Smelting

[Barren Realms 007]

Frank, I was told that by a company I sold very high purity silver to, they said the same of gold. I guess interstitial impurities affect the resistivity(?). I'm no physicist, I just figure out how to get a material to fit an application or specification.

I guess that silver oxide disrupts the flow of electrons to some extent. Maybe like it does for copper:

https://en.m.wikipedia.org/wiki/Oxygen-free_copper

It (O) also seems to be bad for many other metals' physical properties. C, H, N, and O are usually on the spec list for me.

Yea I understand. Theoretcly it it would make sense to me with what 4metals said it does. I was thinking how it would effect it along the line of use in electrical components in which case it probably would not come into play because the manufacturer should know this. But with running silver through a cell I can see now where it would come into play and might pop up in a question from a forum member as an answer to a problem that might be encountered.

 

[4metals]

What Barren just said gave me a thought. Everyone casting anode material for silver cells does it by melting and casting without protection from the oxygen in the air surrounding us. So in theory all silver cell anodes have a degree of adsorbed oxygen in them. I have noticed that the copper in sterling makes it behave beautifully and it never seems, I guess seems is the operative word here, to behave as pure silver melted under the same conditions reacts.

However silver anodes in silver cells (Moebius cells) do slough off and behave in a similar fashion to those recast pure silver anodes I mentioned. And the solids remaining in the anode bag as slimes is always a high percentage silver. I wonder if an anode was cast to be oxygen free if it would dissolve better, faster, and with less silver scale in the anode bag. That could eliminate a large pain in the butt factor in cleaning up anode slimes! Worthy of playing around with I think.

 

[alexxx]

oxygen sparging to oxidize base metals during smelting.

It was mentioned that O2 could be slowly injected into molten metal during the smelting in order to oxidize base metals and have them driven into the slag.

A few questions here ;

Any additional stirring needed during that process or the sparging is enough to move the pool of metal around and have the O2 in contact with a maximum of metal ?

4Metals has mentioned the use of a quartz glass tube to inject the oxygen into the melt. Any other material could be used to handle the high temperature and the oxidizing nature of the melt ? An alumina tube maybe ? What about a stainless steel tube ?

I understand that O2 sparging might be quite dangerous. What type of appartus is usualy used to control the debit of the injected gas ? A simple regulator ? What debit / pressure would you guys use for a pool of 100 lbs of molten metal and a 10mm diameter tube (material being again ashes & oversize non ferrous from circuit boards)?

Would you suggest to simply use embiant air or an O2 concentrator is preferred for the task ?

How long would you keep injecting O2 into the melt & slagging off ?

cheers !

Alex

 

[4metals]

I prefer quartz glass but Morgan materials makes gassing tubes as well
http://www.morganmms.com/produtos/produ ... sing-tubes

When gassing I have used room air pressurized and pumped into the melt, and I have used compressed oxygen. Whichever you choose, start slowly and only begin with a slow bubbling of gas reaching the surface of the melt. Depending on what you are starting with, gassing can take from a half hour up to hours.

The compressed oxygen obviously delivers more oxygen into the melt which can result in shorter gassing times but I have had good success with compressed air. I will always defer to simplicity.

I like to periodically ladle off slag and pour it into a cone mold. This way you know if you are pulling out metal as it settles quickly in the molten slag and can be collected at the bottom of the mold.

a pool of 100 lbs of molten metal, material being again ashes & oversize non ferrous from circuit boards

Typical PCB metallics are very high in copper to begin with, you are choosing the wrong path if you expect to oxidize all of the copper into the slag, copper is the last to go and usually remains with the PM's. This material is usually shipped to a copper refiner as it produces a homogeneous bar which can be sampled and quantified easily. The copper refiner will upgrade this material to high 90's% copper and refine the copper out electrolytically and segregate the PM's in the slimes. Or you can build a copper cell and refine it yourself.

 

[alexxx]

Typical PCB metallics are very high in copper to begin with, you are choosing the wrong path if you expect to oxidize all of the copper into the slag, copper is the last to go and usually remains with the PM's.

The goal is only to remove other base metals besides copper to obtain a 95%+ copper anode quality alloy at the end for a copper cell. 99% prefered, even if it implies a lost of 5% in the copper content.

It was pointed out that copper will react in a different way than other base metals with this procedure, a small % will be oxidized and lost to the slag while a great % of other contaminants such as Zinc, Nickel, aluminum, tin would be removed.

I believe I could live with a sacrifice of a few % in the copper content to save a lot of troubles in prematurely fouling the electrolyte from the copper cell.

 

[4metals]

For what you just suggested the oxygen sparging is fine and actually the preferred treatment. I just don't want you to think all of the copper base metal is going into the flux.

 

[Lou]

The nickel will stay with the copper.

 

[4metals]

While the nickel will remain it is not a game ender.

The nickel will dissolve in the copper cell electrolyte and not report to the slimes. However, since copper plates at a lower applied potential than nickel, the copper will plate out at the cathode and the nickel will accumulate in the electrolyte. So the copper you produce will be very high grade.

Soon I will start working on a thread about electrolytic copper refining.

 

[alexxx]

While the nickel will remain it is not a game ender.

The nickel will dissolve in the copper cell electrolyte and not report to the slimes. However, since copper plates at a lower applied potential than nickel, the copper will plate out at the cathode and the nickel will accumulate in the electrolyte. So the copper you produce will be very high grade.

Soon I will start working on a thread about electrolytic copper refining.

Here comes the nightmare for me, and for many others I believe, even the big boys...
The Nickel build up in the electrolyte.

Any procedure known to deal with the Nickel at the smelting stage ?

 

[4metals]

Any procedure known to deal with the Nickel at the smelting stage ?

Sure, how many million do you want to invest in a flash smelter and a pair of oxygen top blown converters and finishers?

Nickel is tolerable in the electrolyte at a concentration up to 10 times higher than Iron. The upper limit is around 20 grams per liter. It comes down to how much nickel is actually in your copper doré?

You will be running a copper electrolyte around 40 grams per liter copper and there are methods that have been in use for many years to separate the copper sulfate from the nickel sulfate but for small scale refining, the analytics may be a game breaker. Changing out the electrolyte may prove easier.

 

[alexxx]

Here's part of an assay from 4 types of pcb that have been prepared for smelting (pyrolized and milled).
Samples are from unsieved material (fines & oversizes mixed together).
No magnetic separation done yet, it sure will be an important step to get rid of some Fe & Ni.



The Ni & Zn values seems very high.
CRT-001 has a Fe content going trough the roof and was sent for processing at a secondary copper smelter.

 

[4metals]

I do not understand how a representative sample was made for the analysis shown. Did you melt the metallics fraction into a bar and sample the bar?

If they were prepared for smelting and unsieved, I don't see the sample as representative.

 

[Shark]

I would like to Thank everyone for their input on this thread. While I am in no way ready for smelting, I am a small step closer. A very small step, as this furnace is sitting on the bottom of a 10 gallon barrel. I hope to have a small crucible by the weekend to put it to a better test. I can fire it up and bring a 4 inch x 1/2 grade 8 bolt to red/orange hot in less than 3 minutes. I ran it for an hour today with no noticeable problems. It should help to advance my understanding of using a furnace better given time to practice with it.

 

[FrugalRefiner]

I posted a color vs. temperature chart in the Furnace Temperature Colors thread. At red/orange, you might be just short of the melting point of gold.

Dave

 

[Shark]

Thanks Dave. That chart will be handy in the future. If you look close you can see the head of a bolt sticking out on the right side of the furnace. That bright yellow looking spot inside is the end of the bolt glowing. I didn't make the furnace itself, but it has two holes so it could be fired using two propane torch's. I just made the burner, if all else fails, I will add another one just like it. I had to start someplace, and it was a lot of fun.

 

[Shark]

30 second video of it running in the dark, with bolt end still in place.

[youtube]http://www.youtube.com/watch?v=x62eVd2dgus[/youtube]

 

[4metals]

If you didn't say what that video was i would have thought you got some amazing photo's of a meteorite hurling through space!

I hope you do have, or intend to build a lid for the furnace, for that size furnace a hole in the cover about 1 1/2" will suffice. it is amazing how much heat a lid with a hole that large retains in the furnace.

 

[Shark]

It has a lid on it. The actual inside is 3 1/2" wide by 3 3/4" deep. The opening in the lid is 2 inch's wide. I had been thinking that the lid opening might be made a bit smaller to see if that would help retain some of the heat better. With out the lid it doesn't quite roar as loud.

 

[modtheworld44]

If you didn't say what that video was i would have thought you got some amazing photo's of a meteorite hurling through space!

I hope you do have, or intend to build a lid for the furnace, for that size furnace a hole in the cover about 1 1/2" will suffice. it is amazing how much heat a lid with a hole that large retains in the furnace.

4metals

Umm...you might want to go back and cross reference with the picture of the furnace and the video,the lid is on it.Thanks in advance.

Shark

Looks great,we'll see how well it can melt silver and gold when I come down tomorrow.I'll see how much gold I can round up between now and then,now that we have plenty of nitric it won't take to long to get some of my gold done.The silver is ready to go,I think we can get any kinks sorted out of it.I think the burner you built is going to work just fine.Thanks in advance for the picture and video.



modtheworld44

 

[4metals]

Umm...you might want to go back and cross reference with the picture of the furnace and the video,the lid is on it

OK, I see the ring around the OD where the lid starts and the body ends, I thought you cast it in a plastic tank with little ridges and cut off the plastic after it hardened.

The reason I thought you had no lid is because your lid has no handle to pick it off the top easily. You do need to remove the lid to add flux and stir and in the course of using it flux will drip on the edge and sometimes it sticks to the top. Even with a handle it can require a yank to remove it. If you need 2 gloved hands to lift it off, you need to re-think it.

It is difficult to see get an idea of size, what is the OD of the furnace?