Question about collector metals

[SRM]

Good Morning!

My experience has primarily been with producing a saleable dore product. In that world, lead is often used as a collector metal which is later cupelled to produce a gold/silver dore.

In limited instances, a miner may want a purer product to sell or keep. Most of the hardrock and placer operations I have seen have up to 35% silver in their gold. If a miner wanted to use chemical refining to produce high purity gold, would it make sense to smelt the concentrates using sterling as a collector metal and skip the cupelling step? You may still need to adjust the silver/copper content to inquart the gold. You may overshoot and require more time and nitric to remove the silver and copper but you would avoid cupelling and dealing with lead oxide fumes.

Thoughts? Has anyone tried this?

SRM

 

[Yggdrasil]

Good Morning!

My experience has primarily been with producing a saleable dore product. In that world, lead is often used as a collector metal which is later cupelled to produce a gold/silver dore.

In limited instances, a miner may want a purer product to sell or keep. Most of the hardrock and placer operations I have seen have up to 35% silver in their gold. If a miner wanted to use chemical refining to produce high purity gold, would it make sense to smelt the concentrates using sterling as a collector metal and skip the cupelling step? You may still need to adjust the silver/copper content to inquart the gold. You may overshoot and require more time and nitric to remove the silver and copper but you would avoid cupelling and dealing with lead oxide fumes.

Thoughts? Has anyone tried this?

SRM

If you want to try inquarting that is fine, the issue is to find out how much Silver there is in the Mix.
If you manage to quantify the amount of Silver, it easy to bring it to 6 karat and part it in Nitric.
Preferably with Silver but Copper can be used as well, even if it requires more Nitric.
The issue is, if you do not know the amount of Silver in the mix you might overshoot it
and the Gold will end up as a very fine mud during the parting step.
Not a big deal usually, but you might loose some of it during decanting/ siphoning.
You can aim for a slightly richer mix than 6 karat and accept the amount of Silver that will be trapped in the mix.
If you manage to make very fine "popcorn" when pouring the rest Silver should be even less.

 

[fishaholic5]

I prefer Silver to most other collectors if I use them when smelting ore or concentrates and especially so for modified feild assays using a torch.
In practise any gold that carries through in waste solutions during chemical refining can be recovered by cementation and any that is dragged down from solution when dropping the Silver can be recovered later if you refine the Silver in a Silver cell.
It removes one aspect of the waste stream entirely.

Cheers Wal

 

[goldshark]

Would your proposed procedure be used on black sand concentrates, or on a fairly clean table product?

 

[SRM]

Primarily on clean cons, but at least one operation has significant micron Au in and on the pyrites. I would roast the sulfides before attempting to smelt. I have never had much luck smelting Au from black sands.

 

[goldshark]

What are clean cons ? Any assay done on them? ICP would give a lot of info on what are in the cons to possibly make some alterations to needed fluxes. You should have not luck, but skill when smelting most black sand concentrates. You have to dilute the cons way back to get a decent melt. At least a 2/1 ratio on the proper fluxes ( 2 parts flux to 1 part cons ). If that doesn't work, add even more, 3/1. I have not used Silver as a collector metal, but do not see why it wouldn't work. Finely powdered Ag, to give a rain through the melt, will give better results then a blob. That is one advantage to Litharge. Finely powdered mixed intimately, provides thousands of micro collector beads. I am not sure which metal has a higher affinity for Au, Pb or Ag. Maybe someone else can chime in.

 

[SRM]

Sorry for the poor description! Clean cons were from the number 1 port of a table in a gravity/flotation mill of a hardrock mine....primarily the coarse Au/Ag electrum of the area. Fire assay is normal for mine and mill samples, ICP for check samples. Even had QEMSCAN run on some samples, so we have a pretty good idea of what to expect. One of the sulfides cons I mentioned is from the flotation sides....75%-100mesh, pretty typical comminution (Jaw, short head cone, ball mill).
The black sands I see are usually a few pounds from some small-scale placer groups. I will usually look for VG under a decent microscope to get idea of the potential and then make a plan.

Copy that on the Ag size. I might try getting different particle sizes and see if there is a difference in recovery.

Thanks for the replies!

 

[Nountaineer]

What are clean cons ? Any assay done on them? ICP would give a lot of info on what are in the cons to possibly make some alterations to needed fluxes. You should have not luck, but skill when smelting most black sand concentrates. You have to dilute the cons way back to get a decent melt. At least a 2/1 ratio on the proper fluxes ( 2 parts flux to 1 part cons ). If that doesn't work, add even more, 3/1. I have not used Silver as a collector metal, but do not see why it wouldn't work. Finely powdered Ag, to give a rain through the melt, will give better results then a blob. That is one advantage to Litharge. Finely powdered mixed intimately, provides thousands of micro collector beads. I am not sure which metal has a higher affinity for Au, Pb or Ag. Maybe someone else can chime in.

A member posted previously that iron and silver work best for a collector metal with platinum, palladium and gold leaving the other platinum group in the slag.. I will be adding less than an ounce of silver crystals for that purpose in the next firing since I don't know how to make finely chopped copper for that purpose.

 

[Yggdrasil]

A member posted previously that iron and silver work best for a collector metal with platinum, palladium and gold leaving the other platinum group in the slag.. I will be adding less than an ounce of silver crystals for that purpose in the next firing since I don't know how to make finely chopped copper for that purpose.

Gold is the best collector for at least Rhodium, but the price makes it less attractive.

 

[ChopperGreg]

I read something with the last month or so, that nickel was a good collector for PGMs, which is something that I’ve been considering to use besides copper for gold and silver.

Might be something to the thought that nickel has a PGM affinity, because the big Sudbury nickel operation in Ontario Canada, is known to have substantial zones of PGM intrusions.

 

[orvi]

I read something with the last month or so, that nickel was a good collector for PGMs, which is something that I’ve been considering to use besides copper for gold and silver.

Might be something to the thought that nickel has a PGM affinity, because the big Sudbury nickel operation in Ontario Canada, is known to have substantial zones of PGM intrusions.

Nickel is very bad collector for silver. These two don´t mix, similarly to molten zinc and lead. Only at insanely high temperatures...

Not only from diagrams, I also unwillingly experienced that in person. During inquartation of gold contacts from relays (60-70% Au, 25-30% Ag, ca 5% Ni), I obviously cannot obtain homogenous melt I wasn´t aware of the immiscibility of these two back in the day... As the silver content risen (after addition of silver contacts as diluent), nickel precipitated from the melt and formed some sort of granules on the bottom of melt dish. I felt them with graphite rod, when stirring the molten puddle. At a time, I´ve only had propane/air torch, so I wasn´t able to get to the temperature high enough to dissolve the nickel into the melt.
Before the pour, I fished out these granules out of the melt with help of two graphite rods. Gold content in these was similar to the rest of inquart, but major component of them was nickel.

For PGMs, nickel is allright. For gold... I do not see any advantage, it has high melting point. If I imagine using lead, bismuth or copper, all three has better qualities as collector for gold than nickel.

 

[orvi]

Good Morning!

My experience has primarily been with producing a saleable dore product. In that world, lead is often used as a collector metal which is later cupelled to produce a gold/silver dore.

In limited instances, a miner may want a purer product to sell or keep. Most of the hardrock and placer operations I have seen have up to 35% silver in their gold. If a miner wanted to use chemical refining to produce high purity gold, would it make sense to smelt the concentrates using sterling as a collector metal and skip the cupelling step? You may still need to adjust the silver/copper content to inquart the gold. You may overshoot and require more time and nitric to remove the silver and copper but you would avoid cupelling and dealing with lead oxide fumes.

Thoughts? Has anyone tried this?

SRM

I can see this to be used in some circumstances. Only things that should be considered are particle size of silver added and the actual ammount of silver used. I mean, lead is usually added in high excess in comparison with expected gold content. As it can be easily cupelled out afterwards. That does not imply for silver. You can add only certain ammount before making too dilute Au alloy (25% and less), not very good for inquartation (very fine nano violet gold suspensions formed in nitric). And getting rid of excess silver/adding more gold would be another issue.
Particle size is also important to consider, as the beads of molten metal are collecting values while falling to the bottom of the crucible. Yes, if you let the melt cook long enough, you eventually reach equilibrium even if you throw chunk of silver in, instead of powder - but crucibles have finite working time and fuel costs are also to be considered. In addition to this, silver has much higher melting point than lead. This means (I do not know your smelting temps and circumstances) your charge can flux and liquify at lower temperature than the silver melts. Meaning that it won´t catch anything during the descent to the bottom.

You say that average is 65% AuAg alloy. If my quick math is right, you can add around 1,6 times more silver, than you actually have AuAg alloy in the charge. If you have rich cons, maybe it would be sufficient. But if you have low grade cons, that may not be enough.

I know people who add both lead and silver during the smelting process. Then, after cupellation, they obtain dore of suitable Au:Ag ratio for direct inquartation. Not that much helpful, but still, you save that one necessary step of another melting.

 

[ChopperGreg]

Nickel is very bad collector for silver. These two don´t mix, similarly to molten zinc and lead. Only at insanely high temperatures...

Not only from diagrams, I also unwillingly experienced that in person. During inquartation of gold contacts from relays (60-70% Au, 25-30% Ag, ca 5% Ni), I obviously cannot obtain homogenous melt I wasn´t aware of the immiscibility of these two back in the day... As the silver content risen (after addition of silver contacts as diluent), nickel precipitated from the melt and formed some sort of granules on the bottom of melt dish. I felt them with graphite rod, when stirring the molten puddle. At a time, I´ve only had propane/air torch, so I wasn´t able to get to the temperature high enough to dissolve the nickel into the melt.
Before the pour, I fished out these granules out of the melt with help of two graphite rods. Gold content in these was similar to the rest of inquart, but major component of them was nickel.

For PGMs, nickel is allright. For gold... I do not see any advantage, it has high melting point. If I imagine using lead, bismuth or copper, all three has better qualities as collector for gold than nickel.

I think that there has been some misunderstanding.
I didn’t intend to even imply that nickel would be good for gold *and* silver, only that besides the potential of using nickel for PGMs, I’m intending to use copper for gold and silver.

I’m thinking my way through the possibly of smelting chopper/shredded PCBs with CuO, with the baser metals and carbon sources oxidizing to slag and reducing the CuO to Cu, which is then used as the collector metal...in essence relying more on thermo and electrochemistry, due to limited space for wet chemistry. Mostly theory, right now, but in theory it should be possible.

 

[orvi]

I think that there has been some misunderstanding.
I didn’t intend to even imply that nickel would be good for gold *and* silver, only that besides the potential of using nickel for PGMs, I’m intending to use copper for gold and silver.

I’m thinking my way through the possibly of smelting chopper/shredded PCBs with CuO, with the baser metals and carbon sources oxidizing to slag and reducing the CuO to Cu, which is then used as the collector metal...in essence relying more on thermo and electrochemistry, due to limited space for wet chemistry. Mostly theory, right now, but in theory it should be possible.

Thanks for clarification.

You are walking on the good path, but unfortunately, CuO and Cu aren´t that easy put to the work as you intend. As there is also Cu(I) and that is what you will end with...
MBMM has good video on the issue, and when he added CuO to the melt (he explained exactly same logic behind), nearly all metal magically disappeared.

 

[ChopperGreg]

Thanks for clarification.

You are walking on the good path, but unfortunately, CuO and Cu aren´t that easy put to the work as you intend. As there is also Cu(I) and that is what you will end with...
MBMM has good video on the issue, and when he added CuO to the melt (he explained exactly same logic behind), nearly all metal magically disappeared.

You don't happen to recall the name of that particular video, do you?

I watch his videos from time to time, and recall the tests he did with copper as a collector metal, but don't recall one about CuO, and the idea that it just disappeared sounds a bit far-fetched...I suppose that if there isn't enough material to reduce the CuO to Cu, that the remainder of the CuO would end up in the slag, but there are ways to deal with that.

 

[Alondro]

You don't happen to recall the name of that particular video, do you?

I watch his videos from time to time, and recall the tests he did with copper as a collector metal, but don't recall one about CuO, and the idea that it just disappeared sounds a bit far-fetched...I suppose that if there isn't enough material to reduce the CuO to Cu, that the remainder of the CuO would end up in the slag, but there are ways to deal with that.

Copper oxide needs a fair amount of carbon for reduction to work well. I'm not sure why, since copper is less reactive than lead, but lead is MUCH easier to reduce than copper in a smelt. It might have to do with the much higher melting point of copper slowing the reaction. And after checking, I found that CuO has a very high melting point itself, 2419F! Nearly 500F higher than copper's melting point! So, to use it as a collector in the flux, you likely have to add MUCH more carbon AND hold it at a very high temp for much longer.

 

[ChopperGreg]

Copper oxide needs a fair amount of carbon for reduction to work well. I'm not sure why, since copper is less reactive than lead, but lead is MUCH easier to reduce than copper in a smelt. It might have to do with the much higher melting point of copper slowing the reaction. And after checking, I found that CuO has a very high melting point itself, 2419F! Nearly 500F higher than copper's melting point! So, to use it as a collector in the flux, you likely have to add MUCH more carbon AND hold it at a very high temp for much longer.

There are a couple of things that are being missed, suffice it to say that reduction of CuO to Cu, can start below the listed melting point of CuO.

Tell you what, I don’t want to end up hijacking this thread by accident…how about I collect my notes and over the next couple of days ( provided migraines cooperate ), I’ll start a new thread, then once it’s started I’ll post a link to that thread here?