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RaD!
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Removing lead oxide from lead ingots.
Today I casted some lead ingots, but they have bits of lead oxide on the surface. How can I remove this?
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Oops, wrong place to post..
[Edited on 31-5-2015 by RaD!]
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ledob86
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Washing with dilute acid ? Then Washing with water and hand drying.
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RaD!
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10% Acetic acid?
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ledob86
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It should be very slow with dilute AcAc. Try with HCl or HNO3 if you have
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gdflp
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AcAc is not acetic acid, it's diacetyl. Washing with nitric acid is no good as that will oxidize and dissolve the lead, and HCl will only work if the
acid is kept hot, since PbCl<sub>2</sub> is nearly insoluble in cold water. I would try warming some acetic acid, 10% should be fine, and
placing the lead ingot in the solution for several minutes. Cover the top of the beaker to prevent aerobic oxygen from oxidizing the lead while in
the acidic solution and the lead oxide should dissolve, along with a little bit of lead metal, and leave a clean surface of lead.
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ledob86
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Sorry, personal notation 
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WGTR
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Quote: Originally posted by RaD!  | Today I casted some lead ingots, but they have bits of lead oxide on the surface. How can I remove this?
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Oops, wrong place to post..
[Edited on 31-5-2015 by RaD!] |
Flux. It removes the oxide layer from the molten material, and protects it from further oxidation while the metal cools down. Mind the specified
temperature range. They don't work well outside of their respective ranges. Also, note that different types are washed off using different solvents.
Some are water soluble.
http://www.superiorflux.com/rosin_and_paste_flux.html
A local welding shop may have something useful, or even your local hardware store, in the plumbing department.
If there are any further questions, ask away!
[Edited on 5-31-2015 by WGTR]
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RaD!
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| Quote: Originally posted by gdflp | | AcAc is not acetic acid, it's diacetyl. Washing with nitric acid is no good as that will oxidize and dissolve the lead, and HCl will only work if the
acid is kept hot, since PbCl<sub>2</sub> is nearly insoluble in cold water. I would try warming some acetic acid, 10% should be fine, and
placing the lead ingot in the solution for several minutes. Cover the top of the beaker to prevent aerobic oxygen from oxidizing the lead while in
the acidic solution and the lead oxide should dissolve, along with a little bit of lead metal, and leave a clean surface of lead.
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:D Thanks! This will produce some Lead Acetate won't it?
[Edited on 31-5-2015 by RaD!]
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blogfast25
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WGTR is entirely right here: fluxing during casting is the answer here.
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gdflp
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Yes, the lead oxide will dissolve to form lead acetate.
And blogfast, while WGTR's answer is a good way to prevent the formation of lead oxide during the casting process, that's not the question that the OP
was asking, so it is not particularly useful. I see this a lot, answering questions which weren't asked and stating how things should have been done,
rather than solving the issue at hand.
(I removed this passage temporarily not because I regretted it or didn't mean what I said, but because I didn't want to derail the thread. Now that
discussion has continued, I have restored it so as to prevent confusion)
[Edited on 6-1-2015 by gdflp]
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Amos
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I actually like the idea of mechanically polishing the outside of the ingots. Using acid to dissolve the oxide will etch the outer surface, leaving it
more prone to oxidation in the future.
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BromicAcid
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| Quote: Originally posted by Amos | | I actually like the idea of mechanically polishing the outside of the ingots. Using acid to dissolve the oxide will etch the outer surface, leaving it
more prone to oxidation in the future. |
Agreed, a thin oxide coating can likely be removed with a metal polishing pad or even elbow grease and paper towels and maybe a little water.
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blogfast25
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| Quote: Originally posted by gdflp |
And blogfast, while WGTR's answer is a good way to prevent the formation of lead oxide during the casting process, that's not the question that the OP
was asking, so it is not particularly useful. I see this a lot, answering questions which weren't asked and stating how things should have been done,
rather than solving the issue at hand.
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There's nothing wrong with suggesting a better solution to the 'issue at hand'.
[Edited on 31-5-2015 by blogfast25]
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WGTR
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| Quote: Originally posted by gdflp |
And blogfast, while WGTR's answer is a good way to prevent the formation of lead oxide during the casting process, that's not the question that the OP
was asking, so it is not particularly useful. I see this a lot, answering questions which weren't asked and stating how things should have been done,
rather than solving the issue at hand. |
Perhaps; however, the assumption is that the OP is able to successfully cast lead ingots. In my humble opinion, it will save time and effort to
simply recast them, but with flux. It's the way things are normally done. It's very common to redo rough castings by throwing them back into the
pot. 
When mechanically polishing heavy metals, it's a good idea to plan out how the dust will be collected afterwards. Personally I don't polish them
unless it's on our wet grinding bench. That way the dust is captured.
It depends really on how much oxidation there is on the material, and if there are dross inclusions. Casting with flux will deliver a smoother
surface, and dramatically reduce the effort expended in polishing. It also reduces the amount of lead waste.
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blogfast25
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Lalalala.
[Edited on 31-5-2015 by blogfast25]
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violet sin
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@ blogfast25: the now edited out quote from gdflp( below), has merit in my opinion. you basically talked down to a member asking a question because
he didn't do the process correctly the first time,( few amateurs do), and ignored his question about the current situation. then talked down to
another member because you didn't like what he had to say.
gdflp: "And blogfast, while WGTR's answer is a good way to prevent the formation of lead oxide during the casting process, that's not the question
that the OP was asking, so it is not particularly useful. I see this a lot, answering questions which weren't asked and stating how things should have
been done, rather than solving the issue at hand. "
and your response, blogfast25: " There's nothing wrong with suggesting a better solution to the 'issue at hand'. Who are you? The 'Thought Police'?
Please get lost"
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I wholeheartedly feel that you could have handled that better. Like neutrally introducing the fact that the issue could have been avoided, and then
offering a helping hand. not talking down to two members... you may be fed up with some of the content here these days, the lack full questions with
competent knowledge. but for the sake of an inviting learning/discussion environment here on the forum, could you not occasionally cut a guy some
slack. many of those that have asked questions that must annoy you are after all just trying to learn, and learn from mistakes. a situation that is
almost inevitable when introducing your self to new subjects.
of course the easiest way to deal with the problem is not to have it in the first place.
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inline with the OP's question, I think sulfamic acid could be of help dissolving the oxide. cheap and available. lead sulfamate has a rather large
solubility when compared to other lead salts. how fast it will eat off the corrosion however I don't know. I haven't tried it in conjunction with
lead without electrowinning in mind. for which by the way, it works just fine in my experiments.
as for references, they are all still on my dead computer. I requested several papers on sulfamates in the reference request threads, and found
several others on the hathibook trust site. if your gonna try and bust my balls here, I will get them edited in by the end of the day. solubility of
lead sulfamate at least. for the time being I'm busy with daily life.
-Violet Sin-
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aga
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VS is right.
You're getting exceedingly grumpy bloggers.
Anyway, back on topic (preventing trollish behaviour derailing it) ..
What would you actually use as a flux for Lead, and more for myself, what would you use for Aluminium ?
[Edited on 31-5-2015 by aga]
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blogfast25
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For aluminium the KCl/NaCl eutectic is often used. For lead many ordinary solder fluxes would probably do. Maybe a 'heavy duty' type?
aga: it's only you whose entitled to 'behave badly'?  You know, 'casting the first
stone' and all that?
[Edited on 31-5-2015 by blogfast25]
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Amos
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Hey now, aga is a model drunk!
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blogfast25
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And I'm not? Discrimination LIBELZ!!!!101!!!
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Fulmen
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Fine, lets discuss this. The first I would like to know is why and how much. If it's just to freshen up the looks I'd try a wire brush and perhaps
some acetic acid. If the metal needs to be free from impurities the best solution would be to remelt the metal. Large amounts of dross (large
dirt/oxide particles) on the surface is usually accompanied by inclusions below the surface.
As for fluxes for lead the simplest is paraffin wax. It seems to work primarily by adhering to the oxides which reduces the wetting action of the
metal. Simply add a pea-size chunk to the metal and stir, you will end up with loose dross that can easily be skimmed off the surface.
We're not banging rocks together here. We know how to put a man back together.
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CD-ROM-LAUFWERK
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This thread is the first google hit if someone searches "how to remove lead oxide". However, there is no proven answer here. So lets try to change that.
In my case it is not possible to recast the lead (old stained glass window). Mechanical approaches are time consuming, tedious and since the lead is
everything but flat/even also not effective. The remaining options for me are:
Very tedious scratching with a knife to remove the hard oxide and reach down into all the lower areas as well as around sharper corners.
And (of course) chemical removal. I have 3 tests running right now:
10% Na2S2O8 solution with catalytic amounts of copper
10% AcOH
10% AcOH + ~1% H2O2
Is sulfamic acid worth a try or was it just a guess due to the solubility of lead sulfamate? I dont have HCl or HNO3 here right now for this job. But
I guess brushing on 10...30% HNO3 should be very effective. It would quickly dissolve the top layer and nothing structural down below. Any other
ideas?
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Fleaker
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Keep in mind that soluble lead salts are quite toxic.
I would imagine dilute nitric would work better (say 5-10 % w/v).
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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CD-ROM-LAUFWERK
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| Quote: | | lead salts are quite toxic |
This is somewhat OT, but considering how much lead sugar people consumed as a sweetener and seeing that the LD50 is 400mg/kg and that its thus "only"
declared as harmful and not toxic: No, it is not quite toxic. Im not going to somehow ingest a spoonful of the pure salt by accident.
But of course all the solutions have to be disposed of properly etc.
To my test after about 24h:
Useless: 10% Na2S2O8 solution with catalytic amounts of copper
Works, but slowly: 10% AcOH
Works, effects visible after 1h: 10% AcOH + ~1% H2O2
After scrubbing the test samples with a brush it is clear that Na2S2O8 did next to nothing and both AcOH solutions did a great job of removing and/or
loosen up the oxide layer.
[Edited on 15-7-2020 by CD-ROM-LAUFWERK]
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woelen
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Very dilute HNO3 works like a charm. Use somewhere between 5% and 10% concentration, not higher. At such low concentrations, HNO3 is not that strongly
oxidizing. Because HNO3 is a strong acid, it acts much more rapidly than acetic acid. HCl and H2SO4 also are strong acids, but their lead salts are
(nearly) insoluble, so they do not work well.
The best acid for this purpose is dilute HClO4, which is not oxidizing at all, while at the same time it is a strong acid having a freely soluble lead
salt. But not many people will have HClO4, the next best option is more common.
[Edited on 16-7-20 by woelen]
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