zinc help #2

[gunsbrad]

Well I tried sulfuring my contaminated lead this morning. I wasn't aiming for the whole 4-500lbs, I just wanted to clean up 50lbs or so to test out the process, and to get some cleaner stuff to cast a few revolver boolits. I added about 40-50lbs of contaminated lead to the pot on my propane burner, let melt then started adding sulfur a few oz. at a time, stirring until the reaction stopped, let set 5 min, pull crust out and repeat until the reaction stopped.

Only problem was the reaction never stopped. As long as I added sulfur it kept going. In the end I stopped and cast 3 1/2 lbs of ingots. I think I could have kept going and gotten rid of the whole pot full. I did end up with two coffee cans completely full of the crust.

This stuff started off as free wheel weights. I didn't know that clip on wws could be made out of zinc so I didn't check. They have sat around in ingot form for a couple years until I used up my other ww alloy. Could almost all of them have been zinc or am I doing something wrong? Help

Brad Hurt

[44fanatic]

No idea what the chemical action should have been with the sulpher but hard to believe that most of them were zinc unless you got a batch of zinc WW's that were culled from lead WWs. From the posts on here, it seems that you will not get rid of all the zinc. Best of luck.

[sagacious]

How hot did you get the melt before fluxing with sulfur?

[gunsbrad]

I got it to about 600 to start then turned my propane burner all the way down. By the end I was at about 850.

Brad

[sagacious]

Brad,
As a general policy when working with lead alloys, flux as close to the melting point as possible. With your alloy that should be a little under 600*F. 850*F is much too hot. At that temp the heat is then working strongly against you, and my suspicion is that fluxing with sulfur at that temp is not likely to work well. The undesirable components in your lead are less soluble at lower temps, so that's when to apply your sulfur treatment to maximize it's potential effectiveness.

The sulfur will continue to burn for as long as you add it to the melt. Try to keep the temp very low. Good luck.

[gunsbrad]

The sulfur will continue to burn for as long as you add it to the melt. Try to keep the temp very low.


I understand the sulfur will continue to burn. Is it oxidizing the lead at higher temps? If so does it do it at lower temps too? I was under the impression that I should keep adding sulfur until the reaction stops. If this is so I end up with no metal. I am not trying to remove every trace of zinc. I really don't care if zinc is in the mix or not as long as I can have some usable bullet metal.

Thanks for your replies.

Brad Hurt

[mac1911]

new to casting so bear with me.
Last night I decided to melt down a batch of ignots I though had ZINC. When I smelted this batch of WW I did not have a thermometer and didnt really know the melting temps of WW types. I got a cottage cheeze mess that wouldnt even pour well. NOW I got a new High psi burner bigger pot and a thermo meter.
I placed the 30ish pounds of ignots in the pot and turned on the heat to medium. I had a lyman thermo attached to the side of the pot. Temp rose slowly 500,550,650. Things started melting. I cut the temp back stabalized the temp melted @ 650ish never going above 700.
I still got the cottage cheeze but seemed to be isolated to the top. I skimmed it once added a good chunk of toilet ring wax and stir stir stir. Cleaned off the mess and poored into ignots. I still got a little cottage cheeze junk on top of the ignots after pooring. I skimmed that off quickly and was left with some nice looking ignots. I then casted a few 12g lee slugs with a few ignots melted in the smaller electric pot....a touch of cheeze on top but nothing like before. Not sure what it was or what I did......but it was better????

[sagacious]

Brad,
With antimonial lead alloys (like ww lead) poisoned with zinc, my perception is that your goal is to remove as much of both the zinc and antimony as possible. The zinc will bind to antimony within the alloy, so you should flux when the zinc/antimony is least soluble-- which means flux at low temp so as much of the sulfur contacts the zinc/antimony.

When melting ww's, one often sees a foamy dross on the surface of the molten metal. That's the result of the lower-solubility of the antimony within the lead alloy. Increasing the temp allows the antimony to dissolve easier. In your case, as the temp goes up, both the zinc and antimony dissolve better, so getting them out with flux becomes more difficult.

Flux the melt with suflur at low temp, when you see a bunch of foamy dross. I suspect that the sulfur is really only effective in removing the zinc and antimony that is in the foamy dross. Flux it once or twice with sulfur and then test it to see how it actually pours with your molds.

Your other possible remedy is to mix your untreated ingots 1:1 with pure soft lead, and flux with wax. Try that and then test pour. Good luck.

[sagacious]

Mac1911,
Sounds like what you did was to flux your previously unfluxed ww's. Congrats and welcome to the world of fluxing. Like you saw, it makes a difference. Keep up the good work.

[mac1911]

I fluxed the wheel weights the first time. This is the only batch of wheel weights so far thast did this. The other 300lbs came out nice

[gunsbrad]

sagacious,

Thanks for your help. I'll try again since I still have sulfur left. I am not against mixing some with pure lead and trying that. I just don't have any to mix right now.

The foamy dross you mentioned is something I have not seen. Is this common?

Also I reduced a whole pot of 40-50 lbs with sulfur. Does anyone know what the sulfur is doing to the lead, or how to prevent it?

Brad

[sagacious]

The foamy dross you mentioned is something I have not seen. Is this common?
Brad,
You previously described one of the symptoms as "oatmeal." That's what I'm talking about. If that symptom no longer appears when melting your lead, then we should reassess the symptoms.


Also I reduced a whole pot of 40-50 lbs with sulfur. Does anyone know what the sulfur is doing to the lead, or how to prevent it?

Brad
Not sure what you mean. How to prevent exactly what? Can you describe this a little more?

[gunsbrad]

Maybe the oatmeal/foamy dross is the same thing and we are just using 2 different word to describe it.


When I sulfur/fluxed 40-50lbs of lead I added sulfur, mixed, let set for 5min, scraped off the crust, and repeated. I did this probably 5-6 times. The reaction kept happening so I kept going. When I quit there was only about 4lbs of lead in the pot. Thats 4 not 40. I lost 40+ lbs of lead in this operation. I hope you can see my concern.

Brad

[sagacious]

Ay caramba. Yes, that's a huge problem.

I think the best way to treat the zinc-contaminated lead with sulfur is to flux at a low temp, and when the melt is still right at slushy stage. I reviewed the fluxing instructions in the original post of the 'zinc removal with sulfur' thread, and the poster's instructions agree completely with my thoughts on this question. So, at least there's a common understanding on the process. And normal fluxing works best at low temp anyway.

The sulfur will not seek out the zinc and remove it from the entire pot of molten lead-- you need to react the sulfur with the "oatmeal" to form zinc sulfide and antimony sulfide. If you keep adding sulfur, I suspect the sulfur will react with lead and form lead sulfide until the molten lead is all gone.

The chemical reaction we're after should happen pretty quick. Flux the slushy lead with sulfur, stir/mix for a few minutes at most, and then skim off all the floating scum. The sulfur should have reacted with the slushy antimony and zinc that was in the oatmeal. That's about all you can do. Flux with sulfur and then test pour some bullets. Good luck.

[docone31]

I have found it much simpler to "sweeten" it with pure, and deal with it. Less loss that way.
When I do scoop out the mush, I keep it and melt it into pure lead. I am careful to stir so the zinc gets mixed well. I have had issues with the zinc not being blended well.
Zinc works well for me. You can sweeten it out a long way.

[garandsrus]

Brad,

I would try adding sulfur to a known "good" alloy that doesn't contain zinc to see what happens and compare your results with the "bad" alloy. The only time I have had the "oatmeal" consistency was with type metal that contained a lot of antimony. Adding heat did allow the oatmeal to mix back in with the pot.

I have not tried removing zinc with sulfur, but my understanding was that the reaction stopped when the zinc was gone. I had never heard that the sulfur would remove the antimony also.

John

[lwknight]

When I was working with high SB alloy there was a thick slush float up to the top that you could make a hole in with a spoon and watch the liquid move into it.
There were two ways to beat it that I found. One was to add tin to stop the float up and the other was to stir vigorously and pour into ingots very quickly.

As for the oatmeal looking stuff. I did melt some zinc into some lead and it made floaty frothy stuff that really looked like silver-gray oatmeal. The zinc oatmeal is very floaty and really does not look like the high antimony slush.

[sagacious]

OK. I was waiting for this to come up. It should probably be spelled-out here for everyone's interest, because there are people who say "Zinc in your lead is good" and folks who say "Zinc in your lead is a total nightmare." This thread is evidence of the latter fact, but a good explanation of why has never been provided by either side. It's time to address this information vaccuum.

First, it's mostly antimony that causes the oatmeal problems when some zinc gets into the lead melt. Pure lead + a little zinc is a whole different animal than lead+antimony+zinc. When antimony is added, the "oatmeal" problem goes through the roof, and casting a decent bullet becomes very difficult. This vitally important fact gets left out, and it's been the cause of a whole lot of confusion and frustration.

Second, the arsenic in ww lead greatly increases the solubility of zinc in lead. This helps explain why some folks get into serious trouble when they accidentally melt some zinc ww's along with their Pb/Sb/As ww's. The zinc dissolves into solution much easier.

The zinc preferentially combines with the antimony in the melt. That's much of the sludge/foamy dross/oatmeal/crud that rises to the top. It reacts with oxygen and forms an oxide skin on the melt. Every time you pour that alloy, the molten metal actually 'skins-over' during the pour, and the oxide skin prevents good fill-out. This reaction is so strong that adding the usual amounts of tin has little effect on reducing drossing and oxide formation.

OK, now let's talk about pure lead + zinc. Since pure lead will not dissolve much zinc, the problems noted in the Pb/Sb/As are much decreased. The Sb/As compound never forms. It's not very useful to suggest that zinc is no problem unless this tasty little nugget of info is also provided. Newbies will add zinc to their ww alloy, or 'scrap' lead, and inevitably destroy their alloy without knowing why. And consider that those new to pouring lead have very serious and very real problems with getting good results even when pouring known, good alloy. If you're new to pouring, or not checked-out 100% on your alloys, be advised that zinc + ww lead will not make your pouring session trouble-free and productive.

Adding sulfur to the zinc-contaminated melt is an attempt to remove as much of the Sb/As compound as possible. Sulfur readily combines with antimony and zinc to form antimony sulfide and zinc sulfide. Even if one only succeeds in removing most of the antimony, one reduces the amount of Sb/As in the melt.

Even those that purposely use zinc in lead treat the zinc largely as pollution. And of course, the solution to pollution is dilution. They dilute the zinc until the problems mostly subside, and then work around any remaining ones, such as by casting at very high temp. Heavily diluting the zinc-contaminated melt with pure lead reduces the negative consequences of it's presence. Adding more ww lead will not nearly provide the same benefit. Too much zinc in even pure lead will still cause the "oatmeal" problem.

When we suggest alloying recipes or strategies, we really need to provide all the how/what/why info, instead of just saying that zinc is no problem, or zinc is bad. Some techniques are not amenable to general dissemination unless accompanied with extensive explanation, and not all techniques will greet the casual lead pourer with instant success. The lead + zinc recipe is one of them.

Hope this helps, good luck.

[gunsbrad]

I have reread and thought about this alot. I see several pit falls here but the main one is: Is there anyway to tell when most of the zinc is gone as you are sulfur fluxing?

I really appreciate everyones help with this.

Brad

[sagacious]

Not that I am aware of. It's much like ordinary fluxing with wax-- fluxing does not prove or verify anything by itself. One still has to test the alloy by actually pouring into his bullet molds. When it pours OK, it's OK. That may sound simplistic, but verification by pouring is where the rubber meets the road. Good luck.

[45forlife]

I tried this today and it seems to work. All the **** is out and it looks like nice lead. I'll try to cast some tomorrow.

[ashlyngr]

I'm new to boolit casting. I have read the Lyman's #4 Handbook. A question I have pondered is, if one should happen to get Zinc contamination, and bullets pour and fill out well, would the Zinc show any effects in BHN testing?

Thanks,
ashlyngr

[letsmeltlead2693]

Sulfur also dissolves lead. Lead IS SOLUBLE in sulfur meaning it will mix in until ALL OF THE LEAD IS DISSOLVED with the sulfur. Lead react with sulfur to make lead sulfide.