Video discussion. Gold recovery from 14kg of CPU by using the lead bath method.

[Martijn]

A video from our new video section:

I would like to get a discussion going about the methods used in this video.

A short intro:
He puts the cpu's in a very hot bath with silver and lead.
He uses 10kg lead and 300gr of scrap silver as a collector for the gold. Then he fishes the ceramics out and reloads it with more cpu's.

I was thinking about using the lead bath method and cupelling or the parkes process, so any views are more than welcome.

I wonder if only lead would do job, I thought it would take less heat and give off lead fumes?
I have melted lead before in a stainless steel pan on an electric hotplate.
Will gold dissolve at lower temperatures or do you need silver to speed the dissolution up?

Cupelling 10kg of lead seems like a lot to me. Could one kg have been enough?

Then the cupelling: he does it in open air on a stainless steel sheet.
I had my thoughts about it, but would like your opinions if this would work as well, better or worse compared to a bone ash or portland cement cupel.

Not all cpu's are submerged when he lets it alone for a while to dissolve, but all surfaces are covered well with lead before he covers the furnace.

Is all the gold recovered? The final yield was 90 grams, so thats 6.4 gram per kilo. Sounds pretty good to me.

So please ask away and give your insights and opinions. And please keep the discussion about this video and ways to possibly improve the methods used.

Martijn.

 

[4metals]

Will gold dissolve at lower temperatures or do you need silver to speed the dissolution up?

I think the Silver was added simply to combine the inquartation step for later parting into the cupellation step.

Which is planning ahead on Owl Tech's part. I like that.

 

[Yggdrasil]

I think the Silver was added simply to combine the inquartation step for later parting into the cupellation step.

Which is planning ahead on Owl Tech's part. I like that.

I agree, but it still feels a bit fiddly.
Wouldn't crushing it lightly and smelting be faster and more complete?
Nice with an other approach though.

 

[BGDOCK]

Can bismuth be used as a collector ?

 

[4metals]

Can bismuth be used as a collector ?

If you can afford it!

 

[Yggdrasil]

The Parkes process with either Zinc or Aluminum feels like it could simplify things.
Suck the solution through a Glass fiber mesh with vacuum?
You would end up with much less excess.
I think for Gold, Aluminum was recommended if my memory serves me right.

 

[4metals]

I spent considerable time in South America doing cupellations in a much more organized furnace that looked like this.

These are effective and have a benefit of being able to scoop out the bed of bone ash when it can no longer absorb lead and the oxides. On a different scale back in the US, I have used large cupels from Legend in an assay furnace to do the same thing.

What I like about @Owltech's methods are the "home grown" look that you can do this yourself without a large investment of cash. I would like to hear more about the charcoal fired kiln he used and the cupel he made to fit into it.

The lead fumes are an issue. Lead fumes drop out of the air quickly and can be easily captured in a bag house on larger scale use. In a back yard, a respirator on a windy night!

 

[BGDOCK]

If you can afford it!

looks like bismuth is 6$ / lb
Lead .90$/ lb.
Im too cheap for bismuth that’s for sure

 

[4metals]

There was a big push in the 90's to replace assay lead with bismuth. All of the labs started to do duplicate assays just to see the difference. Turns out the big difference was cost. It simply never caught on.....too expensive.

 

[Yggdrasil]

I spent considerable time in South America doing cupellations in a much more organized furnace that looked like this.
View attachment 65963
These are effective and have a benefit of being able to scoop out the bed of bone ash when it can no longer absorb lead and the oxides. On a different scale back in the US, I have used large cupels from Legend in an assay furnace to do the same thing.

What I like about @Owltech's methods are the "home grown" look that you can do this yourself without a large investment of cash. I would like to hear more about the charcoal fired kiln he used and the cupel he made to fit into it.

The lead fumes are an issue. Lead fumes drop out of the air quickly and can be easily captured in a bag house on larger scale use. In a back yard, a respirator on a windy night!

The ones doing similar batches.
How is the yield of this video?
Does 90 g per 14kg sound high, low or spot on?
I think a fine mesh cage to hold the Cpus fully submerged could be a good thing, maybe....
I hope he chimes in himself so we can do a more in depth discussion with more background.

 

[anachronism]

90g from 14kg is pretty much achievable with the right selection of ceramics Ygg.

 

[Yggdrasil]

90g from 14kg is pretty much achievable with the right selection of ceramics Ygg.

Good to know

 

[Martijn]

I think a fine mesh cage to hold the Cpus fully submerged could be a good thing, maybe....

I like that idea.

 

[4metals]

Part of the beauty of this method is the minimalist equipment approach, no granulating, simply dunking the circuits into a pool of molten lead and leaving them in long enough to allow the lead to dissolve out (alloy) the gold. I am sure temperature shock does break up some of the circuits as well. And a ladle is a pretty low tech piece of equipment that seems to efficiently extract the stripped carcasses from the lead pool in which they always float.

And 91 grams of gold at the end is the cream on the cake.

 

[Owltech]

Hi! I'll try to answer some of your questions:

The lead bath temperature is around 600C, the hold time is around 3 minutes, the larger the scrap the better, I no longer add the silver during the stripping step, instead I do it afterwards (I read somewhere that they started adding silver to solders to inhibit the solubility of gold, which is the opposite of what I'm trying to achieve).

Silver is used for couple of reasons:

helps the cupellation;

Collects Pd and Pt

protects the gold (when striping gold from copper/bronze/brass based materials some silver goes to the slag while the amount of the recovered gold is the same);

I can control the size of the button after cupellation (it's easier to handle for example: 300.5g of DORE button, than searching for 0.5g gold prill in a large stainless steel tray);

An alloy ready for parting in nitric acid (something I noticed: a DORE dissolves much, much faster than cement silver or silver contacts for example, especially in un-diluted nitric acid, also I'm able to do so with minimal amount of HNO3 (1:1.5 HNO3ORE and some times even less).

Another benefit is the clear silver nitrate solution left after parting, which (when there are no PGMs present) is easily converted to 4N silver using the formate reduction method outlined by 4metals.


Some side notes:

While preforming the stripping step no flux should be added, just plain lead and a carbon source from time to time, to convert any litharge that might have formed back to lead metal.

There's no need for too high temperature dull red heat is enough. The reaction is extremely fast - it takes less than five seconds to fully strip a CPU. The 2-3 minutes hold time is only to ensure that the bath gets up to temperature after adding the scrap.

Thoroughly stirring is essential. As you've noticed the CPUs float on top of the lead so stirring provides means of contacts between the lead and all CPUs. Another way to go about this is to use the ladle to keep the scrap submerged.

If you have any other questions I'll be happy to answer them (if I can)

 

[Owltech]

The ones doing similar batches.
How is the yield of this video?
Does 90 g per 14kg sound high, low or spot on?
I think a fine mesh cage to hold the Cpus fully submerged could be a good thing, maybe....
I hope he chimes in himself so we can do a more in depth discussion with more background.

SS cage works as long as its not fine mesh. Too fine of a mesh and the "pores" gets clogged by the solidified litharge.

This is the latest lead bath I did:

 

[Yggdrasil]

Hi! I'll try to answer some of your questions:

The lead bath temperature is around 600C, the hold time is around 3 minutes, the larger the scrap the better, I no longer add the silver during the stripping step, instead I do it afterwards (I read somewhere that they started adding silver to solders to inhibit the solubility of gold, which is the opposite of what I'm trying to achieve).

Silver is used for couple of reasons:

helps the cupellation;

Collects Pd and Pt

protects the gold (when striping gold from copper/bronze/brass based materials some silver goes to the slag while the amount of the recovered gold is the same);

I can control the size of the button after cupellation (it's easier to handle for example: 300.5g of DORE button, than searching for 0.5g gold prill in a large stainless steel tray);

An alloy ready for parting in nitric acid (something I noticed: a DORE dissolves much, much faster than cement silver or silver contacts for example, especially in un-diluted nitric acid, also I'm able to do so with minimal amount of HNO3 (1:1.5 HNO3ORE and some times even less).

Another benefit is the clear silver nitrate solution left after parting, which (when there are no PGMs present) is easily converted to 4N silver using the formate reduction method outlined by 4metals.


Some side notes:

While preforming the stripping step no flux should be added, just plain lead and a carbon source from time to time, to convert any litharge that might have formed back to lead metal.

There's no need for too high temperature dull red heat is enough. The reaction is extremely fast - it takes less than five seconds to fully strip a CPU. The 2-3 minutes hold time is only to ensure that the bath gets up to temperature after adding the scrap.

Thoroughly stirring is essential. As you've noticed the CPUs float on top of the lead so stirring provides means of contacts between the lead and all CPUs. Another way to go about this is to use the ladle to keep the scrap submerged.

If you have any other questions I'll be happy to answer them (if I can)

Thanks a lot.

 

[Yggdrasil]

SS cage works as long as its not fine mesh. Too fine of a mesh and the "pores" gets clogged by the solidified litharge.

This is the latest lead bath I did:

The "Crucible" is just a stainless pot or similar?

 

[Owltech]

General rule of thumb regarding yields:

Mixed ceramic CPUs 5g Au/kg
Transistors 6g Au/kg
Small ceramic ICs 10g Au/kg
Soviet ICs mixed 20g Au/kg

This the scrap I use with the lead bath method

 

[Owltech]

The "Crucible" is just a stainless pot or similar?

yes, mild steel can be used too