Purifying lead... got my Thinking Cap on again.

[B.C.Jay]

Long boring winter, time to investigate some ideas.

It's seems that there are 3 major ways to purify (or refine) lead and related metals.
1) Electrolysis - the gold standard for purity
2) Selective oxidation - targeting specific metals in the mix to remove them. (I would put the zinc/sulfer method in here)
3) Vacuum Distillation - just like making whiskey, only higher temperatures

It seems that the removal of zinc, antimony and silver are easily accomplished by high temperature vacuum distillation/condensation of the metals from a raw lead base. Likewise, lead can be distilled from copper base, although at higher temps.

Has anyone ever done any research into this type of process?
If we can cast aluminum/brass/copper in a home hobby setting, I'm sure we can achieve a vacuum distillation as a hobby project; the temperatures are pretty similar. Can we recover nearly pure lead from the wide range of garbage lead alloys that are out there?

Comments and ideas welcome

~J

[Winger Ed.]

Interesting. For my application, it sounds like a lot of extra work too.
I just do the melting pot, or propane stove thing.

What I end up with doesn't have to pass a alloy/purity test since I'm not selling it.
I keep 'the good stuff' to be alloyed to one degree or another for casting boolits & fishing sinkers.
The 'bad stuff' gets thrown out.

[JimB..]

If I may answer a question with a question, are you willing to put $2/lb into such a process, and then need to alloy it since you don’t shoot much pure, when you can currently buy what you need for $1/lb?

I don’t know what it would really cost to setup, I know someone that I could ask, but I’m thinking more than $10k + the power cost at a buck or two per pound.

[B.C.Jay]

I think this is more about the idea and 'can we do it' rather that the economics of it.
Like you, I have more than enough 'stockpiled'

I see this as more about the academia rather than practicality.
Also, there are more than just a few examples of people adapting industrial processes to back yard DIY on a shoestring budget.


I would like to see some input from people that have knowledge and experience in the metalurgial side. Industry has been doing this for many years, but it seems like the knowledge and processes are becoming lost with that generation.
Or, to put it bluntly, we can't find this info on facebook...

[JimB..]

In that case, give this a quick look if you haven’t seen it. https://www.totalmateria.com/page.aspx?ID=CheckArticle&site=ktn&NM=381

[jim147]

Do you have a need to remove the silver and copper? Like maybe bringing something back to pure lead?

I don't have a need to do it so haven't tried.

[kevin c]

Are we talking about literally vaporizing and then condensing metals, and in a partial vacuum to boot? That sounds way beyond the home hobbyist to me. But if metallurgists and engineers think otherwise, I'd like to hear the how-to.

[CraigOK]

Not a metallurgist, but I work with hc distillation, so here are some thoughts. Zinc goes to vapor phase at 1,600 and lead requires temps that are about 3,200. Copper and silver are hotter than that. So in deep vacuum you could achieve those temps and remove the zinc and discard, then raise temps and boil off the lead so you only have copper and silver left. You'd need a column that is made of a material that can handle deep vacuum and high heat. The entire length of it would need to be heated, as well as the path that your overhead vapors travel to keep them from condensing until they get to your collection point. That would also need to be heated, or at least be capable of being heated so the metal could be removed. Not sure if this column would require packing or reflux to help with the purity of your overhead product. In practice lead is way cheaper than the electricity that would be required to make it all work for the home hobbyist. My $.02.

Eta- you'd need a vacuum pump as well and great insulation. Lots of thermocouples. Some hand valves. It would be neat to be able to make it work, hopefully we never get to the point that its seems like a good option :???:

[B.C.Jay]

Are we talking about literally vaporizing and then condensing metals, and in a partial vacuum to boot? That sounds way beyond the home hobbyist to me. But if metallurgists and engineers think otherwise, I'd like to hear the how-to.

I haven't totally wrapped my head around it yet, but it seems that the whole thing revolves around the 'vapor pressure' rather than the actual boiling point.
By applying a vacuum, a certain metal's vapor point alters dramatically and can be 'boiled' out of the alloy.
So yes, it's about vaporizing and condensing metal. Very similar to mercury distillation.
It all happens in the 1700 degree range, so yes hot, but not unachievable.

It also appears that the chinese are heavily looking into this as I think it's the most 'energy efficient' way of separating scrap without running it through the smelting processes.

[B.C.Jay]

Not a metallurgist, but I work with hc distillation, so here are some thoughts. Zinc goes to vapor phase at 1,600 and lead requires temps that are about 3,200. Copper and silver are hotter than that. So in deep vacuum you could achieve those temps and remove the zinc and discard, then raise temps and boil off the lead so you only have copper and silver left. You'd need a column that is made of a material that can handle deep vacuum and high heat. The entire length of it would need to be heated, as well as the path that your overhead vapors travel to keep them from condensing until they get to your collection point. That would also need to be heated, or at least be capable of being heated so the metal could be removed. Not sure if this column would require packing or reflux to help with the purity of your overhead product. In practice lead is way cheaper than the electricity that would be required to make it all work for the home hobbyist. My $.02.

Eta- you'd need a vacuum pump as well and great insulation. Lots of thermocouples. Some hand valves. It would be neat to be able to make it work, hopefully we never get to the point that its seems like a good option :???:


It seems like there's two different processes. The first is removing binary alloys from a lead base and the second, at much higher temp is trying to remove lead and other impurities from a copper base. That makes sense, look at #2 dirty copper pipe - It's mostly contaminated with solder.

Obviously the scrap handlers are looking at cost effective ways to purify their 'raw material' streams. I think electrolysis is getting secondary attention because electricity is not getting cheaper.


And remember - Vacuum is just the air cleaner side of a compressor, until we get to the 'deep vacuum' point.

[B.C.Jay]

In that case, give this a quick look if you haven’t seen it. https://www.totalmateria.com/page.aspx?ID=CheckArticle&site=ktn&NM=381

Yes, that kind of exactly the rabbit hole I'm going down.
Or maybe I'm just tired of the scamdemic and need a distraction.

Either way, it's interesting...

[GregLaROCHE]

This thread is very interesting to me because I have been wondering how to reduce the hardness of my lead. I collect range scrap from an indoor range and it is quite easy compared to mining a berm. Also there are no jacketed bullets in the scrap. Most of the commercial boolits shot are made with very hard lead, probably to keep them from being damaged during shipping. What I recuperate worked fine when I was shooting high velocity rifle boolits, but now I am doing a lot of muzzle loading and a softer lead is better, especially for mini balls that need to expand.

We worry about not getting our lead too hot, because of loosing tin, so I have wondered if heating the range scrap to a high temperature, without a vacuum would remove alloys and reduce the hardness. I concluded that the tin could be removed, but the antimony that is most likely the main source of the hardness could not.

Is there any chance of softening lead just by heating or maybe adding the right flux?

I am sure many would be willing to trade even up with me for soft lead, but I now live in France, so shipping costs rule out that option.

[B.C.Jay]

It seems like you could superheat alloy in a closed container, put some vacuum to it and draw out the unwanted stuff. Running the vacuumed vapor through a condenser would trap the metals and prevent them causing problems further down the line, like solidifying in the vacuum pump.

Zinc, Antimony and Silver seem to some of the first to come out based on the 'vapor pressure' boiling point. I think tin stays pretty much until the end.

Seems like a viable way to soften lead that is not totally out of reach of someone with some skills.

(Note: People that only have the skills to whine should not be included in this discussion)

[GregLaROCHE]

We worry about not getting our alloy too hot in fear of loosing tin. If antimony is lost before tin, there shouldn’t be a problem cooking it off under normal pressures. Or we shouldn’t have to worry about loosing tin if we overheat the alloy. I’ve been told, that you have to get lead really hot before pure antimony will alloy with it. It would nice to hear from others who more about this subject.