Gold recovery from smelter slags

[kurtak]

This thread is starting to drift away from it's original question which is how to recover the gold that is tied up in slag --- it is now drifting into "other" aspects of refining --- we have not yet solved the problem of how to recover the gold that is tied up in A LOT of slag --- there have been "some" suggestions but they may (or not) be the best suggestions - depending on how much slag we are "actually" talking about

So - lets get back to the actual question of --- how to recover the gold that is tied up in slag

The first question in answering that question is --- how much slag are we "actually" talking about

i have tons of slag to trate it by this way

Sometimes people say they have "tons" of something when they really mean they have a lot but it is actually not even "a ton"

A ton is 2,000 pounds (or 907 kilos)

So --- do you "actually" have more then 2,000 pounds ? --- or just "a lot" but not 2,000 pounds or more ?

Even "a lot" means different things to different people - it might mean 10 pound to one person or 100 pound to another person or a 1,000 pound to someone else

I would treat 10 pounds of slag different then I would treat 100 pounds of slag & I would treat 1,000 pounds of slag different then 100 pound --- so ------------

Just how much slag do you "actually" have ??? (roughly)

Pictures would be helpful (is it 5 gallon buckets full - or 55 gallon barrels full ? & how many ?)

Kurt

 

[kurtak]

At some point it is no longer worth the time to chase traces.

I agree - at least to a point

How ever we are talking about 1 - 2 grams per kilo tied up in slag & if we are talking about actual tons (of slag) with that much gold - then we are talking about what would be considered VERY HIGH grade ore (between 25 - 50 ozt per ton) - AND - If I had an actual ton - that is just how I would treat it - just like ore --------

Crush it to 80 or 100 mesh - concentrate on concentrator table - smelt concentrates

Kurt

 

[Yggdrasil]

The OP have not been back since 28 of July.
Lets wait for some more info from him.

 

[user 72133]

Los OP no han regresado desde el 28 de julio.
Esperemos más información de él.

sorry i was on my holydays. i have never used a concentrator table, i will search information about that and if it is the best way i will buy it.
We are a company and we generate larges quantities of slag. we have kept it for long time and we have stored it.
Now is the moment to recover. thanks

 

[4metals]

Do you have a large crucible melt furnace? If so, what is the most you can melt at once? If you have a decent sized furnace and it is a tilt pour, you can concentrate what you have relatively easy.

 

[user 72133]

i have a crucible furnace which has 5kg of slag of capacity. It is not tilt pour...
Too slow

 

[kurtak]

sorry i was on my holydays. i have never used a concentrator table, i will search information about that and if it is the best way i will buy it.

I am currently busy with other things but will do my best to provide info about milling & concentrating when I get a chance

Kurt

i have a crucible furnace which has 5kg of slag of capacity

Pictures of your smelting/furnace/crucible set up would be helpful

Kurt

 

[user 72133]

Actualmente estoy ocupado con otras cosas, pero haré todo lo posible para brindar información sobre el fresado y la concentración cuando tenga la oportunidad.

kurt

Serían útiles fotografías de la instalación de su fundición/horno/crisol.

kurt

 

[4metals]

i have a crucible furnace which has 5kg of slag of capacity. It is not tilt pour...
Too slow

Yes too slow, when you said you had tons of slag I assumed you had a larger furnace. I know shops that have gas furnaces with #400 crucibles that load it up with slag and thin it with fluorspar and let the gold drop in the crucible. When it's molten and had time to settle the molten slags are poured off but the crucible is not emptied. The gold stays in the bottom. Then they add more slag, thin it and repeat. After the day of melting, they pour completely for the last time and all of the values are pooled in the bottom and come out with the last of the slag. Very effective, but not something for 5kg at a time!

 

[Tomcat]

Yes too slow, when you said you had tons of slag I assumed you had a larger furnace. I know shops that have gas furnaces with #400 crucibles that load it up with slag and thin it with fluorspar and let the gold drop in the crucible. When it's molten and had time to settle the molten slags are poured off but the crucible is not emptied. The gold stays in the bottom. Then they add more slag, thin it and repeat. After the day of melting, they pour completely for the last time and all of the values are pooled in the bottom and come out with the last of the slag. Very effective, but not something for 5kg at a time!

 

[Tomcat]

Do they use a collector metal? Without one whatever gold I had just seemed to stay in the slag. If not, what do they do, tilt it slightly when they pour it? How would they know how much to pour out without losing any gold?

 

[4metals]

If you thin the slag it will not hold up beads. And melt slags typically are holding up beads of melt metal. I never had to add a collector metal. This is not true with sweeps because the metal is so finely divided. For sweeps you need a copper collector and a rotating kiln to collect the metals.

If you have ever poured molten metal it is easy to see the metal before it pours out as it is glowing bright in the red glowing slag. So it is easy in practice to pour off most of the slag and leave the metal pool at the bottom.

 

[Tomcat]

Inneresting, thin the slag. Guess thats why they used fluorspar, which is expensive to use in larger quantities I noticed. I was using soda, works okay but not for this. Not sure what sweeps are but I know I had to sweep after every session. It was messy. I cant smelt anymore but have all my ore for future sessions.

 

[ChopperGreg]

Not sure what sweeps are but I know I had to sweep after every session.

In a nutshell, small mixed material that may be swept up from the floor or worktable, of a jeweler.

May contain precious metal filings, very small loose stones of the precious or semiprecious kind, and random assortment of dust and dirt.

 

[kurtak]

i have a crucible furnace which has 5kg of slag of capacity.

Yes too slow, when you said you had tons of slag I assumed you had a larger furnace.

Which kind of brings us back to treating it as an ore as a "possible" alternative (milling to fine powder & running on concentrator table)

Sorry I did not get back to this but got side tracked by other issues & in about a half hour am headed out the door to go fishing - so don't have time right now ether

Here is an example of a concentrator table (for fine gold)

https://mbmmllc.com/products/shaker-tables/
You still have to have away to mill the slag to a "fine" powder

It would be good to see Deano chime in here if he happens to see this thread

Kurt

 

[Deano]

Gold which is present in slag is there because it has a metalloid coating on the gold particles.
The gold is basically present in three particle sizes;
coarse up to around fingernail size comprising large prills and misshapen blobs all larger than 2 mm screen sizing, small prills sized 2mm to 0.1mm and very small prills sized below 0.1mm.
If the slag is run through a small jaw crusher with the jaws set wide and the product is screened on a 2 mm screen you can pick the large gold pieces off the screen.
The material which has passed through the jaw crusher is now screened at 0.6mm and the jaws on the crusher are closed up to the minimum possible.
All of the + 0.6mm slag is now passed through the jaw crusher and re-passed under choke feed conditions until all of the slag now passes through the 0.6mm screen, you are picking the medium sized prills off the screen each pass.
All of the -0.6mm slag is now repassed through the crusher under full choke conditions until all of it passes through a 0.3mm screen.
All of the above is done totally dry.
You now table the slag, beware that many slags will fuse together when wet so you may need to feed the slag onto the table in a slow stream with plenty of water to avoid this.
Because you have not flattened the prills by ball milling or similar the gold will come off the table as a clean line.
The table tails go into a bottle roll using a 200 litre plastic drum or similar as the bottle, run as a dilute pulp of 5 kg maximum ore in 50 litres water with a minimum of 50g cyanide pellets at pH 11 for 24 hours.
The gold cyanide is extracted from the liquor onto carbon and the liquor and solids are replaced in the bottle and run for a further 24 hours.
These cycles continue until only low levels of gold report to the carbon, usually check the gold in solution levels by AAS.
Deano

 

[Deano]

In addition to the recovery post I forgot to mention that if you try to just smelt the prills you will have high loss rates.
By putting the prills in 20% HCl for several weeks you can clean the coating from the prills and get good smelt recovery.
Heating the acid solution will shorten the digestion time for the coating.
Deano

 

[4metals]

I think we have been discussing two entirely different types of slag here. The OP has slag full of beads which has come from melting of karat gold jewelry for refining. As a result he accumulated a substantial pile of slag containing karat gold beads. I don't think the slags Deano is discussing are from the same source. The slags generated from karat gold melting hold up beads because the flux gets too thick and fine beads can be separated from the molten pool of alloy and end up in the slag. A lot of refiners will simply crush and sift this material and this way screen out the values as oversize. When crushing it is possible to crush the beads to the point where they pass through a 40 or 60 mesh screen and remain as values in the powder. While I have seen this it is usually in the range of 1 to 2 ounces per ton as the majority of the beads are in the oversize. For this reason, I prefer the re-melt with a thinning component to the flux so no beads are crushed so small they pass along with the fines.

I think, and please correct me if I am wrong here, Deano is talking about slags remaining after melting the spent carbon from the CIP process. This material is different because the particles of gold can be much smaller to start in the melt. Plus, as Deano will admit, he would gladly leach gold from fines running 1 to 2 ounces per ton as it fits into the normal realm of leach solids. (actually probably a bit higher)

Please clarify the genesis of the slags you are speaking about with your method described above.

 

[Deano]

Most of the slags I have worked with are sourced from smelting of electrowin gold from stripping of activated carbon.
These slags have high levels of base metals from the gold leaching and stripping/electrowin stages of processing.
I have also worked with slags from smelting of material sourced from jewellery scraps and ewaste processing.
These slags are formed from low level base metal materials but the fluxes used contain substantial levels of base metals which are present in quantities high enough to affect the level of base metal coatings on the gold.
You do not need much base metal to put an angstroms thick coating on gold beads, it is invisible to optical methods.
I had to use high powered research type XRF units to demonstrate the presence of these coatings.
Deano

 

[4metals]

You do not need much base metal to put an angstroms thick coating on gold beads, it is invisible to optical methods.
I had to use high powered research type XRF units to demonstrate the presence of these coatings.

And, to follow from this, the angstrom thick will effect solubility in leach solutions preventing complete dissolution in the leach circuit. I wonder if that same coating will, at some concentration, adversely effect the ability of the small beads to coalesce into a pool in the melt.

Apparently, for either slag type, the elimination of the ball milling by jaw crushing is crucial for collecting most beads as the ball milling increases the coating which will limit the ability of the finest particles to leach effectively.

"In addition to the recovery post I forgot to mention that if you try to just smelt the prills you will have high loss rates."

This part I don't fully comprehend, are you saying that the metallic beads, regardless of size, will experience losses due to this coating on melting? This is something I have not experienced. I would assume those losses would show up in either fire assay or instrumental analysis of the remaining slag?

This is something I would like to see quantified in some way, and I hope it will lead to more discussion.