Sciencemadness Discussion Board

Removing lead oxide from lead ingots.

RaD! - 31-5-2015 at 08:00

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!]

ledob86 - 31-5-2015 at 08:06

Washing with dilute acid ? Then Washing with water and hand drying.

RaD! - 31-5-2015 at 08:07

10% Acetic acid?

ledob86 - 31-5-2015 at 08:10

It should be very slow with dilute AcAc. Try with HCl or HNO3 if you have

gdflp - 31-5-2015 at 08:38

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.

ledob86 - 31-5-2015 at 08:46

Quote: Originally posted by gdflp  
AcAc is not acetic acid, it's diacetyl.


Sorry, personal notation :D

WGTR - 31-5-2015 at 09:02

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?
--------
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]

RaD! - 31-5-2015 at 09:32

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.


:D Thanks! This will produce some Lead Acetate won't it?

[Edited on 31-5-2015 by RaD!]

blogfast25 - 31-5-2015 at 09:56

Quote: Originally posted by RaD!  


:D Thanks! This will produce some Lead Acetate won't it?



WGTR is entirely right here: fluxing during casting is the answer here.

gdflp - 31-5-2015 at 10:03

Quote: Originally posted by RaD!  

This will produce some Lead Acetate won't it?

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]

Amos - 31-5-2015 at 10:15

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.

BromicAcid - 31-5-2015 at 11:37

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.

blogfast25 - 31-5-2015 at 11:43

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.



There's nothing wrong with suggesting a better solution to the 'issue at hand'.


[Edited on 31-5-2015 by blogfast25]

WGTR - 31-5-2015 at 12:14

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. :cool:

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.

blogfast25 - 31-5-2015 at 12:50

Lalalala.


[Edited on 31-5-2015 by blogfast25]

violet sin - 31-5-2015 at 14:50

@ 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-

aga - 31-5-2015 at 15:06

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]

blogfast25 - 31-5-2015 at 15:28

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]

Amos - 31-5-2015 at 17:28

Hey now, aga is a model drunk!

blogfast25 - 31-5-2015 at 18:04

Quote: Originally posted by Amos  
Hey now, aga is a model drunk!


And I'm not? Discrimination LIBELZ!!!!101!!! :D

Fulmen - 1-6-2015 at 06:02

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.

CD-ROM-LAUFWERK - 14-7-2020 at 10:36

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?

Fleaker - 14-7-2020 at 12:58

Keep in mind that soluble lead salts are quite toxic.

I would imagine dilute nitric would work better (say 5-10 % w/v).

CD-ROM-LAUFWERK - 15-7-2020 at 08:23

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]

woelen - 15-7-2020 at 23:16

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]

Bezaleel - 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?


Tsjerk - 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).

fusso - 17-7-2020 at 05:07

Whatabout NaOH?

Tsjerk - 17-7-2020 at 08:16

What would sodium hydroxide do?

AJKOER - 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]

Tsjerk - 21-7-2020 at 08:52

AJOEKER: At what temperature does that reaction run?

AJKOER - 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...).

Tsjerk - 21-7-2020 at 10:46

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

CD-ROM-LAUFWERK - 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?

Bezaleel - 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.