A potential cleaner method of removing zinc from alloys

[Gigs]

Hi guys.


Seems to me that it might be feasible to boil zinc out of lead or other alloys (such as zinc bearing pewter).

Boiling points:

Tin 2,603° C (4,717° F)
Copper 2,567° C (4,652° F)
Lead 1,750° C (3,182° F)
Antimony 1,587° C (2,888° F)
Zinc 906.8° C (1,664° F)

Of course I'm assuming that alloys retain the boiling points of their constituent parts. There's surprising little information about boiling points and alloys that I could find on the web.

What I'm thinking of as a test would be to deliberately create a batch of lead contaminated with 20% zinc or so, high enough that it's unquestionably bad for casting bullets. Then take the contaminated batch and heat it to 1800 or so under a blanket of graphite on the surface to prevent excessive oxidation of the lead.

If the zinc does boil, the zinc gas will probably combust somewhere in the graphite blanket, filling it with zinc oxide powder, and producing very little toxic fumes, compared to the sulfur slag method which produces copious sulfur dioxide, zinc sulfate (toxic to fish), and hydrogen gas.

What do you all think? Worth testing?

[quiver]

Inhaling metal fumes is generaly considered unhealthy. I hope you have a resperator with appropiate filters at least.

[btroj]

Not in my yard.
I don't have any desire to try and boil off zinc.

[Oreo]

Try it and let us know.

[mrb7]

What I'm thinking of as a test would be to deliberately create a batch of lead contaminated with 20% zinc or so, high enough that it's unquestionably bad for casting bullets. Then take the contaminated batch and heat it to 1800 or so under a blanket of graphite on the surface to prevent excessive oxidation of the lead.

OK, you want the graphite to exclude O2. So far so good.

If the zinc does boil, the zinc gas will probably combust somewhere in the graphite blanket, filling it with zinc oxide powder, and producing very little toxic fumes, compared to the sulfur slag method which produces copious sulfur dioxide, zinc sulfate (toxic to fish), and hydrogen gas.

Now just above you've gone to the trouble to exclude O2, what is the Zinc going to get its O2 from to support the combustion? Not from thin air, because we've gone to the trouble to exclude the air to keep it away from the lead.

What do you all think? Worth testing?

I think we need a bit further analysis of the chemistry involved before anyone jumps into any testing. Or at least before I would jump on any testing. The beginning thought is good. But that's no guarantee that there's a feasible home based solution, but that's also not saying there isn't one. We haven't shown anything one way or the other yet. That's what I think so far.

[Oreo]

I don't see the harm in just testing it, carefully. Ventilation should be a primary concern of course but we should all be reasonably familiar with that. Do a small batch, just a few lbs, or a half cup or so of melt. Wear a face shield, & appron. Stand back & see what happens.

[lwknight]

What are you going to use to get 1700 degrees with?
That is yellow hot near liquid steel temperatures.
A naturally asparated propane flame will not likely get you there
without setting jets like a blacksmith forge. Even then you have a
logistical problem with concentrated hot spots unless you have a
kiln.

Hmmm... maybe a kiln would work?

[btroj]

The heat is certainly a problem. I also wonder what kind of container he proposes to use.
This isone of those things that industry has the ability to do, we hobbyists do not.

Concept is ok, reality just isn't there.

[Oreo]

I think a creative mind could get it done. The test trial, that is.

I have stainless steel measuring cups that are thick enough to hold a few lbs of lead even if the steel was glowing hot. A few plumber's propane torches would be enough to reach those temps on that size of a sample. No oxygen needed, but hell, a few of us have oxy-acetylene torches at home and that would do it easily, and then some. Hot spots shouldn't be much of a problem on such a small sample but it could be stirred. Temperature regulation would be tricky but not impossible. An appropriate thermocouple would be a necessity.

[bumpo628]

This has bad idea written all over it.

[btroj]

If welding galvanized steel gives off bad fumes what does boiling a zinc containing metal do?

You guys do whatever you want but I don't think this is going to become an accepted method of zinc removal for cast Boolit shooters.

[Oreo]

Unlike welding galvanized steel you don't have to have your face down close to this. I've seen some guys here with elaborate ventilation hoods over their casting pots. That would do fine.

[Gigs]

Sorry for the delay in replies.

I have a home made foundry furnace. It is a top loader that I use with clay-graphite bonded crucibles. It's not something that every caster would have access to, but on the same token, it's not all that difficult or expensive to build, it's basically a galvanized bucket with bonded perlite walls. You'd be surprised how well perlite bonded with furnace cement works as an insulator. The outside stays pretty cool even when the inside is searing.

I have had aluminum melts cherry red in it before, so I'm pretty sure it could hit the temperatures we need for this, assuming I can keep my grill sized propane tanks warm enough to keep the BTU rates up (need a water bath for them for sure).

Regarding mrb7's concerns about the O2, I'm assuming the zinc gas will come into contact with O2 somewhere within the blanket of graphite or right above it, since it's probably an imperfect barrier to O2. It would probably more retard oxidation of the melt rather than completely prevent it. I try to keep my torch with a reducing flame as well to help reduce oxygen in the furnace.

Anyway thanks for the words of caution and the words of encouragement. Both are appreciated.

I was busy last weekend testing out my new sharpshooter #1 buck mold, casted 25 pounds of buckshot or so. I'll try to run the test sometime this week or weekend.