Gold recovery from smelter slags

[user 72133]

I need to know how to recover the gold that remains in the salts after smelting.
I have tried dissolving the salts in aqua regia, filtering, and adding BMS.
It works fine, but I have a huge amount of salts and I think that there would still be a way to dissolve the salts, instead of dissolving the gold.
Does anyone have any ideas?

edited to correct title - FrugalRefiner

 

[Yggdrasil]

I need to know how to recover the gold that remains in the salts after smelting.
I have tried dissolving the salts in aqua regia, filtering, and adding BMS.
It works fine, but I have a huge amount of salts and I think that there would still be a way to dissolve the salts, instead of dissolving the gold.
Does anyone have any ideas?

Welcome.
What is left from smelting is called slag, not salts.
Salts are ionic compounds and most slags may not be that.
If you have too much metal in your slags you are doing something wrong.
It is better to correct these errors first.
The slag you have now is best crushed fine and then gravity separated.

 

[user 72133]

exact the dross that comes from melting borax and other fluxes

 

[user 72133]

Thanks for the correction, I have finely divided slag, I was thinking of treating it by the wet method. How could I separate it by gravity? With a sieve? the amount of gold in the slag is very small, about one or two grams per kilo of slag

 

[Yggdrasil]

Thanks for the correction, I have finely divided slag, I was thinking of treating it by the wet method. How could I separate it by gravity? With a sieve? the amount of gold in the slag is very small, about one or two grams per kilo of slag

With a washing pan or a shaker table just like washing placer Gold.

 

[user 72133]

was there a way to dissolve the slag? i have tons of slag to trate it by this way... too slow

 

[Martijn]

was there a way to dissolve the slag? i have tons of slag to trate it by this way... too slow

Then do you have a way to safely dispose of these toxic chemical solutions?
How much gold was left in there after smelting? Traces or enough to be worth you effort?
I would say if any economically recoverable pm was left after smelting, smelting was not properly.
As said: crush & pan, smelt again, using the right flux, and enough collector metal for cons. Not one big block, but as fine as your cons.
If you still can't get it all out by smelting, smelting might not be the way to go for you.

What do you mean by the wet method?
Shaker table? Cyanide leach? Wet ashing(noooo)? AR?

 

[Yggdrasil]

was there a way to dissolve the slag? i have tons of slag to trate it by this way... too slow

It depends completely what the slag is.
But I do not think it is economically feasible even with bulk price on chemicals.
Mill and concentrate, then re smelt with correct flux and collector metal is the only way that may be economically sound.
Much less waste to treat as well

 

[andu]

You can rid of borax with either hcl or sulfuric, I see gas as being more expensive than the acid, personally. What i would do out of my lack of common sense is turn the borax to boron, then even while it can cost a bit you get all you left behind as byproduct. But note that i do want to turn borax to boron for the lulz so might not make sense to you.

 

[4metals]

Remelt the slags with a thinning flux using fluorspar to make the flux thinner so the beads can drop. Pour into a cone mold and the beads will be a neat button in the bottom of the mold. If you made the flux thin enough.

This may not be the best method depending on your description of huge. But if it is really huge, get a representative sample in a few pails from around the huge pile and melt the samples with a proper thinning flux and you will get an idea of what you are looking at.

What was your starting flux?

 

[Benjamin]

On the same topic do some has idea on how can I recover gold from waste carbon which is already burnt to ashes.

 

[user 72133]

Remelt the slags with a thinning flux using fluorspar to make the flux thinner so the beads can drop. Pour into a cone mold and the beads will be a neat button in the bottom of the mold. If you made the flux thin enough.

This may not be the best method depending on your description of huge. But if it is really huge, get a representative sample in a few pails from around the huge pile and melt the samples with a proper thinning flux and you will get an idea of what you are looking at.

What was your starting flux?

when i smelt gold pieces i add always borax, sometimes sodium carbonate and potassium nitrate. Gold melts forming a ingot and in the top i have the slag. A bit of gold is in that slag, because there is a decrease and matter is not created or destroyed so i save the slag of all funditions i do. when i have enought i crush them, and now i have a lot of slag crushed with a bit of gold that i want to recover.
As i said, i can disolve the gold using AR, next filter and add urea and metabisulphite. By this way i recover more less 2g/kg of slag. i can treat 3kg each time, but i am looking for something fast or easy with less steps because i have a lot!
Remelt the slag is the other way, but i recover less quantity, less than 1g/kg os slag..
when i say the wet method i refer by chemicals , not by smelting.

I'm spanish i don't know if i am writting well...
thanks.

 

[Yggdrasil]

when i smelt gold pieces i add always borax, sometimes sodium carbonate and potassium nitrate. Gold melts forming a ingot and in the top i have the slag. A bit of gold is in that slag, because there is a decrease and matter is not created or destroyed so i save the slag of all funditions i do. when i have enought i crush them, and now i have a lot of slag crushed with a bit of gold that i want to recover.
As i said, i can disolve the gold using AR, next filter and add urea and metabisulphite. By this way i recover more less 2g/kg of slag. i can treat 3kg each time, but i am looking for something fast or easy with less steps because i have a lot!
Remelt the slag is the other way, but i recover less quantity, less than 1g/kg os slag..
when i say the wet method i refer by chemicals , not by smelting.

I'm spanish i don't know if i am writting well...
thanks.

4 metals gave you good advice.
Are you smelting Gold?
If so what is your flux recipe?

Or are you melting Gold into a new form?
If so, no Borax/flux is needed.

Urea is a fertiliser and best used in the garden.
To remove Nitric from solutions use less Nitric (best) or Sulfamic acid (next best)

 

[VK3NHL]

Thanks for the correction, I have finely divided slag, I was thinking of treating it by the wet method. How could I separate it by gravity? With a sieve? the amount of gold in the slag is very small, about one or two grams per kilo of slag

I wouldn’t call 1-2g of Au per kilo a small amount..

 

[kurtak]

when i smelt gold pieces i add always borax, sometimes sodium carbonate and potassium nitrate.

As you know borax (slag) does not dissolve well in water - even when ground to fine powder

on the other hand washing soda (sodium carbonate) does dissolve well in water

side note; - I understand that the (often) "recombination" for fluxing is to use borax - &/or 50/50 borax/washing soda

however - even at 50/50 borax/washing soda the slag (fine ground/crushed) still does not dissolve well in water

What I have found is that if you use a flux made of 1/3 borax & 2/3 washing soda - the slag (finely ground/crushed) will dissolve very well in HOT water - leaving you with you gold (&/or other metals) mixed with a (much) small(er) amount of other duff --- in other words a nice concentrate of gold (&/or metals) with "some" other crap

and as 4metals pointed out a "bit' of fluorspar for thinning (it doesn't take much) in the first place - helps keeps metal from hanging up in the slag

So I would change future smelts to using flux as I just described as any gold (metal) hung up in the slag can be easier recovered by dissolving the slag in hot water

The downside to using that flux is that it is a bit harder on the crucibles due to the washing soda & fluorspar - the washing soda will also cause a bit more foaming during the smelt so you need to leave more room in the crucible when doing the smelt

concerning the current slag - I would follow 4metals directions to remelt with fluorspar - but I would also add washing soda

I would NOT try leaching the fine ground borax slag - it will create a LOT of chem waste & it will still NOT get all of your gold !!!! --- it's a waste of time/chems/money

Kurt

 

[user 72133]

I wouldn’t call 1-2g of Au per kilo a small amount..

i call small amount because when i recover 3g after AR i can't smelt it to do a ingot. and if i melt the slag in the cone mold, i only have 3g and this is really small too...
having tons of slag is a good amount, but i have no form to do the process with a big quantity

 

[4metals]

2 tons in aqua regia is not smart with waste etc. to consider. CN won’t work because the gold is likely in bead form from the first melt and CN will take too long and probably will not dissolve it all anyway.
Have you tried crushing it and panning it? If that works you could table it all.
If your estimates are correct, tons ( assume 2 ) at 1 gram/kg you are looking at somewhere north of $120,000.
Worth figuring out!

 

[Yggdrasil]

i call small amount because when i recover 3g after AR i can't smelt it to do a ingot. and if i melt the slag in the cone mold, i only have 3g and this is really small too...
having tons of slag is a good amount, but i have no form to do the process with a big quantity

Are the slag produced by you?
Or is it old slag you are treating?

 

[Martijn]

On the same topic do some has idea on how can I recover gold from waste carbon which is already burnt to ashes.

Welcome to the forum. How did the gold get there? Cyanide leaching? Is there still carbon or just ash?

 

[NanoCat]

our formula for smelting was always 60 Borax/40 Soda Ash. The melt should be churning away like crazy because basically you are amalgamating just at high temperature. You can also think of it as a high temperature leach. And using Sn as the collector. It is important to keep a light layer of coconut carbon on top of the melt then just before pouring let the Carbon burn off to the last blip. Temperature is a factor also. We would run as high as 2250F and up to 2 hrs. You can always re-fire your slag using this procedure and see what you get.