoal.

3. I used aqua regia to dissolve the sample after I crushed it.
Maybe it should have been incinerated first, it seems to be very high in Carbon still.

4. The result was a gelatinous liquid with floating tiny white particles.
Do you know which Flux they used? Maybe you should have boiled it in weak Sulfuric first to remove as much Flux as possible.

5. It was very hard to filter it, but I did it patiently.

6. I used sodium metabisulfite to precipitate gold from the resulting liquid.
Did you get any proper Gold precipitation? Did you test with Stannous?

7. The gold was suspended in the solution like nanoparticles.
That may be a sign of too low concentration or too much base metals.

8. I let it settle, but some gold was still present in the solution.

9. I tried a pretreatment with nitric acid, and again the gelatinous precipitate appeared.

10. This time, I saw little shiny gold at the bottom of the beaker.

11. I discarded the gelatinous solution by decantation and dissolved the gold in aqua regia.
How do you treat your waste?

The total sample was 600g.

The first run was 400g and yielded 1g of gold.

The second run was a 200g sample, yielding 0.5g of gold.

My problem was the gelatinous solution, which may have trapped some gold inside it. How can I get rid of it?

And how can I make the small gold particles coagulate together?

When I started to read CM Hoke, she mentioned that this book does not cover this issue.

Sorry for my English and for being overly verbose.

Do you know how it was treated before it came to you?

Comments in bold inside the Quote.

I think much can be fixed by proper pre-treatment.
I'd start with crushing the slag as you do but very fine, then boil it with weak Sulfuric 10-20% ish, check what flux they used during smelting.
Then I'd dry it well and incinerate it to get rid of the Carbon.
Then it should be ready for AR.
Make/get some Stannous so you can test your solution.
During precipitation if it won't settle, add a bit of Sulfuric and boil it hard for a while.
This seems to promote forming bigger particles and more complete settling.

This should be a starting point at least.

 

[Ghazx]

Do you know how it was treated before it came to you?

Comments in bold inside the Quote.

bold

I think much can be fixed by proper pre-treatment.
I'd start with crushing the slag as you do but very fine, then boil it with weak Sulfuric 10-20% ish, check what flux they used during smelting.
Then I'd dry it well and incinerate it to get rid of the Carbon.
Then it should be ready for AR.
Make/get some Stannous so you can test your solution.
During precipitation if it won't settle, add a bit of Sulfuric and boil it hard for a while.
This seems to promote forming bigger particles and more complete settling.

This should be a starting point at least.

The flux they used was "sodium bicarbonate and sodium tetraborate decahydrate"

I will try this tonight,
I have stannous chloride test and it give me positive with AR

 

[Yggdrasil]

The flux they used was "sodium bicarbonate and sodium tetraborate decahydrate"

I will try this tonight,
I have stannous chloride test and it give me positive with AR

If there is still carbon left it will grab some of your Gold.
The Carbon should be properly ashed before smelting.

 

[Ghazx]

But how to ash large amounts of slag maybe 10kg for one run in large scale it would be very hard

 

[Yggdrasil]

But how to ash large amounts of slag maybe 10kg for one run in large scale it would be very hard

You need to check if the black color is from Carbon or something else.
Talk with the ones creating the slag.

If they are smelting without ashing they most likely have heavy losses.
Dissolving the surplus salts from the slag by boiling in dilute Sulfuric or even plain water should be your first step.

 

[nickvc]

You can try using HCl on the slag as well , try small samples and see what works the best to remove the gelatinous material, if you can thin it out most of the gold should settle.

 

[Ghazx]

Hi i washed the sample with water and SA 15% two times and several times with hot water dried it and dissolved it with AR
It seems that the gelatinous quality decreased.
But i took 17g of sample only
And this sample i think it does not contain gold so Tomorrow i will crush large quality and add 1g gold to it and test the result
I let sample in water with stirring tonight but without crushing the sample

 

[Ghazx]

You can try using HCl on the slag as well , try small samples and see what works the best to remove the gelatinous material, if you can thin it out most of the gold should settle.

I tried this but it gives me non-filterable solution its in my avatar picture
But i will try it again in lab.
Thanks nickvc

 

[goldshark]

I am wondering out loud here, if re smelting with the addition of a better collector metal is the answer. Without knowing what the original smelter used for fluxes, it is kind of a shot in the dark to address the best method of further metal(s) recovery.

 

[Ghazx]

I am wondering out loud here, if re smelting with the addition of a better collector metal is the answer. Without knowing what the original smelter used for fluxes, it is kind of a shot in the dark to address the best method of further metal(s) recovery.

There are big quantities of these very old slag done in old way as i understand and someone needs to process they chemically
And this is my job in next few weeks

 

[Ghazx]

I hope that