pesco
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Eliminating traces of Pb from Na/Zn sulphates
Hi,
One brain is way worse than a whole swarm of them hence this topic. Just in case I missed something before proceeding 
I have whole lot of zinc-carbon batteries which were treated with NaHSO4 to dissolve Zn casing.. I really want Mn oxides, but Zn is very
usefull byproduct.
Next step will be to eliminate Zn from solution via electrolysis.
I will be dissolving some of the plated Zn in NaOH in order to produce Zn powder via electrolysis.
Whats do you think is the best way to remove any traces of Pb from solution?
Ideally before any electrolysis.
Any ideas highly appreciated.
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Sulaiman
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what makes you think that there is Pb in the mix ?
next time separate the zinc pot mechanically
and clean it mechanically
to get very pure zinc.
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Neptun
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You could try to crash out the lead impurities with sulfate as lead sulfate. Filtrate the sulfate off and electrolyse. Excess sulfate won‘t bother
you in the electrolysis step, i reckon. Also, Sulfate doesn’t react with zinc nor manganese to insoluble compounds. I‘d personally use either dil.
sulfuric acid or an alkali sulfate so you don’t contaminate your electrolysis product. I‘d love to hear opinions on this
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Radiums Lab
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Pb will not be present in such cells.
Water is dangerous if you don't know how to handle it, elemental fluorine (F₂) on the other hand is pretty tame if you know what you are doing.
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pesco
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pesco
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Quote: Originally posted by Neptun  | | You could try to crash out the lead impurities with sulfate as lead sulfate. Filtrate the sulfate off and electrolyse. Excess sulfate won‘t bother
you in the electrolysis step, i reckon. Also, Sulfate doesn’t react with zinc nor manganese to insoluble compounds. I‘d personally use either dil.
sulfuric acid or an alkali sulfate so you don’t contaminate your electrolysis product. I‘d love to hear opinions on this |
Thanks.
I was thinking of sulfate, but not sure about the bisulfate.
Don't really want to neutralize with alkali sulfate as I do want to keep reusing the bisulfate after plating Zn out.
[Edited on 3-1-2026 by pesco]
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Radiums Lab
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I have never seen a Zn/C cell with lead in it before.
[Edited on 3-1-2026 by Radiums Lab]
Water is dangerous if you don't know how to handle it, elemental fluorine (F₂) on the other hand is pretty tame if you know what you are doing.
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egret
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Lead can be removed by partial precipitation by hydrogen sulphide. Lead sulphide is less soluble than zinc sulphide.
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Sulaiman
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| Quote: Originally posted by egret | | Lead can be removed by partial precipitation by hydrogen sulphide. Lead sulphide is less soluble than zinc sulphide. |
I would expect both lead and zinc sulphide to precipitate out together.
this looks interesting https://m.xinhaimining.com/newo/lead-zinc-sulfide-ore-flotat...
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Deathunter88
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I dug into this and the answer is as always - the EU is stupid when it comes to regulations.
https://www.productipedia.com/kb/productipedia/compliance-re...
That symbol is required for "Battery with more than 0.004 % lead (Pb)". This is such a low concentration limit that battery manufacturers are forced
to include it even on non-lead acid batteries like carbon zinc because recycled zinc is often contaminated with small amounts of lead. For example,
this MSDS for a carbon-zinc battery states:
"ANSMANN zinc-carbon cells/batteries do contain lead, and do not contain cadmium and mercury
as defined by the European Directive 2006/66/EC Article 21;"
Even though the concentration listed in the composition section is freaking < 0.4%!!! (For context it lists it as containing 20-35% zinc).
https://asset.conrad.com/media10/add/160267/c1/-/gl/00130546...
In other words, it's like the dumb California Prop. 65 warning "may cause cancer" which is now meaningless because it's on literally everything.
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pesco
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Zinc ore from pretty much all sources contains some amount of Pb. Zinc is cheaper if is not overly purified, so there is some small amount of Pb in
(nearly?) all Zinc-Carbon batteries.
My aim is to eliminate all traces of Pb.
Interesting links. Thanks.
I don't want to play with sulfides for two reasons. Primo, synthesis of sulfides is not so straightforward and very wasteful if you need several kg of
them. Its fine for test tube experiments, but when you scale it to buckets then its different story. Secundo, I am not keen on large scale use of
potentially stinky and volatile poisonous compounds.
So far sulfate is a winning approach.
There is a potential of lead bisulfate formation, but as long as there is some Zn left undissolved there should be no chance for any bisulfate left in
solution.
Carbonate is also a possibility. Nice because it has solubility even lower than sulfate. At least if not accounting for common ion effect. So far
can't see how it could be easier than just sulfate.
.Any comments and suggestions very much appreciated.
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Fery
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pesco, you used NaHSO4 to dissolve Zn
PbSO4 has Ksp = 1.8 * 10-8
you can calculate the concentration of dissolved PbSO4 using the concentration of SO42-, you can round your
concentration of sulfates to 1 mol / l to have some estimation (dissolved ZnSO4 + Na2SO4)
here some examples for solubility / precipitation calculations of poorly soluble compounds
https://mhchem.org/223/223PPT/pdf223/II18b01Solubility.pdf
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Bedlasky
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Zinc sulfide doesn't precipitate from strongly acidic solution (but lead sulfide does).
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Fluorite
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https://www.youtube.com/watch?v=OfI-XpYAqM0
Nilered purified zinc sulfate by boiling it in potassium permanganate solution and then stirring zinc powder to precipitate metals that are less
reactive than zinc so lead should be removed
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bnull
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How much lead is acceptable? The only way to "eliminate all traces of Pb" is by mass spectrometer. No matter how much you purify it, zinc always has
traces of lead and other things.
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RU_KLO
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try first to determine the amount of lead in your product.
If cannot determine lead content as low as 0.1mg in a 10ml solution (because of lack knowledge, regent, apparatus), then is hard to eliminate it.
(you cannot eliminate what you cant confirm if it is there)
If there is a lot of lead (at least 5-10mg/gr of sample) you could detect it with HCl . but for trace/very small amounts you need specialized
reagents:
some ideas
1) photochemistry using perovskite - methylammonium bromide
"The method detects as little as 1.0 ng/mm2"
Direct Environmental Lead Detection by Photoluminescent Perovskite Formation with Nanogram Sensitivity
Lukas Helmbrecht, Sjoerd W. van Dongen, Arno van der Weijden, Christiaan T. van Campenhout, and Willem L. Noorduin
Environ. Sci. Technol. 2023, 57, 20494−20500
2) Chemical Basis: Formation of lead rhodizonate.
Neutral solutions of lead salts react with sodium rhodizonate to produce a blue-violet amorphous precipitate.
Identification Limit: 0.1 -y lead.
Concentration Limit: 1:2,000,000.
page 133 of: LABORATORY MANUAL OF SPOT TESTS
by DR. FRITZ FEIGL
(I think I got this book from Internet archive)
3) Formation of lead dioxide and its reaction on benzidine
Procedure: A drop of the neutral or acid test solution is placed on filter paper and treated successively with one drop of 3 A sodium hydroxide and
one drop of bromine water. One or two minutes later the spot is treated with two drops of concentrated ammonium hydroxide. The spot is then touched
with an acetic acid solution of benzidine, A more or less intense blue fleck appears, according to the quantity of lead involved.
Identification Limit; 1 y lead.
Concentration Limit: 1:50,000.
problem: Mn++ interfere.
page 144: LABORATORY MANUAL OF SPOT TESTS
by DR. FRITZ FEIGL
Attachment: direct-environmental-lead-detection-by-photoluminescent-perovskite-formation-with-nanogram-sensitivity.pdf (6.3MB)
This file has been downloaded 4 times
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MrDoctor
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i dont know how electroplating traces of a dissolved metal might work, i assume that things like displacement and the electrochemical forces that
deposit your metal onto the cathode would still work more or less to the same even as the element is depleted, provided there is something else behind
it, like a chaser of sorts, otherwise it might get increasingly difficult to pull it all out of solution.
My thinking though is that, since lead is dramatically heavier on the reactivity series than zinc and electrodeposition will lead to very high surface
area zinc, any lead that doesnt already plate out will probably displace the high surface zinc. So one would expect the first metal electrodeposited
on the cathode to be lead if present, followed by an increasing amount of zinc or manganese if any salts are present as well, batteries also will have
dissolved iron to bear that in mind, and assuming that the zinc and others will outcompete the lead as the concentration plummets, lead salts should
still displace surface zinc, of which there is a lot. slowly electrodepositing some of the dissolved metals should result in something of
substantially more concentrated lead, if nothing else it might serve as a better source for testing for lead than the bulk dissolved zinc salt.
Zinc dry cell batteries can contain lead indirectly, i used to collect carbon rods at a time from lantern batteries, which are connected in series via
soldered wires and the solder was regular leaded solder not lead-free.
Lead also is not supposed to be present, but it can itself be a contaminant of zinc, sometimes you see batteries that say "no added lead" as opposed
to an absolute assurance of "no lead".
Anyway take what i said with a grain of salt, its at best anecdotal.
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