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Author: Subject: Removing lead oxide from lead ingots.
Bezaleel
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[*] posted on 17-7-2020 at 03:25


1. Woelen, will HClO4 remove only the oxide or will it also attack the lead metal?

2. Sulfamic acid was suggested above, but my experience with sulfamic acid is that it normally contains ~5% of sulfuric acid. Addition of sulfamic acid to BaCl2 solution clearly shows this. Lead sulfate is very insoluble, so I would avoid the chance of creating it.

3. a) Fulmen suggest paraffin wax, but how do you clean the lead from any paraffin that remained on the surface?
b) Also, I guess you can't melt lead under paraffin, can you? So for melting together small oxidised lead pieces, this is not an option, or am I mistaking?


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Tsjerk
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[*] posted on 17-7-2020 at 05:03


HClO4 won't attack the lead (or hardly) as perchlorate is not an oxidizer in water under normal conditions.

Do you have barium hydroxide? It is quite cheap and could be used to get rid of the sulfate in sulfamic acid, as barium sulfamate is pretty soluble. The pKa of sulfamic acid makes it a borderline strong acid (pKa = 0.995).
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fusso
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[*] posted on 17-7-2020 at 05:07


Whatabout NaOH?
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Tsjerk
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[*] posted on 17-7-2020 at 08:16


What would sodium hydroxide do?
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AJKOER
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[*] posted on 21-7-2020 at 08:17


Actually, to the certain disbelief of the general audience, consider the cheapest with no toxic waste product via the least corrosive of all mentioned paths, namely, the employment of dry ammonia gas, as can be harvested from household ammonia and a drying agent:

To quote a source (see https://socratic.org/questions/what-is-the-balanced-redox-re... and also, https://www.kenyaplex.com/questions/28794-dry-ammonia-gas-is...):

3 PbO (s) + 2 NH3 (g) -> N2 (g) + 3 H2O (l) + 3 Pb (s)

Note: The claimed reaction avoids a soluble toxic problematic Lead waste product and actually re-plates the Lead surface itself.

This source (see https://www.osti.gov/servlets/purl/1007235) states in different approach "no need for ammonia" implying there is some history on the NH3 path.

However in not dry conditions, per this source, at https://www.researchgate.net/publication/243950971_Solubilit... suggests with excess ammonia and water, possible mixed Lead salts which may further complex with ammonia.

[Edited on 21-7-2020 by AJKOER]
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Tsjerk
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[*] posted on 21-7-2020 at 08:52


AJOEKER: At what temperature does that reaction run?
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AJKOER
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[*] posted on 21-7-2020 at 09:36


What temperature is the cited combustion tube reaction of dry NH3 and PbO?

Nothing specific yet, but there are general examples of combustion tube reactions occurring at 500, 700, 1000 ◦C, etc, so somewhere in this range I would speculate.

Per this source, http://kintecus.com/Kin_05-OLF-CEJC-Dirtu.pdf, the thermal decomposition of ammonia, itself, under dynamic conditions, occurs at 800 ◦C, which thermally induces radicals (like H). So, this is my high end estimate.

However, assuming a Hydrogen atom path towards the removal of the oxide, speculatively, this could be accomplished also at much lower temperatures in the presence of, for example, a 'zinc spark' in ammonia (see https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1940...).
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Tsjerk
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[*] posted on 21-7-2020 at 10:46


That temperature would make the reaction useless for removal of oxide from ingots wouldn't it?
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CD-ROM-LAUFWERK
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[*] posted on 22-7-2020 at 08:06


Quote:

consider the cheapest with no toxic waste product via the least corrosive of all mentioned paths

Cheapest? Least corrosiv? And then a source(s) where someone asks a theoretical question? That are some pretty wild claims backed by nothing.

Quote:

That temperature would make the reaction useless for removal of oxide from ingots wouldn't it?

Even if that was really possible, it would be useless not just for ingots but for any application with solid lead. E.g. in the recovery of waste product one could use this to remove lead out of this waste stream. But why should that person use corrosive(!) NH3 instead of the cheaper(!) and much less corrosive and less dangerous hydrogen?
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Bezaleel
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[*] posted on 28-7-2020 at 03:11


Quote: Originally posted by Tsjerk  
HClO4 won't attack the lead (or hardly) as perchlorate is not an oxidizer in water under normal conditions.

Do you have barium hydroxide? It is quite cheap and could be used to get rid of the sulfate in sulfamic acid, as barium sulfamate is pretty soluble. The pKa of sulfamic acid makes it a borderline strong acid (pKa = 0.995).
Indeed, with Ba(OH)2 you can easily remove the sulphate. And I do have it around. So wherever the barium (which needs to be added in a slight excess) is not an issue, this of course perfectly works. Thanks.

BTW, the background of my questions is that I'd like to clean a battery electrode, which very likely will contain PbSO4 in addition to PbO. I'd first need to remove the sulphate from it by boiling the electrode in NaCO3 solution for a while.
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