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Thread: Scientifically testing the removal of Zinc via Sulfur Fluxing

  1. #1
    Boolit Mold
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    Scientifically testing the removal of Zinc via Sulfur Fluxing

    So this is something that has perplexed me for many years - It's now been over a decade since Sciguy made his post related to fluxing lead with sulfur to remove zinc, and in that time, nobody has really scientifically tested the idea with anything other than anecdotal evidence as far as I can tell. So I'm going to.

    Two days ago I bought 100lbs of pure lead from a metals supplier. I have also purchased a lead hardness test kit (Lee brand, which was fully reviewed and tested here: http://www.lasc.us/Shay-BHN-Tester-Experiment.htm#Lee) In addition, I bought 4.5oz of pure zinc. My plan is to purposefully and in a controlled manner alloy the zinc and lead at a rate of 2.5% - 2oz of zinc per 5lb batch of lead. With that alloy I'm going to cast some bullets, and test the hardness. Then I'm going to remelt the alloy and flux with a generous amount of sulfur, following the previously attempted methods, and cast more bullets. The hardness of those bullets will also be tested and compared to the previous batch for any significant difference.

    Following that I'm going to try the other method that is frequently mentioned: slowly bringing the alloy up to temp and attempting to skim zinc off the top as it floats out of solution. This will be done with a fresh batch of alloy at the same 2.5% zinc to lead. Again, bullets will be cast before and after the procedure to see if there is any meaningful drop in hardness.

    If those two tests give reasonable results, I will melt some known hardball lead (92% lead/6% antimony/2% tin) and test the hardness there, flux with sulfur and test again. This will test to see if sulfur forms a compound with either the antimony or tin to reduce hardness as well.

    Hopefully this will give the community some actual statistical evidence of what's been said for year. If anyone sees any issues with what I'm proposing to do, let me know so I can take them into account. If anyone knows of testing similar to this, please let me know.

    Thanks!

  2. #2
    Boolit Master
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    Or mix two batches of 2.5% zinc, then try the sulfur treatment on one batch and have them xrf tested.
    Spell check doesn't work in Chrome, so if something is spelled wrong, it's just a typo that I missed.

  3. #3
    AKA: GRMPS Conditor22's Avatar
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    Dr3wcifer Welcome to cast boolits

    Talk about jumping into a forum with both feet

    I think I know what you are going to come up with ; I'll be interested to see your results.

  4. #4
    Boolit Mold
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    Haha, thanks for the welcome! I've been stalking the boards for quite a while, and casting for my flintlocks for a minute as well. I have several hundred pounds of mixed lead (wheelweights, dive weights, race car ballast) that I'd love to be able to bring down to castable hardness for pistols. The sulfur flux question has always come up as an answer, and I've decided that, since nobody else has done it, I'll try and settle it once and for all. I'll be sure to give a thorough writeup when I'm done!

  5. #5
    Boolit Buddy Cast_outlaw's Avatar
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    Advice I can give ware a good mask as Sulfur is not good for you
    Copy an paste from a website
    Burning sulfur creates sulfur dioxide, a gas. If inhaled, coughing, shortness of breath, sore throat, and labored breathing, has been reported. Eye irritation has also been reported.

  6. #6
    Boolit Master
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    Sulfur dioxide is bad news respiratory wise!! I am interested also in your results
    I firmly believe that you should only get treated by how you act, not by who or what you are!!

  7. #7
    Sulfur dioxide sucks from first hand experience.

    training at pohakuloa training area on the big island frequently you encounter VOG volcanic smog which is high in sulfur dioxide.

    a 5 mile run at PTA was one of the worst in my military career. the volcanic glass dust stirred by many people running also made your eyes burn something fierce.

    on the other hand i ran 5 miles in it... and i lived even if i was was really uncomfortable.

    hawaii website about VOG: https://ltgov.hawaii.gov/emergency-i...r%20conditions.

  8. #8
    Boolit Grand Master popper's Avatar
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    Sulfur in hardball actually increases hardness.
    Whatever!

  9. #9
    Boolit Mold
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    Alright, so here's where I am so far. TL;DR, sulfur does work to pull zinc out of the alloy.

    I started by adding 2.2oz of zinc to 4lbs 13.8oz of lead, to give us an alloy of 2.75% zinc to lead by weight. I my mind, if a handful of zinc weights make it through your screening, it can't be THAT much, so let's keep the numbers small. After I pulled three samples and tested each, I increased the overall zinc to lead up to 5.5%, pulled three more samples, and tested those. Following that, I remelted the alloy and fluxed three times with pure sulfur - I happened to have some on hand from my first attempt to make blackpowder. Another story for another day. Anyhow, you all were right - that is some noxious stuff. Although it burns a really beautiful blue, which made for quite a show when working in the dark on the back patio.

    Anyhow, the results:
    Pure lead has a BHN of 5. The Lee tester starts at 8, but I can extrapolate based on the measurements using the tools provided and an excel chart.

    The sample at 2.75% averaged a BHN of about 5.6 - hardly an increase at all.

    The sample at 5.5% averaged a BHN of about 6.2 - again, not an incredible amount of hardening.

    After fluxing with sulfur three times, the BHN fell to almost pure lead levels, around 5.2 to 5.3.

    So what did I learn from this? Well, zinc appears to harden the alloy at about the same rate as tin, which isn't anything close to antimony. However, during the testing it was very noticeable that zinc ruined the cast finish. The telltale surface "wrinkles" started showing up in the 2.75% alloy, and were prominent in the 5.5% alloy. The overall flow of the pour was also not very smooth.

    Next up, I think I would like to take some known hardball I have, which has a BHN around 16.6, and taint it was a known amount of zinc, and see if it's possible to pull the zinc out of that alloy without ruining the hardness using the same method.

  10. #10
    Boolit Buddy
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    Thank you for your effort.

  11. #11
    Boolit Buddy
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    So you added sulphur (powdered I assume) into the melted lead with zinc mix, then stirred it around and what happened?
    It created a dross that contained the extracted zinc that you scooped out from the alloy?

    How much sulphur...a tablespoon or so?

    Thanks for taking the time to test and post your results.
    It's an interesting topic.

  12. #12
    Boolit Mold
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    I used a "spoonful" of powdered sulfur on each fluxing of the 5lb melt. Probably 2 teaspoons per. It quickly melts and ignites, and burns somewhat vigorously in a deep blue. While it was burning, I stirred it pretty well for about 15 seconds, and then let it burn itself out. Afterwards, I skimmed off the new powdery metal slag that had formed, and discarded it.

    My overall goal wasn't to see how much sulfur is needed to pull the zinc out of the alloy efficiently, just to see definitively if sulfur even had that ability.

    I have 4lbs of known hardball lead testing at about 16.6 BHN that I will be testing with tonight or tomorrow to see if sulfur hardens or softens it, and then tainting that with zinc to see how fluxing with sulfur alters the hardness and pour.

  13. #13
    Boolit Grand Master
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    Several years ago I extensively tested alloys (10-12 hardness) with up to 5% Zn contamination in several pistol boolits of various calibers. Did not see any degradation in casting, dropping, or shooting. All were PC'd. Posted in several threads on here in the past 5 years.

    Scientific? No. Does it prove that a little Zn does not "ruin the whole batch" as many frequently bemoan on here? YES.

    And yes Zn is harder than Pb! It will harden it a slight bit. Sb is what we use to harden Pb alloys, not Sn. Problem it is lighter and will change your boolit weights ever so slightly....not enough to worry about. Sn is used to improve the mold fill quality by lowering the surface tension of your alloy. 2-3% is more than sufficient to get the job done.

    Again..................I am talking 1 to 5% Zn contamination here.

    Bottom line..............don't loose sleep if you get a zinker or two melted in your re-melted batch of WW's (if you can even find them these daze!).

    And the SO2 you generate by burning sulfur (BIG health hazard!) in Pb is just not worth the very little you gain trying to remove Zn. Just leave it there and cast some boolits!!!!!

    Happy shooting.

    bangerjim

    ps.............oh yes, glad you finally joined in on the conversations. Lurkers contribute nothing.

  14. #14
    Boolit Grand Master 303Guy's Avatar
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    SO2 is not the only health hazard. Zinc sulfide is not good either plus the zinc oxides that can form. Zinc fume fever. Hydrogen sulfides can also form, also not healthy.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  15. #15
    Boolit Master
    Plate plinker's Avatar
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    I have used the sulfur as well with good results. Thanks for taking the time to do your lab test.

  16. #16
    Boolit Master Traffer's Avatar
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    I tried sulfur once and never again. BAD BAD BAD BAD...Don't do it. Fumes are really bad...very hard to work with... I got "black goo" that formed on top of the melt. It took a while for the goo to get kind of ash/cinderish. I ended up using about 5 table spoons for about 4lb. the goo kept forming. Must have lost more than half of the melt to the goo. But XRF showed no zinc in the alloy afterwards.
    AGAIN BUT, I am not sure there ever was zinc in there. I know one thing. I will never put sulfur in lead again.

  17. #17
    Boolit Mold
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    Why did you flux with an excess of sulfur on an alloy you weren't even sure contained zinc, what was the end goal? And yeah, it's pretty noxious stuff, but I got on just fine doing it on the back patio on a calm night. Unless you were standing over it basking in the glory of the fumes... And I fluxed three times with a couple teaspoons per round, and only lost maybe 8oz from the 5lb melt, of which ~4oz were apparently zinc.

    So far it seems to be a good way to remove a majority of zinc from a lead alloy. I think there may be a legitimate use to the process.
    Last edited by Dr3wcifer; 08-03-2020 at 01:33 PM.

  18. #18
    Boolit Master Traffer's Avatar
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    Quote Originally Posted by Dr3wcifer View Post
    Why did you flux with an excess of sulfur on an alloy you weren't even sure contained lead, what was the end goal? And yeah, it's pretty noxious stuff, but I got on just fine doing it on the back patio on a calm night. Unless you were standing over it basking in the glory of the fumes... And I fluxed three times with a couple teaspoons per round, and only lost maybe 8oz from the 5lb melt, of which ~4oz were apparently zinc.

    So far it seems to be a good way to remove a majority of zinc from a lead alloy. I think there may be a legitimate use to the process.
    Your snarky comment doesn't really deserve an answer but I will give one for the benefit of others:
    I had a pretty good percentage of my lead supply that was acting suspiciously like it had zinc in it. Was just starting in the casting realm and only had very limited tools etc. I read about the zinc thing and thought the symptoms I was having justified trying to use sulfur to fix it.
    Started by using a small bit into a 4 or 5 lb or melt. About a teaspoon. It turned to hard goo immediately and stayed that way for a while...so I kept adding small amounts having the same results. Until I had probably ended up using several tablespoons in that melt. I got about 40% slag. Did the rest of my suspicious alloy and let it go at that. Later had that alloy XRF tested and it came back with no appreciable amt of zinc. I also ended up using it with a bit of tin added and it worked fine.
    I did this outside in the drive way. Had a good rubber (particulate type) mask on upwind of the process. But there was so much smoke and the wind swirled a couple of times getting me with the smoke. NO MORE for Me.
    Is that OK with you Sir? Or should I endure more scornful posts about it?

  19. #19
    Boolit Mold
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    Take a breather, I asked an honest question. You said in your initial comment that you weren't sure it contained zinc, but you fluxed with sulfur anyway, so I was honestly wondering why...

    I offered a reasonable test of whether zinc could be removed from a lead alloy with sulfur with measurements and reproducible tests. I recorded and posted it so that people could potentially learn something helpful about whether or not sulfur is something worth trying. My data showed that sulfur can remove zinc. You came into this discussion with your story about how you tried it once on an alloy that may or may not have had zinc in it and it was "BAD BAD BAD BAD." You offered nothing to the discussion other than an unhelpful personal story about why you don't like it. But you ended with a comment about how an XRF study of the alloy showed no zinc...

    If you would like to contribute something helpful to the discussion, feel free. Otherwise, please ignore this post.

  20. #20
    AKA: GRMPS Conditor22's Avatar
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    this will help




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